Basic Studies of Electrically Controlled Elasticity of Lead Zirconate Titanate (PZT) Ceramic and its Application to Intercepting Elastic Waves
We studied a novel technique for controlling the elastic coefficient of a piezoelectric lead zirconate titanate (PZT) ceramic by connecting a negative-capacitance circuit that behaves as a "negative capacitor". Thus, we can realize control through a mechanism in which PZT is softened and hardened. On the basis of this technology, we developed a simple experimental system for intercepting elastic waves in the frequency range from 8 kHz to 110 kHz. We determined the attenuation factor in transmission loss of the experimental system, which was more than 10 dB in this frequency range. The maximum attenuation factor in transmission loss was about 60 dB at a frequency of 91 kHz.
Sound isolation by piezoelectric polymer films connected with negative capacitance circuits
Sound pressure produces strain and polarization in piezoelectric polymer films. The electric charge induced by the polarization in the electrode of the films is introduced to a negative capacitance circuit and the resulting voltage is fed back to the electrode. The field-induced strain cancels the stress-induced strain, leading to the increase of the elastic coefficient of the films. If the capacitance of the circuit is controlled to be equal to that of the film, the elastic coefficient approaches infinity. Using this principle, the sound isolation by piezoelectric polymer films connected with a negative capacitance circuit was undertaken. A PVDF film with a curved plane was located in the middle of an acoustic tube and the transmission loss through the film was determined in the audio frequency range. At any single frequency, the complete isolation of sound was achieved by adjusting the feedback. The precise matching of complex capacitance of the circuit with that of the film was required to obtain the increase of the transmission loss over a broad frequency range.
Noise shielding system utilizing a thin piezoelectric membrane and elasticity control
The description and theoretical analysis of a noise shielding system are presented. In this system, the noise and/or sound are transmitted through the piezoelectric curved membrane, which is connected to an external feedback circuit. Using the principle of elasticity control, i.e., utilization of both direct and inverse piezoelectric effects simultaneously, the movement of the membrane as well as the sound pressure of the transmitted wave can be controlled to a large extent. Transmission loss of an audible sound through the membrane in such a system is expressed as a function of a sound frequency, geometrical properties of the membrane, and parameters of the feedback circuit. It is used for the comparison of theoretical predictions and experimental data. Using this technique, the increase of the transmission loss of about 60 dB in a narrow frequency range or about 7 dB in the broad frequency range has been achieved. The performance of this system is discussed.