Journal articles: 'Energy chirp'

1

GUPTA, D. N., and H. SUK. "Electron acceleration to high energy by using two chirped lasers." Laser and Particle Beams 25, no. 1 (February 28, 2007): 31–36. http://dx.doi.org/10.1017/s026303460707005x.

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A scheme for electron acceleration by two crossing chirped lasers has been proposed. An important effect of a frequency chirp of the laser is investigated. Two high intensity chirped lasers, with the same amplitude and frequency, crossing at an arbitrary angle in a vacuum, interfere, causing modulation of laser intensity. An electron experiences a ponderomotive force due to the resultant field of lasers and gains considerable energy. For a certain crossing angle, the electron gains maximum energy due to the constructive interference. A frequency chirp of the laser plays an important role during the electron acceleration in a vacuum. The electron momentum increases due to the frequency chirp. Hence, the electron energy is enhanced during acceleration.

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Cheong, Kah-Meng, Yih-Liang Shen, and Tai-Shih Chi. "Active acoustic scene monitoring through spectro-temporal modulation filtering for intruder detection." Journal of the Acoustical Society of America 151, no. 4 (April 2022): 2444–52. http://dx.doi.org/10.1121/10.0010070.

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An indoor acoustic scene monitoring system using a periodic impulse signal was previously developed. Compared with the impulse signal, the chirp signal is more robust against environmental noise due to its specific spectro-temporal structure. Such specific structure makes the chirp sound easily detected using a spectro-temporal modulation filtering mechanism. In this paper, we demonstrated a system that employs a two-dimensional spectro-temporal filtering mechanism on a Fourier spectrogram to measure the total energy of the reverberations of the chirp signal as the representation of the acoustic scene. The system compares the reverberation energy difference between consecutive chirps with a predefined threshold to automatically detect the change in the acoustic scene. Simulations were conducted in real living rooms with various types of background noise. Test results demonstrated that the proposed system is much more effective than previously developed systems for detecting the acoustic scene changes due to the intruder silently walking in the rooms. In the biggest test room (18 × 9.8 × 2.5 m3) with heavy background noise, the proposed system can still yield a correct identification rate higher than 80% to the intruder walking at 7 m from the microphone without producing any false alarms.

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Liu, Weici. "Effect of initial chirp for input pulse on supercontinuum generation." Journal of Physics: Conference Series 2029, no. 1 (September 1, 2021): 012019. http://dx.doi.org/10.1088/1742-6596/2029/1/012019.

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Abstract The generation of supercontinuum spectrum is a very complex nonlinear process. Based on the nonlinear Schrodinger equation (NLSE), the effect of initial chirp on supercontinuum generation is numerically studied by split-step Fourier (SSF) method. The positive chirp and negative chirp have different effects on the supercontinuum generation. The results show that the energy distribution of supercontinuum spectrum can be improved by selecting appropriate chirp value.

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4

Mao, Dong, Zhiwen He, Qun Gao, Chao Zeng, Ling Yun, Yueqing Du, Hua Lu, Zhipei Sun, and Jianlin Zhao. "Birefringence-Managed Normal-Dispersion Fiber Laser Delivering Energy-Tunable Chirp-Free Solitons." Ultrafast Science 2022 (July 30, 2022): 1–12. http://dx.doi.org/10.34133/2022/9760631.

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Chirp-free solitons have been mainly achieved with anomalous-dispersion fiber lasers by the balance of dispersive and nonlinear effects, and the single-pulse energy is constrained within a relatively small range. Here, we report a class of chirp-free pulse in normal-dispersion erbium-doped fiber lasers, termed birefringence-managed soliton, in which the birefringence-related phase-matching effect dominates the soliton evolution. Controllable harmonic mode locking from 5 order to 85 order is obtained at the same pump level of ~10 mW with soliton energy fully tunable beyond ten times, which indicates a new birefringence-related soliton energy law, which fundamentally differs from the conventional soliton energy theorem. The unique transformation behavior between birefringence-managed solitons and dissipative solitons is directly visualized via the single-shot spectroscopy. The results demonstrate a novel approach of engineering fiber birefringence to create energy-tunable chirp-free solitons in normal-dispersion regime and open new research directions in fields of optical solitons, ultrafast lasers, and their applications.

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Wu, Yan Jun, Gang Fu, and Peng Yu. "Performance Analysis on Three Methods for Chirp Signal Parameters Estimation Based on FRFT." Advanced Materials Research 989-994 (July 2014): 3942–45. http://dx.doi.org/10.4028/www.scientific.net/amr.989-994.3942.

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Chirp signal has been used widely in radar signals, and the Fractional Fourier transform is one of the most effective tools to analyze Chirp signal. In this paper, the concept of FRFT and the estimation theory of Chirp signal are introduced firstly. Then, we study three Chirp signal detection algorithms based on character of Chirp signal energy concentrated in a certain FRFT domain. Finally, in order to test the estimation abilities of the frequency modulation rate and the central frequency of FRFT to Chirp signal, and compare the operation time of parameters estimation under different SNR of the three algorithms, we simulate performance of the Three methods, and the final simulation results show that the three method have remarkable capabilities of detecting Chirp signal with low SNR. In contrast, the two-searching method doesn’t need planar search, consumedly reducing the computation cost at the same precision.

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Lu, Xiang, Volker Pickert, Maher Al-Greer, Cuili Chen, Xiang Wang, and Charalampos Tsimenidis. "Temperature Estimation of SiC Power Devices Using High Frequency Chirp Signals." Energies 14, no. 16 (August 11, 2021): 4912. http://dx.doi.org/10.3390/en14164912.

