Electromechanical response of 2-2 layered piezoelectric composites: A micromechanical model based on the asymptotic homogenization method

A micromechanical model based on the asymptotic homogenization technique has been developed to predict the complete elastic, dielectric and piezoelectric properties of a general 2-2 layered piezoelectric composite where the constituent phases are elastically anisotropic and piezoelectrically active. Two classes of layered piezoelectric composites (i.e. longitudinally and transversely layered) are considered in two widely different ceramic- and polymer-based systems and their effective properties are obtained in the limits of both large-volume (i.e. bulk) and small-volume (i.e. thin-film) systems. It is demonstrated that: (i) in the bulk, ceramic–ceramic layered composite system, the elastic, piezoelectric, and dielectric properties of the composites vary linearly with volume fraction of the second phase, while in the bulk ceramic–polymer layered composite system, the corresponding properties vary non-linearly with volume fraction of the second phase; (ii) in the prismatic (thin-film) layered piezoelectric composite system, the non-vanishing, effective elastic, piezoelectric and dielectric properties vary linearly with the volume fraction of the second phase for both the longitudinally and transversely layered composite structures in the ceramic–ceramic and the ceramic–polymer composite systems; (iii) the ceramic–polymer piezoelectric layered composites that incorporate a low density polymeric phase with lower acoustic impedance generally exhibit enhanced piezoelectric coupling constants and lowered acoustic impedance; (iv) the longitudinally layered composites exhibit higher piezoelectric coupling constants and lower acoustic impedance compared to that of the transversely layered composites; and (v) the best combination of properties for applications such as hydrophones (i.e. the highest piezoelectric coupling constants and the lowest acoustic impedance) is obtained in the ceramic–polymer, longitudinally layered, thin-film, piezoelectric composites.     

Finite element modelling of dense and porous piezoceramic disc hydrophones

The acoustic characteristics of dense and porous piezoceramic disc hydrophones have been studied by finite element modelling (FEM). The FEM results are validated initially by an analytical model for a simple disc of dense piezoceramic material and then it is extended to a porous piezoceramic disc replicating a foam-reticulated sample. Axisymmetric model was used for dense piezoceramic hydrophone due its regular geometric shape. 3-dimensional model was used for the porous piezoceramics, since the unit cell model is inadequate to fully represent transducers of finite lateral dimensions. The porous PZT discs have been synthesised by foam-reticulation technique. The electrical impedance and the receiving sensitivity of the hydrophones in water are evaluated in the frequency range 10-100 kHz. The model results are compared with the experimental data. The receiving sensitivity of piezocomposite hydrophones is found to be reasonably constant over the frequency range studied. The sharp resonance peaks observed for the dense piezoceramic hydrophone has broadened to a large extent for porous piezoceramic hydrophones, indicating higher losses. The flat frequency response suggests that the 3-3 piezocomposites are useful for wide-band hydrophone applications.     

Piezoelectric cement-based 1-3 composites

This paper presents a new functional material for smart structure applications. Piezoelectric PZT/cement 1-3 composites that have good compatibility with civil engineering structural materials have been studied. The composites with different volume fractions of PZT ranging from 0.25 to 0.77 were fabricated by the dice-and-fill method. It was found that the 1-3 composites have good piezoelectric properties that agreed quite well with theoretical modeling. The thickness electromechanical coupling coefficient could reach 0.55 in the composite with a ceramic volume fraction of 0.25. Those composites have potential to be used as sensors in civil structure health monitoring systems. PACS 77.65.-j; 77.84.Lf     

A novel drum piezoelectric-actuator

This paper presents a large displacement, piezoelectric-metal structure actuator, named the piezoelectric drum actuator. The drum actuator consists of a short, thick-walled steel cylinder sandwiched by two thin composite disks, which are fabricated from a brass disk bonded with a piezoceramic disk. The piezoceramic disk, which is polarized in its thickness direction, has a large diameter thickness ratio, producing a large radial displacement under an applied voltage in the thickness, leading to a large transverse deflection of the composite disks in the drum. The drum (outer diameter: 12.0 mm) has a displacement that is about eight times larger than that of a cymbal actuator made with the same ceramic material and comparable dimensions under the same dc driving voltage of 270 V. The drum actuator also showed a large resonance displacement of 56.7 μm under an ac voltage of 90 V. The effective piezoelectric charge coefficient d’₃₃ of the drum is about twice as large as that reported for the cymbal. PACS 77.65 -j; 85.50.+k; 43.38.fx     

