Free-space microwave measurement of low moisture content in powdered foods

A free-space microwave transmission technique has been developed and tested for rapid inline noninvasive measurement of the moisture content of various types of food powders. The basis of this technique is the relation between the attenuation of X-band microwave radiation through a sample of the food powder to its moisture content by weight. Since food powders generally lose their utility and desirable properties, such as flowability and resistance to spoilage, at lower levels of moisture content, typically 3-7%, special techniques must be developed in order to accurately characterize the moisture content at these low levels. One such technique is to use frequency averaging to enhance the accuracy of the measurements to avoid multiple reflection effects prevalent in low-loss low-moisture attenuation measurements. This technique was implemented in the moisture content estimation. Overall accuracies in moisture content estimation are generally less than 1%, although in some cases, accuracies are in the vicinity of 5%.