Microwave-Energy

Fundamental knowledge of the dielectric properties of vermiculite, its interaction with electromagnetic fields and bulk materials handling technology was used to design and construct a continuous high throughput microwave processing system operating at 2.45 GHz. The design methodology used to engineer the system is reported. Experimental demonstration of the effects of microwave energy on the product bulk density is provided for the three most industrially relevant grades of material and it is shown as to how the performance of the system is significantly better than conventional exfoliation technology, in terms of produced bulk densities, energy efficiencies, temperature of the product and plant footprint.

In this paper, we propose a microwave energy reception approach for space solar power satellite applications based on the concept of artificial perfectly matched layer. By embedding rectifying diodes into well-designed metamaterial cells, the obtained rectifying surface simultaneously exhibits a nearly perfect impedance matching to the air and the rectifying circuits, and a strong impedance mismatching to the air at harmonic frequencies, leading to a simple structure that can be implemented using commercial multi-layer printed circuit board technology. The fabricated sample shows that, with a thickness of nearly 1/40 of the free-space wavelength, this rectifying surface has an experimental power absorption rate of 99.92% under normal incident power density of 0.1 mW/cm , and a 56.16-dB suppression to the secondorder harmonic. The measured rectifying efficiency complies well with the theoretical expectation. By introducing an additional layer of passive power combiner network, the proposed approach can also be used in applications of harvesting weak ambient RF and microwave energy. We expect a wide range of applications to emerge from this novel concept in the future.

The realization of a software-defined radio has been a particular objective of the military industry and academia in Turkey. Broadband frequency-tunable PAs and matching networks [28], [29] (see Figure 2) were designed at METU–Northern Cyprus Campus’s RF and Telecommunication Laboratory (established by Dr. Tayfun Nesimoglu [30]) using RFT [8]–[18].

Los radares tienen múltiples aplicaciones y su uso es vital en el sector aeroespacial; de ahí la importancia de formar especialistas en esta área y, por lo tanto, la de contar con herramientas pedagógicas adecuadas. Se plantea la necesidad de implementar algún equipamiento a nivel educativo para potenciar el proceso de enseñanza-aprendizaje de aquellas personas que se encuentran transitando la etapa universitaria de ingeniería. Más precisamente, se busca desarrollar un sistema integral para el aprendizaje de los estudiantes de Ingeniería en Electrónica que cursan asignaturas vinculadas al área de microondas y radares en la Facultad de Ingeniería de la Universidad de Mendoza. El presente trabajo expone un caso de resolución práctica que permite satisfacer esta necesidad, al adaptar un equipo existente.

Hydroxyl radicals HO are generated under Fenton-like (Fe 2+ +H 2 O 2 HO − +OH − +Fe 3+ ) catalytic conditions upon microwave irradiation. Liquid-phase direct catalytic oxidation of benzene to phenol was obtained using FeSO 4 supported on silica gel as a solid catalyst and hydrogen peroxide as the oxidant. The effects of various parameters, such as the different solvents, the amount of solvent used, the amount of catalyst used, the reaction time, the reaction temperature and the amount of hydrogen peroxide used on the yield of phenol were studied to identify optimum reaction conditions. Conventionally heated reaction gives a phenol yield of 0.6%. A higher phenol yield of 13.9% with a selectivity of 100% is obtained when the reaction mixture was irradiated with microwave energy. It is concluded that microwave irradiation offers more effective control of energy input for hydroxyl radical generation that is appropriate for various synthetic reactions.

While biologists have demonstrated the cancer killing ability of hyperthermia in combination with radiation and chemotherapy both in vitro and in vivo, clinicians find that it is difficult to raise and to keep the temperature of tumors at therapeutic levels. During the last decade, there has been significant progress in the method of heat delivery, temperature monitoring, and thermal dosimetry. In this presentation, radiofrequency (RF) and microwave heating techniques are reviewed. Examples of heating patterns of various applicators are shown to illustrate the complex energy deposition of RF and microwave energy in tissues.

