A study of sound shielding control of curved piezoelectric sheets connected to negative capacitance circuits

A study is conducted on the control of the sound-induced vibrations of a curved piezoelectric composite sheet connected to a negative capacitance circuit. The amplitudes of the sound-induced vibrations of the sheet are measured using a laser Doppler vibrometer. The piezoelectric voltage generated by the sound and the control voltage of the circuit are also measured. When a normal capacitor is used as a circuit element, the vibration of the sheet over a limited frequency band is selectively attenuated by circuit control. The frequency band is controlled by varying the values of the circuit elements. The effective frequency band is increased over a broad frequency range of 40–200 Hz by installing another composite sheet as a capacitor in the circuit. The frequency characteristics of both the ratio of the amplitude of the control voltage of the circuit to that of the piezoelectric voltage of the sheet and the vibration control level of the circuit are expressed as functions of the absolute value of the complex capacitance ratio and the difference between the loss factors of the circuit and the sheet. A vibration amplitude attenuation of up to 27 dB is achieved when the absolute value is matched with the constant depending on the electromechanical coupling factor of the sheet, and the difference between the loss factors is 0.003.