SBIR-STTR Award

This project, if successful, should provide: a general model and procedure for use in designing piezoelectric sensors -hydrophones, accelerometers, etc.--which would enable the designer of a sensor to predict its sensitivities to the stimulus for which it was designed, and to extraneous stimuli which generate interfering signals; information on how the choice of piezoelectric material and mode of operation, e.g. compression or shear, affect the performance of the device, and how the device should be modified should it sensitivity to extraneous signals be too high; data on how spatial variability in polarization in man-made materials affects sensor performance; an understanding of the acoustic performance of pvdf wire hydrophones and their response to acceleration and flexing; one or more designs for hydrophones that appear suitable for low cost acoustic arrays.

In the Phase I contract, analytical models were developed for predicting the response of piezoelectric hydrophones to sound pressure, force, acceleration, and bending. These models were used to investigate causes of noise in Poly-vinylidene (PVDF) homopolymer wire hydrophones and to predict the responses of thick ribbon and annular PVDF copolymer hydrophones, both with a rigid mandrel and hollow, with estimated values for the dielectric, compliance, and piezoelectric constants of the copolymer material. The models indicate that tensile strains in the central wire in PVDF wire hydrophones, and bending of the wire, because of nonuniformities in the PVDF coating thickness and polarization, are the probable causes of high selfnoise, rather than acceleration. The models also indicate that PVDF copolymer ribbon and annular hydrophones having sizes, shapes, weights, sensitivities, and capacitances suitable for naval applications may be feasible. Since cost of PVDF material for a hydrophone is of the order of a dollar or so, these hydrophones are candidates for low cost sensors. This proposal is to measure the dielectric, compliance, and piezoelectric properties of PVDF copolymer material, construct and evaluate experimental thick ribbon and annular hydrophones suitable for field tests, and investigate low cost methods for their manufacture.