# Towards Flexible Wireless Charging for Medical Implants Using Distributed Antenna System

arXiv: https://arxiv.org/abs/2001.07644 · HTML: https://mlsanity.com/paper/2001.07644/

## Key facts

- Cited by 3 papers in the map (data through 14 Oct 2026).
- First posted on arXiv 21 Jan 2020.

## Built on by (most cited first, 3 of 3)

- [NeRF2: Neural Radio-Frequency Radiance Fields](https://mlsanity.com/paper/2305.06118/) (2023)
- [AuraSense: Robot Collision Avoidance by Full Surface Proximity Detection](https://mlsanity.com/paper/2108.04867/) (2021)
- [Towards Seeing Bones at Radio Frequency](https://mlsanity.com/paper/2509.17979/) (2025)

## Abstract (arXiv)

This paper presents the design, implementation and evaluation of In-N-Out, a software-hardware solution for far-field wireless power transfer. In-N-Out can continuously charge a medical implant residing in deep tissues at near-optimal beamforming power, even when the implant moves around inside the human body. To accomplish this, we exploit the unique energy ball pattern of distributed antenna array and devise a backscatter-assisted beamforming algorithm that can concentrate RF energy on a tiny spot surrounding the medical implant. Meanwhile, the power levels on other body parts stay in low level, reducing the risk of overheating. We prototype In-N-Out on 21 software-defined radios and a printed circuit board (PCB). Extensive experiments demonstrate that In-N-Out achieves 0.37~mW average charging power inside a 10~cm-thick pork belly, which is sufficient to wirelessly power a range of commercial medical devices. Our head-to-head comparison with the state-of-the-art approach shows that In-N-Out achieves 5.4×--18.1× power gain when the implant is stationary, and 5.3×--7.4× power gain when the implant is in motion.