电泳辅助制备伪1-3陶瓷/聚合物压电复合材料

1-3压电复合材料的压电、介电及铁电性能要远远优于0-3压电复合材料.在制备传统的0-3复合材料过程中引入电泳技术,使得压电颗粒在聚合物基体中取向排列,制备得到伪1-3复合材料.实验结果表明:在制备PZT/环氧树脂0-3复合压电材料固化过程中,采用500 V/mm,4 kHz的电场对其进行电泳辅助取向,可使得颗粒呈现珍珠串状排列,得到伪1-3复合材料;其压电、介电、铁电性能均比原来的0-3复合材料有显著的提高.电泳辅助制备技术用于制备伪1-3复合压电材料具有操作简单、成本低廉、压电、介电、铁电性能显著提高等优点,在智能传感领域具有很好的实际应用前景.     

Enhancement of Piezoelectric and Dielectric Properties and Macroscopic Relaxation of Charge and Field Response in 0–3 Ceramic-Pore Composites: Theory and Experiment

In this work, we have theoretically and experimentally described the dielectric and piezoelectric properties of ceramic-based lead zirconate–titanate composites that have a 0–3 bond. Based on the proposed model, the frequency dependences of the dielectric and piezoelectric response have been determined theoretically and experimentally. The influence of the Maxwell–Wagner relaxation and the effective parameter approximation on the physical properties of disordered objects of statistical mixture have been studied. The distribution functions of the times of intercomponent relaxation in the piezoceramic–pores composite system and the concentration dependences of the effective field responses have been determined. The theoretical and experimental results obtained have been compared.     

Experimental investigation of alternative pre-stress components for a 3-1 connectivity multilayer piezoelectric-polymer composite ultrasonic transducer

The most popular configuration for piezoelectric-polymer composites has pillars of piezoelectric ceramic supported by a polymer matrix and material with this structure is now widely available commercially. However, it has significant disadvantages for use in multilayer devices for non-mass-loaded operation below approximately 50 kHz. An alternative configuration is therefore reported here, in which interconnected fingers of piezoelectric ceramic surround polymer plates. This can be termed 3-1 connectivity, since the piezoceramic is fully connected in three dimensions and the polymer in only one. The configuration has been found to have significant manufacturing advantages which feed through to enhanced performance compared with practical 1-3 connectivity multilayer devices. For many potential applications, high-power operation is required, and it is unclear if the multilayer structure has sufficient internal strength to maintain its integrity at high strains. Therefore, an investigation has been carried out into alternative pre-stressing component designs. These comprise back and front stainless steel plates of different shapes, connected by a number of stainless steel rods. In this paper, the fundamental performance of a multilayer device is illustrated with electrical impedance and surface displacement measurements in air, without pre-stressing. Then measurements are reported from three different clamping configurations. It is shown that good results can be achieved at spot frequencies with a suitable clamp, but that unsuitable clamps prevent even this, and broadband performance is unlikely to be achieved easily.     

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.     

The use of distributed pressure receivers based on elastic piezoelectric composite materials for measuring the hydrodynamic noise produced by a near-wall turbulence

Receiving electroacoustic transducers with sensing elements made of an elastic piezoelectric composite material are described. The parameters of a composite material that exhibits a bulk piezoelectric effect are presented. Results obtained by measuring the turbulent noise in a hydrodynamic channel with the use of piezoelectric composite receivers are reported. The results are compared with those of the noise measurements by a miniature piezoceramic receiver and are considered in the light of the known models of near-wall turbulence.     

