Dissertations / Theses on the topic 'Dual frequency'
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Maeser, Anna Marie. "Time-frequency dual and quantization." View electronic thesis (PDF), 2009. http://dl.uncw.edu/etd/2009-1/maesera/annamaeser.pdf.
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Sun, Xiaolei, and 孙肖磊. "Dual-band and frequency-reconfigurable monopole antennas." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2013. http://hub.hku.hk/bib/B50899880.
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The designs of three compact dual-band monopole antennas for wireless-local-area-network (WLAN)applications are presented. In these designs, an L-or U-shaped monopole element with microstrip-fed is used to generate a high-frequency band at around 5.5 GHz to cover the high WLAN bands at 5.2/5.8GHz for the IEEE 802.11a standard. An E-shaped element, loop element or meander-microstrip ground stub element with coupled-fed through the monopole element is used to generate a low-frequency band at around 2.4 GHz to cover the low WLAN band for the IEEE 802.11b/g standards. With such arrangements, the three antenna shave very compact radiators of only 11.3×8 mm2,12.6×9 mm2and11.8×9.4 mm2. To investigate the performances for practical uses, these antennas are also designed on a mobile-phone printed-circuit board and studied using computer simulation and measurement.
Dual-band antennas with reconfigurable
Dual-band antennas with reconfigurable lower band, higher band and dual-band are designed in this thesis. The dual-band antenna consists of two radiating branches generating the frequency bands at around 2.4 GHz and 3.5 GHz for the WiMAX system. Varactors are placed on the corresponding branches for continuously tuning of the operating bands for different WiMAX standards. For frequency tuning of the lower band or higher band, simple and novel DC biasing circuits without requiring any soldering wire are proposed to bias the varactor on a radiating element. While for simultaneous frequency tuning of the two individual bands, simple and novel DC biasing circuits requiring two soldering wires are proposed to bias the varactors on the radiating elements. Both simulation and measurement results show that the DC biasing circuits designed have very little affects on the antennas performances.
The design of a monopole ultra-wide band (UWB)antenna with a reconfigurable notch band is presented. The antenna employs a vertical-ellipse radiator to achieve an UWB. A compact defected-ground structure (DGS)is used to create a notch band for the antenna. To frequency tune the notch band, a varactor is placed on the DGS to control the resonance frequency. The tuning performance, in terms of reflection coefficient, radiation pattern, efficiency and gain, of the antennais studied using simulation and measurement. Results show that the notch band can be tuned continuously from 5.2 to 6.32 GHz for the WLAN bands.
In the measurement of a monopole antenna with a small ground plane, the feeding cable used to connect the antenna to the measurement equipment Satimo Starlab system causes discrepancies between the simulated and measured radiation patterns, efficiencies and peak gains at lower frequencies. In the designs of antennas in this thesis, the cable effects are studied by modeling the feeding cable using the EM simulation tool CST. Results show that, by using the cable model, the simulated and measured results agree very well.published_or_final_version
Electrical and Electronic Engineering
Doctoral
Doctor of Philosophy
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Zhang, Yuning. "Bubble dynamics under dual-frequency acoustic excitation." Thesis, University of Warwick, 2015. http://wrap.warwick.ac.uk/71098/.
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Acoustic cavitation plays an important role in a broad range of biomedical, chemical and engineering applications, because of its magnificent mechanical and chemical effects. Particularly, the irradiation of the multi-frequency acoustic wave could be favouritely employed to promote these effects, such as enhancing the intensity of sonoluminescence, increasing the efficiency of sonochemical reaction, and improving the accuracy of ultrasound imaging and tissue ablation. Therefore, a thorough understanding of the bubble dynamics under the multi-frequency acoustic irradiation is essential for promoting these effects in the practical applications. The objective of this PhD programme is to investigate the bubble dynamics under dual-frequency excitation systematically with respect to bubble oscillations, the acoustical scattering cross section and the secondary Bjerknes force (a mutual interaction force between two oscillating bubbles). Spherical gas bubbles in water are considered. Both analytical analysis based on perturbation method and numerical simulations have been performed in this thesis. The analytical solutions of the acoustical scattering cross section and the secondary Bjerknes force under dual-frequency excitation have been obtained and validated. The value of the secondary Bjerknes force can be considered as the linear combination of the forces derived under the single-frequency approaches. The predictions of those analytical solutions will be impaired for the cases with large acoustic pressure amplitudes. The numerical simulations reveal some unique features of the bubble dynamics under dual-frequency excitation, e.g., the combination resonances (i.e., their corresponding frequencies corresponding to the linear combinations of the two component frequencies) and the simultaneous resonances (i.e., the simultaneous occurrence of two resonances in certain conditions). The influence of a number of paramount parameters (e.g., the pressure amplitude, the equilibrium bubble radii, the power allocation between the component waves, the phase difference and the driving frequency) on the bubble dynamics under dual-frequency excitation is also investigated with demonstrating examples. Based on that, the parameters for optimizing the dual-frequency approach are proposed. In addition, the effects of thermal effects and mass transfer on the bubble dynamics have also been discussed.
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Song, Qiong. "FAST RESPONSE DUAL FREQUENCY LIQUID CRYSTAL MATERIALS." Doctoral diss., University of Central Florida, 2010. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3112.
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Dual frequency liquid crystal (DFLC) exhibits a positive dielectric anisotropy at low frequencies and negative dielectric anisotropy at high frequencies. The frequency where dielectric anisotropy is zero is called crossover frequency. DFLC can achieve fast rise time and fast decay time with the assistance of applied voltage. However, one drawback of DFLC is that it has dielectric heating effect when driven at a high frequency. Thus, the first part of this dissertation is to develop low crossover frequency DFLC materials. The dielectric relaxation and physical properties of some single- and double-ester compounds were investigated. Experimental results indicate that the double-ester compound exhibits a ~ 3 X lower dielectric relaxation frequencies and larger dielectric anisotropy than the single ester, but its viscosity is also higher. More generally, ten groups of dual frequency liquid crystals were compared in terms of dielectric relaxation frequency and dielectric anisotropy. The dielectric relaxation theory was discussed at last. To realize fast response time, high birefringence and low viscosity LC are required. From these two aspects, firstly four new high birefringence laterally difluoro phenyl tolane liquid crystals with a negative dielectric anisotropy were studied. These materials are used to enhance the birefringence of DFLC. They have a fairly small heat fusion enthalpy (~3000 cal/mol) which improves their solubility in a host. We dope 10 wt% of each compound into a commercial negative mixture N1 and measured their birefringence, viscoelastic constant and figure of merit. Birefringence varies very little among homologues while viscoelastic constant increases as alkyl chain length increases. Secondly, we studied the effects of six diluters for lowering the viscosity while stabilizing the vertical alignment (VA) of the laterally difluoro terphenyl host mixture at elevated temperatures. The pros and cons of each diluter are analyzed. These lateral difluoro terphenyls exhibit a high birefringence, fairly low viscosity, and modest dielectric anisotropy, but their molecular alignment in a VA cell is gradually deteriorated at elevated temperatures as their concentration increases. As a result, the device contrast ratio is decreased noticeably due to the light leakage through the crossed polarizers. Finally, liquid crystal doped with metallic nanoparticles, such as Pd, Ag, or Ag-Pd, which are protected with ligand molecules, such as nematic liquid crystal were studied. The metal nanoparticles doped LC exhibit a frequency modulation (FM) electro-optical (EO) response in the millisecond to submillisecond range together with the ordinary root-mean-square voltage response.Ph.D.
Optics and Photonics
Optics and Photonics
Optics PhD
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Lineberger, Ernest R. "Bubble detection using a dual frequency sound field." Thesis, Monterey, California. Naval Postgraduate School, 1988. http://hdl.handle.net/10945/22932.
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Perilla, Rozo Carlos Andres. "Noise model for a dual frequency comb beat." Doctoral thesis, Université Laval, 2019. http://hdl.handle.net/20.500.11794/34414.
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Cette thèse porte sur le raffinement d’un modèle du bruit utilisé pour des mesures spectroscopiques réalisées avec des peignes de fréquences optiques. La majorité des travaux antérieurs utilisaient des peignes de fréquences où le glissement (chirp) est minimisé, en supposant que tout glissement différentiel entre les peignes allait réduire le rapport signal sur bruit. L’hypothèse sous-jacente était que l’impact du bruit multiplicatif serait augmenté, le glissement lui permettant d’agir plus longtemps sur le signal d’interférence. Cependant, d’autres recherches indiquaient plutôt contraire : le chirp pourrait améliorer la mesure. Cette thèse cherche à augmenter la compréhension du comportement du bruit lorsque les peignes ont des glissements différentiels. De plus, celle-ci apporte de nouvelles évidences sur l’utilité du chirp dans ce type de mesure. À cet effet, nous avons fait une révision bibliographique des modèles du bruit dans les peignes de fréquences optiques. Ensuite, du point de vue théorique, nous avons analysé les effets du chirp sur les bruits additifs et multiplicatifs. Pour le bruit d’intensité, nous avons proposé un modèle phénoménologique décrivant le comportement de l’émission spontanée amplifiée (ASE) dans un laser à verrouillage de mode par rotation non linéaire de polarisation. Les spectres des peignes et leurs battements ont été caractérisés en portant une attention particulière à leur relation avec l’ASE. La thèse permet de conclure que le chirp différentiel n’affecte pas les niveaux des densités spectrales de bruit. Grâce au glissement différentiel de fréquence, il est possible d’envoyer plus puissance à l’échantillon et ainsi améliorer le rapport signal sur bruit des instruments à peignes de fréquence. D’un autre côté, la caractérisation de l’ASE a établi sa nature non-stationnaire. Elle a aussi expliqué des attributs spectraux qui sont observés régulièrement dans les signaux de battement des peignes. Finalement, en supposant que l’ASE circule largement dans une cavité opérée sous le seuil, sa caractérisation fournit une méthode pour estimer le déphasage non linéaire que subit le train d’impulsions femtosecondes.This thesis proposes a noise model refinement for spectroscopic measurements using dual optical frequency combs. Until now most studies centered their efforts on noise characterization using chirp free combs based on an unproved hypothesis: measurements would get worse with chirped combs since multiplicative noises would be present over a longer duration on the interference pattern thus leading to a greater impact. However, at least one experimental result hinted to the contrary: differential chirp would actually improve the signal to noise ratio. This thesis therefore aims at increasing the understanding of noise when a differential chirp is present in a dual comb measurement. The specific goal is to provide new insights about the usefulness of chirp in this kind of measurement. With this in mind, we conducted a literature review of noise models in optical frequency combs. We subsequently analyzed the chirp’s effect in the presence of both additive and multiplicative noise. The thesis also proposes a phenomenological model to describe the amplified spontaneous emission - ASE in short pulse lasers mode locked using non linear polarization rotation. Finally the comb spectra and their beat notes are characterized putting special attention to their relation with the ASE components. As conclusions, we can report that noise power spectral density levels do not change with a differential chirp. Chirping allows sending a greater optical power through the sample, such that the measurement signal to noise ratio can be improved. On the other hand, the ASE characterization established its non-stationary nature and explained very well characteristic features routinely observed in dual comb beat notes that were not fully understood. Finally, assuming the ASE experiences a sub threshold linear cavity allows using theses features to estimate the non linear phase shift experienced by the modelocked pulse train in the laser cavity.
