Piezoelectric MEMS resonant dew point meters

This work presents a new class of dew point meters using Thin-film Piezoelectric-on-Silicon (TPoS) resonators. The proposed approach utilizes microelectromechanical resonant balances coupled with a cooling element in which a standard chilled surface technique is used to deposit layers of moisture on the resonator surface. Reducing the temperature causes the resonance frequency of the resonator to increase due to its negative temperature coefficient of frequency (TCF). However, when the temperature of the cooled resonator reaches the dew point (DP) of the surrounding environment, a thin layer of frost starts to form on the resonator surface causing an abrupt negative shift in the resonant frequency due to mass-loading. Therefore, the resonance frequency will be at its maximum value when the dew or frost starts to form i.e., at DP. A custommade setup which includes a MEMS dew point sensor head, a dew point generator and a measurement/control/data collection interface is assembled to enable automated measurements. Using the proposed setup, dew points as low as -41 °C i.e., a dry air containing 145 ppmv H2O, are measured with a standard deviation of 0.1 °C. Long-term reliability and accuracy of the sensors presented here are investigated by conducting 35,000 cycles of uninterrupted measurements. The long-term stability, precision, and durability of the presented dew point meters make them suitable solutions for a wide variety of industrial applications.