Microwave heating in the food industry

Food processing has become an important aspect of microwave heating; several technically and some economically successful developments have been reported over the past 10 years. However, the number of microwave installations in the food industry is still very small and not in proportion to the publicity given in many trade journals. The basic theory for the dielectric heating of foods is first reviewed and examples are given of the methods which can be used to analyze heating applications, a valuable complement to empirical testing. Present applications of microwave heating of foods are reviewed. Promising new applications of partial thawing, cooking, and sterilization are discussed in some detail. Some of the reasons for the apparently slow development of these applications are discussed, pointing out the need for better cooperation between manufacturers and users. The opinion is expressed that microwaves will eventually become a standard tool in the food industry for certain processing steps along a continuous production line where very rapid and uniform heating is required. However, it will be necessary, to a much larger extent than in the past, to adapt microwave heating equipment to the processes rather than to adapt the processes to standard microwave systems.     

快速热工艺氧化法生长超薄SiO_2层的研究

在卤素钨灯和弧光灯二种不同辐射热源的快速热工艺系统中用快速热工艺氧化法制备了超薄(20埃-400埃)的SiO_2薄膜.对快速热工艺氧化的生长动力学进行了研究并计算了氧化生长速率的温度激活能.对二种不同快速热工艺系统所得结果作了比较.本文还讨论了快速热工艺氧化中,温度骤变过程的氧化效应.最后,本文提出了“温度骤变(Temperature Ramp-only)快速热氧化”技术,该技术特别适于制备20埃到60埃的超薄SiO_2层.     

Theoretical Analysis of Acoustic Signal Generation in Materials Irradiated with Microwave Energy

Stress gradients generated by thermal expansion, electrostriction, and radiation pressure are sources of elastic waves in microwave irradiated materials. A theoretical analysis taking into account induced volume and surface forces due to these interaction mechanisms is presented. Complete solutions of the dynamical equations for the one-dimensional special case are given for different boundary conditions. The closed-form solutions were found to consist of both a stationary part, whose effect is important only in the immediate region of the incident electromagnetic wave, and a traveling part which propagates through the elastic material. Expressions for the Fourier transforms of these solutions are also given. To quantify these results, pressure and displacement waveforms in microwave irradiated physiological saline were computed. Thermal expansion was considerably more effective than either electrostriction or radiation pressure in converting electromagnetic energy to acoustic energy.     

Bacterial survival and thermal responses of beef loaf after microwave processing

The effects of wrapping product in polyvinylidene chloride (PVDC) film, load size (150, 600 and 1200 g loaves), microwave output power (713 +/- 5 W and 356 +/- 3 W at 2450 MHz) and processing time on bacterial survival were evaluated in beef loaf. Specifically the survival of aerobic flora, and inoculated Staphylococcus aureus (ATCC 6538) and Escherichia coli (O157:H7) were assessed. Results showed that beef loaf wrapped in PVDC film had lower levels of survival for aerobic bacteria, S. aureus and E. coli than unwrapped beef loaf. When beef loaf was exposed to the same microwave dose (watts x minutes processed/grams of food), the percent of survival remained the same, regardless of load size or microwave output power. Exposed microwave dose, which correlated highly to percent of bacterial survival (R2 = 0.8-0.83) and end point temperature (R2 = 0.84), is suggested in place of output power, time or temperature as a predictor of microbial quality in foods that have been microwave processed.     

Radiation effects in GaAs FET devices

The effects that space and nuclear radiation have on GaAs devices utilized for integrated circuit design are reviewed. The hardness capability of contemporary GaAs devices and logic circuits is presented in terms of four major nuclear and space radiation threat categories: total dose effects, dose rate effects, single particle phenomena, and neutron effects. The experimental test data and theoretical analyses presented demonstrate the tolerance of GaAs discrete JFETs and MESFETs and planar integrated circuits to fast neutron and ionizing radiation, under both transient and cumulative conditions.<>     

Radiation-induced breakdown of a nonuniformly doped PN junction

A quasi-hydrodynamic model is developed for carrier transport under ionizing irradiation subject to the nonsteady-state thermal effect of the current on the semiconductor lattice. Computer simulations are run for the thermal breakdown of a nonuniformly doped pn junction caused by a pulse of ionizing radiation. The simulation model includes the temperature dependence of electron energy and momentum relaxation times and the suppression of impact ionization with increasing temperature. The simulation results are verified by comparison with previously reported experimental data.     

