Location-aware pressure sensing based on a colored porous-cladding polydimethylsiloxane optical waveguide

We report the fabrication and characterization of a new design of a location-aware pressure sensor made with polydimethylsiloxane (PDMS) and color dyes through the casting and molding method. The device is based on an optical waveguide consisting of a millimeter-sized PDMS solid-core, and on the top, by porous PDMS (2% vol. air microbubbles) doped with dyes. The proposed novel waveguide sensor incorporates some micro-porosity in its structure due to air microbubbles and guides light via a mechanism of losses by microbubbles diffusion in the colored cladding. The pressure sensing principle relies on the relative evaluation of the transmitted optical intensity at wavelengths 550 nm and 700 nm, corresponding to the main contributions of the green and red dyes, respectively. An optical sensitivity to external pressure of around 0.0003 dB/mmHg with R² fit coefficient of 0.9605 were measured, along with signal-to-noise ratio values ranging from 1 to 1.7 dB measured in a dynamic range of 2500–5000 mmHg of applied pressure values. The described sensing method allows to locate in which zone (red-dyed, clear, or green-dyed regions) the impactor is applied along the top porous-clad waveguide, thus enabling location awareness pressure sensing capability. The spatial resolution of the quasi-distributed sensor is determined by the largest dimension of the color-dyed zones, which is 7.5 cm, and it is limited by the size of the impactor used to apply the pressure on the waveguide, which is 1.0 ± 0.1 cm in length. This work is another step towards cost-effective location-aware pressure sensors that are stretchable, robust and flexible with potential applications in wearable sensor technology.