Broadband near-infrared LED-based wireless charging for implantable electronic devices

Abstract Most of implantable electronic devices (IEDs) today are powered by non-rechargeable batteries, which have limited lifespans and require frequent replacement once depleted. Wireless power transfer (WPT) is a promising solution for efficiently recharging the batteries of IEDs; therefore, the vision of WPT is to reduce the need for frequent surgical battery replacements. The optical WPT (OWPT) method using near-infrared (NIR) light for wireless charging represents an attractive solution, relatively new field that warrants exploration. OWPT offers safe, secure, and private wireless recharging through biological tissue. NIR light is the best option among other wavelengths for carrying optical energy across biological tissue due to its relatively low absorption and scattering effects when propagating in this medium. Photovoltaic (PV) cells can be used at the receiver end as an energy harvester. However, the PV cell is typically optimized for wide-spectra source (e.g., sunlight or artificial lights), which can lead to inefficiencies when paired with narrow-spectra sources (e.g., NIR light) due to spectral mismatches. For this reason, using a wide-spectrum (broadband) NIR light source is envisioned to enhance energy conversion efficiency. This study investigates OWPT across biological tissues using a broadband NIR LED source. We employed tissue-mimicking phantoms to simulate the optical properties of biological tissues (i.e., human soft tissue) closely . This study investigates the use of tiny monocrystalline silicon PV cells to harvest energy from broadband NIR light penetrating phantoms. Key parameters evaluated include received optical power, open-circuit voltage ( V O C ), the output power of the PV cells, and power conversion efficiency (PCE) of the OWPT system. We also investigate wireless charging performances across various scenarios, including the impact of transmitted optical power on safety considerations, duty cycles, misalignments, and the presence of clothing layers on energy harvesting rates stored in a supercapacitor. The results demonstrate the feasibility of wireless charging for IEDs under broadband NIR LED illumination in realistic conditions, including clothing obstruction and misalignment issues.