Chirp Period Research Articles

Frequency-Chirped Magic Angle Spinning Dynamic Nuclear Polarization Combined with Electron Decoupling.

Magic angle spinning (MAS) dynamic nuclear polarization (DNP) increases the signal intensity of solid-state nuclear magnetic resonance. DNP typically uses continuous wave (CW) microwave irradiation close to the resonance frequency of unpaired electron spins. In this study, we demonstrate that frequency-chirped microwaves improve DNP performance under MAS. By modulating the gyrotron anode potential, we generate a train of microwave chirps with a maximum bandwidth of 310 MHz and a maximum incident power on the spinning sample of 18 W. We characterize the efficiency of chirped DNP using the following polarizing agents: TEMTriPol-1, AsymPolPOK, AMUPol, and Finland trityl. The effects of different chirp widths and periods are analyzed at different MAS frequencies and microwave powers. Furthermore, we show that chirped DNP can be combined with electron decoupling to improve signal intensity by 59%, compared to CW DNP without electron decoupling, using Finland trityl as a polarizing agent.

Numerical characterization of capacitively coupled plasma driven by tailored frequency modulated radio frequency source

Capacitively coupled plasma (CCP) is widely used in plasma etching and deposition processes because of its low cost, simple structure, and easy generation of a uniform plasma in large areas. Conventional CCPs are operated under a fixed frequency power source; however, CCPs driven by a variable frequency power source are poorly understood. In this paper, numerical simulations of CCPs driven by frequency modulated (FM) radio frequency (RF) sources within the frequency range of 2 MHz–18 MHz are carried out with a particle-in-cell/Monte Carlo collision model. Our research indicates that the CCP driven by an FM RF source can maintain a stable glow discharge and form a time-dependent plasma. Plasma density, electron and ion current, energy and heating rate, ion flux, and energy on the electrodes fluctuate consistently with the FM period. The electron and ion energy distribution function can also be modulated by the frequency variation of the FM source. A multi-peak structure that varies and shifts with frequency variation is observed in the ion energy distribution function. In addition, by fixing the chirp period while varying the start or end frequency of the chirp signal (start frequency from 0.4 to 6 MHz, or end frequency from 18 to 48 MHz), effective modulations can be produced on the electron density, electron energy, and the shape of the EEPF and IEDF.

Spectral broadening scheme for high stimulated Brillouin scattering thresholds on multi-harmonic linear frequency modulation

This paper proposes a spectral-broadening scheme for suppressing the stimulated Brillouin scattering (SBS) in fibers using multi-harmonic linear frequency modulation (LFM). The frequency tuning range of the LFM lasers is further expanded by incorporating sinusoidal phase modulation (PM) to achieve more effective spectrum spreading. Furthermore, the ability of multi-harmonic-LFM light sources to suppress SBS is investigated using the effective Brillouin gain spectra (BGS). Meanwhile, the experimental results reveal that at a 3 dB bandwidth of ∼480 MHz, the SBS thresholds of multi-harmonic-LFM light sources were improved by 8.36 times compared to a single-frequency laser, and by appropriately 69% compared to the LFM light sources. Because the spectra of the multi-harmonic-LFM light sources and the multifrequency-sinusoidal-PM light sources have a near-rectangular shape, the capacity of the two schemes to suppress SBS is comparable, which verifies the advantages of the multi-harmonic-LFM light sources in suppressing SBS. Our study also investigated the effects of frequency intervals between each chirp harmonic and the chirp period of multi-harmonic-LFM light sources on the suppression of SBS, which provides guidance for optimizing multi-harmonic-LFM light sources.

When Ramanujan sums meet affine Fourier transform

Ramanujan Fourier transform is one of the efficient multiresolution analysis tools, but it only works for stationary or periodically characterized signals. Affine Fourier transform, a general form of Fourier transform, is suitable for nonstationary signal analysis but with fixed resolution. In this study, the Ramanujan sums are combined with the affine Fourier transform to provide affine multiresolution analysis tools for nonstationary signals. First, affine Ramanujan sums are proposed and their main properties are introduced, based on which the affine Ramanujan Fourier transform (ARFT) for infinite sequences is proposed. Then, the first type ARFT (ARFT-I) for finite sequences is obtained by truncating the ARFT. Meanwhile, the transform matrix of ARFT-I is not orthogonal in general. Thus, the affine Ramanujan subspaces are constructed by affine Ramanujan sums and their canonical circular time shifts, among which different subspaces are orthogonal. Subsequently, the second type ARFT (ARFT-II) for finite sequences is developed, where the transform matrix is block orthogonal. Independent variables of ARFTs are chirp periods, which provides novel and direct methods to estimate (hidden) chirp periods. Different simulations, such as radar moving target detection and velocity estimation, are designed to show superior performance of ARFTs than affine Fourier transform based algorithms.

