Microwave Energy Distribution Research Articles

MICROWAVE-INDUCED THERMO-ACOUSTIC TOMOGRAPHY SYSTEM USING TRM-PSTD TECHNIQUE

Time reversal imaging method based on full wave numerical technique for likely breast tumors biological tissue in the Microwave-Induced Thermo-Acoustic Tomography (MITAT) system is discussed. In this paper, the mechanism of microwave-induced thermo-acoustic is strictly described based on thermodynamics and thermo-difiusion principles; the equivalent relationship between the absorbed microwave energy distribution of the biological tissue and the induced thermo-acoustic source distribution is used as the basis of the imaging algorithm. Due to its unique noise suppression feature and the stability of the algorithm, the Time Reversal Method (TRM) based on the Pseudospectral Time-Domain (PSTD) technique is applied to image heterogeneous phantom tissues from low Signal-to-Noise-Ratio (SNR) thermo-acoustic signals. Thereafter, an integrated MITAT prototype system is presented to obtain the thermo-acoustic signals from some biologic tissue with millimeter scale. The proposed TRM method is based on PSTD technique produced two-dimensional images, presented to study the performances of the MITAT in terms of contrast and resolution. These images prove predominant advantages in both contrast and resolution compared with conventional microwave and ultrasound imaging systems for malignant tumor detection. Based on the current results, our TRM-PSTD MITAT system provides evidence to predict breast tumor in an early stage and millimeter scale.

Microwave Drying of Expanded Perlite Insulation Board

The microwave drying process intensification of new inorganic thermal insulation board, containing expanded perlite and inorganic binder, was investigated in a multimode microwave applicator, with a 1.8 kW, 2.45 GHz microwave source. Ability to generate heat inside moistened material and to avoid the problem of heat conduction to the core of the material is especially important when dealing with efficient thermal insulators. A 3D unsteady mathematical model was developed, considering Lambert’s law of exponential decay of microwave energy and nonuniform power distribution inside the microwave cavity, for temperature and drying rate predictions. The predicted temperature profiles at critical locations of the exposed board and cumulative drying rate were compared and verified with experimental data.

Visualization of Microwave Energy Distribution in a Multimode Microwave Cavity Using CoCl2 on Gypsum Plates

This study provides a facile method to map the microwave field distribution in a multimode microwave cavity. Anhydrous calcium sulfate powder was used to make the gypsum plates that were used as the carrying medium. Cobalt chloride hexahydrate, whose color changes when losing part or all of its crystal waters, was selected as an indicator of the energy absorption. The cobalt chloride aqueous solution at a concentration of 1.6% was absorbed by the dried gypsum plates. After introducing the plates into a microwave field, those areas that receive more microwave energy were preferably heated, resulting in the release of the moisture and consequently the loss of crystal water from the cobalt chloride hexahydrate. The color change on the plate formed a color map indicating the microwave field distribution. This method was used to investigate the energy distribution of a microwave oven by placing single or multiple plates in horizontal or vertical positions at different locations in the cavity.

Application of time reversal mirror technique in microwave-induced thermo-acoustic tomography system

Microwave-induced thermo-acoustic tomography (MITAT) is a promising technique with great potential in biomedical imaging. It has both the high contrast of the microwave imaging and the high resolution of the ultrasound imaging. In this paper, the proportional relationship between the absorbed microwave energy distribution and the induced ultrasound source distribution is derived. Further, the time reversal mirror (TRM) technique based on the pseudo-spectral time domain (PSTD) method is applied to MITAT system. The simulation results show that high contrast and resolution can be achieved by the TRM technique based on PSTD method even for the received signals with very low signal-to-noise ratio (SNR) and the model parameter with random fluctuation.

Characteristics of a chemical reactor that is a loaded microwave resonator

Relationships for calculation of the following parameters of reactors with microwave heating of chemical reagents are presented: the coefficient of absorbed microwave energy distribution in the reactor (in the cavity between the resonator walls and reagents) and the efficiency of transformation of microwave energy into heat of the reagents. The range of variation of microwave properties of the reactor during variation of reagent properties is estimated, and the coupling parameters of the resonator with the external line that provide for a high efficiency are determined.

Microwave Synthesis of Zeolites: 1. Reactor Engineering

Studies in the past decade suggest that microwave energy may have a unique ability to influence chemical processes. These include chemical and materials syntheses as well as separations. Specifically, recent studies have documented significantly reduced time for the fabrication of zeolites employing microwave energy. However, the mechanism and engineering for the enhanced rates of syntheses are unknown. The results from different laboratories are not consistent, and experimental details are sparse. We studied the synthesis of silicalite employing two geometries in an oven with 2.45-GHz microwaves. The distribution of microwave energies within the reactors from simulation differed, and the morphologies and yields of the resultant zeolite also differed. Larger uniform silicalite crystals were formed in the larger reactor in which the variation in microwave energy distribution was greater. Engineering the energy distribution within a microwave synthesis reactor is necessary to understand and control the process.

