Abstract
We have proposed a cavity with the single-mode (TM010) operation and uncovered the intriguing non-thermal microwave effect. An experiment was conducted using an amplifier rather than an oscillator as the radiation source which was injected into the applicator to enhance the electromagnetic fields. The characteristics of the applicator are discussed and the mechanism of field enhancement are illustrated and explained. We also proposed a modified calibration method to determine the complex permittivity and permeability of material based on the cavity-perturbation method. It allows a test sample with relative large in volume or high in dielectric constant. The theory is validated with a full wave solver (HFSS) and an experiment was conducted. A sample of SiC was heated using high-power microwave and characterized with low-power signal, all operating in the same cavity but different in time sequence. It facilitates the study of both microwave/material processing and material characterization. In addition, we reported an intriguing phenomenon - the particles are spouting in a strong microwave field, called the particlespout. It is similar to a waterspout, an intense columnar vortex appeared a funnel shape, is a natural wonder that attracts public attention even today. These ionic crystals (NaCl, KCl, …...) are heated in a microwave applicator with silicon carbide as the susceptor. Beyond the melting point, the particles begin to escape from the surface and move upward due to thermal convection. These particles form a funnel shape as expected but, interestingly, they have two layers. In comparison with convention furnace heating, only a single layer but unstable columnar vortex can be observed. The microwave field in the cavity is analyzed and displayed. Various configurations of the susceptors which all result in the similar behavior are studied. A theoretical model is proposed which attributes the observed phenomenon to the rotational kinematics together with the ponderomotive force. These two effects confine the particles to the inner and outer bounds, respectively. The final work, we employed microwave to process material. The microwave heating takes shorter processing time and lower processing temperature than conventional heating. The microwave-material processing is difficult to characterize because most of the researchers use over-moded applicators as well as free-running oscillators to achieve better uniformity and lower costs. This study reports the reduction of the melting points for nine alkali halide ionic crystals in the microwave fields. The melting points were determined from the abrupt change of the reflected wave due to the detuning of the input microwave frequency and the resonant frequency of the cavity during the phase transition. The reduction of the melting points were systematically characterized, where the lowest reduction is less than 2% for lithium bromide (LiBr) and the highest reduction is greater 5% for potassium fluoride (KF). The bond length of the ionic crystal strongly correlated to the reduction ratio of the melting temperature. A theoretical model is proposed which considers the energy drop due to the electric dipole of the ionic crystal interacting with the applied microwave fields. The proposed model qualitatively explains the melting point reduction, but more elaborated theory is still needed.