Nanocomposite matching layers for high frequency ultrasound transducers

Mismatch of acoustic impedance at the interface between an ultrasound transducer and the probing medium will substantially reduce the amount of ultrasound energy being transmitted into the medium. Therefore, matching layer is a very important part of a ultrasonic transducer. In this work, the spin-coating process was used to fabricate alumina/polymer nano composite films with alumina volume fraction ranged from 14%~32%. The particle size of alumina is in the range of 10 and 40 nm. The thicknesses of the matching layer can be controlled by the spinning-speed and the concentration of solution. The acoustic properties were measured using standard ultrasound methods. Acoustic impedances of these nanocomposite matching layers are in the range of 2.8 to 4.8 MRayls with different alumina contents, which meet the requirement. Attenuation of nano-composite matching layer is very much dependent on the quality and content of the coating layer, varying from 1.5 dB/mm to 12 dB/mm at the frequency of 40 MHz.