Dielectric Characterization Using High Q Microwave Resonators

Abstract

Dielectric Characterization Using High Q Microwave Resonators This dissertation presents a very efficient and robust method of dielectric characterization through high quality factor resonant structures. The resonant structures employed in this work acts as sensing elements which are not only cost effective but also easy to integrate with other components for System-in-Package applications. These sensors work on the principle of resonant perturbation theory due to which there is a shift in resonant frequency and change in bandwidth as soon as they are loaded with a sample material. This perturbation is relative to the dielectric properties of the loaded material hence through prior calibration unknown parameters of the sample material can be determined with excellent accuracy. Two classes of sensors based on Dielectric Resonator (DR) and Substrate Integrated Waveguide (SIW) cavity are reported. The DR sensor offers high accuracy and excellent repeatability with straight forward MUT loading mechanism. The TM01δ resonant mode is excited to keep maximum E-field concentration in the middle of DR. This arrangement ensures maximum perturbation of the DR when the sample material is loaded. Organic liquid mixtures as well as powdered chemicals are measured for their concentration using this DR. SIW cavity is another structure which is investigated for dielectric characterization application of solids and in particular to estimate moisture content in a single wheat kernel. The wheat kernel is loaded inside cavity through a hole drilled in the appropriate location that results in shifting the resonant frequency of SIW cavity which is operated in TE101 or TE102 resonant mode. High quality factor and planar topology of SIW is very attractive for such applications. A relatively different technique of liquid characterization by varying the coupling coefficient of an SIW filter is also proposed. A two pole SIW filter is used in which the two resonators are coupled through a stub line. The sample is mounted on the coupling section of the filter resulting in the variation of the coupling coefficient and xi this variation is proportional to the electrical properties of the liquid under test, thus through prior calibration the liquid mixture concentration is determined. All the proposed techniques in this work can be easily transformed into a standalone handheld device by integrating peripheral electronics for measurements. Since the resonant perturbation technique is applied in association with the standard reference samples which are used for calibrating the system prior to its usage therefore, the handheld system does not require very high precision RF components.