基于遗传算法的涡街信号随机共振检测方法

涡街流量计在工业现场工作时,输出信号易叠加噪声,尤其在小流量测量时,涡街信号易被现场噪声淹没,导致测量受限。针对涡街信号处理,提出一种基于遗传算法的双调制随机共振方法。该方法对输入信号进行频率和幅值双调制后进入非线性双稳系统,以系统输出信号的信噪比为适应度函数,通过二进制编码,将调制频率和幅值组合成一个二进制字符串,同时对两个参数进行并行寻优,得到最优解,使系统产生随机共振,增强涡街信号。搭建涡街流量计实验装置,实验结果表明,使用遗传算法可以有效搜索出调制频率和幅值最优解,搜索效率高,解决现有多参数寻优的困难,适用于涡街信号特别是小流量信号处理,能准确获取涡街频率,实现流量测量。     

Harmonic impedance measurement using a thyristor-controlled short circuit

An effective and easy-to-implement method for measuring power system harmonic impedances is presented. The method uses a thyristor to create a controlled short circuit at the measurement point. The short circuit produces a pulse current and a voltage distortion, which are then used to estimate the system impedance. The strength of the current pulse is controlled through the thyristor firing angle so that enough signal energy is available for precise measurement and yet the disturbance is small enough not to cause power quality problems. The method can be implemented into a portable impedance measurement device. Computer simulations and lab tests were used to verify the effectiveness of the method. A criterion for determining the frequency range of reliable measurements using the proposed device is also established.     

Enhanced architecture for microwave currentmode class-D amplifiers applied to the design of an S-band GaN-based power amplifier

An enhanced architecture for the design of current-mode class-D (CMCD) power amplifiers (PAs) at microwave frequencies is presented. In the proposed structure, the harmonic impedance loading conditions of CMCD amplifiers are realised by using multiharmonic output impedance transformation networks instead of a combination of balun and lumped element tanks, typically used in CMCD PA designs. The advantage of the proposed approach is to remove design complexity from the balun and lumped element tank. A 39 dBm GaNbased CMCD PA was designed at 2.35 GHz ? to the best knowledge of the authors the highest frequency for a CMCD PA reported in open literature ? to validate and to demonstrate the capabilities of this architecture. The fabricated PA achieves 68% DC-to-RF efficiency (η) and 65% power added efficiency. A comparison between this S-band amplifier and a conventional wideband-balun-resonant-tank CMCD PA at 1 GHz using a similar commercial active device demonstrates the frequency coverage and performance improvement of the proposed topology.     

Evaluation of a Wide-Band Method for the Measurement of the Reflection Coefficient of Microwave One-Port Networks

A method for measuring the magnitude and phase of the reflection coefficient of one-port networks is described. The measurements can be extended over wide frequency bands by stepping the signal frequency through the band. The measured value is referred to the impedance of solid conductor air-dielectric transmission lines which are considered primary standards of impedance. An error evaluation has been carried out and shows that this method is at least as accurate as the quarter-wavelength method. Examples of the measurement of coaxial terminations are given and compared to measurements by the quarter-wavelength method.     

Broad-band dielectric spectroscopy of low-permittivity fluids usingone measurement cell

Dielectric spectroscopy is a relevant method for quality characterization of petrochemical products, provided that the permittivity spectra are measured with high precision over a broad frequency range. This paper describes how the permittivity of low-loss liquids such as crude oils can be measured with high precision using a single measurement cell in the broad frequency range 1 kHz to 6 GHz. The use of a single cell ensures that the whole dielectric spectrum is measured under the same conditions, which is an advantage for both on-line and laboratory applications. The permittivity spectrum is obtained by combining impedance and S-parameter measurements of a coaxial transmission/reflection cell with suitable permittivity calculation methods. The high sensitivity of the system is confirmed by measurements on crude oils and known low-loss liquids     

传输线变压器的机理及宽带阻抗匹配的设计

传输线变压器具有频带宽、易于制作的特点，在通信领域得到了广泛的应用。但在超声换能器与超声信号源之间采用传输线变压器实现阻抗匹配的报道较少。文章对传输线变压器实现宽带阻抗匹配的机理进行了详细的分析，通过一个简单的等效电路阐明了传输线变压器如何巧妙地利用传输线间的分布电容，使其由影响高频能量传输的不利因素而转换为电磁能量转换必不可少的条件，从而达到宽频带传输的目的。以500kHz-2MHz范围内的超声换能器的阻抗匹配变压器的设计为例，具体给出了确定传输线变压器特性阻抗、线长、磁心、导线型号和匝数的方法。     

