Impact of a textile layer on joint optical data and power transfer to in-body devices: a study on an ex vivo approach

Wireless connectivity is required in modern in-body electronic devices (IEDs), such as in-body sensors. However, their frequent wireless communication operations will consume more energy than those of conventional IEDs. In addition, energy-limited IEDs require concurrent data and power transfer to maintain uninterrupted operation, enabling medical data communication while continuously supplying energy for battery recharging In this paper, we present a joint optical wireless data and power transfer system for IEDs based on single-carrier transmission, focusing on realistic operating scenarios, with particular emphasis on forward telemetry and energy-harvesting performance. . Commercially available components were employed, including a single-beam 850 nm NIR LED that simultaneously delivers modulated data and optical energy through biological tissue (i.e., ex vivo porcine tissue samples, a representative biological model for human soft-tissue optical propagation). A photodetector receives forward telemetry signals, and a photovoltaic (PV) cell harvests residual optical power concurrently to charge a supercapacitor via a power management integrated circuit (PMIC). In this study, we also account for a real-life factor, namely the impact of clothing on optical light transmission, which may attenuate the incident light depending on fabric type and thickness. Two textile samples were used in this study, representing a thin fabric with high porosity and a thicker fabric with lower porosity (dense yarn). Energy can be harvested through biological tissue during active optical data transmission, thereby providing supplementary energy support for battery-limited IEDs. However, the presence of cloth led to a noticeable decrease in the harvested energy, even with a thin layer. The slower supercapacitor charging is attributed to attenuation of incident optical power by clothing, thereby reducing the PV cell's output voltage. The study is important for developing future wearable-to-implant links for non-invasive medical applications that account for the presence of clothing.