Matching layers design for a plate waveguide ultrasonic transducer for flow measurement in hostile environments

A wetted ultrasonic transducer with an integrated thermal buffer could allow ultrasonic techniques to be used for flow measurement in harsh environments. We have previously presented one such buffer design, consisting of parallel stainless steel strip waveguides. One disadvantage of such a design is the large impedance mismatch which is created between the buffer material and the test fluid, reducing the transmitted energy. The addition of a matching layer, with an intermediate acoustic impedance, to the waveguide can assist in reducing this effect. Such matching layers are commonly used in conventional ultrasonic transducer design, however for this application additional consideration must be given to the material selection to ensure they are suitable for use in hostile environments. In this work we have investigated several materials, selected for their thermal stability, which were then modified by loading, in order to tailor the acoustic properties to best suit our application. These materials have then been investigated using both finite element modelling and experimental techniques quantify their effectiveness as matching layers for a strip waveguide transducer system. This work has shown that and increase in the maximum emitted pressure by a factor of 3.4 may be obtained using a tungsten loaded matching layer.