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Earlier publications of the paper authors have shown that the use of code keying mixed with the CW FM sound signal allows the significant reduction in the distance measurement error, compared to classic silent CW FM sonar. In addition to the code modulation parameters, the magnitude of this error is influenced by the received input acoustic noise. The article shows the dependence of the input signal-to-noise ratio and the sound signal parameters on the target distance measurement error and the detection conditions, such as the output signal-to-noise ratio and the side lobe level. The results of the analysis were compared to the same parameters of the CW FM silent sonar without code modulation. [ABSTRACT FROM AUTHOR]

We report on the response of a monolithic high $\mathrm{T_{c}}$ transition-edge bolometer to about 3 mmWave for the first time. The detector structure consisting of 400-nm $\mathrm{YBa_{2}Cu_{3}O_{7-x}}$ (YBCO) film on buffered yttria stabilized zirconia substrate without any coupled antenna, shows bolometric type responsivity to the 3-mmWave radiation at its transition temperature. The YBCO thin film and $\mathrm{Ce_{0.9}La_{0.1}O_{2}}$ buffer layer are both fabricated by the metal-organic deposition method. The meander line pattern of the bolometer is designed for obtaining maximum absorption and responsivity possible when the polarized radiation of the source is aligned with the pattern. Meander lines are 50 micrometers wide and 1.5-mm long. We have measured amplitude and phase of the response versus modulation frequency of the detector to the linearly polarized 95-GHz source, and the detector was biased at five distinct temperatures at the transition corresponding to five different electrical conductivities of the YBCO film. When the meander lines of the device are parallel to the incident beam polarization, the YBCO pattern is speculated to act as a dissipative antenna resulting in higher absorption leading to high magnitude of the response as observed. The results from the measured phase of the response versus modulation frequency are also in agreement with the discussed absorbed mechanism. The absorption of the YBCO pattern is also measured to depend on the electrical conductivity of the YBCO film and our results show that there is an optimum electrical conductivity for having maximum absorption for this detector. Simulation results for this structure confirm the experiments showing that at electrical conductivity value of $\mathrm{1.33\times 10^{5}}$ S/m we have the maximum absorption for our device. These observations promise design of versatile THz and millimeter-wave detectors with potential for applications in medical and security imaging. [ABSTRACT FROM AUTHOR]

Time–frequency analysis (TFA) is considered as a useful tool to extract the time-variant features of the nonstationary signal. In this paper, a new method called demodulated high-order synchrosqueezing transform (DHST) is proposed. The DHST introduces a two-step algorithm, namely, demodulated transform and high-order synchrosqueezing method to achieve a compact time–frequency representation (TFR) while enabling the reconstruction of the signal from TFR. The performance of the proposed DHST method in this paper is validated by both the simulated and experimental signals including bat echolocation and a vibration signal. The results show that the proposed TFA method is more effective in processing the nonstationary signals with fast varying instantaneous frequency. [ABSTRACT FROM AUTHOR]

This paper reports a fully differential frequency modulated (FM) gyroscope where the superposed clockwise (CW) and counter clockwise (CCW) modes are independently controlled on a single resonator. The CW and CCW mode detectors were developed to control both modes simultaneously on the resonator. A frequency and quality factor mismatch compensation method was developed to perfectly orthogonalize these two modes. A FM gyroscope operation with excellent linearity between applied angular rate and frequency difference was demonstrated. The temperature coefficient of scale factor was as small as −52 ± 136 ppm/°C. The scale factor and bias were stable over 700 hours with the drift less than 0.062 ± 0.100 ppm/hr and 31 ± 121 ppm/hr, respectively. [2018-0103] [ABSTRACT FROM AUTHOR]

This letter extends our recently introduced method which was designed to estimate instantaneous frequency and chirp rate of linearly modulated signals. Indeed, we derive several new estimators related to our previous ones which provide in the time-frequency plane all the signal parameters of the investigated model: amplitude, frequency, and their local modulations (AM/FM). Our estimators are first introduced and compared in terms of statistical efficiency with theoretical bounds and with other state-of-the-art estimators. Then, they are used to improve spectral analysis applied to audio sinusoidal modeling. Finally, they lead to a new source separation technique based on coherent amplitude and frequency modulation that is evaluated on real-world music signals. [ABSTRACT FROM AUTHOR]

This paper considers parameter estimation of a new coupled mixture of polynomial phase signal (PPS) and sinusoidal frequency modulated (FM) signal, recently introduced for industrial systems such as linear electromagnatic encoders. Compared with both conventional PPS-only and independent mixture models, the coupled mixture one captures the coupling between the sinusoidal FM frequency and the PPS parameters induced by structural system configurations. In this paper, we are particularly interested in estimating phase parameters of the coupled mixture signal at low signal-to-noise ratios (SNRs). Specifically, we propose a three-stage approach consisting of instantaneous frequency (IF) extraction (e.g., the short-time Fourier transform) and refining steps that reduce the bias introduced by the IF estimation and the mean-squared errors (MSEs) up to the Cramér-Rao bound (CRB). The proposed method is numerically compared with an existing phase-based approach as well as corresponding CRBs in terms of the empirical MSE. The results show that, compared with the phase-based approach, the proposed method can significantly lower the SNR threshold. The convergence of the measured MSEs from the initial stage to the latter refining stages is also numerically evaluated. [ABSTRACT FROM AUTHOR]

