MyoDEA: A Self-Sensing Dielectric Elastomer Actuator for Real-Time Muscle Stiffness Monitoring

Abstract

Monitoring muscle stiffness in real-time during dynamic muscle activity is critical for rehabilitation, athletic training, and human-robot interaction. Existing technologies often require bulky hardware and complex multi-component systems, limiting reliable stiffness measurement in daily activities. In this work, we introduce MyoDEA, a centimeter-scale and <inline-formula><tex-math notation="LaTeX">$770 \,\mathrm{m}\mathrm{g}$</tex-math></inline-formula> device based on a novel self-sensing dielectric elastomer actuator (DEA) for time-varying muscle stiffness detection. This DEA generates a 2.5 times higher blocked force than previously reported power-dense DEAs at operating frequencies below <inline-formula><tex-math notation="LaTeX">$10 \,\mathrm{Hz}$</tex-math></inline-formula>, while maintaining comparable bandwidth and energy output at resonance. A new self-sensing method is also developed to enable integrated actuation and sensing within a single DEA. The MyoDEA achieves continuous muscle stiffness tracking at <inline-formula><tex-math notation="LaTeX">$10 \,\mathrm{Hz}$</tex-math></inline-formula> over a range of <inline-formula><tex-math notation="LaTeX">$30 \,\mathrm{k}\mathrm{Pa}\,{\mathrm{to}}\, 140 \,\mathrm{k}\mathrm{Pa}$</tex-math></inline-formula>. Human-subject experiments with MyoDEA worn on the forearm over the flexor digitorum superficialis (FDS) muscle belly demonstrate reliable continuous stiffness tracking during isometric gripping across 0%–80% maximum voluntary contraction (%MVC).