Generating the highest power with a tiny and distant inductively coupled coil

Although microsystems today require less power than ever before, they still cannot fit large enough batteries to sustain them for months or years at a time. Ambient energy is appealing, but only when available, which is often not the case for embedded sensors. Transmitting power wirelessly is more practical in these applications. Tiny receivers, however, capture a small fraction of the power that a distant source can deliver. So output power is low and its effects on the transmitting coil are barely noticeable. Receivers should therefore draw as much power as possible, but only as much as breakdown voltages and power losses allow. This paper shows that, although the switched bridge can draw 27% more power than resonant bridges, synchronization and ohmic losses negate that gain. In fact, breakdown voltages limit the switched resonant bridge less than others in the state of the art. Plus, the switched resonant bridge excludes the charger that the others require for maximum output power, so with less space and less added losses, power density can be greater.