Theoretical and Experimental Investigation of a Wireless Passive Pressure Sensor Based on Flexible Printed Circuit Board Technology

In this article, we present a wireless passive pressure sensor based on LC resonance and fabricated by flexible printed circuit board (FPCB) technology. The sensor is designed with a 1-mm-width airhole channel for reducing the reaction force from trapped air and is further optimized according to the proposed multiphysics coupling model, thus achieving a high-sensitivity sensor design with double-sided PI-Cu-PI sandwich film deformation. As a result, during the wired test, the resonant frequency of the fabricated 206-
$\mu \text{m}$
-thick flexible pressure sensor shifts from 35.4 to 30.6 MHz within the pressure range of 0–5 kPa, which exhibits a favorable average sensitivity of −2.71%/kPa for the relative frequency variation. Meanwhile, the wired testing results are aligned closely with the predictions of the proposed theoretical model, which successfully verifies the feasibility of the theoretical model for the optimized pressure sensor design. Additionally, the flexible pressure sensor exhibits a similar performance and response trend in the wireless tests as compared to the wired counterpart, which shows a slightly increased sensitivity of −2.88%/kPa due to the inductive coupling effect from the measured return loss parameter. Furthermore, the proposed wireless flexible pressure sensor achieves competitive sensitivity when compared to the state-of-the-art sensors, making it a promising node for real-time intracranial pressure (ICP) monitoring in the future.