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A rotating spring-mass system is considered using polar coordinates. The system contains a cubic nonlinear spring with damping. The angular velocity harmonically fluctuates about a mean velocity. The dimensionless equations of motion are derived first. The velocity fluctuations resulted in a direct and parametric forcing terms. Approximate analytical solutions are sought using the Method of Multiple Scales, a perturbation technique. The primary resonance and the principal parametric resonance cases are investigated. The amplitude and frequency modulation equations are derived for each case. By considering the steady state solutions, the frequency response relations are derived. The bifurcation points are discussed for the problems. It is found that speed fluctuations may have substantial effects on the dynamics of the problem and the fluctuation frequency and amplitude can be adjusted as passive control parameters to maintain the desired responses. [ABSTRACT FROM AUTHOR]

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]

This paper presents an experimental investigation on the behavior of magnetorheological (MR) fluids in high-frequency oscillatory squeeze mode and proposes a mathematical model to reveal the MR mechanism. A specific MR squeeze structure avoiding the cavitation effect is designed for the experimental tests. The magnetic field- and gap distance-dependent damping force of the MR squeeze structure is presented and compared with the dramatically large damping force under quasi-static excitations, a moderate damping force is observed at high frequencies. Subsequently, in order to interpret the behavior of MR fluids at high frequencies, employing the continuum media theory, a mathematical model is established with consideration of the fluid inertia and hysteresis property. The damping force comparison between the model and experimental tests indicates that in high-frequency oscillatory squeeze mode, the squeeze-strengthen effect does not work and the shear yield stress can be applied well to characterize the flow property of MR fluids. In addition, the hysteresis property has a significant influence on the damping performance. [ABSTRACT FROM AUTHOR]

Modern autonomous vehicles are being equipped with various automotive sensors to perform special functions. Especially, it is important to predict the heading direction of the front vehicle to adjust the speed of the ego‐vehicle and select appropriate actions. Here, we propose a method for estimating the instantaneous heading direction of a vehicle using automotive radar sensor data. First, using a frequency‐modulated continuous wave (FMCW) radar in the 77 GHz band, we accumulate the automotive radar sensor data for different movements of the front vehicle (e.g., stop, going ahead, reversing, turning left, and turning right). To distinguish the different movements of the vehicle, we use the convolutional neural network (CNN) and train it using the acquired radar sensor data. Because the CNN algorithm usually uses image data as input, it is essential to convert radar sensor data into image data. Therefore, we apply a high‐resolution angle estimation algorithm to the obtained radar data and convert it into a two‐dimensional range map. After the CNN model is trained with the obtained radar sensor data, various movements of the front vehicle can be classified with over 94% of accuracy. [ABSTRACT FROM AUTHOR]

In this communication, based upon a squeezed-state trial wave function, we have performed a simple variational study of the spectral collapse of the two-photon Rabi model. Our analysis indicates that the light-matter interaction and the spin-flipping effectively constitute two competing impacts upon the radiation mode. Whilst the former tries to decrease the radiation mode frequency, the latter may counteract or reinforce it, contingent upon the state of the atomic system. The light–matter interaction appears to dominate the frequency modulation as its coupling strength goes beyond the critical value, leading to the emergence of the spectral collapse. However, at the critical coupling the dominance of the light–matter interaction is not complete, and incomplete spectral collapse appears. The extent of incomplete spectral collapse is found to depend upon the energy difference between the two atomic levels as well. [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]

This study presents preliminary results about the multi-sensory recognition of indoor daily activities and fall detection, to monitor the well-being of older people at risk of physical and cognitive chronic health conditions. Five different sensors, continuous wave (CW) radar, frequency-modulated CW (FMCW) radar, and inertial measurement unit comprising an accelerometer, gyroscope, and magnetometer were used to simultaneously collect data from 20 subjects performing 10 activities. Rather than using all of the available sensors, it is more efficient and economical to select part of them to maximise the classification accuracy and avoid unnecessary computation to process information if it is not salient. Each individual sensor and several sensor combinations are trained with a quadratic-kernel support vector machine classifier. In addition, they are validated with an improved statistical approach, which uses data from unknown participants to test model rather than random cross-validation to verify if the model generalises well for unknown subjects. Furthermore, the most suitable sensor combinations are derived for each specific group of tested subjects selected (e.g. the oldest, youngest, tallest, and shortest sub-groups of participants out of the entire group). [ABSTRACT FROM AUTHOR]

