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Method and structure for embedding piezoelectric transducers in thermoplastic composites

Image Number 4 for United States Patent #5920145.

This invention consists of a method for embedding piezoelectric ceramic transducers in thermoplastic composites. The piezoelectric ceramic transducer to be embedded in a graphite/PEEK composite is first bonded with two fine silver wires for electrical connection, one on each major surface. The bonding agent is a high temperature conductive adhesive compound, such as a silver/glass frit. The fusing of the frit bonding agent is done in an over at, a high temperature (i.e. F. or higher) for 5 to 10 minutes. Bonds are applied at several discrete spots on the zig zag wire which relieves thermal stresses induced during cooling due to a mismatch of the coefficient of thermal expansion between the ceramic material and the wire. After the connecting wires are attached, the wires and transducer are wrapped with several plies of insulating glass/PEEK cloth to prevent electrical shorting between the two silver wires through the graphite/PEEK host. The insulating glass cloth and tube sheaths are impregnated with PEEK resin to improve the bonding to the surrounding structural materials. To compensate for non-uniform stresses and prevent the composite plate from warping or distorting during the consolidation process, a compensating layer made from several plies of the same glass/PEEK cloth used to wrap the ceramic transducer is placed under the cutouts on the opposite side of the plate/ply structure. When the consolidation is completed, the piezoelectric ceramic transducer is electrically poled with a high electric field (dependent on the specific ceramic material) at a temperature of around 200 to 350 degrees Fahrenheit, which repoles the ceramic, transducer.

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