Thickness Measurement of Thin Layers With Double E-Shaped Slots Loaded in a Microstrip Line

Abstract

Non-destructive testing of material thickness which leaves materials undamaged is essential for many industries. In this article, we have developed a new simple method for thickness measurement of thin solid materials using E-shaped slots. In the proposed structure, two E-shaped slots are connected in a novel outline on top of a microstrip line. The current flow interruption leads to an inductive effect. Through additional charge accumulation at the slot corners, where electric fields concentrate, capacitance arises. The resonant frequency corresponding to inductance and capacitance of slots changes with the material thickness variation on top of the sensor due to distortion of the continuity of the field concentration of a microstrip line. The operation principle of the proposed sensor is based on the downshifting of the resonant frequency with respect to the material under test (MUT) thickness. The complete characterization of the proposed sensor with different MUT thicknesses including simulation results is provided. Electrical performance details of the whole structure are explained with a circuit model and parametric analysis. A prototype sensor is fabricated and successfully tested for different thin material thicknesses. The sensitivity analysis from measurement results shows 4.3% sensitivity, which is higher than most of the available sensors. The prototype sensor size is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$15.63\times 15.63\times0.508$ </tex-math></inline-formula> mm3.