Alumina/Epoxy Nanocomposite Matching Layers for High-Frequency Ultrasound Transducer Application

Mismatch of acoustic impedance at the inter- face between a piezoelectric transducer and the medium to be probed will substantially reduce the amount of ultrasound energy being transmitted into the medium. Therefore, match- ing layer is a critical component of an ultrasonic transducer. A spin-coating process was used to fabricate alumina/polymer nanocomposite films with alumina volume fractions ranging from 14 to 32%. The particle size of alumina is in the range of 10 to 40 nm. The thicknesses of the matching layer can be con- trolled by the spinning speed and the concentration of solution. Acoustic impedances of these nanocomposite matching layers are in the range of 2.8 to 5.1 MRayls with different alumina contents, which meet the matching layer requirement. The at- tenuation of a nanocomposite matching layer with smooth sur- face is about 15 dB/mm at 40 MHz. The pulse-echo spectrum and frequency spectrum of a high-frequency transducer using this nanocomposite matching layer are reported.