Refrigerant for high temperature acoustic emission piezoelectric transducer

The use of acoustic emission (AE) for diagnosing objects operating at enhanced temperatures is limited by the instability of the properties of piezoelectric materials with variation in temperature. Attempts to produce piezoceramics with temperature stable properties are necessarily accompanied by a deterioration of the piezoelectric modulus, the strength and other useful properties. There is an AE transducer design in which the piezoceramics are placed in the bottom part of the probe body and are separated from the test object by a hollow filled with low melting point refrigerant. In this way the bottom part acts as a sound waveguide and keeps the piezoceramic temperature below the melting point of the refrigerant over the time interval required for complete melting of the refrigerant. It is clear that the volume of the hollow for the refrigerant depends on the working temperature of the object and the necessary time to ensure contact between the AE probe and the object. The acoustic properties of the refrigerants were studied and are reported.