Research On Theories And Methods Of Active Absorption Using Piezoelectric Composite Structure

Passive acoustic absorption is that using the acoustic impedance characteristics of materials and the acoustic resonance which can transfer the sound energy into heat to achieve the goal of sound absorption and noise reduction. Active acoustic absorption is achieved by controlling through the transport path of noise and the absorption structure,and its control target is that making the surface acoustic impedance of absorbing material and absorbing structure match with the anterior medium,in which acoustic wave propagate as if there have no interface. They have their own advantages and disadvantages at different frequency ranges. On the basis of reading a large number of domestic and foreign literature about active absorption and passive absorption, this dissertation proposes the method that combined piezoelectric material with passive absorption material and structure to establish active-passive composite absorption system. Acoustic impedance prediction model and absorption characteristics prediction model and finite element model of piezoelectric composite structure are established, and the absorption mechanism of piezoelectric composite structure is deeply researched. The main work of the dissertation is listed as following:A theoretical method to calculate the absorption coefficient and the surface acoustic impedance of piezoelectric ceramic and piezoelectric composites is proposed. Passive absorption of piezoelectric material is analyzed, the contribution of piezoelectric ceramic and rubber in piezoelectric composite for sound attenuation is discussed, and the feasibility of using piezoelectric material as active absorption material under water is verified. These lay a foundation for the further research.The analytical method of piezoelectric composite structure for active-passive composite absorption is researched. The control voltage amplitude and phase of the uniform rubber layer-single piezoelectric layer, uniform rubber layer-double piezoelectric layer and non-uniform rubber layer-single piezoelectric layer composite structure with different material properties, physical parameters and boundary conditions are theoretically calculated by transfer matrix method. It is proved that piezoelectric material combine with passive absorption material and structure could effectively broaden the absorption band. The research result shows the close relation between controlled voltage amplitude and the absorption coefficient without controlled, when the absorption coefficient without controlled is higher, the corresponding controlled voltage amplitude is lower.The numerical method of piezoelectric composite structure for active-passive composite absorption is researched. Take resonant absorption of the sound wave of cavity and the acoustic-structure coupling of water and absorption structure which are not considered in analytic method into consideration, a multi-physical field coupling finite element model of piezoelectric composite absorption structure is established. Also the reflection characteristics of piezoelectric composite absorption structure in the infinite water is analyzed using finite element software ANSYS and the sound pressure nephogram is calculated before and after the control voltage is added.According to the characteristics of the piezoelectric composite absorption structure, an active control system was designed. Integrate linear quadratic optimal control algorithm and minimizing reflected acoustic pressure method, a new control strategy is applied to the control system. According to the detected incident and reflected sound pressure, this system apply a suitable voltage by the optimal control strategy to match the surface acoustic impedance of piezoelectric composite structure and the characteristic impedance of the medium around so that it can achieve the goal of active absorption. At last, the simulation is carried out. The results denoted that the active control system has very acceptable efficiency.On the basis of theoretical research, a sound characteristics test system of piezoelectric composite structure is built. From the experiment result, we can know that the sound pressure reflection coefficient of piezoelectric composite structure can be effectively reduced in low frequency by applying proper control voltage, this can make up for the shortage of passive absorption, and the experiment results agree with the theoretical calculation results.