Modified SiO 2 aerogels as acoustic impedance matching layers in ultrasonic devices

Abstract

Acoustic impedance matching between a transducer and the irradiated medium can be achieved using quarterwave or impedance gradient layers. SiO 2 aerogels are suitable materials for both purposes. In order to investigate matched transducers for air applications, sound intensity measurements were performed with and without aerogel quarterwave layer for different types of piezoceramic transducers. The measured gains in sound pressure level are compared with theoretical data derived from Mason's equivalent circuit and from finite element simulations. Ways to employ aerogel gradient layers for the acoustic matching of piezoceramics and biological tissue are discussed. Such layers could be obtained by sintering aerogels in a temperature gradient. Under certain conditions, an energy transmission coefficient of more than 99% for all frequencies above a certain frequency, f 0 , is predicted with such systems.