A methodology to perform online self-testing for field-programmable analog array circuits

This paper presents a methodology to perform online self-testing for analog circuits implemented on field-programmable analog arrays (FPAAs). It proposes to partition the FPAA circuit under test into subcircuits. Each subcircuit is tested by replicating the subcircuit with programmable resources on the FPAA chip, and comparing the outputs of the subcircuit and its replication. To effectively implement the proposed methodology, this paper proposes a simple circuit partition method and develops techniques to address circuit stability problems that are often encountered in the proposed testing method. Furthermore, error sources in the proposed testing circuit are studied and methods to improve the accuracy of testing results are presented. Finally, experimental results are presented to demonstrate the validity of the proposed methodology.     

超声波在水中衰减的频率效应及其对脉冲回波的影响

超声波在传播中会发生幅值衰减,该衰减不仅与超声波传播的距离有关,还与超声波的频率有关。为了研究高频超声波衰减的频率效应,本文通过脉冲回波法分析脉冲超声波在水中传播反射回波的幅值和频谱变化,研究了超声波在水中传播时幅值衰减与传播距离及其与超声频率之间的关系,通过测量脉冲超声波在水中传播不同距离时的反射回波,并对其进行傅里叶变换,分析了超声波传播衰减的距离效应和频率效应。研究发现:超声波在水中的传播衰减随距离呈指数规律,且不同频率超声波的衰减系数不相同,频率越高,衰减越大,衰减的频率效应可有效解释反射法高频脉冲超声检测中回波脉冲信号的中心频率远低于换能器标称中心频率的现象。     

Estimating ultrasonic time-of-flight through quadrature demodulation

A new digital signal-processing (DSP) method for ultrasonic time-of-flight (TOF) estimation is presented hereinafter. The method applies a traditional quadrature-demodulation scheme to the acquired ultrasonic signal in order to suitably extract the envelope of the main echo and locate its onset (i.e., the starting time of the echo). It is also possible to assure reduced bias and uncertainty in critical TOF measurements, such as those involving low signal-to-noise ratio (SNR) as well as severe distortion of echo shape. A number of numerical tests are conducted on simulated signals with the aim of highlighting the good performance of the method when operating in critical conditions; to reduce the computational burden without losing significance in the analysis, a statistical experimental design-based technique is enlisted. Results attained in TOF-based distance measurements finally assess the method's reliability and efficacy even in the presence of actual ultrasonic signals.     

基于经验模态分解的超声波管外测压信号去噪

在超声波管外测压中,回波信号往往受到噪声的干扰,所以在提取信号特征时,需对回波信号进行去噪。提出了一种基于经验模态分解（EMD）的超声波信号去噪方法,首先利用EMD求出信号的本征模态函数（IMF）,然后通过对比分析,利用反映信号主要特征的模态分量对信号进行重构以实现去噪。实验结果表明,该方法能够有效地去除噪声,提高超声回波信号的信噪比。     

A measurement method based on Kalman filtering for ultrasonic time-of-flight estimation

A new digital signal-processing method for ultrasonic time-of-flight (TOF) estimation is presented. The method applies the discrete extended Kalman filter (DEKF) to the acquired ultrasonic signal in order to accurately estimate the shape factors of the echo envelope as well as locate its onset. It is also possible to assure reduced bias and uncertainty in critical TOF measurements, such as those involving low signal-to-noise ratio (SNR) as well as severe distortion of echo shape. A number of numerical tests are conducted on simulated signals with the aim of highlighting the good performance of the method when operating in critical conditions. Results attained in TOF-based distance measurements finally assess the reliability and efficacy of the method in the presence of actual ultrasonic signals.     

基于回波信号相似度的气体超声流量计动态阈值法研究

基于双阈值法的气体超声流量计采用第1阈值检测和过零检测确定回波的到达时刻点,然而由于回波波形易受工况环境因素的影响,会导致第1阈值错误,使回波到达时刻点发生错误偏移,影响测量精度,因此提出了一种基于回波信号相似度的动态阈值法.该方法获取回波信号极大值幅值后,计算设定工况和实际工况下回波信号上升区域部分的欧式距离以评估相...     

