Acoustic-electric link budget

The end-to-end accounting of power and signal for an ultrasonic wireless implant: how much acoustic power the external transducer emits (capped by safety limits), how much survives beam spreading and tissue attenuation to reach the mote, what fraction the piezoelectric receiver captures and converts, and — for the return path — how strongly the backscatter is modulated and how it competes with clutter and noise at the receiver.

Key levers are frequency (higher frequencies focus tighter and match smaller motes but attenuate more strongly, roughly in proportion to frequency times depth), near-field versus far-field geometry, impedance-matching layers, and precise alignment of the external transducer with a millimetre target — often the practical bottleneck. The link budget, not transistor count, usually sets how small and how deep an ultrasonic implant can go.