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Silicon carbide devices have become increasingly popular in electric vehicles, predominantly due to their fast-switching speeds, which allow for the construction of smaller power converters. Temperature sensitive electrical parameters (TSEPs) can be used to determine the junction temperature, just like silicon-based power switches. This paper presents a new technique to estimate the junction temperature of a single-chip silicon carbide (SiC) metal–oxide–semiconductor field-effect transistor (MOSFET). During off-state operation, high-frequency chirp signals below the resonance frequency of the gate-source impedance are injected into the gate of a discrete SiC device. The gate-source voltage frequency response is captured and then processed using the fast Fourier transform. The data is then accumulated and displayed over the chirp frequency spectrum. Results show a linear relationship between the processed gate-source voltage and the junction temperature. The effectiveness of the proposed TSEPs is demonstrated in a laboratory scenario, where chirp signals are injected in a stand-alone biased discrete SiC module, and in an in-field scenario, where the TSEP concept is applied to a MOSFET operating in a DC/DC converter.

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Fleming, A. J., A. A. Lindeman, A. L. Carroll, and J. E. Yack. "Acoustics of the mountain pine beetle (Dendroctonus ponderosae) (Curculionidae, Scolytinae): sonic, ultrasonic, and vibration characteristics." Canadian Journal of Zoology 91, no. 4 (April 2013): 235–44. http://dx.doi.org/10.1139/cjz-2012-0239.

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Acoustic signaling is widespread in bark beetles (Scolytinae), although little is known about the physical characteristics of signals, how they are transmitted, and how they differ among behavioural contexts. Signals were studied in the male mountain pine beetle (Dendroctonus ponderosae Hopkins, 1902) during stress, male–female, and male–male interactions. Sounds are broadband with significant energy in the ultrasound (peaks between 15 and 26 kHz) and low amplitude (55 and 47 dB SPL at 2 and 4 cm, respectively), indicating that signaling functions at close range. Signal trains vary among contexts primarily in the proportions of chirp types. Chirps were categorized as being simple or interrupted, with the former having significantly lower tooth strike rates and shorter chirp durations. Stress chirps are predominantly simple with characteristics resembling other insect disturbance signals. Male–female interactions begin with the male producing predominantly interrupted chirps prior to gallery entrance, followed by simple chirps. Male–male (rivalry) chirps are predominantly simple, with evidence of antiphonal calling. Substrate-borne vibrations were detectable with a laser-doppler vibrometer at short distances (1–3 cm), suggesting that sensory organs could be tuned to either air or substrate-borne vibrations. These results have important implications for future research on the function and reception of acoustic signals in bark beetles.

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Wang, Guanglei, Chao Feng, Haixiao Deng, Tong Zhang, and Dong Wang. "Beam energy chirp effects in seeded free-electron lasers." Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 753 (July 2014): 56–60. http://dx.doi.org/10.1016/j.nima.2014.03.015.

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9

Singh, K. P., and H. K. Malik. "Resonant enhancement of electron energy by frequency chirp during laser acceleration in an azimuthal magnetic field in a plasma." Laser and Particle Beams 26, no. 3 (June 19, 2008): 363–69. http://dx.doi.org/10.1017/s0263034608000372.

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AbstractElectron acceleration by a chirped laser pulse in an azimuthal magnetic field in a plasma has been studied. The betatron resonance saturates and the electrons start losing energy beyond a specific point of time without a frequency chirp. The resonance can be maintained for a longer duration and the energy of the electrons can be enhanced if a suitable frequency chirp is introduced. The duration of interaction increases for a lower plasma density or a lower initial electron energy which causes increase in the electron energy gain. The value of magnetic field required for resonance increases with an increase in plasma density and with a decrease in initial electron energy.

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10

Ginzburg, N. S., I. V. Zotova, R. M. Rozental, A. S. Sergeev, M. Kamada, K. Kurihara, H. Shirasaka, R. Ando, and K. Kamada. "Increasing superradiant pulse peak power by using electron energy chirp." Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 507, no. 1-2 (July 2003): 61–64. http://dx.doi.org/10.1016/s0168-9002(03)00838-6.

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11

Wu, Yan Jun, Gang Fu, and Qian He. "Study of VLF Communication Technique Based on FRFT." Applied Mechanics and Materials 556-562 (May 2014): 5116–20. http://dx.doi.org/10.4028/www.scientific.net/amm.556-562.5116.

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The atmospheric noise generated by lightning phenomena is the main source of interference in VLF communications, it is rather difficult to detect the communication signal that not only merged in strong channel noise, but probably interfered by high-tension impulse caused by thunder. This paper, Alpha stable distribution noise model is proposed to simulate atmospheric noise firstly, then, we study a new technique of Chirp Spread Spectrum (CSS) communication based on Fractional Fourier Transform (FRFT), This paper studies a new VLF communication technique of the Chirp Spread Spectrum (CSS) communication based on Fractional Fourier Transform (FRFT), and it demodulates message utilizing energy gathering property of chirp signal in FRFT domain.

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12

Ricci, Stefano, Stefano Caputo, and Lorenzo Mucchi. "FPGA-Based Pulse Compressor for Ultra Low Latency Visible Light Communications." Electronics 12, no. 2 (January 10, 2023): 364. http://dx.doi.org/10.3390/electronics12020364.

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Visible Light Communication (VLC) represents an emerging technology where a short-range data connection is obtained by modulating the energy radiated by Light Emitting Diodes (LEDs) at frequencies from a few kHz up to hundreds of MHz. The bandwidth/distance performance of such links is a compromise related to the available Signal-to-Noise ratio (SNR). At present, VLC links with bandwidth beyond the Gb/s and distance limited to a few cm or distances up to 100 m but data rates of a few kb/s have been demonstrated. Chirp coding with pulse compression is a well-known technique capable of recovering useful data from low SNR signals, widely employed, for example, in radar. In spite of the possible advantages, its application in VLC has never been investigated. Unfortunately, the pulse compressor is quite calculation-intensive, and only devices like Field-Programmable-Gate-Arrays (FPGAs) can support a low-latency real-time implementation. In this paper we demonstrate a real-time VLC link based on chirp coding and pulse compression coded in FPGA. For example, a chirp with bandwidth and length of 1.7 MHz and 17.92 µs, respectively, is demonstrated to support a link at 1.56 Mb/s over 2.8 m distance and a latency below 40 µs. Moreover, the communication-distance increase achievable by chirps of increasing temporal length is demonstrated and compared to the theoretical background.