This paper presents a study on the natural vibration of circular double-layer graphene sheets (DLGSs) using circular plate theory. The circular DLGSs are assumed to be coupled together through the carbon-carbon van der Waals (vdW) force between their two layers. An analytical solution of coupled governing equations is proposed to predict the natural frequencies of circular DLGSs. The vibration behaviors in circular DLGSs are found to have an in-phase mode (IPM) associated with the classical natural frequency, and an anti-phase mode (APM) owing to the influence of the vdW interaction. The natural frequencies of the IPM are independent of vdW interactions between adjacent layers, while those of the APM depend on the vdW interaction, and are larger. Based on the exact solution, the influences of wavenumbers (m, n) on the natural frequencies of simply supported circular DLGSs are also investigated in detail. [ABSTRACT FROM AUTHOR]

Recently, various high quality factor photonic crystal microcavities have been demonstrated theoretically and experimentally with only one-dimensional periodicity. However, in most cases high-index materials such as silicon were chosen for easily achievable large photonic bandgap and elaborate refractive index modulation or taper structure is required for reducing radiation loss. Here, we present a design of high-Q microcavities in one-dimensional multilayer polystyrene photonic crystal slab structures with a low-index contrast of 1.59:1. Microcavities are introduced by simply decreasing the thickness of layers at the center region to form a double-heterostructure. A resonant mode with a quality factor up to 20 000 is obtained and found to originate from the modal gap confinement by comparing with a Fabry-Perot cavity. The dependence of the maximal quality factor on the cavity length further reveals that the small group velocity of light within the heterostructure cavity contributes significantly to the high-Q. In terms of the high quality factor, ease of fabrication, and large Kerr nonlinearity of polystyrene, our double-heterostructure microcavities will find potential application in realizing all-optical modulation devices. [ABSTRACT FROM AUTHOR]

The method described in this article performs thermal diffusivity measurements on bulk materials using a modulated spot heating of the sample surface and measuring the surface temperature on the spot with an infrared detector at different modulation frequencies. Since the method is single sided and it can be performed on a bulk, it does not require the preparation of a sample. Furthermore it does not require a precise alignment nor a movement of the heating source nor of the infrared detector. The diffusivity measurement on a sample of unknown thermal diffusivity requires the knowledge of the shape of the heating and of the sensitivity profile of the infrared detector on the sample surface. This information, difficult to obtain, is not necessary in case a first measurement is performed on a reference sample of known thermal diffusivity and subsequent measurements on samples of unknown thermal diffusivity are performed by positioning them with their surface precisely in the same location as the reference one. [ABSTRACT FROM AUTHOR]

Highlights • Frequency emergency control system classification and control. • Wide area frequency monitoring, protection and control. • Growing a decision tree to classify the emergency frequency contingencies. • Heat ventilation air conditioning system application in frequency regulation. Abstract Without a balanced compensation power for connected load demands, the power system frequency may be subjected to a severe drop during a massive loss of generation units. The emergency frequency control system traditionally depends on under-voltage and under-frequency load shedding techniques of power system feeders in cascading steps to control frequency during an emergency. As a result, the power systems suffer from a series of internal and external disturbances, leading to various degrees of blackouts due to the cascading failure effect, which may occur due to the nonlinear dynamic response of frequency at different locations. Smart grids have become a very important trend nowadays. Traditional electric power grids are developed to be smarter, especially with control and protection issues underpinned by advanced measurement and communication technologies. This paper presents a new controlling action to limit the probabilities of disconnecting loaded feeders from power grids due to maloperation of under-frequency load shedding (UFLS) relays. The suggested technique is based on a decision tree algorithm to take an accurate decision for controlling thermostatically controllable loads (TCL). A comparison among the suggested technique, UFLS, and centralised frequency control of TCL is conducted. The proposed technique satisfies a high degree of power system stability, lower cost, and faster response. Moreover, it prevents the operation of the first stage of UFLS relays. [ABSTRACT FROM AUTHOR]