94 GHz 수신 4채널, 송신 1채널 FMCW 레이다 시스템

This paper describes a 94 GHz FMCW radar system for unmanned vehicles using 94 GHz 1 Tx and 4 RX chips designed in a 65-nm CMOS process. The measured output power of the transmitter and the conversion gain of the receiver were 9.77 dBm and 26 dB, respectively. The simulated noise figure of the receiver chip was 8 dB. The Tx and Rx antennas were microstrip patch antennas with a gain of 11 dBi on a Duroid substrate. The chirp period of the sawtooth FMCW waveform was 50 μs. The baseband signal was bandpass-filtered with a passband gain of 26 dB and sampled at a rate of 50 MSPS with a 14-bit ADC. The output of the ADC was acquired using an FPGA. The distance and angle information of the target were calculated using the FFT-based algorithm. The processed results closely matched the calculated results based on the specifications of TRx chips and processing gain, which confirmed the validity of the developed radar system.

Secure Mobile Two-Factor Authentication Leveraging Active Sound Sensing

The two-factor authentication ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$2$</tex-math></inline-formula> FA) has drawn increasingly attention as the mobile devices become more prevalent. For example, the user's possession of the enrolled phone could be used by the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$2$</tex-math></inline-formula> FA system as the second proof to protect his/her online accounts. Existing <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$2$</tex-math></inline-formula> FA solutions mainly require some form of user-device interaction, which may severely affect user experience and creates extra burdens to users. In this work, we propose a secure <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$2$</tex-math></inline-formula> FA system utilizing the proximity of a user's enrolled phone and the login device as the second proof without requiring the user's interactions. The basic idea of our <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$2$</tex-math></inline-formula> FA system is to derive location signatures based on acoustic beep signals emitted alternately by both devices and sensing the echoes with microphones, and compare the extracted signatures for proximity detection. Moreover, to further enhance the security of our system, we also design a device authentication scheme which derives the acoustic fingerprint between the login device and enrolled phone to verify the identity of two devices. Given the received beep signal, our system designs a period selection scheme to identify two sound segments accurately: the chirp period is the sound segment propagating directly from the speaker to the microphone whereas the echo period is the sound segment reflected back by surrounding objects. To achieve an accurate proximity detection, we develop a new energy loss compensation extraction scheme by utilizing the extracted chirp periods to estimate the intrinsic differences of energy loss between microphones of the enrolled phone and the login device. Our proximity detection component then conducts the similarity comparison between the identified two echo periods after the energy loss compensation to effectively determine whether the enrolled phone and the login device are in proximity for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$2$</tex-math></inline-formula> FA. Moreover, to provide higher security, our device fingerprint-assisted proximity detection further utilizes the overall energy loss between the login device and enrolled phone as their hardware fingerprint to authenticate the identity of two devices. Our experimental results show that our system is accurate in providing <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$2$</tex-math></inline-formula> FA and robust to both man-in-the-middle (MiM) and co-located attacks across different scenarios and device models.

Optical FMCW Signal Generation Using a Silicon Dual-Parallel Mach-Zehnder Modulator

We experimentally demonstrate optical frequency-modulated continuous-wave (FMCW) signal generation utilizing a silicon dual-parallel Mach-Zehnder modulator (DP-MZM). The sideband suppression ratio (SSR) and the sideband-to-carrier suppression ratio (SCSR) of the single-sideband suppressed carrier (SSB-SC) modulation are higher than 15 dB when RF frequency is lower than 20 GHz. With the generated triangular modulated FMCW signal, we demonstrate simultaneous ranging and velocimetry. The chirp bandwidth is 10 GHz and the chirp period is 1 μs, corresponding to a ranging resolution of 13 mm and a velocimetry resolution of 0.5 m/s, consistent with the theoretical calculation. These results show that wideband FMCW signal generation by a silicon DP-MZM is promising for high-resolution light detection and ranging.