利用微波诊断等离子体的方法

等离子体是物质的四个基本形态之一,近年来被广泛应用于能源、材料以及国防等方面.介绍了利用微波诊断等离子体的几种常用方法,即微波干涉法、微波反射法、微波辐射法、微波散射法、微波吸收法以及微波透射法.文中详细介绍了微波干涉法、微波反射法、微波辐射法以及微波散射法的原理、特点和国内外研究现状.     

Transient radiation effects in microwave monolithic integrated circuits based on heterostructure field-effect transistors: Experiment and model

The results of experimental studies and simulations of transient radiation effects in microwave monolithic integrated circuits, based on heterostructure field-effect transistors, affected by the pulse ionizing radiation, are presented. The physical model, which adequately describes transient radiation effects in field-effect transistors in dose rate range up to 10¹² rad/s, is proposed. Based on the physical model, the equivalent electric circuit, taking into account the dominating ionization effects, intended for using in the computer-aided design (CAD), is constructed. The simulated ionizing responses of the microwave low-noise amplifier (LNA) MIC are in accordance with the experimental data.     

The effect of ionizing radiation on the characteristics of silicon-germanium microwave integrated circuits

The effect of ionizing radiation on the characteristics of silicon-germanium microwave ICs has been experimentally studied. Radiation tolerance criteria have been established and absolute tolerance levels of the SiGe ICs to dose and pulse ionizing radiation have been determined. Comparative analysis of the tolerance factors of the microwave ICs fabricated using different technologies is made.     

Problems of development of a mobile system of remote energy supply of small unmanned aerial vehicles by microwave radiation

Methods and systems of remote energy supply of unmanned aerial vehicles (UAVs) are reviewed. It is expedient to use microwave radiation for efficient energy supply of UAVs at distances of several hundred meters. It is shown that energy transfer with the use of microwave radiation is realizable for recharging of UAVs at distances of about 100 m with an efficiency of 50–80%. It is demonstrated that main difficulties in implementation the UAV remote energy supply systems is associated with the lack of Schottky-barrier microwave rectifying diodes, reduction of the mass and overall dimensions of the receiving antenna, hardware and software efficiency increase methods, and methods for ensuring the electromagnetic compatibility.     

微波能在农业上的应用前景

本文综述了微波能在农业上的应用现状，着重介绍了微波技术在作物生长调节、防治病虫害和农产品加工处理等方面的应用，讨论了应用中存在的一些问题，井展望了微波能的农业应用前景。     

Experimental validation of a combined electromagnetic and thermalFDTD model of a microwave heating process

Microwave cooking, tempering, and pasteurizing of foods involves several complex and interacting physical phenomena. Although such processes are widely used, the interactions between the food product, packaging, and the microwave oven itself are particularly complicated, are not well understood, and applicable simulation tools are lacking. In this contribution we describe a combined finite difference time domain model for the electromagnetic and the heat transfer processes which include temperature dependence of the electrical and thermal properties of the food product. This model is validated by comparison to experiment     

Radiation effects in transit-time microwave diodes

There has been considerable progress in the direct generation of microwave power using two-terminal semiconductor devices during the last decade. Permanent and transient radiation effects on bulk (Gunn and LSA) and junction (IMPATT, TRAPATT, and BARITT) transit-time microwave diodes are reviewed. Emphasis is placed upon relating the primary effects of radiation to the physics of device operation. The principal permanent damage is attributed to carrier removal effects, impairing the RF performance of bulk diodes below 10¹⁴neutrons/cm²and junction transit-time diodes at fluences near 10¹⁵neutrons/cm². The principal transient effect is the generation of free carriers by ionizing radiation, affecting the RF performance of bulk diodes above 10⁹rad/s and junction transit-time diodes at dose rates near 10⁸rad/s.     

