一种非均匀厚度压电复合材料片宽带换能器的实验研究

本文利用１－３压电复合材料作为换能元件，通过特殊工艺制备成一面是平面，一面是球面的非均匀厚度压电振子，这种压电晶片加上激励电压后，不同厚度处以不同的共振频率振动，从而使压电晶片的振动频带加宽，本文介绍了这种压电晶片的机电特性，以及用这种压电晶片制成的宽带聚焦超声换能器的脉冲回波特性，此外，文中还对这种换能器与均匀厚度压电晶片换能器的脉冲回波特性进行了比较。     

1-3型压电复合材料宽带水声换能器研究

1-3型压电复合材料换能器具有重量轻、声阻抗率低等优点,复合材料换能器带宽的拓展一般采用匹配层的方法。采用厚度振动模态理论、横向模态理论和有限元方法对1-3型压电复合材料换能器进行研究,应用ANSYS软件建立换能器的有限元模型,然后进行结构优化,最终制作了一个利用厚度振动模态和一阶横向模态的13型压电复合材料宽带换能器,其工作带宽为190~390 kHz,发送电压响应起伏不超过±2dB。研究结果表明:利用厚度振动模态和一阶横向模态可以拓展1-3型压电复合材料换能器的带宽,同时也给出了一种高频换能器实现宽带发射的方法。     

Response of bare 1-3 piezocomposite array to localized electrical excitation

The theoretical response of a 1-3 piezocomposite plate submitted to localized electrical excitation was studied with the theory of guided waves. The theoretical modeling was based on the global matrix method, and the piezocomposite material was considered as a homogeneous medium. To validate the theoretical results, experimental displacement measurements were performed with an interferometric probe on two piezocomposite plates, one with a single element and one with an array of electrodes. The measured response on the single-element plate was mainly supported by the S0 and S3 modes of the plate. Homogenization limits of the composite in terms of frequency and wave number are defined on the basis of data from this sample. Within these limits, the piezocomposite material operates as a homogeneous medium, and comparison between theoretical and experimental results allows the equivalent electroacoustic parameters to be evaluated. A second sample was measured to study the effects of the electrode array on the electroacoustic response of the plate. Two kinds of electrical excitation were studied.     

Experimental and finite element modelling studies on single-layer and multi-layer 1-3 piezocomposite transducers

Finite element modelling (FEM) using ATILA code and experimental studies have been carried out on 1-3 piezocomposite transducers. FEM study was initially carried out on a piezocomposite infinite plate and then extended to transducers of finite size. The infinite-plate model results agree well with that of a simple analytical model and experiments. The acoustic performance of multi-layer finite-size piezocomposite transducers was also studied. Transducer stacks were fabricated with different number of layers. The transducer characteristics such as the electrical impedance, the transmitting voltage response (TVR) and the receiving sensitivity (RS) of the 1-3 piezocomposite transducers were evaluated as functions of frequency, ceramic volume fractions and the number of layers. TVR increases and RS decreases with increase in ceramic volume fractions. The model results are found to agree with the experimental data, especially when the number of layers is less.     

1-3型压电复合材料

1－3型压电复合材料是目前研究和应用得比较广泛的一种压电材料．本文简述了这种压电复合材料的理论模型、制作方法和实验结果；指出除了圆形PZT压电材料所具有的径向模和厚度模以外，1－3型压电复合材料还具有横向结构模．本文介绍了这种压电复合材料的特点，如低声阻抗、低介电常数、高静水压压电常数以及PZT相分布的可控制性等．这些特点有利于改善压电复合材料换能器的时间响应和空间响应．     

Experimental and theoretical determination of 1-3 piezocomposite electroacoustic tensor

We report the development of two methods for determining the effective electroacoustic tensor of 1-3 piezocomposite material, one experimental and one theoretical based on homogenization techniques. The main aim was to compare and validate the results provided by these approaches. The slowness surfaces of bulk wave were computed in the large wavelength domain and were fitted to obtain the effective properties of the composite. Model predictions are discussed and compared with the Smith's model. The experimental method is an inversion technique comparing measurement of transmission coefficient through the piezocomposite plate with the simulated coefficient. The accuracy and stability of the minimization procedure is discussed. Experimental results obtained from two piezocomposite test plates are presented and compared with theory.     

