Journal articles on the topic 'Resonant over-reflection'
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1
Benilov, E. S., and V. N. Lapin. "On resonant over-reflection of waves by jets." Geophysical & Astrophysical Fluid Dynamics 107, no. 3 (June 2013): 304–27. http://dx.doi.org/10.1080/03091929.2012.709515.
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Xu, Wei, Chun Chen, Min Han Htet, Mohammad Saydul Islam Sarkar, Aifeng Tao, Zhen Wang, Jun Fan, and Degang Jiang. "Experimental Investigation on Bragg Resonant Reflection of Waves by Porous Submerged Breakwaters on a Horizontal Seabed." Water 14, no. 17 (August 29, 2022): 2682. http://dx.doi.org/10.3390/w14172682.
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Submerged breakwaters based on Bragg resonance could be one of the measures used for mitigating marine disasters and coastal erosion in nearshore areas. Here, flume experiments were conducted to investigate the Bragg resonant reflection of waves propagating over porous submerged breakwaters. Furthermore, the influence of permeability, relative width, relative height, and section shapes of submerged breakwaters on Bragg resonant reflection were considered. This revealed that the Bragg resonant reflection coefficient increased with the decrease in permeability and increase in the relative height of submerged breakwaters. However, a slowing trend occurred when the Bragg resonant reflection coefficient peak decreased with the increase in permeability and increased with the increase in relative height. Moreover, the primary peak Bragg resonance increased with the increase in the relative width of submerged breakwaters in the range of 0.1–0.3. This was consistent with the numerical results of Ni and Teng (2021), to a certain extent, as the reflection coefficient first increased and then decreased with the relative bar width. In addition, rectangular submerged breakwaters demonstrated a better reflection effect than the trapezoidal submerged breakwaters, and the triangular submerged breakwaters demonstrated a poor reflection effect.
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Dragna, Didier, Ariane Emmanuelli, Sébastien Ollivier, and Philippe Blanc-Benon. "Sonic boom reflection over urban areas." Journal of the Acoustical Society of America 152, no. 6 (December 2022): 3323–39. http://dx.doi.org/10.1121/10.0016442.
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Sonic boom propagation over urban areas is studied using numerical simulations based on the Euler equations. Two boom waves are examined: a classical N-wave and a low-boom wave. Ten urban geometries, generated from the local climate zone classification [Stewart and Oke (2012), Bull. Am. Meteorol. Soc. 93(12), 1879–1900], are considered representative of urban forms. They are sorted into two classes, according to the aspect ratio of urban canyons. For compact geometries with a large aspect ratio, the noise levels and the peak pressure, especially for the N-wave, are highly variable between canyons. For open geometries with a small aspect ratio, these parameters present the same evolution in each urban canyon, corresponding to that obtained for isolated buildings. A statistical analysis of the noise levels in urban canyons is then performed. For both boom waves, the median of the perceived noise levels mostly differs by less than 1 dB from the value obtained for flat ground. The range of variation is greater for open geometries than for compact ones. Finally, low-frequency oscillations, associated with resonant modes of the canyons, are present for both compact and open geometries. Their amplitude, frequency and decay rate vary greatly from one canyon to another.
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Xiong, Lei, Hongwei Ding, Yuanfu Lu, and Guangyuan Li. "Active tuning of resonant lattice Kerker effect." Journal of Physics D: Applied Physics 55, no. 18 (February 10, 2022): 185106. http://dx.doi.org/10.1088/1361-6463/ac4ec5.
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Abstract The Kerker effect has been generalized in nanophotonics and meta-optics, and has recently been of great interest by relating it to various fascinating functionalities such as scattering management and perfect transmission, reflection or absorption. One of the most interesting generalizations is the resonant lattice Kerker effect in periodic nanostructures. However, its active tuning has not been explored yet. Here, we report, for the first time, the active control of the resonant lattice Kerker effect in periodic Ge2Se2Te5 nanodisks. By changing the crystalline fraction, we show that the electric dipole surface lattice resonance (ED-SLR), the magnetic dipole resonance (MDR), and thus the resonant lattice Kerker effect are all red-shifted. We therefore realize the transition from the ED-SLR to the resonant lattice Kerker effect, which enables multilevel tuning of reflection, transmission and absorption with modulation depths above 86%. Taking advantage of the MDR redshifts, we also observe broadband and multilevel tuning of transmissions with modulation depth of 87% over a broadband range of 588 nm. Our work establishes a new path for designing high-performance active nanophotonic devices.
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Mei, Chiang C. "Resonant reflection of surface water waves by periodic sandbars." Journal of Fluid Mechanics 152 (March 1985): 315–35. http://dx.doi.org/10.1017/s0022112085000714.
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One of the possible mechanisms of forming offshore sandbars parallel to a coast is the wave-induced mass transport in the boundary layer near the sea bottom. For this mechanism to be effective, sufficient reflection must be present so that the waves are partially standing. The main part of this paper is to explain a theory that strong reflection can be induced by the sandbars themselves, once the so-called Bragg resonance condition is met. For constant mean depth and simple harmonic waves this resonance has been studied by Davies (1982), whose theory, is however, limited to weak reflection and fails at resonance. Comparison of the strong reflection theory with Heathershaw's (1982) experiments is made. Furthermore, if the incident waves are slightly detuned or slowly modulated in time, the scattering process is found to depend critically on whether the modulational frequency lies above or below a threshold frequency. The effects of mean beach slope are also studied. In addition, it is found for periodically modulated wave groups that nonlinear effects can radiate long waves over the bars far beyond the reach of the short waves themselves. Finally it is argued that the breakpoint bar of ordinary size formed by plunging breakers can provide enough reflection to initiate the first few bars, thereby setting the stage for resonant reflection for more bars.
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Lee, Jun-Whan, Koo-Yong Park, and Yong-Sik Cho. "Shear Current Effects on Monochromatic Water Waves Crossing Trenches." Journal of Applied Mathematics 2015 (2015): 1–11. http://dx.doi.org/10.1155/2015/256084.
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The reflection coefficients of monochromatic water waves over trenches with shear current are estimated analytically. The diffraction of waves by an abrupt depth change and shear current is formulated by the matched eigenfunction expansion method. The proper number of steps and evanescent modes are proposed by a series of convergence tests. The accuracy of the predicted reflection coefficients is checked by estimating the wave energy. Reflection and transmission characteristics are studied for various shear current conditions. The different combinations of strength, width of shear current, and incident wave angle with constant water depth topography are examined. The optimal figure of the trench with shear current is obtained by estimating the reflection coefficients for various sloped transitions. The resonant reflection of the water waves is found by multiarrayed optimal trenches and the interaction of sinusoidally varying topography with shear current.
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Decker, M., T. Pertsch, and I. Staude. "Strong coupling in hybrid metal–dielectric nanoresonators." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 375, no. 2090 (March 28, 2017): 20160312. http://dx.doi.org/10.1098/rsta.2016.0312.
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We study resonant photonic–plasmonic coupling between a gold dipole nanoantenna and a silicon nanodisc supporting electric and magnetic dipolar Mie-type resonances. Specifically, we consider two different cases for the mode structure of the silicon nanodisc, namely spectrally separate and spectrally matching electric and magnetic dipolar Mie-type resonances. In the latter case, the dielectric nanoparticle scatters the far fields of a unidirectional Huygens’ source. Our results reveal an anticrossing of the plasmonic dipole resonance and the magnetic Mie-type dipole resonance of the silicon nanodisc, accompanied by a clear signature of photonic–plasmonic mode hybridization in the corresponding mode profiles. These characteristics show that strong coupling is established between the two different resonant systems in the hybrid nanostructure. Furthermore, our results demonstrate that in comparison with purely metallic or dielectric nanostructures, hybrid metal–dielectric nanoresonators offer higher flexibility in tailoring the fractions of light which are transmitted, absorbed and reflected by the nanostructure over a broad range of parameters without changing its material composition. As a special case, highly asymmetric reflection and absorption properties can be achieved. This article is part of the themed issue ‘New horizons for nanophotonics’.
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Zagitova, Azaliya Azatovna, Andrey Sergeevich Zhuravlev, Leonid Viktorovich Kulik, and Vladimir Umansky. "Spin Transport in a Quantum Hall Insulator." Applied Sciences 11, no. 17 (September 1, 2021): 8131. http://dx.doi.org/10.3390/app11178131.