A wideband dipole signal is required for dipole dispersion correction and near-borehole imaging. To obtain the broadband flexural wave dispersion, we use a nonlinear frequency modulation (NLFM) signal and propose a segment linear frequency modulation (SLFM) signal as the dipole excitation signal to compensate for the excitation intensity. The signal-to-noise ratio (SNR) of the signal over the entire frequency band is increased. The finite-difference method is used to simulate the responses from a Ricker wavelet, a linear frequency modulation (LFM) signal, an NLFM signal, and an SLFM signal in two borehole models of a homogeneously hard formation and a radially stratified formation. The dispersion and radial tomography results at low SNR of the sound source signals are compared. Numerical modeling suggests that the energy of the flexural waves excited by the Ricker wavelet source is concentrated near the Airy phase. In this case, the dispersion is incomplete and information regarding the formation near or far from the borehole cannot be obtained. The LFM signal yields dispersion information near the Airy phase and the high-frequency range but not in the low-frequency range. Moreover, the information regarding the formation far from the borehole is not accurate. The NLFM signal extends the frequency range of the flexural waves by compensating for the excitation intensity and yields information regarding the formation information, but it is not easy to obtain. The SLFM signal yields the same results as the NLFM signal and is easier to implement. Consequently, the dipole detection range expands and the S-wave velocity calculation accuracy improves. [ABSTRACT FROM AUTHOR]

Microstepping drive for a stepper motor is a well-known technique to improve the stepper motor performance. Normally, microstepping is carried at fixed pulse width planned. However, this method is suitable only when motors are driven at fixed predefined speeds for non-real-time applications. The problem discussed in this paper considers an application where motors need to track a given reference position profile precisely in real time, whose speed is varying at every interval of time. In such a scenario, fixed speed microstep drive does not meet the high pointing requirements and leads to poor system performance. For such applications, an innovative frequency modulation (FM) based microstep drive algorithm is developed that meets the high degree of motor pointing even at higher output angular rates. As per this scheme, pulse width and the number of steps that motor is supposed to move are derived from the reference position itself in a given amount of time, and the motor is actuated with a corresponding number of steps in real time. FM-based microstep drive is implemented with pulse-width modulation based chopper current controller in an optimized way without compromising on the motor torque margins. Transient error plots obtained through experiments clearly show the advantages of FM-based microstepping over fixed rate. This paper presents the design, analysis, simulation, and experimental results of FM-based microstep drive. [ABSTRACT FROM AUTHOR]

Estimating azimuth offset with double-difference interferometric (DDI) phase, which is called multiple-aperture interferometric synthetic aperture radar (InSAR) or spectral diversity, is increasingly used in recent years to measure azimuth deformation or to accurately coregister a pair of InSAR images. We analyze the effect of frequency modulation (FM) rate error in focusing on the DDI phase with an emphasis on the azimuth direction. We first comprehensively analyze the errors in various focusing results caused by the FM rate error. We then derive the DDI phase error considering different acquisition modes including stripmap, ScanSAR, and TOPS modes. For stripmap mode, typical DDI phase error is a range ramp, while for burst modes including ScanSAR and TOPS modes it is an azimuth ramp within a burst. The correction methods for the DDI phase error are suggested for different acquisition modes. [ABSTRACT FROM PUBLISHER]

This paper proposes an energy efficient instrumentation set-up for pulse-compression thermal-wave imaging with a low-power LED excitation source. The set-up consists of three different subsystems that are synchronised in time. The individual systems consist of a LED modulation circuitry, reference signal measurement circuitry, and an IR camera trigger signal generation circuitry for frame capture. A separate reference acquisition circuitry is useful in quantifying defect depth resolution. This paper also proposes a nonuniform frame capture technique to reduce the memory allocation space of the recorded video. The technique is based on varying the sampling rate with a change in instantaneous frequency and is specifically useful for frequency modulated excitation signal. The proposed technique is implemented on a carbon fiber reinforced polymer test-piece. The variation of pulse compression parameters with different defect dimension is studied, and the results are verified with an electro-thermal simulator. Further, an objective comparison of pulse compression experiment for different experiment duration is presented. [ABSTRACT FROM PUBLISHER]

In a self-mixing interferometer based on a diode laser, the measurement of the external reflector displacement $s(t)$ is carried out by looking at the optical-phase signal $\cos 2ks(t)$ , a signal readily detected as an amplitude modulation (AM) of emitted power. In contrast, the other available signal, sin $2ks(t)$ , a frequency modulation (FM) of the emitted field at optical frequency, is never used because difficult to recover. Recently, Contreras et al. used a narrow-band acetylene cell to convert the FM into an amplitude signal, finding it is larger and has a better SNR than the AM. In this paper, we analyze the advantages of the new CFM (converted-FM) signal, calculating both amplitude and SNR, and compare theoretical results to published experimental evidence, finding good agreement. We then present options for realizing the selective filter in different configurations and technology. Finally, we evaluate the improvement offered by CFM in a number of measurements, like sub-wavelength vibrations, digital readout displacement, and diode laser alpha factor. [ABSTRACT FROM PUBLISHER]

A method of processing microwave sensor signals is proposed. Application of this method allows substantially improving the accuracy of determination of Doppler frequency and associated information parameters. Here, frequency modulation changing by the symmetric saw-tooth law is used with spectral processing of the output signal on rising and falling sections. The Doppler frequency is calculated from the cross-correlation function of the spectral envelope, which makes it possible to eliminate error caused by the spectral structure of the Doppler signal. [ABSTRACT FROM AUTHOR]