基于小波变换的高精度测距系统设计及DSP实现

目的为了解决传统物流行业机器人避障系统中存在的测距精度低、抗干扰性差等问题。方法提出一种基于DSP的温补与小波阈值滤噪的高精度超声测距系统,包括DSP最小系统、超声波传感器、LCD显示模块、温度补偿电路和报警电路等。超声波测距系统通过实时采集环境温度来修正声速值,采用小波阈值变换算法对回波信号进行处理,以提升回波信号的信噪比和起始点锐度。结果应用CCS4.2软件与DSP芯片进行调试、实验,实验表明在距离0～1200 mm内,系统的测量误差为±4 mm。结论采用小波阈值变换算法和温补电路,提高了传统物流机器人避障系统的测距精度。     

伪随机码超声扩频测距系统设计与算法

针对单脉冲回波方式的超声测距方法存在的缺陷,借鉴雷达中的脉冲压缩技术,介绍了基于伪随机二进制序列(m序列)的超声扩频测距实现方法.伪随机码与超声载波采用ASK(幅移键控)调制方式,介绍了伪随机码超声扩频测距硬件方案和超声测距时延估计模型.针对超声换能器带宽特性和单脉冲回波特点,分析了m序列参数设计方法.提出了一种基于FFT的伪随机码包络相关快速时延估计算法,该算法将信号解调与匹配相关融合,大大降低了运算量.实验表明,本文介绍的伪码超声扩频测距硬件方案和快速算法可在便携式超声测距系统中实现,并可在多基站超声定位系统中推广使用.     

基于相关函数包络峰细化的高精度超声测距法

建立了超声测距时延估计模型,由于窄带超声回波参考信号与接收信号的相关函数在极值点附近具有慢衰减高频振荡特性,所以有必要将搜索直接相关函数的极值点转化为搜索相关函数包络的极值点.针对相关峰常规插值方法在多倍插值的情况下存在计算复杂、时延估计精度不高等缺点,结合超声回波信号的窄带带通特性和相关峰细化(Fine Interpolation of Correlation Peak)原理,提出了直接提取相关函数包络及包络峰细化方法,并分析了其计算复杂度.仿真与实验研究表明,该方法能大大提高相关函数包络峰值分辨率,适用于类超声回波信号的带通信号精细时延估计问题.     

Plant acoustic density profile model of CTFM ultrasonic sensing

Many applications require the sensing of plants. When an ultrasonic sensor insonifies a plant, the resultant echo is the superposition of the echoes from the leaves. As a result, the echo contains information about the geometric structure of the foliage. In this paper, we present a model of sensing that facilitates the extraction of geometric features from the echo for plant classification, recognition and discrimination. We model the echo from a CTFM ultrasonic sensor with the acoustic density profile model. Then, we identify a set of features that represent plant geometric characteristics and use these to perform an inverse transform from echo features to plant geometry     

Numerical method for transit time measurement in ultrasonic sensorapplications

In this paper, the implementation of a novel algorithm for the measurement of the transit time is reported. It has been applied to implement a smart, ultrasonic sensor for the fluid level measurement on a tank by processing the detected signal. A prototype of an on-line operating device, assembled to demonstrate the performance of the algorithm, is also described. Simulation tests have been carried out to investigate the algorithm performance, and we report on the results obtained. In addition, the results obtained during the field testing and application of the developed sensor are reported     

Intervening attenuation affects first-order statistical properties of ultrasound echo signals

Previous studies show that first-order statistical properties of ultrasound echo signals are related to the effective number of scatterers in the "resolution cell" of a pulse-echo ultrasound system. When the effective number of scatterers is large (~10 or more) this results in echo signals whose amplitude follows a Rayleigh distribution, with the RF echo signal obeying Gaussian statistics; deviation from Rayleigh or Gaussian statistics yields information on scatterer number densities. In this paper, the influence of the medium's attenuation on non-Gaussian properties of the echo signal is considered. Preferential attenuation of higher frequency components of a pulsed ultrasound beam effectively broadens the beam and increases the resolution cell size. Thus, the resultant non-Gaussian parameter for broad bandwidth excitation of the transducer depends not only on the scatterer number density but also on the attenuation in the medium. These effects can be reduced or eliminated by using narrow-band experiments.     

仿生皮肤等效材料超声波测试方法的研究

为评定汽车安全碰撞实验模拟人的皮肤肌肉等效复合材料的力学特性,提出仿生皮肤等效材料的超声检测方法。通过测试仿生皮肤等效材料对超声波声速、衰减、散射和吸收率的变化,建立仿生皮肤等效材料力学性质与超声回波信号频率之间的关系模型,对仿生皮肤等效材料的弹性模量、组织特性、粘弹性和松弛模量进行等效性的分析与评定。对3种不同密度的仿生皮肤等效材料的声速、弹性模量和声衰减等参数进行了测算,结果表明:该测试方法正确可行,测试数据为仿生皮肤等效材料的设计合成、制备提供力学参数依据,对仿生材料的力学等效性能评定有着重要的参考价值。     

管道腐蚀超声波在线检测技术

提出一种用于管道在线腐蚀检测的方法,基于超声波脉冲反射法检测原理,依据超声波在介质中的传播特性,研究系统的超声波发射电路和程控放大电路。实验结果表明:发射电路产生的高压负脉冲信号能够有效激励超声探头;程控放大电路可以解决回波信号因深度增加能量衰减的问题,获得的信号达到技术要求。系统能够完成管道在线腐蚀检测的需要,具有良好的应用价值。     

Processing of Ultrasonic Echo Envelopes for Object Location With Nearby Receivers

Ultrasonic sonar systems are commonly used for obstacle location in robotics and autonomous navigation applications. When irregular objects have to be located, optimal algorithms for time-of-flight (TOF) estimation, like cross correlation, might be unreliable since complex reflecting surfaces can destroy phase coherence during the duration of the echo. Direct threshold methods acting on the envelope are equally inaccurate. This paper proposes a simple digital processing technique, called selective normalization, that works with the signal envelope and robustly determines the differential TOF (DTOF) of the ultrasonic echoes received by two or more nearby transducers. It is empirically demonstrated that this method improves the positioning accuracy of nonpointlike objects.      

