Phase FFT Research Articles

Precision improvement in laser self-mixing nanoparticle sizing with all phase FFT amplitude correction

As a well-known noncontact optical sensing technique, laser self-mixing interferometry (SMI) exhibits outstanding merits of low-cost, self-alignment, compactness, and high sensitivity, and it has been applied to typical geometrical quantity measurements, tomography, object imaging, as well as nanoparticle sizing. In SMI nanoparticle detection, as a result of Brownian motion, laser beam stochastically interacts with each particle in the illuminating volume, producing self-mixed signals with Lorentz shape power spectra, whose spectral broadening width is directly related with particle sizes. In general, FFT is always the first choice to obtain signals’ power spectra, but due to the influence of spectrum leakage, the heights of spectral lines may rise or fall and then change original Lorentz shapes and further increase sizing errors. Here, an all phase FFT (apFFT) method has been proposed to greatly suppress spectrum leakage, correct spectral line heights and further improve nanoparticle sizing errors for Rayleigh scattering cases. The apFFT method proposed is advantageous to developing precise SMI particle sensors or instruments, which may be applicable to chemical or medical applications.

High Accuracy and Low Complexity Frequency Offset Estimation Method Based on All Phase FFT for M-QAM Coherent Optical Systems

The traditional fast Fourier transform based frequency offset estimation (FFT-FOE) estimates the frequency offset by searching the spectral peak of the signal after the fourth power operation, which is suitable for multiple modulation formats. But the accuracy of FOE is limited by the number of FFT points. In this paper, we propose a high accuracy and low complexity FOE algorithm based on all phase FFT (APFFT-FOE). The accuracy of FOE can be improved effectively with lower additional computational complexity. Simulation results show that the mean square error of APFFT-FOE is reduced by more than one order of magnitude compared with the FFT-FOE. Compared with other FOE algorithms that can achieve the same accuracy, the additional computational complexity required by APFFT-FOE is reduced by more than 50 $\%$ . Finally, the APFFT-FOE is experimentally verified with 20 GBaud 16/64-QAM modulation signal. The experimental results show that the required OSNR for 16-QAM signal to reach 6.7 $\%$ hard-decision forward-error correction is relaxed by 0.23 dB. For 64-QAM signal, the required OSNR at 20 $\%$ soft-decision forward-error correction threshold is relaxed by 0.68 dB.

A Detection Method of Dense Harmonics/Inter-harmonics Based on Improved All-phase Time-shifting Method and ZoomFFT

Aiming at the complex situation of intensive harmonics/inter-harmonics in power signals, this paper proposes an analysis method based on improved all phase time shift phase difference method and ZoomFFT. Firstly, the Hankel matrix of the input signal is constructed, and the TLS-ESPRIT algorithm is used to obtain the frequency components in the signal. The relationship between the peak spectral line and the frequency offset in the all phase time shift method is derived. The amplitude information of the input signal is calculated. The phase information of the input signal is obtained by analyzing the “phase invariant” characteristic of the all phase FFT spectrum. The frequency interval of adjacent frequencies is used to judge whether there is density. If there are intensive harmonics/inter-harmonics, TLS-ESPRIT method is used to calculate the center frequency of the dense spectrum and construct a complex analytic band-pass filter to improve the ZoomFFT method to extract the frequency and amplitude information of the signal at the dense spectrum; If there is no intensive harmonic/inter-harmonic, the improved all phase time shift method is used to extract the parameters of the input signal. Simulation results show that the proposed algorithm can effectively and accurately extract the frequency, amplitude and phase parameters of dense harmonics/inter-harmonics under the conditions of multiple dense spectrum, fluctuation of fundamental frequency and noise interference.

