Experimental study of the acoustical properties of polymers utilized to construct PVDF ultrasonic transducers and the acousto-electric properties of PVDF and P(VDF/TrFE) films.

ABSTRACT

Several acoustic transmission and reflection technique measurements were carried out to determine mechanical properties (acoustic attenuation and velocity) versus frequency of polyvinylidene-fluoride (PVDF) and six other polymers. Acoustic measurements (0.5 to 12 MHz) included time-delay spectrometry (TDS; in which separate transmitting and receiving transducers utilize a swept frequency signal) and two pulse-echo methods (short tone burst echoes utilizing transducers with different center frequencies and Fourier analysis of echoes sent and received by damped transducers operating in the broadband pulse mode). Electrical impedance measurements of piezoelectric thin films of PVDF and P(VDF/TrFE) yielded comparable high frequency mechanical parameters. Of the seven acoustically examined polymers, PVDF had the greatest acoustic impedance, lowest acoustic velocity, and greatest mechanical loss (13.4 dB/cm per MHz). Polymethyl-methacrylate (PMMA; lucite) and polydimethyl-pentane (TPX) had the lowest loss. PMMA had the highest acoustic velocity, and TPX had the lowest acoustic impedance and a velocity almost identical to that of PVDF. These data are useful in the design of backing, matching, and lens materials to be used in association with PVDF transducers.