18 Microwave Properties of Dielectric Materials
In recent years, the study of newer types of dielectric materials and compositions has been of great interest. The quest for new, innovative and easily obtainable dielectric materials that yield predictable and controllable permittivity and permeability values with very low dielectric loss has always been fruitful. New ideas and designs to implement these materials in microwave devices and structures with the most efficiency and performance are also of equal importance. The book chapter covers the synthesis and characterization of new dielectric material compositions and the design, implementation and testing of a prototype dielectric resonator antenna and filter utilizing the fabricated dielectric material. It also covers the use of different design and testing techniques in this research. By studying different methodologies and new material types that were previously published in cited technical journals such as Science Direct, different types of materials and synthesis methods were able to be identified. The appropriate materials and method of synthesis were then derived and utilized in the fabrication of the new type of dielectric ceramic substrate material. After extensive literature reviews, research and analysis, various methods used in dielectric resonator designs were studied and analyzed. An overview of the synthesis process associated with the fabrication of the new dielectric composition will be discussed. Next, with the primary objective of investigating the microwave properties of a new composition of high permittivity ceramic dielectric substrate at microwave frequencies, research is then carried out on designing an electrical model in order to utilize the newly fabricated dielectric material in a microwave environment. The electrical model that is proposed will be of dielectric resonator devices which will incorporate the new dielectric material type. Tests and measurements will also be carried out at various microwave frequencies in order
On the Image Approximation for Electromagnetic Wave Propagation and PEC Scattering in Cylindrical Harmonics
A closed-form formula, the discrepancy parameter, which has been defined as the ratio of the modal expansion coefficients between the electromagnetic field obtained from the image approximation and the incident electromagnetic field, has been proposed for the evaluation of the validity of the image approximation in the electromagnetic wave propagation, i.e., Love’s equivalence principle, and the electromagnetic wave scattering, i.e., the induction equivalent and the physical equivalent, in the cylindrical geometry. The discrepancy parameter is derived through two equivalent methods, i.e., the vector potential method through the cylindrical addition theorem and the dyadic Green’s function method, for both the TE and TM cylindrical harmonics. The discrepancy parameter justifies the fact that the image approximation approaches the exact solution for the cylindrical surface of infinite radius. For the narrow-band field with limited spectral component in k space, the cylindrical modal expansion of the electromagnetic wave into the TE and TM cylindrical harmonics can be separated into the forward-propagating wave that propagates forward and the back-scattered wave that is back-scattered by the PEC surface, within the image approximation. The discrepancy parameter shows that the validity of the image approximation depends on the property of the incident field and the radius of the cylindrical surface, i.e., the narrow-band field and the surface of a large radius are in favor of the image approximation, which has also been confirmed by the numerical result.
Experimental Study on Acoustic Agglomeration of Fine Particles from Coal Combustion
The removal of fine particles in coal-fired fumes was experimentally studied based on acoustic agglomeration. An experiment facility was designed and set up. In this facility, a fluidized bed coal combustor was used as fume generator, and an Electrical Low Pressure Impact or (ELPI) was used to measure the fine particle concentration and size distribution in the fumes. The results show that under the effect of high intensity sound waves, there is good performance to remove fine particles in coal-fired fumes, which with a number mean diameter of 0.07μm. Especially, under the conditions of the frequency of 1 000Hz and the sound intensity of 161.5dB, the number concentration of 0.0233~9.314μm particles decreased by 85.2%, and their mass concentration decreased by 92.5%.