Multi-mode Control in a Two-stage Piezoelectric Transducer for an Application of Physical Therapy

Abstract

A novel as well as unique piezoelectric-driven system constructed with two sets of ceramic actuators connected in a series is able to produce both mechanical vibration and electric power at the output end. With power input to the first ceramic actuator to oscillate, the connected second one makes use of the transmitted mechanical vibration energy to generate electricity via piezoelectric direct effect. An application example of physical therapy including ultrasonic diathermy and electrotherapy is selected for further investigation in this article. Different from the traditional ultrasonic diathermy and electrotherapy systems that are built with their own specific method and independent structure, the developed two-stage piezoelectric transducer can achieve the same application purpose alone. Multi-mode control scheme is proposed by using Frequency- Hopping method to oscillate the first ceramic actuator with different vibration amplitude at various resonance frequencies under schematic switching process. Hence, the second ceramic actuator receives the transmitted energy and generates equivalent electricity with modulation amplitude signal for electrotherapy. The residual energy in the first ceramic actuator is also collected at the output end for ultrasonic diathermy. From the satisfactory experimental outcome, it indicates such a two-stage system not only can generate vibration and electricity but produce composite effect for desired application purpose under well-defined input control signal.