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A novel experimental optical method, based on photoluminescence and photo-induced resonant reflection techniques, is used to investigate the spin transport over long distances in a new, recently discovered collective state—magnetofermionic condensate. The given Bose–Einstein condensate exists in a purely fermionic system (ν = 2 quantum Hall insulator) due to the presence of a non-equilibrium ensemble of spin-triplet magnetoexcitons—composite bosons. It is found that the condensate can spread over macroscopically long distances of approximately 200 μm. The propagation velocity of long-lived spin excitations is measured to be 25 m/s.
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Belibassakis, Kostas, Julien Touboul, Elodie Laffitte, and Vincent Rey. "A Mild-Slope System for Bragg Scattering of Water Waves by Sinusoidal Bathymetry in the Presence of Vertically Sheared Currents." Journal of Marine Science and Engineering 7, no. 1 (January 7, 2019): 9. http://dx.doi.org/10.3390/jmse7010009.
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Extended mild-slope models (MMSs) are examined for predicting the characteristics of normally incident waves propagating over sinusoidal bottom topography in the presence of opposing shearing currents. It is shown that MMSs are able to provide quite good predictions in the case of Bragg scattering of waves over rippled bathymetry without a current, but fail to provide good predictions concerning the resonant frequency in the additional presence of a current. In order to resolve the above mismatch, a two-equation mild-slope system (CMS2) is derived from a variational principle based on the representation of the wave potential expressed as a superposition of the forward and backward components. The latter system is compared against experimentally measured data collected in a wave flume and is shown to provide more accurate predictions concerning both the resonant frequency and the amplitude of the reflection coefficient. Future work will be devoted to the examination of the derived model for a more general wave system over realistic seabed topography.
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Rotshild, David, and Amir Abramovich. "Ultra-Wideband Reconfigurable X-Band and Ku-Band Metasurface Beam-Steerable Reflector for Satellite Communications." Electronics 10, no. 17 (September 4, 2021): 2165. http://dx.doi.org/10.3390/electronics10172165.
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A continuously reconfigurable metasurface reflector based on unit cell mushroom geometry that was integrated with a varactor diode is presented in this paper. The unit cell of the metasurface was designed and optimized to operate in the X-band and Ku-band, improving satellite communication’s quality of service. The losses mechanisms of continuous control over the unit cell phase reflection in beam steering resolution are considered and the analysis results are presented. The unit cell design parameters were analyzed with an emphasis on losses and dynamic reflection phase range. The unit cell magnitude and phase reflection are shown in the wide frequency bandwidth and showed a good agreement between all the measurements and the simulations. This metasurface enabled a high dynamic range in the unit cell resonant frequency range from 7.8 to 15 GHz. In addition, the reflection phase and absorption calibration are demonstrated for multiple operating frequencies, namely, 11 GHz, 12 GHz, and 13.5 GHz. Furthermore, design trade-offs and manufacturing limitations were considered. Finally, a beam-steering simulation using the designed metasurface is shown and discussed.
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WISMANTO, WILZUARD YONAN, RAHMAT HIDAYAT, MAY ON TJIA, YASUMASA FUJIWARA, KOJI MURATA, YASUHIRO OGAWA, HIROYUKI YOSHIDA, AKIHIKO FUJII, and MASANORI OZAKI. "EMISSION ENHANCEMENT CHARACTERISTICS OF OXAZINE IN PMMA MATRIX INFLUENCED BY SURFACE PLASMON POLARITON INDUCED ON SINUSOIDAL SILVER GRATING." Journal of Nonlinear Optical Physics & Materials 21, no. 01 (March 2012): 1250013. http://dx.doi.org/10.1142/s0218863512500130.
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We present the result of an experimental study on the photoluminescence of a thin layer of oxazine molecules doped into the poly(methyl methacrylate) (PMMA) matrix which is coated on top of sinusoidal silver grating. The surface plasmon polaritons that occur on the metallic grating surface were excited by a He-Ne laser of 633 nm wavelength. The effect of the grating was investigated by angle-resolved reflection and emission spectroscopy performed on the thin film samples with and without the grating. Incident light of both s- and p-polarizations were considered in this experiment and the measurement was performed in the reflection and the photoluminescence modes as well. The results exhibit remarkable resonant effect of photoluminescence enhancement over those observed from the sample with planar silver coating for both incident light polarizations. The much larger enhancement factor of ~50.0 found for the case of p-polarized light can be attributed to the combined contributions of surface plasmon polariton enhanced absorption of excitation light and the resonant coupling between the SPP and the fluorophore, while only the latter was operating in the case of s-polarized incident light which showed a smaller enhancement factor of 6.0.
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Dawar, Parul, and Asok De. "Tunability of Triangular SRR and Wire Strip (TSRR-WS) Metamaterial at THz." Advances in Optical Technologies 2014 (April 27, 2014): 1–10. http://dx.doi.org/10.1155/2014/405301.
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This paper adumbrates a novel tunable metamaterial consisting of triangular split ring resonator (TSRR) and wire strip (WS) at THz frequency. Ansoft high frequency structure simulator (HFSS) has been used to design and analyse the metamaterial having Rogers RT/duroid 5870 (εr = 2.33) and FR4 (εr = 4.4) as substrate material. Nicolson Ross Weir (NRW) method has been used to retrieve the material parameters from transmission and reflection coefficient. 4% maximization has been obtained in the location of the negative region (or resonance frequency for permeability) by using FR4 with 0.75 μm instead of 1.25 μm as substrate thickness. In addition, 18% minimization has been achieved by using FR4 with 0.25 μm instead of RT/duroid 5870 substrate with the same thickness. Tunability has been proved by showing dependence of resonant frequency over the substrate thickness and substrate material.
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McNamara, Gerry, Joe O’Hara, Martin Brown, and Irene Quinn. "Quality assurance in Irish schools: Inspection and school self-evaluation." Administration 68, no. 4 (December 1, 2020): 161–80. http://dx.doi.org/10.2478/admin-2020-0029.
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Abstract In this paper, we provide an overview of the development of school inspection in Ireland over the past twenty years using the analytic and critical lens developed by Richard Boyle in partnership with the current authors. The paper is fundamentally a reflection on the nature, purpose and operation of evaluation in the Irish public sector through the lens of education. The paper provides a historical overview of developments in the linked areas of school evaluation and inspection, and goes on to explore how the implementation of this mode of quality assurance has influenced, and been influenced by, a wide range of policy actors. The argument made is that education has embedded a culture of evaluation in a unique yet systemically resonant manner and that a reflection on this reality will help illuminate our understanding of the role of evaluation across the public sector as a whole.
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Weidman, Patrick D., Andrzej Herczynski, Jie Yu, and Louis N. Howard. "Experiments on standing waves in a rectangular tank with a corrugated bed." Journal of Fluid Mechanics 777 (July 16, 2015): 122–50. http://dx.doi.org/10.1017/jfm.2015.318.
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An experimental investigation of resonant standing water waves in a rectangular tank with a corrugated bottom is reported. The study was stimulated by the theory of Howard & Yu (J. Fluid Mech., vol. 593, 2007, pp. 209–234) predicting the existence of normal modes that can be significantly affected by Bragg reflection/scattering. As a result, the amplitude of the standing waves (normal modes) varies exponentially along the entire length of the tank, or from the centre out in each direction, depending on the phase of the corrugations at the tank endwalls. Experiments were conducted in a 5 m tank fitted with a sinusoidal bottom with one adjustable endwall. Waves were excited by small-amplitude sinusoidal horizontal movement of the tank using an electrical motor drive system. Simultaneous time-series data of standing oscillations were recorded at well-separated positions along the tank to measure the growth in amplitude. Waveforms over a section of the tank were filmed through the transparent acrylic walls. Except for very shallow depths and near the tank endwalls, the experimental measurements of resonant frequencies, mean wavelengths, free-surface waveforms and amplitude growth are found in essential agreement with the Bragg resonant normal mode theory.
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Costanzo, Sandra, and Adil Masoud Qureshi. "Compact and Wideband PIFA Design for Wireless Body Area Sensor Networks." Electronics 10, no. 21 (October 21, 2021): 2576. http://dx.doi.org/10.3390/electronics10212576.
