A time-reversal acoustics system includes a transmitter configured to send a high intensity acoustic waveform signal focused on an implantable receiver. The receiver includes a piezoelectric transducer configured to convert received acoustic energy to an electrical signal used to energize an internal electrical circuit. Such circuit may be used to operate at least one tissue stimulating electrode, at least one sensor such as an ECG sensor, charge an internal battery or perform another useful function. The system of the invention may be used as a wireless cardiac pacemaker or a neurostimulator.