The present invention reduces the scale of circuitry and shortens the code phase detection time needed to achieve initial synchronization. In one embodiment, an electrochemical cell includes an anode comprising lithium and a multi-layered structure positioned between the anode and an electrolyte of the cell. The at least one optical microphone comprises an acoustic-optical transformer for transforming an acoustic input signal into an optical signal, the optical signal is processed in the hearing aid using an optical signal processing unit, and the processed optical signal is transformed into an acoustic output signal using an opto-electrical transformer.