Tiny Inductively Powered Battery Chargers

Although wireless 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 in this respect, but only when an ambient source is available, which is often not the case for structurally embedded microsensors and biomedical implants. Transmitting power wirelessly is often the only practical alternative in these applications. Unfortunately, tiny power receivers capture a small fraction of the power that a wireless source can deliver. So output power is low and its effects on the transmitting coil are barely noticeable. Power receivers should therefore draw as much power as possible, but only as much as breakdown voltages and power losses allow. This talk discusses the state of the art in inductively coupled power receivers that draw power from tiny coils that are millimeters to centimeters away from their transmitting sources.