Sound transmission behavior through a sandwiched electrorheological layer

The sound transmission behaviors through a thin electrorheological (ER) layer sandwiched between two sheets of flexible electrodes were investigated experimentally. The transmission spectrum of the ER layer shows frequency selective characters. The relative transmittance T of the ER layer with a particle volume fraction of 31% exhibits an enhanced hump within 100-160 Hz with the increase of the external electric field E, while T doesn't change with E at other frequencies. The relative transmittance T at the hump peak of 130 Hz under E = 2.0 kV/mm is nearly 7 times that of zero electric field strength. The phase angle of transmitted sound increases with E also. At the frequency of 105 Hz, the long axis of Lisajous ellipse figure rotates clockwise by 45° as E increases from 0 to 2.0 kV/mm. With the increase in E, the amplitude and phase of the transmission hump show tunable features. As φ increases from 16% to 31%, the maximum T changes from 1.8 to 7 (E = 2.0 kV/mm) and the responding frequency band of the enhanced hump moves towards the high frequency direction. The interaction between the field induced microstructures and the sound waves may be the cause of the phenomenon.