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Microwave Field (microwave + field)

Distribution by Scientific Domains

Life Sciences	33%
Chemistry	33%

Selected Abstracts

Microwave characteristics of substrate integrated waveguide photodetector

MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 9 2009
Ebrahim Mortazy
Abstract In this article, using a novel structure, simulated and measured microwave characteristics from substrate integrated waveguide photodetector (SIWPD) are obtained and compared with the conventional microstrip waveguide photodetector. A Ka-band microstrip to rectangular waveguide multilayer transition for OC-768/STM-256 optical systems is designed and fabricated. Attenuation constant results shows that by replacing substrate integrated waveguide (SIW) instead of conventional microstrip in waveguide photodetectors, operation frequency can be increased. Microwave fields in the proposed structure show a good transition from quasi-TEM mode to TE10 mode in multilayer structure. The multilayer structure is considered to separate SIW and DC bias of the photodetector. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2204,2207, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24528 [source]

Microwave Activation of Electrochemical Processes at Glassy Carbon and Boron-Doped Diamond Electrodes

ELECTROANALYSIS, Issue 5-6 2005
Kumar Sur, Ujjal
Abstract Voltammetric experiments under intense microwave field conditions have been carried out at a carbon microfiber electrode, an array of carbon microfiber electrodes, and at a boron-doped diamond electrode. For the reversible one electron redox systems Fe(CN) and Ru(NH3) in aqueous KCl solution increased currents (up to 16 fold at a 33,,m diameter carbon microelectrode) and superheating (up to ca. 400,K at all types of electrodes) are observed. Electrodes with smaller diameter allow better signal enhancements to be achieved. From the missing effect of the supporting electrolyte concentration on the microwave enhanced currents, it can be concluded that effects observed at carbon electrodes (microwave absorbers) are due to the interaction of microwaves with the electrode material whereas for metal electrodes (microwave conductors) effects are dominated by the interaction of the microwaves with the aqueous dielectric. Short heat pulses can be applied by pulsing the microwave field and relatively fast temperature transients are observed for small electrodes. For the irreversible two electron oxidation of L -dopa in aqueous phosphate buffer, different types of effects are observed at glassy carbon and at boron-doped diamond. Arrays of carbon microfibers give the most reproducible and analytically useful current signal enhancements in the presence of microwaves. [source]

Determination of iodine and bromine compounds in foodstuffs by CE-inductively coupled plasma MS

ELECTROPHORESIS, Issue 22 2007
Jing-Huan Chen
Abstract A CE-inductively coupled plasma mass spectrometric (CE-ICP-MS) method for iodine and bromine speciation analysis is described. Samples containing ionic iodine (I, and IO3,) and bromine (Br, and BrO3,) species are subjected to electrophoretic separation before injection into the microconcentric nebulizer (CEI-100). The separation has been achieved in a 50,cm length×75,,m id fused-silica capillary. The electrophoretic buffer used is 10,mmol/L Tris (pH,8.0), while the applied voltage is set at ,8,kV. Detection limits are 1 and 20,50,ng/mL for various I and Br compounds, respectively, based on peak height. The RSD of the peak areas for seven injections of 0.1,,g/mL I,, IO3, and 1,,g/mL Br,, BrO3, mixture is in the range of 3,5%. This method has been applied to determine various iodine and bromine species in NIST SRM 1573a Tomato Leaves reference material and a salt and seaweed samples obtained locally. A microwave-assisted extraction method is used for the extraction of these compounds. Over 87% of the total iodine and 83% of the total bromine are extracted using a 10% m/v tetramethylammonium hydroxide (TMAH) solution in a focused microwave field within a period of 10,min. The spike recoveries are in the range of 94,105% for all the determinations. The major species of iodine and bromine in tomato leaves, salt, and seaweed are Br,, IO3,, I,, and Br,, respectively. [source]

Effects of decay-induced coherence and microwaveinducedcoherence on the index of refraction in a three-level , -type atomic system

LASER PHYSICS LETTERS, Issue 4 2004
Wei-Hua Xu
Abstract We study the dispersion-absorption properties in a three-level , -type atomic system with two closely lying lower levels. We consider two schemes: in the first, the two lower levels are coupled by decay-induced coherence, and in the second, quantum coherence is created by coupling the two lower levels to each other by a microwave field. We found that due to the decay-induced coherence or microwave-induced coherence, the dispersion-absorption properties can be controlled by the relative phase of applied fields, large index of refraction without absorption always can be obtained just by choosing proper values of the (© 2004 by ASTRO, Ltd. Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) [source]

A small temperature rise may contribute towards the apparent induction by microwaves of heat-shock gene expression in the nematode Caenorhabditis Elegans

BIOELECTROMAGNETICS, Issue 2 2006
Adam S. Dawe
Abstract We have previously reported that low intensity microwave exposure (0.75,1.0 GHz CW at 0.5 W; SAR 4,40 mW/kg) can induce an apparently non-thermal heat-shock response in Caenorhabditis elegans worms carrying hsp16-1::reporter genes. Using matched copper TEM cells for both sham and exposed groups, we can detect only modest reporter induction in the latter exposed group (15,20% after 2.5 h at 26 °C, rising to ,50% after 20 h). Traceable calibration of our copper TEM cell by the National Physical Laboratory (NPL) reveals significant power loss within the cell (8.5% at 1.0 GHz), accompanied by slight heating of exposed samples (,0.3 °C at 1.0 W). Thus, exposed samples are in fact slightly warmer (by ,0.2 °C at 0.5 W) than sham controls. Following NPL recommendations, our TEM cell design was modified with the aim of reducing both power loss and consequent heating. In the modified silver-plated cell, power loss is only 1.5% at 1.0 GHz, and sample warming is reduced to ,0.15 °C at 1.0 W (i.e., ,0.1 °C at 0.5 W). Under sham:sham conditions, there is no difference in reporter expression between the modified silver-plated TEM cell and an unmodified copper cell. However, worms exposed to microwaves (1.0 GHz and 0.5 W) in the silver-plated cell also show no detectable induction of reporter expression relative to sham controls in the copper cell. Thus, the 20% "microwave induction" observed using two copper cells may be caused by a small temperature difference between sham and exposed conditions. In worms incubated for 2.5 h at 26.0, 26.2, and 27.0 °C with no microwave field, there is a consistent and significant increase in reporter expression between 26.0 and 26.2 °C (by ,20% in each of the six independent runs), but paradoxically expression levels at 27.0 °C are similar to those seen at 26.0 °C. This surprising result is in line with other evidence pointing towards complex regulation of hsp16-1 gene expression across the sub-heat-shock range of 25,27.5 °C in C. elegans. We conclude that our original interpretation of a non-thermal effect of microwaves cannot be sustained; at least part of the explanation appears to be thermal. Bioelectromagnetics 27:88,97, 2006. © 2005 Wiley-Liss, Inc. [source]

Multimode Microwave Reactor for Heterogeneous Gas-Phase Catalysis

CHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 11 2003
H. Will
In order to investigate heterogeneously catalyzed gas-phase reactions, e.g. the oxidation of propane, on heterogeneous catalysts in the multimode microwave field, a microwave device was modified to achieve an adequate field homogeneity and a continuous power control. To date, no similar apparatus has been described in the literature. The presented microwave apparatus is suitable for carrying out reproducible catalytic investigations in the multimode microwave field. [source]