A semiconductor technology has been developed to improve the wireless charging efficiency of implantable medical devices. By adjusting the power transfer path based on the device's internal load to reduce losses and heat generation, this technology is evaluated as capable of enhancing the operational stability of medical devices that require long-term use.

Ulsan National Institute of Science and Technology (UNIST) announced on the 27th that a research team led by Professor Young-Jae Byun of the Department of Electrical and Electronic Engineering has developed wireless power transmission technology that adjusts the power delivery structure in accordance with changes in power consumption of implantable medical devices.

This technology is characterized by a method of changing power delivery conditions based on the internal circuit characteristics of the device, which complements the limitations of existing fixed charging structures.

Implantable medical devices contain both high-load circuits requiring high current, such as nerve stimulation, and low-current based circuits, such as data processing. As load conditions change, optimal power delivery conditions also change; however, existing wireless charging methods fixed this to a single state, which resulted in power loss.

To solve this problem, the research team distinguished load conditions and applied a dedicated matching network tailored to each. Power transfer efficiency was enhanced by utilizing internal electronic switches to connect to the appropriate circuit depending on high or low load conditions.

The matching circuit is a circuit that regulates the efficient flow of power transmitted from an external transmitting coil into the medical device through a receiving coil, and is described as a key element of the power transmission process.

The research team improved not only power transmission but also the efficiency of the rectification process that converts alternating current (AC) to direct current (DC). Since the power delivered from the outside is in the form of alternating current, it must be converted to direct current to be used in medical devices.

The research team stated that a method for controlling switch operation timing was applied during this process, reducing losses occurring in the conversion phase.

Experimental results showed that the power transfer efficiency varied by condition: △low load (3mA) condition: link efficiency 94.4% △high load (30mA) condition: link efficiency 92.7% △rectifier conversion efficiency: maximum 94.5% △input voltage range of 2.5–5.0V: efficiency maintained at 92.3% or higher.

This figure was presented as a result demonstrating that stable power delivery is possible even with load changes and fluctuations in input conditions.

The research team explained that this technology could be used to extend the battery life of implantable medical devices used for extended periods, such as pacemakers and nerve stimulators. Accordingly, it is expected to contribute to alleviating the burden of periodic battery replacement surgeries.

In addition, the possibility was also presented that the same technology could be expanded into the field of low-power electronic devices, such as wearable devices and ultra-small Internet of Things (IoT) devices.

Meanwhile, this research was conducted with support from the Ministry of Science and ICT and the Institute of Information and Communication Technology Planning and Evaluation (IITP), and the results were published online on April 29 in the semiconductor circuit and systems journal 'IEEE Transactions on Very Large Scale Integration Systems'.