基于FPGA的相控超声发射系统设计与实现

设计了一种以FPGA为核心的相控超声发射系统,对该系统工作原理及相控聚焦方法进行了研究;设计了一种二维相控阵列,并进行了阵列定点聚焦延时仿真;最后运用该系统实现了对相控阵列的高精度聚焦延时控制,并经过DA转换、电压及功率放大,产生了幅值及波形可控的激励信号,测试了该系统对实际目标的定位精度;实验结果显示对实际目标定位偏差在3%左右,该超声相控发射系统可实现相控聚焦发射,延时控制精度高,可靠性好。     

脉冲激光探测的最大探测距离的研究

脉冲激光探测的最大探测距离与发射信号功率有关,根据系统发射端瞬时功率的形式,通过计算得出了脉冲激光平均发射功率和最大瞬时功率分别与驱动电流的脉冲上升沿时间、脉冲宽度、脉冲重复周期的关系.结合传输衰减、弱信号检测和信号预处理过程中的信号功率变化,得出了最大探测距离与激励电流波形参数、光电探测器参数、信号预处理电路噪声、信...     

相位可控的核四极矩共振激励脉冲发生器设计

在核四极矩共振（NQR）领域，射频激励脉冲信号的优劣对NQR响应信号有重要影响.针对常规方法中射频激励脉冲参数不可控的问题，本文基于32位闪存微型控制器STM32和直接数字频率合成（DDS）芯片AD9910设计了一种相位可控激励脉冲发生器.采用STM32控制AD9910产生波形参数（脉冲宽度、脉冲间隔、脉冲个数和共振频率等）可控的射频激励脉冲，利用LabVIEW软件平台设计脉冲参数设置界面，并建立计算机与微控制器通信，实现波形参数的精确优化控制.实验结果表明，该方法实现了相位可控的NQR激励脉冲序列，可为后续NQR信号检测提供有效激励源.     

脉冲波形对级联相敏放大器光传输系统性能的影响

研究了相敏光放大器（PSA）中抽运光和信号光之间存在相位漂移时,信号脉冲波形对级联相敏光放大器光纤通信系统传输性能的影响。通过系统仿真,得到了在不同的相位漂移下高速信号脉冲眼图劣化度随光纤色散变化的曲线,以及在给定的光纤色散下放大器有相移与无相移时信号眼图劣化度随信号脉冲指数变化的曲线。由仿真结果可知,脉冲波形不同对系统性能的影响亦不同。采用超高斯脉冲的系统性能优于采用高斯脉冲,耐用超高斯脉冲指数存在最佳值。     

带内干扰抑制的超宽带脉冲设计

采用不同幅度和延迟的高斯函数脉冲组合来拟合抽样函数脉冲，利用拟合的抽样函数脉冲设计超宽带脉冲信号,实现美国联邦通信委员会制定的辐射掩蔽要求的高效逼近.该方法产生的脉冲波形具有实现简单、持续时间短、带外辐射功率小、容易进行时域或频域调节等特点.与已报道的几种脉冲比较，设计的脉冲可携带更多的能量, 同时具有良好的带内（窄带或宽带）干扰抑制能力，能够和带内的其他通信系统更好的共存.最后，对设计的脉冲波形和最佳高斯波形的通信性能进行了比较，表明文中波形的性能明显优于最佳高斯波形.     

基于超声相控阵的环焊缝缺陷检测方法研究

针对传统超声探头焦距固定,检测位置的改变就要更换相应焦距的探头而影响检测效率的问题,提出一种基于超声相控阵换能器的环焊缝缺陷检测方法。而超声相控阵具有电子偏转和电子聚焦特性,能在不移动的情况下发射偏转聚焦超声束,有效地解决了上述问题。首先基于超声相控线阵换能器的声场特点,采用数值分析方法,研究了影响声束偏转聚焦性能的几个主要参数。然后给出了与超声相控阵换能器相连接的多通道数据采集系统结构。介绍了单通道声信号的硬件结构及相应的信号处理方法,实现了对换能器中单个阵元的精确延时的控制。实验结果表明,优化设计的超声相控线阵换能器具有较高的检测精度和检测效率。     

面向CMUT声发射特性的驱动电路优化设计

根据电容式微机械超声换能器(CMUT)的工作原理,设计了用于驱动CMUT发射超声波的电路.通过适当的串行匹配,消除了脉冲激励信号的过冲现象.在此基础上进一步探究了脉冲激励参数对CMUT声发射特性影响.结果表明,随着激励脉冲个数的增加,CMUT输出超声信号的有效带宽逐渐变窄,二次谐波逐渐增强;随着激励脉冲占空比的增加,C...     

