超声波的光外差接收

激光接收超声是一种非接触式的超声接收技术，它在超声无损评估及检测领域有重要的应用。本文设计研制了激光外差干涉接收超声的实验系统，该系统由声光调制器产生光频的频移，锁相环进行位相解调。文中重点讨论：（１）在光学部分，外差干涉光路空间准直性对信噪比的影响。（２）在信号处理电路部分，锁相环电路特性分析及其参数确定     

非线性超声相控阵无损检测系统及实验研究

相控阵超声无损检测技术近年来在无损检测领域得到了越来越广泛的应用。但当前相控阵超声检测基于传统线性超声,对于材料或结构的微缺陷、微裂纹等缺陷不敏感。研究基于超声的非线性效应的非线性超声无损检测技术对于克服线性超声相控阵技术的不足具有积极的意义。本文设计和开发了基于非线性超声相控阵的无损检测系统,并利用超声检测的标准试件对该系统的性能进行了检验。对比测试了常规线性超声方法、基于滤波的非线性超声方法以及基于反相脉冲的非线性超声方法对于钨丝线靶、超声仿体以及碳钢试块的检测效果。测试结果表明,非线性超声相控阵无损检测技术与传统线性超声相控阵无损检测相比具有空间分辨力高、缺陷分辨力强等优点,而基于反相脉冲的非线性相控阵超声无损检测在空间分辨力上比基于滤波的非线性超声检测方法又有比较显著的提高。     

超声马达梯度涂层摩擦材料研究

超声马达摩擦材料应同时具有良好的摩擦学特性和一定的接触变形要求,目前所用单一均质结构摩擦材料较难满足这一要求,需要研制新型摩擦材料.本文从摩擦学的减摩结构模型反推出一种增摩结构模型,针对超声马达对摩擦材料的要求,提出梯度涂层摩擦材料的设计思想,采用表面黏涂法研制了一种具有梯度结构的涂层摩擦材料.利用超声马达模拟试验装置考察了涂层厚度对超声马达性能的影响,初步验证了模型的正确性.在本文的试验条件下,当涂层材料表层厚度为1mm,底层厚度为0.7mm左右时,超声马达具有较好的性能.与其它种类的摩擦材料相比较,梯度涂层摩擦材料可以满足超声马达的使用要求,可望提升超声马达的性能,具有良好的发展前景.     

基于细观混凝土模型的时间逆转损伤成像方法

提出了一种针对混凝土结构损伤检测的时间逆转损伤成像方法.以检测混凝土结构中与骨料尺寸相近的微小损伤为目的,引入细观混凝土随机骨料模型,该模型将混凝土结构视为由水泥浆基底、骨料及粘接层组成的三相复合材料,基于Monte Carlo随机样本原理并结合真实试件的骨料级配曲线建立.在数值模拟分析中,将生成含损伤的细观模型导入有限元分析软件进行超声波场模拟,同时采用自适应性强的时间逆转模型(time reversed model,TRM)进行损伤定位.TRM分为正向检测和逆时成像两个部分:正向检测过程得到包含损伤的一系列散射回波信号,从数值角度进行时间反演并作为逆时过程的输入信号;逆时成像过程选用等效弹性参数模型,几何尺寸与随机骨料模型相同,时反信号在相应几何位置同时加载形成时反波场,时反波场在损伤位置会发生干涉叠加从而导致能量峰值的出现,通过确定干涉峰值时刻,并获取该时刻对应原始波场以及小波变换能量场完成成像.与原始数据波场图相比,小波变换处理成像结果消除了杂波干扰,成像结果更加清晰.进一步对等效弹性参数的取值进行讨论,并且在骨料尺寸范围内调整损伤大小,结果显示成像结果匹配度高,对于非均质混凝土结构的损伤检测能很好满足损伤定位需求.由此证明,时间逆转成像方法对于具有复杂结构的混凝土材料的损伤检测具有较好的适用性.     

