Specific acoustic impedances of piezoelectric ceramic and polymer composites used in medical applications.

The specific acoustic impedance of the piezoelectric composites over the frequency range of 0.5-7.5 MHz was measured using the reflection, the echo-shift, and the resonance techniques. There was a significant difference between the values obtained by the reflection technique in comparison with the other two techniques. It is argued that the difference is inherent in the measurement techniques and they measure different properties of the composite such as acoustic impedance and reflectivity. The specific acoustic impedance and the reflectivity were found to be a function of the volume fraction of the ceramic and not a function of frequency.