Antenna-resonator integrated wireless passive temperature sensor based on low-temperature co-fired ceramic for harsh environment

This paper proposes a resonator-antenna integrated microstrip antenna temperature sensor based on a low-temperature co-fired ceramic (LTCC), whose permittivity varies monotonously with the temperature. The dimensional design process was first analyzed in detail, and by combining the standard LTCC technology, the sensor was fabricated using 15 layers of a green tape. To interrogate the sensor, a coplanar waveguide (CPW)-fed microstrip antenna, possessing a relatively large bandwidth, was designed and optimized using high frequency structure simulator software, and then fabricated on alumina ceramic through a screen-printing process. The sensor was then tested on a developed high-temperature measurement system. Because the original detected sweep signal was difficult to distinguish, a time-domain (T-D) gating method for filtering a background signal was introduced. The extracted peak frequency was found to decrease linearly with an increase in temperature to within 400 °C at a 30-mm reading distance, with a measurement sensitivity of 0.24 MHz/°C. Simultaneously, the antenna polarity was found to have a significant influence on the readout signal. Finally, for the introduced T-D gating method, this study analyzes that the sensor can be sensed at a long distance when using a high-gain interrogation antenna. It is expected that the proposed sensor can be used in monitoring the temperature in a harsh environment.