Nils Kroemer

Modified SiO2 aerogels as acoustic impedance matching layers in ultrasonic devices

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 Masons 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.

Ultrasonic transducer with piezoelectric polymer foil

Ultrasonic transducer in which strips (1), metallised on both sides, of piezoelectric polymer film are arranged parallel to one another along a straight line adjacent to one another on a support (2) which is flat at least in sections, and sections (3) in each case at the ends of these strips (1) are fixed flatly on the surface of the support (2) so close together that the strip (1) is bulged forwards in the shape of a hat, and in which the strips are mechanically decoupled from one another and are electrically insulated with respect to one another.