Noncontacting low-cost instrument for film thickness measurement

The authors present a noncontact, nondestructive technique for measuring the thickness of thin liquid or solid films and coatings in real time by utilizing the resonance properties of microstrip structures based upon the work of Hurley, Kaufman, and Roy (see Review of Scientific Instruments, 61, Sept. 1990). This work is extended by confining all microwave aspects of the system internal to the instrument, thereby eliminating the need for any microwave test equipment. Only a low-voltage DC source, such as a 9-V battery, is required to power the unit, while the output is again a DC voltage or current. Using linear modeling equations, the system successfully determines the film thicknesses of water, enamel paint, and silicone rubber up to 0.8., 1.5, and 2 mm, respectively. Copper sheet metal up to 0.9 mm in thickness is also measured