用分数阶微分实现时频重叠多模式兰姆波的模式分离

为了分离时频重叠多模式超声兰姆波,提出了一种用分数阶微分理论实现多模式兰姆波模式分离的方法。以时频重叠的S1和A1模式混合信号为例,用赛利斯分布作为幅值谱的模型,首先对信号做频散补偿,由补偿后信号幅值谱分数阶微分推导了幅值谱特征参数的计算式并根据信号模型重建幅值谱,然后结合兰姆波的频散特性推导出对应的相位谱,并通过幅值谱和相位谱重构各模式的信号,实现模式分离。对1 mm钢板中仿真时频重叠的S₁和A₁模式信号分离结果显示分离出信号的幅值和带宽相对误差小于6%,中心频率相对误差小于0.25%。实验结果也证实了方法的可行性。因此当混合信号幅值谱不完全交叠时,本方法可以实现多模式兰姆波信号的分离,有助于多模式兰姆波频散信号的分析和识别。      

Separation of multimode Lamb waves overlapped in time and frequency domains by using fractional differential

To separate multimode Lamb wave overlapped both in time and frequency domains,a multimode Lamb wave signal separation method by using fractional differential is proposed.The Tsallis function is used as the model of the amplitude spectrum.The amplitude spectra of Lamb wave signals are divided into fractional order differential.The characteristic parameters of each mode are extracted by using the polynomial between the maximum amplitude and the differential order as well as the polynomial between the peak frequency and the differential order.The corresponding phase spectrum of each mode is derived from the dispersion characteristics.The signal of each mode is constructed through the amplitude spectrum and phase spectrum.The simulated results of S1 and A1 modes in a 1 mm-thick steel plate show that the relative errors of amplitude and bandwidth of both modes are less than 6%,and that the relative errors of central frequency of both modes are less than 0.25%.Therefore,this method could be used to separate the time-frequency overlapped multimode Lamb wave signals.It is helpful for the analysis and recognition of multimode Lamb wave signals.     

Identification of acoustic emission source mechanisms by energy spectrum spectrum analysis

The purpose of energy spectrum analysis is to calculate random signal parameters which, when considered statistically, may show characteristic differences between similar signals and hence indicate different source mechanisms generating the signals. A computer programme has been written to compute mean and median frequency, mean amplitude spectral density, mean energy spectral density and amplitude spectrum variance. Plots of amplitude spectra, normalized energy spectra and energy difference spectra (the difference between pairs of spectra) may also be selectively generated by the programme.The results obtained were from real data, from specially prepared reactor-grade zirconium test pieces.     

Estimation of ultrasound attenuation and dispersion using short time Fourier transform

Determination of the acoustic attenuation and dispersion has important applications in ultrasound tissue characterization and non-destructive material testing. Current signal processing methods Fourier transform of ultrasound signals to get the spectra of amplitude and phase to estimate respectively the attenuation and dispersion of a given medium. These methods are frequency domain method and obsessed with ambiguity issue in the phase unwrapping calculation. Conventional ultrasound velocity measuring method detects the time of arrival of a pulse (or echo) signal, which is a time domain method to compute group velocity (not phase velocity). This paper presents a novel approach based on the short time Fourier transform (STFT)--a time-frequency analysis, to estimate the ultrasonic dispersion and attenuation. Only the amplitude information of the pulse-signal spectra is used. Based on the time-frequency presentation, the attenuation coefficient of the signal is obtained by computing the amplitude decay of pulse spectrum in time domain, while phase velocities are obtained based on the "time-of-flight" (TOF) of the mono frequency component of the pulse signals. As a result, we eliminate the ambiguity issue in phase angle calculation. Furthermore, the proposed method makes the phase velocity pedagogically intuitive for novice users. The paper presents experiments to evaluate demonstrate the performance of the proposed method.     

