Design and Characterization of a Flexible Relative Pressure Sensor with Embedded Micro Pressure Channel Fabricated by Flexible Printed Circuit Board Technology

This paper presents a relative pressure sensor fabricated by a standard industrial flexible printed circuit board (FPCB) technology. The passive wireless sensor consists of a variable sensing capacitor and a planar coil inductor. When the external pressure is applied to the sensing capacitor, it changes the air gap and shifts the LC resonance frequency which is detected by an antenna wirelessly. The sensing cavity of the variable capacitor is extended to the opening at the end of an embedded pressure channel in the FPCB strip to enable relative pressure measurement. Measurement results showed that the proposed sensor with such an open sensing cavity had much higher frequency sensitivity (up to 0.4 %/mmHg) compared with the sensor with a sealed cavity (< 0.01 %/mmHg in this work and ≤ 0.08 in literature). With the enhanced sensitivity, the measured pressure resolution could reach 0.2 mmHg. The potential application of the proposed sensor includes gauge pressure measurement with respect to local atmospheric pressure, such as intracranial pressure (ICP) monitoring, without complicated re-calibration procedures. The flat FPCB structure facilitates applications with limited space for sensor installation, such as in the subdural implantation procedures. Furthermore, the proposed technology enables future development of flexible microfluidic devices.