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The specific advantage of fractal geometry to realize compact antenna features is exploited in this work for the design of a miniaturized Planar Inverted-F Antenna configuration with a large bandwidth. The conventional quadrilateral radiating element of a Planar Inverted-F Antenna is replaced by a Minkowski pre-fractal-based shape, thus increasing the resonant wavelength without affecting the overall antenna dimensions. Consequently, with the new design, a physically smaller antenna can achieve the same resonant frequency of a larger conventional configuration. Measured as well as simulated reflection coefficient and radiation patterns are presented to validate the assumptions. The impedance bandwidth of the antenna (2.19 to 2.52 GHz) covers the ISM band with a boresight gain of 1.5–2 dB over the entire band. Furthermore, to demonstrate the miniaturization effect, a successful comparison is provided with an identically sized, conventional square Planar Inverted-F Antenna design. The proposed antenna design can be usefully adopted for power-efficient communications in the framework of Wireless Body Area Sensor Networks.
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Sheng, Xianjun, Xiaolong Lu, Ning Liu, and Yunhong Liu. "Design of Broadband High-Gain Fabry–Pérot Antenna Using Frequency-Selective Surface." Sensors 22, no. 24 (December 11, 2022): 9698. http://dx.doi.org/10.3390/s22249698.
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In this paper, a broadband high-gain Fabry–Pérot (F-P) antenna composed of the air-loaded slot-coupled broadband microstrip antenna and the frequency selective surface (FSS) based positive gradient reflection phase structure is proposed. Taking advantage of the superposition effect of multiple reflections and transmissions occurring between layer structures, the gain enhancement was realized. Meanwhile, by cascading the single-layer FSS and the dielectric substrate, the positive gradient reflection phase over a wider frequency range was achieved. Simulated results show that the resonant frequency of the designed F-P antenna is 10 GHz, the impedance matching band (S11 < −10 dB) ranges from 8.3 GHz to 11.25 GHz with a bandwidth of 29.5%, and the antenna gain is improved significantly in the range of 8.1 GHz~11.25 GHz with a gain bandwidth of 31.5%. For further verification, a prototype was fabricated, and the experimental and simulated results are in good agreement.
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Rotshild, David, Efraim Rahamim, and Amir Abramovich. "Innovative Reconfigurable Metasurface 2-D Beam-Steerable Reflector for 5G Wireless Communication." Electronics 9, no. 8 (July 24, 2020): 1191. http://dx.doi.org/10.3390/electronics9081191.
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A tunable reflector component based on metasurface (MS) with a low profile and reduced mass is offered for indoor and outdoor 5G communication methods to overcome obstacles such as buildings, walls, and turns, and to allow wireless quasi-line of sight path communication at 37 GHz. Integrating varactors with MS unit cells allows tunability and reconfigurability. This approach was presented in many studies, with frequencies of up to K–band. However, today, higher frequencies are used, especially in communication. This work presents the design of a reconfigurable MS reflector, at Ka-band frequencies, based on a new type of resonant unit cell, with uniformed reflection for wide-incident-angular-range, and a simple stimulating DC bias for each MS unit cell, which allows a two–dimensional (2-D) continuous reflection phase manipulation. The unit cell provides a dynamic reflection phase range of over 300° at a wide bandwidth. Simulations of one-dimensional (1-D) and (2-D) at 37 GHz are presented. A steering range of up to ±48° was obtained for azimuth or elevation. A simultaneous independent 2-D beam steering range of up to ±10° in azimuth and up to ± 5° in elevation, allowing obstacles to overcome covering at a practical angular spatial cone of 20° and 10°, is presented.
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Singha, R., and D. Vakula. "Low Side Lobe Tapered Slot Antenna with High Gain Using Gradient Refractive Index Metamaterial for Ultra Wideband Application." Advanced Electromagnetics 6, no. 4 (November 8, 2017): 63–69. http://dx.doi.org/10.7716/aem.v6i4.575.
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A broadband gradient refractive index (GRIN) metamaterial is used to improve the gain of the tapered slot antenna. The proposed metamaterial is capable of reducing the side lobe level of the antenna. The gradient refractive index (GRIN) metamaterial is constructed by using non-resonant parallel-line unit cells with different refractive index. Due to the non-resonant structure, the proposed unit cell exhibits low loss and large frequency bandwidth. The metamaterial, whose effective refractive index is lower than that of the substrate on which the antenna is printed. Therefore, the proposed metamaterial is act as a regular lens in beam focusing. The GRIN metamaterial is integrated in front of the antenna which has the capability to manipulate electromagnetic wave accurately. The measurement results indicate that the reflection coefficient of the antenna is below -10 dB over the frequency band from 3 to 11 GHz. The radiation pattern of the antenna shows the beam width becomes narrow and directive with low side lobe level. The peak gain is increased by 2.1 dB at 9.5 GHz.
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Lin, Ding-Bing, Jui-Hung Chou, Son-On Fu, and Hsueh-Jyh Li. "A Compact Dual-Band Printed Antenna Design for LTE Operation in Handheld Device Applications." International Journal of Antennas and Propagation 2014 (2014): 1–9. http://dx.doi.org/10.1155/2014/897328.
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A novel internal printed antenna suitable for triple long-term evolution (LTE) bands for handheld devices is presented. The operating bandwidths of the design are LTE700 (698~800 MHz), LTE2300 (2300~2400 MHz), and LTE2500 (2500~2690 MHz). Through the use of a C-shape broadside coupled feed structure, full operation in the lower band is achieved. The antenna itself uses two unequal path lengths to produce a low frequency band with two resonant modes. The required bandwidth is then adjusted using a couple feed, and finally placed over a ground plane via another C-type coupling element in order to enhance the two low-frequency matches. In the definition of the −6 dB reflection coefficient, the bandwidth of two basic modes in the low frequency band is 0.689~0.8 GHz. We adopt the definition of the −10 dB reflection coefficient for the high frequency mode, and its working frequency bands are shown to be 2.3~2.72 GHz. The antenna size is only 40 × 12 × 0.8 mm3with a ground plane of 98 × 40 mm2.
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Triapthi, Shivesh, B. Mohapatra, Prabhakar Tiwari, Nagendra Prasad Pathak, and Manoranjan Parida. "Design of RF Receiver Front end Subsystems with Low Noise Amplifier and Active Mixer for Intelligent Transportation Systems Application." Defence Science Journal 70, no. 6 (October 12, 2020): 633–41. http://dx.doi.org/10.14429/dsj.70.13917.
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This paper presents the design, simulation, and characterization of a novel low-noise amplifier (LNA) and active mixer for intelligent transportation system applications. A low noise amplifier is the key component of RF receiver systems. Design, simulation, and characterization of LNA have been performed to obtain the optimum value of noise figure, gain and reflection coefficient. Proposed LNA achieves measured voltage gains of ~18 dB, reflection coefficients of -20 dB, and noise figures of ~2 dB at 5.9 GHz, respectively. The active mixer is a better choice for a modern receiver system over a passive mixer. Key sight advanced design system in conjunction with the electromagnetic simulation tool, has been to obtain the optimal conversion gain and noise figure of the active mixer. The lower and upper resonant frequencies of mixer have been obtained at 2.45 GHz and 5.25 GHz, respectively. The measured conversion gains at lower and upper frequencies are 12 dB and 10.2 dB, respectively. The measured noise figures at lower and upper frequencies are 5.8 dB and 6.5 dB, respectively. The measured mixer interception point at lower and upper frequencies are 3.9 dBm and 4.2 dBm.
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Dunklin, Jeremy R., Gregory T. Forcherio, Keith R. Berry, and D. K. Roper. "Plasmon optics and thermal dissipation in nanocomposite thin films." MRS Proceedings 1788 (2015): 23–28. http://dx.doi.org/10.1557/opl.2015.672.
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ABSTRACTOptical properties and thermal relaxation dynamics of resonantly excited plasmons are important in applications for optoelectronics, biomedicine, energy, and catalysis. Geometric optics of polydimethylsiloxane (PDMS) thin films containing uniformly or asymmetrically distributed polydisperse reduced AuNPs or uniformly distributed monodisperse solution-synthesized AuNPs were recently evaluated using a compact linear algebraic sum. Algebraic calculation of geometric transmission, reflection, and attenuation for AuNP-PDMS films provides a simple, workable alternative to effective medium approximations, computationally expensive methods, and fitting of experimental data. This approach allows for the summative optical responses of a sequence of 2D elements comprising a 3D assembly to be analyzed. Thin PDMS films containing 3-7 micron layers of reduced AuNPs were fabricated with a novel diffusive-reduction synthesis technique. Rapid diffusive reduction of AuNPs into asymmetric PDMS thin films provided superior photothermal response relative to thicker films with AuNPs reduced throughout, with a photon-to-heat conversion of up to 3000°C/watt which represents 3-230-fold increase over previous AuNP-functionalized systems. Later work showed that introduction of AuNPs into PDMS enhanced thermoplasmonic dissipation coincident with internal reflection of incident resonant irradiation. Measured thermal emission and dynamics of AuNP-PDMS thin films exceeded emission and dynamics attributable by finite element analysis to Mie absorption, Fourier heat conduction, Rayleigh convection, and Stefan-Boltzmann radiation. Refractive-index matching experiments and measured temperature profiles indicated AuNP-containing thin films internally reflected light and dissipated power transverse to the film surface. Enhanced thermoplasmonic dissipation from metal-polymer nanocomposite thin films could affect opto- and bio-electronic implementation of these systems.
