Patients with implantable medical devices such as pacemakers and neurostimulators are expected to face significantly less burden from periodic replacement surgeries, as Korean researchers have developed a wireless charging technology that dramatically reduces heat loss during charging and extends battery life.
A research team led by Professor Byun Young-jae of the Department of Electrical and Electronic Engineering at Ulsan National Institute of Science and Technology (UNIST) announced on the 27th that it has developed a new wireless power transfer system that flexibly delivers energy in line with the real-time power consumption of in-body medical devices.
Inside advanced devices such as pacemakers, "stimulation circuits" that require strong currents coexist with "data processing circuits" that operate rapidly with small currents. Conventional wireless charging technology had a single, fixed power pathway. As a result, depending on what task the device was performing, power matching would fail and energy would leak out. This lost energy turned directly into "heat," irritating body tissue and causing side effects.
To solve this problem, the research team embedded a smart electronic switch inside the device. The system detects in real time whether the device is using large or small currents and instantaneously redirects the power pathway to a "dedicated matching circuit (gateway circuit)" tailored to each situation.
The team also refined the "rectification process," which converts the alternating current (AC) coming in from the outside into direct current (DC) usable by the device. By precisely controlling the timing at which switches turn on and off in sync with current transitions, they sealed off even the power that leaked during the conversion process.
The efficiency demonstrated in actual experiments was highly stable. The "link efficiency" of power transfer between coils inside and outside the body maintained a high rate of 94.4% under low-load conditions with small currents (3 mA), and 92.7% even under high-load conditions with large power consumption (30 mA).
The conversion efficiency of the active rectifier, which converts AC to DC, also reached a peak of 94.5%, and stably extracted more than 92.3% of power even under unstable conditions where voltage fluctuated sharply from 2.5V to 5.0V.
The research is significant in that it simultaneously resolves the two greatest weaknesses of implantable devices: "short battery life" and "heat generation during charging." As battery life is extended, the cycle of incision surgeries that patients had to repeat every few years to replace devices will also be dramatically lengthened.
"The wireless charging technology developed this time will significantly enhance the reliability of implantable medical devices that must operate safely for long periods," Professor Byun's research team said. "It can be immediately applied not only in the medical field but also in various industries where power efficiency is key, such as wearable devices worn on the body or ultra-small IoT (Internet of Things) devices."
Meanwhile, the research, conducted with support from the Institute of Information & Communications Technology Planning & Evaluation (IITP) under the Ministry of Science and ICT, was published online in IEEE Transactions on Very Large Scale Integration Systems, a world-renowned journal in the field of semiconductor and circuit systems.
