Flexible Capacitive Sensor Based on Multilayer Pore-Architectural Dielectric Composite With Carbon Nanotube Filler for Biophysical Signal Monitoring

The monitoring of biophysical signal parameters, including respiration, heartbeat, and fetal movement (FM), is essential for disease prevention and diagnosis. In this article, to achieve long-term monitoring of biophysical signals, a high-sensitivity flexible capacitive sensor (FCS) based on carbon nanotube (CNT)-filled dielectric composite (DC) with multilayer pore architecture is designed and fabricated, where the exquisite structure of DC is constructed based upon the characteristics of low surface vapor pressure of 1,2-propanediol (1,2-PG) and 3-D printing technology (3-D-p), while the electrode material has consisted of conductive silicone rubber (CSR) filled with silver-coated glass fiber (AGF). The fabricated sensor exhibits a low detection limit (12 Pa), a high sensitivity in a wide range (2.3 kPa<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{-{1}}$ </tex-math></inline-formula> to pressure load less than 1.5 kPa, and 0.73 kPa<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{-{1}}$ </tex-math></inline-formula> to the pressure between 1.5 and 12.5 kPa), fast response time (0.3 s), and excellent stability (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\gt 10^{{4}}$ </tex-math></inline-formula> cycles). Numerical simulation and mechanism analysis indicate that the varying dielectric constant of CNT-filled DC with pressure is the key to high sensitivity for the sensor, and the pore architecture enlarges the load response range. The FCS is sensitive enough to capture simultaneously multiple signals of subtle movements, including breathing, heartbeat, and skin touching in the abdomen, which could be distinguished with the help of post-digital analysis. It is foreseeable that the sensor has a broad perspective application in the field of biophysical signal monitoring in-home or medical electronic healthcare.