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Marathe, Dushyant, and Kishore Kulat. "A Compact Triple-Band Negative Permittivity Metamaterial for C, X-Band Applications." International Journal of Antennas and Propagation 2017 (2017): 1–12. http://dx.doi.org/10.1155/2017/7515264.
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We report a new design of triple-band electric metamaterial resonator (TBEMR) based on integration of open delta loops within square ring resonator. This metamaterial resonator has three distinct ε-negative regions (ENG) over C, X frequency bands. The transmission and reflection response of the proposed subwavelength resonator is analyzed using full-wave electromagnetic solver Ansys HFSS to demonstrate the presence of electrical resonances within frequencies 4–12 GHz. Effective medium parameters permittivity and permeability are extracted from simulated complex scattering parameters to verify existence of ENG regions. The investigations are also carried out regarding dependence of resonant frequencies on design parameters of the TBEMR unit cell. The effective medium ratio (λ0/a) for proposed subwavelength resonator is compared with various other metamaterial resonators to indicate its compact nature.
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Saleem, Muhammad, and Xiao-Lai Li. "Low Scattering Microstrip Antenna Based on Broadband Artificial Magnetic Conductor Structure." Materials 13, no. 3 (February 6, 2020): 750. http://dx.doi.org/10.3390/ma13030750.
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In this summary, we have suggested a new technique in which destructive interference principle is incorporated into a chessboard like a reflective screen, and the proposed antenna realizes a remarkable in-band and also out-of-band backscattered energy reduction by using a metasurface (MS). Two different MS unit cells are designed to provide the resonant frequency with a zero-degree reflection phase. Metasurface unit cells are configured in a chessboard-like reflector screen to achieve the reflection phase difference of 180° ± 37° over a broadband range of frequencies to redirect the scattering field into four quadrants. It is implemented to reduce the backscattered energy level of the microstrip antenna, which is based on destructive interference principle. The simulations indicate that the proposed antenna possesses significant backscattered energy reduction from 6 GHz to 16 GHz in both x– and y– polarization and also −10 dB backscattering reduction at antenna working band (7.4–7.8 GHz) is covered. Moreover, the radiation performance is preserved well and artificial magnetic conductor (AMC) unit cells work at different frequencies which are not influenced on the radiation properties. The bistatic performance of the antenna at different frequencies is also presented. Measurements and simulations of the fabricated design coincide well and the proposed design is verified and validated successfully.
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Xu, Dongdong, Fenping Cui, and Gaige Zheng. "Dynamically Switchable Polarization-Independent Triple-Band Perfect Metamaterial Absorber Using a Phase-Change Material in the Mid-Infrared (MIR) Region." Micromachines 12, no. 5 (May 11, 2021): 548. http://dx.doi.org/10.3390/mi12050548.
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A tunable metamaterial absorber (MMA) by reversible phase transitions in a mid-infrared regime is theoretically investigated. The absorber is composed of a molybdenum (Mo)-germanium-antimony-tellurium (Ge2Sb2Te5, GST)-Mo nanodisk structure superimposed on the GST-Al2O3 (aluminum oxide)-Mo film. Studies have shown that the combination of the inlaid metal-medium dielectric waveguide mode and the resonant cavity mode and the excitation of the propagating surface plasmon mode are the main reasons for the formation of the triple-band high absorption. Additionally, through the reversible phase change, the transition from high absorption to high reflection in the mid-infrared region is realized. The symmetry of the absorber eliminates the polarization dependence, and the near unity absorption efficiency can be maintained by incidence angles up to 60°. The presented method will enhance the functionality of the absorber and has the potential for the applications that require active control over light absorption.
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D’Aloia, Alessandro Giuseppe, Marcello D’Amore, and Maria Sabrina Sarto. "Low-Terahertz Transparent Graphene-Based Absorber." Nanomaterials 10, no. 5 (April 28, 2020): 843. http://dx.doi.org/10.3390/nano10050843.
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A new, transparent, metal-free absorber, based on the use of multilayer graphene/dielectric laminates (GLs), is proposed for applications in the low-terahertz frequency range. The designed absorber has a total thickness of around 70 µm and consists of a front matching dielectric layer followed by a GL, a dielectric spacer and a back GL. The laminates are periodic structures constituted of graphene sheets separated by 50-nm-thick polyethylene terephthalate (PET) interlayers, while the matching layer and the spacer are one-quarter-wavelength thick and made of PET. The GLs are modeled as homogeneous-equivalent single layers (ESLs) characterized by their sheet resistances Rs. An innovative analytical method is proposed in order to select Rs values optimizing the electromagnetic wave absorption either in low-gigahertz or low-terahertz frequency range. The frequency spectra of the absorption, reflection and transmission coefficients are computed in the range up to 4 THz by using different values of Rs. Then, realistic Rs values of chemically doped graphene monolayers over PET substrates are considered. The designed absorbers are characterized by an absorption coefficient with a peak value of about 0.8 at the first resonant frequency of 1.1 THz, and a 1.4 THz bandwidth centered at 1.5 THz with reflection coefficient below - 10 dB. Moreover, the optical transmittance of the proposed absorbers are computed by means of the optical matrix theory and it is found to be greater than 86% in all the visible ranges.
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Vummadisetty, P. N., and A. Kumar. "Compact Uniplanar Multi Feed Multi Band ACS Monopole Antenna Loaded With Multiple Radiating Branches for Portable Wireless Devices." Advanced Electromagnetics 7, no. 2 (March 2, 2018): 68–75. http://dx.doi.org/10.7716/aem.v7i2.661.
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This research article presents, a compact 0.19 λ x 0.32 λ size ACS fed printed monopole wideband antenna loaded with multiple radiating branches suitable for LTE2300/WiBro, 5 GHz WLAN and WiMAX applications. The proposed triple band uniplanar antenna encompasses of C shaped strip, L shaped strip, rectangular shaped strip and a lateral ground plane. All the radiating strips and ground plane are etched on the 26 × 15 m size low cost FR4 epoxy substrate. This designed geometry evoked three independent reonances at 2.3 GHz, 3.5 GHz and 5.5 GHz with precise impedance matching over each operating band. The reflection coefficient ( ) response of the presented antenna demonstrates three distinct resonant modes associated with -10 dB bandwidths are about 2.24-2.40 GHz, 3.38-3.83 GHz and 5.0-6.25 GHz respectively. From the study, it is also observed that the proposed design works perfect with microstrip as well as CPW feedings. Hence the designed Multi Feed Multi Band (MFMB) antenna can be easily deployed in to any portable wireless device that works for 2.3/3.5/ 5 GHz frequency bands.
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Ullah, Naqeeb, Ruizhe Zhao, and Lingling Huang. "Recent Advancement in Optical Metasurface: Fundament to Application." Micromachines 13, no. 7 (June 28, 2022): 1025. http://dx.doi.org/10.3390/mi13071025.
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Metasurfaces have gained growing interest in recent years due to their simplicity in manufacturing and lower insertion losses. Meanwhile, they can provide unprecedented control over the spatial distribution of transmitted and reflected optical fields in a compact form. The metasurfaces are a kind of planar array of resonant subwavelength components that, depending on the intended optical wavefronts to be sculpted, can be strictly periodic or quasi-periodic, or even aperiodic. For instance, gradient metasurfaces, a subtype of metasurfaces, are designed to exhibit spatially changing optical responses, which result in spatially varying amplitudes of scattered fields and the associated polarization of these fields. This paper starts off by presenting concepts of anomalous reflection and refraction, followed by a brief discussion on the Pancharatanm–Berry Phase (PB) and Huygens’ metasurfaces. As an introduction to wavefront manipulation, we next present their key applications. These include planar metalens, cascaded meta-systems, tunable metasurfaces, spectrometer retroreflectors, vortex beams, and holography. The review concludes with a summary, preceded by a perspective outlining our expectations for potential future research work and applications.
