Instantaneous Frequency Method Research Articles

Nanoscale visualization of fast carrier dynamics in organic thin-film transistors by time-resolved electrostatic force microscopy

Fast carrier dynamics in organic thin-film transistors (OTFTs) was investigated by time-resolved electrostatic force microscopy (tr-EFM). We found that the carrier diffusion in the OTFTs proceeded in two stages: fast diffusion and slow diffusion. By applying the instantaneous frequency method to EFM, the temporal evolution of the spatial distribution of fast carriers in the channel region of the OTFTs, which took place on the timescale of several hundreds of nanoseconds, was evaluated. The inhomogeneous distribution of the local decay time constant showed that the carrier diffusion of the OTFTs was limited by the grain boundaries between each crystalline region. The quantitative capability of the method was verified by comparing the values of the carrier mobility estimated by the tr-EFM measurement and a numerical simulation. The mobility estimated from the experiment and the simulation showed good agreement, showing the possibility of the tr-EFM to evaluate the time evolution of dynamic phenomena in semiconductor devices.

Structural instantaneous frequency identification based on synchrosqueezing fractional Fourier transform

The fractional Fourier transform can transform the signal or function into any intermediate domain between time and frequency domains called fractional Fourier domain, in which the non-stationary signals can be processed. To be a time-frequency analysis tool, the fractional Fourier transform may face the same ridge line blurred problem for noisy signals as other time-frequency analysis methods. To improve the instantaneous frequency identification accuracy of fractional Fourier transform, this paper proposes the synchrosqueezing fractional Fourier transform by using the mechanism that can rearrange the energy in the time-frequency plane and make the frequencies more concentrated on the real frequency of the signal. The synchrosqueezing fractional Fourier transform and its corresponding inverse transformation are theoretically derived. Then the corresponding instantaneous frequency identification based on synchrosqueezing fractional Fourier transform is formulated. The accuracy and effectiveness of proposed instantaneous frequency method is verified by a numerical example of three-degree-of-freedom damped time-varying structural system and experiments of moving vehicle-beam system with simply supported and continuously supported beam tested in the laboratory. Compared with the fractional Fourier transform without synchrosqueezing transform, synchrosqueezing wavelet transform and Fourier synchrosqueezing transform, it is demonstrated that the synchrosqueezing fractional Fourier transform can effectively improve the time-frequency distribution divergence and enhance the accuracy of the instantaneous frequency identification. The method has a certain anti-noise performance. Due to quick calculation by means of traditional fast Fourier transform and superior orthogonal transform feature, the proposed synchrosqueezing fractional Fourier transform can be used as an effective time-frequency signal processing tool for multi-component non-stationary signals.

Natural Gas Load forecasting based on the fusion of VMD-SE and CNN-BiLSTM-Attention

The rational dispatch and steady supply of natural gas resources can be effectively supported by accurate forecasting of the natural gas load. The accuracy of natural gas load forecasting is, however, low due to the fundamental characteristics of the non-stationary and non-linear natural gas load. Based on this, this paper proposes a new natural gas load forecasting model based on the fusion of VMD-SE and CNN-BiLSTM-Attention. First, the average instantaneous frequency method is used to determine the optimal K value of VMD, and then the sample entropy method is introduced to reconstruct the sub-sequence of VMD decomposition, which effectively reduces the computational overhead of the algorithm. Then, using CNN to mine the level information of multi-dimensional time series variables, using BiLSTM to mine the time series feature information, and introducing the Attention mechanism to give corresponding weight to different feature factors, highlighting the influence of key factors, the anticipated values of each reconstructed sub-series are superimposed to provide the final predicted value of the natural gas load. The model proposed in this paper has lower error than other forecasting models, can effectively improve the precision of natural gas load forecasting, and has a better forecasting effect, according to the results of establishing various forecasting models using the natural gas load data of one region of China as an example.

