Computer Interfacing A Microwave Spectrometer: An Educational Approach

A laboratory procedure for introducing undergraduate students to the principles of analog to digital converters is described. The procedure involves interfacing an analog to digital chip, the ADC 0804, to a PC via a cable connected to the PC's parallel port. Exploiting the parallel port minimizes equipment cost and is safer for the students and the computers. Evidence that students are in a position to understand and use interface equipment properly is provided by describing a technique to computerize a microwave spectrometer for the purpose of studying the dielectric behavior of materials. A cylindrical microwave resonant cavity in the TE 011 mode is used as a probe for dielectric relaxation studies as a function of temperature. The computer interface allows a very precise measurement of the frequency shifts and Q-changes of the microwave signal as the material under investigation goes through a dielectric change. These values of the frequency shifts and Q-changes translate into the real and imaginary parts of the dielectric constant through the Slater’s perturbation equations.