We propose a method for diagnostics of the density of weakly magnetized plasma using a resonance microwave probe, which allows decreasing the minimum measurable value of the density by three orders of magnitude, thus expanding the dynamic range of the measuring system significantly. Within the framework of this method, measurements are performed at a fixed frequency corresponding to the resonance frequency of a microwave probe in the absence of plasma, while minor variations in the resonance frequency of the system within the limits of the width of the inherent resonance are recorded by the method of amplitude-phase measurements. The paper presents a theoretical model of the measurement method and its experimental verification.
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.
We briefly describe the features of the functional diagram and design of an uncooled solid-state objects. The main characteristics of the spectrometer are presented.
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