New Microwave Thickness Gage

Abstract

In the rolling processes, the thickness or shape measurement of products is one of the most important problems. Among non-contact measurements X-ray or γ-ray thickness gages are widely used today, but they are not satisfactory with respects to the accuracy, response time, and safety.
The present authors have proposed a new microwave thickness measurement method using cylindrical open cavities. The principle of this method is based on the fact that the resonant frequency of the open cavity is proportional to the gap, x, between the given metal and the cavity edge. The characteristics of the open cavity are essentially important in designing the measuring device. In this paper, a theoretical analysis of the open cavity and the quality factor, Q, are discussed. These characteristics have been ascertained experimentally.
A prototype microwave thickness gage has been designed and built in the laboratory. In the laboratory experiment, the proposed new method provides better results regardless of the thickness of metal plate than the conventional instruments. The results obtained through the experiments at a hot finishing line confirmed the possibility of the practical use, but several problems associated with the practical application still remain unsolved.