Fast Acquisition Scheme of the Spread Spectrum Signals for Satellite Communications

A four-channel parallel acquisition scheme combining partial matched filters and fast Fourier transforms (PMF-FFT) is proposed for the fast acquisition of the spread spectrum signals in satellite communication terminals installed into the offshore buoys with the high-dynamic movement, which is used tofinish data communication missions between the buoys and the satellite. Compared with traditional code phase FFT scheme, the new scheme reduces the maximum acquisition time to 26.5% and the maximum computation amount to 46.9%. It also improves about 4 times in the frequency resolution and 1.6 dB in the receiving sensitivity at the expense of computation complexity compared to PMF-FFT scheme. The parallel PMF-FFT scheme greatly reduces scallop loss, thus ensuring acquisition sensitivity. The parallel PMF-FFT scheme within the satellite communication terminal can ensure the fast and stable tracking of satellite signal by the violently moving antenna within 20 ms under level-4 sea state.

Improved Correlation Identification of Subsurface Using All Phase FFT Algorithm

Improved Correlation Identification of Subsurface Using All Phase FFT Algorithm

Nonlinear dynamics of a viscoelastic sandwich beam with parametric excitations and internal resonance

Nonlinear dynamical behaviors of an axially accelerating viscoelastic sandwich beam subjected to three-to-one internal resonance and parametric excitations resulting from simultaneous velocity and tension fluctuations are investigated. The direct method of multiple scales is adopted to obtain a set of first-order ordinary differential equations and associated boundary conditions. The frequency and amplitude response curves along with their stability and bifurcation are numerically studied. A great number of dynamic behaviors are presented in the form of phase portraits, time traces, Poincare sections, and FFT power spectra. Due to modal interaction, various periodic, quasiperiodic, and chaotic behaviors are displayed, depending on the initial conditions. The largest Lyapunov exponent is carried out to determine the midly chaotic response by the convergent form of exponents. Numerical results show various oscillatory behaviors indicating the influence of internal resonance and coupled effects of fluctuating axial velocity and tension.

Effect of boundary conditions on the non-linear forced vibration response of isotropic plates

The effect of boundary conditions on the linear and nonlinear steady state forced vibration response of rectangular isotropic plates have been investigated. For thin components subjected to dynamic forces the amplitude of vibration is comparable to its thickness which requires inclusion of nonlinear terms in the strain displacement relation. In the present work the non-linear governing equations of motion have been obtained using standard finite element procedure based on displacement field of FSDT. The governing equation of motion is solved using modified shooting method. The unstable portions of frequency response curves are obtained using continuation algorithm [1]. The non-linear responses are compared with linear response and very large difference between the two has been obtained. Unlike frequency domain methods such as Harmonic balance and IHB the present method does not require any assumption on participating modes. The time history, phase plane plots and FFT of the response have also been obtained to explain the physics of the peculiar nature of the nonlinear response.

APOFDM system design based on all phase FFT technology

The traditional OFDM system as an important part of current wireless communication technology, its advantages are obvious, but one of shortcoming is easily affected by the frequency deviation. An effective solution is to improve data signal processing technology in the front of the system, thus can reduce the effects of system faults and improve the performance of the system. All phase data processing under the research idea of it is in this, after 20 years of research and development, now all phase FFT technology has been applied to image processing, signal processing, signal spectrum analysis, wireless communication transmission, etc. In this paper, using all phase FFT processing technology and detailed the APOFDM, Finally, using MATLAB simulation tools to analyze its advantages.

Research of Spectrum Correction Method Based on All Phase FFT for Induction Magnetometer

基于法拉第电磁感应定律的感应式磁力仪是用于测量低频磁场的空间探测仪器,常具有在轨FFT频谱分析功能,直接获得波动磁场的频率及幅度等信息.利用FFT方法对截断信号进行计算时,整周期采样会产生频谱泄露和栅栏效应,频谱信息产生偏差,而影响实时监测磁场变化的准确性.全相位FFT与常规FFT相比,有相位不变性和良好的抑制频谱泄露能力.采用基于全相位FFT的时移相位差方法(apFFT/apFFT)校正在研的某卫星感应式磁力仪直接采集的波形数据.仿真和实验结果表明,apFFT/apFFT方法可有效提高感应式磁力仪低频磁场测量的频谱准确性.研究工作为提高感应式磁力仪科学数据的应用水平奠定了基础,为下一代星载感应式磁力仪在轨频谱分析提供了一种可能的新方法.

