In this study, an ultrasonic motor for use at ultralow temperatures has been fabricated and evaluated. The motor has a bolt-clamped Langevin-type transducer using lead magnesium niobate--lead titanate (PMN--PT) single crystal. The transducer is proposed as an oscillator for use at ultralow temperatures by simulation of the thermal stress and evaluation of the pre-load. The thermal effect of the transducer was evaluated when the temperature was changed. As a result, the pre-load of the transducer was concluded to be affected by thermal stress. In addition, the ultrasonic motor using the transducer was fabricated and evaluated. By adjusting the contact pre-load between the rotor and the transducer, the motor has successfully rotated at an ultralow temperature. The rotation speed was 144 rpm at 4.4 K when the applied voltage was 150 V. This rotation speed is larger than that of previous same size actuators that can be used at ultralow temperatures.
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