1-3型压电复合材料非均匀振动换能器的研究

通过调整1－3型压电复合材料换能器中压电相的分布，可以控制换能器辐射面上振动幅度和相位的分布，从而获得具有特殊性能的声场．作为辐射源表面振动速度等相位不等幅和等幅不等相位的两种典型情况，本文对边线高斯型换能器和Wesnel聚焦换能器进行了实验研究，讨论了其声场特性．     

1-3型压电复合材料非均匀振动换能器的研究

通过调整１－３型压电复合材料换能器中压电相的分布，可以控制换能器辐射面上振动幅度和相位的分布，从而获得具有特殊性能的声场。     

1-3型二维柱形凹面线聚焦换能器声场特性

设计并研制了柱面结构的1-3型复合材料凹面线聚焦换能器,在提高换能器带宽的同时,可以实现声场的线聚焦。将换能器内部PZT柱作为独立声源,应用瑞利积分和叠加原理,推导出了柱形凹面换能器总声场的理论表达式。通过仿真计算分析了换能器在聚焦线上的声场特点以及相关参数对聚焦性能的影响。对换能器参数做出合理设计,使换能器在实现线聚焦的同时,声场在聚焦线上的起伏较小,从而设计并制作出聚焦性能良好的线聚焦凹面换能器探头。实验测试结果表明采用本文方法计算得到的换能器声场与实测的声场分布基本符合,柱形凹面换能器在其几何焦点附近范围内均可实现聚焦,并在侧向上形成清晰的聚焦线,其聚焦线长度为换能器的侧向结构长度,在聚焦线上声场分布起伏较小。     

Computational and experimental investigation of the fields generated by a 1-3 piezocomposite transducer

Large-scale three-dimensional numerical simulations using the finite-difference time domain technique are used to compute the continuous wave fields associated with a composite transducer. The interior of the transducer is made of a periodic array of square rods. This lattice causes elastic wave Bragg diffraction similar to electrons in a periodic lattice. A low frequency mode shape is assumed for the rods. This prescribed motion includes longitudinal and transverse components. It is shown that the transverse motion in the rod gives rise to shear waves causing standing waves (lateral resonances) in the polymer regions. This is also confirmed by experimental results presented here and other independent analytical and experimental work. The full-scale numerical simulation is performed on a large parallel supercomputer and permits modeling of not only the composite transducer but the radiated pressure from near to far field. In addition, cover plates and edge effects are included, unlike analytical treatments. Although only mechanical effects are included, the wave propagation approach captures many essential features.     

用1-3及2-2连通复合换能器测量冻土

根据冻土弹性波测试要求，研制了一种测试冻土用的500kHz纵波，横波1-3及2-2连通复合超声换能器，其灵敏度高，频带宽，声阻抗低，波形简单及脉冲波形前沿徒削，亦适用于其它介质力学特性测试。文章介绍了换能结构原理及测量系统特性，实测了不同含水量（7%-25%）及负温（-2℃--20℃）条件下兰州黄土试块的纵，横波声速，获得很高测量精度（10ps级）。     

1-3 connectivity piezoelectric ceramic-polymer composite transducers made with viscous polymer processing for high frequency ultrasound

Potential applications of high frequency ultrasound exist because of the high spatial resolution consequent upon short wavelength. The frequencies of interest, typically from 25 MHz upwards, are easily supported by modern instrumentation but the capabilities of ultrasonic transducers have not kept pace and the transducers in high frequency commercial ultrasonic systems are still made with single-phase crystal, ceramic or piezopolymer materials. Despite potential performance advantages, the 1-3 connectivity piezoelectric ceramic-polymer composite materials now widely used at lower ultrasonic frequencies have not been adopted because of manufacturing difficulties. These difficulties are centred on fabrication of the 1-3 piezoceramic bristle-block comprising tall, thin pillars upstanding from a supporting stock. Fabrication techniques which have been explored already include injection moulding, mechanical dicing, and laser machining. Here, we describe an alternative technique based on viscous polymer processing (VPP) to produce net shape ceramic bristle-blocks. VPP produces green-state ceramic with rheological properties suitable for embossing. We outline how this can be created then report on our work to fabricate PZT bristle-blocks with lateral pillar dimensions of the order of 50 microm and height-to-width ratios of the order of 10. These have been backfilled with low pre-cure viscosity polymer and made into complete 1-3 piezocomposite transducer elements. We outline the performance of the transducers in terms of electrical impedance and pulse-echo behaviour and show that it corresponds well with computer modelling. We conclude that VPP is a promising technique to allow the established advantages of piezocomposite material to be exploited at higher frequencies than have been possible so far.     