Continuous-time frequency modulation (CTFM) technique is extensively used in Sonar signal processing to estimate the range of received echoes. In this, the range resolution is inversely proportional to the bandwidth of the probe signal. A dual-demodulator continuous-time frequency modulation (DD-CTFM) technique that was proposed to improve the range resolution does not offer any significant improvement in range resolution over CTFM in practice. The super-resolution based analysis techniques for CTFM also offer limited improvement over the conventional CTFM technique. This paper describes a new method for CTFM analysis that has the potential to make the range resolution independent of the probe signal bandwidth. The proposed enhanced range resolution dual-demodulator continuous-time frequency modulation (ER-DD-CTFM) algorithm has two phases; one is the training phase and other is the test phase. In the training phase the complex weights are calculated in frequency domain due to all the possible echoes from the range of interest, while in the test phase the information of the echoes that are actually present in the received signal is estimated by solving a set of linear equations. The ER-DD-CTFM algorithm has been analyzed in simulation studies and in experiments conducted in an acoustic anechoic chamber. Both the studies and experiments demonstrate that up-to ten times better range resolution can be obtained using the proposed ER-DD-CTFM algorithm over DFT analysis based CTFM. Further, the improvements in the range resolution compared to Root-MUSIC analysis based CTFM are 2.8 times and 2.35 times for the simulation and experimental study respectively. [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]

We propose the piecewise re-scaled vibrational resonance (VR) method and the piecewise twice sampling VR method to amplify the weak linear frequency-modulated (LFM) signal. The system used to amplify the weak LFM signal is a typical bistable system with fractional-order deflection nonlinearity. The concrete procedures of both the piecewise re-scaled VR method and the piecewise twice sampling VR method are explained in detail. Through studying the effect of the factional-order exponent on VR, we find that the traditional bistable system is not the optimal model to improve the weak LFM signal. By investigating different parameters on the VR phenomenon, we verify the effectiveness of the two proposed methods. [ABSTRACT FROM AUTHOR]

The authors construct the piecewise vibrational resonance (VR) method by introducing the piecewise idea and combine the re-scaled and twice sampling methods for the linear frequency modulated (LFM) signal. Importantly, they put forward a new spectral amplification factor to quantify the VR. The new spectral amplification factor has some advantages as compared with the cross-correlated coefficient, which can also be used to quantify the aperiodic VR. The top value of the spectrum amplification factor is the necessary and sufficient condition for the occurrence of the optimal VR phenomenon. Here, they discuss the effects of different parameters on VR by using some numerical examples. The method described in this study provides an effective way to improve the LFM signal, and even other kinds of frequency modulated signals. [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 work proposes a unified framework for linear system identification in frequency subbands using wavelet packets. To that end, a previous wavelet-packet technique is extended to allow for the use of general model structures and standard identification procedures. The technique can be straightforwardly applied to the identification of models with different structures, such as subspace models, provided that their parameters can be identified using a least-squares approach. Models with autoregressive structures are used here for means of illustration. The proposed technique is illustrated with the examples of the longitudinal dynamics of a flexible aircraft and with the model of a cantilever beam. The proposed wavelet-packet approach is favorably compared with the technique on which it was based and with a recently proposed wavelet-based subspace identification technique. [ABSTRACT FROM AUTHOR]