A C-Band FMCW SAR Transmitter Based on Synthetic Bandwidth Technique

A $C$ -band frequency-modulated continuous wave (FMCW) transmitter based on synthetic bandwidth technique for synthetic aperture radar (SAR) imaging is presented. A 500-MHz narrowband chirp signal is up-converted to two adjacent carriers to obtain 1-GHz chirp at the $C$ -band. The adjacent carriers are obtained through fast switching subharmonic injection locking oscillator (SHILO) technique with 14-ns settling time. For narrowband chirp, a wideband fractional- $N$ phase locked loop (PLL) is used, covering 1.8–2.3 GHz and achieving low in-band phase noise of −115 to 120 dBc/Hz. The proposed technique achieves reconfigurable chirp period ranging from 0.3 to 6.3 ms. It can also be easily extended for wider chirp bandwidth by simply increasing the number of SHILO carriers. The chip consumes 84 mW, while occupying a total active area of 2.24 mm2.

A general fraction-of-time probability framework for chirp cyclostationary signals

The fraction-of-time (FOT) framework, a pseudo-probability framework, is proposed to promote the stochastic signal processing theory into practical applications. Technically, the ensemble averaging that requires infinite realizations is replaced by the time averaging of a single realization. This skill is further generalized for cyclostationary signals and accordingly the periodic FOT framework is obtained. However, neither the FOT nor the periodic FOT is proper for the chirp cyclostationary (CCS) signals which are utilized to model most of the nonstationary signals in mobile communications, radar/sonar systems. In this paper, a novel general FOT framework is proposed, which is obtained by constructing an isomorphic map associated with fractional Fourier transform (FrFT). Specifically, a CCS signal and its fractional shift form a Hilbert space, which is isomorphic to the Hilbert space formed by the CCS stochastic processes. The chirp-period FOT framework for CCS signals with a single chirp period is obtained directly, which is further extended for CCS signals with incommensurate chirp periods. Then the statistics of the CCS signals are defined and their properties are introduced in this framework. Finally, their estimators are investigated.

Two-Scale Envelope-Domain Analysis of Injected Chirped Oscillators

The response of chirped oscillators under the injection of independent signals, for spectrum sensing in cognitive radio, and under self-injection, for radio frequency identification, is analyzed in detail. The investigation is performed by means of a semianalytical formulation, based on a realistic modeling of the free-running oscillator, extracted from harmonic-balance simulations or from experimental measurements, through a new characterization technique. In the new formulation, the oscillator is linearized about a free-running solution that varies with the control voltage. This enables its application to oscillators having a frequency characteristic that deviates from the linear one. In the case of injection by independent signals, the two-scale envelope-domain formulation will enable an efficient handling of the difference between the slow chirp frequency and the beat frequency. The input carriers can be detected from their dynamic synchronization intervals or, at lower input-power levels, from the dynamics of the beat frequency. Noise perturbations are introduced into the formulation, which enables an estimation of the minimum detectable signal. In the case of a self-injected oscillator for radio frequency identification, an insightful formulation is derived to predict the propagation and tag-resonance effects on the instantaneous oscillation frequency. The tag-resonance signature gives rise to a distinct modulation of the oscillation frequency during the chirp period, which can be detected from the variation of the oscillator bias current. The analysis methods are illustrated through their application to a chirped oscillator, operating in the band 2–3 GHz.

Research on Debonding Defects in Thermal Barrier Coatings Structure by Thermal-Wave Radar Imaging (TWRI)

In this paper, thermal-wave radar imaging (TWRI) is introduced to detect debonding defects in SiC-coated Ni-based superalloy plates. Linear frequency modulation signal (chirp) is used as the excitation signal which has a large time–bandwidth product. Artificial debonding defects in SiC coating are excited by the laser beam with the light intensity modulated by a chirp signal. Cross-correlation algorithm and chirp lock-in algorithm are introduced to extract the thermal-wave signal characteristic. The comparative experiment between TWRI reflection mode and transmission mode was carried out. Experiments are conducted to investigate the influence of laser power density, chirp period, and excitation frequency. Experimental results illustrate that chirp lock-in phase has a better detection capability than other characteristic parameters. TWRI can effectively detect simulated debonding defects of SiC-coated Ni-based superalloy plates.

Analysis of a Special Period Sampled Bragg Grating (PSBG) Structure Combined with the Large Chirp Parameter

Chirped fiber Bragg grating (CFBG) provides an attractive solution for low cost dispersion compensation in a fiber optic transmission system. This kind of grating can be produced with a large chirp parameter and period sampled distribution along the grating length. The present work carries out the design optimization of a chirped FBG in respect of chirp bandwidth and apodization in achieving optimum dispersion compensation in a 20Gbps optical transmission link for different modulation formats.