An advanced instantaneous frequency method for ground-penetrating radar cavity detection

Instantaneous frequency attributes of ground penetrating radar are extremely helpful in revealing cavities and thin layers, it is susceptible to noise, however, and it has limited resolution. This study develops a new method to resolve these issues. First, we transform trace data to obtain a high-resolution time-frequency representation by performing a multi-synchrosqueezing. Then an advanced ridge estimation method was proposed to extract the instantaneous frequency which improves the anti-interference performance of ridge tracking. The proposed method was evaluated by applying synthetic and field data. The results showed that the method has higher resolution and noise robustness compared with the conventional method results. It is helpful to assess the shape and filling material of the cavity by using the proposed method, extracting instantaneous frequency attribute, and analyzing the time-frequency characteristics of ground-penetrating radar data.

Filtering of cross spreads using multichannel singular spectrum analysis and instantaneous frequency methods

ABSTRACT. The orthogonal geometry of 3D seismic data acquisition generates cross-spreads, which are small subsets of multidimensional data. These subsets present unique properties, where ground roll and linear noises become geometrically easy to detect, and multidimensional filters play an essential role in seismic processing. In the present paper, we show the application of combined time-domain Recursive and Iterative Multichannel Singular Spectrum Analysis and average instantaneous frequency methods for random and coherent noise attenuation and enhancement of the reflections in the cross spread. The methodology starts decomposing the cross spread into a set of components, by the recursive-iterative Singular Spectrum Analysis method. The average instantaneous frequency method identifies the low-frequency areas associated with the ground roll to attenuate by muting and stacking each 3D component, where the instantaneous frequency values match the ground roll bandwidth; then the 3D volume filtering is performed by Multichannel Singular Spectrum Analysis, after NMO correction, enhancing the reflections and increasing the lateral coherence in filtered pre-stack seismic data. Numerical experiments using an example of a cross-spread from 3D land seismic data have shown excellent results of the extension of our methodology for random noise and ground roll attenuation in the cross-spread domain.Keywords: time-series analysis; seismic noise; image processing; Fourier analysis; spatial analysis; cross-spreads; interface waves. Filtragem sísmica de cross-spreads através da aplicação dos métodos análise espectral singular multicanal e frequência instantâneaRESUMO. A geometria ortogonal da aquisição de dados sísmicos 3D gera cross-spreads ou lancos cruzados, que são pequenos subconjuntos de dados multidimensional, os quais apresentam propriedades únicas, nos quais ruídos lineares e ground roll tornam-se geometricamente fáceis de serem detectados por filtros multidimensionais. Neste artigo apresentamos uma abordagem de filtragem no domínio do tempo que combina as aplicações do método Análise Espectral Singular e do método de obtenção da frequência média instantânea, que possibilita a atenuação do ground roll e o aumento da coerência lateral das reflexões. A metodologia se inicia com a decomposição dos dados em componentes, através do método Análise Espectral Singular recursiva e iterativa. Essa etapa e seguida da aplicação do método de frequência média instantânea, que permite identificar as áreas de baixa frequência associadas ao ground roll. Assim, efetuamos o silenciamento das amplitudes das componentes, nas áreas em que a frequência média instantânea corresponde a frequência do ground roll. Ao final, fazemos a correção de NMO e aplicamos o método Análise Espectral Singular Recursivo e Iterativo multicanal, que favorece o aumento da coerência lateral das reflexões no dado pré-empilhado. Experimentos numéricos usando um cross-spread de dados sísmicos 3D terrestres mostraram excelentes resultados.Palavras-chave: geofísica aplicada; processamento digital de sinais; processamento de dados sísmicos; métodos sísmicos.

Novel Fault Location for High Permeability Active Distribution Networks Based on Improved VMD and S-transform

Aiming at the problem of the inaccurate fault location in high-permeability active distribution network, a novel method of fault location for active distribution network based on improved variational mode decomposition (IVMD) and S-transform is proposed in this paper. Firstly, the judgment method of instantaneous frequency is adopted to determine the value of decomposition layers k . Meanwhile the algorithm of variational mode decomposition (VMD) is utilized to decompose the fault signal of traveling wave. Then, the kurtosis criterion is employed to select the appropriate intrisic mode functions (IMFS) for S-transform in order to obtain the S-matrix with higher resolution. The high-frequency components in the matrix are extracted to determine the arrival time for the head of the fault traveling wave. Finally, the fault distance can be calculated by the special distance formula without considering the velocity of the traveling wave. The simulations show that the proposed method can accurately measure the fault distance for the transmission lines in high permeability active distribution network, and the measurement error is limited within 200m, which verifies the accuracy and effectiveness of the proposed algorithm.

