Sound transmission behavior through a sandwiched electrorheological layer

The sound t ransmission behaviors through a thin elect rorheological ( ER) layer sandwiched between twosheet s of flexible elect rodes were investigated experimentally. The t ransmission spect rum of the ER layer shows frequency selective characters. The relative t ransmittance T of the ER layer with a particle volume fraction of 31 %exhibit s an enhanced hump within 100～160 Hz with the increase of the external elect ric field E , while T doesnptchange with E at other f requencies. The relative t ransmittance T at the hump peak of 130 Hz under E = 2. 0 kV/ mmis nearly 7 times that of zero elect ric field st rength. The phase angle of t ransmitted sound increases with E also. Atthe f requency of 105 Hz , the long axis of Lisajous ellipse figure rotates clockwise by 45°as E increases f rom 0 tO₂. 0 kV/ mm. With the increase in E , the amplitude and phase of the t ransmission hump show tunable features. Asφincreases f rom 16 % to 31 % , the maximum T changes f rom 1. 8 to 7 ( E = 2. 0 kV/ mm) and the respondingf requency band of the enhanced hump moves towards the high f requency direction. The interaction between the fieldinduced microst ructures and the sound waves may be the cause of the phenomenon.