Microwave-based low-cost instrument for film thickness measurement

The use of an inverted microstrip resonators for noncontacting real-time thickness measurement of thin liquid or solid films and coatings described by R.B. Hurley et al. (1989) has been developed into a low-cost instrument for general laboratory or industrial use. Although microwave based, the instrument described functions without microwave test equipment. Insight into the oscillator behavior was obtained by the use of equivalent circuits and an ABCD matrix technique while several options were considered for the frequency discrimination function. The system successfully determined the film thickness of water, enamel paint, silicone rubber, and copper sheet metal.<>