Investigation of Thunder™ Actuators as Underwater Propulsors

Abstract

Piezoelectric actuators have been used for active vibration control, noise suppression, health monitoring, etc. The large appeal in using smart material actuators stems from their high mechanical energy density. A relatively new actuator Thin Layer Composite Unimorph Ferroelectric Driver and Sensor (THUNDER) has overcome the displacement hurdles that have plagued traditional piezoelectric based actuators. It is capable of providing a displacement of the order of 0.5 cm. This allows the actuator to be used in some underwater applications, such as propulsion. To date the electrical power consumption and electro-mechanical efficiency of these actuators has not been quantified; specifically, applied as underwater propulsors. Some of the challenges in obtaining this information stems from the actuator’s nontraditional actuating architecture, high voltage requirements, and its electrical nonlinearity. This work experimentally determines the mechanical displacement and the electrical power consumption of the THUNDER actuators used as underwater propulsors. An estimate of a lower bound of the thrust that can be generated by the clamshell actuator is obtained. It is found that the actuator has a peak flow rate of approximately 1500 cm3/s and can generate a peak thrust greater than approximately 4.5 N. This preliminary analysis neglected the pressure forces acting on the actuator and therefore, the actual thrust is not computed. It is found that the average electrical power consumed by two THUNDER actuators placed in a clamshell configuration operating at 14 Hz is approximately 8 W, which is significantly less than that consumed by other autonomous underwater vehicles. The displacement response and the current draw of the actuators are determined to be nonlinear. The result of this work indicates that the use of THUNDER actuators has great potential to create an underwater propulsor that has low power consumption, can operate at great depths, and eliminates the need for seals, bearings and a propeller.