Piezoelectric composite materials

A laminated structural devices has the ability to change shape, position and resonant frequency without using discrete motive components. The laminate may be a combination of layers of a piezoelectrically active, nonconductive matrix material. A power source selectively places various levels of charge in electrically conductive filaments imbedded in the respective layers to produce various configurations in a predetermined manner. The layers may be electrically conductive having imbedded piezoelectrically active filaments. A combination of layers of electrically conductive material may be laminated to layers of piezoelectrically active material

Multi-layered piezoelectric composite transducers

Multilayered piezoelectric materials present themselves as a suitable technology for the development of sub 100kHz transducers. A variety of different configurations have been proposed, including stacked 2-2, 1-3 and 3-1 connectivity configurations. Historically multilayer devices designed for low frequency of operation have comprised uniform layer thickness through the height of the device. The potential for extended bandwidth through the use of non-uniform layers through the thickness dimension has been investigated. In addition commercially available stacked ceramic mechanical actuators have been investigated. A combination of theoretical and experimental assessment has been employed to evaluate each transducer technology. Selection of the passive phase for these multilayer devices is critical. Typically, these devices operate in the high power regime and as such selection of the passive polymer material is crucial - thermal stability coupled with thermal conductivity would be a virtue. To this end a number of polymer materials possessing the appropriate thermal properties have been investigated

A theoretical and experimental investigation into multilayered piezoelectric composite transducers

The behaviour of a number of 3-1 connectivity piezoelectric composite plate transducers is presented. The fundamental thickness mode resonance of such devices is found to be contaminated by lateral resonant activity; this is evidenced in the measured and predicted electrical impedance profile and the surface displacement data at the,fundamental thickness mode. Measurements taken on the 3-1 devices infer that they are not acting as true composites. In addition to this the finite element technique is applied to a number of stacked 3-1 and 1-3 connectivity devices to predict the mechanical Q-factor, and hence bandwidth, as a function of polymer filler properties

Investigating the thermal stability of 1-3 piezoelectric composite transducers by varying the thermal conductivity and glass transition temperature of the polymeric filler material

The thermal behaviour of a number of 1-3 piezoelectric composite transducers is discussed. In particular, devices manufactured from a polymer filler with a relatively high glass to rubber transition temperature (T-g), and from polymer systems with increased thermal conductivity, are evaluated. The mechanical properties of the various filler materials were obtained via ultrasonic measurements, with the thermal properties extracted using dynamic mechanical thermal analysis (dmta), differential scanning calorimetry (dsc) and laserflash studies. A range of ultrasonic transducers were then constructed and their thermal stability studied using a combination of impedance analysis and laser surface displacement measurement

Performance of periodic piezoelectric composite arrays incorporating a passive phase exhibiting anisotropic properties

This paper explores the minimisation of interelement cross talk in 1-D and 2-D periodic composite array structures through the incorporation of a passive phase exhibiting anisotropic elastic properties. Initially the PZFlex finite element code was used to monitor array aperture response as a function of material properties. It is shown that in array structures comprising passive polymer materials possessing low longitudinal loss and high shear loss, inter-element mechanical cross talk is reduced, without a concomitant reduction in element sensitivity. A number of polymer materials with the desired properties were synthesised and their elastic character confirmed through a program of materials characterisation. Finally, a range of experimental devices exhibiting improved directional response, as a result of a significant reduction in interelement cross talk, are presented and the predicted array characteristics are shown to compare favourably in each case

Experimental assessment of periodic piezoelectric composite arrays incorporating an anisotropic passive phase

This paper discusses the experimental assessment of a number of piezoelectric composite array structures incorporating a novel passive phase exhibiting anisotropic elastic properties. The passive polymer phase has been designed to limit inter-element crosstalk by attenuating lateral propagation across the array aperture. A selection of water coupled linear array coupons, operating with a nominal 400 kHz fundamental thickness mode frequency, has been prepared comprising the novel anisotropic passive phase. As a control, comparisons are made to similarly configured devices employing isotropic filler materials. Scanning laser vibrometry and measurements of electrical impedance characteristic on the array substrate demonstrate that the fundamental thickness mode of the devices configured with anisotropic polymer fillers is not contaminated by parasitic modes of vibration. The reasons for this are explained by considering the dispersion characteristics of the substrate. Water coupled hydrophone measurements of array element directivity; transmit voltage response and subsequently efficiency calculations illustrate that the observed reduction in mechanical cross talk has not been achieved at the expense of element sensitivity. Finally, comparisons between the experimental data and the PZFlex derived array responses are made, with good corroboration demonstrate

Investigating the influence of the constituent materials on the performance of periodic piezoelectric composite arrays

This paper describes a theoretical investigation into the influence of the constituent materials on periodic composite array transducer performance. A finite element (FE) model, configured in PZFlex, is used to analyze the performance of a wedge coupled array transducer operating into a steel component. Here, the improvements offered by new single crystal piezoelectric materials are compared to standard PZT‐based configurations. In addition, new passive polymer materials, possessing low longitudinal loss and high shear loss, are evaluated for their potential to significantly reduce inter‐element mechanical cross talk. The FE results illustrate the potential for the next generation of array transducers incorporating these new materials and this is highlighted in the A‐scan predictions from simulated defects

Improving the thermal stability of 1-3 piezoelectric composite transducers manufactured using thermally conductive polymeric fillers

With a view to improving the thermal stability of ultrasonic transducers prepared using 1-3 piezoelectric composites, the use of front face layers manufactured from thermally insulating and partially thermally conductive polymeric materials has been investigated. Experimentally, heat dissipation was investigated, in air and in water, using different transducer configurations and the advantage of including a front face layer manufactured from thermally conductive polymeric material is demonstrated. The PZFlex finite element modelling package was utilised to assess the thermal diffusivity of each polymer in the different transducer configurations and was found to compare well with experiment

Incorporation of viscoelastic loss into the plane wave expansion approach to modelling composite transducers

The plane wave expansion (PWE) method has been proposed as a theoretical model for periodic composite ultrasonic transducers. This paper extends previous work by importantly including viscoelastic loss in the material parameters. Some of the issues with model formulation, such as ill-conditioning in the large matrices, have been addressed through parameter scaling and Tikhonov regularisation. Identification of each mode of vibration has been carried out by visualising the spatial and temporal profiles of the displacement, electrical potential and Poynting vector. A comparison between the theoretical predictions and experimental data from a piezoelectric composite device is presented. The effect that the elastic properties of the passive phase have on device performance is also investigated. It is found that high shear attenuation in the passive phase gives rise to a large frequency stop band gap around the fundamental thickness mode