Piezoelectric Ceramic-polymer Research Articles

The Horizontally Polarized Shear Waves in Multilayered Piezo-Composites with 2-2 Connectivity

Following the advances in structural applications, composite structures are being used commonly in transducer applications to improve acoustic, mechanical and electrical performance of piezoelectric devices. Functional composite transducers for sensors and actuators generally consist of ceramics and polymers, the disadvantage of the brittleness nature of the piezoelectric ceramics can be overcome and the structures especially good for sensing can be allowed for building up. Propagation behavior of horizontally polarized shear waves (SH-waves) in piezoelectric ceramic-polymer composites with 2-2 connectivity is taken into account. The multilayer structures are consisted of piezoelectric thin films bonded perfectly with polymeric thin films alternately. The phase velocity equations of SH-waves propagation in the piezoelectric ceramic-polymer composites with 2-2 connectivity are obtained for the cases of wave propagation in the direction perpendicular to the layering and along the layering, respectively. Filter effect of this kind of structure and the effect of volume fraction and shear modulus ratio of piezoelectric layer to polymer layer on the phase velocity are discussed in detail, respectively. One practical combination of piezoelectric thin film-polymer thin film multilayer system is chosen to carry out the numerical simulation, some basic properties of SH-waves propagation in above multilayered structures are revealed.

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 μm 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.

Broadband sonar considerations for small underwater vehicle applications

As underwater vehicles become more prevalent, so too does the design and integration of compact broadband sonar arrays. Rather than rely on conventional tonpilz technology, where the bandwidth is governed by the width of the transducer’s mechanical resonance, designers must consider other transducer technologies that are better suited to small vehicle packaging constraints. These constraints include operational ruggedness, light weight, conformability, and low cost. This talk advocates the use of 1–3 piezocomposite and discusses the rationale behind such a selection. In going to a wideband material such as a 1–3 piezocomposite, with typical mechanical quality factors (Qm) around 2, the selection of where to place the resonance frequency differs from that of its tonpilz counterpart. For the tonpilz array, the sonar operational bandwidth is totally governed by the resonance response of the array element and is typically limited to approximately its 3-dB or half power points. Relaxor-based ferroelectric materials such as single crystal PMN-PT, which exhibit extremely large electromechanical coupling coefficients, cannot attain 3-dB bandwidths of a decade or more when configured in a tonpilz design. This presentation will discuss a 1–3 piezocomposite-based approach that places mechanical resonance near the upper band edge of an operational bandwidth of 1 decade (10–100 kHz).

Gelcasting based solid freeform fabrication of piezoelectric ceramic objects

Selective laser sintering (SLS) in combination with gelcasting are developed to form complex-shaped lead zirconate titanate (PZT) ceramic frameworks for piezoelectric ceramic polymer composites. SLS is utilized to fabricate lost molds for the ceramic parts. Based on the gelcasting technique and specially selected composite plastic powders for SLS, complex-shaped PZT parts are successfully fabricated.

Fabrication of Piezoelectric Ceramic/Polymer Composite Transducers Using Fused Deposition of Ceramics

The fused deposition of ceramics (FDC) technique was used to fabricate piezoelectric ceramic skeletons for the development of piezoelectric composite transducers with 2–2 connectivity for medical imaging. The green parts were designed to have 30 vol% lead zirconate titanate ceramic (PZT‐5H) in the final composites. Physical characterization of the sintered samples revealed that 96% of the theoretical density was achieved. Optical microscopy showed that defects due to the FDC mode of deposition, such as small roads and bubbles, were eliminated, because of improvements in powder processing. The electromechanical properties of the final composites were similar to the properties that were obtained for conventionally made composites. A matching layer and a backing layer, as well as wires and an inductor, were added to each FDC composite to fabricate a functional medical imaging transducer. The devices were tested in water using a steel target 3.5 cm thick. Echoes from the target could be detected with all the transducers that were fabricated using FDC. The sensitivities of the transducers were similar to that of a commercial transducer. However, the ringing was much longer than that for a commercial transducer, because the backing layer was not optimized in the transducers that were fabricated using FDC.

