Q.C. Xu

Piezoelectric composites with high sensitivity and high capacitance for use at high pressures

A type of piezoelectric composite has been developed for oceanographic applications. The composites have a large figure of merit (d/sub h/*g/sub h/ or d/sub h/*g/sub h//tan delta , where d/sub h/ is the hydrostatic piezoelectric voltage coefficient), a large dielectric constant (K) and low dielectric loss, and great mechanical strength. A shallow cavity between the PZT ceramics and thick metallic electrode is designed to convert a portion of the z-direction stress into a large radial and tangential stress of opposite sign. thereby causing the d/sub 33/ and d/sub 31/ contributions to d/sub h/ to add rather than subtract, and raising the figure of merit. Theoretical stress analysis was carried out using an axisymmetric finite element method. Experimental results show that the d/sub h/*g/sub h/, K, and withstandable pressure are extremely high.<<ETX>>

High displacement ceramic metal composite actuators (moonies)

Abstract The two most common type of piezoelectric actuators are the multilayer actuator with internal electrodes and the cantilevered bimorph actuator[1]. A new type of composite ceramic actuator is the multilayered multistacked moonie (multi-multi moonie). Normal multilayer actuators produce a large generative force, but only a small displacement. Conversely, bimorphs produce large displacements but the forces are very small. The moonie actuator combines the advantages of both, producing a large displacement as well as a reasonably large generative force.

Ceramic-metal composite actuator

The main objective of this work was to develop a new type of actuator. It consists of a piezoelectric ceramic disk or multilayer stack and two metal end plates with a crescent-shaped cavity on the inner surface. The plates are used as mechanical transformers for converting and amplifying the lateral displacement of the ceramic into a large axial motion in the plates. Both d31 and d33 contribute to the axial displacement. Sizeable strains were obtained with both PZT-metal and PMN-metal actuators. Displacement amplification principle, fabrication, and measurement results are presented.

Design optimization for metal-ceramic composite actuator, “moonie”

Abstract A piezoelectric ceramic-metal composite actuator has been developed to amplify the displacement of the piezoelectric ceramic. In this structure, the PZT ceramic is sandwiched between end caps with shallow cavities. This paper describes the design optimization of the flextensional transducer using finite element analysis (FEA). By using FEA, shape, material, and geometrical contributions to the displacement of the actuator were calculated. The effect of load on the displacement was also estimated. It was found that the displacement of the actuator increases with cavity diameter and depth, and that introducing a ring-shaped groove on the metal end caps of the actuator greatly enhances the displacement.

Measurement of Complex Coefficients for Thick PVDF Polymer

A new measuring technique of complex coefficients for low k2Q, piezoelectric materials has been described. The complex elastic, dielectric and piezoelectric coefficients for the longitudinal length mode and for the thickness mode of thick polymer produced at Raytheon, and their temperature and frequency dependence are measured by this technique. Following the method of time-temperature superposition, logoa, is plotted as abscissa. The real parts of d,,, d,, poisson ratio and their temperature dependence are also obtained.

Composite transducer with multiple piezoelectric matching layers

Trilaminate transducers have been constructed from fired 0-3 piezoelectric materials and nonvoided thick piezoelectric polymer as two matching layers on ceramic PbTiO/sub 3/. Based on the physical properties of the constituent materials, the equivalent circuit of this composite transducer has been established. The frequency response of transmitting, receiving, and voltage transition gain (VTG) for different layers and their hybrid connection was computed and compared with the experimental results. The frequency response of the composite transducer is considerably improved by changing the connecting modes between the layers. Different layers are shown to make different contributions to the frequency dependence of the sensitivity. The transducer impedence and sensitivity response can be adjusted depending on the application.<<ETX>>

Preparation and Piezoelectric Properties of Fired 0-3 Composites

A new method of p reparing 0-3 composites with more than 70 volume percent filler particles is presented. C onventional and corona discharge poling techniques h ave been u sed to pole the composites. PZT-polymer composites p repared by this method (fired composites) exhibited five times larger ahgh figure of merit compared to those prepared by the conventional method. In fired PbTi03-polymer composites, almost saturation poling was achieved and the ahgh figure of merit was 1750~10-~~ m2N-l. A resonance technique was used to determine the piezoelectric coupling factors corresponding to different modes of v ibration. The technique is useful for analyzing the dynamic performance of single mode low mechanical Q transducers.

Composite flextensional transducers for sensing and actuating

Abstract A ceramic-metal composite flextensional transducer has been developed which integrates both sensing and actuating functions into a single device for the purpose of suppressing low-level vibration noise. This prototype sensor/actuator composite is capable of detecting and completely suppressing in real time, small (<1μm) vibration displacements with low (<100gf) forces. The dynamic frequency range of the device spans from 100Hz to at least 2500Hz. The actuator portion of the composite consists of a standard (11 mm diameter, 3 mm thick) “moonie” transducer. The sensor is a separate piece of piezoceramic, 0.1mm thick, imbedded within the surface of the actuator. Vibrations are detected by the sensor; then, via a feedback loop, the vibration noise is suppressed by the actuator. Potential applications for this device include active optical systems, rotor suspension systems, and other low-level vibration suppression devices.

Zig-Zag Piezoelectric Actuators: Geometrical Control of Displacement and Resonance

The Zig-Zag actuator is a hybrid design combining bimorph and multilayer characteristics that is capable of producing and sensing usable motion in two dimensions. The mechanical impedance can be optimized by changing the angle between the legs and the actuators working parameters controlled by changing the driving voltage and its frequency. Two interesting features of this actuator are its performance as a linear motor and its ability to drive a load in two directions.

Effect of particle size on the dielectric and piezoelectric properties of PbTiO/sub 3/-polymer composites

Piezoelectric composites were prepared by mixing 67-vol% modified PbTiO/sub 3/ with a polymer. Composites were cured at 80 degrees C for 10 h and poled with an electric field of 40 kV/cm for 1 h at 80 degrees C. The dielectric constant, piezoelectric d/sub 33/, and hydrostatic coefficient d/sub h/ were found to increase with increasing particle size and the hydrostatic g/sub h/ coefficient decreased with increasing particle size of PbTiO/sub 3/. The hydrostatic figure of merit, d/sub h/g/sub h/ was shown to be independent of particle size. Composites prepared with large particles were found to have lower breakdown strengths. The difference in properties with particle size indicates a probable change in connectivity due to variation of particle size and morphology.<<ETX>>