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Wu, Wai-Man Monica. "Characterisation of a dual frequency conversion superheterodyne receiver." Master's thesis, University of Cape Town, 2008. http://hdl.handle.net/11427/5076.
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Includes abstract.Includes bibliographical references.
This dissertation starts off with a brief introduction of the SKA project, and explain how it relates to the KAT project. Then certain receiver design techniques and parameters will be discussed together with receiver design trade-offs will be presented. This dissertation will then focus on the actual simulations of the 3x4 receiver module using the time-domain RF simulator, SystemView. An overview of the design for the 24-channel RF rack integrated locally by Tellumat (Pty) Ltd is presented and acceptance tests will be conducted and the test results will be presented.
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Foroudi, Navid Carleton University Dissertation Engineering Electrical. "A high-speed CMOS dual-modulus frequency divider for mobile radio frequency synthesizers." Ottawa, 1991.
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Tangen, Thor Andreas. "Imaging of Nonlinear Scattering using Dual-frequency Band Ultrasound." Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for teknisk kybernetikk, 2010. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-11493.
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The work presented in this thesis is focused on developing a method for imaging of nonlinear scattering from stiff particles using dual-frequency band pulses. The pulse complexes are comprised of a low-frequency manipulation pulse and a high-frequency imaging pulse where the the two pulses overlap in time and there is a frequency relationship of 1:8-10. It may be shown that the polarity of the nonlinear scattering follows the polarity of the low-frequency pulse, while linear scattering does not. By transmitting two such dual-frequency band pulses in each beam direction where the polarity of the low-frequency pulse is inverted from the first to the second, nonlinear scattering may be detected. The low-frequency pulse not only manipulates the scattering but also the propagation of the high-frequency imaging pulse. These nonlinear propagation effects will mask the nonlinear scattering and must be corrected for in order to suppress the linear scattering and detect the nonlinear scattering.In the first paper of this thesis, the nonlinear propagation effects using confocal low-frequency and high-frequency beams are investigated in a water tank setup. A dual-frequency band annular array, where the low-frequency element is place behind the high-frequency element, to form a stack, was used. When the high-frequency pulse is short compared to the low-frequency pulse period, the nonlinear propagation effects can be approximated by a nonlinear propagation delay and frequency shift. It is shown how the delay and frequency shift increases close to linearly with increasing manipulation pressure and how axis the profiles of the high-frequency beam are affected. On transmit, the size relationship between the low and high-frequency apertures can be varied, and it is shown how the nonlinear propagation effects is dependent on the array setup.By transmitting an unfocused low-frequency beam together with a focused high-frequency beam, the position of the high-frequency pulse relative to the low-frequency pulse can be kept close to constant over the whole imaging region. By placing the imaging pulse at the peak of the manipulation pulse, the frequency shift due to nonlinear propagation can be minimized. In the second paper, the suppression of linear scattering using such a beam setup and only correcting for the propagation delay is investigated. Applying a low-frequency pressure of 85 to 500 kPa, the linear scattering could be suppressed 35 to 17 dB. It is shown that there is an amplitude difference between the first and second received pulse which is due to diffraction differences of the first and second beam. Since the low-frequency beam is unfocused, the manipulation pressure will vary over the focused high-frequency beam and distort the spherical focusing. This distortion will be different for the first and second beam and produce different diffraction of the two beams, which will yield an amplitude difference. Frequency shift due to nonlinear propagation will also affect the diffraction but it is indicated that the nonlinear aberration is the dominating factor.In the third paper three different beamforming strategies for dual-frequency band imaging is investigated; 1. Focused low freq. + Focused high freq., 2. Unfocused low freq. + Focused high freq. and 1. Unfocused low freq. + Unfocused high freq. The nonlinear propagation delay and frequency shift are estimated and predicted based on the estimated low-frequency manipulation pressure experienced by the high-frequency pulse. There is good accordance between the estimated and predicted values until diffraction becomes significant. When diffraction becomes significant, differences in diffraction between the first and second pulse will also introduce a frequency shift and delay other than that generated by the nonlinear manipulation pressure. Differences in the pulse form of the first and second pulse is thus not only due to manipulation of the propagation of the high-frequency pulse by the low-frequency, but also by differences in diffraction.The nonlinear propagation and scattering are generated by equal processes but are different in the way that nonlinear propagation is an accumulative effect while scattering is a local effect. In the last part of the thesis the difference between nonlinear propagation and scattering is investigated using simulations, where the bandwidth of the high-frequency pulse relative to the center frequency of the manipulation pulse is varied. It is shown that when the high-frequency pulse is shorter in time than one period of the low-frequency pulse, the nonlinear propagation and scattering becomes different and the nonlinear scattering can be detected if the nonlinear propagation is corrected for.The correction of nonlinear propagation can be in the form of a filter, and a method for estimating this filter is also presented in the last part. Based on statistical analysis of the filter, it is shown that the average suppression of linear scattering using the proposed correction filter, is dependent on the homogeneity of the relation between the first and second pulse over the receive beam. Said in another way; if this relation is not constant over the receive beam, the optimal correction for a given signal segment is dependent on the unknown distribution of scatterers within the beam.The level of suppression of linear scattering using the proposed filter method will be dependent on the transmit beam setup. A simulation study where the effect of aperture size relationship between the low- and high-frequency beams and f-number of the high-frequency beam on the level of suppression of linear scattering is presented. In order to achieve a high degree of homogeneity, the diffraction of the HF and LF beams should be equal, which is not trivial to achieve in a medium with attenuation. Choosing the aperture sizes in order for the fresnel numbers to be equal for the two beams was thought to yield the optimal setup, but as attenuation affects the low and high-frequency pulses differently, this is not necessarily true. The level of suppression of linear scattering increases when the the high-frequency aperture is increased, making the beam narrower, but the low-frequency aperture must also be increased accordingly.
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Meda, Venkatesh. "Integrated dual frequency permittivity analyzer using cavity perturbation concept." Thesis, McGill University, 2002. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=38236.
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Optimal utilization of microwave energy requires more basic knowledge of the dielectric properties of the material under investigation. The dielectric properties of materials subjected to microwaves are known to depend on moisture content, temperature and density of the material as well as the frequency of the applied microwave field. This thesis is focussed on the development and evaluation of the new Permittivity Analyser to measure the dielectric properties of agri-food materials at 915 and 2450 MHz using cavity perturbation concept.In this study, the dielectric properties measuring system was designed and developed using cavity perturbation concept to measure the essential and fundamental parameters of microwave-material interaction; dielectric constant and dielectric loss factor of selected agri-food substances and organic solvents. The TM010 mode of electromagnetic energy was selected and configured to operate at the peakresonant condition for both ISM (Industrial, Scientific and Medical) approved frequencies of .915 and 2450 MHz frequencies. The resonant perturbation cavities were designed, fabricated and tested using the network analyser and the permittivity analyser. High Q (ratio of energy supplied to absorbed) values were reported for both frequencies. Basic calibration of the measurement system was performed using standard media such as air, water and alcohol. Necessary mathematical steps and algorithms were written and integrated into a user-friendly software program (Visual basic 6.0) to carry out the entire measurement.
The dielectric properties (epsilon' & epsilon ″) of materials such as; edible oils---canola, soya and sunflower oils, neem oil/pulp, homogenized milk (1, 2 and 3.25% fat), organic solvents such as ethanol, hexane and their mixtures were determined at various temperatures and frequency (915, 2450 MHz) combinations, using cavity perturbation technique. Linear relationships between the dielectric properties and temperature found in the literature were confirmed to be valid for certain ranges in case of edible oils, organic solvents and milk samples tested with the cavity perturbation method. Repeatibility and variability aspects of the permittivity analyzer at both the frequencies are presented.
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De, Syamsundar. "Noise in dual-frequency semiconductor and solid-state lasers." Thesis, Paris 11, 2015. http://www.theses.fr/2015PA112114/document.