基于阵列超声传感器的气液界面检测

利用超声波声束对两相流参数检测的优点,使用阵列超声传感器探究了气液界面下的超声波声束和液面的关系。实现了超声波声束对整个气液界面的参数检测,测量了静态气液界面高度,实现动态超声波声束对分层流气液界面的重构。并在河北大学多相流循环装置进行实验验证,实验结果表明,阵列超声波声束可以实现对气液界面高度检测,可分辨最小2mm气液界面高度;重构图像的截面含气率和高速相机拍摄得到的截面含气率误差不超过4%。     

Measurement of Broadband Temperature-Dependent Ultrasonic Attenuation and Dispersion Using Photoacoustics

The broadband ultrasonic characterization of biological fluids and tissues is important for the continued development and application of high-resolution ultrasound imaging modalities. Here, a photoacoustic technique for the transmission measurement of temperature-dependent ultrasonic attenuation and dispersion is described. The system uses a photoacoustic plane wave source constructed from a polymethylmethacrylate substrate with a thin optically absorbent layer. Broadband ultrasonic waves are generated by illuminating the absorbent layer with nanosecond pulses of laser light. The transmitted ultrasound waves are detected by a planar 7-μm high-finesse Fabry-Perot interferometer. Temperatureinduced thickness changes in the Fabry-Perot interferometer are tracked to monitor the sample temperature and maintain the sensor sensitivity. The measured ?6-dB bandwidth for the combined source and sensor is 1 to 35 MHz, with an attenuation corrected signal level at 100 MHz of ?10 dB. The system is demonstrated through temperature-dependent ultrasound measurements in castor oil and olive oil. Power law attenuation parameters are extracted by fitting the experimental attenuation data to a frequency power law while simultaneously fitting the dispersion data to the corresponding Kramers-Kr?nig relation. The extracted parameters are compared with other calibration measurements previously reported in the literature.     

基于超声相控技术的船舶吃水测量方法

为了解决内河船舶因超吃水引起的通航阻塞以及船舶安全问题,提出一种基于超声相控技术的船舶吃水测量方法。以超声相控技术为理论基础,通过控制一维线型超声相控阵列换能器发射聚焦声波,实现对目标船舶的相控扫描,获取各扫描点的回波信号;利用匹配滤波算法对回波信号进行滤波,改善信噪比;利用阈值法提取回波信号的时延;利用渡越时间法,计算出扫描点到各发射振元中心的距离,利用双曲交汇法计算出扫描点的空间坐标;分析回波信号幅值和扫描点位置坐标即可得到船舶吃水深度。为验证方法的可靠性,搭建了小比尺船模吃水测量实验系统,分析了110~140 mm不同吃水深度下的实验结果,计算了实际吃水与测量吃水间的相对误差。实验结果表明,使用匹配滤波法处理后的回波信号信噪比从15.26 dB提高至36.39 dB,实验时,最大相对误差出现在船舶实际吃水130 mm时,绝对误差为2.3 mm,相对误差为1.7%。     

A robust correlation receiver for distance estimation

Many methods for distance estimation, such as the ultrasonic pulse-echo method, involve the estimation of a time-of-flight (TOF). In this paper, a signal model is developed that, apart from the TOF, accounts for an unknown, linear frequency dependent distortion as well as for additive noise. We derive a TOF estimator for this model based on the criteria of maximum likelihood. The resulting receiver can be seen as an extension or generalization of the well known cross-correlation, or “matched filter”, estimator described, e.g., by Nilsson. The novel receiver is found to be more robust against unknown pulse shape distortion than the cross-correlation estimator, giving less biased TOF estimates. Also, bias versus noise sensitivity can be controlled by proper model order selection     

反相叠加减小超声检测盲区的方法

对于收发合置应用的换能器,在发射脉冲信号的激励下,会产生一定的拖尾,在大尺度声学测量应用中这种拖尾可以被忽略,但是在短距离声学测量应用中,回波信号会淹没在激励信号的拖尾之中,导致测量盲区的加大.为了提高超声波的短距离测量能力,从换能器等效电路入手,通过分析换能器的频率特性,设计了换能器的等效高斯带通滤波器模型,提出了一...