喷流耦合式超声位移传感器的设计

本文主要研究一种新型微位移传感器。它用超声波原理进行检测，以喷流的水柱作为超声波传播的介质，可以在恶劣环境下进行位移测量。位移等于超声波传播的速度与超声波从发到收之间传播时间的乘积。考虑到声速会随介质一水的温度的升高而增大，设计时进行了实时温度补偿，提高了系统的精度。     

超声相控阵距离幅度曲线计算方法

超声相控阵偏转聚焦声场能量分布不均匀,造成不同位置的缺陷回波幅度差异,针对该缺陷量化问题,提出超声相控阵系统距离幅度曲线理论计算方法。在非近轴近似声场模型的基础上,结合缺陷散射模型来建立相控阵系统测量模型,再利用该方法来预测不同位置横通孔缺陷的回波信号,进而获得信号幅度随位置的变化曲线。分析对比了不同偏转聚焦声束理论计算结果与实验测量结果,两者幅度在焦点附近具有较好的一致性,偏差在5%以内,验证了超声测量模型计算方法的有效性。     

Long-gauge length embedded fiber optic ultrasonic sensor for large-scale concrete structures

A fiber optic ultrasonic sensor based on Fizeau interferometer has been developed and demonstrated. A helium–neon laser light source with wavelength 0.6328 μm is used in our experiment. A special feature is its Fizeau configuration, which enables one to eliminate much undesirable noise by combining both the reference arm and the sensing arm within the same length of fiber. The dynamic response model of photo-elastic effect of ultrasonic wave and optical fiber is established. The fiber optic ultrasonic sensor experimental results are obtained and compared with the convenient PZT transducer.     

油-气-水三相流超声传感器持气率测量

为探索油-气-水三相流持气率测量难题,该文开展了脉冲透射式超声传感器持气率测量动态实验研究。首先,利用超声传感器与光纤传感器组合,测取了油-气-水三相流中段塞流、混状流、泡状流的响应信号;其次,提取了超声脉冲信号的最大值序列来反映不同流型时超声传感器响应特性,同时,借助双头光纤传感器与相关测速法,计算得到了流体中气泡弦长序列;最后,结合流型与泡径信息,利用超声传感器测量了不同流型下持气率,并分析了不同流型持气率预测的误差来源,为其他油-气-水三相流持气率测量传感器设计提供了借鉴。     

基于广义合成阻抗超声传感器电端匹配的研究

超声波测距具有非接触、高准确度、价格低和使用方便等优点,被广泛应用于工业生产、医学检查、日常生活,如无人驾驶汽车、机器人、液位计等。在这些应用中,超声波传感器是应用中的最关键部件之一。因此,本文在分析了超声波传感器在谐振频率点等效电路的基础上,分别采用无源电感和有源电感对超声换能器的发射探头和接收探头进行电端匹配,提高了收发探头的效率。实验表明,匹配方法是有效的。     

Long distance laser ultrasonic propagation imaging system for damage visualization

Wind turbine blade failure is the most prominent and common type of damage occurring in operating wind turbine systems. Conventional nondestructive testing systems are not available for in situ wind turbine blades. We propose a portable long distance ultrasonic propagation imaging (LUPI) system that uses a laser beam targeting and scanning system to excite, from a long distance, acoustic emission sensors installed in the blade. An examination of the beam collimation effect using geometric parameters of a commercial 2 MW wind turbine provided Lamb wave amplitude increases of 41.5 and 23.1 dB at a distance of 40 m for symmetrical and asymmetrical modes, respectively, in a 2 mm-thick stainless steel plate. With this improvement in signal-to-noise ratio, a feasibility study of damage detection was conducted with a 5 mm-thick composite leading edge specimen. To develop a reliable damage evaluation system, the excitation/sensing technology and the associated damage visualization algorithm are equally important. Hence, our results provide a new platform based on anomalous wave propagation imaging (AWPI) methods with adjacent wave subtraction, reference wave subtraction, reference image subtraction, and the variable time window amplitude mapping method. The advantages and disadvantages of AWPI algorithms are reported in terms of reference data requirements, signal-to-noise ratios, and damage evaluation accuracy. The compactness and portability of the proposed UPI system are also important for in-field applications at wind farms.     

