The active control of underwater sound using piezoelectric materials

Abstract

A smart material structure (SMS) is a structure that contains a sensor and actuator constructed in such a way that its actuator responds to its sensor. SMS have been fabricated using a 0–3 piezocomposite sensor and actuator. Two types of structure have been investigated. The first type was built with a central sensor and surrounding actuator. The second type was built with a layered sensor and actuator. Both structures have been used with a fast feedback electronic control system. In active reduction mode, the actuator surface moves in the direction to reduce the sensed pressure. In active enhancement mode, the active surface moves in the opposite direction to increase the sensed pressure. The reflection and transmission coefficients have been measured in a pulse tube and the acoustic energy determined. For the concentric type of SMS, the acoustic energy was reduced by up to 79% in the active reduction mode and increased by up to 24% in the active enhancement mode from 1.5 to 8.5kHz. With the SMS air backed, the echo reduction was increased by up to 12dB from 1 to 8kHz in active reduction mode. For the layered type of SMS, the energy was reduced by up to 66% in active reduction mode and increased by up to 28% in active enhancement mode from 500Hz to 6.75kHz. With the SMS air backed, the echo reduction was increased by up to 10.25dB from 500Hz to 6.75kHz with 3dB of echo reduction achieved at 500Hz.