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13

Wu, Yan Jun, Gang Fu, and Gang Cheng. "An Adaptive Filtering Method for Chirp Signal Based on FRFT." Advanced Materials Research 989-994 (July 2014): 3934–37. http://dx.doi.org/10.4028/www.scientific.net/amr.989-994.3934.

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In this paper, an adaptive filter method for Chirp signal in additional white Gaussian noise (AWGN) is studied. First, we analyze conception and character of FRFT (Fractional Fourier Transform), and the results shows that Chirp signal has energy concentration character in FRFT domain. Then, an adaptive filtering method is introduced in FRFT domain, and a test is done for separating Chirp signal from AWGN by the filtering method. Last, performance of this filtering method is studied, and the SNR improvement expression is concluded to verifying its advantages, it depends on the performance of adaptive filter basically. At last, the results show that this filtering algorithm is simple in computation and easy in implementation.

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14

Foroozandeh, Mohammadali, Mathias Nilsson, and Gareth A. Morris. "Improved ultra-broadband chirp excitation." Journal of Magnetic Resonance 302 (May 2019): 28–33. http://dx.doi.org/10.1016/j.jmr.2019.03.007.

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15

Fadini, Alisia, Sven Reiche, Karol Nass, and Jasper J. van Thor. "Applications and Limits of Time-to-Energy Mapping of Protein Crystal Diffraction Using Energy-Chirped Polychromatic XFEL Pulses." Applied Sciences 10, no. 7 (April 9, 2020): 2599. http://dx.doi.org/10.3390/app10072599.

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A broadband energy-chirped hard X-ray pulse has been demonstrated at the SwissFEL (free electron laser) with up to 4% bandwidth. We consider the characteristic parameters for analyzing the time dependence of stationary protein diffraction with energy-chirped pulses. Depending on crystal mosaic spread, convergence, and recordable resolution, individual reflections are expected to spend at least ≈ 50 attoseconds and up to ≈ 8 femtoseconds in reflecting condition. Using parameters for a chirped XFEL pulse obtained from simulations of 4% bandwidth conditions, ray-tracing simulations have been carried out to demonstrate the temporal streaking across individual reflections and resolution ranges for protein crystal diffraction. Simulations performed at a higher chirp (10%) emphasize the importance of chirp magnitude that would allow increased observation statistics for the temporal separation of individual reflections for merging and structure determination. Finally, we consider the fundamental limitation for obtaining time-dependent observations using chirped pulse diffraction. We consider the maximum theoretical time resolution achievable to be on the order of 50–200 as from the instantaneous bandwidth of the chirped SASE pulse. We then assess the ability to propagate ultrafast optical pulses for pump-probe cross-correlation under characteristic conditions of material dispersion; in this regard, the limiting factors for time resolution scale with crystal thickness. Crystals that are below a few microns in size will be necessary for subfemtosecond time resolution.

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Wu, Xuan Li, Lu Kuan Sun, and Wan Jun Zhao. "Semi-Definite Programming Based Waveform Design for Spectrum Sensing." Applied Mechanics and Materials 457-458 (October 2013): 1491–97. http://dx.doi.org/10.4028/www.scientific.net/amm.457-458.1491.

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In order to solve the problem of spectrum shortages, dynamic spectrum access based cognitive radio technology was proposed, and the technology of spectrum sensing is the foundation of cognitive radio. In this paper, a semi-definite programming based waveform design algorithm is proposed for spectrum sensing. Considering the energy concentration property of Chirp signal, the Chirp signal is adopted as the basic function, which makes the composite waveform perform like impulse function in fractional Fourier transform domain. Simulation results show that the NESP (Normalized Effective Signal Power) of the designed waveform using the proposed algorithm can be over 70%, and the designed waveform also retains good energy concentration property in fractional domain.

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17

Fu, Gang, Yan Jun Wu, and Qian He. "Simulation of VLF CSS System in Atmospheric Noise." Applied Mechanics and Materials 556-562 (May 2014): 1874–78. http://dx.doi.org/10.4028/www.scientific.net/amm.556-562.1874.

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Very Low Frequency (VLF) communication is designed to operate in the frequency between 3 kHz and 30 kHz. The atmospheric noise generated by lightning phenomena is the main source of interference in VLF communications, it is rather difficult to detect the communication signal that not only merged in strong channel noise, but probably interfered by high-tension impulse caused by thunder. This paper, Alpha stable distribution noise model is proposed to simulate atmospheric noise firstly, then, we study a new technique of Chirp Spread Spectrum (CSS) communication based on Fractional Fourier Transform (FRFT), This paper studies a new VLF communication technique of the Chirp Spread Spectrum (CSS) communication based on Fractional Fourier Transform (FRFT), and it demodulates message utilizing energy gathering property of chirp signal in FRFT domain.

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18

Taylor, Joseph H. "From Einstein’s Theory to Gravity’s Chirp." Proceedings of the International Astronomical Union 13, S337 (September 2017): 127. http://dx.doi.org/10.1017/s1743921317007657.

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The tortuous journey from theoretical suspicions to direct detection of gravitational waves took a hundred years and followed a crooked course. The field equations of general relativity evidently have wave-like solutions, but physical reality of these implied waves was doubted by many — including Einstein himself — for nearly fifty years. The question of physical reality was settled theoretically by the late 1950s, but for several more decades serious questions remained about what types of astrophysical systems might generate gravitational waves, and with what energies. The discovery of binary pulsar PSR B1913+16 led to dedicated development of much more accurate pulsar timing techniques, and results of these experiments motivated further theoretical work to clear up the quantitative questions about energy generation. By the late 1980s the generation of gravitational waves by the Hulse-Taylor binary pulsar was firmly established to be in quantitative agreement with general relativity. This experimental proof was almost surely a prerequisite for the funding of LIGO, the Laser Interferometer Gravitational-Wave Observatory, in 1992, which after nearly another quarter century achieved the first direct detection of gravitational waves.

