Two Dimension Structural Sound Radiation Mode Sensor Is Designing In ASAC System

In order to reduce sound radiation of a structure, the method of Active Structural Acoustic Control (ASAC) was developed in the 1980s. People are interested in the study of ASAC system based on the radiation modes of radiation structure in recent years, and the system can reduce sound radiation power by controlling radiation modes. The aim of ASAC is to control radiation power. Because radiation modes are orthogonal each other, the corresponding sound power of each order radiation mode is completely independent. Radiation modes are dependent on the radiator's geometry shape and vibration frequency, but are not relative to the material characteristic and the border condition of the radiator. Further more, the radiation efficiency of the radiation modes falls off very rapidly with the increase of modes order at low frequency .The adjoint coefficient of sound radiation modes is proportional to the corresponding sound radiation power.The total sound radiation power can be reduced by counteracting the adjoint coefficients of sound radiation modes of the first N radiation modes. That is to say, in order to measure the adjoint coefficients of sound radiation modes, we should design the particular shape of error sensor. As a new kind of piezoelectricity macromolecule material, PVDF (Polyvinylidene fluoride) has not only lower density, but also better piezoelectricity, good mechanical performance and plasticity .When aparticular shaped PVDF film is used as an error sensor and is bonded to the surface of the measured structure, there will be little effect on the system.According to the integral characteristic of PVDF film, two PVDF sensors are designed to measure adjoint coefficient of sound radiation mode in this paper. Based on the theory of sound radiation and two-dimensional modal sensors equation, and taking a simply supported plate as example, we measure mode l,mode 2 and mode 3 adjoint coefficient of its sound radiation by the sensors. Finally, by numerical calculation we can conclude that the particular shaped PVDF that act as error sensor is desirable.