A Microwave Sensor for Evaluation of Plastic Wall Thickness
AbstractA proximity–fed electromagnetic coupled patch microwave sensor for evaluation of plastic wall thickness is presented in this article. Sensor is suitable to measure the thickness of the low permittivity and relative high total loss materials, when the opposite wall is not– or metal–backed and only one side of materials is an accessible. The main element of the sensor is electromagnetic coupled patch–feed transmission line resonator, which allows to evaluate the thickness of composites via recording of resonant frequency or phase deviation. It showed, that phase detector would achieve highest sensor sensitivity. Loaded resonance quality varies in range from 235 to 980 depending of measurement object loss. Sensor phase sensitivity factor range is from 185 to 770. Method is suited when the fixed air gap up to 1 mm between the wall and sensor occurs, and total loss tangent of dielectric is up to 0,1. With this method was evaluated polypropylene wall thickness measurement from 1 to 10 mm. Showed good spatial resolution, microwave penetration depth and detection sensitivity. Ill. 11, bibl. 10, tabl. 3 (in English; abstracts in English and Lithuanian).
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