A two-stage technique for estimating micro-Doppler signal parameters has been proposed. In the first stage, rough parameter estimations are performed by regression of instantaneous frequency estimate obtained from the short-time Fourier transform. Afterwards, rough estimates are refined in the second stage. The proposed technique has better performance with respect to current state-of-the-art algorithms, and it reaches the Cramer–Rao lower bound for sinusoidal frequency-modulated signal parameters. [ABSTRACT FROM PUBLISHER]

This paper addresses the coherent integration problem for detecting a high-speed target, involving range walk (RW) within the coherent processing time. A fast method based on sequence reversing transform is proposed to eliminate the RW and achieve the coherent accumulation. The proposed method is simple and fast since it can be easily implemented by using complex multiplications, the fast Fourier transform (FFT) and the inverse FFT. Compared with the Radon–Fourier transform and moving target detection methods, the presented algorithm can avoid the blind speed sidelobe and make a good balance between the computational cost and the detection ability. Finally, several simulations are provided to demonstrate its effectiveness. [ABSTRACT FROM PUBLISHER]

In image and video processing fields, Discrete Cosine Transform (DCT)-based just-noticeable difference (JND) profiles have effectively been utilized to remove perceptual redundancies in pictures for compression. In this paper, we solve two problems that are often intrinsic to the conventional DCT-based JND profiles: 1) no foveated masking (FM) JND model has been incorporated in modeling the DCT-based JND profiles and 2) the conventional temporal masking (TM) JND models assume that all moving objects in frames can be well tracked by the eyes and that they are projected on the fovea regions of the eyes, which is not a realistic assumption and may result in poor estimation of JND values for untracked moving objects (or image regions). To solve these two problems, we first propose a generalized JND model for joint effects between TM and FM effects. With this model, called the temporal-foveated masking (TFM) JND model, JND thresholds for any tracked/untracked and moving/still image regions can be elaborately estimated. Finally, the TFM-JND model is incorporated into a total DCT-based JND profile with a spatial contrast sensitivity function, luminance masking, and contrast masking JND models. In addition, we propose a JND adjustment method for our total JND profile to avoid overestimation of JND values for image blocks of fixed sizes with various image characteristics. To validate the effectiveness of the total JND profile, an experiment involving a subjective distortion-visibility assessment has been conducted. The experiment results show that the proposed total DCT-based JND profile yields significant performance improvement with much higher capability of distortion concealment (average 5.6-dB lower PSNR) compared with state-of-the-art JND profiles. The MATLAB source code of the proposed total DCT-based JND profile is publicly available online at https://sites.google.com/site/sunghobaecv/jnd. [ABSTRACT FROM AUTHOR]

Multilevel cascaded H-bridge converters have become a mature technology for applications where high-power medium ac voltages are required. Normal operation of multilevel cascaded H-bridge converters assumes that all power cells have the same dc voltage, and each power cell generates the same voltage averaged over a sampling period using a conventional phase-shifted pulse width modulation (PWM) technique. However, this modulation method does not achieve good results under unbalanced operation per H-bridge in the power converter, which may happen in grid-connected applications such as photovoltaic or battery energy storage systems. In the paper, a simplified mathematical analysis of the phase-shifted PWM technique is presented. In addition, a modification of this conventional modulation method using variable shift angles between the power cells is introduced. This modification leads to the elimination of harmonic distortion of low-order harmonics due to the switching (triangular carrier frequency and its multiples) even under unbalanced operational conditions. The analysis is particularized for a three-cell cascaded H-bridge converter, and experimental results are presented to demonstrate the good performance of the proposed modulation method. [ABSTRACT FROM PUBLISHER]

In recent years, increasing attention is given to parametric resonators, in which an unbounded response may be induced by periodically modulating one of the system parameters. Parametric resonators with a single degree of freedom have many windows of unbounded response in which the response frequency is different from the modulation frequency. This difference between input and output frequencies may be relevant to sensing applications. In this paper, we explore the solution map of the Meissner parametric resonator, and we experimentally characterize odd-ordered windows of unbounded response, up to the 15th window. Another interesting feature of the Meissner resonator is discrete crossover points in which an unbounded response is possible at distinct modulation frequencies and distinct modulation amplitudes. In this paper, we experimentally characterize one such crossover point. Our parametric resonator is based on an electrostatic anti-spring, which allows to modulate stiffness that is otherwise unaffected by motion. This is in contrast to many previous experimental studies in which the modulated stiffness was affected by motion and thus included unwanted nonlinear effects. [2016-0209] [ABSTRACT FROM AUTHOR]

The combination of Wigner–Ville distribution (WVD) and Hough transform (HT) has been successfully used in detection and parameter extraction of frequency modulated continuous waveform (FMCW) signals. In this paper, a combination of Cross–Wigner–Ville and HT [(Cross Wigner–Hough transform (XWHT)] is proposed for detection and parameter extraction of FMCW signals with a novel methodology. The XWHT method makes use of the cross-terms created by WVD instead of trying to suppress them. Utilization of the properties of the cross-terms to detect and unveil the parameters of FMCW signals on HT space is a new approach. The performance of the method is compared with other Wigner–Hough transform-based methods in terms of transform speed, parameter extraction, and detection performance. As a result, this study proposes that the XWHT is a candidate method to be used in digital electronic support receivers’ automatic signal detection and analysis capabilities due to its speed and performance. [ABSTRACT FROM AUTHOR]

