Fig. 2: Design and characterization of the dual-ring sensor.

a Planar layout of the dual-ring sensor, designed with a 7-layer parallel-plate sensing architecture. b Optical images of the dual-ring sensor. c Effect of the dielectric layer thickness on the electrical performance of the sensor, given a fixed electrode layer width. d Capacitance responses of the sensor with electrode layer widths of 3 mm, 5 mm, and 7 mm when subjected to 0.1 mm deformation. e Mechanical performances of samples made from various silicone rubbers. The design specifications require the measuring ring’s maximum tension to be less than the force used by RigiScan for rigidity measurement (T_m), with the reference ring’s maximum tension being less than 20% of this value. f Capacitance-circumferential displacement and tension-circumferential displacement responses for the reference and measuring rings. g Capacitance and tension recordings for the measuring ring when subjected to stepped 1 mm deformation. h Comparison of the initial capacitance of the measuring ring in both the noncontact and contact states across five volunteers. i Mechanical and electrical performance of the measuring ring during 1000 tensile cycles. Inset: Performance during the 1st-10th, 496th-505th, and 991st-1000th cycles. j Mechanical and electrical performance of the measuring ring during cyclic stretching, holding for 10 minutes, relaxing, and then holding for another 10 minutes