Microwave Sensor Applications in Industry

Microwave measuring methods can be applied to determine the properties of materials and hence it is possible to develop microwave sensors for processing industry. The first applications were in moisture measurement but lately many new sensor applications have appeared. Microwave sensors especially suitable in forest industry (wood, paper), in chemical industry (plastics, chemicals), in food industry (tobacco, butter) etc. In developing sensors several problems must be solved. The dielectric properties of the material in question must be known. They can be measured or in some cases determined theoretically by applying mixing theories. The sensor is often some kind of a resonator. Its structure must be such that the electric field penetrates the material as required, and allows free flow of material. Displacements occurring normally in the material flow or dirt in the sensor must not cause measuring errors. Several examples of lately developed sensors are given.