The two-tone frequency modulation spectroscopy (TTFMS) is widely used for gas trace detection with its low noise absorption signal. In this paper we propose and implement the TTFMS scheme for frequency offset locking a single diode laser to an atomic resonance line by using its dispersion signal. The TTFMS theory is first discussed under the assumption that the intermediate modulation frequency is comparable to the linewidth of the absorption feature, and the dependence of the TTFMS absorption and dispersion features on the intermediate modulation frequency and modulation index are investigated theoretically. Based on a fiber-coupled electro-optic modulator (EOM) with two-tone modulation, we experimentally demonstrated the performance of the frequency offset locking method. The result shows a short-term frequency stability of the frequency offset locked laser reached around 1.1 × 10 −11 , with an averaging time of 2 s. This method can find wide applications in fields requiring widely tunable frequency offset locking a single laser to the atomic resonance line, like precision spectroscopy and Raman optics for atom interferometers. [ABSTRACT FROM AUTHOR]

Abstract This paper presents a fully digital binary phase-shift-keying (BPSK) demodulator. The proposed system employs a proposed clipper circuit to clamp all peaks of the negative and positive of the received BPSK signal and to generate a synchronous reset signal. The time domain analysis of the voltage clipper shows that the proposed clipper can reduce the output low-to-high and high-to-low times, compared to conventional inverter. This causes two digital signals are generated at the extremum of the modulated BPSK with shrunk pulse widths and removes the need for voltage controlled oscillator (VCO) signal. The proposed BPSK demodulator is designed and post layout simulated in 0.18 μm standard CMOS technology at 10 MHz carrier wave. Monte Carlo's simulation results of the voltage clipper show that the maximum voltage offset never exceed from the nominal value. The proposed demodulator consumes 14 μW using a 1.8 V power supply and occupies 32 × 35 μm2 core area and 500 × 500 μm2 total chip area. [ABSTRACT FROM AUTHOR]

A broadband beam‐forming antenna is designed for intelligent emergency detection and rescue systems. Recognizing emergencies hinges on identifying and analyzing the motion of humans. Combined with deep learning, the radio frequency signal of an antenna can capture the motion of humans behind a wall and in closed rooms using frequency‐modulated carrier wave (FMCW) signals operating in broadband from 5.56 GHz to 7.25 GHz (26%). The beam‐forming antenna is composed of four slot‐coupled patch antennas. The proposed array antenna satisfies a broad FMCW bandwidth and sufficient gain over 15.8 dBi in the overall bandwidth. To extend the focusing capability, we specifically design a 4 × 1 array structure and optimize the distance of antenna to 32.9 mm (0.7 λ0). The antenna is compact enough to realize a handheld motion‐tracking device. The array antenna forms a fan beam with a wide beam coverage and low side lobe level. The motion of a human body is tracked as a beam scanning by the antenna array. To accomplish this goal with adaptive array architectures, we implement beam‐forming techniques with a phase shifter, an amplifier, and a power divider. [ABSTRACT FROM AUTHOR]

Multistage reducer vibration signals have complicated spectral structures owing to the amplitude and frequency modulations of gear damage-induced vibrations and the multiplicative amplitude modulation effect caused by time-varying vibration transfer paths (in the case of local gear damage) when the multistage reducer contains both planetary and spur gears. Moreover, the difference between the vibration energies of these gears increases the difficulty of fault feature extraction when multiple failures occur in the reducer. As the meshing frequency of each gear group often varies significantly, variational mode decomposition can be performed to decompose the vibration signal according to frequency, enabling separation of the vibration signals of the spur and planetary gears. The common fault features of these gears can be extracted from the spectrum of the amplitude demodulation envelope. To verify the effectiveness of this method, we first analyzed a simulation signal, and then utilized the experimental signals from a laboratory multistage reducer for verification. In the multistage reducer simulation, we considered the amplitude and frequency modulation of the gear damage and transfer paths. In the experimental verification, we processed local faults (broken teeth) and uniform faults (uniform wear) on the sun gear and the spur gear of the planetary gear separately. [ABSTRACT FROM AUTHOR]

