Liquid Metal-Based Strain Sensor with Improved Robustness and Sensitivity

This research heavily involves improving the fabrication process of liquid metal soft strain (LMSS) sensors, which improves the robustness and sensitivity of the sensors. Traditional LMSS sensors can experience channel collapse as microchannels deform and lose conductivity under higher elongation when created manually without the use of advanced equipment. To address this issue, pressurizing the liquid metal (LM) was initially proposed as a solution after liquid metal sensors fabricated manually were characterized. After iterating the fabrication method with the use of a spin coater and a resin printer, the most recent sensors that were created during this project were able to not only withstand strains up to 800% but also increase the minimum aspect ratio of channel dimensions. The final sensor designs were fabricated using Ecoflex 00-10 silicone filled with Eutectic Gallium-Indium (EGaIn). This specific type of liquid metal was chosen because of its low toxicity, high conductivity, and liquid state at room temperature. The smallest microchannel dimensions at which the sensors were fabricated at were (WxH) 0.4 mm x 0.2 mm, 0.3 mm x 0.15 mm, and 0.2 mm x 0.1 mm channels. Small aspect ratios were considered to maximize sensitivity and improve resolution. The robustness of the sensor was achievable through different fabricating methods, the main differences being manual vs spin coating techniques. This was confirmed through tensile testing, where the sensors demonstrated improved reliability and consistent conductivity at higher strains compared to the sensors that were created without the spin coater. Shrinking the dimensions and the channel size not only provide a more sensitive sensor that is useful for measurement, but it can also open opportunities in human assisting technology where enhanced LMSS sensors have potential applications in biomechanical monitoring, such as human joint angle measurement and wearable motion tracking.