基于MATLAB语言设计的电生理信号分析系统

MATL AB语言以其强大的数据处理能力和卓越的信号分析性能在计算机辅助分析、设计、仿真等领域得到广泛的应用 ,人体电生理信号是隐含疾病信息的重要信号 ,由于该信号在时域上的复杂性 ,往往需要借助于现代信号分析技术手段 ,对电生理信号进行频谱分析 ,辅助医生进行临床诊断或研究 ,文章通过对电生理信号的特征分析 ,设计了基于 MATL AB语言的电生理信号分析系统 ,系统可对电生理数字信号进行时域和频域分析     

水下高速活动目标辐射噪声模拟器的设计与实现

水下活动目标辐射噪声模拟技术被广泛应用于水下目标信号源生成、目标识别算法研究、声呐训练模拟设备和水声对抗设备研制等领域。为了给这类研究工作提供快速、便捷且有效的测试方法,文中利用水下高速运动目标的航行参数及其辐射噪声级,建立了一个数学模型用于计算目标通过一个相对固定测量点时接收到的辐射噪声级,据此设计并实现了水下高速活动目标辐射噪声模拟器。该模拟器采用人工方式设置工作参数,由嵌入式计算机在线加载,实时计算后产生航行辐射噪声模拟信号,最后通过水声信号发射机进行声输出。实验表明,该设计合理可行,满足使用要求。     

基于小波变换的结构模态参数识别

及时、准确地识别出结构的模态参数是结构健康监测与损伤识别的重要前提。小波分析是众多识别方法中较优越的一种，因其在时一频两域都具有表征信号局部特征的能力，近年来这一方法在线性及非线性系统的参数识别中开始应用。探讨了基于小波脊（Ridge）与小波骨架（Skeleton）的模态参数识别方法，针对小波变换中遇到的边端效应问题，提出了基于自回归滑动平均模型（ARMA）的“预测延拓”方法，并以美国土木工程师学会（ASCE）提供的Benchmark模型为例进行了数值模拟。结果表明，本文提出的方法可以有效地抑制小波边端效应，通过小渡变换可以准确地识别出结构的模态参数。     

Bayesian versus Fourier spectral analysis of ion cyclotron resonance time-domain signals

The frequency-domain spectrum obtained by Fourier transformation (FT) of a time-domain signal is accurate only for a continuous noiseless time-domain signal of infinite duration. For discrete noisy truncated time-domain signals, non-FT (e.g., Bayesian analysis) methods may provide more accurate spectral estimates of time-domain signal frequencies, relaxation time(s), and relative abundances. In this paper, we show that Bayesian analysis of simulated and experimental ion cyclotron resonance (ICR) time-domain noisy signals can produce a spectrum with mass accuracy improved by a factor of 10 or more over that obtained from a magnitude-mode discrete fast Fourier transform (FFT) spectrum. Moreover, Bayesian analysis offers the useful advantage that it automatically estimates the precision of its iteratively determined spectral parameters. The main disadvantage of Bayesian analysis is its lengthy computation time compared to that of FFT (hours vs seconds on the same hardware for approximately 4K time-domain data points); the Bayesian computation time increases rapidly with the number of spectral peaks and (less rapidly) with the number of time-domain data points. Bayesian analysis should thus prove useful for those FT/ICR applications involving relatively few data points and/or requiring high mass accuracy.     

一种有效的机载合成孔径雷达动目标成像方法

为实现机载合成孔径雷达(Synthetic Aperture Radar,简称SAR)实际回波数据中的运动目标聚焦成像,本文在用前置滤波法检测出运动目标的基础上,提出了利用目标子图像匹配方法来估计动目标的方位向速度,得到相应的运动目标聚焦参考函数,然后对运动目标进行聚焦成像,并给出了利用该方法得到的运动目标聚焦图像．成像结果表明,目标子图像匹配方法对动目标成像是有效的,易于工程实现,有实际应用价值．     