Modeling of micromachined silicon–polymer 2-2 composite matching layers for 15 MHz ultrasound transducers

Silicon–polymer composites fabricated by micromachining technology offer attractive properties for use as matching layers in high frequency ultrasound transducers. Understanding of the acoustic behavior of such composites is essential for using them as one of the layers in a multilayered transducer structure. This paper presents analytical and finite element models of the acoustic properties of silicon–polymer composites in 2-2 connectivity. Analytical calculations based on partial wave solutions are applied to identify the resonance modes and estimate effective acoustic material properties. Finite Element Method (FEM) simulations were used to investigate the interaction between the composite and the surrounding load medium, either a fluid or a solid, with emphasis on the acoustic impedance of the composite. Composites with lateral periods of 20, 40 and 80 μm were fabricated and used as acoustic matching layers for air-backed transducers operating at 15 MHz. These composites were characterized acoustically, and the results were compared with analytical calculations. The analytical model shows that at low to medium silicon volume fraction, the first lateral resonance in the silicon–polymer 2-2 composite is defined by the composite period, and this lateral resonant frequency is at least 1.2 times higher than that of a piezo-composite with the same polymer filler. FEM simulations showed that the effective acoustic impedance of the silicon–polymer composite varies with frequency, and that it also depends on the load material, especially whether this is a fluid or a solid. The estimated longitudinal sound velocities of the 20 and 40 μm period composites match the results from analytical calculations within 2.7% and 2.6%, respectively. The effective acoustic impedances of the 20 and 40 μm period composites were found to be 10% and 26% lower than the values from the analytical calculations. This difference is explained by the shear stiffness in the solid, which tends to even out the surface displacements of the composites.     

A study of a 1-3-2 type piezoelectric composite

A novel 1-3-2 type piezoelectric composite is developed. There are piezoelectric ceramic framework supports at transverse and longitudinal directions in its structure, so it is free from the influence of any outside mechanic impact and environmental temperature change. The sample characteristic is good coherence. It has many advantages, such as a high piezoelectricity, lower density and acoustic impedance matching with water and tissue easily. Based on Newnham's series and parallel theory of composites, the calculation formulae of dielectric and piezoelectric constants of a 1-3-2 type piezoelectric composite are deduced. The sample's characteristics indicate that a 1-3-2 type piezoelectric composite's theoretic calculation values are in good agreement with the measurement results. Element samples have been designed, manufactured and measured. The results indicate that the resonant frequency, resonant impedance, piezoelectricity and static capacity of these samples are stable. It is easy to design sensor array elements using this material.     

Properties of PZT/PZT ceramic piezocomposites

A method for obtaining PZT/PZT ceramic piezocomposites is developed. Samples of piezocomposites with a volume fraction of components from 0 to 100% are prepared and investigated. Various types of PZT type piezoceramics powders and milled PZT piezoceramics particles, as well as presintered piezoceramic granules, are used as matrix and filling components, respectively. Sets of complex elastic, dielectric, and piezoelectric parameters of piezocomposites are measured. The microstructure of the obtained ceramic composites is investigated.     

Atomic force microscopy study of ferroelectric films of P(VDF-TrFE) copolymer and composites based on it

The surface structure and local piezoelectric response of film samples of P(VDF-TrFE) copolymer and composites based on it were studied by atomic and piezoelectric force microscopy. Lamellar crystals 2.0 × 0.6 μm in size were detected in nominally pure P(VDF-TrFE) samples. Introduction of crystalline ferroelectrics increases the crystalline phase fraction in the polymer matrix and changes the shape and sizes of lamellar crystallites. Hysteresis loops of the local piezoelectric response for composite regions corresponding to the polymer matrix and crystalline ferroelectric inclusions were obtained.     

圆环状复合材料高频宽带水声换能器

研制了一种圆环状高频宽带水声换能器。利用压电复合材料Q值低从而频带宽的特点,采用双环轴向堆叠产生双模态耦合的结构方式拓宽换能器的带宽。通过理论分析与仿真计算,确定敏感元件几何尺寸。用切割-浇注-被覆电极等工艺制备出压电复合材料圆环;再将制备出的外径相同,壁厚不等的压电复合材料圆环轴向叠堆制成叠堆敏感元件,最后灌注防水透声层制成换能器。对制得的换能器进行水下性能测试,测得该换能器谐振频率为410 kHz,最大发射电压响应为150 dB,-3 dB带宽达60 kHz,水平指向性开角(-5 dB)为360°,-3 dB垂直指向性开角约20°。结果表明将复合材料圆环轴向堆叠可显著拓展换能器的带宽,且实现声波的水平全向发射。      

0-3型压电复合材料覆盖层水下 吸声性能的理论研究

目前压电分流阻尼技术在振动和噪声领域的应用得到了广泛的关注. 本文尝试将压电分流阻尼技术应用于水下吸声领域, 以提高覆盖层的吸声性能. 将压电覆盖层厚度模态的机电方程和声波传播的传递矩阵相结合, 建立一维电声模型. 该模型可以用于分析多层压电和非压电水下吸声覆盖层的吸声性能. 采用该模型分析了0-3型压电复合材料覆盖层的水下吸声性能. 压电复合材料的参数是采用Furukawa的模型计算的. 研究结果表明, 采用合适的分流电阻, 负电容分流电路可以在较宽的频率范围显著提高覆盖层的吸声性能. 其原理可以从阻抗匹配的角度解释, 负电容分流电路可以调整压电覆盖层的表面声阻抗, 使之与水的特性声阻抗相匹配.     

