Figure 3: Response of hydrogel capacitors to deformations in air.
From: Hydrogel microphones for stealthy underwater listening
(a) Deformable network of metal nanoparticles (MNPs) makes the hydrogel sensitive to external load: (stress free) MNP network has fractal branches not yet wide open for EDL (electric double layer) build-up; (Compression) vertical pressure separates fractal branches apart (dc>d and dc’>d’), promoting charge trapping (increased capacitance due to EDL insertion); and (shear) lateral pressure squeezes branches together (ds<d and ds′<d′), closing gaps for EDL (reduced capacitance). (b) Array of MNP in the hydrogel can be used to map out contour of shaped loads of 8.0 kPa, from left to right for the shape of an ‘O’, an ‘L’ and a small dot. Capacitance increases (green; arrow up) or decreases (red; arrow down) due to location of the loads. (c) Angle-dependent sensing of airflows (red dot) suggests shear-induced pore closing in MNP for capacitance reduction. Inset photo illustrates the airflow angle (Θ).
