Lead-free KNLNT piezoelectric ceramics for high-frequency ultrasonic transducer application

This paper presents the latest development of a lead-free piezoelectric ceramic and its application to transducers suitable for high-frequency ultrasonic imaging. A lead-free piezoelectric ceramic with formula of (K_0.5Na_0.5)_0.97Li_0.03(Nb_0.9 Ta_0.1)O₃ (abbreviated as KNLNT-0.03/0.10) was fabricated and characterized. The material was found to have a clamped dielectric constant ε₃₃^S/ε₀ = 890, piezoelectric coefficient d₃₃ = 245 pC/N, electromechanical coupling factor k_t = 0.42 and Curie temperature T_c > 300 °C. High-frequency (40 MHz) ultrasound transducers were successfully fabricated with the lead-free material. A representative lead-free transducer had a bandwidth of 45%, two-way insertion loss of -18 dB. This performance is comparable to reported performances of popular lead-based transducers. The comparison results suggest that the lead-free piezoelectric material may serve as an alternative to lead-based piezoelectric materials for high-frequency ultrasonic transducer applications.     

液氮温区下应变式位移传感系统测量性能的研究

文中研究了一种应变式位移传感系统在室温和液氮温度下的静态传输特性。实验结果表明,该系统在液氮温区下具有良好的输出特性,系统非线性度低于1%,滞环率低于5%,其灵敏系数与温度相关,293K和77K温度下的灵敏系数分别为-0.3654mV/V/mm和-0.3886mV/V/mm。实验结果为该位移传感系统在低温环境中的应用提供了一定基础。     

夹心式压电换能器的谐振频率跟踪方案设计

分析了夹心式压电换能器的阻抗特性,讨论了基于相位方式的现有跟踪方案的不足,提出了一种新的频率跟踪方案,介绍了实现该方案的电路系统。该方案的特点是:采用先扫频后跟踪的策略,解决了频率范围设定难的问题;增加解锁控制,使得系统在死锁或误跟踪时自动回到频率搜索状态;采用直接数字合成器(DDS)作为频率调整和信号产生的器件,实现了全数字系统,调整方便,精度高;采用复杂可编程逻辑器件(CPLD)做相位比较和DDS控制,使频率跟踪速度快,并且跟踪精度和速度均可控制。     

一种拓宽凸球面压电换能器指向性的方法

利用有限元和边界元耦合的方法对涂环氧树脂后的压电陶瓷凸球面换能器进行了指向性仿真计算,发现这种形式的换能器具有较宽的指向性开角。实验测量结果证明了上述结论。     

基于多元线性阵列探测器的快速光声层析成像

报道了一种基于相控聚焦的多元线性阵列探测器进行快速光声层析成像的方法和装置,并实现了模拟组织的光声层析成像。实验中采用波长为532nm脉宽为7ns的倍频Q-YAG激光器作为激发光源。多元线性阵列探测器由320个振元组成,采用相控聚焦的方法成像,每次由11个振群的探测器接受信号并合并1路,一幅图像由64路这样的信号组成。实验结果能够正确反映样品中的光学吸收分布。与现有的方法比较,本系统具有快速方便的特点,它有望成为一种组织功能在体成像的新方法,发展成为一种低成本的实用的临床诊断装置。     

Modeling nonlinear Rayleigh wave fields generated by angle beam wedge transducers—A theoretical study

Nonlinear Rayleigh wave fields generated by an angle beam wedge transducer are modeled in this study. The calculated area sound sources underneath the wedge are used to model the fundamental Rayleigh sound fields on the specimen surface, which are more accurate than the previously used line sources with uniform or Gaussian amplitude distributions. A general two-dimensional nonlinear Rayleigh wave equation without parabolic approximation is introduced and the solutions are obtained using the quasilinear theory. The second harmonic Rayleigh wave due to material nonlinearity is given in an integral expression with these fundamental Rayleigh waves radiated by the wedge transmitter acting as a forcing function. Multi-Gaussian beam (MGB) models are employed to simplify these integral solutions and to extract the diffraction and attenuation correction terms explicitly. The effect of nonlinearity of generating sources on the second harmonic Rayleigh wave fields is taken into consideration; simulation results show that it will affect the magnitude and diffraction correction of the second harmonic waves in the region close to the Rayleigh wave sound sources. This research provides a theoretical improvement to alleviate the experimental restriction on analyzing the effects of diffraction, attenuation and source nonlinearity when using angle beam wedge transducers as transmitters.     

Understanding a time reversal process in Lamb wave propagation

This study investigates the time reversal process (TRP) of Lamb wave signals which are transmitted and received by piezoelectric transducers bonded on plate-like structures. A number of previous studies have paid attention to spatial and temporal refocusing capability of an original excitation through the TRP in highly dispersive and complex media. However, when the TRP is applied to Lamb waves in a homogeneous regular waveguide, the refocusing capability is limited due to permanent residual side bands even if the duration of the time reversed signal increases. Based on the reciprocity of elastodynamics and linear piezoelectricity, theoretical interpretation is conducted for the main and residual side bands of the reconstructed signal in the time domain. In particular, the interpretation includes the temporal effect of velocity and amplitude dispersions, the existence of multimodes, and the reflections from boundaries during the TRP. Then, numerical and experimental tests are conducted to validate the theoretical findings of this paper. Practical issues for the successful implementation of the TRP of Lamb waves are briefly addressed as well.     

DYNAMIC CHARACTERISTICS OF AXIALLY-SYMMETRICAL ANNULAR CORRUGATED SHELL PIEZOELECTRIC TRANSDUCERS

The coupled extensional and flexural vibrations of an annular corrugated shell piezoelectric transducer consisting of multiple circularly-annular surfaces smoothly connected along the interfaces were investigated in the paper. Only a time-harmonic voltage is applied across two electrodes of the piezoelectric shell as the external loading. A theoretical solution was obtained using the classical shell theory. Based on the solution, basic vibration characteristics of resonant frequencies, mode shapes were calculated and examined.     

悬浮振子对中耳声传播特性影响的数值研究

为研究悬浮式中耳植入式助听装置中悬浮振子对中耳声传播特性的一些影响,建立了包括绑定悬浮振子的中耳有限元模型. 该模型基于一无任何听力损伤病史的成年志愿者的左耳,利用CT扫描和逆向成型技术建成. 模型的可靠性通过鼓膜及镫骨底板的位移计算结果与国外文献实验测得数据进行对比加以验证. 研究结果表明:悬浮振子的绑定会显著恶化中耳的高频传输特性;振子输出8.9\times10^5N的激振力才能激起100dB声压所对应的激振效果;振子在砧骨长突上的绑定位置离砧镫关节越近,高频段激振效果越好.      

ACOUSTICAL TRANSMISSION LINE MODEL FOR ULTRASONIC TRANSDUCERS FOR WIDE-BANDWIDTH APPLICATION

An improved model for ultrasonic transducers is proposed.By considering only the first symmetric mode,each layer is represented as an acoustical transmission line in modeling of bulk wave transducers.In imaging applications,wide bandwidth and short time duration are required.The approach we have used consists of impedance matching the front face of the piezoelectric transducer to the propagating medium with a quarter wavelength impedance matching layer and inserting an unmatching quarter wavelength acoustical layer between the rear face and backing material.A heavy backing would degrade the wide-band phenomena,but show a time duration shorter than 0.5 μs for imaging applications.PSPICE code of the controlled source model is implemented to precisely predict the performance of the matched transducers such as impedance,insertion loss,bandwidth and duration of the impulse response.Good agreement between the simulation and experimental results has been achieved.