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Liu, Hang, Cui-Yan Xu, Xiao-Dan Jing, Yan Qiao, and Li-Qiang Feng. "Chirp waveform control to produce broad harmonic plateau and single attosecond pulse." Zeitschrift für Naturforschung A 76, no. 9 (June 25, 2021): 747–55. http://dx.doi.org/10.1515/zna-2021-0115.

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Abstract Waveform control of three kinds of chirped pulses (i.e. βt, βt 2 and βt 3) to produce harmonic spectra and attosecond pulses has been investigated. It is found that by properly choosing the chirps, the chirp delays and the other laser parameters, not only the instantaneous frequency of some specific half profiles can be decreased, but also its intensity can be increased. As a result, the free electron can receive more energy when it accelerates in these regions, thus leading to the extension of the harmonic cutoff and harmonic plateau. Finally, through the Fourier transformation of the harmonic spectra and by superposing some harmonics, three single attosecond pulses with the durations of 30 as, 33 as and 39 as can be obtained.

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ABOBAKER, ABDOSLLAM M., A. B. MOUBISSI, TH B. EKOGO, and K. NAKKEERAN. "ANALYTICAL SOLUTIONS FOR THE VARIATIONAL EQUATIONS DERIVED FOR THE NONLINEAR SCHRÖDINGER EQUATION: DISPERSION-MANAGED FIBER SYSTEM." Journal of Nonlinear Optical Physics & Materials 17, no. 03 (September 2008): 285–97. http://dx.doi.org/10.1142/s0218863508004226.

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We consider the nonlinear Schrödinger equation which governs the pulse propagation in dispersion-managed (DM) optical fiber transmission systems. Using a generalized form of ansatz function for the shape of the pulse, we derive the variational equations. For a particular case of DM fiber systems when the Hamiltonian is zero, we solve the variational equations analytically and obtain the expressions for the pulse energy, amplitude, width and chirp. Finally for Gaussian and hyperbolic secant shaped pulses, we show through numerical simulations that the analytically calculated energy (for the given pulse width and chirp) is good enough to support the periodic evolution of the DM soliton. The simulations are carried out for conventional and dense DM fiber systems for both lossless and lossy cases.

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Wang, Liang, Chao Xuan Shang, Qiang He, Zhuang Zhi Han, and Hong Wei Ren. "Study on Imaging Algorithm for Stepped-Frequency Chirp Train Waveform." Applied Mechanics and Materials 347-350 (August 2013): 1101–5. http://dx.doi.org/10.4028/www.scientific.net/amm.347-350.1101.

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A range profile synthetic algorithm of the stepped-frequency chirp train waveform is designed to obtain HRRP (High Resolution Range Profile) in this paper. Based on waveform model, grating lobes restraining method is proposed with the help of autocorrelation function. Due to the matched filter operation, image energy spill over the close range bins, which causes “ghost images”. Set parameters of inner pulse bandwidth, stepped frequency and chirp compression envelop sampling frequency properly, and then carry the synthetic algorithm, the “ghost images” are restrained. All of the results are validated by simulation.

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Braig, Christoph, and Alexei Erko. "Broadband Time-Delay and Chirp Compensator for X-ray Pulses." Photonics 9, no. 5 (April 28, 2022): 302. http://dx.doi.org/10.3390/photonics9050302.

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A new type of aberration-corrected time-delay compensating monochromator (TDCM) for soft X-rays is presented. Composed of two identical reflection zone plates (RZPs) on spherical substrates and an intermediate flat mirror for band-pass selection, the TDCM can operate in a wide energy range of about ±20% around the design energy of 410eV. Assuming a source size of 50μm and an angular acceptance of 1 mrad, the spectral resolving power may reach 6×102, at a pulse length as short as 4.3femtoseconds(fs). In the case of μm-sized sources, the resolution can be better than 0.1eV and the sub-fs regime could become accessible. The overall transmission efficiency varies within (4.2–6.0)% across the energy range (310–510) eV. In the complementary mode, chirped-pulse compression works as well. Depending on the properties of the source, simulations predict an up to 9-fold reduction in pulse duration, whereas ≤50% of the peak intensity is maintained.

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Wu, Ying, Changhai Yu, Zhiyong Qin, Wentao Wang, Zhijun Zhang, Rong Qi, Ke Feng, et al. "Energy Enhancement and Energy Spread Compression of Electron Beams in a Hybrid Laser-Plasma Wakefield Accelerator." Applied Sciences 9, no. 12 (June 23, 2019): 2561. http://dx.doi.org/10.3390/app9122561.

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We experimentally demonstrated the generation of narrow energy-spread electron beams with enhanced energy levels using a hybrid laser-plasma wakefield accelerator. An experiment featuring two-color electron beams showed that after the laser pump reached the depletion length, the laser-wakefield acceleration (LWFA) gradually evolved into the plasma-driven wakefield acceleration (PWFA), and thereafter, the PWFA dominated the electron acceleration. The energy spread of the electron beams was further improved by energy chirp compensation. Particle-in-cell simulations were performed to verify the experimental results. The generated monoenergetic high-energy electron beams are promising to upscale future accelerator systems and realize monoenergetic γ -ray sources.

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Das, Sreya, and Navin Khaneja. "Composite pulse combinations for chirp excitation." Journal of Magnetic Resonance 347 (February 2023): 107359. http://dx.doi.org/10.1016/j.jmr.2022.107359.

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25

Deng, Zhixiang, and Meng Zhang. "Dynamics of Dispersive Wave Generation in Gas-Filled Photonic Crystal Fiber with the Normal Dispersion." Advances in Condensed Matter Physics 2017 (2017): 1–9. http://dx.doi.org/10.1155/2017/1268230.

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The absence of Raman and unique pressure-tunable dispersion is the characteristic feature of gas-filled photonic crystal fiber (PCF), and its zero dispersion points can be extended to the near-infrared by increasing gas pressure. The generation of dispersive wave (DW) in the normal group velocity dispersion (GVD) region of PCF is investigated. It is demonstrated that considering the self-steepening (SS) and introducing the chirp of the initial input pulse are two suitable means to control the DW generation. The SS enhances the relative average intensity of blue-shift DW while weakening that of red-shift DW. The required propagation distance of DW emission is markedly varied by introducing the frequency chirp. Manipulating DW generation in gas-filled PCF by the combined effects of either SS or chirp and three-order dispersion (TOD) provides a method for a concentrated transfer of energy into the targeted wavelengths.