Investigation of zonal flows by using the collective scattering measurement of density fluctuations

The poloidal rotation velocities in the core plasma region are studied using the instantaneous frequency method (IFM) with the density fluctuations measured by the CO2 laser collective scattering diagnostics on the HT-7 tokamak. A coherent mode is observed in the fluctuations of poloidal velocities with the mode frequency from 10 to 20 kHz. It is identified as geodesic acoustic mode (GAM) zonal flow with poloidal symmetry (m = 0) and its mode frequency coinciding with the theoretical expected GAM frequency. The nonlinear interactions are investigated by applying the envelope analysis on the density fluctuations. The results confirm that the envelope modulation in the high frequency density fluctuations only comes from the shearing by GAM. The comparison between IFM and envelope analysis is also discussed.

Differential t* measurements via instantaneous frequency matching: observations of lower mantle shear attenuation heterogeneity beneath western Central America

SUMMARY We infer shear attenuation in the lower mantle by using the method of instantaneous frequency matching to calculate differential t* between core-reflected ScS and direct S (δt*ScS-S). The instantaneous frequency at the envelope peak of a seismic phase is related to the average Fourier spectral frequency of that phase. To estimate δt*ScS-S for a given trace, we first calculate the instantaneous frequency at the envelope peak of S and ScS. The trace is then attenuated through convolution with a suite of t* operators until the instantaneous frequency at the envelope peak of the seismic phase with the initially larger instantaneous frequency matches the value of the smaller instantaneous frequency from the initial calculation. The differential t* operator required to accomplish the match is then δt*ScS-S. We also calculate δt*ScS-S from the slope of the spectral ratio of windowed ScS and S. Both the spectral ratio and instantaneous frequency methods produce consistent results for high signal-to-noise ratio synthetic waveforms with S and ScS well separated in time, and where there are no other interfering phases. The instantaneous frequency method gives more stable results for low signal-to-noise ratio waveforms, and where S and/or ScS are affected by other interfering seismic phases. The instantaneous frequency matching method is applied to broadband data from South American earthquakes recorded in California that sample the lower mantle beneath Central America and the Cocos plate. δt*ScS-S ranges from approximately –4 to 2 s, but are predominately negative, suggesting S is more attenuated than ScS for these data. We estimate the possibly contaminating effects of 3-D velocity heterogeneity on δt*ScS-S through analysis of synthetic seismograms computed for a cross-section through a tomographically derived model of global shear wave heterogeneity, using an axisymmetric finite difference algorithm. Synthetics for path geometries of our data predict a δt*ScS-S of ∼0.2 s. We investigate the effect of seismic anisotropy by comparing δt*ScS-S before and after a subset of the data were corrected using splitting parameters obtained by linearizing the particle motion of the S and ScS phases. The rms error of the residuals between the corrected and uncorrected δt*ScS-S is ∼0.2 s. Neither of these efforts, however, match the large negative observed δt*ScS-S values, suggesting the mid-mantle beneath western Central America is in fact much more attenuating than the lowermost mantle below it, or S may be broadened by out-of-plane propagation effects, involving the remains of the Farallon plate containing stronger velocity heterogeneity than is imaged by seismic tomography.