Commercial dielectric materials placed around a sample are studied as load-matching elements for multimode microwave-heating applicators. The dimensions of these dielectric materials are optimized with an iterative procedure in order to achieve high-power efficiency, thus enhancing electric-field deposition within the sample. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 41: 414–417, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20156

This paper proposes a numerical study to simulate the effects of dielectric shield on the specific absorption rate (SAR) and the temperature increase in the human body exposed to leakage microwave energy. In this study, the effects of shield dielectric properties on distributions of SAR and temperature increase within the human body at various operating frequency are systematically investigated. Based on the obtained results, the installed dielectric shield strongly affects the SAR and the temperature increase in human body. The SAR and the temperature increase in human body can be reduced simultaneously by setting the appropriate dielectric properties of the dielectric shield. The appropriate dielectric properties of the dielectric shield greatly depend on the operating frequencies. These fundamental data for the implementations of the radiation protection shielding materials, with focusing on the human organism, are provided as well.

The characteristics of cementitious materials subjected to microwave energy are presented. First, the dielectric properties of cementitious materials during a 24-hour first-hydration period were measured at a frequency of 2.45 GHz. Second, the characteristics of hardened cement paste as subjected to heating for a short period (without loss of moisture) by microwave energy with a single-mode rectangular wave guide, with specific attention to temperature rise, compressive strength, and the use of the maturity function was investigated experimentally and theoretically. The obtained results show that dielectric properties are relatively high and remain constant during the dormant period. After this period, the hydration reaction resumes and dielectric properties decrease rapidly. With the use of microwave heating, early-age strength increases during the first 14 days; however, during the next 14 days, early-age strength decreases slightly, until it reaches its lowest at the 28-day mark. The temperature rise as actually recorded at the center of the sample during microwave heating in our experiment consistently agreed with figures calculated by a mathematical model.

The effects of microwave receptor to coal (receptor/coal) ratio and the period of heating by microwave energy on the solubilization of Turkish coals in tetralin have been investigated. CuO was used as microwave receptor. The amount of receptor and the type of coal ...

Edible films can be produced from kafirin but the diverse food product requirements necessitate modification of the films. To modify their functional properties, kafirin films were cast, with and without plasticizer, from glacial acetic acid (GAA) and aqueous ethanol (AE), then heated using microwave energy. A power of 80 W for 2 min caused an approximately two-and fourfold increase in the tensile strength of nonplasticized and plasticized films, respectively. Film glass transition temperature increased by about 15%. Film biodegradability was slowed. However, only the digestibility of the non-plasticized films cast from AE heated for the longest time (4 min) was decreased, by about 25%; while that of the other films was not affected. GAA cast films had higher digestibility than AE cast ones, possibly as a result of acid-mediated deamidation of kafirin. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicated heat-induced kafirin oligomers. Scanning electron microscopy of heated plasticized films showed more wrinkled structures compared to non-heated films, whereas the non-plasticized films appeared more brittle with heating. The results indicate that heat-induced intermolecular disulfide cross-linking was involved in modifying the properties of kafirin films.

Edible films can be produced from kafirin but the diverse food product requirements necessitate modification of the films. To modify their functional properties, kafirin films were cast, with and without plasticizer, from glacial acetic acid (GAA) and aqueous ethanol (AE), then heated using microwave energy. A power of 80 W for 2 min caused an approximately two- and fourfold increase in the tensile strength of non-plasticized and plasticized films, respectively. Film glass transition temperature increased by about 15%. Film biodegradability was slowed. However, only the digestibility of the non-plasticized films cast from AE heated for the longest time (4 min) was decreased, by about 25%; while that of the other films was not affected. GAA cast films had higher digestibility than AE cast ones, possibly as a result of acid-mediated deamidation of kafirin. Sodium dodecyl sulfate–polyacrylamide gel electrophoresis indicated heat-induced kafirin oligomers. Scanning electron microscopy of heated plasticized films showed more wrinkled structures compared to non-heated films, whereas the non-plasticized films appeared more brittle with heating. The results indicate that heat-induced intermolecular disulfide cross-linking was involved in modifying the properties of kafirin films. Copyright © 2006 Society of Chemical Industry

