High-Temperature and High-Sensitivity Pressure Sensors Based on Microwave Resonators

This paper reports a novel diaphragm-assisted open-ended hollow coaxial cable resonator (OE-HCCR) for highly sensitive pressure measurements at elevated temperatures. The coaxial line resonator is constructed using two highly reflective reflectors in a homemade hollow coaxial cable, including a metal post shorting the two concentric conductors (i.e., the inner conductor and the outer conductor) and the open end of the coaxial line. In the pressure sensor device design, a sealed metal diaphragm is mounted on the open end of the OE-HCCR and is employed as the pressure responsive element. The diaphragm’s deflection can be accurately captured by the coaxial line resonator in real-time, in response to a change in differential pressure. The sensor device’s responses to hydraulic pressures at ambient temperature and air pressures at elevated temperatures up to 1000 °C were investigated in the demonstration experiments, showing user-configurable measurement sensitivity and high-temperature survivability. The device’s pressure measurement resolution is also demonstrated as high as sub-Pascal by probing tiny hydrostatic pressure changes. A positive feedback loop is constructed as an alternative interrogator for the novel device, showing high signal quality and ease of demodulation. The pressure sensor described in this work is robust, easy-to-manufacture, user-configurable, low-cost, highly sensitive, and has great potential for industrial applications involving high-temperature and harsh environments. The presented work opens new avenues to develop a new generation of high-sensitivity and high-temperature microwave sensors based on well-known open-ended coaxial probes.