This study used a correlational approach to clarify the mechanisms involved in modulation coding. Amplitude-modulation (AM) and frequency-modulation (FM) detection thresholds (AMDTs and FMDTs, respectively) were assessed for 70 normal-hearing listeners. In order to increase between-listeners variability in peripheral coding, participants with a wide range of age (20–70 years) were included. AMDTs and FMDTs were measured at a 5-Hz rate, using a 500-Hz sinusoidal carrier. FMDTs were also measured in the presence of an interfering AM to discourage the use of temporal-envelope cues. The results showed that AMDTs were significantly correlated with FMDTs, but not with FMDTs measured with interfering AM. FMDTs with and without interfering AM were significantly correlated with each other. This pattern of correlation proved to be robust, providing additional evidence that for low carrier frequencies, (i) low-rate AM and FM detection is based on a common code using temporal-envelope cues and (ii) low-rate FM detection is based on an additional code using cues distinct from temporal-envelope. The analyses also showed that age was correlated with FMDTs only. However, no significant difference was found when comparing the various correlations with age. Hence, the effects of age on modulation sensitivity remain unclear. [ABSTRACT FROM AUTHOR]

This paper presents an algorithm for finding carriers of frequency-modulated (FM) and amplitude-modulated (AM) electromagnetic (EM) emanations from computer systems. Computer systems create EM emanations across the RF spectrum making it difficult, error-prone, and time consuming to find the relatively few emanations that expose sensitive information. One of the most common and simplest mechanisms for information leakage occurs when an amplitude or a frequency of an existing strong signal (e.g., a processor or memory clock) is amplitude or frequency modulated by a system activity. If the system activity can be linked to sensitive information, this results in information leakage. We present an algorithm for automatically finding these AM and FM signals, demonstrate the algorithm's performance on several different types of processors and systems (desktop, laptop, and smartphone), and compare the results to an exhaustive manual search. We also verify that all signals identified by the algorithm can be traced to plausible unintentional modulation mechanisms to illustrate that these signals can potentially cause information leakage. This algorithm can be an important tool for system designers to quickly identify circuits that are leaking sensitive information. [ABSTRACT FROM PUBLISHER]

The classical time-invariance assumption is often not (exactly) met in real-life applications. As a natural extension of the frequency response function (FRF), the time-variant FRF (TV-FRF) provides quick insight into the complex dynamics of time-variant systems. Recently, a procedure has been proposed to estimate nonparametrically the TV-FRF from known input, noisy output measurements of time-variant systems operating in open loop. However, in many applications, feedback is present either due to an explicit control action or due to the interaction between a nonideal actuator and the system under test. The extension of the open-loop approach to noisy input, noisy output measurements of time-variant systems operating in closed loop requires the deconvolution of the time-variant impulse response of the cascade of two time-variant systems. In this paper, this nontrivial problem is solved for a particular class of time-variant systems. The robustness of the approach with respect to the system assumption is demonstrated via simulations and measurements on an electronic circuit. [ABSTRACT FROM PUBLISHER]

The purpose of this paper is to investigate the impact of switching harmonics on the instantaneous power distribution in the cells of a cascaded H-bridge-based STATCOM when using phase-shifted pulse width modulation. The case of high- and low-switching frequency for the converter cells is investigated and the interaction between voltage and current harmonics is analyzed. It is shown that in both cases, this interaction results in an uneven power distribution among the cells in the same phase leg, leading to drifting of the dc-capacitor voltages and thereby the need for proper stabilization control loops. It is also shown that the selected frequency modulation ratio affects the active power distribution among the cells. In particular, the selection of a noninteger frequency modulation ratio helps in providing a more uniform power distribution among cells of the same phase leg, thus contributing to the capacitors balancing. A methodology for optimal selection of the frequency modulation ratio is given. Theoretical conclusions are validated through simulation and experimental results. [ABSTRACT FROM AUTHOR]

This paper investigates the capacity and energy consumption metrics of small-cell networks that are enabled with sleep mode (SL) functionality. A novel method is introduced to systematically and accurately identify the potential SL cells that can maximize the spectrum reuse efficiency without the need for an exhaustive search. The performance of the proposed technique is assessed and compared with the always-on approach and an optimal benchmark. The results show that the proposed method significantly outperforms the always-on system and approaches the performance of the optimal benchmark with notably reduced computational burden. [ABSTRACT FROM PUBLISHER]

This paper presents a high-efficiency 165-GHz ON–OFF keying transmitter in a 65-nm CMOS technology with the record efficiency to the best of our knowledge. This is due to the proposed holistic design and optimization procedure, which links all the performance and figure-of-merits to the device sizes, including both actives and passives. This transmitter includes a high-efficiency transformer-based fundamental frequency cross-coupled oscillator and a high-speed and high ON–OFF ratio single-pole single-throw switch-based modulator. The transmitter demonstrates the highest dc-to-RF efficiency (10.6%) beyond 140 GHz in silicon processes, with a high output power (0.66 dBm), a high ON–OFF ratio (>32 dB), and a low phase noise (−104.8 dBc/Hz at 1-MHz offset). The transmitter achieves 9.4-Gbps data rate of less than 1 \times 10^-12 bit error rate with 0.68-pJ/b energy efficiency. The standalone oscillator also demonstrates the record dc-to-RF efficiency of 25.9% beyond 140 GHz in silicon processes. The transmitter consumes core area of 240 \mu \text m \times 130~\mu \textm . [ABSTRACT FROM AUTHOR]

