Dual layer matching (20 MHz) piezoelectric transducers with glass and parylene

This study describes a method of applying very thin broadband matching layers to 2 mm diameter 20 MHz transducers. Dual layer acoustic matching between the ceramic and the medium at the front face of the transducer was accomplished by selecting 1/4 wavelength glass layers from a commercial source, epoxying them to the ceramic, and vapor depositing parylene to 1/4 wavelength thickness on the glass. A 8 dB fractional bandwidth of 0.75 and insertion loss of -10 dB was found on the average for these transducers. This method allowed fabricating probes that performed well, were reproducible, provided both a matching and protection coating, and could be fabricated in a practical manner.