Sinusoidal modeling for nonstationary voiced speech based on a local vector transform

A voiced speech signal can be expressed as a sum of sinusoidal components of which instantaneous frequency and amplitude continuously vary with time. Determining these parameters from the input, the time-varying characteristics are crucial error sources for the algorithms, which assume their stationarity within a local analysis segment. To overcome this problem, a new method is proposed, local vector transform (LVT), which can determine instantaneous frequency and amplitude for nonstationary sinusoids. The method does not assume the local stationarity. The effectiveness of LVT was examined in parameter determination for synthesized and naturally uttered speech signals. The instantaneous frequency for the first harmonic component was determined with an accuracy almost equal to that of the time-corrected instantaneous frequency method and higher accuracy than that of spectral peak-picking, autocorrelation, and cepstrum. The instantaneous amplitude was also determined accurately by LVT while considerable errors were left in the other algorithms. The signal reconstructed from the determined parameters by LVT agreed well with the corresponding component of voiced speech. These results suggest that the method is effective for analyzing time-varying voiced speech signals.

Elasticity Analysis by MR Elastography using the Instantaneous Frequency Method

Elasticity Analysis by MR Elastography using the Instantaneous Frequency Method

Sediment classification based on impedance and attenuation estimation

This paper presents a remote marine sediment classification model that can be implemented in real time while underway in a survey. The model is based on the estimation of impedance and attenuation of subbottom sediments from normal incident reflection seismograms. A robust impedance inversion model utilizing layer detection was developed which is implemented with significantly less computation when compared to full inverse methods, and hence runs in real time. A new ‘‘weighted least-squares fitting’’ procedure is proposed for evaluating the impulse response of the sediment column. The acoustic attenuation in the sediment is determined by measuring the frequency shift of the pulse spectrum using an instantaneous frequency method. The impedance inversion model requires an input of the estimated attenuation to account for the loss in signal energy due to absorption. A recently developed model relating sediment acoustic properties to sediment physical properties for a given depositional environment is employed. The constants appearing in the classification model are evaluated using measurements from a few core samples. Impedance and attenuation estimates are used to predict sediment properties such as porosity, density, mean grain size, and sound speed. The reflection data for the present study were acquired by a linear wideband (full spectrum) sonar. It is used because of its linear system components, high resolution, and wide bandwidth. Analysis of acoustic data acquired by the full spectrum sonar demonstrates the feasibility of remote acoustic seafloor sediment classification.

Sonar attenuation modeling for classification of marine sediments

An attenuation-based model for classification of marine sediments is developed for the chirp sonar operating in the frequency range of 2–10 kHz. A relaxation-time model is proposed that combines the various dissipative energy loss mechanisms of sound in marine sediments into a single parameter. Historical data were analyzed by converting attenuation values reported in ‘‘dB/m@kHz’’ to a single relaxation time value. Analysis of these previous attenuation measurements supports the use of a relaxation-time model. Based on this large collection of data, an empirical equation is developed that relates relaxation time to grain size (in phi units). Using this model, very little phase dispersion is observed for a correlated chirp pulse traveling through 40 m of sand, silt, or clay. Yet, this is not so for a pulse in the ultrasonic frequency range (0.2–1.0 MHz) traveling through only 10 cm of clay. Here, significant dispersion is noted. Because of the unique Gaussian-like shape of the correlated chirp pulse power spectrum, pulse elongation due to attenuation is minimized. Using the center frequency shift in the pulse spectrum, a new ‘‘instantaneous frequency’’ method of attenuation estimation is proposed that overcomes the problems associated with interfering reflections. Based on the relaxation-time model, the correlated chirp pulse was synthetically attenuated to establish a relation between the relaxation time and the center frequency shift. In situ sediment-type predictions from chirp sonar data using the instantaneous frequency method and analyses of core samples taken in the Narragansett Bay, Rhode Island are in good agreement.

A DSP Chip-Based Processor for Ultrasonic Bloodflow Doppler Signals

An ultrasonic Doppler method, by which blood flow velocities can be detected, is noninvasive and effective means for diagnosis of cardiovascular disease. In this paper, a Doppler signal processor for estimating the blood flow velocity and a color Doppler system for imaging the velocity profile are described. The processor using a programable DSP chip is developed to process the sensed Doppler signal by both instantaneous frequency method and FFT power spectrum method. In preliminary clinical trials, a new visualizing method of a cardiac structure is proposed and a clear imaging result is obtained.