Electrical response during indentation of a 1-3 piezoelectric ceramic-polymer composite

The electrical response during indentation of a piezoelectric ceramic-polymer 1-3 composite has been investigated. The current (quasistatic charge increment) induced in the indentor due to the polarized layer on the contact surface increases with load as the contact area increases. Good agreement was found between the measured currents as a function of load with those predicted using an analytical model. In addition, the current increases with increasing indentation velocity and indentor diameter. It uses known analytical results to develop a new tool for characterizing the electrical response of piezoelectric composites. As such, linear elastic indentation with simultaneous measurement of load and electric current is shown to be a new, fast, and nondestructive technique that can be used for quality assurance and to study the effect of aging and development/presence of damage/microcracking in monolithic piezoelectric and 1-3 piezoelectric composites.

Considerations in the Development of a Piezoelectric Transducer Cochlear Implant

AbstractSensorineural hearing loss results from the inability of the inner ear cochlear organ of Corti to transduce mechanical energy incident in the cochlea to electrical signals in auditory nerve fibers. Cochlear implant devices are used to alleviate this condition. Piezoelectric materials offer the unique scope of functioning as cochlear implants, possibly enabling simplification of the process of electrical stimulation and enhancing knowledge of the workings of both the healthy and artificially stimulated inner ear. The requirements imposed on such a device are discussed. It is believed that flexible piezoelectric PVDF and ceramic-polymer composites are best suited for this application. The design of a device which utilizes the bending piezoelectric mode, and results of testing the same in air are presented. Present work is aimed at understanding the fundamental dynamic piezoelectric properties in this mode and is expected to result in a device suitable forin vitroandin vivotesting.

Piezoelectric Sensors and Sensor Materials

This paper reviews the current trends and historical development of piezoelectric sensors and sensor materials technology. It begins with a discussion of the bases of piezo- and ferroelectric activity, followed by an overview of the most commonly used piezoelectric ceramic: lead zirconate titanate (PZT). A discussion of the properties and applications of piezoelectric crystals and additional piezoelectric ceramics is followed by a description of several sensor configurations prepared from bulk ceramics. An extensive review and comparison of piezoelectric ceramic—polymer composite sensors based on the connectivity of the constituent phases is also presented. We conclude our discussion of sensor configurations with recent examples of piezoelectric ceramic—metal composite sensors, and expected future developments in the area of piezoelectric sensors.

PZT/polymer composites for medical ultrasound

Piezoelectric ceramic polymer composites with 1–3 connectivity (i.e., parallel rods in polymer) using lead zirconate titanate and epoxy have been fabricated with different ceramic rod widths. The velocity of sound was measured for these composites using the Time-Delay technique. The values of acoustic impedance obtained by this method are compared with the results determined by the Resonance technique. The electromechanical coupling coefficient k tand planar coupling coefficient k p were determined from the thickness mode resonance and planar mode resonance peaks. The effect of addition of phenolic microballoons on these composites was also investigated. The microballoons had little effect on the acoustic impedance; however, they considerably improved the values of k t and k p.

Measurement of surface displacements in 1-3 and 1-1-3 piezocomposites

In a piezoelectric ceramic–polymer composite, the piezoceramic and the nonpiezoelectric polymer will have different deformations when subjected to an external electrical or mechanical stimulus. This local, nonuniform deformation eventually determines the overall electromechanical behavior of the composite. In the current investigation, static surface displacements of piezocomposites with 1-3 and 1-1-3 connectivity were measured using a scanning heterodyne laser interferometer. The influence of a thin interlayer surrounding the piezoceramic rods on the resulting displacement profiles was investigated and correlated with rod/polymer adhesion. The elastic stiffness of the interlayer as well as the interfacial adhesion had a significant effect on the rod displacement. Rods coated with a very compliant interlayer had a much larger displacement than untreated rods, while rods treated with a silane coupling agent to enhance adhesion had a much lower displacement. Experimental displacement profiles were found to be in good agreement with theoretical predictions.

