Fig. 3
From: Controlled mechanical assembly of complex 3D mesostructures and strain sensors by tensile buckling
A 3D strain sensor with LED readout: design principle, quantitative modeling, and experimental measurements. a FEA results that illustrate the design principle of a strain sensor that uses mechanically actuated electrical switches and LEDs. Without stretching, the LED is off; as the tensile strain reaches a critical value, the two electrically conducting ribbons contact each other, thereby turning on the LED. b FEA predictions of the critical strain for the onset of contact versus the width-to-radius ratio (W/R1) for a fixed radius ratio (R2/R1 = 2). c Experimental images and FEA predictions on the deformed configurations of a strain sensor at different stages of stretching. The device consists of nine LEDs (lateral dimension: 820 × 450 µm) and nine electrical-switch elements with different width-to-radius ratios. The colors in the FEA results correspond to the maximum principal strains. d 2D precursor designs and the deformed configurations at the onset of contact (i.e., εapplied = εcritical) for three representative electrical-switch elements. The colors in the FEA results correspond to the out-of-plane displacements. e Measured and computed results of strain ranges under conditions that result in different numbers of lighted LEDs. Scale bars, 4 mm
