UNIST develops wireless charging technology for implanted medical devices

Researchers have developed a technology that can wirelessly charge implanted medical devices stably and efficiently even while a patient is moving — whether turning over in bed or walking.

A research team led by Byun Young-jae, a professor in the Department of Electrical and Computer Engineering at the Ulsan National Institute of Science and Technology (UNIST), announced Wednesday that it has developed a next-generation wireless charging technology that maintains a constant voltage and supplies only as much power as needed, regardless of patient movement or changes in device operating state.

Wireless charging is critical for implanted medical devices such as pacemakers, neurostimulators and biotech sensors, because replacing their batteries through surgery is difficult. These devices draw different amounts of power depending on whether they are actively performing treatment or communication functions or sitting in standby. By detecting whether the implanted receiver actually needs power and switching between full-power and low-power modes accordingly, the external transmitter can deliver sufficient power only when required, reducing unnecessary energy consumption.

The technology the team developed is an "adaptive mode-switching" system that accurately assesses the receiver's status and adjusts transmission output even as the patient moves. In wireless charging, the distance and alignment between the transmitting coil and the receiving coil are critical, and body movement changes the signals measured at the transmitter. If the transmitter keeps sending power when none is needed, heat builds up and energy is wasted; conversely, if the system stays in low-power mode when the device actually needs power, the implant may malfunction or shut down entirely.

In experiments, the system demonstrated strong performance even when the distance between the transmitting and receiving coils was varied from 7 millimeters to 20 millimeters. The output voltage held steady at 3.3 volts even as the device's operating current surged from 6 milliamps to 16 milliamps, with voltage ripple remaining as low as 18 millivolts.

"Even when a patient moves or the device shifts position, the system can accurately assess the receiver's status and reduce both malfunctions caused by insufficient power and voltage spikes caused by oversupply," Byun said. He added that the technology could eventually be applied to wearable electronics and ultra-compact Internet of Things sensors, where coil alignment and power consumption change frequently.

The findings were published June 19 in IEEE Transactions on Circuits and Systems I: Regular Papers, an international journal covering circuits and systems.