Evaluation of thermal stress of transducers for cryogenic ultrasonic motors

An ultrasonic motor which can be driven at the condition from room temperature to cryogenic temperature has been designed, fabricated and evaluated. This motor has a bolt-clamped Langevin-type transducer which is suitable for cryogenic temperature. The aim of this paper is to evaluate the thermal stress of transducers. Each transducer is made of materials which had different thermal expansion coefficient, such as stainless, Ti, or invar. The thermal stress in the transducer made of Ti was the smallest. The rotation speed of the motor using the transducer made of Ti was evaluated at cryogenic temperature. The rotation speed was 1102 rpm at 4.6 K when the applied voltage was 100 V_p-p.