Research on the Sound Characteristic in the Active Sound Absorption and Isolation of the Piezoelectric Ceramics

The sound characteristic of the piezoelectric ceramics is posed for the excellent mechanic and electric coupling performance of piezoelectric material.Two pieces of piezoelectric ceramic are used as materials of active absorption and active isolation,two pieces of PVDF with equal distance are placed in the front of the material in order to measure the incidence plane wave and the reflected wave,the voltages are applied on the surface of the material in order to make the reflected wave and transmission wave be zero using the adaptive controlling.At last,emulation is carried out with plane wave,and good absorption and isolation effect is achieved.

Research on Sound Absorption Method of Perforated Tube with Shunt Hedge

The exhaust flow velocity of the engine is an important parameter affecting the comprehensive performance of the muffler.The exhaust flow velocity increases by the regenerated noise generated in the muffler,which makes the sound absorption effect of the muffler worse.In order to solve this problem,a sound absorption method was proposed to reduce the flow rate of exhaust air by diverting and hedging the exhaust air,so as to improve the sound absorption.First of all,the airflow into the muffler was shunted by a conical shunt unit.Subsequently,the airflow entered the cavity of the perforated tube through the hole on the perforated tube.When the airflow was offset in the cavity of the perforated tube,it could reduce the flow rate of the exhaust airflow and improve the sound absorption effect.It could be concluded that the influence factors and the characteristics of the transmission loss were obtained by dividing the anechoic sub units of the whole structure,calculating the transfer matrix,and analyzing the function relationship between the independent variable and the dependent variable of the transmission loss,and the theoretical model was verified by experiments.The results of the experiment showed that the proposed sound absorption method can keep the transmission loss at a stable state under the condition of high⁃speed exhaust flow.For example,when the inlet air velocity increases from 15 m/s to 45 m/s,the maximum reduction of transmission loss is 6.5 dB in the range of 0-3000 Hz,which proves that the structure has a good effect of sound absorption.