Enhanced Low Frequency Transmission Loss of Light Weight Trim Panels Using PZT Inertial Actuators

One method of enhancing the low frequency transmission loss of noise into the cabin of a propeller driven aircraft or helicopter is to replace selected sections of the interior trim with stiff, ultra light panels that are driven with PZT inertial actuators. Given the proper control signals, the panels can be driven by the actuators such that their net volume velocity is minimized. Experiments are described that measure the sound transmission loss for a soft mounted, double layer corrugated aluminum panel driven by four actuators consisting of symmetrically-mounted, cantilevered beams with end masses driven by unimorph piezoelectric elements. A feedback control system is designed by serially connecting three Tow-Thomas biquad filters which are based on a Motorola LF347N integrated circuit design. Using this simple analog controller with the panel’s accelerations as an input, experimental results show that the inertial actuators mounted at the center of the panel produce up to 13 dB improvement in both vibration reduction and noise transmission loss of the panel.