Fabrication of Concentration Gradient Structures for High-Performance Capacitive Pressure Sensors by Novel Acoustic Resonance Mixing

The capacitive pressure sensors are widely used in medical devices, aerospace, and consumer electronics. However, due to the conflicting nature between sensitivity and measurement range, it is challenging to achieve a satisfactory balance. In order to balance the sensitivity and measurement range of the capacitive pressure sensors, a variety of micro/nanostructures or high dielectric constant media have been proposed, but the fabrication of micro/nanostructures and doping of high dielectric constant media for high-performance capacitive pressure sensors are still not easy. In this study, a capacitive pressure sensor with concentration gradient structures is designed and fabricated by a novel acoustic resonance mixing method. The concentration gradient structures comprise of various concentrations of polypyrrole (PPy) doping in polydimethylsiloxane (PDMS) matrix, which shows good dispersibility. The capacitive pressure sensor exhibits a superior sensitivity (0.185 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>) with a wide measurement range (0–100 kPa), whose sensitivity is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.8\times $ </tex-math></inline-formula> of single-layer PPy/PDMS structures and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.3\times $ </tex-math></inline-formula> of two-layer PPy/PDMS composite structures. The capacitive pressure sensors also demonstrate a fast response time (20 ms), a low-limit detection (100 Pa), and an excellent stability (>4000). In practical applications, pulse detection, respiration monitoring systems, and sensor arrays show the proposed sensors having sufficient potential for application in wearable electronics. The proposed acoustic resonance mixing method is facile of fabricating composite structures and has great potential in many fields, such as robotics, pharmacy, and automobile.