Rapid Determination of Moisture Content in Soil Samples Using High Power Microwaves

This paper describes the results of an investigation which shows that a considerable reduction in the testing time required for a standard laboratory soil-moisture test can be effected by using microwave ovens instead of thermal ovens to dry the samples. It is shown that both the load voltage standing wave ratio of the oven, as well as the temperature of the sample, can be used as guides to estimate the exposure time required to obtain a properly dried sample. Typical exposure times obtained were 3 minutes at 2 kW and 30 minutes at 200-watt source power levels, for sample weights of about 200 to 300 grams with 25 to 30 percent initial moisture content. The results of moisture tests made on this basis agree within ±0.5 percent with those obtained using the conventional technique employing thermal oven drying.