宽带多普勒测速技术中跨周期模糊问题的研究

宽带声学多普勒流速剖面仪,利用伪随机编码调制发射脉冲信号以及复相关算法计算各水层反射回波的多普勒频移,进而达到测速的目的。复相关算法中,在排除模糊速度干扰的情况下,测速精度与脉冲信号的长度存在正比的关系。而脉冲宽度越长,所用来调制发射脉冲信号的编码阶数也越高,随之带来的便是速度模糊的问题。在复相关测频算法的基础上,针对长编码脉冲信号出现的周期性测频模糊情况,利用短编码脉冲信号的测频结果作为判别标准,选取恰当的周期性频偏作为计算结果,既提高了测速精度,又解决了精度提高所带来的周期性速度模糊问题,并且在实际应用中,提高了低信噪比条件下的测速精度。     

An electrochemical impedance measurement technique employing Fourier transform

We describe a novel technique for measuring electrochemical impedance, in which the electrode potential is ramped to a desired bias potential and a small potential step is applied to the working electrode after a short time delay. Fourier transform of the first derivative of the current signal thus obtained provides ac currents in the frequency domain, which allows the computation of impedances of the electrode/electrolyte interface in the whole frequency range. A home-built data acquisition system for these measurements and the results obtained therefrom were used for the measurements. The advantage of the technique includes an extremely short time of less than 1 ms for impedance measurements in the whole frequency region while equilibrium conditions of the electrochemical system are being maintained before and after the measurements, among many others. This technique is expected to revolutionize electrochemical measurements and to find important applications such as in situ measurements during battery cycling, corrosion testing, and other electrochemical experiments.     

聚四氟乙烯微孔膜的透声性能实验

为研究微孔薄膜材料的透声性能,搭建了改进的四传声器阻抗管隔声量测试系统,推导了阻抗管中隔声量的传递损失矩阵算法,此算法可以有效地分离隔声管中透射波与二次反射波,使测试结果不受隔声管末端材料吸声性能的影响,与原四传声器算法相比物理意义更明确．对3种微孔薄膜样品进行了实验和分析,结果表明改进的测试方法可以精确地测试样品隔声量,尤其能提高低频段隔声量的测试精度,测试结果重复性优于原方法．     

Optimal measurement of frequency instability in a multi-channel comparator

It is proposed that the weighted-mean estimator of the Allan variance be used as an optimal estimator in measurements of the frequency instability of a particular signal by means of a multi-channel measurement system. The article presents an algorithm for numerical selection of the weight actors for an arbitrary number of signals used in the measurement that makes it possible to minimize the dispersion of the weighted-mean estimator. It also presents results from an analysis of analytic expressions and a numerical simulation based on the proposed algorithm.     

A Simple Method for Design of Adaptive Filters for Sinusoidal Signals

Filtering of input signals in algorithms for measurement of power system electrical parameters is very important. Filters are used to minimize the noise effect and eliminate the presence of higher order harmonics. In addition to that, a number of measurement algorithms apply orthogonal signal components obtained by two orthogonal finite-impulse response filters. The frequency response of the filters must have nulls at the higher order harmonic frequencies that are expected to be present in the signal and must have a unity gain at the main harmonic frequency. In the case of a time-varying frequency, the filter parameters have to be adapted during frequency estimation. In this paper, a simple method for online design of digital filters for sinusoidal signals is proposed. It is based on closed-form solutions for calculating filter coefficients. A simple linear algorithm for frequency estimation was used, and a derived algorithm for online adaptation of the filter coefficients is computationally very efficient. The number of subsections in the cascade and data window lengths can also be changed, depending on the frequency variations during measurement.      

A filter for on-line estimation of spectral content

A robust filter algorithm to extract, a posteriori, the rational signal model from a noisy measurement, with little a priori information, is proposed. The spectrum and the statistics of the signal and of the corrupting noise are assumed unknown, except that the signal is assumed to have a rational spectrum. An algorithm based on system and signal theory is derived to select a set of frequencies where the signal-to-noise ratio (SNR) is high from a given measurement spectrum. The density of selected frequencies weights the importance of the measurement as a function of frequency, An estimate of the signal model is obtained from the best weighted least-squares fit to the measurement spectrum at the selected frequencies. The proposed filter has applications to control and signal processing, and a wide variety of applications are presented. Applications include: system identification of a dc motor and a two-link manipulator, extraction of a myo-electric signal from a noisy measurement, the assignment of a rational model to a vegetation tissue's impedance, and to the number density profile of atmospheric oxygen     

Battery impedance spectroscopy using bidirectional grid connected converter

Battery impedance can provide valuable insight into the condition of the battery. Commercially available impedance measurement instruments are expensive. Hence their direct use in a battery management system is not justifiable. In this work, a 3-kW bi-directional converter for charging and discharging a battery bank has been implemented with the capability of impedance measurement. The converter is grid connected and controlled to operate at unity power factor. Additional requirements on filter design and control structure of battery converter for impedance measurement are discussed. An algorithm has been developed to measure impedance by frequency sweep, avoiding transients. The measured impedance has been compared to that from a commercially available impedance measurement equipment and is shown to have a good match.     