Randomized nonuniform sampling and reconstruction in fractional Fourier domain

The fractional Fourier transform (FRFT) is one of the most useful tools for the nonstationary signal processing. In this paper, the randomized nonuniform sampling and approximate reconstruction of the nonstationary random signals in the fractional Fourier domain (FRFD) are developed. The nonuniform samples are treated as random perturbations from a uniform grid. The samples used for the sinc interpolation reconstruction are placed on another nonuniform grid which is not necessarily equal to the samples originally acquired. When considering the second-order random statistic characters, the nonuniform sampling is equivalent to the uniform sampling of the signal after a pre-filter in the FRFD, where the frequency response is related to the characteristic function (with its argument scaled by cscα) of the perturbations. The effectiveness of the reconstruction is analyzed and the mean square error (MSE) is computed by utilizing the equivalent filter system. Furthermore, the randomized reconstruction of the chirp period stationary random signal is proposed. At last, the minimum MSE on the special cases of the randomized sampling and reconstruction is discussed. The effectiveness of the proposed reconstruction method is verified by the simulation.

On inheritance of calling song characteristics in the cricket Gryllus bimaculatus

Singing crickets are an appropriate object for analyzing genetic aspects of acoustic communication in insects. The calling song (CS) of male crickets, specifically, Gryllus bimaculatus, is a sequence of chirps consisting of 3–5 pulses. The average values of parameters used by females to identify conspecific males—pulse repetition period, number of pulses per chirp, chirp repetition period—are different for various geographic populations of crickets. In particular, populations of Gryllus bimaculatus from the south-eastern part of its distribution area, as compared to the Mediterranean population, are characterized by a longer chirp repetition period, greater number of pulses per chirp and shorter pulse repetition period [1]. These differences are genetically determined because they are retained in laboratory colonies of these populations under controlled conditions. In the present work, the rules of inheritance of the calling song parameters in interpopulation hybrids of crickets Gryllus bimaculatus were investigated. Two laboratory cultures of these crickets were used: of South Asian origin (A) descending, presumably, from Indo-China, and of Israeli origin (I). Both cultures have been cultivated for several years at Sechenov Institute of Evolutionary Physiology and Biochemistry. The calling songs of

Speckle reduction of synthetic aperture imaging ladar based on wavelength characteristics

We propose a speckle-reduction method based on wavelength characteristics of speckle effect in synthetic aperture imaging ladar (SAIL). The return signal, which is the back scattering field with speckle effect from the rough surface of target, can be integrated over N chirp periods and heterodyne detected with a local-oscillator signal. After performing image processing respectively, the final image can be regarded as the incoherent superposition of the N sub-images. Numerical simulations indicate the effectiveness of this method. Our research may facilitate practical applications of SAIL.

Call intensity is a repeatable and dominant acoustic feature determining male call attractiveness in a field cricket

Acoustic signal variation and female preference for different signal components constitute the prerequisite framework to study the mechanisms of sexual selection that shape acoustic communication. Despite several studies of acoustic communication in crickets, information on both male calling song variation in the field and female preference in the same system is lacking for most species. Previous studies on acoustic signal variation either were carried out on populations maintained in the laboratory or did not investigate signal repeatability. We therefore used repeatability analysis to quantify variation in the spectral, temporal and amplitudinal characteristics of the male calling song of the field cricket Plebeiogryllus guttiventris in a wild population, at two temporal scales, within and across nights. Carrier frequency (CF) was the most repeatable character across nights, whereas chirp period (CP) had low repeatability across nights. We investigated whether female preferences were more likely to be based on features with high (CF) or low (CP) repeatability. Females showed no consistent preferences for CF but were significantly more attracted towards signals with short CPs. The attractiveness of lower CP calls disappeared, however, when traded off with sound pressure level (SPL). SPL was the only acoustic feature that was significantly positively correlated with male body size. Since relative SPL affects female phonotaxis strongly and can vary unpredictably based on male spacing, our results suggest that even strong female preferences for acoustic features may not necessarily translate into greater advantage for males possessing these features in the field.