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Boumagouda, Ridha, Fadhéla Otmane, Zineb Hamlati, Samir Bellal, Sabrina Zeghdoud, and Mohammed Azzaz. "Microwave Absorption Properties of Fe<sub>40</sub>Co<sub>60</sub> Based Nanocomposites." Defect and Diffusion Forum 413 (December 17, 2021): 209–16. http://dx.doi.org/10.4028/www.scientific.net/ddf.413.209.
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Microwave absorbing materials are applied in stealth, communications and information processing technologies. This kind of material dissipates an electromagnetic wave by converting it into thermal energy. The nanostructuration of materials became a reliable route over the years to enhance the dielectric and magnetic properties, which induce the required interaction. Nanostructured Fe-Co alloys are soft magnetic materials that make them promising candidates for microwave absorption when combined with other materials. The aim of our study was therefore to investigate the microwave absorption properties of based nanocomposites. The nanocomposites were obtained by the solution dispersion method. Nanocrystalline alloys elaborated by mechanical alloying (MA) in a high-energy planetary ball mill (RETSCH PM400) were dispersed into commercial epoxy resin matrix to form thin polymer nanocomposites. The grain size refinement and structural properties changes during milling process were characterized using powder’s X-ray Diffraction (XPERT PRO MPD diffractometer) at different milling durations. XRD spectra analysis show that a grain size refinement of 4.54 nm was reached after 60h milling accompanied with 1.2 % microdeformations. Obtained powders were shaped in small discs for which resonant cavity measurements were undertaken. The based nanocomposites have been subject to an experiment of two-port S parameters measurement in a rectangular waveguide (R120). The microwave experiments involved a Network Analyzer (VNA). Obtained results in terms of reflection losses show a good absorbing characteristic over the [8-15] GHz microwaves band.
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Littman, Nickolas, Steven G. O’Keefe, Amir Galehdar, Hugo G. Espinosa, and David V. Thiel. "Bandwidth control of loop type frequency selective surfaces using dual elements in various arrangements." Flexible and Printed Electronics 6, no. 4 (November 17, 2021): 045009. http://dx.doi.org/10.1088/2058-8585/ac361a.
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Abstract Frequency selective surfaces (FSSs) have applications across multiple disciplines due to their unique electromagnetic properties. This paper investigates the use of both rounded square loops, and simple loop type dual elements arranged in unique patterns, to control the transmission and reflection bandwidth and resonant frequencies over KU and K frequency bands supported by equivalent circuit models. The FSSs were fabricated using laser engraving to create conductive loop type elements on a thin, flexible and optically transparent Mylar substrate (relative permittivity of 2.7 and thickness of 65 μm). The frequency response of the surfaces are controlled through the element self-inductance and capacitive coupling with neighbouring elements. This work shows that different arrangements result in the formation of multiple distinct resonances. The theoretical and experimental results were in good agreement where rounded squares and dual element arrays were employed to create broadband and multiband band-stop FSSs. A polarization sensitive surface exhibited stop-bands at 12 and 16 GHz in transverse electric polarization and a stop-band at 14.4 GHz in transverse magnetic polarization. This technique can be applied to any periodic array through careful selection of the individual elements in the array, as well as their arrangement.
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Nej, Sanjukta, Anumoy Ghosh, Sarosh Ahmad, Adnan Ghaffar, and Mousa Hussein. "Compact Quad Band MIMO Antenna Design with Enhanced Gain for Wireless Communications." Sensors 22, no. 19 (September 21, 2022): 7143. http://dx.doi.org/10.3390/s22197143.
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In this paper, a novel microstrip line-fed meander-line-based four-elements quad band Multiple Input and Multiple Output (MIMO) antenna is proposed with a gain enhancement technique. The proposed structure resonates at four bands simultaneously, that is, 1.23, 2.45, 3.5 and 4.9 GHz, which resemble GPS L2, Wi-Fi, Wi-MAX and WLAN wireless application bands, respectively. The unit element is extended to four elements MIMO antenna structure exhibiting isolation of more than 22 dB between the adjacent elements without disturbing the resonant frequencies. In order to enhance the gain, two orthogonal microstrip lines are incorporated between the antenna elements which result in significant gain improvement over all the four resonances. Furthermore, the diversity performance of the MIMO structure is analyzed. The Envelope Co-Relation Coefficient (ECC), Diversity Gain (DG), Channel Capacity Loss (CCL), Mean Effective Gain (MEG) and Multiplexing Efficiency are obtained as 0.003, 10 dB, 0.0025 bps/Hz, −3 dB (almost) and 0.64 (min.), respectively, which are competent and compatible with practical wireless applications. The Total Active Reflection Coefficient (TARC) resembles the characteristic of the individual antenna elements. The layout area of the overall MIMO antenna is 0.33 λ × 0.29 λ, where λ is the free-space wavelength corresponding to the lowest resonance. The advantage of the proposed structure has been assessed by comparing it with previously reported MIMO structures based on number of antenna elements, isolation, gain, CCL and compactness. A prototype of the proposed MIMO structure is fabricated, and the measured results are found to be aligned with the simulated results.
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ARDHUIN, FABRICE, and RUDY MAGNE. "Scattering of surface gravity waves by bottom topography with a current." Journal of Fluid Mechanics 576 (March 28, 2007): 235–64. http://dx.doi.org/10.1017/s0022112006004484.
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A theory is presented that describes the scattering of random surface gravity waves by small-amplitude topography, with horizontal scales of the order of the wavelength, in the presence of an irrotational and almost uniform current. A perturbation expansion of the wave action to order η2 yields an evolution equation for the wave action spectrum, where η = max(h)/H is the small-scale bottom amplitude normalized by the mean water depth. Spectral wave evolution is proportional to the bottom elevation variance at the resonant wavenumbers, representing a Bragg scattering approximation. With a current, scattering results from a direct effect of the bottom topography, and an indirect effect of the bottom through the modulations of the surface current and mean surface elevation. For Froude numbers of the order of 0.6 or less, the bottom topography effects dominate. For all Froude numbers, the reflection coefficients for the wave amplitudes that are inferred from the wave action source term are asymptotically identical, as η goes to zero, to previous theoretical results for monochromatic waves propagating in one dimension over sinusoidal bars. In particular, the frequency of the most reflected wave components is shifted by the current, and wave action conservation results in amplified reflected wave energies for following currents. Application of the theory to waves over current-generated sandwaves suggests that forward scattering can be significant, resulting in a broadening of the directional wave spectrum, while back-scattering should be generally weaker.
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Kishore, Siddharth, and A. R. Abdul Rajak. "Microstrip Patch Antenna with C Slot for 5G Communication at 30 GHz." Emerging Science Journal 6, no. 6 (September 13, 2022): 1315–27. http://dx.doi.org/10.28991/esj-2022-06-06-06.
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A novel design of a 30 GHz microstrip line-fed antenna for 5G communication has been presented in this paper. 5G is the latest industry standard in mobile communication, which is designed to deliver higher data speeds, lower latency, greater network capacity, and higher reliability. It uses major parts of the mmWave spectrum (28 GHz to 40 GHz), allowing for a wide range of applications like mobiles, vehicles, medical devices, and other IoT networks. This mmWave network requires efficient antennas for its effective communication. Patch antennas use the function of oscillating their physical structure to the wavelength of the transmitting wave. Thus, higher efficiency can be achieved in the mmWave spectrum due to its proximity to the actual dimensions of the patch antenna, which also allows us to design antennas at small sizes and high reliability. The design in this report has a patch antenna with a centre frequency of 30 GHz. The antenna was optimized for this frequency based on the best reflection coefficient and gain while keeping the restraints of staying within the FR-2 band of 28 GHz to 33 GHz. The proposed antenna has been implemented using Rogers RT5880 substrate for high gain and performance across a wide range of frequencies. The feed is also accompanied by a quarter-wave feed cut for performance increase and impedance matching. The design has a gain of 8.45, with a reflection coefficient of -8 dB at a resonant frequency of 30 GHz. It shows great directivity of 5o and VSWR of 2.3 over a bandwidth of 3.5 GHz. It also employs a 0.4 mm C slot, which induces a dipole effect, thereby increasing the directivity and gain of the antenna. Hence, it is recommended for use in applications related to 5G mobile communication. Doi: 10.28991ESJ-2022-06-06-06 Full Text: PDF
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Shah, S. M., A. A. Rosman, M. A. Z. A. Rashid, Z. Z. Abidin, F. C. Seman, H. A. Majid, S. H. Dahlan, et al. "A compact dual-band semi-flexible antenna at 2.45 GHz and 5.8 GHz for wearable applications." Bulletin of Electrical Engineering and Informatics 10, no. 3 (June 1, 2021): 1739–46. http://dx.doi.org/10.11591/eei.v10i3.2262.