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Islam, Md Torikul, Md Abdus Sami Akanda, Md Abu Jafar Pikul, and Xiansi Wang. "Fast magnetization reversal of a magnetic nanoparticle induced by cosine chirp microwave field pulse." Journal of Physics: Condensed Matter 34, no. 10 (December 23, 2021): 105802. http://dx.doi.org/10.1088/1361-648x/ac3f66.

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Abstract We investigate the magnetization reversal of single-domain magnetic nanoparticle driven by the circularly polarized cosine chirp microwave pulse (CCMP). The numerical findings, based on the Landau–Lifshitz–Gilbert equation, reveal that the CCMP is by itself capable of driving fast and energy-efficient magnetization reversal. The microwave field amplitude and initial frequency required by a CCMP are much smaller than that of the linear down-chirp microwave pulse. This is achieved as the frequency change of the CCMP closely matches the frequency change of the magnetization precession which leads to an efficient stimulated microwave energy absorption (emission) by (from) the magnetic particle before (after) it crosses over the energy barrier. We further find that the enhancement of easy-plane shape anisotropy significantly reduces the required microwave amplitude and the initial frequency of CCMP. We also find that there is an optimal Gilbert damping for fast magnetization reversal. These findings may provide a pathway to realize the fast and low-cost memory device.

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Solyman, Ahmad AA, Hani Attar, Mohammad R. Khosravi, and Baki Koyuncu. "MIMO-OFDM/OCDM low-complexity equalization under a doubly dispersive channel in wireless sensor networks." International Journal of Distributed Sensor Networks 16, no. 6 (June 2020): 155014772091295. http://dx.doi.org/10.1177/1550147720912950.

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In this article, three novel systems for wireless sensor networks based on Alamouti decoding were investigated and then compared, which are Alamouti space–time block coding multiple-input single-output/multiple-input multiple-output multicarrier modulation (MCM) system, extended orthogonal space–time block coding multiple-input single-output MCM system, and multiple-input multiple-output system. Moreover, the proposed work is applied over multiple-input multiple-output systems rather than the conventional single-antenna orthogonal chirp division multiplexing systems, based on the discrete fractional cosine transform orthogonal chirp division multiplexing system to mitigate the effect of frequency-selective and time-varying channels, using low-complexity equalizers, specifically by ignoring the intercarrier interference coming from faraway subcarriers and using the LSMR iteration algorithm to decrease the equalization complexity, mainly with long orthogonal chirp division multiplexing symbols, such as the TV symbols. The block diagrams for the proposed systems are provided to simplify the theoretical analysis by making it easier to follow. Simulation results confirm that the proposed multiple-input multiple-output and multiple-input single-output orthogonal chirp division multiplexing systems outperform the conventional multiple-input multiple-output and multiple-input single-output orthogonal frequency division multiplexing systems. Finally, the results show that orthogonal chirp division multiplexing exhibited a better channel energy behavior than classical orthogonal frequency division multiplexing, thus improving the system performance and allowing the system to decrease the equalization complexity.

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Sabato, L., P. Arpaia, A. Giribono, A. Liccardo, A. Mostacci, L. Palumbo, C. Vaccarezza, and A. Variola. "Effects of energy chirp on bunch length measurement in linear accelerator beams." Measurement Science and Technology 28, no. 8 (July 17, 2017): 084002. http://dx.doi.org/10.1088/1361-6501/aa6c8a.

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Rakesh Kumar, V., Kamalesh Jana, Indranuj Dey, K. Chandra Vardhan, Amit D. Lad, Jeffrey M. Brown, Mette B. Gaarde, Arnaud Couairon, and G. Ravindra Kumar. "Spectral and intensity control of high energy terahertz radiation from bulk liquids." Journal of Physics D: Applied Physics 55, no. 9 (November 23, 2021): 095107. http://dx.doi.org/10.1088/1361-6463/ac3455.

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Abstract High power, broadband terahertz (THz) radiation from liquids, excited by intense, femtosecond 800 nm laser pulses has been demonstrated recently, overturning the long held belief that liquids would not give such emission due to their absorption in the THz region. Given the widespread interest in the use of THz radiation for several applications and the energy and bandwidth limitations of existing sources, liquids are expected to attract great attention in the future. While the emission at tens of microjoules from liquids is very promising, it is important to explore whether control of the THz flux and spectrum is achievable by manipulating the laser or liquid parameters. In this paper we present results on manipulating the spectrum of THz radiation from liquids by chirping the input laser pulse and optimizing the THz output energy by laser chirp as well as optimizing the focal position. We demonstrate tunability by varying the chirp of the laser pulse and show that the THz emission predominantly comes from the region near the end of the liquid path, consistent with the absorption of THz radiation by liquids. This control gives us an opportunity to tune the THz radiation to suit experimental needs. We present simulations that support the results.

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Sarkar, Sambeda, Rudra N. Purusottam, Ashutosh Kumar, and Navin Khaneja. "Chirp pulse sequences for broadband π rotation." Journal of Magnetic Resonance 328 (July 2021): 107002. http://dx.doi.org/10.1016/j.jmr.2021.107002.

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31

Wili, Nino, and Gunnar Jeschke. "Chirp echo Fourier transform EPR-detected NMR." Journal of Magnetic Resonance 289 (April 2018): 26–34. http://dx.doi.org/10.1016/j.jmr.2018.02.001.

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Ouellette, Scott A., and Michael D. Todd. "Modulating the bistable potential energy separatrix for augmented broadband vibration energy harvesting." Journal of Intelligent Material Systems and Structures 28, no. 3 (July 28, 2016): 294–306. http://dx.doi.org/10.1177/1045389x16634210.