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Les sources cohérentes de lumière émettant deux fréquences optiques avec une différence largement accordable dans le domaine radiofréquence et un fort degré de corrélation entre leurs fluctuations respectives peuvent être d’un grand intérêt pour de nombreuses applications telles que la photonique micro-onde, les horloges atomiques ultra stables, la physique atomique, la métrologie, etc. C’est le cas des lasers bifréquences émettant deux modes de polarisations linéaires croisées avec une différence de fréquence dans le domaine radiofréquence. Nous comparons les caractéristiques de telles sources bifréquences basées sur des lasers à semiconducteurs (VECSEL: vertical-external-cavity surface-emitting laser) ou des lasers à solide (notamment les solides dopés Nd3+ ou Er3+). Au-delà de la différence évidente entre les mécanismes de gain dans les lasers à semiconducteurs et dans les lasers à solide, le VECSEL bifréquence et le laser Nd:YAG bifréquence ne présentent pas la même dynamique. Le VECSEL bifréquence, comme pour un laser de classe A, a une dynamique dénuée d’oscillations de relaxation puisque la durée de vie des photons dans la cavité est beaucoup plus longue que celle de l’inversion de population. A l’opposé, le laser Nd:YAG bifréquence possède une dynamique présentant des oscillations de relaxation comme pour un laser de classe B, en vertu du fait que la durée de vie des photons dans la cavité est plus courte que celle de l’inversion de population. Dans cette thèse, nous explorons les mécanismes par lesquels cette dynamique, en plus du couplage non linéaire entre les deux modes, gouverne le bruit dans les lasers bifréquences. En particulier, nous analysons à la fois expérimentalement et théoriquement les propriétés spectrales des différents bruits (intensité, phase) ainsi que leurs corrélations dans le cas d’un VECSEL bifréquence de classe A et d’un laser Nd:YAG bifréquence de classe B. Enfin, un modèle de réponse linéaire de deux oscillateurs amortis couplés permet d’interpréter les résultats obtenus sur la corrélation entre ces différents bruitsCoherent sources emitting two optical frequencies with a widely tunable frequency difference lying in the radio-frequency range and having a high degree of correlation between their fluctuations can be useful for numerous applications such as microwave photonics, ultra-stable atomic clocks, atom manipulation and probing, metrology, etc. Dual-frequency lasers, which emit two orthogonal linearly polarized modes with a frequency difference lying in the radio-frequency range, have huge potentials for the above mentioned applications. We compare the characteristics of such dual-frequency oscillation in lasers based on either semiconductor (VECSEL: vertical-external-cavity surface-emitting laser) or solid-state active media (mainly Nd3+, or Er3+ doped crystalline host). Apart from the obvious difference between the gain mechanisms in semiconductor and solid-state laser media, the dual-frequency VECSEL and the dual-frequency Nd:YAG laser exhibit different dynamical behaviors. The dual-frequency VECSELs exhibit relaxation oscillation free class-A dynamics as the photon lifetime inside the cavity is longer than the population inversion lifetime. On the contrary, the dual-frequency Nd:YAG lasers obey class-B dynamics linked with the fact that the photon lifetime inside the cavity is shorter than the population inversion lifetime, leading to the existence of relaxation oscillations. In this thesis, we figure out how the laser dynamics, in addition to the nonlinear coupling between the two laser modes, governs different noise phenomena in dual-frequency lasers. In particular, we demonstrate, both experimentally and theoretically, the influence of the laser dynamics and the nonlinear coupling between the two modes on the laser noise, by analyzing the spectral properties of the different noises (intensity, phase) and their correlation in a class-A dual-frequency VECSEL (vertical-external-cavity surface emitting laser) and a class-B dual-frequency Nd:YAG laser. Moreover, the noise correlation results are interpreted in terms of the linear response of two coupled damped oscillators
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Sullivan, Arthur. "AN UNCOMPROMISING DUAL FREQUENCY ANTENNA FOR TELEMETRY TRACKING APPLICATIONS." International Foundation for Telemetering, 1986. http://hdl.handle.net/10150/615383.
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International Telemetering Conference Proceedings / October 13-16, 1986 / Riviera Hotel, Las Vegas, NevadaCurrently, the majority of telemetry tracking systems in use throughout the world operate in the S-Band frequency range. While this frequency band serves as an adequate vehicle for most applications, some require an additional higher frequency for high bit-rate data. This requirement necessitates use of a dual frequency antenna and, more often than not, suffering an attendant performance compromise at both frequencies which is typically realized in such a device. One agency had such a requirement but was unwilling to accept the usual compromise in the S-band and X-band down-links used in aircraft testing. The design implemented by EMP Inc. satisfied the S-band requirements with the reputable, EMP developed, RADSCAN conical scan feed positioned at the focal plane of an eight foot paraboloidal reflector. The RADSCAN feed radome was redesigned, shaping the frontal surface to form a hyperboloidal dichroic subreflector for the X-band Cassegrain antenna. The subreflector was transparent to S-band while presenting a highly reflective surface to X-band energy. The hyperboloid was fed by a profiled corrugated horn mounted at the vertex of the paraboloidal reflector. The X-band Cassegrainian system produced optimum performance with no degradation whatsoever from the S-band Newtonian antenna. The degradation of the S-band system was less than 0.15 dB. The system provided simultaneous reception of both bands with collimated beams. The S-band system also included a side lobe comparison antenna which precludes acquisition of a target vehicle on a side lobe.
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Newton, Cory Nelson. "Design and Frequency Characterization of Dual-Piezoresponsive Foam Sensors." BYU ScholarsArchive, 2016. https://scholarsarchive.byu.edu/etd/9264.
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Multifunctional "self-sensing" materials at the frontiers of current research are generally designed to gather only a single type of information (such as quasi-static strain data). This project introduces a new sensor that is both multifunctional and dual-response, indicating its ability to not only perform in mechanical and sensing functions but also in its ability to sense multiple types of response. The proposed new class of sensing materials, comprised of nanocomposite polymer foams, exhibits measurable piezoresistive and quasi-piezoelectric phenomena in the form of change in resistance and voltage generation in response to deformation, respectively. An initial sampling of the envelope of dual-response nanocomposite foam sensors is mapped. The sensing materials can also be tailored to provide desired mechanical compliance and damping. Nanocomposite foam sensors decrease in resistance with increased strain in both static and cyclic compression environments. The quasi-piezoelectric voltage response of nanocomposite foam sensors increases linearly with compression frequency. A circuit and signal demodulation system was developed enabling simultaneous capture of a dual-response foam sensor's change in resistance and voltage generation. Measuring the two responses provides both long-term and immediate performance and health status of mechanical systems, enabling improved monitoring and decreased risk of failure.
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Lindy, Fred L. "Differential solutions using long-range, dual-frequency GPS correction data." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2002. http://library.nps.navy.mil/uhtbin/hyperion-image/02sep%5FLindy.pdf.
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Thesis (M.S. in Operations Research)--Naval Postgraduate School, September 2002.Thesis advisor(s): James R. Clynch, James N. Eagle, Samuel E. Buttrey. Includes bibliographical references (p. 77-79). Also available online.
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Chen, Luyi. "DUAL FREQUENCY PATCH ANTENNA DESIGN FOR GLOBAL NAVIGATION SATELLITE SYSTEM." Ohio University / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1178633247.
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Thierman, Jonathan S. (Jonathan Sidney) 1976. "Sources of difference frequency sound in a dual-frequency imaging system with implications for monitoring thermal surgery." Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/28762.
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Thesis (Ph. D.)--Harvard-MIT Division of Health Sciences and Technology, 2004.Includes bibliographical references (leaves 138-145).
(cont.) parametric effect, which can be considered an imaging artifact. Additionally, it may be possible to use the nonlinear interaction of scattered waves to form images that rely on the presence of small scatterers; a technique that may be enhanced with the use of contrast agents containing small scattering micro-bubbles in vivo.
This thesis explores the nature of the ultrasound-stimulated vibro-acoustography (USVA) imaging method introduced by Fatemi and Greenleaf in 1998. The USVA method relies upon the generation of a difference frequency signal from the interaction of two pressure fields with a target. A thorough understanding of USVA will be necessary to further advance this dual-frequency method. Prior studies demonstrate a correlation between difference frequency signal response and tissue temperature, and difference frequency signal response and tissue coagulation, suggesting that USVA may be well suited for monitoring focused ultrasound surgery. This thesis explores three possible sources of the difference frequency signal: 1) the parametric effect, 2) linear reflection of the local difference frequency field, and 3) nonlinear interaction of linearly scattered waves. The research compares the relative significance of these three possible sources using mathematical analysis, computer simulations, and experimental results. The results set forth in this thesis suggest that the parametric effect may be the most significant source of difference frequency signal, reaching pressures of 1-10 Pa and significantly overshadowing the other two enumerated effects. The second effect, the linear reflection of the local evanescent difference frequency field, is undetectable experimentally. Finally, the third effect, the nonlinear interaction of linearly scattered waves for a single bubble, contributes to the difference frequency signal only slightly, albeit detectably, reaching levels of .1-1 Pa. These results have a number of implications for future implementations of USVA. In order to utilize USVA as a successful imaging tool, one must take measures to avoid the signal from the
by Jonathan S. Thierman.
Ph.D.
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Parvex, Pichaida Taky. "Astrometric precision spectroscopy: Experimental development of a dual-frequency laser synthesizer based on an optical frequency comb." Tesis, Universidad de Chile, 2018. http://repositorio.uchile.cl/handle/2250/159288.
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Ingeniero Civil EléctricoLa tecnología de terahercios se encuentra en un estado de desarrollo atrasado con respecto a las tecnologías usadas en las bandas adyacentes, como la óptica infrarroja o la electróni- ca de microondas. En particular, no se poseen fuentes compactas de radiación que operen dentro esta banda logrando buenos niveles de potencia y amplios rangos de frecuencia. Las útiles propiedades de la radiación de terahercios como su capacidad de detectar moléculas complejas, buena resolución espacial y ser radiación no ionizante, hacen que el desarrollo de tecnología para esta banda sea un área con creciente interés. En el contexto del desarrollo de una nueva línea de investigación sobre espectroscopía molecular, en el Laboratorio de Terahertz y Astrofotónica de la Universidad de Chile, se realiza este trabajo que consiste en el desarrollo experimental de un sistema láser para la ali- mentación de fotomezcladores. Este sistema tiene como objetivo la generación de dos señales ópticas de alta estabilidad y coherencia, cuya diferencia de frecuencias puede ser ajustada de forma continua dentro del rango de 10 GHz a 300 GHz. Para esto, se utiliza un esquema basado en un peine de frecuencias óptico sobre el cual se enclava por inyección un láser de diodos de frecuencia sintonizable. Esto consigue tener una fuente infrarroja de alta precisión dentro de un gran rango. Además, se genera una segunda señal por medio de modulación en amplitud (AM), la cual es sintonizable dentro de un rango igual al espaciado producido por el peine óptico. En conjunto, estas señales logran abarcar un amplio espectro de frecuencias de forma continua sin perder estabilidad ni calidad de las señales. En este trabajo se logra implementar los subsistemas para la generación de cada una de las señales requeridas y se estudia la capacidad de estos para trabajar dentro del rango deseado. Para la señal generada por enclavamiento por inyección, se logra probar el concepto dentro de un rango reducido, principalmente por falta de un buen sistema de medición de altas frecuencias. Para la señal generada por modulación AM, se logran resultados positivos en todo el rango de diseño. Finalmente, se proponen modificaciones al sistema para mejorar su desempeño.
Este trabajo ha sido parcialmente financiado por Conicyt, a través de su fondo ALMA para el desarrollo de la astronomía, Proyecto 31140025, QUIMAL, Proyecto 1500010, CATA-Basal PFB06 y Fondecyt 1151213
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Park, Youngcheol. "Dual-Band Transmitters Using Digitally Predistorted Frequency Multipliers for Reconfigurable Radios." Diss., Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/5107.
