Spoof Surface Plasmon Polariton Enabled Flexible e-Skin for Cross-Media Proximity Sensing and Material Identification

With the increasing deployment of intelligent robotics in medical rehabilitation and elderly care, sensing modalities and functionalities eventually become a critical issue in achieving comprehensive awareness regarding operational tasks. Except multidimensional tactile sensing, penetrable sensing capability with both physical and chemical sensing information can further improve operation safety and efficiency. This study presents a flexible spoof surface plasmon polariton (SSPP) sensor, fabricated by screen-printing conductive silver paste onto a thermoplastic polyurethane (TPU) substrate, which enables simultaneous contact sensing and substance identification. Operating in the 4.7-5.4 GHz frequency band, the sensor detects physical contact through time-domain phase variations, while spectral responses in the frequency domain facilitate discrimination of liquids based on their dielectric properties. The sensor exhibits remarkable mechanical robustness, with a frequency drift of less than 3% under bending and twisting deformations up to 80°, and achieves 100% classification accuracy for 12 common liquids through machine learning models. This work provides a viable pathway toward cross-media perceptual intelligence for next-generation assistive robots, supporting safe and context-aware human-robot interaction.