Effect of spectrum processing procedure on the linearity of EPR dose reconstruction in tooth enamel

Electron Paramagnetic Resonance (EPR) spectroscopy with tooth enamel is a widely used method of dosimetry. The accuracy of EPR tooth dosimetry depends on the spectrum processing procedure, the quality of which, in its turn, relies on instrumental noise and the signals from impurities. This is especially important in low-dose evaluation. The current paper suggests a method to estimate the accuracy of a specific spectrum processing procedure. The method is based on reconstruction of the radiation-induced signal (RIS) from a simulated spectrum with known RIS intensity. The Monte Carlo method was used for the simulations. The model of impurity and noise signals represents a composite residual spectrum (CRS) obtained by subtraction of the reconstructed RIS and the native background signal (BGS) from enamel spectra measured in HMGU (Neuherberg, Germany) and IMP (Yekaterinburg, Russia). The simulated spectra were deconvoluted using a standard procedure. The method provides an opportunity to compare the simulated “true” RIS with reconstructed values. Two modifications of the EPR method were considered: namely, with and without the use of the reference Mn²⁺ signals. It was observed that the spectrum processing procedure induces a nonlinear dose response of the reconstructed EPR amplitude when the height of the true RIS is comparable with the amplitudes of noise-like random splashes of CRS. The area of nonlinearity is below the limit of detection (DL). The use of reference Mn²⁺ signals can reduce the range of nonlinearity. However, the impact of the intensities of CRS random signals on nonlinearity is two times higher than the one observed when the reference signals were not used. The reproducibility of the software response is also dependent on both the amplitude of the CRS and the use of a reference signal, and it is also two times more sensitive to the amplitude of the CRS. In most EPR studies, all of the data are used, even those for which the dose value is lower than the DL. This study shows that low doses evaluated with the help of linear dose–response can be significantly overestimated. It is recommended that linear dose response calibration curves be constructed using only data above the DL. Data below the DL should be interpreted cautiously.     

频域稀疏采样和激光成像方法

激光的单色性和自然图像频谱稀疏且集中在低频区间的特点,使图像频谱稀疏采样成像成为可能.基于小规模激光探测器,引入参考激光,本文提出了频域稀疏采样激光成像方法.介绍了频域稀疏采样激光成像的原理和成像系统结构,推导了激光回波重构复频谱的表达式,给出了重构频谱和复图像的仿真结果并分析了信号参数对重构效果的影响,同时采用相干系数、均方误差和结构相似度来评价其重构效果.规模为256×256的激光回波复图像仿真表明, 5个拼接1/4×1/4规模频域探测器组成的近似十字型稀疏采样结构,在约31.25%(5/16)的频域稀疏采样条件下,仍可获得较好的重构频谱和重构复图像.     

Measurements of Time-Varying Characteristics of Optical Signals and Inhomogeneities of Tested Substances with Additional Phase Modulation

The problem of investigation of the amplitude and phase structure of a time-varying probing optical signal and the structure of time-varying inhomogeneities of a substance tested by this signal is considered. The analysis is concerned, in particular, with determination of the structure of signals and processes with resolution in the pico- and femtosecond range. The scheme used for the analysis is based on registration of four spatially separated spectra of the studied radiation. The spectra are formed in a four-channel scheme with a twin-wave Michelson interferometer and a spectral device. Modulators based on electrooptical crystals (perovskites) are placed in the channels. The sum spectra are formed: without modulators, with the effect of either of the modulators, and with both of them affecting the radiation. The effect of the studied substance implies either modulating the radiation (in this case it is described by multiplication) or redistributing the radiation (then it is described by convolution).     

一种基于广义Duffing振子的水中弱目标检测方法

海洋环境中,在水下目标的线谱频率未知或者目标辐射噪声的连续谱很弱时,很难实现水中弱目标的准确检测,本文提出基于广义Duffing振子检测系统的水下目标辐射噪声检测方法.通过对传统周期扰动的Duffing振子信号检测系统的分析和推广,提出了一种可输入非周期、非平稳信号的广义Duffing振子检测系统,可检测输入的无先验信息目标信号.为实现广义Duffing振子系统运动状态的精确、有效判断,提出了一种相空间图形的离散分布列计算方法,通过类网格函数实现了利用统计复杂度对系统输出的嵌入式表征,从而实现了无先验信息时的水中弱目标的嵌入式检测.相同条件下与传统检测方法仿真对比可知,本文提出的方法可以检测到更低信噪比下的目标,并能满足水中检测实时性要求.     

Spectral shape discrimination of narrow-band sounds.

