Tunable characteristics of a flexible thin electrorheological layer for low frequency acoustic waves

A composite layer with an electrorheological (ER) fluid sandwiched between two flexible electrodes of conducting-glue-painted plastic film is devised and its sound transmission properties are investigated. Within 80-150 Hz the transmitted sound pressure level (SPL) dramatically increases with the applied electric field and the plot of SPL versus frequency exhibits a resonant peak within 80-150 Hz at each electric-field strength. It is also found that the phase angle of the transmitted sound varies manifestly with the electric field. With an increase in starch volume fraction, the responding frequency band in which the SPL can be electrically tuned, moves in the direction of high frequency, and the maximal increment of SPL also increases. It is thought that the variations in the layer vibration and the sound radiation from the layer surface due to the complex electric-field-induced viscoelasticity in the ER fluid are responsible for the observed results. The proposed thin ER layer is thought to be useful in designing tunable phononic crystals and other acoustic devices.