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In recent years, increased interest in broadband vibration energy harvesting schemes has been a main topic of interest among researchers. One of the most successful approaches toward broadband vibration energy capture has been with bistable inertial generators. These devices leverage a nonlinear restoring force to exploit the hardening spring response to increase the resonant frequency bandwidth beyond the characteristically narrowband resonant frequency associated with conventional linear inertial generators. However, one issue with bistable energy harvesters is the presence of low-amplitude oscillations whose energy is insufficient to overcome the potential energy separatrix barrier between the competing potential wells. This article presents the effects of controlling the magnitude of the potential energy separatrix by means of a high-permeability electromagnet in order to increase the resonant response bandwidth for low-amplitude harmonic excitations. An analytical model of the bifurcation space resulting from two control parameters is presented along with an experimental validation study. Finally, an open-loop control law is developed and tested to validate the resonant frequency bandwidth augmentation for harmonic chirp excitations.

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Ginzburg, N. S., I. V. Zotova, and A. S. Sergeev. "Generation and Amplification of Cherenkov Superradiance Pulses by Electron Beams with Energy Chirp." Radiophysics and Quantum Electronics 46, no. 10 (October 2003): 790–96. http://dx.doi.org/10.1023/b:raqe.0000026872.66269.42.

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Chen, Zhigang, Lei Wang, and Mengya Zhang. "Virtual Antenna Array and Fractional Fourier Transform-Based TOA Estimation for Wireless Positioning." Sensors 19, no. 3 (February 2, 2019): 638. http://dx.doi.org/10.3390/s19030638.

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In this paper, a novel virtual antenna array and fractional Fourier transform (FRFT)-based 2-dimension super-resolution time-of-arrival (TOA) estimation algorithm for OFDM WLAN systems has been proposed. The proposed algorithm employs channel frequency responses (CFRs) at the equi-spaced positions on a line or quasi-line moving trajectory, i.e., the CFRs of a virtual antenna array, to extract multipaths’ TOA information. Meanwhile, a new chirp-like quadratic function is used to approximate the channel multipaths’ phase variation across the space dimension, which is more reasonable than the traditional linear function, especially for relatively big virtual antenna array sizes. By exploiting the property of chirp-like multipaths’ energy concentration in the FRFT domain, the FRFT can be first used to separate chirp-like multipath components, then the existing TOA estimation methods in frequency domain can be further employed on the separated multipath components to obtain the multipaths’ TOA estimates. Therefore, the proposed algorithm can make more use of the multipaths’ characteristics in the space dimension, thus it can efficiently enhance the multipath resolution and achieve better multipaths’ TOA estimation performance without requiring a real antenna array. Simulation results demonstrate the effectiveness of the proposed algorithm.

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Feng, Liqiang, Wenliang Li, and Hang Liu. "Intensity enhancement of attosecond XUV pulse by using asymmetric inhomogeneous mid-infrared down-chirped field." International Journal of Modern Physics B 31, no. 26 (October 17, 2017): 1750185. http://dx.doi.org/10.1142/s0217979217501855.

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Intensity enhancement of the attosecond pulse generation from the high-order harmonic spectra has been theoretically investigated through solving the three-dimensional time-dependent Schrödinger equation. It is found that with the introduction of the down-chirped pulse, the temporal frequency of the down-chirp region is decreased. As a result, the ionized electrons can receive much more energy during its acceleration in this region, showing the extension of the harmonic cutoff. Moreover, due to the multi-harmonic emission events contribute to the higher harmonics, the intensity of the harmonic cutoff from the down-chirped pulse is 1.5 orders of magnitude higher than those from the chirp-free pulse. Further, by properly introducing the asymmetric inhomogeneous effect, the plasmonic enhancement of the laser intensity in the negative direction is larger than that in the positive direction. As a consequence, the ionized electron from the down-chirp region with the negative amplitude can obtain the additional acceleration, thus leading to the further extension of the harmonic cutoff. Especially when the spatial position of the inhomogeneous field is chosen to be the negative value, due to the improved enhancement of the laser intensity, not only the harmonic cutoff is extended but also the harmonic yield is near-stable, showing a 175 eV supercontinuum with the single short quantum path contribution. Finally, by directly superposing the selected harmonics, three attosecond XUV pulses with the full widths at half maximum of 38, 35 and 36 as can be obtained, which are nearly 1.5 orders of magnitude enhancement compared with the chirp-free homogeneous field case.

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de Souza, Vinicius Alexandre Sikora, Daniel Medeiros Moreira, Otto Corrêa Rotunno Filho, Anderson Paulo Rudke, Claudia Daza Andrade, and Lígia Maria Nascimento De Araujo. "Spatio-temporal analysis of remotely sensed rainfall datasets retrieved for the transboundary basin of the Madeira River in Amazonia." Atmósfera 35, no. 1 (January 1, 2022): 39–66. http://dx.doi.org/10.20937/atm.52783.

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Rainfall is recognized as the most important driving force of the hydrologic cycle. To accurately represent the spatio-temporal rainfall variability continues to be an enormous hydrological task when using commonly sparse, if available, rain gauges networks. Therefore, the present study devoted a special effort to analyze the robustness of some satellite rainfall products, notably the datasets hereafter named as (i) CHIRP (Climate Hazards Group InfraRed Precipitation), (ii) CHIRPS (Climate Hazards Group InfraRed Precipitation with Station data), (iii) 3B42, and (iv) 3B42RT of the Tropical Rainfall Measuring Mission (TRMM), to adequately represent the pluviometric regime in the Madeira river basin. To assess the accuracy of acquired remotely sensed rainfall products, comparisons to observational available rain gauges usually taken as ground-truth in the literature, despite their well-known limitations, were performed. Wavelet analysis was also used to validate the performance of the referred satellite products by means of extracting the corresponding cycles, frequencies, and tendencies along the available time series across the studied basin. The results showed that the data sources CHIRPS and CHIRP better represent the pluviometric phenomenon by means of their monthly accumulated rainfall in the Madeira river basin when compared to the 3B42 and 3B42RT products taking into account rain gauges as baseline information. The CHIRPS product performed the best among the selected rainfall estimators for the Madeira river basin. Further analysis brought up also another very interesting result related to non-rainfall periods, which is usually not reported. However, such evaluation is quite important in hydrology when examining run sequences of droughts and consequent effects in the water balance at the watershed scale. Highly accurate estimates in the sense of identifying non-rainfall periods by remotely sensed information was achieved, which represents an additional and valuable asset of satellite rainfall products. It is worthwhile to say that this perspective deserves to receive much more attention in the literature in order to deeply discuss the water-energy-food nexus.