Measurements are reported on the detectability of signals added to narrow-band sounds. The narrow-band sounds had a bandwidth of 20 Hz and were either Gaussian noise with flat amplitude spectra or sets of equal-amplitude sinusoidal components whose phases were chosen at random. Four different kinds of sinusoidal signals were used. Two signals produced symmetric changes in the audio spectrum adding a component either at the center of the spectrum or at both ends. The other two signals produced asymmetric changes adding a component at either end of the spectrum. The overall level of the sound was randomly varied on each presentation, so that the presence of a signal was largely unrelated to the absolute level of the signal component(s). A model is proposed that assumes the detection of the symmetric signals is based on changes in the shape of the power spectrum of the envelope. Such changes in the envelope power spectrum are probably heard as changes in the "roughness" or "smoothness" of the narrow-band sound. The predictions of this model were obtained from computer simulations. For the asymmetric signals, the most probable detection cues were changes in the pitch of the narrow-band sound. Results from a variety of different experiments using three listeners support these conjectures.     

Linear synchronization and circuit implementation of chaotic system with complete amplitude control

Although chaotic signals are considered to have great potential applications in radar and communication engineering,their broadband spectrum makes it difficult to design an applicable amplifier or an attenuator for amplitude conditioning.Moreover, the transformation between a unipolar signal and a bipolar signal is often required. In this paper, a more intelligent hardware implementation based on field programmable analog array(FPAA) is constructed for chaotic systems with complete amplitude control. Firstly, two chaotic systems with complete amplitude control are introduced, one of which has the property of offset boosting with total amplitude control, while the other has offset boosting and a parameter for partial control. Both cases can achieve complete amplitude control including amplitude rescaling and offset boosting. Secondly,linear synchronization is established based on the special structure of chaotic system. Finally, experimental circuits are constructed on an FPAA where the predicted amplitude control is realized through only two independent configurable analog module(CAM) gain values.     

快速正交搜索算法在水声信号处理中的应用*

信号的谱估计技术作为一种十分重要且应用广泛的信号分析处理手段,对其性能的不断提升和改进一直是水声信号处理领域研究的重点和热点。对此,该文将快速正交搜索算法应用于水声信号的谱估计中,通过隐式正交对参数进行搜索,实现对信号频率、幅度、相位的估计。仿真和实验数据处理结果表明,相较于传统的谱估计方法,该方法能稳定且准确地估计水声信号的多个参数,获得频率分辨率较高的谱估计结果。     

Bispectrum and reconstruction of modulation signal extracted from ship-radiated noise

I.IntroductionRecentyearshigh-ordcrstatisticshavebeguntofindwideapP1icabilityindiversefie1dssuchassonar,radar,plasmaphysics,biomedicine,seismicdataprocessing,harmonicretrieva1,adaptivefi1teringandarrayprocessingl'-'l=Thcsestatisticsnotonlyrevea1amp1itudeinforma-honaboutaprocess,butalsorevca1phaseinformation.Insigna1processing,thesearethreemotivationsbehindtheuseofhighcr-ordcrspectra:1.TosupprcssGaussiannoiseofunknownspectra1charactcristicsindctcction,paramcterestimation,andsignalreconstructi…     

Application of factor analysis to elemental detection limits in sputter depth profiling

Factor analysis of Auger spectra acquired during sputter depth profiling is superior to the conventional peak-to-peak amplitude method for determining elemental compositions, especially when the Auger signal strength is near the detection limit. The reason for the improvement is that factor analysis utilizes information from all the data channels in the Auger spectrum while the peak-to-peak amplitude method uses information from only two data channels. In addition, factor analysis can separate much of the spectral noise from the signal during processing, while peak-to-peak amplitude additively measures signal plus the range of the spectral noise. Procedures can also easily account for interfering species, even when their spectra are not known. In one example, at least a factor of five improvement in the minimum detection limit was achieved. In application to secondary ion mass spectrometry, only a marginal improvement in detection and precision was achieved. This is because our existing procedure (peak area measurement) already utilizes spectral information content fairly efficiently. However, factor analysis is capable of handling spectral interferences that the peak area method cannot.     

Blind dereverberation in the deep sea

Experimental data are presented on the blind dereverberation of the noise-type signal generated by a sound source moving in the deep sea. The noise emitted by a towed source is received by a drifting hydrophone with a high excess of the signal over the ambient noise, which results in a stable interference pattern of high contrast. The observed interference structure indicates that the signal arrives at the receiver along different paths. With the use of the blind dereverberation technique for the signal processing and without any a priori information on the properties of the propagation channel, the parameters (the delay, the amplitude, and the phase) of each of the seven interfering signals are determined. From the data obtained, the frequency response of the filter that provides a strong suppression of the reverberation is calculated and the spectrum of the received signal is obtained without any interference distortions.     