Full textAbstract:
The objective of the proposed research is to develop simplified reconfigurable transmission systems with frequency multipliers for the transmission of complex modulated signals. Because they rely on nonlinear properties, frequency multiplier-based transmission systems require proper linearization techniques and accurate modeling of the signal transfer function. To accomplish these two goals, the author has developed techniques to model and linearize frequency multipliers and to digitize feedback signals for nonlinear characterization.
First, adaptive predistortion techniques and zonal transfer theories have been developed for modeling and linearization. The predistortion system has been verified by applying an IS-95B signal to various frequency multipliers built by the author.
Second, because the output signals at higher harmonic zones occupy wider frequency bandwidths than the signal in the fundamental zone does and thus make it harder to use traditional sampling techniques, a simplified but effective method called the sub-Nyquist sampling rate was developed and verified.
Third, two methods for reconfigurable transmitters using frequency multipliers in conjunction with digital predistortion linearizers were developed. Both methods make it possible to transmit complex signals via frequency multipliers by using dual-band transmission systems that incorporate frequency multipliers that are based on linearization techniques. One of these methods uses a circuit topology that can be switched between a fundamental-mode in-phase combined amplifier and a push-push frequency doubler using input phasing. The second suggested method uses a fundamental-frequency power amplifier followed by a varactor multiplier that can be bypassed with an RF switch.
This work will contribute to the development of low-cost and size-effective reconfigurable transmission systems because it requires fewer transmitting components and needs less sampling of the feedback networks.
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Li, Pei. "Novel wideband dual-frequency L-probe fed patch antenna and array /." access abstract and table of contents access full-text, 2006. http://libweb.cityu.edu.hk/cgi-bin/ezdb/thesis.pl?phd-ee-b21471447a.pdf.
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Thesis (Ph.D.)--City University of Hong Kong, 2006."Submitted to Department of Electronic Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy" Includes bibliographical references (leaves 179-189)
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Lai, Xiongliang. "Design and Analysis of a Dual-Mode Cascaded-Loop Frequency Synthesizer." BYU ScholarsArchive, 2009. https://scholarsarchive.byu.edu/etd/2187.
Full textAbstract:
A new architecture for a frequency synthesizer with adjustable output frequency range and channel spacing is introduced. It is intended for the generation of closely spaced frequency channels in the GHz range while producing minimal spurious phase noise components. The architecture employs two independent phase-locked loops that are driven in cascade by a single reference oscillator. The approach provides fine resolution and wide bandwidth as well as low phase noise and should find application in many contemporary communication systems. The synthesizer can be operated in either of two different modes: nonfractional and mini-denominator fractional modes. The architecture produces no fractional spurs in the first mode and relatively small phase spurs when operated in the second mode. For example, in an application to a P-GSM 900 system, it is capable of tuning from 890 – 915 MHz with a channel spacing of 200 kHz and shows worst case phase spurs of -100 dBc at an offset frequency of 833 kHz. Because of the low magnitude and location of the worst case spurs, the phase-locked loop filters can be designed with a wide bandwidth which in turn results in a fast settling time. A linear frequency-switching settling time (to 0.01% of frequency increments) of 128 μs is typical in the P-GSM 900 application.
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Draper, Anthony Diego. "Towards Fast Dual Frequency Comb Spectroscopy in Dynamic High Pressure Systems." Thesis, University of Colorado at Boulder, 2019. http://pqdtopen.proquest.com/#viewpdf?dispub=10982919.
Full textAbstract:
Laser absorption spectroscopy is a non-intrusive diagnostic tool particularly well-suited to investigate the dynamic and harsh conditions commonly found within combustion systems. By measuring the amount of light absorbed at specific wavelengths that are resonant with rotational-vibrational transitions in molecules, absorption spectroscopy gives a measure of the molecular population in particular quantum states. Experimental spectra are fit with a simulation generated from spectral line shape models combined with a spectroscopic database to infer species concentrations, temperature, and pressure. Dual frequency comb spectroscopy (DCS) with mode-locked frequency comb lasers is an emerging form of absorption spectroscopy that yields both high resolution (< 1 GHz) and broad bandwidth spectra (> 10 THz) on rapid timescales (< 2 ms). There are two key challenges facing DCS in dynamic combustion environments. First, obtaining high signal-to-noise-ratio (SNR) spectra has traditionally involved coherently averaging hundreds of individual spectra over seconds to minutes before fitting. Second, at the high temperatures and pressures commonly found within combustion systems, the existing line shape models and spectroscopic databases are known to not capture all of the key molecular physics, thereby requiring empirical extension and validation. This work presents techniques to enable rapid DCS measurements of thermodynamic properties in dynamic high-pressure, high-temperature, environments through power optimization and apodization to improve the short-term SNR. A rapid compression machine at Colorado State University is instrumented with a portable DCS spectrometer and temperature is recovered at 704 µs resolution from 1–21 bar and 294–566 K. This demonstrates the ability of DCS to be applied to combustion-relevant timescales for both broad bandwidth and high resolution non-intrusive measurements of harsh systems. The design development of an optical testbed that creates a well-known, high-temperature, and high-pressure environment is additionally discussed. This subsequently will enable determination of the accuracy limitations of existing molecular absorption models, as well as allow for model expansion. Together these abilities enable laser measurements to better evaluate and optimize combustion systems, including improved understanding of the underlying molecular processes. Proper understanding of the molecular dynamics will allow for instrumentation and quantification of more extreme environments such as inside rocket engines or the atmospheres of distant planets.
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Pinto, Jayawardena Talini. "Topside ionosphere/plasmasphere tomography using space-borne dual frequency GPS receivers." Thesis, University of Bath, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.669039.
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This research demonstrates the potential of novel technology for space-based remote sensing of the topside ionosphere-plasmasphere, supported by ionospheric imaging, which can augment and enhance our current understanding of the Earth’s plasmasphere. The research was conducted in two phases. The first was the development of a technology demonstrator ‘TOPCAT’ that installed a dual-frequency GPS receiver dedicated for topside ionosphere-plasmasphere imaging into a Low Earth Orbit (LEO). The novelties of TOPCAT were that it was designed from commercial-off-the-shelf (COTS) components and was installed on-board the CubeSat ‘UKube-1’, greatly reducing development and launch costs of the instrument. The successful launch of TOPCAT for space-borne remote sensing of the topside ionosphere and plasmasphere could provide the necessary proof of concept for the installation of a constellation of CubeSats – a possible next phase that may be implemented in the future. Thus, in its first stage, the thesis discusses the development of TOPCAT, together with design challenges encountered from constraints imposed by CubeSat technology. The discussion also includes the series of qualification tests performed to successfully qualify TOPCAT as a space-worthy payload design that can remotely image regions beyond the ionosphere. The second phase of research was the validation of the Multi-Instrument Data Analysis System (MIDAS) for the topside ionosphere and plasmasphere. A tomography algorithm originally developed for the ionosphere, MIDAS uses total electron content (TEC) measurements from differential phase of GPS signals, and inverts them to derive the electron density of the region. The thesis investigates the extension of MIDAS to image regions beyond the ionosphere by validating the algorithm for the topside ionosphere and plasmasphere. The process was carried out by first reconstructing a simulation by Gallagher et al. [1988] to verify the quality of the images. This was followed by the use of real GPS phase data from the COSMIC constellation to reconstruct the topside ionosphere-plasmasphere, and the qualitative comparison of the images with previous independent observations obtained through COSMIC and Jason-1 missions. Results showed that MIDAS can successfully reconstruct the undisturbed (quiet) topside ionosphere-plasmasphere using COSMIC data. However, imaging the storm-time topside ionosphere-plasmasphere requires better data coverage (i.e. more receivers) as the resolution offered by COSMIC was not sufficient to reconstruct fast-evolving structures – thereby emphasising the need for more data sources providing high resolution global coverage, such as a constellation of CubeSats with LEO-based GPS receivers.
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Garza, Felipe J. III. "A power electronic approach to improved dual-frequency vibration energy harvesting." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/112850.
Full textAbstract:
Thesis: M. Eng., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2017.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 121-122).
Vibration energy harvesters may be used as power sources for low-power, self-sufficient, wireless industrial sensors. State-of-the-art vibration energy harvesting uses switching power electronics to synthesize compact conjugate matched loads allowing for maximum harvested power. Previous work demonstrating dual-frequency vibration energy harvesting used a piezoelectric harvester loaded with analog-controlled power electronics but was unable to cancel the parasitic output capacitance typical of piezoelectric harvesters at both frequencies. This thesis addresses the technical challenge of achieving maximum power transfer from multi-frequency vibration energy sources, simultaneously. Improved dual-frequency energy harvesting is demonstrated using a piezoelectric vibration energy harvester loaded with digitally-controlled power electronics. The digital controller - performing fixed-point computations - allows for synthesis of a band-limited negative capacitor needed to improve dual-frequency energy harvesting.
by Felipe J Garza III.
M. Eng.
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Wang, Cheng. "Wideband and fast THz spectrometer using dual-frequency-comb on CMOS." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/118025.
Full textAbstract:
Thesis: S.M., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2018.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 71-75).
Millimeter-wave/terahertz rotational spectroscopy of polar gaseous molecules provides a powerful tool for complicated gas mixture analysis. Here, a 220-to-320 GHz dual-frequency-comb spectrometer in 65-nm bulk CMOS is presented, along with a systematic analysis on fundamental issues of rotational spectrometer, including the impacts of various noise mechanisms, gas cell, molecular properties, detection sensitivity, etc. The spectrometer utilizes two counter-propagating frequency-comb signals to seamlessly scan the broadband spectrum. The comb signal, with 10 equally-spaced frequency tones, is generated and detected by a chain of inter-locked transceivers on chip. Each transceiver is based on a multi-functional electromagnetic structure, which serves as frequency doubler, sub-harmonic mixer and on-chip radiator simultaneously. In particular, theory and design methodology of a dual transmission line feedback scheme are presented, which maximizes the transistor gain near its cut-off frequency fmax. The dual-frequency-comb scheme does not only improve the scanning speed by 20 x, but also reduces the overall energy consumption to 90 mJ/point with 1 Hz bandwidth (or 0.5 s integration time). With its channelized 100-GHz scanning range and sub-kHz specificity, wide range of molecules can be detected. In the measurements, state-of-the-art total radiated power of 5.2 mW and single sideband noise figure (NF) of 14.6~19.5 dB are achieved, which further boost the scanning speed and sensitivity. Lastly, spectroscopic measurements for carbonyl sulfide (OCS) and acetonitrile (CH3CN) are presented. With a path length of 70 cm and 1 Hz bandwidth, the measured minimum detectable absorption coefficient reaches [alpha] gas,min=7 .2 x 10-7 cm- 1 . For OCS, that enables a minimum detectable concentration of 11 ppm. The predicted sensitivity for some other molecules reaches ppm level (e.g. 3 ppm for hydrogen cyanide (HCN)), or 10 ppt level if gas pre-concentration with a typical gain of 10 5 is used.
by Cheng Wang.
