Ultrastrong and High‐Stroke Wireless Soft Actuators through Liquid–Gas Phase Change

DOI: 10.1002/admt.201800381 production inside the actuator through heating by electrical power to obtain the necessary pressure.[10–12,16,19] However, in those examples power and control have been achieved either by external electrical connections to an off-board power source or using an on-board battery. Batteries and external wire connections hinder the use of robotic devices significantly and thus wireless power and control of robotic agents has been a topic of interest recently.[20–23] Following the demonstration of foldingbased small wireless robotic devices equipped with shape memory alloy actuators, small pneumatic wireless soft actuators actuated by the pressure produced by liquid–gas phase change are expected to provide another useful component for compact battery-free wireless actuation.[23] In this work, we demonstrate that the advantages of pneumatic soft actuators can be conveyed to battery-free wireless robots. By removing the necessity of external power connections and batteries through the use of magnetic fields to control a phase change in the internal working fluid—a method that differs from previous studies using phase change materials—we demonstrate the feasibility of ultralow profile, light, wireless soft actuators exhibiting large stroke and high output forces.[10–12,16,19] The fabricated prototypes, including the on-board electronics and the working liquid, weigh 1–2 g and are as thin as 2–3 mm before actuation. These prototypes can apply forces up to ≈1000 times their weight and can extend to approximately eight times the initial thickness (see Figure 1 and Movie S1, Supporting Information).