On the spectrum of large-scale inhomogeneities of the upper ionosphere

The possibility of measuring the large-scale turbulence structure of the upper ionosphere by vertical and oblique short-wave (SW) radio-sounding techniques is considered. General expressions have been derived for the phase fluctuation spectrum of a short-wave signal reflected at the ionospheric layer with an arbitrary regular permittivity profile and given spectrum of inhomogeneities. We have analyzed a number of particular cases which are most typical of phase measurements in the vertical and oblique SW radio-sounding of the randomly inhomogeneous ionosphere. It is shown that when these methods are used the phase fluctuation spectra of reflected signals may critically depend on the form of the ionospheric electron density profiles. The correct interpretation of the measurement data requires use of stations of synchronous vertical and oblique sounding to obtain proper ionograms and calculate the current spectra of a regular permittivity distribution of the ionosphere. Specific difficulties in interpreting the phase measurements of ionospheric inhomogeneity spectra by vertical and oblique radio-sounding methods are mentioned.Radiophysical Research Institute, Nizhny Novgorod. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 38, No. 7, pp. 653–659, July, 1995.     

叠栅条纹信号细分误差的一种动态补偿方法

缺乏有效的误差补偿方法足制约长光栅测最精度提高的关键原因之一.提出一种动态的误差补偿方法.可以消除由直流漂移、两路信号不等幅和非止交导致的细分误差.其原理是跟踪光栅信号在一个周期上的8个特征值点(正余弦信号的过零点及绝对值交点),从特征值点的幅度值中首先分解出正弦信号的直流漂移误差.对其进行补偿;然后继续跟踪补偿后的信号.从中义能分解出余弦信号的直流漂移误差.再补偿.再跟踪.又能依次分解出不等幅误差和非正交误差.最多只需要3个光栅信号周期,就能对三种误差依次实现补偿.分析了谐波对该方法的影响并提出r改进措施.实验证实了该方法的有效性.     

The contributions of amplitude-and phase-sensitive detection to the synchronous demodulation in a RF SQUID magnetometer

It is known that the tank-circuit voltage of the rf SQUID carries information about the magnetic flux to be detected in amplitude and phase. The coherent demodulationtechnique utilizes mixing circuits to shift the rf tank voltage spectrum to dc without loss of any signal-information both in amplitude and phase (AM & Pm-detection). Vice versa such a combined detection can be devided into two several detection channels, amplitude sensitive detection (AM) and phase sensitive detection (PM). The contribution of each single mode to the combined detection AM & PM is analysed theoretically in the limit of small magnetic signals and measured in special rf circuits of the magnetometer, which apply PLL-techniques. The influence of feedback is also calculated. For refined studies of the interesting parameters the reference signal of the rf mixer allows to be phase-shifted by an arbitrary amount. All three modes of detections are sketched in diagrams as magnetometeroutput versus phase-shift of that reference signal. In addition, noise analysis is included and measured for vanishing signal. Basic formulas are derived for signal-to-noise ratios. A correlation coefficient is defined for recording correlated noise sources between AM and PM, whereby the possibility of S/N-improvement is pointed out. By computer support the graphs of equations are fitted to measured data with least mean-square deviation. More logical than functional circuit diagrams complete the insight into the treated basic ideas.     

Extraction and enhancement of spectral structure by the cochlea

The intensity dependence of signal processing in the cat cochlea was studied in responses of single auditory-nerve fibers for harmonic complexes having various amplitude and phase spectra. Analyses were based on information present in temporal discharge cadences, and they consisted of assessing Fourier spectra of period histograms synchronized to the period of the waveform fundamental. At low intensities, response spectra resembled filtered versions of the stimulus spectrum, with the amounts of filtering being determined by fibers' tuning curves. At high intensities, response spectra exhibited nonlinear behavior and could differ dramatically from spectra obtained at low intensities. The high-intensity response typically emphasized one or more aspects of the stimulus spectrum. When the stimulus possessed equal component amplitudes and phases, the features that were emphasized at high intensities were the high- and low-frequency edges of the spectrum, and when the component at fiber CF was changed in phase or amplitude relative to the others, fibers primarily signaled the presence of the phase- or amplitude-shifted component. Many of the intensity-dependent changes in response spectra are accounted for by considering the effects of the compressive input-output nonlinearity operating at or peripheral to the hair-cell level on the temporal waveform.