On-Line Transverse Control of Materials by Means of Microwave Imaging Techniques
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ON-LINE TRANSVERSE CONTROL OF MATERIALS BY MEANS OF MICROWAVE IMAGING TECHNIQUES J.Ch.BOLOMEY 0 , G.COTTARD 0° AND B.J.COWN * o Groupe d'Electromagn6tisme, Ecole Sup6rieure d'electricit6, Plateau du Moulon,
91192 Gif-sur-Yvette Cedex, France 00 SATIMO, Ferme du Moulon, 91190 Gif-sur-Yvette, France * Georgia Tech Research Institute, EMED Division, Atlanta, GA 30332, USA ABSTRACT This paper analyzes of the impact of a new generation of microwave sensors on the transverse control of conveyed products and materials. Such sensors, resulting from recent developments in microwave imaging technology, offer significant improvements in comparison to other more classical microwave sensors. The main features of the new sensors are presented and discussed. INTRODUCTION Microwaves have been used for a long time in the control of materials [1]. They are expected to provide some information or measurement capabilities of important physical or chemical factors such as humidity, temperature, composition, etc... These factors affect the complex permittivity and permeability and, consequently, introduce some kind of perturbation in the mechanism of interaction between the materials and the interrogating microwave beam. Different techniques have been considered, involving resonant mode or traveling wave sensors, according to the desired sensitivity. The sensitivity depends on the shape and size of the material sample and of its electromagnetic characteristics at the considered frequency of operation. This paper is more primarily devoted to the case of "flat" conveyed products for which transverse controls have to be performed over widths extending from 1 to a few meters. Such configurations are commonly encountered in many sectors of industrial activity such as food industry, chemistry, wood, paper, textile, composite materials, etc... In these applications which involve large products, the rapidity of the transverse control is of prime importance, either for continuous and homogeneous quality insurance or for real-time control of the fabrication or transformation processes. TRANSVERSE CONTROL SPECIFICATIONS The first specification may concern the rapidity of the transverse control. Indeed, conveyor speeds can reach high values, typically a few meters per second and then comparable rapidity is required for transverse control. Secondly, convenient detection and localization of small gradients in the electromagnetic or structural properties of the material under investigation require adequate spatial sampling rates. In many applications, suitable sampling intervals are of the order of 1 centimeter, but, in some cases, a few millimeters are necessary. As a result, the number of sampling points is high, about a few hundred to a few thousands. Mat. Res. Soc. Symp. Proc. Vol. 189. @1991 Materials Research Society
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Figure 1 : Classical solutions for the transverse contr
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