Cross-Medium Networking With Transflective Flexible Metasurfaces

Emerging wireless networks increasingly venture beyond over-the-air communication, such as deep-tissue networking for medical sensors, air-water communication for oceanography, and soil sensing for agriculture. They face the fundamental challenge of significant reflection and power loss at medium interfaces. We present RF-Mediator, a transflective metasurface placed near a medium interface to program the behavior of the physical boundary. Our hardware design comprises a single layer of varactor-based surface elements with specific metallic patterns and wiring. With the biasing voltage tuned element-wise, the surface dynamically mediates between the adjacent media to control and utilize both signal reflection and transmission, enhancing connectivity for wireless endpoints on both sides. A multi-stage control algorithm efficiently determines the surface configuration to handle dynamic adaptation needs for joint medium impedance matching and beamforming towards multiple endpoints simultaneously. We implement a lightweight and flexible metasurface prototype and experiment with diverse cross-medium setups. Extensive evaluation shows that RF-Mediator provides a median power gain of 8 dB for air-tissue links, reaching up to 30 dB gain for backscatter links, and up to 18 dB for multiple links concurrently.