To keep the implants small, many microstimulators will have no battery. When users want to generate pulses to relieve pain or read data from an embedded sensor, they will place over the affected area a credit-card sized charger, such as the thin 6x6 cm device the Stanford team used.
Other stimulators or sensors may have tiny batteries so they can work automatically. Users will charge the implants with the external device.
Within the next 12 months, Poon's team hopes to implant its microstimulator in a human for the first time, probably on peripheral nerves for pain therapy. It could take several years of tests before such products are approved for medical use.
Poon's device is an order of magnitude smaller than today's centimeter-sized pacemakers from Medtronic and St. Jude Medical. The larger devices must resist greater forces to stay anchored to tissues amid the flow of body fluids.
Poon is interested in exploring the limits of what electromagnetic energy can deliver over how great a distance.
"My training is in information theory," she says. "It's one of the most mathematically intensive branches in electrical engineering. We always ask the question: What's the highest data rate through a given channel?"
Her career started with work on reconfigurable radio at Intel, trying to make baseband chips as agile as possible. She later worked at SiBeam, which pioneered 60 GHz chips in CMOS, delivering wireless, high-definition video for consumer electronics gear.
"When I started work on electromagnetics in biological tissue, I applied the same curiosity about what's the limit. Everyone was using inductive coupling, but what was the optimal solution was not answered."
The question remains an open one she has now been pursuing six years, with several more years of work ahead. "It's a long journey," says Poon.
"One interesting thing about this work was that it was incredibly broad, ranging from physics to medicine," says Ho. "There were times where I performed mathematical studies and animal experiments on the same day -- as primarily a theorist by training, this was exhilarating/"
The microstimulator could be inserted via a catheter.
— Rick Merritt, Silicon Valley Bureau Chief, EE Times