Predicting temperature range in food slabs undergoing short-term/high-power microwave heating

A closed-form solution to the heat equation, derived for one-dimensional microwave-heated slabs, is presented. The microwave energy distribution used in the heat equation is obtained from Maxwell’s equations. Therefore, the potential exists of standing waves of microwave energy within the food. This phenomenon contributes to the nonuniform temperature pattern characteristic of microwave heating but is often neglected in theoretical predictions of temperatures. The solution allows temperature to be calculated as a function of thermal, geometric and dielectric properties of the food being heated and is valid for all microwave power levels and durations of heating. Previous work allowed such a solution only if very long durations and very low power levels of microwave heating were used. That the solution is closed-form allows its implementation in spreadsheet format. Simplifications to the closed-form solution that retain the standing wave phenomenon are shown. Their accuracy, however, is limited to approximately 40 s of heating. Results from the full closed-form solution, using parameters measured in beef, show that the range of temperatures experienced by a microwave-heated beef slab is a sensitive function of slab width and time, with ranges as great as 50°C. It is shown that thermal insulation at the slab faces slightly increases the temperature range. Another feature of the theoretical solution is the extreme sensitivity of temperature range to slab width in the 1–3 cm width interval, with decreasing sensitivity as slab widths increase beyond 4 cm. Sensitivity increases, however, as time increases, regardless of slab width. Lastly, a time-invariant temperature range minimum is seen in the 3–4 cm slab width interval.

Microwave Processing of Cell Monolayers in Situ for Postembedding Immunocytochemistry with Retention of Ultrastructure and Antigenicity

Abstract Increasingly, cells isolated from blood and body fluids and cells grown in culture are becoming the experimental models of choice for biological research. The demand for demonstrating biochemical processes morphologically is also becoming commonplace in the electron microscopy laboratory. Successful fixation, in situ embedment, and ultrathinsectioning of cell monolayers can be difficult to achieve for routine transmission electron microscopy. For postembedding immunocytochemistry, processing becomes more complex due to fixation constraints and the use of acrylic resins. The object of this paper is to present a reliable, rapid method for processing monolayers that preserves both the ultrastructure of the cells and antigenicity. The equipment used for this procedure was a Pelco Model 3440 MAX laboratory microwave oven equipped with a temperature probe and a maximum power output of 800 watts. Using a neon bulb array, the oven cavity is calibrated to determine the microwave energy distribution.

MOISTURE DISTRIBUTION IN SPHERICAL FOODS IN MICROWAVE DRYING

Moisture distribution in spheres of potato (Solanum tuberosum) and yam (Dioscorea japonica) tubers during microwave drying was investigated. Moisture variation at various locations within the samples was experimentally determined for different drying times. A numerical simulation model was developed based on a modified form of Lambert's law for microwave penetration in spheres and on moisture transfer in both liquid and vapor phases. This model was used to study various factors influencing moisture distribution. Moisture profile during microwave drying was strongly influenced by non-uniform microwave energy distribution within the foods. The core moisture contents were lower than other parts of potato and yam spheres of the various sizes tested in this study (2.6 cm to 6.0 cm diameter). The sphere radius to microwave penetration ratio (2αro) was an important parameter affecting the moisture profile in spherical foods. For 2αro of less than 2.0, the moisture content in the center of potato and yam spheres was markedly lower than the rest of the food, but for 2αro between 2.5 and 4, moisture contents at the center and close to the surface were lower than the average moisture content.

The determination of the electromagnetic field and SAR pattern of an interstitial applicator in a dissipative dielectric medium

The spatial distribution of microwave energy absorbed per unit mass (the specific absorption rate or SAR) in biological tissue is calculated for a class of interstitial antennas. The insulated interstitial applicator is simulated as an asymmetrically drive antenna. An expression for the electric field intensity near the antenna is derived and calculated by direct numerical evaluation of a surface integral over the insulation. The predicted SAR patterns obtained using the calculated electric field intensity and the tissue conductivity agree very well with the measured SAR distributions around three different applicators in muscle-equivalent phantoms.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Microwave energy distribution measurements in proximity to man and other their practical application.

Annals of the New York Academy of SciencesVolume 247, Issue 1 p. 473-480 MICROWAVE ENERGY DISTRIBUTION MEASUREMENTS IN PROXIMITY TO MAN AND THEIR PRACTICAL APPLICATION D. E. Beischer, D. E. Beischer Naval Aerospace Medical Research Laboratory Pensacola. Florida 32512Search for more papers by this authorV. R. Reno, V. R. Reno Naval Aerospace Medical Research Laboratory Pensacola. Florida 32512Search for more papers by this author D. E. Beischer, D. E. Beischer Naval Aerospace Medical Research Laboratory Pensacola. Florida 32512Search for more papers by this authorV. R. Reno, V. R. Reno Naval Aerospace Medical Research Laboratory Pensacola. Florida 32512Search for more papers by this author First published: February 1975 https://doi.org/10.1111/j.1749-6632.1975.tb36022.xCitations: 8AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Citing Literature Volume247, Issue1Biologic Effects of Nonionizing RadiationFebruary 1975Pages 473-480 RelatedInformation