Microwave Capacitive Pressure Sensor Based on an Additively Manufactured Elastic Layer

This paper presents a capacitive sensor useful for measuring pressure in the range 0 Pa - 2460 Pa. The transduction mechanism is capacitance variation caused by changes in the force exerted on the sensing element. Such sensing element is a one-port coplanar waveguide (CPW) terminated with a conductive patch wider than the CPW central strip and a step impedance resonator (SIR), etched in an independent substrate and capacitively coupled to the patch. By sandwiching an additively manufactured malleable (elastic) material between the CPW and the SIR substrate, pressure changes modify the capacitance of the SIR due to the variation of (i) the dielectric constant of such material and (ii) the separation between the SIR and CPW metal layers. The output variable is the phase of the reflection coefficient at the operating frequency, set to a value (within the microwave range) where the phase response exhibits a high phase slope (since this boosts the sensitivity). Thus, the device is a single-frequency sensor that simply necessitates a microwave oscillator, or a voltage-controlled oscillator (VCO), for signal generation in operative environment. The maximum achieved sensitivity is 65°/kPa.