Method of making electromechanical transducers using improved flexible composite piezoelectric material
First Claim
1. A method of making a flexible composite piezoelectric material by steps comprising polarizing particles of a piezoelectric material that are dispersed in a prepolymer material by applying an electric field to said prepolymer material, while simultaneously inducing a dipole moment in said particles, wherein said prepolymer material at least partially polymerizes during said polarizing,CHARCTERIZED IN THAT the shear modulus of the at least partially polymerized material after said polarizing is (less than 20 pounds per square inch) sufficiently small that the hydrostatic piezoelectric response of said composite is substantially stable over time, and wherein said electric field is in the range of 100 to 1,000 kilovolts per meter, and the ratio of the major-to-minor axes of said piezoelectric particles is less than 2 to 1, and wherein said piezoelectric material is selected from the group consisting of lithium sulfate monohydrate and tartaric acid.
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Abstract
A method of making flexible composite piezoelectric materials exhibiting hydrostatic response and having a stable response over time is given. A prepolymer material is combined with a piezoelectric material and polarized by applying an electric field while inducing an electric dipole in the piezoelectric material, typically by applying hydrostatic pressure or changing the temperature. To ensure stable response characteristics, the polymer material is chosen to have a shear modulus of less than 20 pounds per square inch. To help ensure good contact between the piezoelectric material and the polymer material, controlled shrinkage may be induced in the composite materials by heat or the removal of a volatile material. The prepolymer material desirably has an electrical resistivity greater than 1010 ohm/meters. Typical piezoelectric materials include lithium sulfate and tartaric acid. Typical polymer materials include RTV rubber, urethanes, and polybutadienes, and may be in the form of oligomers.
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12 Claims
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1. A method of making a flexible composite piezoelectric material by steps comprising polarizing particles of a piezoelectric material that are dispersed in a prepolymer material by applying an electric field to said prepolymer material, while simultaneously inducing a dipole moment in said particles, wherein said prepolymer material at least partially polymerizes during said polarizing,
CHARCTERIZED IN THAT the shear modulus of the at least partially polymerized material after said polarizing is (less than 20 pounds per square inch) sufficiently small that the hydrostatic piezoelectric response of said composite is substantially stable over time, and wherein said electric field is in the range of 100 to 1,000 kilovolts per meter, and the ratio of the major-to-minor axes of said piezoelectric particles is less than 2 to 1, and wherein said piezoelectric material is selected from the group consisting of lithium sulfate monohydrate and tartaric acid.
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