The Steppengrille (Gryllus spec./assimilis): Selective Filters and Signal Mismatch on Two Time Scales

In Europe, several species of crickets are available commercially as pet food. Here we investigated the calling song and phonotactic selectivity for sound patterns on the short and long time scales for one such a cricket, Gryllus spec., available as “Gryllus assimilis”, the Steppengrille, originally from Ecuador. The calling song consisted of short chirps (2–3 pulses, carrier frequency: 5.0 kHz) emitted with a pulse period of 30.2 ms and chirp rate of 0.43 per second. Females exhibited high selectivity on both time scales. The preference for pulse period peaked at 33 ms which was higher then the pulse period produced by males. Two consecutive pulses per chirp at the correct pulse period were already sufficient for positive phonotaxis. The preference for the chirp pattern was limited by selectivity for small chirp duty cycles and for chirp periods between 200 ms and 500 ms. The long chirp period of the songs of males was unattractive to females. On both time scales a mismatch between the song signal of the males and the preference of females was observed. The variability of song parameters as quantified by the coefficient of variation was below 50% for all temporal measures. Hence, there was not a strong indication for directional selection on song parameters by females which could account for the observed mismatch. The divergence of the chirp period and female preference may originate from a founder effect, when the Steppengrille was cultured. Alternatively the mismatch was a result of selection pressures exerted by commercial breeders on low singing activity, to satisfy customers with softly singing crickets. In the latter case the prominent divergence between male song and female preference was the result of domestication and may serve as an example of rapid evolution of song traits in acoustic communication systems.

대탄도탄 FMCW 탐색기를 위한 탄두부 추적 필터 설계

In this paper, a practical warhead tracking filter is proposed for developing a FMCW (Frequency Modulation Continuous Wave) seeker with anti-ballistic missile capability. For reliable warhead tracking, the measurement originated from the warhead section of a ballistic target should be separated from other measurements. Futhermore, since the FMCW seeker is based on triangular frequency modulation, the multiple measurements obtained in different chirp periods should be properly associated. As a systematic way to solve the problem, the measurement pairing problem under cluttered environment is reformulated as a data association filtering problem and the PDA (Probabilistic Data Association) scheme is applied. The proposed warhead tracking filter provides better warhead tracking performance compared to the conventional range tracking algorithm and nearest neighbor warhead tracking filter. The effectiveness and reliability of the proposed method are verified using the FMCW seeker simulator.

Auditory processing at two time scales by the cricketGryllus bimaculatus

The acoustic display of many cricket species consists of series of pulses grouped into chirps, and thus information is distributed over both short and long time scales. Here we investigated the temporal cues that females of the cricket Gryllus bimaculatus used to detect a chirp pattern on a longer time scale than the fast pulse pattern. First, over a range of chirp and pause durations (100-400 ms), the duty cycle of the chirp pattern emerged as the most important cue for detection. The songs of males showed a distribution at lower duty cycles than preferred by females. The duty cycle also limited the responses of females at very short durations and pauses (below 80 ms). Second, by systematic variation of pulse and chirp periods of stimuli, an intermediate response field emerged that revealed the best responses of female crickets to patterns with amplitude modulations on both short and long time scales. On average, females also responded weakly to stimuli that contained amplitude modulations of only one time scale. Third, test patterns were constructed by addition of modulation frequencies rather than rectangular pulses. These tests showed that female crickets processed the chirp pattern in the time domain and tolerated noise levels up to a modulation depth of 50%. The combined evidence from all three approaches indicated inhibitory effects of unattractive patterns on both time scales. The fusion of short and long time scales during auditory processing by female crickets corresponded to a weighted AND-like operation of two processing modules, the pulse and the chirp filter.

Acoustic signal perception in a noisy habitat: lessons from synchronising insects

Acoustically communicating animals often have to cope with ambient noise that has the potential to interfere with the perception of conspecific signals. Here we use the synchronous display of mating signals in males of the tropical katydid Mecopoda elongata in order to assess the influence of nocturnal rainforest noise on signal perception. Loud background noise may disturb chorus synchrony either by masking the signals of males or by interaction of noisy events with the song oscillator. Phase-locked synchrony of males was studied under various signal-to-noise ratios (SNRs) using either native noise or the audio component of noise (<9 kHz). Synchronous entrainment was lost at a SNR of −3 dB when native noise was used, whereas with the audio component still 50 % of chirp periods matched the pacer period at a SNR of −7 dB. Since the chirp period of solo singing males remained almost unaffected by noise, our results suggest that masking interference limits chorus synchrony by rendering conspecific signals ambiguous. Further, entrainment with periodic artificial signals indicates that synchrony is achieved by ignoring heterospecific signals and attending to a conspecific signal period. Additionally, the encoding of conspecific chirps was studied in an auditory neuron under the same background noise regimes.