Woodward?s ambiguity function measures the ability of a radar signal to simultaneously measure the range of an object via time delay and its velocity using Doppler shift. The ambiguity function is a foundational staple in radar signal processing. Six myths concerning Woodward?s ambiguity function (AF) are addressed in this paper: 1) the AF is uniquely defined, 2) the magnitudes of the various definitions of the AF are the same, 3) the AFs of the baseband and corresponding radio frequency signal are the same, 4) the maximum of a correlation?s magnitude determines optimality, and 5) multiplying a signal by a complex linear chirp rotates the AF and 6) the AF is not invertible. Each myth is explained, analyzed, and resolved. In discussing myth 6, the formula for inversion of the ambiguity function to its spawning signal is derived. [ABSTRACT FROM AUTHOR]

Accurate focusing of high-resolution highly squinted azimuth variant bistatic synthetic aperture radar is a more challenge issue than its translational azimuth invariant bistatic counterpart due to the following two reasons: 1) higher order terms spatial variant feature in azimuth caused by removing relatively large range migration and 2) the azimuth-dependent range offset (RO) induced by inherent azimuth variant bistatic geometric configuration. In this paper, to solve those two issues, a geometry information-aided extended azimuth nonlinear chirp scaling algorithm to provide a better focus is proposed. First, the range compression containing two procedures, namely a linear range walk correction operation and a bulk secondary range compression, is utilized. Second, based on the geometry property of azimuth variant bistatic geometric configuration, the azimuth-dependent RO is obtained and then compensated to enhance focusing ability in the azimuth dimension. By evaluating the spatial variant characteristic of the frequency modulation (FM) rate and the higher order terms, a new azimuth scaling function is derived by adopting higher order approximation operation. With this new azimuth scaling function, not only the azimuth spatial variances of the higher order terms of FM rate and cubic phase terms are equalized, but also the azimuth-dependent RO is eliminated. Compared with existing azimuth nonlinear chirp scaling method, large azimuth depth of focusing can be realized without changing the overall imaging procedure. The experimental results with simulated data verify the effectiveness of the proposed algorithm. [ABSTRACT FROM AUTHOR]

This paper presents a combined phase-shift and frequency modulation scheme of a dual–active-bridge (DAB) ac–dc converter with power factor correction (PFC) to achieve zero voltage switching (ZVS) over the full range of the ac mains voltage. The DAB consists of a half bridge with bidirectional switches on the ac side and a full bridge on the dc side of the isolation transformer to accomplish single-stage power conversion. The modulation scheme is described by means of analytical formulas, which are used in an optimization procedure to determine the optimal control variables for minimum switch commutation currents. Furthermore, an ac current controller suitable for the proposed modulation scheme is described. A loss model and measurements on a 3.3-kW electric vehicle battery charger to connect to the 230 \textV_\textrms  / 50-Hz mains considering a battery voltage range of 280–420 V validate the theoretical analysis. [ABSTRACT FROM AUTHOR]

Nonlinear spectroscopic experiments were performed on a quantum well in a reflective pump-probe geometry, detecting weak four-wave mixing signals copropagating with the excitation pulses. By demodulating the nonlinear response at unconventional frequencies, we were able to isolate individual terms contributing to the nonlinear signal. Signal components linear in the electric field amplitudes of excitation pulses exhibit unusual properties compared with more familiar signals that are linear in excitation pulse intensities. The isolated signal terms may be used to perform multidimensional spectroscopic measurements to completely characterize the phase and amplitude of the nonlinear response. [ABSTRACT FROM PUBLISHER]

We present a novel concept of a modulated transmission line: a low-pass dynamic transmission line (DTL) whose capacitors are replaced by varactors that are externally modulated in tandem. The modulation voltages are periodic in time and identical in all the unit cells (and there is no pump wave). Accurate modeling leads to two bands, \beta 1(\omega ) and \beta 2(\omega ) for the propagation constant, separated by a gap \Delta \beta . We have fabricated an eight-cell DTL and measured \beta _{1,2}(\omega ) for a range of frequencies of the signal wave up to the modulation frequency f_{M} = 310$ MHz, finding very good agreement between the experimental and theoretical results. These are also compared with an effective medium description, with the dynamic permittivity \varepsilon (t)$ being equal to the distributed capacitance C(t)/a$ at every instant t$ and the permeability \mu $ equal to the distributed inductance L/a , including the \beta $ -gap, which, for negligible resistive effects, is proportional to the modulation strength. Such gaps are characteristic of periodicity in time of a parameter and were predicted for “temporal photonic crystals.” We have also confirmed experimentally that for every frequency f$ , a harmonic of frequency is excited, giving rise to beats when f\cong f_{M} /2 . We expect these experimental and theoretical results to open a new platform for useful applications. [ABSTRACT FROM AUTHOR]

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We present a method for the suppression of frequency shifts in pulsed atomic clocks based on the Ramsey scheme, caused by unwanted interaction of the atoms with the resonant interrogation field during the free atomic evolution time (Ramsey time). The method relies upon a precise control of the field’s frequency detuning during the period of free evolution. The frequency detuning reduces the frequency shift caused by the interaction between the free precessing atoms and the interrogation field. We present measurements that allow us to limit the uncertainty contributions due to such an interaction at the atomic fountain clock PTB-CSF2 to 3.8\times 10^-17 . [ABSTRACT FROM PUBLISHER]