Nylon denture base material could be a useful alternative to poly (methyl methacrylate) (PMMA) in special circumstances such as patient allergy to the monomer. The aim of this study was to evaluate the flexural properties of a nylon denture base material (Lucitone FRS), a conventional compression-moulded heat-polymerized (Meliodent), a compression-moulded microwave-polymerized (Acron MC) and an injection-moulded microwave-polymerized (Lucitone 199) PMMA polymers. The effect of aldehyde-free, oxygen releasing disinfectant solution (Perform((R))) on these properties was also investigated. The flexural modulus and the flexural strength were assessed with a three-point bending test. Specimens were stored in water at a temperature of 37 degreesC for 30 days. For each material, half of the prepared specimens were randomly selected and immersed in the disinfectant 24 h prior to testing. Results were compared statistically at a confidence level of 95%. The result showed that in both the control and disinfected groups, the flexural modulus of nylon was significantly lower than the three PMMA polymers. The flexural strength of nylon was significantly lower than those of Meliodent and Acron MC but was comparable with Lucitone 199. A 24-h immersion in the disinfecting solution increased the rigidity of nylon denture base material.

Purpose: The purpose of this study was to evaluate the effect of microwave disinfection (3 minutes at 650 W) on the dimensional stability of hard chairside reline resins (Kooliner, Tokuyama Rebase II, Ufi Gel hard, New Truliner) and one heatpolymerizing denture base resin (Lucitone 550). Materials and Methods: A split mold with reference points was used to make specimens (50.0-mm diameter, 0.5-mm thick) from each material, divided into five test groups (n = 8). The distances between the points on the mold were measured (gold standard), and compared with those obtained from the specimens after polymerization (baseline readings) after one, two, three, and four cycles of disinfection by microwave irradiation. Results: ANOVA and Tukey tests (α = 0.05) showed that Kooliner was significantly affected by all disinfection cycles (p < 0.05) when compared with baseline measurements. New Truliner resin was significantly affected by three and four cycles of microwave disinfection when compared with baseline measurements (p < 0.05). For Tokuyama Rebase II, Ufi Gel hard, and Lucitone 550, no significant dimensional changes were found. Conclusions: Microwave disinfection promoted shrinkage of Kooliner and New Truliner. The dimensional stability of Tokuyama Rebase II, Ufi Gel Hard, and Lucitone 550 was not affected by microwave disinfection.

This study focused on the enhanced debromination of decabromodiphenyl ether (BDE-209) and 2,2′,4,4′tetrabromodiphenyl ether (BDE-47) by Fe-Ag nano-particles under microwave radiation (Fe-Ag/MW). Fe-Ag bimetallic nano-particles were synthesized by reductive deposition of Ag on nano-iron and characterized with a number of techniques, including BET, XRD, TEM and XPS. Approximately 97% of BDE-209 or 78% of BDE-47 were rapidly transformed to its degradation products within 8 min in the Fe-Ag/MW system. The dehalogenation efficiency of polybrominated diphenyl ethers (PBDEs) was enhanced apparently by microwave radiation. Moreover, the microwave thermal energy played a significant role in accelerating the degradation reactions. Compared with nano-iron alone, the deposition of Ag also increased the rates of degradation. GC-MS and LC-MS/MS analyses of PBDEs' degradation products reveals that the possible degradation pathway proceeds through stepwise debromination from [n]-bromo-to [n-1]-bromo-DE, with bromine being substituted by hydrogen sequentially. Di-to nona-brominated congeners were formed during BDE-209 reduction, while diphenyl ether to tri-BDEs were observed during BDE-47 degradation. These results suggest that PBDEs can be debrominated rapidly by the innovative processes that may be environmentally friendly in applications.