A LC wireless passive temperature-pressure-humidity (TPH) sensor integrated on LTCC ceramic for harsh monitoring

In this study, a LC wireless passive TPH sensor based on low-temperature co-fired ceramic (LTCC) technology for harsh TPH monitoring was presented. The LC wireless passive TPH sensor was frame-optimized by performing HFSS simulations and fabricated on DuPont® 951 AT ceramic using the screen-printing technique, low-temperature co-fired process, imidization process. The microscopy and spectroscopy of as-prepared thin polyimide (PI) film were characterized by the dint of scanning electron microscope (SEM) and fourier transform infrared spectroscopy (FT-IR). The experimental tests indicate the as-prepared LC wireless passive TPH sensor can stably operate at an ambient environment of 25-200 °C, 70-220 kPa, and 24-90%RH, which attributes to the HFSS simulation optimization and the algorithm we proposed for solving the interrelationship of TPH sensor. The frequency shift of the pressure sensor was 0.4875 MHz with a sensitivity of 3.25 kHz/kPa in the environment of 64%RH, 150 °C, 70-220 kPa, while the temperature sensor was 1.6 MHz, 9.143 kHz/°C in the environment of 64%RH, 1 atm, from 25 °C (room temperature, RT) to 200 °C. Moreover, the humidity sensor, which has the frequency shift of about 7.23 MHz at RT, 1 atm, 24-90%RH, realized a sensitivity of 20 kHz/%RH at low humidity and a sensitivity up to 200 kHz/%RH at high humidity(60-90%RH). What's more, the as-prepared PI film is highly selective to H2S, NH3, CH4, which is significant for some harsh environments (e.g., chemical & medical synthesis and chemical painting) and mine environmental monitoring (where CH4 and H2S often exist). Therefore, the proposed LC wireless passive TPH sensor, which shows stable performance in a TPH environment with a wide range of variation, is suitable for simultaneous TPH monitoring in harsh environments.