Thermal Behaviour of Ultrasonic Transducer Materials

The behaviour of piezoelectric composites subjected to elevated temperatures is of increasing interest. The increased temperatures can result from high electrical drive or from applications subject to hostile environments. Since polymer properties are a function of temperature, it is important to correlate any shift in mechanical properties with the temperature rise. For example, a polymer that is hard and glass like at room temperature will soften as the temperature increases and will undergo a dramatic shift in elastic properties at the glass transition temperature, Tg, where the properties become like those of a rubber. Such changes can significantly affect the vibrational behaviour of the piezoelectric composite, detracting from the uniform piston like behaviour as shown below. Limiting these effects is an essential part of transducer design for elevated temperatures.

Materials that impart improved temperature stability to piezoelectric composites by increasing the polymer Tg have been developed; the inclusion of thermally conductive particles into the polymer also improves thermal dissipation.