In this paper, a new 7-bit frequency discriminator for instantaneous frequency measurement applications is presented for the first time. The proposed discriminator is designed using microstrip band-stop spiral filters to achieve a compact size structure with high reject values between pass and reject bands. As these passive filters are fabricated on available ordinary substrates, the proposed structure is ultralow cost. Rectangular and circular spiral resonators are used to reject the specific frequency bands in each channel. The designed filters for each channel divide the frequency bandwidth into several pass/reject bands to produce the desired binary code. The proposed structure works in S-band with the maximum frequency error of 16 MHz. The proposed discriminator was simulated by a momentum simulator of an advanced design system (ADS) and fabricated on a 20-mil Rogers RO4003 substrate with tan($\delta$) and a conductor thickness about 0.002 and $18~\mu \text{m}$ , respectively. An excellent agreement was achieved between the simulation results obtained by ADS and those of measurements; the average frequency shift is less than 10 MHz. [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]

Discusses the theory of operation of the frequency modulation (FM) which enhances the sensitivity of attractive mode force microscopy and conventional methods. Limitations of the conventional detection method; Behavior of the FM detection system; Sources of noise which limit the sensitivity of the FM detection system; Advantages of FM detection.

A novel mixed mode radar coincidence imaging (MMRCI) system, which combines the coherent radar detection and incoherent radar coincidence imaging function during the radar coincidence imaging (RCI) process, is presented in this paper. The target location function of the MMRCI system gives the target position information synchronously with imaging tests, and this makes the MMRCI work independently with low target position estimation error. In the MMRCI system, the resolution of target distance estimation is proportional to the whole bandwidth assisted by the double-frequency linear frequency modulation (DFLFM) signal when the occupied bandwidth of the DFLFM signal is less than one-tenth of the whole bandwidth. The target position estimation error caused by the target motion can be reduced effectively so that the image quality of the moving target can be guaranteed in a longer detection time. The RCI is reconstructed using the incoherent part of the transmitting signal. A general relationship between the spatial correlation of the random radiation field in the imaging plane and the deployments of linear random source is analyzed in the paper. The imaging efficiency is ensured through the grading imaging method based on the imaging requirement. The effectiveness of the MMRCI method is validated via a set of simulations and experiments, including superresolution RCI of both stationary and moving targets in various scenes using the convex optimization algorithms. [ABSTRACT FROM AUTHOR]

One of the main challenges in signal denoising is to accurately restore useful signals in low signal-to-noise ratio (SNR) scenarios. In this paper, we investigate the signal denoising problem for multi-component linear frequency modulated (LFM) signals. An effective time-frequency (TF) analysis-based approach is proposed. Compared to the existing approaches, our proposed one can further increase the noise suppressing performance and improve the quality of the reconstructed signal. Experimental results are presented to show that the proposed denoising approach is able to effectively separate the multi-component LFM signal from the strong noise environments. [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]

The use of robotic motion platforms in vehicle simulators is relatively common. However, the process of testing and tuning the so-called washout algorithms, used for motion cueing generation in motion-based vehicle simulators, is complex. This process can be reduced in cost, simplified, improved, shortened and performed safer if virtual motion platforms are used instead of real devices. This paper deals with identifying a method to perform a fast but reliable simulation of parallel mechanisms to be used for motion cueing generation. The method relies on the use of Laplacian polynomial transfer function models by means of using AM-FM bi-modulated signals as reference inputs to achieve system identification. The proposed simulation scheme is implemented and assessed using optical tracking methods by testing a real 2-DOF pitch-roll parallel robot, although the method is not intrinsically restricted to this type of device. The performance of the proposed solution is also assessed with the classical washout algorithm. Results show that the accuracy of the method is satisfactory and the performance of the proposed simulation scheme is very high, being suitable to test and tune washout algorithms. [ABSTRACT FROM AUTHOR]

