The Institute of Paper Chemistry

Willmer A Wink

Charles C Habeger, Jr

An ultrasonic transducer for coupling ultrasonic energy to a web-like porous sample includes a sample-contacting layer of soft neoprene, 5-15 durometer hardness, which conforms to the surface of the sample being tested when pressed thereagainst. A non-polarized backing layer of polyvinylidene fluoride eliminates reflections at the end of the transducer remote from the sample. A polystyrene impedance-matching layer is located between the sample-contacting and the backing layer to provide a low-loss, low-impedance coupling of ultrasonic energy to the sample-contactiong layer. A stack of two, and preferably four, metallized polyvinylidene fluoride films is located between the impedance-matching layer and the backing layer. The outer surfaces of the stack are grounded, while the inner surfaces are energized by the ultrasonic energy source. The outer layers are polarized in a first direction, opposite that of the polarization direction of the middle layer.

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Appleton, WI, United States of America

Willmer A Wink