New hydrogels from interpenetrated physical gels of agarose and chemical gels of polyacrylamide: Effect of relative concentration and crosslinking degree on the viscoelastic and thermal properties

In this article, we report on the viscoelastic and thermal properties of agarose–polyacrylamide (PAAm) interpenetrating polymer hydrogels (IPHs) and semi‐IPHs as a function of agarose concentration and PAAm crosslinking degree. The results demonstrated that the agarose is able to gel in the presence of crosslinked and linear IPHs. In addition, the reticulation of PAAm in the presence of agarose is confirmed for the case of IPHs giving rise to systems with dimensional stability at high temperatures. The formation of a fully IPH was ascertained at low agarose concentrations. A study of the morphology and nanoscale elasticity of the different systems has been carried out with atomic force microscopy/ultrasonic force microscopy (UFM). UFM data provide further evidence of interpenetration, allowing us to visualize—if present—phase‐separated domains with nanoscale resolution for the various crosslinking degrees and PAAm and agarose concentrations used during the formation of the IPHs. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

Intermediate regime of light diffraction by surface ultrasonic waves in planar gyrotropic optical waveguides

The intermediate regime of optoacoustic interaction, similar to the Bragg one, with Rayleigh surface ultrasonic waves in gyrotropic planar waveguides is studied. A system of equations of bound waves is presented that describes planar optoacoustic interaction in the intermediate, Raman-Natoh, and Bragg regimes of light diffraction by surface ultrasonic waves. It is shown that the optical activity of a wavequide film favors the incident light energy pumping to diffracted light for a TE-polarization wave and decelerates this process for an incident TM-polarization wave. Mozyr' State Pedagogical Institute, 28, Studencheskaya St., Mozyr', 247760, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 3, pp. 412–416, May–June, 1997.     

Ultrasonic velocity hydration numbers of polyamines

Ultrasonic velocity hydration numbers of diamines, triamines and tetraamines and hydrochlorides of these amines were determined by measuring the maximum velocity of ultrasound in aqueous-ethanolic solutions. The results are interpreted on the basis of the hydrogen-bonded framework model of the water structure.     

非线性工作状态压电换能器匹配技术

针对压电换能器在大功率下存在复杂非线性而导致匹配参数难以优化的问题,以大功率超声金属焊接为例,通过采集测试焊接过程换能器两端电压的幅值与频率,建立换能器反谐振电阻与驱动电压有效值、频率之间的数学模型;提出基于反谐振电阻模型的最优功率匹配方法,推导了匹配电感电容的计算公式。最后实验验证了数学模型的准确性,且当换能器输入功率在最优功率附近时,匹配网络电能传输效率最高。     

基于深度学习的材料超声回波衰减预测方法

材料超声回波衰减是评价材料均匀一致性的常用方法, 针对具有复杂结构的航空发动机盘件难以进行材料底面超声回波衰减评价的问题, 本文提出了利用超声背散射波信号直接预测底面回波衰减的方法。采用10MHz聚焦探头进行超声背散射波数据的采集, 利用深度学习技术构建和训练模型,建立了基于深度学习的材料底面回波衰减预测方法, 同时讨论了采用不同信号形式的超声波信号分类识别模型的准确率差异。研究发现：基于深度学习技术可实现通过超声背散射波预测材料的底面回波衰减, 预测结果和实际底面回波衰减试验结果具有良好的一致性。     

Velocity profile measurement by ultrasonic doppler method

The ultrasonic velocity profile measuring method has been developed at PSI for application in fluid mechanics and fluid flow measurement. It uses pulsed ultrasonic echography together with the detection of the instantaneous Doppler shift frequency. This method has the following advantages over the conventional techniques: (1) an efficient flow mapping process, (2) applicability to opaque liquids, and (3) a record of the spatiotemporal velocity field. After a brief introduction of its principle, the characteristics and specifications of the present system are given. Then examples in fluid engineering for oscillating pipe flow, T-branching flow of mercury, and recirculating flow in a square cavity are described that confirm the method's advantages. Several other works under way by other investigators are introduced. A potential for in-depth study of fluid dynamics is demonstrated by several examples from an investigation of modulated wavy flows in a rotating Couette system. The position-averaged power spectrum and the time-averaged energy spectral density were used to study the dynamic characteristics of the flow, and subsequently the velocity field was decomposed into its intrinsic wave structure based on two-dimensional Fourier analysis.