We introduce a phase calibration scheme for an interferometric frequency-modulated continuous-wave (FMCW) synthetic aperture radar (SAR) to correct range-dependent phase errors in FMCW SAR interferograms. We demonstrate that the receiver filters operating on the FMCW beat frequency signal account for most of the phase mismatch between the different receiver channels. The scheme presented estimates the phase error in each channel. We present results of the scheme for three estimation approaches (curve fitting, joint least squares, and maximum likelihood) for two different phase models. The results are quantified by computing the reduction in spectral energy associated with the phase mismatch. We find that phase error can be reduced by 14 dB using the approach. [ABSTRACT FROM AUTHOR]

Generalized spatial modulations (GSM) represent a novel multiple input multiple output (MIMO) scheme, which can be regarded as a compromise between spatial multiplexing MIMO and conventional spatial modulations, achieving both spectral efficiency and energy efficiency. Due to the high computational complexity of the maximum likelihood detector in large antenna settings and symbol constellations, in this correspondence paper we propose a lower complexity iterative suboptimal detector. The derived algorithm comprises a sequence of simple processing steps, namely, an unconstrained Euclidean distance minimization problem, an element-wise projection over the signal constellation, and a projection over the set of valid active antenna combinations. To deal with scenarios where the number of possible active antenna combinations is large, an alternative version of the algorithm, which adopts a simpler cardinality projection, is also presented. Simulation results show that, compared with other existing approaches, both versions of the proposed algorithm are effective in challenging underdetermined scenarios where the number of receiver antennas is lower than the number of transmitter antennas. [ABSTRACT FROM AUTHOR]

The vibration signals are usually characterized by nonstationary, nonlinearity, and high frequency shocks, and the redundant features degrade the performance of fault diagnosis methods. To deal with the problem, a novel fault diagnosis approach for rotating machinery is presented by combining improved local mean decomposition (LMD) with support vector machine–recursive feature elimination with minimum redundancy maximum relevance (SVM-RFE-MRMR). Firstly, an improved LMD method is developed to decompose vibration signals into a subset of amplitude modulation/frequency modulation (AM-FM) product functions (PFs). Then, time and frequency domain features are extracted from the selected PFs, and the complicated faults can be thus identified efficiently. Due to degradation of fault diagnosis methods resulting from redundant features, a novel feature selection method combining SVM-RFE with MRMR is proposed to select salient features, improving the performance of fault diagnosis approach. Experimental results on reducer platform demonstrate that the proposed method is capable of revealing the relations between the features and faults and providing insights into fault mechanism. [ABSTRACT FROM AUTHOR]

Micro-Electro-Mechanical Systems (MEMS) gyroscopes are inertial sensors for the measurement of angular rates. They have a variety of applications from consumer electronics to drones and the need of stability against environmental fluctuations, such as temperature, is a key factor in order to avoid expensive calibration procedures. Frequency Modulation (FM) has been recently proposed as an innovative working principle for MEMS gyroscopes and as the desired solution in terms of stability against environmental fluctuations. In this paper, the FM working principle is formalized for the three-axial case for the first time and the governing equations are derived both in the idealized case of a point-mass gyroscope and in the real case of a distributed-mass gyroscope. Moreover, the mechanical structure of the first three-axial MEMS FM gyroscope is proposed and studied. Preliminary experimental measurements prove the validity of both the model and the simulations results employed during the design process. The proposed structure overcomes lots of the constraints of the surface micromachining fabrication processes and represents an important step towards the development of a new class of MEMS gyroscopes. [ABSTRACT FROM AUTHOR]

In this paper, the bimodal amplitude-and frequency modulation method of atomic force microscopy (AFM) is applied to investigate the residual oil film on KDP crystal surface after polishing and surface cleaning. The thickness map of residual oil film is obtained based on the relationship between the cantilever resonant frequency shift and the surface stiffness. The thickness maps measured by AFM and spectroscopic imaging ellipsometry methods are compared, and the results obtained by two methods are consistent. The measurement scheme extends the application of AFM technology to characterize the residual oil on the KDP surface quality quantitatively after polishing and surface cleaning. [ABSTRACT FROM AUTHOR]

