Wireless capacitive pressure sensor with directional RF chip antenna for high temperature environments

This paper presents the design, fabrication and characterization of a wireless capacitive pressure sensor with directional RF chip antenna that is envisioned for the health monitoring of aircraft engines operating in harsh environments. The sensing system is characterized from room temperature (25°C) to 300°C for a pressure range from 0 to 100 psi. The wireless pressure system consists of a Clapp-type oscillator design with a capacitive MEMS pressure sensor located in the LC-tank circuit of the oscillator. Therefore, as the pressure of the aircraft engine changes, so does the output resonant frequency of the sensing system. A chip antenna is integrated to transmit the system output to a receive antenna 10 m away. The design frequency of the wireless pressure sensor is 127 MHz and a 2% increase in resonant frequency over the temperature range of 25 to 300 °C from 0 to 100 psi is observed. The phase noise is less than -30 dBc/Hz at the 1 kHz offset and decreases to less than -80 dBc/Hz at 10 kHz over the entire temperature range. The RF radiation patterns for two cuts of the wireless system have been measured and show that the system is highly directional and the MEMS pressure sensor is extremely linear from 0 to 100 psi.