Modelling of Implantable Photovoltaic Cells Based on Human Skin Types

Implantable electronic devices are emerging as important healthcare technologies due to their sustainable operation and low risk of infection. To overcome the drawbacks of the built-in battery in implantable devices, energy harvesting from the human body or another external source is required. Energy harvesting using appropriately sized and properly designed photovoltaic cells enable implantable medical devices to be autonomous and self-powered. Among the challenges in using PV cells is the small fraction of incident light that penetrates the skin. Thus, it is necessary to involve such physical properties in the energy harvesting system design. Consequently, we propose a novel photodiode model that considers skin loss in different ethnic groups. Our physical simulations have been implemented using COMSOL and MATLAB. Circuit and system modelling have been performed using Cadence 180nm TSMC technology. Our results show that the transmittance of near infrared light is almost the same in three skin types: Caucasian, Asian and African. Maximum power delivery of 12 μW (African skin) and 14 μW (Caucasian and Asian skin) were achieved at 0.45 V. With the help of a power management unit, an output voltage of 1.8-2 V was achieved using the PV cells.