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Poling flexible piezoelectric composites

Abstract Flexible piezoelectric composites made from PZT and polymer with 0–0–3 connectivity were fabricated using several types of Eccogel polymer. The conductivity of the composite is controlled by adding small amounts of a semiconductor filler such as carbon, germanium or silicon. By controlling conductivity, poling can be carried out very rapidly at low voltages, resulting in properties comparable to composites prepared without a conductive phase. For composites optimized for hydrophone performance, the hydrostatic voltage coefficient [gbar]h and hydrostatic figure of merit [gbar]h[dbar]h are an order of magnitude larger than those of single phase PZT.

Composite Piezoelectric Sensors

A hydrophone is an underwater microphone or transducer used to detect underwater sound. The sensitivity of a hydrophone is determined by the voltage that is produced by a hydrostatic pressure wave. The hydrostatic voltage coefficient, gh, relates the electric field appearing across a transducer to the applied hydrostatic stress, and is therefore a useful parameter for evaluating piezoelectric materials for use in hydrophones. Another piezoelectric coefficient frequently used is the hydrostatic strain coefficient, dh, which describes the polarization resulting from a change in hydrostatic stress. The gh coefficient is related to the dh coefficient by the relative permittivity (K): gh = dh/ɛoK, where ɛo is the permittivity of free space.

Perforated pzt-polymer composites for piezoelectric transducer applications

Abstract Composites of PZT and polymer with 3-1 and 3-2 connectivity patterns have been fabricated by drilling holes in sintered PZT blocks and filling the holes with epoxy. The influence of hole size and volume fraction PZT on the hydrostatic properties of the composite was evaluated. By decoupling the piezoelectric [dbar]33 and [dbar]31 coefficients in the composite, the hydrostatic coefficients are greatly enhanced. On samples optimized for hydrophone performance, the dielectric constants of 3-1 and 3-2 composites are 600 and 300 respectively. The piezoelectric coefficients [dbar]h, [gbar]h, and [dbar]hdh for 3-1 composites are 230 (pCN−1), 34 (x10−3 VmN−1), and 7800 (10−15 m2N−1) respectively, and the corresponding values for 3-2 composites are 372 (pCN−1), 123 (10−3 VmN−1), and 45000 (10−15 m2N−1).

Thin film 0–3 polymer/piezoelectric ceramic composites: Piezoelectric paints

Abstract In this paper we summarize our investigation of the electrical properties of thin-film 0–3 polymer-ceramic composites. The main objective of this study was to demonstrate the principle that a piezoelectric paint can indeed be prepared. Two polymers, an acrylic copolymer and a polyurethane, were utilized in our research. Both were loaded with 60–70 volume percent PZT and a coprecipitated PbTiO3. The addition of various surfactants and dispersing agents to the acrylate-based composites was necessary to aid in dispersing the ceramic particles in the polymer matrix. The hydrostatic strain and voltage coefficients, along with the ‘figures of merit’ for PZT-filled acrylic and polyurethane composites were found to be significantly larger than values reported previously for other 0–3 polymer-PZT composites. For acrylic copolymer-coprecipitated PbTiO3 composites, the hydrostatic coefficients were found to be roughly 50% larger than the comparable PZT-filled materials. For example, gh dh ranged from about ...

Electroceramic-polymer composite thermistors

Abstract Transition metal oxide fillers such as VO2, V2O3 and Ti2O3 were incorporated in polymeric matrices to give composite materials with low room temperature resistivities and sizable thermistor effects. Percolation limits were determined by mixing ceramic powders in different proportions with both rigid and flexible epoxy resins. These composites exhibited unusually large PTC effects with resistance increases as high as nine orders of magnitude.

TiO—epoxy composite thermistors

Abstract TiO powder was incorporated into a rigid epoxy matrix to produce composite materials that exhibit unusually large PTC resistivity increases of up to ten orders of magnitude. The composites have a room-temperature resistivity (1–5 ω-cm) that is comparable with commercial carbon-black-loaded polyethylene thermistors.

Grain oriented glass-ceramics: New materials for hydrophone applications

Abstract Grain oriented glass-ceramics of fresnoite (Ba2TiSi2O8) and its modifications Sr2TiSi2O8 and Ba2TiGe2O8 have been prepared by recrystallizing glasses in a temperature gradient. Piezoelectric voltage coefficients g33 and hydrostatic voltage coefficient gh of these glass-ceramics are comparable to those of PVF2 and an order of magnitude higher than the corresponding values of PZT. These glass-ceramics seem to be attractive candidate materials for hydrophones and several piezoelectric devices. Hydrostatic piezoelectric properties of Ba2TiSi2O8 and Ba2TiGe2O8 single crystals are also reported.

(Pb, Bi)(Ti, Fe, Mn)O3/Polymer 0-3 composites for hydrophone applications

The hydrostatic piezoelectric response of composite materials incorporating (Pb1-xBix)(Ti1-xFex)O3 ceramic fillers from the highly anisotropic tetragonal region of the solid solution system in the vicinity of the morphotropic phase boundary were measured and compared. The considerable difficulty in poling and, hence, the diminished piezoelectric response encountered as the composition of the filler is shifted closer to the phase boundary was determined to be largely due to the high conductivity of the BiFeO3-rich compositions. The ceramic was modified with Mn in an attempt to lower its conductivity. Composites incorporating the Mn-doped filler poled more rapidly and easily than the undoped material and ultimately achieved a hydrostatic figure of merit, dhgh, 40% better than that observed for the undoped samples. Among the samples investigated, the highest hydrostatic figures of merit were exhibited by samples containing the doped and undoped x = 0.5 fillers. The hydrostatic response remains stable over a ...

The incorporation of rigid composites into a conformal hydrophone

Abstract During the past five years, numerous composite configurations have been analysed for hydrostatic transducer application. Although some of these composite configurations have been flexible, a configuration with good sensitivity and mechanical durability has not been produced. The need for a sheet or mat, large area transducer that will conform to the hull of a ship has led to the incorporation of small rigid composite elements into a macrocomposite. The goals set for the conformal transducer were sensitivity greater than -200 dB re 1 V/μPa, operation to at least 7 MPa, maximum frequency of 100 Hz, conforming to a 0·10 m radius and a hydrophone section of at least 0·01 m2. In the study three types of rigid composites are used to determine the effect of compliant hinge material and flexible electrodes on the hydrostatic sensitivity. Typical response of a 1–3 rod composite in flexible form is a sensitivity of -193 dB re 1 V/μPa, with a capacitance of 14 μf per m2 and only 2 dB degradation when operat...

Sol-gel derived PbTio3-polymer piezoelectric composites

Abstract Amorphous lead titanate powder was prepared using a sol-gel process. The powder was fired to temperatures ranging from 500°C to 1200°C and soaked for various lengths of time. X-ray diffraction confirmed that the fired powders were tetragonal PbTiO3. Surface area measurements indicated that the specific surface area of the powder decreased with increasing heat treatment. The powders were mixed with Eccogel polymer to make composites in which the ceramic phase constituted 60 percent by volume. Piezoelectric coefficients were found to be greatest for those composites containing powder fired to 1100°C and soaked for 1 hour. The dhgh value obtained for this heat treatment was 540×10−15m2N−1.