S.M.
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Nagarajoo, Karthigesu. "Improved ionospheric correction for dual frequency and differential GPS positioning methods." Thesis, University of Leeds, 2007. http://etheses.whiterose.ac.uk/704/.
Full textAbstract:
A new three dimensional (3-D) electron density model has been developed that can give a very accurate description of the real ionospheric variation; latitudinally,longitudinally and altitudinally. An important advantage of this model is that the electron density and all its spatial derivatives are continuous as required for high accuracy in a ray tracing program. This model was then incorporated in the Jones 3-D ray-tracing program in order to determine the effect of ionospheric horizontal gradient on Global Positioning System (GPS) ray paths. This was used to investigate the accurate mapping of slant to vertical in the presence of horizontal gradient. In differential GPS (DGPS), the effect of the ionosphere is assumed to be the same for two closely spaced Earth receiving stations (e. g. 10km baseline distance). However, the presence of ionospheric horizontal gradient, especially for receivers in the equatorial and polar regions and the difference in elevation angle at these two spaced receivers, that are observing the same satellite, do introduce some range errors. These range errors need to be considered when the ionospheric error is corrected in the single difference approach. Some mathematical expressions have been developed to show the significance of these errors in final DGPS user positioning by performing ray tracing calculations between a reference station and a user station using a simple block ionospheric model incorporating a linear horizontal gradient. The baseline distance between the stations was 10km. Then, these models have been used to show the improvement in DGPS positioning by taking into account the error due to the effect of an ionospheric horizontal gradient and the difference in the elevation angle at the reference and user receivers observing the same satellite. Final positioning improvement of about 10cm has been obtained. Additionally, methods have been proposed to determine the magnitude of the ionospheric gradient from real data (e. g. from GPS satellites). It has been found that the Rutherford Appleton Laboratory United Kingdom's (RAL UK's) Total Electron Content (TEC) online map (updated at every 10 minutes) can give a gradient magnitude and direction which can be applied in DGPS horizontal gradient correction. This determined gradient, which is 1.6853/rad (in all direction), was then used in the ray tracing program (linear gradient approach) to show the improvement possible in the user positioning. Further, since it has been found that the RAL UK's TEC map correlates very well with the vertical TEC from International Reference Ionosphere (IRI), the gradient was then obtained from IRI for GPS receiving stations in the equatorial region, such as Malaysia. 15cm of improvement in the user positioning was then obtained showing the importance of correcting for the effect of the horizontal gradient for GPS stations in the region like Malaysia. The amount of improvement was also investigated for different Geometrical Dilution of Precision(GDOP) factors to see for what satellite configurations there would be the most positional improvement. In addition, the component of the gradient in the satellite direction was approximated by using a simple mathematical relation taking account of the elevation angle and the azimuths of the satellite from the navigation data. Then, these `corrections' were applied to the carrier phase measurements of GPS observation data to show positional improvement at the user in DGPS using GPSurvey. The resolution of the ambiguity 3 minutes and 30 seconds earlier than for the case before corrections, shows the improvement in the user positional when the magnitude and direction of the gradients was taken into account. The dual frequency correction scheme uses the dispersive nature of the ionosphere to eliminate the ionospheric range error. Nevertheless, the dual frequency model cannot totally remove the effect of the ionosphere as it does introduce some approximations. For an example, it does not take into account the presence of the higher order terms in the phase refractive index equation's expansion (in the power of X-1). Though the higher order terms are about two orders of magnitude lower than the first order term at L-band frequencies, in applications such as geophysics and surveying which require millimetre level positioning accuracy, these terms need to be considered. In this work, these higher order terms have been obtained by using a program based on an analytical perturbation method (which required as input the azimuth and elevation angle of the satellite and an approximate electron density profile), which is much less numerically intensive than using the numerical ray tracing method based on the Haselgrove equations. Then, about 4cm of improvement in the final positioning using a dual frequency receiver has been shown to be possible by correcting for these higher order terms.
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Kong, Fanqi. "Dual-frequency Optoelectronic Oscillator and its Application in Transverse Load Sensing." Thesis, Université d'Ottawa / University of Ottawa, 2014. http://hdl.handle.net/10393/31537.
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In this thesis, dual-frequency optoelectronic oscillators (OEOs) and their applications to transverse load sensing are studied. Two configurations of dual-frequency OEOs are proposed and investigated. In the first configuration, a polarization-maintaining phase-shifted fiber Bragg grating (PM-PSFBG) is employed in the OEO loop to the generation of two oscillating frequencies. The beat between the two oscillating frequencies is a function of the load applied to the PM-PSFBG, which is used in transverse load sensing. To avoid the frequency measurement ambiguity, a second configuration is proposed by coupling a dual-wavelength fiber laser to the dual-frequency OEO. A single tone microwave signal with the frequency determined by the birefringence of the grating is generated in the OEO and is fed into the fiber ring laser to injection lock the dual wavelengths. The sensitivity and the resolution are measured to be 9.73 GHz/(N/mm) and 2.06×10-4 N/mm, respectively. The high stability of the single-tone microwave signal permits accurate measurement, while the frequency interrogation allows an ultra-high speed demodulation.
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Angell, Jonathan Price. "Topex dual frequency altimeter studies : ionospheric corrections and ocean surface measurements." Thesis, University of Leicester, 1997. http://hdl.handle.net/2381/30618.
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The TOPEX/Poseidon altimetry mission was developed as a NASA/CNES collaboration to provide accurate sea surface height (SSH) measurements. The TOPEX mission's altimeter is the first, and so far only, dual frequency system in space. The use of two frequencies allows a correction to be made for the radar pulse delay imposed by the Earth's ionosphere which would otherwise lead to an underestimation of SSH. Not only does TOPEX/Poseidon provide the most accurate SSH measurements yet from space, it also provides the first ever quasi-global measure of the integrated electron content (IEC) of the ionosphere. This thesis utilises TOPEX/Poseidon data in a combined study of both the oceans and the ionosphere. Firstly a study of the dependence of the IEC on geomagnetic disturbances, and the spatial coherence scale of the IEC is performed by comparison with the International Reference Ionosphere, an empirical ionospheric model. A systematic dependence of IEC with geomagnetic disturbance is found, and the first ever quasi-global maps of IEC spatial coherence distance are produced. This investigation may lead to an improvement in the accuracy of the model, and hence also that of single frequency altimeter systems, which must rely on such empirical models for their correction to the ionospheric delay. Secondly the tropical Pacific Ocean is studied, in particular the characteristics of large scale wave activity in relation to the devastating climatic/oceanic phenomena known as El Nino. Kelvin, Rossby and tropical instability waves are identified, and their interactions and possible mechanisms related to El Nino are investigated. Evidence for both western and eastern boundary reflections are presented, and their significance to the delayed oscillator mechanism is discussed. The study illustrates the necessity for highly accurate SSH measurements.
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Hipke, Arthur [Verfasser], and Theodor W. [Akademischer Betreuer] Hänsch. "Dual-frequency-comb two-photon spectroscopy / Arthur Hipke. Betreuer: Theodor W. Hänsch." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2016. http://d-nb.info/1098130847/34.
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Wu, Meng-che, and 吳孟哲. "Dual-Polarization Frequency Reuse with Frequency Shifting." Thesis, 1999. http://ndltd.ncl.edu.tw/handle/30765252025043363279.
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碩士國立臺灣大學
電信工程學研究所
87
In this thesis, the performance of dual-polarized signals transmitted in the terrestrial radio links is discussed. Because of the imperfection of the terrestrial transmission channel, the dual-polarized signals can be interfered more easily. It's necessary to design a new scheme to improve system performance to resist the channel interference. We apply the concept of the orthogonal frequency division multiplexing (OFDM) systems. By using the frequency shifting and frequency allocation between two different polarized signals, there is one more orthogonal dimension existing in the system. And the system performance is improved. In the thesis, we analyze both the original system (without pulse shaping) and the pulse shaped system, and we prove that the proposed system scheme improves the transmission performance significantly.
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Hsiao, Chih-Hung, and 蕭志宏. "Magnetically Enhanced Dual Frequency Capacitive Discharge." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/41686023723778605140.
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碩士國立東華大學
電機工程學系
91
Abstract According to the technical roadmap, the density of transistor will be double in every 18 months, therefore the size of the transistor ruled keep shrinking 0.7 in every generation. Plasma processes must be served at low enough pressure for anisotropic process relative to device scale, but the plasma density corresponding etching rate will be extremely low. A new high density plasma source with independently controlled density and ion current is needed for the future development. Magnetically enhanced dual frequency capacitive discharge has been used in oxide etcher for enhancing plasma density, decreasing ion bombardment damage, and enhancing selectivity. In this study, we calculate the parameters of the magnetically enhanced dual frequency capacitive discharge, and model the system in an equivalent circuit. Theoretically derive the sheath width, conductivity, equivalent resistance and equivalent capacitance with intensity of magnetic field, pressure and magnitude of RF power variations. An exactly solution for a dynamic variable is our attempt. The purpose is to separate linear and nonlinear effects in the discharge and try to minimize the un-predicable variation in the manufacturing process. From the plasma parameters with the intensity of magnetic field variation, we can know the plasma density increased by the magnetic enhanced capacitive discharge due to more collision chance induced from magnetic confinement, therefore ionization rate increases. These results could be obtained from our equivalent dual frequency circuit model which is mainly dominated by sheath thickness. In which, the plasma generated is controlled by the high frequency source and the low frequency source mainly control ion current. Power consumption ratio of the high frequency source and low frequency source has been computed in the plasma bulk and sheath from the equivalent circuit model.
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Hsu, Chun-Wei, and 許君瑋. "Planar Dual-Frequency Dual-Sense Circularly Polarized Asymmetric Crossed-Dipole Antennas." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/28018837039812767373.
