Measurement of Evaporation Rate of Liquid Droplet Using Resonant Radio Frequency Coaxial Probe

Measurement of liquid’s evaporation rate is important for basic research, industrial, environment protection, daily life, and so on. There are kinds of evaluation methods for evaporation rate, such as mass sensors, charge coupled device camera (CCD), laser interferometer, optical fiber, capacitance sensor, and so on. Here, we show that microwave near-field sensing using a high-sensitivity resonant coaxial transmission line probe can be used to monitor the evaporation rate of both liquid droplet and liquid level. Due to the evanescent field around the tip of the coaxial probe, the proposed method is sensitive to mass, size as well as composition variation of the liquid under evaluation. With a coaxial probe working at ~1.8 GHz, we demonstrate evaporation rate evaluation of both pendant and sessile droplets as well as liquid level. The effect of air flow and temperature on evaporation is also presented. Besides, the low-cost version of the proposed method is verified. The proposed technique has potential applicability to many fields related to evaporation.