Two-frequency parametric excitation and internal resonance of a moving viscoelastic beam

In this paper, analytical and numerical approach is applied to find the steady-state and dynamic behaviors of an axially accelerating viscoelastic beam subject to two-frequency parametric excitation in presence of internal resonance. Direct method of multiple scales is employed to solve the cubic nonlinear integro-partial differential equation. As a result, the governing equation of motion is reduced to a set of nonlinear first-order partial differential equations. These equations are solved through continuation algorithm approach to find the frequency and amplitude response curves and their stability and bifurcation. The system reveals the presence of Hopf, saddle node, and pitchfork bifurcations. The dynamic bevavior of the system is estimated through phase portraits, time traces, Poincare maps, and FFT power spectra obtained via direct time integration. The evolution of maximum Lyapunov exponent reveals the system parameter where the dynamic response changes from stable periodic to unstable chaotic motion of the system.

Self-mixing interferometry based on all phase FFT for high-precision displacement measurement

Self-mixing interferometry is an extreme simple and compact laser technique to develop non-contact displacement sensors. In order to enhance the precision of this type of sensor, an improved FFT algorithm, based on all phase FFT instead of conventional FFT, has been proposed to provide a phase reference for self-mixing displacement measurement system which has only single light path and lacks reference. The principle and the experimental realization of the proposed algorithm have been presented. The operation mechanism utilizes all phase FFT, which can estimate the phase from signal accurately, to achieve phase reference when the external target is held stationary and then compensate this reference to the phase when the target starts to move. Resultant displacement value reflects the actual position of the target. Reconstruction errors are on the order of nanometers in the displacements ranging from 100nm to 1μm. Therefore, the proposed method can find application in displacement measurement in industrial and scientific environments.

Calculation of Lumped Parameter of Two-Port Network for Volume Conduction Energy Delivery

Skin electrode unit is the channel through which energy can be transferred to the implanted device by volume conduction. The unit can be equivalent to lumped circuit, but so far there are no appropriate calculation methods of these circuit parameters. In this paper, the field- circuit coupling model of skin electrode unit is established to compute the voltages and currents at electrode ports, then their amplitudes and phases are extracted by using all phase FFT spectrum analysis, at last the equivalent impedance parameters of the skin electrode unit are calculated by the application of variable load method. These impedance parameters can be used for optimizing the volume conduction energy delivery system.

Application of Two-dimensional Wavelet Transformation to Analysis of Deformed Gratings

Many methods of measuring the three-dimensional shape of objects have been proposed. For noncontact measurement optical techniques, moire and grating projection methods are desired. Their measurement sensitivity depends on grating pitch and illumination angle. Therefore, the accuracy of measurement is low. To raise the accuracy, a suitable analytical method is necessary. The phase shift, FFT and wavelet methods are used for the analysis of fringes or modulated gratings. The phase shift method is suitable for a static analysis because several images recorded at different times are used. The FFT and wavelet methods are suitable for dynamic analysis because only one image is used. In the FFT method, the spatial resolving power is low. On the other hand, the spatial resolving power in the wavelet method is chosen automatically according to the pattern of the image. When the image pattern is used for analysis by the one-dimensional wavelet method, the pattern is analyzed along many lines. The shape of the whole surface of the object is analyzed by connecting the phase between adjacent lines. Therefore, the analytical process is difficult.In this study, we focus on the grating projection method, and the analysis by a two-dimensional wavelet method is proposed. In this analytical method, the frequency, direction and phase of the modulated grating were obtained continuously, and the phase connection in the two-dimensional image analysis could be realized.

Irregular Behavior in the Light Variations of 29 Cyg

After reviewing the general observational properties of the Lambda Bootis star 29 Cygni, we study samples of its light curve and apply the phase space and FFT tools to investigate the nature of its light curve irregularities.

Irregular Behavior in the Light Variations of 29 Cyg

AbstractThe phase space and FFT tools are applied to investigate the irregular behavior of the existing light curves of the λ Boo star 29 Cyg.

Chaos in stimulated Raman scattering

Coherent state technique and maximal Lyapunov exponent method are used for the study of deterministic chaos in a system governing stimulated Raman scattering. The influence of the external pumping on dynamics of the system is investigated. Phase portraits and FFT spectra are presented.