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Steiskal, A. B., S. O. Kovtun, O. A. Iliashov, and V. V. Voitko. "Identification of Energy-Hidden Chirp Signals of Telecommunication Systems in Conditions of Parametric Uncertainty." Radioelectronics and Communications Systems 63, no. 8 (August 2020): 398–404. http://dx.doi.org/10.3103/s0735272720080026.

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Wang, Fei, Yonghui Wang, Junyan Liu, and Yang Wang. "The Feature Recognition of CFRP Subsurface Defects Using Low-Energy Chirp-Pulsed Radar Thermography." IEEE Transactions on Industrial Informatics 16, no. 8 (August 2020): 5160–68. http://dx.doi.org/10.1109/tii.2019.2954718.

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Milián, Carles, Amélie Jarnac, Yohann Brelet, Vytautas Jukna, Aurélien Houard, André Mysyrowicz, and Arnaud Couairon. "Effect of input pulse chirp on nonlinear energy deposition and plasma excitation in water." Journal of the Optical Society of America B 31, no. 11 (October 22, 2014): 2829. http://dx.doi.org/10.1364/josab.31.002829.

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Khazanov, E. A. "Post-compression of femtosecond laser pulses using self-phase modulation: from kilowatts to petawatts in 40 years." Quantum Electronics 52, no. 3 (March 1, 2022): 208–26. http://dx.doi.org/10.1070/qel18001.

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Abstract The pulse duration at the output of femtosecond lasers is usually close to the Fourier limit, and can be shortened by increasing the spectral width. To this end, use is made of self-phase modulation when a pulse propagates in a medium with cubic nonlinearity. Then, the pulse with a chirp (frequency dependence of the spectrum phase) is compressed due to a linear dispersion element, which introduces a chirp of the same modulus, but opposite in sign. This pulse post-compression, known since the 1960s, has been widely used and is being developed up to the present for pulses with energies from fractions of a nJ to tens of J. The review is devoted to the theoretical foundations of this method, problems of energy scaling, and a discussion of the results of more than 150 experimental studies.

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Petrillo, Vittoria, Illya Drebot, Geoffrey Krafft, Cesare Maroli, Andrea R. Rossi, Marcello Rossetti Rossetti Conti, Marcel Ruijter, and Balša Terzić. "A Laser Frequency Transverse Modulation Might Compensate for the Spectral Broadening Due to Large Electron Energy Spread in Thomson Sources." Photonics 9, no. 2 (January 25, 2022): 62. http://dx.doi.org/10.3390/photonics9020062.

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Compact laser plasma accelerators generate high-energy electron beams with increasing quality. When used in inverse Compton backscattering, however, the relatively large electron energy spread jeopardizes potential applications requiring small bandwidths. We present here a novel interaction scheme that allows us to compensate for the negative effects of the electron energy spread on the spectrum, by introducing a transverse spatial frequency modulation in the laser pulse. Such a laser chirp, together with a properly dispersed electron beam, can substantially reduce the broadening of the Compton bandwidth due to the electron energy spread. We show theoretical analysis and numerical simulations for hard X-ray Thomson sources based on laser plasma accelerators.

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Denich, Eleonora, Aldo Vesnaver, and Luca Baradello. "Amplitude Recovery and Deconvolution of Chirp and Boomer Data for Marine Geology and Offshore Engineering." Energies 14, no. 18 (September 10, 2021): 5704. http://dx.doi.org/10.3390/en14185704.

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The processing of Chirp data is limited by the usual recording of the signal envelope, which enhances its immediate visibility but prevents applying methods based on wave equations. This is normally not the case for Boomer data. However, both systems are monochannel instruments, which cannot estimate properly the propagation velocity of the signal in the rocks. In this paper, we present two theorems: the first one links the Chirp or Boomer source spectrum with an expected amplitude decay curve; the second one defines conditions for the deconvolution stability of the enveloped Boomer signal when the full waveform of the source signal is known. In this way, we can jointly process and integrate heterogeneous surveys including both data types. We validated the proposed algorithms by applying them to synthetic and real data. The presented tools can improve the image resolution and the characterization of geological formations in marine surveys by reflectivity anomalies, which are distorted by standard equalization methods.

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Calderbank, Robert, and Andrew Thompson. "CHIRRUP: a practical algorithm for unsourced multiple access." Information and Inference: A Journal of the IMA 9, no. 4 (December 5, 2019): 875–97. http://dx.doi.org/10.1093/imaiai/iaz029.

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Abstract Unsourced multiple access abstracts grantless simultaneous communication of a large number of devices (messages) each of which transmits (is transmitted) infrequently. It provides a model for machine-to-machine communication in the Internet of Things, including the special case of radio-frequency identification, as well as neighbour discovery in ad hoc wireless networks. This paper presents a fast algorithm for unsourced multiple access that scales to ${\mathscr{C}}=2^{100}$ (active or non-active) devices (arbitrary $100$ bit messages). The primary building block is multiuser detection of binary chirps, which are simply codewords in the second-order Reed–Muller code. The chirp detection algorithm originally presented by Howard et al. (2008, 42nd Annual Conference on Information Sciences and Systems) is enhanced and integrated into a peeling decoder designed for a patching and slotting framework. In terms of both energy per bit and number of active devices (number of transmitted messages), the proposed algorithm is within a factor of $2$ of state-of-the-art approaches. A significant advantage of our algorithm is its computational efficiency. We prove that the worst-case complexity of the basic chirp reconstruction algorithm is ${\mathscr{O}}[nK(\log _2^2 n + K)]$, where $n$ is the codeword length and $K$ is the number of active users. Crucially, the complexity is sublinear in ${\mathscr{C}}$, which makes the reconstruction computationally feasible—a claim we support by reporting computing times for our algorithm. Our performance and computing time results represent a benchmark against which other practical algorithms can be measured.

