Soft, Pressure-Tolerant, Flexible Electronic Sensors for Sensing under Harsh Environments

Energy-efficient, miniaturized electronic ocean sensors for monitoring and recording various environmental parameters remain a challenge because conventional ocean sensors require high-pressure chambers and seals to survive the large hydrostatic pressure and harsh ocean environment, which usually entail a high-power supply and large size of the sensor system. Herein, we introduce soft, pressure-tolerant, flexible electronic sensors that can operate under large hydrostatic pressure and salinity environments, thereby eliminating the need for pressure chambers and reducing the power consumption and sensor size. Using resistive temperature and conductivity (salinity) sensors as an example for demonstration, the soft sensors are made of lithographically patterned metal thin films (100 nm) encapsulated with soft oil-infused elastomers and tested in a customized pressure vessel with well-controlled pressure and temperature conditions. The resistance of the temperature and pressure sensors increases linearly with a temperature range of 5-38 °C and salinity levels of 30-40 Practical Salinity Unit (PSU), respectively, relevant for this application. Pressure (up to 15 MPa) has shown a negligible effect on the performance of the temperature and salinity sensors, demonstrating their large pressure-tolerance capability. In addition, both temperature and salinity sensors have exhibited excellent cyclic loading behaviors with negligible hysteresis. Encapsulated with our developed soft oil-infused elastomer (PDMS, poly(dimethylsiloxane)), the sensor has shown excellent performance under a 35 PSU salinity water environment for more than 7 months. The soft, pressure-tolerant and noninvasive electronic sensors reported here are suitable for integration with many platforms including animal tags, profiling floats, diving equipment, and physiological monitoring.