A microwave powered polymeric artificial muscle

Twisted and coiled polymer fibres are vastly used to fabricate artificial muscles with stroke and stress outputs rivalling those of mammalian muscles. The thermal stimulation of these fibres, however, requires a tethered power source, limiting their application as truly autonomous system. Here, a novel type of coiled polymer actuator is demonstrated where thermal stimulation is realized via microwave radiation. This helical writhe shaped actuator is made of carbon nanotube (CNT) filled highly-drawn nylon 6 fibres and offers muscle-like linear movements when microwave-irradiated. The embedded CNTs absorb the external electromagnetic energy and act as volumetric heating sources in the fibres. When stimulated via microwave radiation, the unique anisotropic thermal expansion phenomenon of highly-drawn fibres provides >8% reversible length contraction of the writhe muscle with a starting actuation speed of ~0.8%/sec. The maximum specific work output is calculated to be ~0.2 kJ/kg, which is >5 fold higher than that for natural muscle. The developed technology offers an opportunity to stimulate the state-of-art thermoresponsive artificial muscles wirelessly and/or to use them for autonomous soft robotic application.