A novel technique of combating the effects of high peak to average power ratio (PAPR) arising due to the non-linearity of the LED in a typical optical-OFDM (O-OFDM) for visible light communication (VLC) systems used in optical wireless channel (OWC) is proposed in this research work. The concept of constant envelope (CE) using frequency modulation (FM) for a composite O-OFDM system formed by uniting Asymmetrically Clipped Optical OFDM (ACO-OFDM) and Direct Current biased Optical OFDM (DCO-OFDM) termed as ADO-OFDM is mathematically presented with its numerical simulation results. The proposed system FM-CE-ADO-OFDM shows improvement in the PAPR with narrowing down to the least possible 0 dB theoretically. The analysis is extended to be compared with the phase modulation (PM) technique of CE-OFDM. The magnitude of phase discontinuity in the two systems is evaluated in the form of metrics yielding favorable results for the proposed system. This system is as spectrally efficient as the DCO-OFDM and as power efficient as the ACO-OFDM with the added advantage of major reduction in the effects due to PAPR arising as a result of the nonlinearity of the LED . The so formed FM-CE-ADO-OFDM is fed to the LED biased in the linear most region of its operation for simulation purpose. We also evaluate the depth of modulation required to obtain least bit error rate (BER). The frequency modulation at 30% depth has been observed to give suitable performance. The entire system is evaluated for an OWC length of 2m resembling the indoor illumination scenario. The receiver sensitivity shows an improvement of 1.2 dB at the FEC threshold for the proposed system. [ABSTRACT FROM AUTHOR]

In this study, results of wideband dual polarised measurements conducted in indoor environments including office, factory, corridor and computer foyer, using state-of-the-art 2×2 multiple-input-multiple-output frequency modulated continuous wave-based channel sounder, are presented. The measurements were performed in two frequency bands with 6 GHz bandwidth, centred at 54 and 70 GHz, with directional steerable ~20 dBi (18° beamwidth) horn antennas. Using twists at the transmitter and at the receiver simultaneous co-polar and cross-polar measurements were performed to quantify the polarisation effects on channel parameters such as angular spread, delay spread and path loss. The results show that the co-polarised radio links experienced lower angular spread and delay spread compared with the cross-polarised links. For co-polarised links, the estimated synthesised omnidirectional path loss exponent was found to be in the range of 1.5-2 (close-in model) and 0.9-1.9 (log-distance model) in the respective environments. In individual scenarios, the median cross-polarisation ratio was found to be within 11.7-14.4 and 7.5-17.6 dB at 54 and 70 GHz, respectively. [ABSTRACT FROM AUTHOR]

As an important means in electrical impedance tomography (EIT), multi-frequency phase-sensitive demodulation (PSD) can be viewed as a matched filter for measurement signals and as an optimal linear filter in the case of Gaussian-type noise. However, the additive noise usually possesses impulsive noise characteristics, so it is a challenging task to reduce the impulsive noise in multi-frequency PSD effectively. In this paper, an approach for impulsive noise reduction in multi-frequency PSD of EIT is presented. Instead of linear filters, a singular value decomposition filter is employed as the pre-stage filtering module prior to PSD, which has advantages of zero phase shift, little distortion, and a high signal-to-noise ratio (SNR) in digital signal processing. Simulation and experimental results demonstrated that the proposed method can effectively eliminate the influence of impulsive noise in multi-frequency PSD, and it was capable of achieving a higher SNR and smaller demodulation error. [ABSTRACT FROM AUTHOR]

This article presents a simple and efficient method for the design of a self-diplexed antenna based on loading asymmetric grounding-vias. The structure consists of two antenna elements loaded with two asymmetric grounding-vias, specifying the uplink and downlink operation frequencies. By choosing the appropriate positions of the two grounding-vias, high isolation between the two antennas can be achieved. To validate the feasibility of the proposed structure, two self-diplexed antennas with different operational frequencies have been fabricated and tested. Experimental results verify the multi-functionalities of the proposed compact structure in terms of high isolation and low cross-polarization discrimination. [ABSTRACT FROM AUTHOR]