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In this work, a compact dual-band semi-flexible antenna operating at 2.45 GHz and 5.8 GHz for the industrial, scientific and medical (ISM) band is presented. The antenna is fabricated on a semi-flexible substrate material, Rogers Duroid RO3003™ with a low-profile feature with dimensions of 30×38 mm2 which makes it a good solution for wearable applications. Bending investigation is also performed over a vacuum cylinder and the diameters are varied at 50 mm, 80 mm and 100 mm, that represents the average human arm’s diameter. The bending investigation shows that reflection coefficients for all diameters are almost similar which imply that the antenna will operate at the dual-band resonant frequencies, even in bending condition. The simulated specific absorption rate (SAR) in CST MWS® software shows that the antenna obeys the FCC and ICNIRP guidelines for 1 mW of input power. The SAR limits at 2.45 GHz for 1 g of human tissue is simulated at 0.271 W/kg (FCC standard: 1.6 W/kg) while for 10 g is at 0.0551 W/kg (ICNIRP standard: 2 W/kg. On the other hand, the SAR limits at 5.8 GHz are computed at 0.202 W/kg for 1 g and 0.0532 W/kg for 10 g.
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Bai, Xudong, Fuli Zhang, Li Sun, Anjie Cao, Chong He, Jin Zhang, and Weiren Zhu. "Dynamic millimeter-wave OAM beam generation through programmable metasurface." Nanophotonics 11, no. 7 (February 17, 2022): 1389–99. http://dx.doi.org/10.1515/nanoph-2021-0790.
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Abstract Millimeter-wave (mmWave) and orbital angular momentum (OAM) multiplexing are two key technologies for modern wireless communications, where significant efforts have been devoted to combining these two technologies for extremely high channel capacities. Recently, programmable metasurfaces have been extensively studied for stimulating dynamic multi-mode OAM beams, owing to their ability of subtle dynamic modulation over electromagnetic waves in a digital manner. However, programmable metasurfaces for mmWave OAM stimulation are rarely mentioned, due to the requirement of extremely high processing precision for mmWave applications. In this paper, a programmable metasurface is presented to stimulate dynamic multi-mode mmWave vortex beams. The proposed metasurface is composed of electronically reconfigurable units, which is obtained through configuration integration of a PIN diode within each radiation patch for modulating the unit resonant property. Both low reflection losses and stabilized inverse phase states are obtained for the binary unit coding states within the operation band. Through modulating the real-time coding distribution on the metasurface by programmable bias circuit, the generation of mmWave OAM beams with mode numbers l = 0, l = +1, l = +2, and l = +3 are numerically designed and experimentally verified. Our study paves a new perspective for the cross amalgamation of both mmWave and multi-mode OAM technologies.
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Randriamampianina, Anthony, and Emilia Crespo del Arco. "Inertia–gravity waves in a liquid-filled, differentially heated, rotating annulus." Journal of Fluid Mechanics 782 (October 6, 2015): 144–77. http://dx.doi.org/10.1017/jfm.2015.522.
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Direct numerical simulations based on high-resolution pseudospectral methods are carried out for detailed investigation into the instabilities arising in a differentially heated, rotating annulus, the baroclinic cavity. Following previous works using air (Randriamampianina et al., J. Fluid Mech., vol. 561, 2006, pp. 359–389), a liquid defined by Prandtl number $Pr=16$ is considered in order to better understand, via the Prandtl number, the effects of fluid properties on the onset of gravity waves. The computations are particularly aimed at identifying and characterizing the spontaneously emitted small-scale fluctuations occurring simultaneously with the baroclinic waves. These features have been observed as soon as the baroclinic instability sets in. A three-term decomposition is introduced to isolate the fluctuation field from the large-scale baroclinic waves and the time-averaged mean flow. Even though these fluctuations are found to propagate as packets, they remain attached to the background baroclinic waves, locally triggering spatio-temporal chaos, a behaviour not observed with the air-filled cavity. The properties of these features are analysed and discussed in the context of linear theory. Based on the Richardson number criterion, the characteristics of the generation mechanism are consistent with a localized instability of the shear zonal flow, invoking resonant over-reflection.
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Jairath, Kapil, Navdeep Singh, Mohammad Shabaz, Vishal Jagota, and Bhupesh Kumar Singh. "Performance Analysis of Metamaterial-Inspired Structure Loaded Antennas for Narrow Range Wireless Communication." Scientific Programming 2022 (May 19, 2022): 1–17. http://dx.doi.org/10.1155/2022/7940319.
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Nowadays, the demand for low-cost, compact, and interference rejected antennas with ultrawideband capability has been increased. Metamaterial-inspired loaded structures have capability of providing exceptional solutions for narrow range wireless communication and low consuming power while transmitting and receiving the signal. It is a difficult task to construct ideal metamaterial-inspired antennas with a variety of features such as extremely large bandwidth, notching out undesirable bands, and frequency. Metamaterial-inspired structures such as SRR and CSRR, and triangle-shaped TCSRR are most commonly used structures to achieve optimized characteristics in ultrawideband antennas. In this paper, an extensive literature survey is accomplished to get conception about metamaterial-inspired patch antennas. This review paper elucidates variants of metamaterial-inspired structures/resonators utilized in order to acquire sundry applications such as WiMAX, WLAN, satellite communication, and radar. Various researchers have used different methodology to design, stimulate, and analyze the metamaterial-inspired structure loaded antennas. Also, the results of different metamaterial-inspired antennas such as bandwidth, gain, return loss, and resonant frequency have been also represented in this paper. This manuscript also gives brief introduction about the metamaterial, its types, and then its application in microstrip patch antenna over the last decade. This manuscript throws light over the various studies conducted in the field of metamaterial-inspired antenna in the past. It has been seen that with the inclusion of metamaterial in conventional antenna, various characteristics such as impedance bandwidth, reflection coefficient, gain, and directivity have been improved. Also, frequency rejection of narrow bands which exits in ultrawideband frequency range can be done by embedding metamaterial-inspired structures such as SRR and CSRR.
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Mahmud, Rashad Hassan. "Terahertz Microstrip Patch Antennas For The Surveillance Applications." Kurdistan Journal of Applied Research 5, no. 1 (April 30, 2020): 16–27. http://dx.doi.org/10.24017/science.2020.1.2.
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This paper presents a new design of the microstrip patch antenna operated at the terahertz frequencies (700-850 GHz). The conventional microstrip patch antenna dimensions shrink to a few microns when operating at such terahertz frequencies. Thus, the design of the patch and its feeding network will be miniaturized extremely, and their fabrications would be extremely difficult. In this paper, the configuration of the proposed microstrip patch antenna is suited in a way that it can be modeled using multilayers structure. This multilayer structure facilitates the modeling, and considering its fabrication. The proposed microstrip antenna has been designed using three layers. The top layer is used to model the rectangular patch; while the second layer is for the substrate, and the bottom layer is for the ground plane. The physical dimensions of the layers and the fed-line are optimised using the microwave Computer Simulation Technology (CST) simulator in order to enhance the electrical parameters of the antenna such as antenna realised gain, bandwidth, total and radiation efficiencies, and radiation patterns. In addition to that, the impact of the physical dimensions of the rectangular patch on controlling the resonant frequency of the dominant mode (TM01) have been investigated. Keeping the lower and higher propagating modes out of the frequency band of interest is another aspect which has been addressed in this paper. The antenna has been simulated, and its realised gain fluctuates from 6.4 dBi to 9.7 dBi over the operating frequency range (700-850 GHz). Also, it provides extremely large reflection coefficient bandwidth (S11) which it is below -10 dB over the entire operating frequency band. The total efficiency is more than 75 %. Due to its simplicity and providing large bandwidth, the proposed antenna could be of interest in many security and surveillance applications.
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Dragna, Didier, Ariane Emmanuelli, Sebastien Ollivier, and Philippe Blanc-Benon. "Reflection of sonic boom over realistic urban areas." Journal of the Acoustical Society of America 151, no. 4 (April 2022): A86. http://dx.doi.org/10.1121/10.0010741.