Range migration algorithm for airborne squint mode spotlight SAR imaging

Since the reference signal based on the fixed reference range is used in the range migration algorithm (RMA), the RMA is not available to process an airborne squint-mode spotlight synthetic aperture radar (SAR) data. Thus, the modified reference signal to transform a squint-mode data to a broadside-mode data is introduced on the basis of the coordinate transformation and the extended Taylor approximation. Then, using the principle of the stationary phase, the presented formulation is analysed. Moreover, to compensate curvature errors, the proposed method is extended on the basis of the subarea technique. Finally, the effectiveness of the proposed method is demonstrated by some numerical simulations via a pulsed spotlight SAR simulator     

Pure absorption-mode spectra from Bayesian maximum entropy analysis of ion cyclotron resonance time-domain signals

Fourier transform ion cyclotron resonance (FT/ICR) mass spectra are normally reported in the (phase-independent) magnitude-mode format. In principle, the absorption-mode format offers spectral resolution enhanced by a factor ranging from square root of 3 to 2 over the corresponding magnitude-mode spectrum obtained by discrete FT of the same unapodized time-domain data. However, an absorption-mode display is generally unsuitable in practice because of the auxiliary spectral peaks (Gibbs oscillations) resulting from the relatively long time delay between excitation and detection. Although the resulting large phase variation (up to 100 pi rad or more across the Nyquist spectral bandwidth) can be corrected exactly for a continuous time-domain signal, phase correction of a discrete time-domain signal results in Gibbs oscillations even for a perfectly phased absorption-mode spectrum. In this paper, we show that a Bayesian "maximum-entropy" analysis of simulated and experimental ion cyclotron resonance time-domain noisy signals can recover a precisely phased absorption-mode frequency-domain spectrum that is devoid of Gibbs oscillations, is less sensitive to noise, and offers improved mass accuracy over that obtained from a conventional magnitude-mode discrete fast Fourier transform (FFT) spectrum.     

Azimuth-invariant bistatic multichannel synthetic aperture radar for moving target detection and location

Ground moving target indication (GMTI) is one of the most important applications of the bistatic synthetic aperture radar (SAR) system as well as the monostatic system. An algorithm for moving target detection and location is presented with an azimuth-invariant bistatic multichannel SAR, which consists of one transmitter (channel) and multireceivers (multichannel). The algorithm is based on the discussion of the particularities of the bistatic SAR configuration including coherence improvement and clutter characteristics. Then, the corresponding compensating methods including two-dimensional range-azimuth prefiltering and bistatic differential range correction are proposed to solve these particularities. It is shown that using the compensating methods, the stationary clutter can be suppressed and the moving parameters of ground targets can be estimated accurately. Finally, simulation results demonstrate the effectiveness of the proposed algorithm.     

Hartley transform ion cyclotron resonance mass spectrometry

The Hartley transform offers a useful alternative to the Fourier transform for the conversion of a time-domain ion cyclotron resonance (ICR) signal into its corresponding frequency-domain mass spectrum. The Hartley transform has the advantage that it eliminates the need for complex variables, when (as for linearly polarized signals) the time-domain signal can be represented by a mathematically real function. Moreover, the Hartley transform produces the same spectra (absorption mode, dispersion mode, magnitude mode) as does the Fourier transform. In particular, the discrete fast Hartley transform (FHT) produces the same spectrum at twice the speed of a complex fast Fourier transform (FFT), making the FHT equivalent in speed to a "real" FFT. Hartley and Fourier transform methods in ICR mass spectrometry are compared and demonstrated experimentally. Essentially the same advantages and computational methods should apply to the use of the Hartley transform in place of the Fourier transform in other forms of spectrometry (e.g., nuclear magnetic resonance, infrared, etc.).     

