Microwave Cavity Sensor for Measurements of Air Humidity under Reduced Pressure

Abstract

A high-sensitivity sensor for measuring moisture content in the air or air humidity under low pressure was designed on the basis of a half-wave coaxial microwave cavity. The method of measuring small variations in the signal phase at a cavity excitation frequency of 1.63 GHz was applied to detect low densities of water vapor. It allows the detection of variations in dielectric air permittivity in the seventh decimal place. A prototype of the sensor was tested in a vacuum chamber. It was calibrated by comparing the test results with the readings of a commercial pressure gauge and using the independent method of measuring the moisture content in rarefied air on the basis of the absorption of millimeter waves in the local line of water vapor at 183 GHz. The developed sensor can be used in laboratory experiments and full-scale geophysical research in the atmosphere onboard various aircrafts.

Self-Oscillating Parametric Humidity Sensor With Frequency Output Signal

“…Studies in this area have shown that reactive properties and negative differential resistance are inextricably linked, and the versatility and simplicity of radio electronic devices based on transistor structures with negative resistance is the prospect of their practical use. Self-oscillating parametric humidity sensors that implement the "humidityfrequency" conversion principle are characterized by simplicity and versatility, as well as accuracy and noise immunity [6,7,22].…”