V.G. Anisimov – Senior Lecturer, Department «RadioEngineering», Ulyanovsk State Technical University
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A.G. Tashlinskii – Dr.Sc.(Eng.), Professor, Head of Department «RadioEngineering», Ulyanovsk State Technical University
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In modern microwave devices, dielectric coatings are used as protective elements that protect the conductive layer from the influence of the external environment, and also as elements that separate the conductive coating and functional layers. To measure the thickness of coatings on a conductive base, a variety of different methods are used: ultrasonic, eddy current, radio wave. For thin dielectric films and with low dielectric constant, the radio wave resonator method is most applicable. A resonator method for measuring the thickness of dielectric coatings on a conductive base, which is aimed at reducing the measurement error for thin dielectric films and with low dielectric constant is proposed. The method is based on the dependence of the resonant frequency and quality factor of the dielectric resonator on the distance to the conductive base, taking into account the coating parameters. When determining the field, the partial areas method is used, which introduces a certain error in the measurement result, since electromagnetic fields outside the regions are not taken into account. Nevertheless, the analysis showed that the proposed method provides a relatively high accuracy in measuring the thickness of thin dielectric films with low dielectric constant.
The dielectric cavity has the shape of a parallelepiped and is directly placed on the coating. The main type of oscillation in the resonator is excited. The thickness of the dielectric coating is determined indirectly by measuring the Q factor of the resonator, which is found by the components of the magnetic field of the resonator tangential to the metal surface, and the Leontovich boundary conditions.
The numerical calculations of the dependence of the resonance frequency on the thickness of the dielectric coating at different values of the dielectric constant of the coating showed that the resonant frequency of the system decreases both with increasing thickness and the relative dielectric constant of the coating. Calculations of the dependence on the same factors of relative Q factor showed that the Q factor of the system «dielectric resonator – dielectric coating – conductive base» increases both with increasing thickness and with a decrease in the relative dielectric constant of the coating.
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