基于频域导频时域处理的OFDM系统信道估计算法

针对正交频分复用(OFDM)系统,提出了一种适用于时变信道的信道估计算法。该方法利用频域导频,经离散傅立叶变换(DFT),获得的信道冲击响应等效于利用频域导频对应的时域序列和接收信号进行循环相关获得的信道冲击响应。因此,避免了在时域采用复杂的循环相关运算。同时,通过消除频域导频时域序列的自相关误差,能有效降低由DFT谱泄漏导致的信道估计误差。仿真和分析表明,在时变多径衰落信道下,提出的信道估计方法的性能比传统的基于DFT的算法和频域维纳滤波算法有明显提高。     

多运动平台红外场景仿真

为了能对多运动平台条件下的红外信息处理算法进行验证与评估,进行了多运动平台红外场景仿真的研究与实现。首先,回顾了现有的红外场景仿真方法,指出其主要针对单平台条件设计。接着,分析了目标模型,提出了目标辐射模型和目标群运动模型。然后,在分析多运动平台红外信息处理算法特点基础上,提出了基于虚拟观测平台的成像观测模型,并据此得到了多运动平台红外场景仿真的基本流程。最后,对提出的场景产生方法进行了仿真验证。仿真结果表明:提出的多运动平台红外场景仿真方法,能够满足多运动平台协同条件下的红外信息处理算法的验证与评估的需求。     

Measuring power system harmonics and interharmonics by an improved fast Fourier transform-based algorithm

The fast Fourier transform (FFT) has been widely used for the signal processing because of its computational efficiency. Because of the spectral leakage and picket-fence effects associated with the system fundamental frequency variation and improperly selected sampling time window, a direct application of the FFT algorithm with a constant sampling rate may lead to inaccurate results for continuously measuring power system harmonics and interharmonics. An improved FFT-based algorithm to measure harmonics and interharmonics accurately is proposed. In the proposed algorithm, a frequency-domain interpolation approach is adopted to determine the system fundamental frequency, and the interpolatory polynomial method is applied to reconstruct the sampled time-domain signal; it is followed by using the FFT to calculate the actual harmonic components. Then, the frequency-domain interpolation is again applied to find the interharmonic components. The performance of the proposed algorithm is validated by testing the actual measured waveforms. Results are compared with those obtained by directly applying a typical FFT algorithm and by the IEC grouping method. It shows that the solutions determined by the proposed algorithm are more accurate, and a reasonable computational efficiency is maintained.     

Finite-element time-domain modelling of plane wave scattering by a periodic structure using an exact boundary condition

A two-dimensional singly-periodic structure, at plane wave oblique incidence, is modelled using the finite-element time-domain method. Over the non-periodic boundaries of the computational domain, an exact Floquet modal absorbing boundary condition is developed, in detail, for the finite element method in the time domain. The proposed formulation is validated by comparing its results with that of the finite-element frequency-domain method and with independently obtained published results. Very accurate numerical results, over a wide frequency range and incident angle range, are obtained for both transverse electric and transverse magnetic polarised plane wave illuminations     

大跨空间结构风模拟的改进方法及其小波识别

大跨空间结构风速时程模拟需考虑风的时间相关性和空间相关性。利用线性滤波器法并结合快速Foutier变换（FFT）对球面网壳结构进行多点脉动风速时程模拟，较好地解决风速时程的模拟精度、模拟速度和计算稳定性问题。利用小波变换良好的时频局部化性质和可变的聚焦特性，针对模拟的风速时程低频含量较少的特点，利用haar小波对风速时程进行小波分解和识别，修正分解后的低频含量。计算显示，重构修正后的风速时程在时域和频域上均更逼近目标风速时程。     

Optical Fourier processor and point-diffraction interferometer for moving-object trajectory estimation

A hybrid optical-digital signal processing system that estimates the trajectory of moving targets in a two-dimensional field at video frame rates was developed and constructed. The hybrid system is particularly well suited to the trajectory estimation of small, barely discernable, moving objects of unknown position and velocity in high-resolution image sequences. The system uses an optical Fourier processor and a point-diffraction interferometer to calculate the frequency-domain representation of moving objects from which their trajectory is estimated by use of conventional electronic processing techniques. In a series of experiments, target velocities were estimated to within 4% of their actual value and direction was estimated to within 3 deg.     