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碩士國立臺灣大學
電信工程學研究所
100
Design of dual-frequency dual-sense circularly polarized asymmetric crossed-dipole antennas is proposed in this thesis. The antenna design of conductive dipole and slot dipole are inspired by the developed two different circuit models, which are in shunt and series forms, respectively. By selecting the proper lengths of the arms, the proposed antenna may operate in two different frequency bands. Furthermore, by arranging the positions of the arms, the senses of the circular polarized (CP) radiation can be adjusted arbitrarily in the two bands. In this thesis, the proposed dual-band dual-sense CP antennas are designed and fabricated. The experimental results only show the case of the CP antennas in the same senses (both LHCP or RHCP). On the dual-band performances, the frequency ratio of the proposed antenna of conductive crossed-dipole achieves 3.3:1 in this thesis. Lastly, for practice applications, such as GPS or point-to-point wireless communication, a planar reflector is added the proposed antennas to improve the radiation performance in terms of the enhanced zenith gain and unidirectional patterns.
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Tsai, Zhen-An, and 蔡鎮安. "Fabrication of CPW-fed planar dual-frequency and tri-frequency antennas." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/14941563621524174206.
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碩士樹德科技大學
電腦與通訊研究所
93
In this thesis, we propose compact designs of CPW-fed dual-band、 tri-band planar monopole antenna and dual-band planar slot antenna operation. We use the technique of the radiating metal line printed directly on the substrates, it makes the antennas are light、thin、short and small, and it integrates with circuit substrates that to promote convenient for fabrication and to decrease the cost. In monopole antennas, the operation frequency is fit for GSM/DCS (900/1800 MHz) systems, the structure of a rectangle metal loop will resonate the first frequency (900 MHz), and inserts metal line in a side of rectangle metal loop that will resonate the second frequency (1800 MHz). In the other monopole antenna, we use the modification of ground plane that will resonate the third frequency, and fit for GSM/DCS (900/1800 MHz) dual-band and GSM/DCS/IEEE 802.11 b/g (900/1800/2450 MHz) tri-band antennas. In the slot antenna, the operation frequency is fit for IEEE 802.11 a/b/g (2.45/5.2 GHz), the structure is embedding a L shape metal patch in a rectangle slot, and inserts a L shape metal line at a corner of the rectangle slot, and connects with ground plane to forms dual-slot, we use the dual-slot and L shape metal patch to resonate dual-band with 2.45 GHz and 5.2 GHz.
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Liao, Ping-Hsiao, and 廖秉孝. "CPW-Fed Dual-Frequency and Triple-Frequency Microstrip Patch Antenna Design." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/45146736695487941224.
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碩士國立中央大學
電機工程研究所
91
Dual-frequency and triple-frequency operations of coplanar waveguide (CPW) fed microstrip patch antennas are presented in this thesis. For excitation of the proposed antennas, the capacitively coupled CPW-fed structures are proposed. By properly adjusting the dimension and location of the coupled slot, impedance matching at each operating frequencies can be achieved simultaneously. For dual-frequency operation, the proposed designs are obtained by loading one or two narrow slots in the square patch. An extended tunable frequency ratio range of the two operating frequencies can be obtained by varying the widths or positions of the loaded slots. Using the similar slot-loaded approach, a triple-frequency operation can also be realized. In addition, experimental results for the proposed structures are presented and discussed.
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Hwang, Nam. "A dual-frequency diode laser displacement sensor." Thesis, 1990. http://hdl.handle.net/1957/37969.
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Brotchie, Adam Robert. "Acoustic cavitation in dual frequency ultrasound fields." 2010. http://repository.unimelb.edu.au/10187/7087.
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Multiple frequency ultrasonic systems have become of interest in recent years in the context of scaling up and improving the efficiency of sonochemical reactors, having been found to offer certain advantages over single frequency systems. This thesis investigates dual frequency sound fields over a broad parameter space, addressing a large range of aspects of acoustic cavitation and the factors that influence these systems. Three different transducer types were employed: a low frequency sonotrode, a high frequency standing wave type transducer and a high intensity focused ultrasound (HIFU) transducer.The combination of two 20 kHz horns was found to be synergetic, with respect to sonoluminescence emission and sonochemical yields, only when the respective sizes of the two horns differed significantly, and the larger of the two horns was operated at low power and in a pulsed mode. The combination of a low frequency sonotrode with a HIFU field was highly synergistic under appropriate pulse and acoustic power conditions. This was attributed to cavitation fragments from the low frequency field providing a new source nuclei for cavitation in the HIFU cavitation zone. These results corroborate and extend upon those of previous reports, and are of relevance to the field of ultrasound lithotripsy. When a standing wave emitter was used in combination with the HIFU transducer, the reverse situation was observed, whereby HIFU cavitation stimulated cavitation in the standing wave field. This was only possible when the two frequencies were closely matched. A similar requirement was found for a system comprising two geometrically opposing standing wave emitters. It was proposed that this was due to the similar bubble active sizes rendering the stimulating mechanism more effective or due to more favourable superposition of the two sound waves with respect to bubble dynamics.
For the combination of a sonotrode and standing wave system, it was found that considerable synergy (sonochemical and sonophysical) could be attained through pulsed, low power operation, and that this was further extended at low temperature, high viscosity and in the presence of coalescence inhibiting solutes. High-speed photographic observations demonstrated that the presence of the high frequency source stimulated cavitation in the vicinity of the low frequency sonotrode surface. This effect was more dramatic in the presence of coalescence inhibiting solutes. This can be ascribed to the existence of a much greater high frequency bubble population, which may act as cavitation nuclei under the horn, where the radial dynamics are dictated by the low frequency field. A combination of higher bubble density and the bubbles being driven relatively more asymmetrically and non-linearly in the dual frequency field led to a higher degree of fragmentation. The fragments of cavitation were able to (in the solute solutions) in turn, stimulate cavitation in the high frequency field, which was confirmed through analysis of the acoustic emission spectra. Sonochemical and sonoluminescence studies demonstrated a large synergy in these systems.
Modelling of the radial bubble dynamics indicated that only at very low acoustic power can the combination of a high and low frequency source bring about a significant enhancement in collapse temperature. Experimental temperature determination, however, which represents a spatially and temporally averaged ‘chemical’ temperature, revealed that the collapse temperature was significantly lower than that measured during single frequency irradiation. This is likely due, at least in part, to bubbles being driven in a more asymmetric environment. This was substantiated by sonoluminescence spectra measured in the presence of sodium salts, which exhibited a much more prominent sodium emission line in the dual frequency system. Further, single bubble growth measurements indicated that dual frequency operation did not increase the rate of rectified diffusion, and actually suppressed it at elevated acoustic power, presumably because the bubbles were translocated away from the low frequency antinode. The bubble lifetime in the dual frequency field was calculated to be longer than those in either of the single frequency fields. It is plausible that this is due to a large number of bubbles pre-existing in the high frequency field prior to nucleation near the low frequency horn, extending their lifetime relative to single, low frequency sonication. Despite the fact that growth was retarded in the single bubble system, it is unclear to what extent rectified diffusion is affected in the multi-bubble field. Irrespective of the mechanism, the longer lifetime in the dual frequency field is consistent with the lower collapse temperature measured and with SL quenching studies.
Bubble size distributions were determined using a pulsed ultrasound method and were found to be affected strongly by the driving frequency, acoustic power, pulse width and dissolved gas concentration. The inverse dependence of the bubble size on the driving frequency is consistent with linear resonance theory and the main implication of the studies with power, pulse duration and gas concentration is that bubble-bubble coalescence is the major determinant of the bubble size at a given frequency. Another important outcome of this investigation is that the coalescence inhibitive effect of simple electrolytes, a highly contentious issue, can be completely attributed to their effect on the dissolved gas concentration.
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Huang, Ting-Yu, and 黃亭諭. "Dual-Frequency Excitation in Ultrasound Molecular Imaging." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/91816499535286391464.
Full textAbstract:
碩士國立清華大學
生醫工程與環境科學系
99
In the past decade, ultrasound molecular imaging has become a promising tool for cancer research, but there remain several challenges for its use in vivo. Low adhesion efficiency of microbubbles at the target sites decreases the contrast resolution of ultrasound molecular images. Conventional strategy to image the adherent microbubbles is based the clearance of freely circulating microbubbles after a period of time, which limits the development of real-time ultrasound molecular imaging. Motion artifacts may therefore affect the quality of acquired images. Thus, ultrasound radiation force (USRF) was recently proposed to increase the adhesion efficiency of targeted microbubbles and reduce the imaging time duration. Since ultrasound frequency close to lower resonance frequency of microbubbles can provide available USRF to drive microbubbles, USRF on commercialized microbubbles becomes a potential challenge on high-frequency ultrasound. In this study, we proposed a dual-frequency (DF) excitation with a high-frequency carrier and various low-frequency envelope components to optimize the targeting efficiency of microbubbles. Results show that DF excitation with envelope frequencies (i.e., 10–30 MHz) close to the resonance frequency of submicron in-house bubbles (i.e., 9–35 MHz) resulted in targeting enhancement of 3.3–6.2 folds at the duration of 2 minutes. In addition, the high-frequency carrier of DF excitation provides a more localized microbubbles adhesion area, showing great promise to reduce the biological effect of ultrasound targeted therapy. In the second part, we combined DF excitation with chirp reversal technique (referred to DF-chirp reversal) to selectively image the adherent microbubbles. Since DF chirp excitation can be compressed by matched filtering to suppress tissue components, the contrast-to-tissue ratio can be up to 24.8 dB in-vitro phantom experiments. Therefore, the DF-chirp reversal method has the potential to be implemented in a real-time ultrasound molecular imaging system.
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Chen, Jing-Fen, and 陳靜芬. "DOA Estimation Using Dual Frequency GNSS Receiver." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/10641151986471269965.
Full textAbstract:
碩士國立臺灣海洋大學
通訊與導航工程學系
101
In this thesis, an ESPRIT-based direction-of-arrival (DOA) estimation method is proposed to estimate the azimuth and elevation angles of dual-frequency measurements coming from independent signal sources. ESPRIT (Estimation of Signal Parameter via Rotational Invariance Techniques) is a well-known algorithm for estimating DOA based on rotational invariance technique. For the traditional ESPRIT method, however, the array of sensors (usually more than four) has to be placed in a specific geometric structure. In this paper, we propose a new way to approach the similar result without imposing constraints on the array geometry by using dual frequency GNSS (Global Navigation Satellite System) receiver. In the proposed method, the DOA of GNSS signals can be estimated using only one dual frequency receiver and the physical structure limitation can be circumvented by assuming that the velocity of the satellite is known. This is generally not a very stringent requirement since the velocity of GNSS satellite can be predicted in an accurate manner using the broadcast ephemeris. Finally, some simulation results are given to verify the proposed algorithm.
