Enhanced spectral resolution FFT for step-like signals

A method is presented for obtaining a sampled Fourier transform of a steplike signal with a spectral resolution greater than previously reported. The method is related to zero padding, which is used for enhancing the spectral resolution of an FFT of a limited duration signal. The new method involves final value padding when the extension function outside the observation window is a step, or it involves padding with a sampled exponential function when the extension function is a decaying exponential     

基于长序列FFT和LMS原理的调制线谱分析

从数学上证明了长序列FFT分析可实现噪声抑制,从而提高信噪比,其实质相当于时间积累。利用变步长的自适应线谱增强器进行线谱增强,可以提高信噪比。用两种方法分析了实际舰船信号的调制谱,讨论了合理选取参数的方法。实验证明,合理运用这两种方法,可以达到较好的分析效果。     

A field-portable plasma source monitor for real-time air particulate monitoring

In this research, a novel portable instrument for on-site, real-time air particulate monitoring was developed. It is highly desirable to use microwave plasmas for on-site, real-time environmental and occupational hazard monitoring because they can be sustained with various gases at relatively low power and possess excellent detection capabilities for both metal and nonmetal air pollutants. In the new instrument design, a microwave plasma was selected as an excitation source and was used in conjunction with atomic emission spectrometry. A small, integrated spectrometer with a charge-coupled detector (CCD) was used for optical signal detection. An efficient, in situ air-sampling system was developed for direct sampling of air particles into the plasma. Characterization and calibration of the new instrument were achieved with an in-house-fabricated high-efficiency nebulization-desolvation system. Tolerance of the microwave argon plasma source to air introduction was tested, and the operational parameters were optimized. Analytical performance and the feasibility of the newly developed portable instrument for aerosol particle analysis were evaluated. Some advantages and possible applications of the new instrument are discussed. The instrument provides an innovative tool for rapid environmental and occupational hazard monitoring.     

Development of a real-time hand dose monitor for personnel in interventional radiology

Medical procedures denoted as interventional radiology require operation near an X ray beam, which brings high dose exposures to the operators' hands. For the effectual control of their extremity doses, a prototype of a real-time wrist dosemeter has been developed, hand dose monitor (HDM), based on a single silicon detector. Experiments were performed to test its response to diagnostic X rays. The HDM was highly sensitive and showed a linear response down to doses of a few tens of microsieverts. Though dose rate, energy and angular dependence of the response were observed in some extreme conditions, the HDM was proved to be of practical use if it was appropriately calibrated. Since an HDM enables personnel to check their hand doses on a real-time basis, it would enable medical staff to control the exposure themselves.     

采用双DSP的实时傅里叶变换系统设计

系统设计目的是使FFT变换能够实时完成,以便能够在图像处理等方面应用于实际工程中。系统应用两片TI公司的数字信号处理器TMS320C6416为核心,以可编程逻辑阵列CPLD进行逻辑控制,采用两片现场可编程门阵列FPGA分别作为图像预处理和两片DSP之间的通讯,系统在运算1024点FFT与反傅里叶变换iFFT时耗仅为178μs,实现了实时的图像傅里叶处理。     

一种少数点FFT递归算法

FFT广泛应用于数字信号处理中，其算法主要为“同址运算”FFT算法，即使用从前往后逐层算出各结点的数据，因其在计算时总是用当前层替代前一层，具有地址不变的关系而得名，该算法在计算全部分析点数据时具有很高的效率，但是在大部分应用中求出全部谱线是多余的。给出了一种只求有限谱线的高效方法的递归表达式及推导过程，以及在使用此方法的旋转因子的规范化处理方法，比较了此方法与传统方法的时间与空间的效率，得出此方法在计算谱线数少于层数时具有更高的效率，而占用空间大小只有传统方法的1／3。列举了几种应用实例，说明了用于系统计算机时程序编制的方法，特别说明了用于嵌入式系统中的表达式及生成方法。具有更直接和方便的应用形式。这些方法特别适用于少数谱线的分析，如ZOOM分析、实验模态分析、局部谱线识别数字信号处理中。     

采用设备驱动的实时监测控制系统在激光雷达中的应用

以差分吸收激光雷达为背景,对基于WDM的实时监测控制系统的设计中涉及的关键技术进行研究。结合具体的实际系统,采用模块化设计的方法,利用中断调用及线程调度、对象同步技术加以实现,使得整个系统在系统维护、实时处理能力上有了很大的提高。     

Sensitivity analysis practices: Strategies for model-based inference

Fourteen years after Science's review of sensitivity analysis (SA) methods in 1989 (System analysis at molecular scale, by H. Rabitz) we search Science Online to identify and then review all recent articles having “sensitivity analysis” as a keyword. In spite of the considerable developments which have taken place in this discipline, of the good practices which have emerged, and of existing guidelines for SA issued on both sides of the Atlantic, we could not find in our review other than very primitive SA tools, based on “one-factor-at-a-time” (OAT) approaches. In the context of model corroboration or falsification, we demonstrate that this use of OAT methods is illicit and unjustified, unless the model under analysis is proved to be linear. We show that available good practices, such as variance based measures and others, are able to overcome OAT shortcomings and easy to implement. These methods also allow the concept of factors importance to be defined rigorously, thus making the factors importance ranking univocal. We analyse the requirements of SA in the context of modelling, and present best available practices on the basis of an elementary model. We also point the reader to available recipes for a rigorous SA.     