一种高效的弱目标线谱检测算法

为实现弱目标线谱检测,在自适应线谱增强(Adaptive Line Enhancement,ALE)算法的基础上,结合频域批处理技术,提出了一种能降低计算量的高效线谱检测算法——归一化频域批处理最小均方(Normalized Frequency-domain Block Least Mean Square,NFBLMS)算法;所提NFBLMS算法在权值迭代过程中,步长参数不受输入信号功率的影响。理论分析和数值仿真结果表明:相比于已有的线谱检测算法,NFBLMS算法能较好地解决ALE算法实时处理运算量问题,并可获得较高的系统增益,且其步长参数具有较强的鲁棒性,能同时兼顾算法的收敛速度和稳态误差。因此NFBLMS算法更适合实际工程应用。     

铝合金回填式搅拌摩擦点焊缺陷的超声检测及信号识别

目的 利用水浸聚焦超声C扫描对2524铝合金回填式搅拌摩擦点焊（RFSSW）接头进行检测并完成缺陷识别。方法 以A扫描时域信号为对象,绘制能量谱与金相作对照,确定焊合区;分析未焊合、聚集型孔洞及弥散型孔洞的时域和频域波形特征,并对频域信号进行小波分析,提取特征量。结果 缺陷区反射回波的归一化能量不低于0.02;不同形式的缺陷（聚集型孔洞、弥散型孔洞、弱连接）其频谱形状特征不同,具有不同的峰值个数。结论 通过金相验证,表明超声波C扫描对接头缺陷可进行有效的检测和区分。     

Quality enhancement of image generated with bistatic ground based noise waveform SAR

A new method for quality enhancement in a noise synthetic aperture radar (SAR) image and the first results of its application to the SAR image generated with the use of a bistatic Ka-band ground-based noise waveform SAR (GB NW-SAR) are presented. A SAR image generated with a noise SAR suffers from the masking effect which is tied to residual random fluctuations in noise radar response from bright scatterers in the scene. This is similar to the masking effect present in the deterministic waveform SAR when the signal sidelobes of echoes from bright scatterers may mask the main response from a weaker target. The procedure presented is a variation of the CLEAN algorithm. Knowing precisely the emitted signal and finding positions of the strongest scatterers one may model the echo signal originated from a selected scatterer. Extraction of the modelled signal from the received one reduces the residual fluctuations and makes it possible to clean the image and increase its dynamic range. The final image is constructed from the cleaned signal and the previously removed strongest scatterers. A theoretical background is provided to the proposed procedure and its application to enhance the SAR image using simulated data as well as data generated by the Ka-band bistatic GB NW-SAR is demonstrated. The GB NW-SAR, recently developed and tested in LNDES IRE NASU, may operate in CW and pulse random signal regimes for short range applications.     

Efficiency improvement of the frequency-domain BEM for rapid transient elastodynamic analysis

The frequency-domain fast boundary element method (BEM) combined with the exponential window technique leads to an efficient yet simple method for elastodynamic analysis. In this paper, the efficiency of this method is further enhanced by three strategies. Firstly, we propose to use exponential window with large damping parameter to improve the conditioning of the BEM matrices. Secondly, the frequency domain windowing technique is introduced to alleviate the severe Gibbs oscillations in time-domain responses caused by large damping parameters. Thirdly, a solution extrapolation scheme is applied to obtain better initial guesses for solving the sequential linear systems in the frequency domain. Numerical results of three typical examples with the problem size up to 0.7 million unknowns clearly show that the first and third strategies can significantly reduce the computational time. The second strategy can effectively eliminate the Gibbs oscillations and result in accurate time-domain responses.     

Noise filtering of DC voltages in both the time and frequencydomain

We describe a method of obtaining a smaller statistical uncertainty on the DC component of a voltage signal by using a combination of time- and frequency-domain methods than by using time-domain averaging only. This measurement technique is compatible with precision DC voltmeters that poll the input signal less than 100% of the time. The frequency-domain strategy captures information during the time that the voltmeter is not reading the input signal. Alternatively, one can map out low frequency noise spectra using this approach