Nonlinear contact between tip and sample in tapping mode atomic force microscopy (AFM) systems induces higher harmonics, which may be useful for extraction of some characteristics of the sample. In this paper, a new efficient method for implementing multichannel digital lock-in technique is presented, which is able to measure the amplitude and phase of multiple modulated frequency signals. In order to solve the two most important problems in AFM systems, which are resolution and cost, previous multichannel lock-in amplifier methods are investigated and an improved algorithm for amplitude and phase extraction using fast Fourier transform is developed. In addition, we propose a novel multichannel digital lock-in algorithm including an $N$ -slow digital filter and a multichannel direct digital synthesis block for generating reference signals. We achieve optimal noise reduction using the appropriate decimation filters prior to harmonic extraction. This modification results in a significant hardware reduction in implementation compared with classical designs. Since the precision of the design is sensitive to the sampling frequency, we perform the suitable sampling rate conversion using fractional delay and decimation filters, which enhance the accuracy and noise resiliency of the designed architectures. Experimental results prove the efficiency of the proposed method in multiple modulated frequencies extraction. Also, FPGA implementation results show that the proposed architecture is superior to previous structures, especially in the aspect of area. [ABSTRACT FROM PUBLISHER]

One of the main disturbances in a frequency-modulated continuous wave radar system for range measurement is nonlinearity in the frequency ramp. The intermediate frequency (IF) signal and consequently the target range accuracy are dependent on the type of the nonlinearity present in the frequency ramp. Moreover, the type of frequency ramp nonlinearity cannot be directly specified, which makes the problem even more challenging. In this paper, the frequency ramp nonlinearity is investigated with the modified short-time Fourier transform method by using the short-time Chirp-Z transform method with high accuracy. The random and periodic nonlinearities are characterized and their sources are identified as phase noise and spurious. These types of frequency deviations are intentionally increased, and their influence on the linearity and the IF-signal is investigated. The dependence of target range estimation accuracy on the frequency ramp nonlinearity, phase noise, spurious, and signal-to-noise ratio in the IF-signal are described analytically and are verified on the basis of measurements. [ABSTRACT FROM PUBLISHER]

In this paper, we introduce a novel concept for frequency-modulated continuous-wave radar. The approach is based on an interlaced chirp sequence waveform, which is controlled by phase-locked loops (PLLs). The use of PLLs improves frequency chirp linearity and reduces phase noise compared with open-loop voltage-controlled oscillators commonly used to generate the fast chirps. In contrast to basic range–Doppler processing, it enables higher target velocities to be detected unambiguously at the same resolution, which makes it suitable for automotive applications. Separate frequency synthesizers generate the interlaced ramps in the system. An RF switch combines these two signals to suppress transients caused by oscillator overshoot and to avoid incoherencies due to programming times of the PLL ICs. We built a prototype radar system in K-band. The test results are promising and bode well for other applications. [ABSTRACT FROM PUBLISHER]

This paper presents an input shaping strategy for vibration control of multimode systems. The strategy combines the use of single-mode input shaping techniques with a model-based frequency-modulation system. The strategy utilizes the fact that a single-mode input shaper can eliminate vibrations in a multimode system provided that, there exists a common frequency for which all frequencies of the system are odd multiples of that common frequency. Model-based feedback is used to modulate the frequencies of the system to the point where the odd multiple frequencies condition is satisfied. The primary mode frequency of the model-based feedback system is designed to be the common frequency that satisfies the aforementioned condition. Several single-mode input shapers are implemented with design frequencies equal to the primary mode frequency of the modulated system, thus eliminating vibrations in all modes of the system simultaneously. Simulations and experiments on multiple pendulum models are used to demonstrate the effectiveness of the performance of the frequency-modulation input shaping strategy. [ABSTRACT FROM AUTHOR]

Through the ferroelectric nanoparticles of BaTiO3(BTO) doping, the response time for the frequency modulation of the polymer-dispersed liquid crystal (PDLC) was improved. The BTO-doped PDLC cells were prepared by polymerisation induced phase separation (PIPS) process using UV light. The capacitance of the PDLC composites was measured with an impedance analyzer in the frequency range of 100 Hz–1 MHz at 1 V. The dynamic signal for the response time of the PDLC devices was monitored through a digital oscilloscope. The electro-optical properties of the PDLC were found to strongly depend on the doped BTO concentration. The BTO doping caused a large increase in the capacitance. The dielectric constants were drastically decreased in the samples with rather low BTO doping ratio at a high frequency. No outstanding difference in the rising time of the LC was observed in the BTO-doped PDLC device, but the falling time was significantly decreased from 0.334 to 0.094 s. The present results imply that the nanoparticle-doping technology could improve the electro-optical performance of the PDLC requiring fast response and frequency modulation, such as optical modulators and PDLC-hybrid electroluminescence device for flexible electronic devices. [ABSTRACT FROM AUTHOR]

The article discusses the design and principles of operation of three diagnostic testers constructed by the authors of this study, intended for three, different aircraft propulsion units. These design have one common way of processing the original diagnostic signal - they use one FAM-C method. This method is based on natural processing of the rotational speed fluctuations of individual kinematic cells of the propulsion unit, by the on-board generator into frequency modulations. The method, thanks to its properties, is extremely beneficial for the automatic digital diagnostic processing. The tester can be connected at any, convenient for the crew, location of the power grid, away from dangerous zones of the aircraft. [ABSTRACT FROM AUTHOR]