An object-oriented simulation architecture with real-time capabilities

Simulation that approximates real-time system response has previously been used to train operators in the use of system controllers. These simulations typically use architectures that are highly specific and tightly coupled to the system hardware. A formalized generic real-time simulation architecture is presented to decouple the simulation and provide a mechanism for implementation and rapid reconfiguration. This architecture distributes the state variables in the system by coupling them with manufacturing process equipment, specifically for the continuous process industries such as chemical, food and pharmaceutical. This design provides a mechanism for rapidly interchanging manufacturing equipment and simulation model components for discrete and continuous simulation, that facilitates operator training.     

Digital analyzers for dynamic spectral analysis

A comparative analysis of recurrent spectrum computation algorithms for dynamic spectral analysis is given and possibilities for expanding the frequency range of the analyzed signals are indicated.Translated from Izmeritel'naya Tekhnika, No. 12, pp. 13–16, December, 1993.     

An algorithm for stress and mixed control in Galerkin-based FFT homogenization

A new algorithm is proposed to impose a macroscopic stress or mixed stress/deformation gradient history in the context of nonlinear Galerkin-based fast Fourier transform homogenization. The method proposed is based on the definition of a modified projection operator in which the null frequencies enforce the type of control (stress or strain) for each component of either the macroscopic first Piola stress or the deformation gradient. The resulting problem is solved exactly as the original variational method, and it does not require additional iterations compared to the strain control version, neither in the linear iterative solver nor in the Newton scheme. The efficiency of the proposed method is demonstrated with a series of numerical examples, including a polycrystal and a particle-reinforced hyperelastic material.     

Automatic spectral analysis with time series models

The increased computational speed and developments in the robustness of algorithms have created the possibility to identify automatically a well-fitting time series model for stochastic data. It is possible to compute more than 500 models and to select only one, which certainly is one of the better models, if not the very best. That model characterizes the spectral density of the data. Time series models are excellent for random data if the model type and the model order are known. For unknown data characteristics, a large number of candidate models have to be computed. This necessarily includes too low or too high model orders and models of the wrong types, thus requiring robust estimation methods. The computer selects a model order for each of the three model types. From those three, the model type with the smallest expectation of the prediction error is selected. That unique selected model includes precisely the statistically significant details that are present in the data     

An electro-optic holography system with real-time arithmetic processing

This paper reports the use of a real-time arithmetic image processor in an electro-optic holography system. A speckle interferometer is used to combine an image of an object, lit by laser light, with a mutually coherent reference beam. A CCD TV camera detects the interference pattern, and the phase of the reference beam is advanced by 90° between frames. An image is generated from each set of four sequential TV frames by subtracting alternate frames, squaring, and adding the two results. The result is improved picture quality compared with the use of binary pixels and compared with electronic speckle pattern interferometry. Experimental results are shown.     

An investigation into the spectral analysis of dielectric aging in ferroelectrics

This study shows how Fourier analysis can be applied to an aged PMN-PT-BT composition to characterize and quantify the effects of aging. The average weak-field permittivity is measured as a function of time, temperature, and frequency. A typical "saddle" in the permittivity and dielectric loss is apparent, and the magnitude decays logarithmically with time. Harmonic analysis of the strain response reveals a slight time-dependent amplitude variation and logarithmic dependence of the phase of the 6th order harmonic. Similar analysis of the polarization response, as a function of time, fully characterizes the development of constriction or wasting seen in a typical aged electrostrictive material. Variations in the amplitudes of the 5th and higher order harmonics of polarization, logarithmic in nature, and the phase of the 5th order harmonic combine to define aging on the harmonic level.     

An accelerated FFT algorithm for thermoelastic and non‐linear composites

A fast numerical algorithm to compute the local and overall responses of non‐linear composite materials is developed. This alternative formulation allows us to improve the convergence of the existing method of Moulinec and Suquet (e.g. Comput. Meth. Appl. Mech. Eng. 1998; 157 (1–2):69–94). In the present method, a non‐linear elastic (or conducting) material is replaced by infinitely many locally linear thermoelastic materials with moduli that depend on the values of the local fields. This makes it possible to use the advantages of an algorithm developed by Eyre and Milton (Eur. Phys. J. Appl. Phys. 1999; 6 (1):41–47), which has faster convergence. The method is applied to compute the local fields as well as the effective response of non‐linear conducting and elastic periodic composites. Copyright © 2008 John Wiley & Sons, Ltd.     

重叠FFT频域窄带干扰抑制的改进方法

为了克服基于FFT(Fast Fourier Transform)的频域干扰抑制算法通常采用数据加窗以降低频谱泄漏而引起扩频信号失真和信噪比损耗,提出了一种重叠加窗频域干扰抑制改进方法.该方法的特点是能实现信号的完全重构,避免加窗处理引起PN码相关特性的改变.理论分析和仿真结果验证了算法的有效性.仿真结果表明,该方法能有效消除加窗引起的频谱失真和信噪比损失,降低误码率,并适用于多种类型的窗函数.该方法的代价是增加了少量复数运算.     

An adaptive SC spectral analyzer with power determined frequencyresolution

A switched-capacitor (SC) adaptive spectral analyzer is described that has power-determined frequency resolution. Using commercially available SC filters, the circuit is capable of real-time analysis of input spectra below 150 kHz. The time window analyzed and the tracking speed are user selectable     

Quantitative spectral analysis for flaw detection in concrete

The resonance method of transient stress wave propagation is employed for the detection of flaws in concrete. Quantitative analysis of the spectra identifies the resonance mode due to reflection from the flaw, and enables the exclusion of the flexural modes of the concrete plate above the flaw. Two-dimensional scanning of a test point provides the information about the depth of internal flaws. The test results of a large concrete block containing several types of artificial flaws are presented.