Passive Wireless Mechanical Overload Sensing: Proof of Concept Using Agarose Hydrogels

This paper presents a proof of concept system for a wireless, capacitance-based, mechanical overload sensor which uses an agarose hydrogel as sensing element. Simultaneous compression and electrical studies showed that by reliably overloading the hydrogel at large mechanical strains, it fractures, experiencing irreversible changes to its capacitance. This irreversibility can be readily exploited by using the hydrogel as the capacitive element of a resonant circuit, as fracturing the hydrogel results in an irreversible shift in the resonant frequency of the circuit. Furthermore, the use of a suitable inductive element for the circuit permits for the wireless interrogation of the system.