从换能器技术的变化看声波测井技术的发展

无论是在电缆测井还是在随钻测井方面,声波换能器结构和振动模式的变化导致了声波测井技术的进步和重大演化.文章以声波测井换能器技术的变化为主线,分析了声波测井技术的发展和进步以及我国在该技术领域取得的进步.单极子声波测井技术已经成为我国成熟的声波测井技术,包括非对称声源技术在内的多极子声波测井技术是我国刚刚攻克的先进声波测井技术并已经进入产业化进程,以井下声波的定向辐射和定向接收为最主要特征的相控声波测井技术是正在研发的新一代声波测井技术,我国在此领域也已经取得显著突破.     

A new design on broadband flextensional transducer

The new flextensional transducer presented is driven by a tube stacked by longitudinally polarized piezoelectric ceramic rings. The rings are compressed between two annulus steel end plates which are coupled by a dual convex aluminum shell with slotted gaps. The transducer is a free-flooded design with the interior of the tube open to the surrounding water. Three main vibrating modes including the cavity, the longitudinal and the radial can be utilized by appropriately coupling design to broaden the working bandwidth. A prototype is fabricated and measured. The results confirm the three vibrating modes mentioned above and the broad band of transmitting voltage response is gained successfully with difference less than 10 dB from 2200 Hz to 9000 Hz.     

用锁相环电路跟踪压电换能器并联谐振频率区

本在介绍用PLL（Phase-Locked Loop锁相环）电路进行频率跟踪的原理和实质的基础上,给出一种够跟踪压电换能器并联频率fP区间的具体电路,并通过实验研究了匹配电感和负载等对电路跟踪性能的影响,结果表明,这个电路具有很好的频跟踪和功率自动调节性能。     

复频聚焦超声换能器水中焦区商场特性的研究

本文对新研制的一种复频聚焦超声换能器的辐射声场进行了实验研究,测定了辐射压在轴向上的分布曲线,进而确定了焦区位置,这与理论所得结果符合较好,测定了辐射声压在焦平面上的分布曲线,并对焦区声场进行了定位,最后对换能器在水中焦区辐射声的频谱进行了研究,不仅观测到了两个源波,而且还观测到了和频波,差频波以及倍频波,证实了声散射声效应的存在。     

多路CCD位移传感器用于路面纵断面检测研究

本文提出了一种运用多路电荷耦合器件(CCD)位移传感器快速检测路面纵断面的测量系统,介绍了测量原理,给出了数据处理方法和实验结果.此系统设计时速最高为60km/h,路面高度分辨率为0.5mm,检测范围为±120mm.实验证明,此系统用于路面纵断面快速检测是可行的.     

基于应力波传播机理的混凝土无损检测研究综述

混凝土结构在基础设施中应用广泛,但环境与荷载导致材料和结构的老化损伤问题,势必影响材料性能及耐久性和结构完整性及安全性．构建有效的混凝土材料性能评估和结构损伤识别体系是当前研究热点．现有研究因对应力波传播机理不深入理解、损伤定位定量模型理想化、损伤形式简化等问题仍存在局限性．因此,开发普适全面、稳定可靠的无损检测系统,对在建或既有混凝土结构服役状况进行长期、实时跟踪,具有重要学术意义和工程应用价值．本文结合混凝土无损检测领域的国内外研究现状及进展,从智能压电材料振动机理研究、混凝土无损检测方法发展、基于应力波的无损检测研究进展这三个逻辑层面,即按照研究手段到研究方法再到具体研究方案的顺序,循序渐进地对混凝土材料性能评估和结构损伤识别的研究进行了成果总结和方法提炼;基于此进一步概述了该领域所存在的瓶颈问题、研究重难点,最后提出了针对这些局限性的混凝土无损检测研究展望．     

Air-coupled detection of nonlinear Rayleigh surface waves to assess material nonlinearity

This research presents a new technique for nonlinear Rayleigh surface wave measurements that uses a non-contact, air-coupled ultrasonic transducer; this receiver is less dependent on surface conditions than laser-based detection, and is much more accurate and efficient than detection with a contact wedge transducer. A viable experimental setup is presented that enables the robust, non-contact measurement of nonlinear Rayleigh surface waves over a range of propagation distances. The relative nonlinearity parameter is obtained as the slope of the normalized second harmonic amplitudes plotted versus propagation distance. This experimental setup is then used to assess the relative nonlinearity parameters of two aluminum alloy specimens (Al 2024-T351 and Al 7075-T651). These results demonstrate the effectiveness of the proposed technique – the average standard deviation of the normalized second harmonic amplitudes, measured at locations along the propagation path, is below 2%. Experimental validation is provided by a comparison of the ratio of the measured nonlinearity parameters of these specimens with ratios from the absolute nonlinearity parameters for the same materials measured by capacitive detection of nonlinear longitudinal waves.     

Improving the air coupling of bulk piezoelectric transducers with wedges of power-law profiles: A numerical study

An air-coupled ultrasonic transducer is created by bonding a bulk piezoelectric element onto the surface of a thick plate with a wedge of power-law profile. The wedge is used to improve the ultrasonic radiation efficiency. The power-law profile provides a smooth, impedance-matching transition for the mechanical energy to be transferred from the thick plate to the air, through the large-amplitude flexural waves observed in the thinnest region of the wedge. The performance of the proposed transducer is examined numerically and compared to that of a design where the piezoelectric element is isolated and where it is affixed to a thin plate of uniform thickness. The numerical analysis is first focused on the free-field radiation of the transducers. Then, time-reversal experiments are simulated by placing the transducers inside a cavity of arbitrary shape with some perfectly reflecting boundaries. In addition to time-reversal mirrors, the proposed concept could be integrated in the design of phased arrays and parametric arrays.     

The measurement of the diameter change of a piezoelectric transducer cylinder with the white-light interferometry

The measurement of the diameter change of a piezoelectric transducer (PZT) cylinder with the white-light interferometry is proposed and experimentally demonstrated. One arm of a Mach–Zehnder interferometer (MZI) is wrapped on the PZT cylinder, and the phase change of the interferogram of the MZI is used to determine the diameter change when a DC voltage is applied on the PZT cylinder. The Fourier transform white-light interferometry is used for recovering the phase change of the interferometer. The experimental results show that the diameter change resolution of 0.8 nm for the PZT cylinder with diameter of 40 mm is achieved.     

光弹法测量超声换能器声场

超声换能器声场的测试对于超声检测具有基础性作用,而传统的超声换能器声场测试方法具有一些局限性。本文介绍了搭建的动态激光光弹实验平台,并利用动态光弹法测量了纵波换能器和横波换能器辐射声场的特征,由瞬态声场图像获得了传声介质的声波速度及超声换能器的中心频率;由稳态声场图像获得了声场的近场长度、指向性和扩散角等参数;分析了光弹实验系统和测量方法可能引起测量误差。本文结果表明动态光弹法是一种有效的定量测量超声换能器声场的方法。