Table 1.

Measured system efficiency with USER operating at 1 MHz, for different transducer diameters, source power, and propagating medium.

Expt. #	Transmitter-Receiver transducer diameter (mm)	Medium	Pin (W)	Battery current (mA)	Efficiency (%)
1	25	None, direct charging	0.6	93	50
2	10	1-cm water	4.0	29	3
3	25	1-cm water	4.0	155	15
4	40	1-cm water	4.0	208	20
5	25	10 mm porcine tissue	4.0	150	15
6*	Ti+PZT 25*	3–5 mm porcine tissue	2.0	110	22
7*	Ti+PZT 25*	6–10 mm porcine tissue	3.0	67	10
8	25	50 mm of 10 mm slices	7.0	20	1.1
9	25	50 mm beef muscle	7.0	70	4

^*Experiments performed with receiver transducer bonded inside a titanium pacemaker casing.