Liquid dielectric layer-based microfluidic capacitive sensor for wireless pressure monitoring

Microfluidic capacitive sensors with enhanced performance and wireless sensing capability present great advantages for various pressure sensor applications. In this work, a liquid dielectric layer (LDL)-based wireless capacitive sensor for high sensitivity and low-pressure detection has been demonstrated. The wireless capacitive sensor was designed based on an LC resonant circuit model and integrated into a microfluidic device by introducing liquid-metal Galinstan into polydimethylsiloxane (PDMS) microchannels. The effect of various dielectric mediums (air, deionized (DI) water, and saline) on the performance of the capacitive sensor was characterized to study the sensitivity and robustness of the devices. Moreover, the high permittivity of liquid dielectric mediums enhances the sensitivity of the pressure sensor. The sensitivities of 0.0043 kPa⁻¹, 0.0111 kPa⁻¹, and 0.0125 kPa⁻¹ were achieved for air, DI water, and saline-based dielectric mediums, respectively, for a low-pressure region of 0–10 kPa. Furthermore, we fabricated the wireless pressure sensor in three different form factors to enhance the applicability of the flexible wireless sensor. We also demonstrated the possibility of wirelessly monitoring human motion through real-time pressure detection using capacitive sensors fabricated with a liquid dielectric medium. The proposed LDL-based capacitive sensor, with high sensitivity, could be a potential candidate for low-pressure sensor applications, especially in detecting subtle pressure from the human body.