Researchers at Harvard University have demonstrated a new type of loudspeaker transducer which works on a different principle to the conventional moving coil design. It is made up of a thin sheet of transparent rubber sandwiched between two layers of salt water gel. A modulated high voltage signal passed across the two outer gel layers exerts pressure on the rubber membrane, causing it to vibrate and produce sound. The prototype speaker has a frequency response from 20 to 20 kHz.
The effect is produced by the electrical charges carried by ions and not the movement of electrons so strictly speaking this is not an electronic device. The new transducer could be used as an adaptive lens in an optical system or as a window-mounted noise cancellation device. The electrolyte gel is biocompatible so there could also be applications as artificial skin or muscle.