In the state of oil-film instability coupled with rub-impact, the vibration signal of rotor-bearing system generally presents the weak non-linear frequency modulation (FM) features. In order to get a deep insight into the complicated FM phenomenon, the mechanism analysis is carried out on the motion model of non-linear Jeffcott rotor in oil-film instability coupled with rub-impact fault. The method of directional cyclic demodulation is proposed to extract the weak FM information embodied in the strong oil-film instability vibration. In this method, the directional cyclic autocorrelation density (DCRD) is adopted to infuse the information of two-directional vibration signals, and then is sliced along the cyclic frequency axis. The FM features and rotor motion direction are extracted from the slice of DCRD. Then the experimental research on the rotor-bearing system demonstrates the validity of the proposed method. [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]

The measurement precision of frequency-modulated continuous-wave (FMCW) laser distance measurement should be proportional to the scanning range of the tunable laser. However, the commercial external cavity diode laser (ECDL) is not an ideal tunable laser source in practical applications. Due to the unavoidable mode hopping and scanning nonlinearity of the ECDL, the measurement precision of FMCW laser distance measurements can be substantially affected. Therefore, an FMCW laser ranging system with two auxiliary interferometers is proposed in this paper. Moreover, to eliminate the effects of ECDL, the frequency-sampling method and mode hopping influence suppression method are employed. Compared with a fringe counting interferometer, this FMCW laser ranging system has a measuring error of ± 20 μ m at the distance of 5.8 m. [ABSTRACT FROM AUTHOR]

Differential amplitude phase shift keying (DAPSK) is a promising modulation technique for use in high-mobility environments, as it does not require channel estimation. In this paper, a novel reduced complexity soft demodulator for high-order DAPSK constellations is proposed. The main idea relies on a two-step approximation of the sum-log demapper. In the first step, a parallel factor analysis (PARAFAC) decomposition is used to approximate log-likelihood ratios. Next, the basis functions obtained through the first step are approximated by piecewise-linear curves. Numerical optimization techniques are employed for the PARAFAC decomposition and its piecewise-linear approximation whose parameters are then stored in a lookup table. It has been verified through computer simulations that the proposed scheme clearly outperforms the scheme proposed in the paper “Reduced-complexity noncoherent soft-decision-aided DAPSK dispensing with channel estimation,” (IEEE Trans. Veh. Technol., vol. 62, pp. 2633–2643, 2013.), while also having lower computational cost. Moreover, it is shown that the performance of the exact sum-log demapper and the proposed demapper is very close for \text2\times \text4 and \text4\times \text16 DAPSK constellations. [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]

The majority of techniques that deal with the mitigation of in-phase and quadrature-phase (I/Q) imbalance at the transmitter (pre-compensation) require long training sequences, reducing the throughput of the system. These techniques also require a feedback path, which adds more complexity and cost to the transmitter architecture. Blind estimation techniques are attractive for avoiding the use of long training sequences. In this paper, we propose a blind frequency-independent I/Q imbalance compensation method based on the maximum likelihood (ML) estimation of the imbalance parameters of a transceiver. A closed-form joint probability density function (PDF) for the imbalanced I and Q signals is derived and validated. ML estimation is then used to estimate the imbalance parameters using the derived joint PDF of the output I and Q signals. Various figures of merit have been used to evaluate the efficacy of the proposed approach using extensive computer simulations and measurements. Additionally, the bit error rate curves show the effectiveness of the proposed method in the presence of the wireless channel and Additive White Gaussian Noise. Real-world experimental results show an image rejection of greater than 30 dB as compared to the uncompensated system. This method has also been found to be robust in the presence of practical system impairments, such as time and phase delay mismatches. [ABSTRACT FROM AUTHOR]