Measuring the best linear approximation of systems suffering nonlinear distortions: an alternative method

When measuring the best linear approximation of systems suffering nonlinear distortions, a specific class of periodic multiharmonic signals is normally used. These are signals with uniformly distributed random phases, termed random phase multisines. In this paper, it is shown that measurements of the best linear approximation of nonlinear systems can also be obtained by using a special type of low crest factor multisines. These signals are compared to random phase multisines and their properties are analyzed in detail.     

近代现场吸声测量技术

驻波管法和混响室法是吸声测量技术中常用的方法,用于现场测量时不满足特殊声场环境假设、样品尺寸、频率限制等。脉冲回波方法和声强测量法对测量环境没有严格要求,适用于现场测量。这类方法的共同特点是在频域处理数据,往往需要将反射波与入射波分离,测量步骤较多,不利于在线测量。参数反演方法直接利用测量的声压时间序列获得声学阻抗或吸声系数,是一种时域测量方法,更适用于在线测量。在声学理论指导下,借助于计算机与数字信号处理技术的研究成果,一些新的测量方法不断被提出,但要成为一种成熟的技术,还有大量的研究工作去做。     

Tunnel diode oscillator circuit for surface impedance measurement of thin films near 20 MHz

We describe and analyse a simple method for the measurement of thin film surface impedance in the frequency range 10–20 MHz. This method is based on the analysis of both the frequency shift and the amplitude variation of the signal in a tunnel diode oscillator circuit inductively coupled to the sample. The sensitivity of the method to the conducting properties of the thin films is a function which is greatly dependent on geometrical parameters and which can be easily optimized and included in the response calculation. The analysis is illustrated by examples with superconducting and normal metal films. The resolution of the measurements is also discussed.     

New digital multimeter for accurate measurement of synchronously sampled AC signals

An approach to the design of a digital multimeter based on the use of dual-slope ADC is described in this paper. Based on this approach, a new technique for algorithm design is developed. The main advantage of this approach is the determination of all electric values in electric utilities by the same algorithm. The algorithm has high accuracy and a regular structure. Measurements of voltage and current are made in successive periods by a stroboscopic technique (synchronous undersampling). The assumed stationarity of the electric utilities is validated by measurements with an experimental setup, consisting of a fast high-precision sigma-delta ADC. The necessary synchronization is reached by software measurements of the frequency of the measured signal. Assuming stationarity of the observed system (electric utilities) in the stated 1-s interval, it is proved that precise digital processing can be achieved without using a sample-and-hold circuit. The suggested measuring system was simulated, realized in a practical setup, and tested. The obtained results completely confirmed the starting postulates. A processing precision of 0.01% was achieved.     

Mechanical properties of single cells by high-frequency time-resolved acoustic microscopy

In this paper, we describe a new, high-frequency, time-resolved scanning acoustic microscope developed for studying dynamical processes in biological cells. The new acoustic microscope operates in a time-resolved mode. The center frequency is 0.86 GHz, and the pulse duration is 5 ns. With such a short pulse, layers thicker than 3 microm can be resolved. For a cell thicker than 3 microm, the front echo and the echo from the substrate can be distinguished in the signal. Positions of the first and second pulses are used to determine the local impedance of the cell modeled as a thin liquid layer that has spatial variations in its elastic properties. The low signal-to-noise ratio in the acoustical images is increased for image generation by averaging the detected radio frequency signal over 10 measurements at each scanning point. In conducting quantitative measurements of the acoustic parameters of cells, the signal can be averaged over 2000 measurements. This approach enables us to measure acoustical properties of a single HeLa cell in vivo and to derive elastic parameters of subcellular structures. The value of the sound velocity inside the cell (1534.5 +/- 33.6 m/s) appears to be only slightly higher than that of the cell medium (1501 m/s).     

Digital correction techniques for accuracy improvement in measurements of SnO/sub 2/ sensor impedance

In this paper, the performance improvement of a gas-sensing system by digital correction techniques is discussed. The considered system operates as a vectorial impedance meter and performs impedance measurements of eight sensors arranged in an array in the frequency range 10 Hz-15 MHz. The measurements of the chemical sensors' impedance is an innovative technique that allows highlighting different adsorption mechanisms taking place when the sensors are exposed to gases. Of course, impedance analyzers are commercially available, but they usually make measurements on only one device at time and they are very expensive. The proposed PC-based impedance analyzer is a versatile one and shows good performances for gas-sensing applications. A digital correction technique is used in this work to improve the impedance measurement accuracy of each channel of the gas-sensing system (eight sensors /spl rarr/ eight channels), in order to compensate for the conditioning electronics response. The latter is evaluated in a characterization procedure. A linear black box two-port model is used to take into account crosstalk, amplitude, and phase distortions. Two different techniques to evaluate the response of the measurement system are discussed in this paper, and experimental results are presented on both the measure of reference impedances and on the measure of chemical sensors.