大口径天线短脉冲微波辐射特性

为了开展大口径天线短脉冲微波辐射特性研究,建立了一套大口径天线微波短脉冲特性测试系统。该系统可产生快上升沿、脉冲可调(脉宽最短可到0.5 ns)的微波激励脉冲、接收动态范围大于52 dB。利用该测试系统进行实验,获得了不同微波激励脉冲宽度条件下,天线方向图和辐射场波形脉冲宽度变化曲线。测试结果表明:在天线远场距离处,改变微波激励脉冲宽度,对天线主轴辐射场波形基本无影响;而在偏离主轴处,辐射场波形会出现不同程度的脉冲展宽及幅值减小等波形畸变现象,偏离主轴角度越大,微波激励脉冲宽度越小,畸变越明显。     

机载多脉冲激光雷达目标信号模拟器的研究

研究多脉冲激光雷达目标信号模拟器,用以评估回波数字信号处理算法及其实现平台的性能。结合信号能量与波形关系指出由激光雷达方程建立回波信号波形模型是不充分的。对空中目标回波脉冲展宽进行建模及数值仿真,得到不同倾角、目标距离及目标尺寸下的波形展宽时间数据。根据展宽前后能量保持不变的性质,利用高斯脉冲函数特征参数求解建立回波波形数学模型。基于目标距离误差及目标回波噪声统计特性建立回波仿真模型,提出了依信噪比发生回波观测信号的方法。对比两种模拟器的信噪比误差、最小模拟信噪比、连续工作时间等性能指标,总结了新型模拟器的优势。     

纳秒脉冲电压的波形重建

 介绍了一种根据脉冲电压测量系统的输入输出波形对纳秒脉冲电压信号测量系统进行参数计算的方法和技术，该方法基于最优化原理，并将其应用于快脉冲电压波形的重建。重建的波形用电容分压器实测波形进行了检验，表明重建波形有比用积分器更好的效果。     

楔块中脉冲声场及相控阵成像自检研究

相控阵横波检测必须在换能器前方加上楔块,对于楔块中的声场进行研究具有重要意义。本文通过数值计算和物理实验研究了超声相控阵楔块中的脉冲声场,分析并解释了超声相控阵系统自检成像过程中各种波形的产生机理和转换过程。首先从固体中超声传播理论出发,采用时域有限差分方法对相控阵楔块中各阵元独立发射条件下的脉冲声场进行仿真计算,给出了超声脉冲在楔块中的传播过程;然后开展了对应边界条件下相控阵楔块的B模式成像实验。数值模拟和物理实验的结果基本一致。本文的研究初步展示了楔块中的脉冲声场,其结果可为超声相控阵系统自检和楔块设计提供参考。     

带斜楔相控声束偏转聚焦延时特性研究

带斜楔的相控阵超声检测广泛应用于低碳钢薄壁工件焊缝的检测,研究带斜楔的相控阵超声偏转聚焦检测延时法则和对应的声场将使检测可靠性进一步提高。本文利用费马原理探究了相控阵超声探头辐射声波至楔块中,在楔块-工件平面界面发生模式转换入射到工件中的横波聚焦时各阵元延时的计算方法,数值求解指定焦点时各阵元的延时,并利用计算得到的延时进行声场仿真和实验测量,发现声波能很好的聚焦在目标点,仿真和实验结果吻合。     

Improved pulsed broadband ultrasonic spectroscopy for analysis of liquid-particle flow

The paper contains an investigation of broadband pulsed ultrasonic spectroscopy techniques, intended for testing of suspensions, such as a liquid-particle flow containing small diameter particles. Influence of traditional and novel broadband pulse shapes on quality of frequency spectra is analysed, as well as pulse design aspects leading to an optimal shape of an ultrasonic excitation wave. Effects that may influence signal quality and method reliability in a given setup, in particular resonances and noise are discussed. Solutions for signal acquisition and averaging techniques are presented, as well as results of testing of instrumentation limits and overall performance. Results of acoustic spectroscopy measurement of a concentrated liquid-particle flow are provided. A number of experimental and numerical examples, together with comprehensive explanations, show a potential for ultrasonic attenuation spectroscopy to be a successful methodology for an on-line measurement of fluid-particle suspensions and composite non-homogeneous materials in general.     

Quinary excitation method for pulse compression ultrasound measurements

A novel switched excitation method for linear frequency modulated excitation of ultrasonic transducers in pulse compression systems is presented that is simple to realise, yet provides reduced signal sidelobes at the output of the matched filter compared to bipolar pseudo-chirp excitation. Pulse compression signal sidelobes are reduced through the use of simple amplitude tapering at the beginning and end of the excitation duration. Amplitude tapering using switched excitation is realised through the use of intermediate voltage switching levels, half that of the main excitation voltages. In total five excitation voltages are used creating a quinary excitation system. The absence of analogue signal generation and power amplifiers renders the excitation method attractive for applications with requirements such as a high channel count or low cost per channel. A systematic study of switched linear frequency modulated excitation methods with simulated and laboratory based experimental verification is presented for 2.25 MHz non-destructive testing immersion transducers. The signal to sidelobe noise level of compressed waveforms generated using quinary and bipolar pseudo-chirp excitation are investigated for transmission through a 0.5 m water and kaolin slurry channel. Quinary linear frequency modulated excitation consistently reduces signal sidelobe power compared to bipolar excitation methods. Experimental results for transmission between two 2.25 MHz transducers separated by a 0.5 m channel of water and 5% kaolin suspension shows improvements in signal to sidelobe noise power in the order of 7–8 dB. The reported quinary switched method for linear frequency modulated excitation provides improved performance compared to pseudo-chirp excitation without the need for high performance excitation amplifiers.     

