Fig. 4

a Layout of our piezoelectric stimulator (PolyUStimulator). The conditioning circuit and the connections of the stimulation wires are on one layer of the double-layered PCB, while the other layer is connected to a piezoelectric disc. Finally, the stimulator is encapsulated with a biocompatible silicone elastomer. b-c Face-up and face-down side views of the prototype stimulator