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Wu, Ching-Yen, and 吳清延. "A 1.5V 5GHz Dual-Band Frequency Synthesizer." Thesis, 2002. http://ndltd.ncl.edu.tw/handle/19166291217408720287.
Full textAbstract:
碩士國立清華大學
電子工程研究所
90
While wireless local area networks (WLAN) standards in the 2.4-GHz range have recently emerged in the market, the data rates supported by such systems are limited to a few megabits per second. The demand for WLAN systems that can support data rates in excess of 20 Mb/s with very low cost and low power consumption is rapidly increasing. Hence, a number of standards, such as high-performance radio LAN Type 2 (HIPERLAN2) and 802.11a, have been defined in the 5-GHz range that allow data rates greater than 20 Mb/s, offering attractive solutions for real-time imaging, multimedia, and high-speed video applications. In this thesis, we present the design of an integer-N frequency synthesizer for 5-GHz WLAN applications. To target realistic specifications, HIPERLAN2 is chosen as the framework. Employing an integer-N architecture, the circuit generates 5.18-5.32 GHz and 5.5-5.7GHz outputs for the whole HIPERLAN2 specification. Realized in a 0.18-μm CMOS technology, the synthesizer provides a channel spacing of 20 MHz while dissipating 27 mW from a 1.5-V supply. The VCO phase noise at 1-MHz offset is equal to—109 dBc/Hz.
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Chen, Kai-Chih, and 陳凱志. "Research in Dual-Frequency Ultrasonic Distance Measurement." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/91596677214692348052.
Full textAbstract:
碩士國立中央大學
機械工程研究所
92
This paper proposes two new ultrasonic distance measurment methods. The first is the dual-frequency. In order to improve traditional ultrasonic distance measurement, it takes all detectable received waves to estimate the real time-of-flight. In addition, considering the measurement efficiency and accuracy, we develop a changed-frequency exciting signal instead of dual-frequency one. It can do more measurement in a constant time. Simulation results reveal that arrival time analyses of two measurement methods have much better accuracy than traditional measurement. The maximun error in dual-frequency measurement is 4.15um and 3.61um in changed-frequency. The real implementation is based on theoretical analys because the accuracy of two methods have been proved. In real measurement data analysis, we examine the feasibility and discuss the error source. Finally, we develop a measurement system with 4mm error accuracy in the 3m range.
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Chiang, Yen-Ting, and 江衍霆. "28/38 GHz dual mode frequency synthesizer." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/xn7pyx.
Full textAbstract:
碩士國立臺灣科技大學
電機工程系
107
A 28/38 GHz dual-band frequency synthesizer for 5th generation mobile communication is implemented using TSMC 90-nm CMOS technology. The on-chip VCO achieves the tuning range from 23.5 GHz to 28 GHz, and exhibits the phase noise of -105.57 dBc/Hz~ -107.08 dBc/Hz at 1 MHz offset, from the 23.5 GHz~28 GHz carriers. With dividers and mixers, the 28/38 GHz carrier is synthesized from the VCO output signal in two operation modes, where the synthesizer dissipates 143.16 mW at 28 GHz band with the resolution of 281.25 MHz and the in-band phase noise is -75.57 dBc/Hz ~-81.38 dBc/Hz @ 100 kHz offset, the out-band phase noise is -93.27 dBc/Hz ~-106.32 dBc/Hz @ 10 MHz offset, and 129.64 mW at 38 GHz band with the resolution of 375 MHz and the in-band phase noise is -77.11 dBc/Hz ~-84.75 dBc/Hz @ 100 kHz offset, the out-band phase noise is -98.34 dBc/Hz ~-105.29 dBc/Hz @ 10 MHz offset. The sideband rejection ratio is 17.8 dB ~ 39.73 dB. The LO leakage rejection ratio is 6.07 dB ~ 56.47 dB. The locking time is 4~6 μs. The chip area is 2.154 mm2.
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Kuo, Wei-Luien, and 郭瑋倫. "Design of a Dual Frequency Pseudolite Transmitter." Thesis, 2002. http://ndltd.ncl.edu.tw/handle/8ze2es.
Full textAbstract:
碩士國立成功大學
電機工程學系碩博士班
90
Pueuodolite(pseudo-satellite)can transmit GPS-like signal to enhence the accuracy and integrity in GPS positioning. The thesis describes the design of implementation, and fest of a dual frequency pseudolite. Through the implementation of dual frequency pseudolite, RTK positioning can be greatly enhanced.
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YANG, KAI-PING, and 陽開平. "STUDIES OF COMPACT DUAL-FREQUENCY MICROSTRIP ANTENNAS." Thesis, 1999. http://ndltd.ncl.edu.tw/handle/20133591310125531151.
Full textAbstract:
博士國立中山大學
電機工程學系
88
The compact dual-frequency antennas with slot have been investigated in this dissertation. By insetting slot at the patch edges or cutting slot in the patch center, a single-feed rectangular microstrip antenna with compact dual-frequency operation can be obtained. The two operating frequencies are of orthogonal polarization planes and can be controlled by adjusting the patch dimensions and the slot size in the patch. And, by increasing the slot size, both the two operating frequencies are significantly lowered. This suggests that, for a fixed dual-frequency operation, the present proposed dual-frequency design can provide a much smaller required antenna size. Results show that an antenna size reduction about 23~44%, as compared to a regular-size dual-frequency rectangular microstrip antenna, can be achieved using the proposed designs. Details of the design methods are described, and experimental results of the proposed antenna performance are presented and discussed.
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Lee, Tzeng-Shen, and 李曾申. "Investigation of frequency dependence of molecular reorientation in dual frequency liquid crystals." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/45552458947396568616.
Full textAbstract:
碩士國立中正大學
光機電整合工程所
94
This thesis is probed into the frequency dependence of molecular reorientation in dual frequency liquid crystals. Maier and Meier have extended the Onsager theory to nematic liquid crystals. They first applied the Onsager’s theory of the dielectric constant to the isotropic polar liquids, and then extended it to liquid crystal in nematic phase,. They considered two types of polarizations that contribute to the dielectric constant: (1) induced polarization and (2) orientational polarization. The field-induced polarization follows the external field rapidly. However, the orientation polarization exhibits a longer rising and decay time(τ). According to Debye’s equation, the dielectric constant can be described as . When the frequency of an applied field is much higher than , the orientation polarization can’t follow the variations of the external field any longer. Thus, the dielectric constant drops to which is contributed solely by the induced polarization. In dual frequency liquid crystals, the strongly hindered rotation of nematic molecules around their short axes leads to the dispersion of the parallel dielectric constant with increasing angular frequency . At the cross-over frequency the positive dielectric anisotropy turns to be zero, i.e., . Further increase of turns to be negative. On the other hand, the rotation around the long molecular axes is almost not hindered in nematic molecules. Consequently, no dispersion of the perpendicular dielectric constant is expected up to microwave frequencies. iii From the theory of dual-frequency liquid crystals, application of electric fields with frequencies across serves as an optical switch. This thesis deals with the following two aspects. First of all, we will measure the crossover frequency. Secondly, we will place a dual frequency liquid crystal in between two crossed placed polarizers, apply electric field of different voltage and frequencies across , and then measure the transmittance of a HeNe laser beam as a function of the voltage and frequency.
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Almalki, Mazen S., and 艾莫山. "A Dual-Frequency and Dual-Polarized Patch Antenna for Ka-Band Satellite Communication." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/39723640395434838182.
Full textAbstract:
碩士國立臺灣大學
電信工程學研究所
104
Antennas are an essential part in a communication system as they control a spatial and temporal coverage of the signal. Circularly polarized (CP) patch antennas have a wide range of applications because of their low profile, low cost, and easy fabrication. In this thesis, two antenna structures are presented for the Ka-band communications. Initially, two square patch antennas configured with side by side are designed at two different frequencies. Each patch element is excited by using two separate probe feeds for the right- and left-hand circular polarization operations. The cavity wall is used to improve the isolation of the design. For the second approach, dual stacked patch antenna is presented for the enhanced impedance bandwidth with reduced antenna area. Both designs used a 90-degree hybrid coupler to achieve LHCP & RHCP.
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楊明忠. "Simulation and Implementation of Dual Frequency Microstrip Antennas." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/25432408728143687370.
Full textAbstract:
碩士明新科技大學
電機工程研究所
93
In recent years, personal wireless communication systems have been booming rapidly. Light, thin, short, and small components of the systems are demanded in fashion. Therefore, the antennas are designed to be compact, planar, and integrated to fit into the systems. In this thesis, we design and simulate the compact antennas. By utilizing the characteristics of new-type slotted microstrip antennas we design a miniature and adjustable dual-frequency microstrip antennas, which can be applied to wireless communication systems. In three popular bands, GSM (890 MHz ~ 960 MHz), DCS (1710 MHz ~ 1880 MHz), and PCS (1850 MHz ~ 1990 MHz), we design different microstrip antennas. Using IE3DTM, commercial simulation software, to design and simulate each antenna, we study and compare the parameters, like shapes, feed points, and finite ground plane effects, of each antenna. The equilateral triangular microstrip antenna with a pair of embedded side-by-side line troughs of Spurs-Lines on the microstrip is an innovated design. The antenna can be easily implemented to be adjustable dual-frequency and circular polarized.
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Yeh, Chorng-Horng, and 葉崇宏. "Dual-Frequency GPS Rapid Surveys of Short Baselines." Thesis, 1995. http://ndltd.ncl.edu.tw/handle/94313506847367347380.
Full textAbstract:
碩士國立海洋大學
航海技術學系
83
Since the semi-kinematic and the pseudo-kinematic survey deloped , two methods of kinematic survey provide more efficiency than the traditional static survey of short baselines. But in the semi-kinematic survey, it is necessary to lock up satellite signals continuously, and in the pseudo- kinematic survey, it is necessary to take re-occupation. We use Rapid-Static survey to improve these shortcomings of semi- kinematic survey and pseudo- kinematic survey. When the AS (Anti-Spoofing)is activated, the P-code on the L1 and L2 carrierrs is replaced with Y-code. It's for authorized userrs only. We used the Ashtech Z-12 receivers to tracking the underlying P-code and W-code in the Y-code. Using the base station in the NTOU (National Taiwan Ocean University) and several rover stations between 1 Km to 30 Km, we derived results from Rapid-Static survey. The results show that, just 2 minutes site occupation time, the accuracy can reach up to cm- level. It will improve the accuracy of GPS navigation and survey.
