In order to solve the problem wherein wireless passive pressure sensors capture pressure signals with difficulty in high-temperature environments, the authors have proposed a sensor based on an alumina ceramic. Alumina is a high-temperature ceramic and has stable electrical properties and mechanical robustness in high-temperature environments. In addition, the proposed sensor is not a wireless passive pressure sensor, and signal collection is performed by supplying power to the sensor, as shown in Figure 1. Further, the design method realizes pressure parameter sensing by monitoring of the resonant frequency variation caused by the capacitance change. The inductor and variable capacitance are integrated in the alumina ceramic substrate through a thick-film integrated technology to complete the sensor fabrication.
The high-temperature characterization of the fabricated sensor will be tested in a high-temperature sintering furnace from room temperature to 850 ��C to verify the performance of the sensor in high-temperature environments. Finally, the achieved sensor was tested to realize pressure testing between atmospheric pressure and 5 bar in a high-temperature pressure test setup in the range from room temperature to 600 ��C to demonstrate the pressure sensing capabilities of the sensor in high-temperature environments.Figure 1.(Left) Pressure testing schematic; (Right) Design schematics of the sensor.2.?Model Analysis and Structure DesignThe schematic of the pressure sensing system is shown in Figure 1.
From Figure 1, the sensor is designed to have a constant inductance and a variable capacitive, and the capacitive reactance and inductive reactance change with increasing of the working frequency. Therefore, the input impedance of the series resonance AV-951 circuit changes with the variation of the working frequency. In addition, the equivalent impedance Zeq of the sensor is defined as:Z(jw)eq=R+j(wl?1wc)��=arctanwl?1wcR(1)where R is the resistance of the sensor, w is the angular frequency of the signal source, l is the inductance value of the sensor, and c is the capacitance value of the sensor.From Equation (1), it can be seen that the impedance phase is equal to 0 when the inductive reactance of the inductance is equal to the capacitive reactance of the capacitance. Therefore, a minimum occurs at the resonant frequency. In addition, when the excitation frequency is equal to the resonance frequency of the LC series resonance circuit, the series resonant circuit impedance is equal to R.