An Electromagnetic Microwave Stealth Photothermal Soft Actuator with Lightweight and Hydrophobic Properties

Electromagnetic (EM) microwave stealth soft robots are in urgent need in military application. Photothermal soft actuators with photomechanical energy conversion have attracted significant interest owing to their remote control, flexibility, and contactless operation. The innovative combination of an electromagnetic microwave absorption (EMA) function with a photothermal actuator paves the way for this aspect. Here, a composite with unique dual three-dimensional foam is fabricated based on graphene and hollow carbon spheres (HCSs). When exposed to 1 sun illumination, the temperature could increase to 50 °C within 1 min and plateaus at 80 °C for hollow carbon spheres-graphene foam-polydimethylsiloxane (HCSs-GF-PDMS), which shows great photothermal performance. A wormlike crawling robot has been constructed based on this composite material, which could move forward under only 1 sun illumination. Remarkably, the EM stealth could be successfully realized because the composite material exhibits great EMA performance with a minimum reflection loss of -56.99 dB at a thickness of 2.5 mm, and the maximum effective absorption bandwidth is 8.65 GHz. In addition, the HCSs-GF exhibits hydrophobic and lightweight functions as well, which lighten the weight of soft robots and lead to self-cleaning and energy saving. This work provides a promising direction of multifunctional EM stealth soft robots.