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Askeland, Bjørn, Halvor Hobæk, and Rolf Mjelde. "Semiperiodic chirp sequences reduce autocorrelation side lobes of pulsed signals." GEOPHYSICS 73, no. 3 (May 2008): Q19—Q27. http://dx.doi.org/10.1190/1.2903820.

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A time-coded sequence of source pulses has been designed to allow for increased range to the target and reduced side-lobe energy with correlation. The method was designed for a new type of marine-combustion seismic source that can be fired repeatedly, but the method also can be applied to other acoustic-pulsed sources. The basic concept is that one can reduce autocorrelation side lobes by using semiperiodic sequences to concentrate much of the side-lobe noise into time intervals corresponding to the semiperiod. Signals can then be detected with better sensitivity in the time interval after the first autocorrelation peak and before the first periodic side lobe, because this interval contains only lower-level crosscorrelations between the sequence components. Compared with a source which fires pulses randomly, an 8-dB reduction of autocorrelation side lobes has been simulated for sequences of [Formula: see text] duration.

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Liu, Gaogao, Wenbo Yang, Yuqian Bao, Youming Wang, and Peng Li. "Joint Communication and Jamming System Design Based on Filter Bank Multicarrier Chirp Waveform: Using for Curvilinear Flight Scenario." Remote Sensing 15, no. 5 (February 23, 2023): 1239. http://dx.doi.org/10.3390/rs15051239.

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A joint communication jamming waveform is proposed in this study based on the FBMC- chirp. To increase the number of false targets in a single pulse period, the chirp signal is modulated to different subcarrier groups. Since the subcarriers of the FBMC-OQAM signal are orthogonal, the signals are naturally orthogonal. This allows the transmitter and receiver to be separated and achieve multiple false target jamming, allowing the CFAR threshold to be raised by about 20 dB and protecting the target from detection. The ratio of the frequency shift of the designed jamming signal to the frequency modulation depends on the delay time, making the joint signal more robust in response to jamming and resistant to frequency modulation. The use of intercepted radar signals allowed channel estimation, providing high-speed digital transmission while ensuring multi-false-target jamming. The simulation results show that the joint signal has jamming effects on the pulse Doppler radar. The proposed FBMC chirp joint waveform requires about 20dB less jamming signal ratio than the existing method, and thus the energy saved can ensure the robust performance of the communication subsystem in the joint communication jamming system. The proposed system has excelled in communication rate and bit error rate performance, ensuring that instructions are accurately and completely transmitted while implementing effective jamming.

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Swiercz, Ewa, Dariusz Janczak, and Krzysztof Konopko. "Detection of LFM Radar Signals and Chirp Rate Estimation Based on Time-Frequency Rate Distribution." Sensors 21, no. 16 (August 10, 2021): 5415. http://dx.doi.org/10.3390/s21165415.

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Linear frequency-modulated (LFM) signals are the most significant example of waveform used in low probability of intercept (LPI) radars, synthetic aperture radars and modern communication systems. Thus, interception and parameter estimation of the signals is one of the challenges in Electronic Support (ES) systems. The methods, which are widely used to accomplish this task are mainly based on transformations from time to time-frequency domain, which concentrate the energy of signals along an instantaneous frequency (IF) line. The most popular examples of such transforms are the short time Fourier transform (STFT) and Wigner-Ville distribution (WVD). However, for LFM waveforms, methods that concentrate signal energy along a line in the time-frequency rate domain may allow to obtain better detection and estimation performance. This type of transformation can be obtained using the cubic phase (CP) function (CPF). In the paper, the detection of LFM waveform and its chirp rate (CR) parameter estimation based on the extended forms of the standard CPF is proposed. The CPF was originally introduced for instantaneous frequency rate (IFR) estimation for quadratic frequency modulated (QFM) signals i.e., cubic phase signals. Summation or multiplication operations on time cross-sections of the CPF allow to formulate the extended forms of the CPF. Based on these forms, detection test statistics and the estimation procedure of LFM signal parameters have been proposed. The widely known estimation methods assure satisfying accuracy for high SNR levels, but for low SNRs the reliable estimation is a challenge. The proposed approach based on joint analysis of detection and estimation characteristics allows to increase the reliability of chirp rate estimates for low SNRs. The results of Monte-Carlo simulation investigations on LFM signal detection and chirp rate estimation evaluated by the mean squared error (MSE) obtained by the proposed methods with comparisons to the Cramer-Rao lower bound (CRLB) are presented.

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Kaffanke, J., T. Dierkes, S. Romanzetti, M. Halse, J. Rioux, M. O. Leach, B. Balcom, and N. J. Shah. "Application of the chirp z-transform to MRI data." Journal of Magnetic Resonance 178, no. 1 (January 2006): 121–28. http://dx.doi.org/10.1016/j.jmr.2005.09.002.

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Lutman, Alberto A., Giuseppe Penco, Paolo Craievich, and Juhao Wu. "Impact of an initial energy chirp and an initial energy curvature on a seeded free electron laser: the Green's function." Journal of Physics A: Mathematical and Theoretical 42, no. 4 (December 11, 2008): 045202. http://dx.doi.org/10.1088/1751-8113/42/4/045202.

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Li, Feng, Yunpeng Gao, Yijia Cao, and Reza Iravani. "Improved Teager Energy Operator and Improved Chirp-Z Transform for Parameter Estimation of Voltage Flicker." IEEE Transactions on Power Delivery 31, no. 1 (February 2016): 245–53. http://dx.doi.org/10.1109/tpwrd.2015.2448943.

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Li, H. Y., and J. S. Liu. "Influence of laser frequency chirp on deuteron energy from laser-driven deuterated methane cluster expansion." European Physical Journal D 58, no. 3 (April 26, 2010): 423–28. http://dx.doi.org/10.1140/epjd/e2010-00112-x.

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Journal articles on the topic 'Energy chirp'

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