微波激发下非线性磁表面波传播特性

研究了微波激发下非线性反铁磁晶体与线性铁磁晶体交界面上transverseelectric(缩写为TE)表面波的传播特性.用反函数形式给出了反铁磁晶体中TE表面波磁场的精确解.分析了小功率和大功率传输时的场分布特征.求得了TE表面波的色散方程,进而讨论了系统的微波频率特性.分析表明,非线性TE表面波存在频率通带和禁带,其带宽是功率的函数,通过调节导波功率可以有效地实现通带和禁带之间的转换 关键词： 反铁磁晶体 铁磁晶体 非线性表面波     

Nonlinear optical studies of 1-3-diaryl-propenones containing 4-methylthiophenyl moieties

The third-order nonlinear optical properties of chalcone derivatives have been studied using the single beam Z-scan technique. The dependence of χ⁽³⁾ on different donor and acceptor type substituents demonstrates the electronic nonlinearity of compounds. The largest value of nonlinear refractive index, n₂, measured for a high electron donor substituted molecule is −2.033 × 10⁻¹¹ esu. These molecules exhibit a strong two-photon absorption and interesting optical limiting of nanosecond laser pulses at 532 nm.     

1-3 piezoelectric composite transducers for swept-frequency calibration of hydrophones from 100 kHz to 2 MHz

Rapid calibration of hydrophones used in biomedical ultrasound is possible with swept frequency techniques such as time delay spectrometry. However, calibrations below 2 MHz largely have been neglected because of insufficient transmitting transducer bandwidth, even though important medical applications operate in this range. To address this deficiency, several transmitting transducer designs were developed and tested, and two 1-3 piezoelectric composite designs were found to have the requisite bandwidth and uniformity of response. In one the element has a plane front face and spherically concave back face (plano-concave), and in the second both faces are concave, but with different radii of curvature (biconcave). The nonuniform thickness disperses the thickness resonance, and the composite structure suppresses radial-mode resonances. Also, the composite's lower acoustic impedance provides a more efficient match to water. The piezoelectric composite transducers were found to have transmitting pressure sensitivities superior to ceramic single-element and segmented designs having similar dimensions, and their responses were significantly more uniform (< 25 dB variation from 0.1-2 MHz, with < 1 dB fine structure variation), likely due to decreased contributions from radial modes.     

对2-2型压电复合材料横波换能器产生的纵波特性的研究

在固体测量中，横波换能器所产生的波列中常伴随有纵波，认识纵波产生的原因可以解释横波测试中出现的现象，以及抑制纵波提供有效的方法，本文利用实验研究的方法，用一对纵波偶极子换能器的对比实验，分析了２－２型压电复合材料厚度切变换能器产生纵波的机理，发现这是一种伴随着晶片厚度切变振动而产生的“偶极子”纵波，并由此解释了这种纵波的伴随性，频率特性及其首波与横波首波位相相反等问题。     

Nonlinear dynamics of oscillators with bilinear hysteresis and sinusoidal excitation

The transient and steady-state response of an oscillator with hysteretic restoring force and sinusoidal excitation are investigated. Hysteresis is modeled by using the bilinear model of Caughey with a hybrid system formulation. A novel method for obtaining the exact transient and steady-state response of the system is discussed. Stability and bifurcations of periodic orbits are studied using Poincaré maps. Results are compared with asymptotic expansions obtained by Caughey. The bilinear hysteretic element is found to act like a ‘soft spring’. Several sub-harmonic resonances are found in the system, however, no chaotic behavior is observed. Away from the sub-harmonic resonance the asymptotic expansions and the exact steady-state response of the system are seen to match with good accuracy.     

Design guidelines of 1-3 piezoelectric composites dedicated to ultrasound imaging transducers, based on frequency band-gap considerations

Periodic piezoelectric composites are widely used for imaging applications such as biomedical imaging or nondestructive evaluation. In this paper such structures are considered as phononic crystals, and their properties are investigated with respect to periodicity. This approach is based on the investigation of band gaps, that strongly depend on the properties of the considered composites (geometry, size, nature of materials). It is motivated by the fact that band gaps in principle allow one to excite the thickness mode without exciting other parasitic propagating waves. The used plane-wave-expansion method has already been applied to periodic piezoelectric composites, but, in contrast to previous approaches, not only waves propagating in the symmetry plane of the composite are considered, but also waves propagating with a nonzero angle of incidence with this plane. The method is applied to a representative 1-3 connectivity piezocomposite in order to demonstrate its potentialities for design purposes. The evolution of band gaps is explored with respect to the wave vector component parallel to piezoelectric transducer-rod axis. All bulk waves that contribute to the setting up of plate modes in the vicinity of the thickness mode are found and identified.