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.     

一种高灵敏压电平面水声换能器

设计并制作了一种高灵敏压电平面水声换能器。该换能器敏感元件是对1-3-2型压电复合材料结构的改进,即在带基底的压电陶瓷小柱阵列间不注入聚合物,并在其上表面直接覆盖金属板,构成“带基底的压电小柱阵列+金属盖板”结构敏感元件(称为“空气填充型”敏感元件)。对“空气填充型”敏感元件的谐振频率进行了理论计算和有限元仿真,与实测结果较吻合。为便于对比性能,同时制作了同尺寸“1-3-2型压电复合材料+金属盖板”结构敏感元件(称为“聚合物填充型”敏感元件)换能器。分别对“空气填充型”和“聚合物填充型”敏感元件换能器的有效机电耦合系数、发送电压响应和接收灵敏度进行有限元仿真和实测,结果均显示,“空气填充型”敏感元件换能器具有较高的接收灵敏度,相较于“聚合物填充型”敏感元件换能器可提高21 dB。该敏感元件换能器能有效提高灵敏度,可为研制高灵敏换能器提供参考。      

High-yield boron nitride nanosheets from 'chemical blowing': towards practical applications in polymer composites

An improved 'chemical blowing' route presuming atmospheric-pressure pre-treatment and moderate heating rate of designated precursors was developed to synthesize ultra-thin boron nitride (BN) nanosheets with high yield and large lateral dimensions. The yield reached as high as 40 wt% with respect to raw materials (ammonia borane). The strong oxygen-related ultraviolet luminescence together with a blue emission of these BN nanosheets was then documented and analyzed. This implies potential applications in solid-state lighting, ultraviolet lasing and full-color luminescence. Mechanical strength of different polymeric composites with a small fraction of BN nanosheet fillers was dramatically increased by tens of per cent, while high transparency of composite materials was still maintained in the visible optical range. The increased yield and reduced cost of BN nanosheets should promote their wide practical applications in various composites.     

0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3单晶/环氧树脂1-3型复合材料的压电性能研究

模拟了0.7Pb(Mg_1/3Nb_2/3)O₃-0.3PbTiO₃(PMN-0.3PT)单晶1-3型压电复合材料的性能与单晶体积分数的关系,得出性能最优时压电相的体积分数为64%, 在这一体积分数下,采用切割-填充法,并使用了不同类型的环氧树脂填充制备复合材料.系统地研究了聚合物相对复合材料性能的影响,研究表明,减小聚合物相的刚度系数c和密度ρ有利于提高复合材料的性能,且聚合物相与压电相的结合强度对性能的影响非常明显,制备的PMN-0.3 PT单晶1-3型复合材料的厚度伸缩机电耦合系数k_t高达90.1%,压电系数d₃₃大于1000pC/N,机械品质因数Q_m为10.39,声阻抗Z也大大降低,性能明显优于传统的Pb(Zr_xTi_1-x)O₃(PZT)陶瓷及其1-3复合材料,在压电换能器和传感器中显示出广阔的前景. 关键词： PMN-PT单晶 压电复合材料 压电相 聚合物相     

Specific acoustic impedances of piezoelectric ceramic and polymer composites used in medical applications

The specific acoustic impedance of the piezoelectric composites over the frequency range of 0.5-7.5 MHz was measured using the reflection, the echo-shift, and the resonance techniques. There was a significant difference between the values obtained by the reflection technique in comparison with the other two techniques. It is argued that the difference is inherent in the measurement techniques and they measure different properties of the composite such as acoustic impedance and reflectivity. The specific acoustic impedance and the reflectivity were found to be a function of the volume fraction of the ceramic and not a function of frequency.