A Wireless Implantable Sensor Design With Subcutaneous Energy Harvesting for Long-Term IoT Healthcare Applications

In this paper, a wireless implantable sensor prototype with subcutaneous solar energy harvesting is proposed. To evaluate the performance of a flexible solar panel under skin, ex-vivo experiments are conducted under natural sunlight and artificial light sources. The results show that the solar panel covered by a 3 mm thick porcine flap can output tens of microWatts to a few milliWatts depending on the light conditions. The subcutaneous solar energy harvester is tested on different body parts, which suggests the optimal position for the harvester to implant is between neck and shoulder. A wireless implantable system powered by the subcutaneous energy harvester is presented, which consists of a power management circuit, a temperature sensor, and a Bluetooth low energy module. An application is developed for data visualization on mobile devices, which can be a gateway for future IoT-based healthcare applications. The entire device is embedded in a transparent silicone housing (38 mm × 32 mm × 4 mm), including a 7 mAh rechargeable battery for energy storage. The average power consumption of the implants is about 30 μW in a 10 min operation cycle. With the subcutaneous solar energy harvester, the self-powered operation of the implantable sensor prototype is demonstrated by long-term experimental results. Two worst-case scenarios (no exposure to light and battery depletion) are considered with ex-vivo experiment simulations.