In some cases, such as at a boiler tank and other large-size mechanical systems, it is more realistic to employ a non-contacting sensor to detect small displacement or vibration. In this paper, a non-contacting sensor for monitoring small displacement or vibration based on measurement of antenna reflection coefficient is proposed. A theoretical and numerical study is performed to investigate the proposed method and to determine the post processing method associated with the antenna reflection coefficient data. To avoid the ambiguity in the measured data, the detection of both the magnitude and phase components of the antenna reflection coefficient is required to compute the small displacement of the target. The distance between antenna and target has to be determined in order to minimize the ambiguity range in the data. The frequency domain observation is more appropriate for determining the amplitude and frequency of the target vibration. Magnitude detection, phase detection and Fourier analysis are used as main tools in the post-processing part of the proposed method.
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