A stretchable optical sensor can quantify the strain generated by human movement, which has been widely studied in the development of health monitoring systems, human–machine interfaces and wearable devices. This paper reports a graphene-added polydimethylsiloxane (PDMS) fiber, which has high tensile properties and good light transmittance suitable for detecting human movement. When the graphene-added PDMS fiber is stretched, the concentration of graphene per unit volume is constant, and the sensor uses the optical loss of the beam through the graphene PDMS fiber to detect the tensile strain. The fiber has excellent strain-sensing performance, outstanding sensitivity, a tensile property of 150%, and an excellent waterproofing performance. The linear response and repeated response in large dynamic range could reach 100% stability. The results show that the sensor can be used to detect human motion detection. These excellent properties indicate that the fiber has potential applications in wearable devices, soft robots and electronic skin.

Sensitivity is a key factor in the performance of a sensor. To achieve maximum guided-mode resonant optical biosensor sensitivity, a comparison of biosensor sensitivity for Transverse Electric (TE) and Transverse Magnetic (TM) modes based on the distribution of electric fields is presented in this article. A label-free guided-mode resonant optical biosensor is designed using the quarter-wave anti-reflection method to reflect only a narrow band of wavelengths modulated by the adsorption of a biochemical material on the sensor surface at the reflected frequency. With the distribution of electric fields simulated according to the Rigorous Coupled Wave Analysis (RCWA) theory, it is found that the full width at half maximum of the TM mode is (~4 nm) narrower than that of the TE mode (~20 nm), and the surface sensitivity of the TE mode incident light is three times that of the TM mode. It is proposed in this article that the light mode plays an important role in the sensitivity of guided-mode resonant biosensors.

Uniformly dispersed graphene effectively improves the strain-sensing capability of the composite film under a low graphene load in nanocomposites prepared with polydimethylsiloxane (PDMS) and graphene (GNP) monolayer powder. The threshold concentration of graphene was determined by loading nanocomposites at different temperatures. For different concentrations, when using traditional uniaxial stretching, the rate of resistance change of films near the threshold concentration is five times higher than the rate of films with a high concentration. Compared with traditional uniaxial stretching, the biaxial stretching we introduced can effectively improve the sensitivity of the film by an order of magnitude. The change in the resistance of the film near the threshold concentration is due to the change of the tunnel length and the cross-section of the tunnel, whereas the high concentration of the film is due to the change of the conductive path inside the film. Biaxial stretching has different effects on films with different concentrations, but the final effect of increasing sensitivity is the same. This study provides guidance for improving the strain-sensing sensitivity of GNP/PDMS composite films and the application of biaxial tension in detecting human motions.

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In this paper we introduce a polydimethylsiloxane (PDMS) composite fabricated using a simple production process and demonstrate the optical transmittance properties of this composite in the 300–1000 nm wavelength region. We control the material’s transmittance by varying the microcrystalline graphite powder concentration or the composite film’s thickness. In addition, we tailor the specimens into various trapezoidal shapes and load these specimens by mechanically stretching them in the direction perpendicular to both their base lines and their top lines. The advantage of this method is that a wide range of transmittance properties can be obtained for a given specimen. Furthermore, samples with different trapezoidal shapes have different transmittance tuning capabilities.

We report a facile method to prepare gradient wrinkles using a controlled-gradient light field. Because of the gradient distance between the ultraviolet (UV) lamp and polydimethylsiloxane (PDMS) substrate during UV/ozone treatment, the irradiance reaching the substrate continuously changed, which was transferred into the resulting SiO_x film with a varying thickness. Therefore, wrinkles with continuously changing wavelength were fabricated using this approach. It was found that the wrinkle wavelength decreased as the distance increased. We fabricated 1-D wrinkle patterns and ring wrinkles with a gradient wavelength. The ring wrinkles were prepared using radial stresses, which were achieved by pulling the center of a freely hanging PDMS film. The resulting wrinkles with changing wavelength can be used in fluid handling systems, biological templates, and optical devices.