This paper deals with switching-frequency modulation (SFM) for conducted electromagnetic interference (EMI) suppression in active power factor correctors (PFCs) operating in discontinuous conduction mode (DCM). The effect of SFM on different performance characteristics of DCM PFC is studied in details. It is shown that the use of SFM in PFC with conventional control approach leads to significant increase in total harmonic distortion (THD) and harmonic content of input current. Moreover, SFM leads to noticeable increase in peak power components currents. In order to use SFM for EMI reduction more effectively without significantly worsening THD, power factor, and harmonic content of DCM PFC, an improved control technique and a control circuit are proposed and verified by simulations and experimentally. The technique is based on the use of specific time delay injection to power MOSFET control signal. As show simulations and experiments, SFM PFC with the proposed delay technique in comparison to PFC without SFM has noticeably lower conducted EMI and THD of input current, at the cost of slightly decreased efficiency and moderately increased peak currents. [ABSTRACT FROM AUTHOR]

In this paper, locally repairable codes with all-symbol locality are studied. Methods to modify already existing codes are presented. It is also shown that, with high probability, a random matrix with a few extra columns guaranteeing the locality property is a generator matrix for a locally repairable code with a good minimum distance. The proof of the result provides a constructive method to find locally repairable codes. Finally, constructions of three infinite classes of optimal vector-linear locally repairable codes over a small alphabet independent of the code size are given. [ABSTRACT FROM AUTHOR]

We report on the resonant frequency modulation of inertial microelectromechanical systems (MEMS) structures due to squeeze film stiffness over a range of working pressures. Squeeze film effects have been studied extensively, but mostly in the context of damping and $Q$ -factor determination of dynamic MEMS structures, typically suspended over a fixed substrate with a very thin air gap. Here, we show with experimental measurements and analytical calculations how the pressure-dependent air springs (squeeze film stiffness) change the resonant frequency of an inertial MEMS structure by as much as five times. For capturing the isolated effect of the squeeze film stiffness, we first determine the static stiffness of our structure with atomic force microscope probing and then study the effect of the air spring by measuring the dynamic response of the structure, thus finding the resonant frequencies while varying the air pressure from 1 to 905 mbar. We also verify our results by analytical and Finite Element Method calculations. Our findings show that the pressure-dependent squeeze film stiffness can affect a rather huge range of frequency modulation (>400%) and, therefore, can be used as a design parameter for exploiting this effect in MEMS devices. [ABSTRACT FROM AUTHOR]

This paper presents a study on linear frequency modulation (LFM) pulsed signal transmission by four-dimensional (4-D) antenna arrays. LFM pulse is used as the input of 4-D antenna arrays and the influence brought by the periodic time modulation is analyzed. The relationship among pulse duration, chirp rate, sample frequency, time-modulation frequency, and propagation direction is analyzed and the restrictions to these parameters are highlighted. The transmitting and receiving structures are introduced and relevant signal processing steps are described. Numerical examples with several different time schemes, including the pulse shifting (PS) scheme and binary phase center motion (BPCM) scheme, are presented to demonstrate the effectiveness of the LFM signal transmission by 4-D arrays. Simulation results validate that original chirp signal can be correctly recovered and low sidelobe power patterns can be simultaneously achieved by 4-D antenna arrays, as long as the proposed limitations are satisfied. [ABSTRACT FROM PUBLISHER]

With the introduction of thermal fly-height control sliders, the local head-disk clearance can be reduced to a range from $\sim10$ nm to contact. This actively controlled touchdown (TD) has been used as a way to study the head–disk interface (HDI), the characteristics of which greatly affect the areal density and reliability of drives. In this paper, a high spatial resolution TD study is performed at the drive level using TD sensor signals and head-media spacing signals. Different flying stages, including passive flying, TD transition, and over push modulation, are identified from the experimental results. A correlation between the aforementioned signals at the passive flying stage is found to represent the disk surface property. The passive flying stage and over push modulation stage of TD are further analyzed in both the time and frequency domains. By establishing a correlation between the fly height and the temperature response, we can provide insight into the heat transfer model for the HDI. [ABSTRACT FROM AUTHOR]

The present paper, aside considering the influence of a forcing signal, discusses the effect of frequency modulated synchronizing signal on optoelectronic oscillator and the corresponding FM–AM conversion for the injection synchronized optoelectronic oscillator is studied. A method to calculate the locking range of a synchronized angle modulated OEO is presented. The amplitude and phase equations are derived using the cyclic passage theory utilizing Barkhausen's criteria. The variation of modulation index and locking range with fiber delay has been presented. Finally, the growth of oscillation amplitude and the phase-plane plot of the system are studied. It is to be noted that nothing has been reported on the synchronizing capability of the angle modulated OEO as far as the knowledge of the authors goes. [ABSTRACT FROM AUTHOR]

Spread-spectrum clocking is an established approach to mitigate electromagnetic interference (EMI) of digital circuits, by intentionally sweeping the clock frequency. In this way, the energy of each clock harmonic is spread over a larger bandwidth, thereby reducing the peak of the interfering spectrum. This paper describes an highly flexible all-digital spread-spectrum clock generator (SSCG) realized with a standard-cells design flow. The developed circuit supports discontinuous frequency modulation profiles (with improved EMI reduction capability) and features reduced output jitter, due to delay interpolators and digital compensation of delay path asymmetries. The proposed SSCG is ideally suited for complex system on chips applications, having programmable spreading parameters, frequency synthesis capability and reduced recovery time to support local standby modes. The SSCG is implemented in bulk 28 nm CMOS technology, presents a maximum working frequency of 3.3 GHz and less than 3.2 psrms output jitter. The measured peak level reduction of the clock power spectrum, at 1.0 GHz output frequency, is 27.0 dB with a 10% modulation depth. The power dissipation is 29.3 mW @ 3.3 GHz and the area occupation is 0.031 mm. [ABSTRACT FROM AUTHOR]

