ASA 127th Meeting M.I.T. 1994 June 6-10

2pEA6. Loss processes in piezoelectric PVDF and their effect on broadband transducers.

D. A. Summa

Sound Solutions, 11718 Tallow Field Way, Austin, TX 78758-3520

E. L. Hixson

Univ. of Texas at Austin, Austin, TX 78712

Classic electromechanical models are extended to transducers fabricated from inherently lossy polymeric materials. To augment sparse data, phenomenological models and molecular estimation techniques based upon structure-property relationships are used to examine relaxation processes and reconstruct elastic and dielectric loss tangent surfaces as a function of frequency, temperature, and pressure (f,T,P). The improved material descriptions are used to assess the acoustic performance of a typical thickness-mode PVDF hydrophone over a range of environmental parameters of interest in sonar. Variations in elastic parameters shift the resonance frequency, cause a departure from a truly ``(rho)c-matched'' condition, and introduce a dynamic variation in the open-circuit receive sensitivty. Variations in the dielectric parameters of similar magnitude occurring at the same (f,T,P) coordinates ensure that the wideband response remains flat to within 1 dB, depending upon the geometry of the device and operating parameters chosen. The effects of intrinsic material losses are most pronounced in the internal noise spectrum of the PVDF hydrophone. In warm waters noise levels average 10 dB lower than predicted by a constant loss model, whereas in cool waters noise levels are 6--10 dB below the predictions based upon these models at low frequencies [O(10[sup 2]) Hz], rising to 10--18 dB above the constant loss predictions at frequencies on the order of 10[sup 4]--10[sup 5] Hz. [Partial support provided by the Independent Research & Development Program, Applied Research Laboratories, The University of Texas at Austin, Austin, TX.]