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This study aims at analyzing sonic boom reflection over realistic urban areas. For this purpose, numerical simulations are performed. The 2D Euler equations are solved using high-order finite-difference methods, following Emmanuelli et al. [ J. Acoust. Soc. Am. 149, 2437–2450 (2021)]. The local climate zone classification of urban morphologies [Steward and Oke, Bull. Am. Meteorol. Soc. 93, 1879–1900 (2012)] is used to generate ten typical geometries. Two booms, an N-wave and a low-boom wave, are considered. The pressure waveforms along the profiles are analyzed first. In addition to the geometric arrivals, low-frequency oscillations, associated with resonance modes of the street canyons, are noted. They induce an important increase in the duration of the signals. Their frequency and amplitude depend on the street width and on the boom wave. The noise levels are then investigated. Depending on the urban geometry, two behaviors are highlighted. For a sparse arrangement of buildings, the evolution of the levels is similar than for isolated buildings, with an amplification on the front facade and a reduction on the rear facade. For a dense arrangement, it is more complex due to the multiple reflections on the buildings. Finally, the levels follow a comparable evolution for both boom waves.
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Kumar, Ashok, and A. L. Verma. "Nonlinear absorption of intense short pulse laser over a metal surface embedded with nanoparticles." Laser and Particle Beams 29, no. 3 (July 11, 2011): 333–38. http://dx.doi.org/10.1017/s0263034611000383.
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AbstractThe anomalous absorption of laser, incident at an arbitrary angle of incidence on a metal surface embedded with nanoparticles, is studied. The electrons inside a nanoparticle resonantly absorb laser energy when the laser frequency equals the frequency of surface charge oscillations of the nanoparticle. A monolayer of nanoparticles of radius rnp0 ≈ 50 A with inter-particle separation d ~ 10rnp0 can cause up to 40% reduction of the reflection of p-polarized laser light. The absorption coefficient increases with the angle of incidence and has a sharp peak at a resonant frequency width of about 1%. At high laser power, even if the nanoparticles are initially off resonant with the laser, the particle heating and subsequent expansion reduces the resonance frequency, and the resonance absorption is realized after a time delay. The delay is found to be directly proportional to the cluster size and inversely proportional to the laser intensities.
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Polyachenko, E. V., and I. G. Shukhman. "Effect of inner Lindblad resonance on spiral density waves propagation in disc galaxies: reflection over absorption." Monthly Notices of the Royal Astronomical Society 483, no. 1 (November 3, 2018): 692–703. http://dx.doi.org/10.1093/mnras/sty3005.
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Hein, Sebastian S. V., Vanessa Sohrt, Edgar Nehlsen, Thomas Strotmann, and Peter Fröhle. "Tidal Oscillation and Resonance in Semi-Closed Estuaries—Empirical Analyses from the Elbe Estuary, North Sea." Water 13, no. 6 (March 19, 2021): 848. http://dx.doi.org/10.3390/w13060848.
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Many tidal influenced estuaries and coastal basins feature tidal amplification because of, e.g., convergence and reflection. Increasing amplification rates were observed in the Elbe estuary, with consequences for construction measures, nautical manoeuvring, flood protection, riverbed morphology and ecosystems. Although many studies were conducted investigating the tidal wave transformation in estuaries, studies based on spatially well-distributed empirical data covering periods over more than a year are rare. To fill this gap, a self-developed adapted harmonic analysis method of least squares was applied to hydrographs from 25 gauges, distributed over the tidal influenced estuary from the river mouth to the tidal border which is given by the weir 160 km upstream of the river mouth. The investigation period for the harmonic analyses covers a whole nodal cycle of 18.613 a beginning in the year 2000. The tidal constituents’ oscillatory behaviour including the appearance of compound tides, generated by nonlinear shallow water processes, and the formation of reflection induced partially standing waves are determined. The tidal constituents show shared frequency-group specific partial clapotis, but also have significant differences in amplification within those groups. The latter fact contributes to the detected inverse proportionality of tidal range amplification inside the estuary to incoming tidal wave height. As reflection can cause resonance in tidal influenced rivers, tests are developed to analyse whether criteria for resonance are met. To determine the system’s specific resonance frequency, a new method was introduced with the three-parameter Lorentzian curve-fitting. As the detected resonance frequency is not close to tidal frequencies, full-established resonance of the tidal wave and of the tidal constituents is not observed in the Elbe estuary. Migrating nodes of the partially standing tidal wave hint at increasing latent resonance.
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Dang, Phuc Toan, Khai Q. Le, Quang Minh Ngo, Hieu Pham Trung Nguyen, and Truong Khang Nguyen. "Guided-mode Resonance Filter with Ultra-narrow Bandwidth over the Visible Frequencies for Label-free Optical Biosensor." Journal of Advanced Engineering and Computation 3, no. 2 (June 30, 2019): 406. http://dx.doi.org/10.25073/jaec.201932.233.
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A practical guided-mode resonance filter operating in the visible band of the electromagnetic spectrum is numerically designed in this paper. The filter provides high background transmission (>90%) with almost perfect reflection at resonance wavelengths of 623 nm and 641 nm for TE and TM modes, respectively. Our filter is also characterized by its sensitivity to incident angles, polarizations, and a refractive index of the surrounding environment which are utilized in practical applications such as tunable optical filters, imaging or detection. We show that the resonant transmission spectral response can be used for highly sensitive, a potential label-free refractive index biosensor having sensitivities of 90 nm/RIU and 103 nm/RIU, and figure of merits of 1.93 and 2.13 for TM and TE polarizations, respectively.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium provided the original work is properly cited.
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Solovyeva, Maria. "Agnes’ Self-Reflection in Ingmar Bergman’s Cries and Whispers." Journal of Flm Arts and Film Studies 11, no. 4 (December 30, 2019): 114–25. http://dx.doi.org/10.17816/vgik114114-125.
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The essay explores Ingmar Bergmans film Cries and Whispers (Viskningar och rop, 1972) from the perspective of the protagonists selfreflection as the main plot-constructing tool. The self-reflection of the main protagonist Agnes is presented by Bergman in a variety of forms which create, by mixing with each other, a polyphony of senses and images.
The author analyses those dramatic tools which make it possible to immerse a spectator into Agness inner feelings. Her diary is her conscious self-reflection and, therefore, becomes a cinematic instrument for a study of her psychology. Bergman explores the visual images of the main protagonists self-reflection and, logically, turns them into symbols. This is exemplified by the symbolic comparison of her mothers and her sisters images to a bouquet of magnificent white roses. And then, a close-up of a flower shows symbolically the true nature of Agness mother: the flower turns out to be an artificial one, revealing the hypocrisy of Agness externally beautiful mother. The protagonists conscious striving to understand herself is also revealed through the use of an analytical voice-over monologue accompanying a sequence of reminiscences about the mother.
The essay analyses the same sequence from the viewpoint of the objectorientation of Agness self-reflection. Within this sequence, self-reflection changes its object, becoming either introspective or extrospective. Agnes recomprehends herself either through the prism of herself or through the prism of the others. Quick alternation of these two types of self-reflection indicates the causal connection between Agness identity and her relationship with her mother. Significantly, the sequence's ending is the moment of the closest rapprochement between Agnes and her mother - that is, between two types of self-reflection.
A protagonist's self-reflection could be an effective tool of creating semantic resonance. An example of this is provided in the film's final sequence, in which Anna, the servant, reads the diary of the dead Agnes. This sequence is a reminiscence of those several minutes of Agness life when she was absolutely happy. It begins with Anna reading the diary and turns into the visualisation of a diary entry accompanied by the Annas voice-over on Agnes's behalf. This creates a triple resonance of the film's semantic content.
In the author's opinion, the above examples confirm that a characters selfreflection can become an effective dramatic tool for exploring a characters psychology and a technique of revealing the meanings in their polyphony.
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Dash, Sasmita, Christos Liaskos, Ian F. Akyildiz, and Andreas Pitsillides. "Graphene Hypersurface for Manipulation of THz Waves." Materials Science Forum 1009 (August 2020): 63–68. http://dx.doi.org/10.4028/www.scientific.net/msf.1009.63.