Ultrasound fields in attenuating media

For medical ultrasonic imaging and for nondestructive testing, the attenuation of pressure waves and the resulting shift in wave velocity are important features in commonly used transmission media such as biological tissue. An algorithm for the numerical evaluation of pressure field distributions generated by ultrasonic transducers is presented. The attenuation and dispersion of the sound transmission medium are taken into consideration. The sound fields are computed numerically for continuous wave as well as pulse excitation. The transducer has plane or gently curved geometry and is embedded in a plane rigid baffle. The numerically determined pressure fields are presented as 3D plots, as gray-scale images for a fixed time stamp (like a snapshot), or as isobars regarding the maximum values over time for each local point in the area under investigation. The algorithm described here can be utilized as a tool for design of ultrasound transducers, especially array antennas.     

基于空耦超声Lamb波的金属板状结构内部缺陷检测方法

针对接触式超声检测方法在金属板结构内部缺陷实际工程检测中存在的环境要求高、效率低、操作难度高等问题,提出了空耦超声Lamb波检测方法,该方法能更好地适应现场应用环境,提高检测效率,减少传感器数量。通过有限元仿真和实验分析比较了空耦超声检测与接触式超声检测两种方法接收到的信号和成像效果。结果表明:有限元仿真和实验中,空耦超声检测方法对缺陷位置的定位误差分别为2 mm和3.6 mm,接触式检测方法对缺陷位置的定位误差分别为2 mm和11.3 mm,空耦检测具有较高的定位精度;单侧激励条件下,适合采用A0模态Lamb波对板内缺陷进行检测;空耦超声检测可以通过调整信号接收角度接收单一模态Lamb波,避免伪像产生。该方法为后续金属板状结构内部缺陷的空耦超声检测提供参考。     

Schlieren visualization of ultrasonic wave fields with high spatial resolution

The visualization of ultrasonic wave fields in optically transparent liquids using the acousto-optic interaction is a well proven tool for the experimental investigation of wave propagation including wave field interaction effects with certain discontinuities and obstacles like reflection, refraction, and diffraction effects as well as for transducer testing and design. For high resolution visualization of wave fields including pulsed waveforms, pulsed light sources and sensitive optical imaging sensors with certain specifications are needed. In this paper the technical requirements of optical and electronic components for high resolution visualization of ultrasound wave fields will be presented. Also, specifications and operation results of a new designed, inexpensive Schlieren optical system will be presented, which is capable of pulsed wave field visualization in the MHz frequency range. The spatial resolution is high enough, not only for accurate beam shape and wave pattern visualization, but also for a gray-scaled display of wave amplitudes including amplitude zero crossings in ultrasound pulses. Consequently, ultrasonic wavelengths can be visualized quantitatively as well as wavelength changes of the ultrasound pulses while traveling through transparent media with different sound velocities. Results to be presented will include 2 MHz and 10 MHz experiments using single transducers as well as linear arrays of commercial medical scanners during their standard operation showing the system beamforming characteristics.     

Acoustic field excited by a pulsed laser line source in a cylinder

The excitation and propagation of the acoustic waves in an elastic cylinder are studied by laser ultrasonics both theoretically and experimentally. The theoretical analysis of the two-dimensional acoustic field excited by a pulsed laser line source impacting on the generatrix of an elastic cylinder is presented. The dispersive properties for both cylindrical Rayleigh wave and the higher modes--whispering gallery (WG) modes are analyzed in detail. The numerical transient displacement waveforms for a detecting point located another terminal of the cylinder diameter opposite the source are calculated. The experimental excitation and detection of the acoustic waves in an aluminum cylinder are carried out on a laser ultrasonic system, which mainly consists of a Q-switched Nd:YAG laser and a laser interferometer. The wave components of bulk waves and surface waves (cylindrical Rayleigh waves and WG modes) are analyzed by comparing the numerical and experimental waveforms. The results are in good agreement.     

Simulation on laser-induced surface acoustic wave on isotropic cylinders by finite element method

Based on the thermoelastic theory, a finite element model is developed to simulate the process of laser inducing ultrasonic field in isotropic cylinders, which can take the temperature dependence of thermal parameters into account. Using the finite element model, we have simulated the ultrasonic fields induced by a pulse laser line source impacting on the generatrix of aluminum cylinders with different diameters. And the intact waveforms of surface acoustic wave (SAW including cylindrical Rayleigh and Whispering gallery (WG) modes) are presented, which are in very good agreement with the calculated and experimental waveforms in other literatures. Furthermore, the dispersion properties of cylindrical Rayleigh waves are analyzed by the method of phase spectral analysis, and the results show that with the increasing frequency, the phase velocity of cylindrical Rayleigh wave rapidly increases to the maximum value, and then gradually decreases to that of plane Rayleigh wave. With the diameter of cylinder decreasing, the maximum value of phase velocity and the corresponding frequency increase.