Capacitive Low-Frequency Hydrophone Based on Micronanostructured Iontronic Hydrogel for Underwater Monitoring.

Hydrophones play a crucial role in underwater target detection within sonar systems. However, existing hydrophones often encounter challenges such as low sensitivity and poor signal-to-noise ratio (SNR) in the detection of low-frequency acoustic signals. This work introduces a capacitive hydrophone (CH) designed for highly sensitive detection of low-frequency underwater sound signals. Comprising a latex film/silver electrode and a structured hydrogel as the electrolyte layer, the CH is enclosed in a cylindrical casing. By strategically integrating a carbon nanotube (CNT) topology network within a pyramid microarray in the hydrogel, the sensor efficiently forms the electric double layer (EDL), enhancing sensitivity and precision. The CH showcases exceptional low-pressure sensitivity across a wide frequency spectrum (20 to 800 Hz), achieving a receiving sensitivity of up to -159.7 dB in the critical low-frequency band (20 to 125 Hz), surpassing the performance of the commercial hydrophone (RHC-14) by a substantial margin of 33.29 dB. Furthermore, the CH maintains a superior SNR, enabling the detection of sound waves as faint as 0.3 Pa. This study demonstrates the capabilities of the CH in detecting maritime vessels and underwater sounds, underscoring the potential of the CNT-enhanced EDL sensing mechanism for future low-frequency hydrophone design.

Carbon Nanotube Network Topology-Enhanced Iontronic Capacitive Pressure Sensor with High Linearity and Ultrahigh Sensitivity.

Flexible capacitive pressure sensors with high sensitivity over a wide pressure range are highly anticipated in the fields of tactile perception and physiological signal monitoring. However, despite the introduction of microstructures on the electrolyte layer, the deformability is still limited due to the size limitation of the microstructures, making it difficult to significantly improve the sensitivity of iontronic capacitive pressure sensors (ICPSs). Here, we propose an innovative strategy of combining carbon nanotubes (CNTs) topological networks and ionic hydrogel micropyramid array microstructures that can significantly enhance the sensitivity of flexible ICPSs for ultrasensitive pressure detection. Compared with other previously reported ICPSs, the sensor developed in this work exhibits an unprecedented sensitivity (Smin > 1050 kPa-1) and a high linear response (R2 > 0.99) in a wide pressure range (0.03-28 kPa) enabled by CNT percolation networks inside the microstructred electrolyte layer. This ultrasensitive and flexible ICPS also can effectively detect pressure from a variety of sources, including sound waves, lightweight objects, and tiny physiological signals, such as pulse rate and heartbeat. This work provides a general strategy to achieve an ICPS with both broader pressure-response range and higher sensitivity, which provides a stable and efficient way for a low-cost, scalable sensor for sensitive tactile sensing in human-computer interaction applications.