Soft, Pressure-Tolerant Ocean Sensors for Oceanographic Measurements and Exploration

The ability to monitor and record various environmental and population parameters using ocean sensors enables significant understanding of changes in marine systems including geographical position and animal behaviors. Current ocean sensors including conductivity, temperature, and depth (CTD) sensors require high-pressure chambers and seals in the oceanographic environment, which entails a large power supply and footprint of the sensor system. The emerging soft matter electronics, with stretchable electronic sensors embedded in incompressible soft elastomers, can potentially eliminate the need for high-pressure chambers due to their capability of potentially withstanding large hydrostatic pressure, and therefore may substantially reduce the power requirements and the size of electronic ocean sensors. Therefore, they are a promising candidate for sensing in the ocean environment. In addition, these power-efficient, small, and non-invasive electronics are suitable for integration with many platforms including animal tags, profiling floats, diving equipment, and physiological monitoring.

In this talk, I will 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. By using resistive temperature, pressure 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 °C-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, temperature, pressure and salinity sensors have exhibited excellent cyclic loading behaviors with negligible hysteresis. Encapsulated with our developed soft oil-infused rough polydimethylsiloxane (PDMS), the sensor has shown excellent performance under 35 PSU salinity water environment for more than 7 months. The soft ocean CTD sensors are further integrated with acoustic transducers for underwater data transmission. The soft, pressure-tolerant, and non-invasive electronic sensors reported here are suitable for integration with many platforms including animal tags, profiling floats, diving equipment, and physiological monitoring.