Noncontacting low-cost instrument for film thickness measurement |
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Authors: | Root L.F. Kaufman I. |
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Affiliation: | Motorola, Arlington Heights, IL; |
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Abstract: | A low-cost, noncontacting, nondestructive technique is presented for measuring the thickness of thin liquid or solid films and coatings in real time by utilizing the resonance properties of microstrip structures. A new measurement system in which all the microwave components are internal to the instrument, thereby eliminating the need for microwave test equipment, is described. Only a low-voltage DC source, such as a battery, is required to power the unit; the output is also a DC voltage or current. Using a linear model, sample coefficients of determination, r2, greater than 0.98 have been obtained for film thickness measurements of water, enamel paint, and silicon rubber up to 0.8-1.5- and 2-mm thick, respectively. Copper sheet metal up to 0.9-mm thick has been measured with an r2 greater than 0.99. The measurement range can be extended or improved even further if nonlinear circuit behavior is accounted for |
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