Kirigami-Enabled Microwave Resonator Arrays for Wireless, Flexible, Passive Strain Sensing

Wireless and highly sensitive flexible strain sensors would have widespread application across a number of different fields. Here, the novel combination of two different metamaterials, one mechanical and one electronic, is demonstrated for its potential as such a sensor. An array of split-ring resonators (SRRs) were mounted on a bespoke kirigami sheet. The hybrid kirigami structure was designed specifically for the resonator array, in terms of both its physical dimensions and elastic response. Mechanical tests in concert with finite element modeling confirmed that the hybrid kirigami structure, containing two disparate kirigami motifs, exhibited a high range of strain and out-of-plane rotation without plastic deformation. The microwave sensing was designed to monitor variations in the S₁₁ response of the resonators as a function of out-of-plane kirigami hinge rotation. The mounted array of SRRs on the hybrid kirigami sheet could wirelessly detect changes in strain with high sensitivity (>30 MHz shift in resonant frequency; >30 dB shift in resonant amplitude) over a large range of strain, from 0.6 to 21.3%.