A new transverse piezoelectric mode 2-2 piezocomposite for underwater transducer applications

In this paper, we present a new type of 2-2 piezoelectric ceramic-polymer composite operated at the transverse piezoelectric mode (TP). The new TP mode piezocomposite has exceptionally high hydrostatic piezoelectric response, high reliability, and can be made at low cost. Based on the isostrain approximation, an analytical model is developed to analyze and optimize the effective piezoelectric and the effective elastic properties of the composite. Several composites with the new structure were fabricated and tested. The calculated and experimental results show good agreement. It is shown that a TP 2-2 composite made of PZT plates in a soft polymer matrix with elastically unidirectional face plates yields an effective hydrostatic piezoelectric coefficient d/sub h/ of 6000 (pC/N) and a hydrostatic figure of merit d/sub h/g/sub h/ higher than 30000 (10/sup -15/ m/sup 2//N). >

Mechanisms in damping of mechanical vibration by piezoelectric ceramic-polymer composite materials

The piezoelectric ceramic (piezoceramic) component of a polymer-piezoelectric ceramic composite converts mechanical energy into electrical energy and this electrical energy is dissipated as heat in a load resistance, R x, simulated by a shunted resistance, but provided in practice by a conductive polymer composite matrix. The composite therefore dissipates the input mechanical energy via the damping mechanism provided by piezoelectric ceramic-conductive matrix material, as well as the conventional viscoelastic damping provided by the polymer. Mathematical models have been developed to characterize the damping behaviour of the composites, and the maximum damping ratio of composites can be as high as 23%. A two degrees-of-freedom (2DOF) experimental setup was developed to test the validity of the models. The experimental results are in good agreement with the theoretical predictions.

Development of piezoelectric composites for transducers

For the past decade and a half, many different types of piezoelectric ceramic-polymer composites have been developed intended for transducer applications. These diphasic composites are prepared from non-active polymer, such as epoxy, and piezoelectric ceramic, such as PZT, in the form of filler powders, elongated fibers, multilayer and more complex three-dimensional structures. For the last four years, most of the efforts have been given to producing large area and fine scale PZT fiber composites. In this paper, processing of piezoelectric ceramic-polymer composites with various connectivity patterns are reviewed. Development of fine scale piezoelectric composites by lost mold, injection molding and the relic method are described. Research activities of different groups for preparing large area piezocomposites for hydrophone and actuator applications are briefly reviewed. Initial development of electrostrictive ceramics and composites are also

Theoretical study on the static performance of piezoelectric ceramic-polymer composites with 2-2 connectivity

The static equilibrium conditions have been derived for piezoelectric-ceramic-polymer composite structures. Rigorous solutions are obtained for a 2-2 composite of lamellar configuration. Under a uniaxial stress or an electric field the strain profile becomes inhomogeneous due to different elastic stiffness of the two components (hard piezoelectric ceramics and soft polymer). The stress transfer between the two components is identified as due to an additional shear stress produced at the ceramic-polymer interface, and the amplification factor is defined for the enhancement of the response of the active piezoelectric ceramic resulting from this stress transfer. It is shown that this enhancement effect not only depends on the volume percentage of the active component but also on the aspect ratio of the two components.

Theoretical study on the static performance of piezoelectric ceramic-polymer composites with 1-3 connectivity

Inhomogeneous displacement profiles have been derived for a single-rod composite and a single-tube 1-3 ceramic-polymer composite under both uniaxial and hydrostatic stress. The effective piezoelectric constants for the composites have been derived in terms of the ceramic content, the piezoelectric and elastic constants of each component, and the aspect ratio of the ceramic rod. The stress concentration inside both phases is derived from the calculated inhomogeneous displacement profiles. It is found that only a finite portion of the polymer in the vicinity of the ceramic-polymer interface actually contributes to the stress transfer, and the induced additional stress on the ceramic also has a higher magnitude near the interface. The theoretical results quantitatively predict the performance of a given 1-3 structure, and can be used to optimize the design parameters, such as ceramic content, aspect ratio of the ceramic rods, rod geometry and rod arrangement, resin hardness, etc., for 1-3 structures designed for specific purposes.

Method of detecting sound in water using piezoelectric-polymer composites with 0–3 connectivity

First Page

Underwater piezoelectric arrangement

Underwater piezoelectric arrangement in which it comprises two piezoelectric elements made of piezoelectric ceramic-polymer composites and juxtaposed to form a single layer structure, one of the element(s) having larger hydrophone constant than that of the other element(s), and by noise cancelling of the piezoelectric assembly there can be selectively detected only charges or voltages generated by acoustic waves which acts on each element.