一种简单高精度超声液位计系统的设计与实现

介绍了超声时延法测距的基本原理,设计并实现了一种基于DSP的超声液位计系统,改进国内同类产品精度和稳定度偏低的问题。利用选用的AD、DSP芯片特点,给出了一种简单高效率的超声换能器驱动电路和回波采集放大电路的实现方案;使用通用16位定点DSP芯片TMS320VC5502,实现测距算法,增强了后端数字信号处理能力;使用收发一体窄带超声换能器发射和接收超声信号,其中心频率20kHz,3dB带宽1kHz。实验结果表明,本系统测量范围为0.5～18m,测量精度可达到测量距离的0.5%。     

电容应变式压力传感器原理及检测电路设计

论述了电容应变式压力传感器的原理，给出了一种电容应变式压力传感器的电路，并分析了压力大小与电路输出电压之间的关系。     

用于测量流量和含沙量的超声波液位测定系统

本文介绍了实验室内用于测量流量和含沙量的超声波液位测定系统，此系统采用气介式方案，选用复合材料高频换能器作为超声波发射／接收器件，结构简单，静态测量时测量误差在１５０ｍｍ范围内不超过１ｍｍ，并可与微机进行远距离通讯。     

基于Fabry-Perot模型设计亚波长金属狭缝阵列光学异常透射折射率传感器

研究了在水溶液环境中亚波长金属狭缝阵列光学异常透射的折射率传感特性.采用严格的全矢量方法计算了狭缝阵列的透过率谱.建立了Fabry-Perot半解析模型,能够精确预言全矢量方法的计算结果.基于该模型给出的共振条件,提出并解释了当透射峰精确位于瑞利异常位置时,透射峰能达到最尖锐的状态,给出了设计狭缝阵列达到该状态的方法.设计得到的透过率谱峰值半高宽δλ可达0.01 nm,对应的溶液折射率测量不确定度δn_s达到2×10^-6RIU.系统地给出了阵列周期、狭缝宽度、入射角等参数对设计得到的传感灵敏度,δλ,δn_s,峰值透过率等的影响.     

基于LMS自适应时延估计和FPGA的超声波测风系统研究

利用超声波传感器进行风速测量时,温度对超声波传播有很大影响,时延估计对超声波测风系统的精度起到很大的作用。本超声波测风系统为避免温度对风速测量中的影响,采用了基于时差法的测量原理,为了提高时延估计值的精度,提出了基于最小均方(LMS)自适应时延估计的测量方法,研制了以单片机Atmega128和现场可编程门阵列(FPGA)为核心的硬件系统。仿真和实际测试的结果表明,该超声波测风系统的时延估计值精确度较高,具有很高的应用价值。     

超声测断面形状误差分析及测试方法探讨

本文对超声波斜入射情况下存在的测距误差进行了分析，给出了数学修正的公式，并通过实验进行了验证，对测量不同形状空间的测试方法了探讨。本文的讨论对提高测试精度和选择工程测试方案有参考意义。     

阵元固体指向性补偿对超声全聚焦成像的 优化研究*

超声全聚焦成像中,声波的传播受到阵元指向性的影响,位于阵元不同方位的缺陷成像幅度不同。缺陷相对阵列中心偏角越大,回波幅度越低,容易造成漏检。为提高超声全聚焦算法对固体中大偏角缺陷的成像能力,该文引入了矩形阵元固体指向性函数,建立了基于固体指向性补偿的超声全聚焦优化算法,利用指向性系数对不同角度区域的成像进行幅值补偿。实验结果表明,相对于基本超声全聚焦和传统指向性补偿的超声全聚焦算法,该文固体指向性优化算法对大偏角缺陷的成像幅度补偿效果更好,检测灵敏度更高,有效避免了缺陷漏检,扩展了超声全聚焦算法检测范围。     

超声探头的响应特性及暂态回波模型

建立检测系统的数学模型,可以更好地理解超声检测的物理本质。分析了超声波从产生、介质中传播、缺陷耦合以及接收的全过程,将缺陷回波表示为探头响应函数与缺陷响应的时域卷积。利用空间脉冲响应和基尔霍夫近似建立了超声波与平面型缺陷的耦合模型,用大平面试块底面回波和大平面响应进行反卷积求得了探头的响应函数,并详细分析了探头在不同偏置位置时不同大小缺陷响应的特点,发现缺陷回波由直达回波和边缘回波组成,直达回波和边缘回波极性相反,且直达回波的幅值远远大于边缘回波。     

An ultrasonic method for measuring the elastic properties of human tibial cortical and cancellous bone

Ultrasonic techniques have been used to measure the elastic properties of bone. Eight human tibiae were used to determine and map the elastic properties of cortical and cancellous bone. The present study shows cortical bone to be at least orthotropic in its material symmetry. The mechanical properties of cortical bone are more homogeneous along the length than around the circumference. The variations in the properties around the quadrant of cortical bone are small, less than 10%, while differences in the properties around the circumference of cancellous bone are more apparent, approximately 5 times those of cortical bone. The elastic properties of cancellous bone exhibited inhomogeneity and some consistency pattern along both the length and the circumference.     