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Iang, Sheng-Iu, and 楊勝裕. "Dual Frequency Microstrip Antenna Circuit Design and Application." Thesis, 1999. http://ndltd.ncl.edu.tw/handle/26670186287982030378.
Full textAbstract:
碩士義守大學
電子工程學系
87
The applications using wireless communication have been increased significantly in recent years, which requires for more functionality in wireless handset. In order to fit into different service needs, systems such as DECT, PACS, GSM, DCS, etc, are designed. For a wireless user, a handset for each set will not only cumbersome but it will also be very inconvenient. To allow a single handset to be used for different wireless system, i.e., a dual band or even multiple bands handset, has become the trend of wireless communication. Radiation hazard has also become an important issue in recent years. Dipole antenna used by most handset is an omni-directional radiator. In order to reach the far away base station, it will also radiate the same amount of energy to the user that causes potential danger. The use of microstrip antenna will reduce the radiation in half the space significantly due to the ground plane. This type of antenna will significantly reduce the amount of radiation to the user while provide the same power to a distant base station. We design the rectangle dual frequency microstrip antenna which operation frequencies at 900MHz and 1.9GHz by FR-4 substrate ( =4.7). In this dissertation, we have studied the control of operation frequencies and usable bandwidth for microstrip multiple frequency band antenna. The operation frequency of the antenna can be modified through the change of feed location and the locations of load. The usage bandwidth of different frequency band can be controlled by the use of resistive load. Then, we can design the dual frequency broadband microstrip antenna of. The size of the antenna patch is reduced significantly by applying slots in the patch. Since the size of each antenna element is small, it is easy to integrate the antenna elements as part of circuits. Also, it is possible to make an antenna array according to the convenience of outlook design, e.g., the outside surface of a handset. The antenna array allows a more efficient radiation design or even a directional control for a safer usage.
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Chen, Jen-Ke, and 陳仁格. "RF Frequency Divider Implemented by Dual Injection-Locking." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/5kk9u2.
Full textAbstract:
碩士國立中正大學
電機工程研究所
102
The study of this thesis focuses on the design of frequency divider which is used in the phase lock loop of the wireless transceiver. All the proposed circuits were implemented by TSMC 0.18μm 1P6M CMOS and TSMC 0.18μm 3P6M BiCMOS process. In this thesis, two wide locking-range frequency dividers are proposed for X-band and Ku-band applications; and one injection-locked frequency divider by 5 for K-band application. The dual injection-locked frequency dividers proposed in this thesis demonstrate a simple but efficient method to enhance the injection strength. Based on the locking range formula, the strength enhancement of injection signal will make the locking range wider. Therefore, the proposed ILFD demonstrates dual-injection topology achieving high locking range. In chapter II, a dual-mode and wide locking-range dual injection-locked frequency divider by two and by three is demonstrated. This proposed ILFD can function as divider by two and three. The measured locking-range is from 7.95 GHz to 11.78 GHz (38.8%) with an injection power of 0dBm in divider by two and 13.39 GHz to 16.39 GHz (20.1%) with an injection power of 0dBm in divider by three. The power consumption of the core circuit takes 6.48mW from a 1.2V power supply. In chapter III, a wide locking range dual injection-locked frequency divider by three is demonstrated. This proposed ILFD uses dual direct-injection technique. The measured locking range is from 11.78 GHz to 14.81 GHz (22.8%) with an injection power of 0dBm. The power consumption of the core circuit takes 6.12mW from a 1.2V power supply. In chapter IV, a direct injection-locked frequency divider by five with wide locking range is demonstrated. This proposed ILFD uses the direct-injection technique which includes a direct injection-locked frequency divider by two to enhance the locking range and output power. But the proposed high modulus ILFD suffers a problem from the circuit layout. The measured results do not meet with the expectations. It needs more attentions on the circuit layout. The simulation and measurement results provide the proof of the dual-injection topology proposed in this thesis effectively enhancing the locking-range. In the future, it can support the study on the ultra low power consumption injection-locked frequency divider.
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Cheng, Chih-Hao, and 鄭致灝. "Dual-Frequency Ultrasound Excitation in Contrast-Enhanced Imaging." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/82925807668832215757.
Full textAbstract:
碩士國立清華大學
生醫工程與環境科學系
98
Microbubbles detection techniques such as phase inversion and nonlinear harmonic methods have become popular in blood perfusion imaging due to its capability to distinguish bubbles from background tissue. The aforementioned techniques require the microbubbles to effeciently oscillate by insonation with pulse transmission near to the resonance frequency of the contrast agents. However, for most commercial ultrasound contrast agents (UCAs), they are originally designed to resonate at lower frequencies ranging from 2-3 MHz, so it makes difficult in imaging by high frequency ultrasound, thus limiting the spatial resolution of imaging. To oversome this problem, a dual-frequency difference excitation tenique has been proposed in our previos studies. The proposed dual-frequency (DF) excitation waveform is an amplitude modulated wave comprising two sinusoids (f1 and f2), it can be transmitted at high frequency band while produce low frequency driving force to excite microbubbles by resultant envelope component at frequency of (f1-f2). Based on the advantages of this technique, the thesis further investigates their potential applications. First, we concentrate the energy of nonlinear scattering induced by DF excitation to enhance the contrast to tissue ratio (CTR) of sub-harmonic imaging. In the study, the f2 at twice of the resonance frequency of UCAs is adopted to efficiently generate sub-harmonic component, and f1 is included as an ehancing component to induce high-order nonlinearity of UCAs at sub-harmonic frequency. The second and third-order nonlinear components related to envelope component would coincide at sub-harmonic frequency if a proper set of f1 and f2 are selected. We further optimize the sub-harmonic generation by tuning the phase between second and third-order component. The results show that, with dual-frequency excitation, the sub-harmonic CTR improves as compared to conventional method. Moreover, the CTR changes periodically with the phase of dual-frequency excitation, leading to a difference up to 9.1 dB between the maximal and minimal CTR. Moreover, the echo produced from the envelope component seems to be specific for UCAs and thus the proposed method has the potentials to improve both SNR (signal-to-noise ratio) and CTR in sub-harmonic imaging. Second, we focus on reconstructing the DF technique degraded axial resolution, because pulse length has to be enlongated to provide sufficient driving force at envelope frequency. To achieve this goal, we propose a method called as dual-frequency chirp (DF chirp) excitation which comprised two linear chirp signals, the resultant envelope component is modified from a single frequency tone bursts into the chirp form for pulse compression. This method is based on selectively extracting and compressing the second order nonlinear response by a matched filter with same center frequency and bandwidth as envelope component. The results show that DF chirp is feasible to improve the axial resolution and increase SNR of conventional DF excitation technique. However, no matter the DF chirp or DF tone bursts excitations, the second-order nonlinear response appeared at region of tissue background as acoustical pressure up to 800 kPa. To solve this problem, we further discuss the feasibilities of two methods including fourth-order nonlinear compression and chirp reversal two techniques for tissue suppression.
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Sandhu, Jagmit S. "High precision dual frequency timing of millisecond pulsars." Thesis, 2001. https://thesis.library.caltech.edu/3590/1/Sandhu_js_2001.pdf.
Full textAbstract:
NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.
The science of precision millisecond pulsar timing can yield the most precise astrometric measurements ever made. This potential can only be realized through an extraordinary amount of investment in the experimental apparatus, the effort of many observers, and the close attention to details required to avoid the many pitfalls along the way. This thesis describes the work and results from a precision timing project aimed at monitoring the brightest millisecond pulsar, PSR J0437-4715. This pulsar is a very suitable target for such a study because of its small period (5.75 ms), low DM (2.69 pc cm[...]), and high flux density (~ 90 mJy at 1.4 GHz). The initial work for this thesis involved completion and installation of the Fast Pulsar Timing Machine (FPTM) at Parkes observatory, Australia. With a bandwidth of 128 MHz and time resolution of 4 [...], this machine made a quantum jump in the time of arrival precision for PSR J0437-4715. The precision improved from ~ 2 [...] to ~ 0.2 [...]. In order to further enhance the signal-to-noise ratio achievable with this pulsar and probe the limits of precision pulsar timing, we have subsequently improved the FPTM significantly by doubling its bandwidth, so that it can record the pulsar radio emission over a 256 MHz bandwidth. This required us to double the IF processing hardware in the FPTM and implement numerous software modifications to control the observing apparatus, interface the FPTM with the observatory control computers, as well as process the data to produce final times of arrival.
Integration of just a few minutes with the 64 m Parkes radio telescope yield times of arrival for PSR J0437-4715 with a precision of 100 nanoseconds. The longer term residuals (3 years) show root-mean-square deviations of 500 nanoseconds. This excessively large scatter in the residuals has been traced to inaccurate polarization calibration, and a systematic quadratic trend of ~ 5 [...] in the times of arrival as a function of baseband frequency. The latter phenomenon has been simulated in software and shown to arise from the large dynamic range in the baseband spectrum. Despite the systematic errors, our measurement of the pulsar's astrometric and binary parameters match the best obtained so far with other millisecond pulsars. This has allowed us to measure the pulsar's parallax, and the secular change in the binary's projected semi-major axis due to the system's proper motion. The latter effect restricts the inclination angle of the binary, [...] < 43[...]. The parallax, along with the period derivative and orbital period derivative, enable us to constrain the distance of the pulsar, 162 < d < 205 pc. A stability analysis of the pulsar's time of arrival residuals demonstrates that it matches the long term stability of the best studied millisecond pulsars, PSRs B1937+21 and B1855+09, at least on the time scale of the data available so far, 3 years. The precision in the pulsar position now matches the amplitude of the modulation of position expected from the pulsar's binary motion. Detection of this effect will require reduction of the calibration and spectral shape errors, as well as further refinements in the timing software used. Along with radio interferornetric observations of the pulsar and optical detection of the white-dwarf companion, the pulsar timing position will provide the best contraints for frame tie between the ecliptic and extragalactic reference frames.