We present an electrostatic transducer in which voltage remains constant while charge is stored or extracted from the device. We achieve this by designing a nonlinear mechanical spring, which exactly counteracts the nonlinearity associated with electrostatic attraction forces. In essence, the new device responds like a rechargeable battery, only that here we store electric energy in elastic deformation, whereas in common batteries, electric energy is stored as chemical potential. The capacitance of the presented test devices is currently too small to be practical, and we are not, by any means, suggesting that this transducer can replace chemical rechargeable batteries. Nevertheless, some necessary steps toward constructing a more viable device with larger energy density are discussed. [2014-0093] [ABSTRACT FROM PUBLISHER]

This paper introduces an $H_\infty$ fuzzy control synthesis method for a nonlinear large-scale system with a reduced number of linear matrix inequalities (LMIs). It is well known that a nonlinear large-scale system can be transformed to a Takagi–Sugeno (T–S) fuzzy system by using “sector nonlinearity” or “local approximation in fuzzy partition spaces” methods. Next, in order to achieve the fuzzy control design for this T–S fuzzy system, we solve the stabilization conditions that are represented by the LMIs. However, if the number of LMIs is large, the control design process may become very complicated. In this study, based on the Lyapunov method and S-procedure, several theorems are proposed for the synthesis of parallel distributed compensation (PDC)-type fuzzy control such that the nonlinear large-scale system achieves $H_\infty$ control performance, and the number of LMIs to be solved is reduced explicitly. As a result, the control design process will become much easier. Furthermore, if the modeling error between the nonlinear system and T–S fuzzy system exists, the robust $H_\infty$ control performance and the number reduction of LMIs are also achieved by the proposed theorem. Several examples are presented in this paper to show the number reduction effect of LMIs and the effectiveness of the proposed controller synthesis. [ABSTRACT FROM AUTHOR]

We consider a new signal processing method for the difference frequency of an FM microwave distance sensor, based on a sinusoidal signal model with three independent parameters - amplitude, frequency, and phase, which avoids the discretization error in spectral processing. [ABSTRACT FROM AUTHOR]

A simple wireless strain sensor using a frequency modulation technique is presented. The sensor employs a piezoelectric transducer that produces electric voltage as it is mechanically strained. When the piezoelectric sensor is connected to a single-transistor frequency modulation circuit, the sensor output voltage causes the modulation circuit frequency to shift. This modulated signal is then wirelessly transmitted to a remote station, where a demodulation circuit retrieves the buried strain measurement data in real time. Using this technique, a dynamic strain measurement is possible without any wire connection between the sensing point and the monitoring station. In order to demonstrate the performance of the wireless strain sensor and the measurement system, a wireless measurement of a vibrating cantilevered beam is experimentally conducted. This type of sensor has numerous applications in the strain or vibration measurement of moving or rotating structures such as turbo machinery. [ABSTRACT FROM AUTHOR]

Electric power system instantaneous frequency, also referred to as electrical network frequency (ENF), pollutes digital recordings due to a variety of factors (e.g., transformer hum). This unwanted interference has been used as a forensic tool in conjunction with a database of ground truth ENF measurements to determine the time at which a recording was made, as well as to detect tampering. Recent work has suggested that that ENF could be used to geolocate a digital recording under the assumption that the low-energy location-unique power system dynamics are observable, which is not always the case in the presence of noise and interference. This letter aims to take advantage of the intrinsic nature of power system instantaneous frequency in order to frame the ENF extraction problem as one of FM demodulation. By considering the ENF as a sinusoid of nominal power system frequency that is frequency modulated by a weak stochastic signal, a 0-Hz Intermediate Frequency (IF) signal can be created and analyzed rather than direct measurements. In doing so, significant data reduction can be achieved through extensive downsampling, FM demodulation algorithms can be applied to extract the ENF, and the spectrum of the IF signal provides a straightforward way of estimating the maximum observable frequency content of the ENF buried in a digital recording. These findings are supported through the analysis of audio recordings made in the presence of ENF interference in the U.S. Eastern Interconnection power system. [ABSTRACT FROM AUTHOR]

Monopulse radar receivers employing phase locked loop (PLL) invariably track the target in range and angle (frequency) domains. In this paper, the tracking performance of PLL for a highly application specific airborne tracking radar in frequency domain is presented. Two different signals such as the linear frequency modulated (LFM) interference signal from repeater source and the radar echo signal are injected into the PLL simultaneously with an assumption that initially, the PLL locks onto the echo signal frequency. The effectiveness of key parameters of LFM signal such as frequency deviation, modulation rate and LFM signal power on break-lock are demonstrated. The simulation results show that break-lock is achieved at frequency deviation of 0.35 MHz for a typical LFM signal power of -14 dBm and 200 kHz modulation rate when the radar echo power at the PLL input is -14 dBm. The break-lock is studied for a typical loop bandwidth of 200 kHz and different values of radar echo signal power at input of the PLL. The computer simulation is carried out using visual system simulator (VSS) AWR software and potential conclusions are demonstrated. [ABSTRACT FROM AUTHOR]