用声波速度确定骨组织弹性参数

本文用超声方法确定密质骨的弹性特征,其基本原理是基于弹性波理论中的Christoffel方程。本文应用液浸、声波穿透技术,对牛胫骨样品中一些特殊入射方向的声波速度进行了测试,利用固体中沿任意方向的弹性波传播速度与材料的弹性系数间的关系,通过计算机编程反演出具有六方晶体对称结构的密质骨组织的5个独立弹性常数。结果与相关文献中其它方法所得结果一致。     

一种测量温度和流速的光纤光栅传感器

提出一种基于铝片的测量温度和流速的光纤布喇格光栅(FBG)传感器。采用一种耐高温胶将光纤布喇格光栅封装在一小铝片上，经过高温固化处理，可保持光纤光栅传感器的稳定性。通过-20℃～100℃温度实验，得到该传感器的温度灵敏度系数为0.0392nm/℃,是封装前的3.5倍，且传感器温度响应保持了很好的线性和重复性。从水温14.5℃时的流速实验中得到水流速在0～20m/s范围变化时，FBG峰值波长漂移了0.13nm,验证了此光纤光栅传感器测量流速的可行性。试验结果表明，该传感器既可以作为温度传感器，又可以作为流量传感器，并且制作简单，成本较低。     

Resonance tracking and vibration stablilization for high power ultrasonic transducers

Resonant frequency shift and electrical impedance variation are common phenomena in the application of high power ultrasonic transducers, e.g. in focused ultrasound surgery and in cutting. They result in low power efficiency and unstable vibration amplitude. To solve this problem, a driving and measurement system has been developed to track the resonance of high power transducers and to stabilise their vibration velocity. This has the ability to monitor the operating and performance parameters of the ultrasonic transducers in real time. The configuration of the system, with its control algorithm implemented in LabVIEW (National Instruments, Newbury, UK), ensures flexibility to suit different transducers and load conditions. In addition, with different programs, it can be utilised as a high power impedance analyser or an instantaneous electrical power measurement system for frequencies in the MHz range. The effectiveness of this system has been demonstrated in detailed studies. With it, high transducer performance at high power can be achieved and monitored in real time.     

超声波电源中数字鉴相器设计

超声波电源系统中电压电流相位差测量精度影响着换能器振幅稳定性以及系统工作效率。目前基于异或门原理,采用分立数字芯片实现鉴相的方案,存在信号调理电路复杂、线性范围小、精度低等问题。为提高电压电流鉴相精度,该文提出了一种数字鉴相器设计。该数字鉴相器采用正交解调原理鉴相,并使用坐标旋转数字算法在FPGA上实现了鉴相器的设计,简化了电路,减少了杂散信号的干扰。经过Modelsim仿真测试表明在30 dB信噪比条件下鉴相误差为0.21°,最后经过实验测试,数字鉴相器鉴相最大误差绝对值为0.256°,提高了测量精度。     

A comparison between ultrasonic array beamforming and super resolution imaging algorithms for non-destructive evaluation

In this paper the total focusing method, the so called gold standard in classical beamforming, is compared with the widely used time-reversal MUSIC super resolution technique in terms of its ability to resolve closely spaced scatterers in a solid. The algorithms are tested with simulated and experimental array data, each containing different noise levels. The performance of the algorithms is evaluated in terms of lateral resolution and sensitivity to noise. It is shown that for the weak noise situation (SNR > 20 dB), time-reversal MUSIC provides significantly enhanced lateral resolution when compared to the total focusing method, breaking the diffraction limit. However, for higher noise levels, the total focusing method is shown to be robust, whilst the performance of time-reversal MUSIC is degraded. The influence of multiple scattering on the imaging algorithms is also investigated and shown to be small.