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In this work, we investigated graphene hypersurface (HSF) for the manipulation of THz waves. The graphene HSF structure is consists of a periodic array of graphene unit cells deposited on silicon substrate and terminated by a metallic ground plane. The performance of the proposed HSF is numerically analyzed. Electromagnetic parameters of HSF such as permeability, permittivity, and impedance are studied. The proposed graphene HSF has active control over absorption, reflection, and transmission of THz waves. The graphene HSF provides perfect absorption, zero reflection and zero transmission at resonance. Moreover, the graphene HSF structure has the advantage of anomalous reflection and frequency reconfiguration. Incident waves can be reflected in the desired direction, depending on the phase gradient of the HSF and the perfect absorption is maintained at all reconfigurable frequencies upon reconfiguration. The results reveal the effectiveness of the graphene HSF for the manipulation of THz waves.
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Wang, Dandan, Qiang Li, Yunbin Ying, Runhu Li, Mingliang Cheng, Yingxin Chen, Jian Zhang, and Xuefeng Zhang. "Dynamic transmission-reflection dichroism based on humidity-responsive metal-hydrogel-metal nanocavities." EPJ Applied Metamaterials 9 (2022): 18. http://dx.doi.org/10.1051/epjam/2022016.
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“Lycurgus cup” effect, referring dichroism between reflection and transmission modes of the same structures, is a peculiar phenomenon of multi-faceted display in structural color. Beyond the static dichrotic display, the realization of dynamic dichroism desires active materials and tunable structures, and owns the great demand from smart display, anti-counterfeiting and environmental sensing. We hereby propose a metal-hydrogel-metal (MHM) nanocavity for dynamic dichrotic display. This structure includes thin silver layers to induce the partial transmission with the existing reflection, and a polyvinyl alcohol (PVA) hydrogel layer owning the swelling/deswelling deformability to humidity change. The following experimental measurements and theoretical analysis prove that the reflection and transmission modes exist at distinct wavelengths, and the swelling hydrogel layer by humidity change between 10 and 90% RH can dynamically modulate the dichrotic resonance with the wavelength shift over 100 nm. Such environmental-sensitive and real-time tunable dichroism with hydrogel-based structural color is then verified for multi-color printing, resolution test, and cycling test.
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Mendivelso, Camilo, John Pantoja, Felix Vega, Chaouki Kasmi, and Fahad Al Yafei. "Use of Dielectric Spectroscopy for the Study of Concentration of Glyphosate in Distilled Water." Applied Computational Electromagnetics Society 35, no. 11 (February 5, 2021): 1404–5. http://dx.doi.org/10.47037/2020.aces.j.351171.
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In this paper, the capability of sensing low concentrations of glyphosate in water of two interdigital capacitive transducers are analyzed using numerical simulations and measurements. Each microwave sensor is analyzed using the surface electric field produced at the resonance frequency. In addition, the reflection coefficient of each transducer submerged in water with glyphosate is measured and compared with distilled water. Prepared samples with concentrations of 1ppm/L (1 part per million over a liter of distilled water) are used for the experimental tests.
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PLANAT, M. "ON THE GEOMETRY AND INVARIANTS OF QUBITS, QUARTITS AND OCTITS." International Journal of Geometric Methods in Modern Physics 08, no. 02 (March 2011): 303–13. http://dx.doi.org/10.1142/s0219887811005142.
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Four-level quantum systems, known as quartits, and their relation to two-qubit systems are investigated group theoretically. Following the spirit of Klein's lectures on the icosahedron and their relation to Hopf sphere fibrations, invariants of complex reflection groups occurring in the theory of qubits and quartits are displayed. Then, real gates over octits leading to the Weyl group of E8 and its invariants are derived. Even multilevel systems are of interest in the context of solid state nuclear magnetic resonance.
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SAMANTA, ARNAB, and JONATHAN B. FREUND. "Finite-wavelength scattering of incident vorticity and acoustic waves at a shrouded-jet exit." Journal of Fluid Mechanics 612 (October 10, 2008): 407–38. http://dx.doi.org/10.1017/s0022112008003212.
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As the vortical disturbances of a shrouded jet pass the sharp edge of the shroud exit some of the energy is scattered into acoustic waves. Scattering into upstream-propagating acoustic modes is a potential mechanism for closing the resonance loop in the ‘howling’ resonances that have been observed in various shrouded jet configurations over the years. A model is developed for this interaction at the shroud exit. The jet is represented as a uniform flow separated by a cylindrical vortex sheet from a concentric co-flow within the cylindrical shroud. A second vortex sheet separates the co-flow from an ambient flow outside the shroud, downstream of its exit. The Wiener–Hopf technique is used to compute reflectivities at the shroud exit. For some conditions it appears that the reflection of finite-wavelength hydrodynamic vorticity modes on the vortex sheet defining the jet could be sufficient to reinforce the shroud acoustic modes to facilitate resonance. The analysis also gives the reflectivities for the shroud acoustic modes, which would also be important in establishing resonance conditions. Interestingly, it is also predicted that the shroud exit can be ‘transparent’ for ranges of Mach numbers, with no reflection into any upstream-propagating acoustic mode. This is phenomenologically consistent with observations that indicate a peculiar sensitivity of resonances of this kind to, say, jet Mach number.
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Budnarowska, Magdalena, Szymon Rafalski, and Jerzy Mizeraczyk. "Vector-Field Visualization of the Total Reflection of the EM Wave by an SRR Structure at the Magnetic Resonance." Energies 15, no. 1 (December 24, 2021): 111. http://dx.doi.org/10.3390/en15010111.
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Metamaterials are artificially structured composite media with a unique electromagnetic (EM) response that is absent from naturally occurring materials, which appears counterintuitive and aggravates traditional difficulties in perceiving the behavior of EM waves. The aim of this study was to better understand the interaction of EM waves with metamaterials by virtual visualizing the accompanying physical phenomena. Over the years, virtual visualization of EM wave interactions with metamaterials has proven to be a powerful tool for explaining many phenomena that occur in metamaterials. In this study, we performed virtual visualization of the interaction of an EM plane wave with a split-ring resonator (SRR) metamaterial structure, employing CST Studio software for modeling and comprehensive simulations of high-frequency EM fields of 3D objects. The SRR structure was designed to have its magnetic resonance at the frequency f = 23.69 GHz, which is of interest for antennas supporting wireless microwave point-to-point communication systems (e.g., in satellite systems). Our numerical calculations of the coefficients of absorption, reflection, and transmission of the EM plane wave incident on the SRR structure showed that the SRR structure totally reflected the plane EM wave at the magnetic resonance frequency. Therefore, we focused our research on checking whether the results of numerical calculations could be confirmed by visualizing the total reflection phenomenon on the SRR structure. The performed vector-field visualization resulted in 2D vector maps of the electric and magnetic fields around the SRR structure during the wave period, which demonstrated the existence of characteristic features of the total reflection phenomenon when the EM plane interacted with the studied SRR, i.e., no EM field behind the SRR structure and the standing electric and magnetic waves before the SRR structure, thus, confirming the numerical calculations visually. For deeper understanding the interaction of the EM plane wave with the SRR structure of reflection characteristics at the magnetic resonance frequency f = 23.69 GH, we also visualized the SRR structure response at the frequency f = 21 GHz, i.e., at the so-called detuned frequency. As expected, at the detuned frequency, the SRR structure lost its metamaterial properties and the obtained 2D vector maps of the electric and magnetic fields around the SRR structure during the wave period showed the transmitted EM wave behind the SRR structure and no EM (fully) standing waves before the SRR structure. The visualizations presented in this study are both unique educational presentations to help understand the interaction of EM plane waves with the SRR structure of reflection characteristics at the magnetic resonance and detuned frequencies.
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Babu, Sachin, and Jeong-Bong Lee. "Axially-Anisotropic Hierarchical Grating 2D Guided-Mode Resonance Strain-Sensor." Sensors 19, no. 23 (November 28, 2019): 5223. http://dx.doi.org/10.3390/s19235223.
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Guided-mode resonance strain sensors are planar binary gratings that have fixed resonance positions and quality factors decided by material properties and grating parameters. If one is restricted by material choices, the quality factor can only be improved by adjusting the grating parameters. We report a new method to improve quality factor by applying a slotting design rule to a grating design. We investigate this design rule by first providing a theoretical analysis on how it works and then applying it to a previously studied 2D solid-disc guided-mode resonance grating strain sensor design to create a new slotted-disc guided-mode resonance grating design. We then use finite element analysis to obtain reflection spectrum results that show the new design produces resonances with at least a 6-fold increase in quality factor over the original design and more axially-symmetric sensitivities. Lastly, we discuss the applicability of the slotting design rule to binary gratings in general as a means of improving grating performance while retaining both material and resonance position choices.