微波能工业应用研究进展

微波作为一种新型高效加热能源广泛地应用于众多领域。随着其应用的逐渐深入,微波所具有的优点越来越明显,并且已经在工业上产生了良好的经济效益。本文首先介绍了微波能应用机理与大功率微波源,综述了在工业领域内微波能应用的现状和进展,随后指出了微波技术现有的发展状况,并展望了国内微波能在产业方向上的应用前景。     

Interaction Between 2450-MHz Microwaves and Ionizing Radiation in Tribolium Confusum

The combined effect of single or fractionated /sup 137/Cs gamma radiation and 2 h of 2450-MHz microwave radiation at two different power levels, resulting in specific absorption rates of 680 or 760 W/kg in distilled H/sub 2/O, was investigated in the flour beetle, Tribolium confusum. The potentiating effect of microwave treatment after single gamma irradiations was observed only if applied within 60 min; in contrast, the potentiating effect of microwave treatment given before gamma-irradiation lasted at least 8 h. Microwave treatment also altered the kinetics of split-dose recovery. At the higher power level, split-dose recovery was abolished for at least 36 h; at the lower power level, split-dose repair of ionizing radiation damage was delayed for 8-10 h, and then, with longer interfraction intervals, survival increased. All of the foregoing observations essentially mimic those previously reported for appropriate hyperthermic treatment by means of immersion in hot water. These findings are in keeping with the hypothesis that heating, whether by microwaves or by water immersion, affects the repair capabilities of the beetle, either by damaging some of the enzymes that repair radiation-damaged DNA or by altering the cytostructural integrity of the DNA-chromatin membrane complex, rendering the DNA lesions less amenable to repair.     

Effects of ionizing radiation on glow discharge detectors

Glow discharge detectors in the abnormal glow mode can be used as sensitive detectors of microwave and millimeter wave radiation even in the presence of very intense γ ionizing radiation fields where semiconductor devices cannot operate. In the subnormal glow mode, glow discharge detectors give promise of being able to monitor ionizing radiation fields so intense that the usual electronic detectors saturate.     

Potentially hazardous microwave radiation source--a review.

An increasing proliferation of microwave sources and their continuously broadening scope of applications result in the necessity of an assessment of the potential radiation hazard in various situations. Recently, there has appeared quite a large number of references dealing with specific sources. This paper provides a review of various microwave radiation sources to assist in a general understanding of the basic characteristics of the sources which are pertinent to microwave radiation hazards.     

Impact of the radiation environment on integrated-circuit technology

Techniques used to design and produce silicon monolithic integrated circuits for use in the radiation environment found near a nuclear detonation are reviewed. The procedures used to define an anticipated threat are given, and interactions between typical radiations and IC materials are discussed. Circuit selection and design with respect to these interactions are considered process developments needed to implement these designs reviewed. The electrical and radiation performance currently available in production from several sources is described.     

Integrated modeling of microwave food processing and comparison with experimental measurements.

This paper presents an integrated electromagnetic and thermal model for the microwave processing offood packages. The model is developed by combining the edge finite element formulation of the 3-D vector electromagnetic field in the frequency domain and the node finite element solution of the thermal conduction equation. Both mutual and one-way coupling solution algorithms are discussed. Mutual coupling entails the iterative solution of the electromagnetic field and the thermal field, because the physical properties are temperature-dependent. The one-way coupling is applicable when the properties are temperature independent or this dependence is weak. Mesh sensitivity and shape regularity for the edge element based formulation for computational electromagnetics are discussed in light of available analytical solutions for a simple wave guide. The integrated model has been used to study the electromagnetic and thermal phenomena in a pilot scale microwave applicator with and without the food package immersed in water. The calculated results are compared with the experimentally measured data for the thermal fields generated by the microwave heating occurring in a whey protein gel package, and reasonably good agreement between the two is obtained.     

Gas phase approaches to the near millimeter wave source problem

The lack of appropriate sources of radiation in the spectral region between 100 GHz and 1000 GHz is a major impediment to the development of many otherwise advantageous systems and applications. Because the NMMW spectral region lies between the microwave region where classical electronic techniques are optimum, and the optical where laser and thermal sources are favorable, many approaches to the generation of NMMW radiation are viable. These include: 1) gas phase devices, 2) bulk solid-state devices, 3) junction solid-state devices, and 4) electron beam devices. This paper addresses the first of these categories, gas phase devices. These are complex and archetypically interdisciplinary. While this may make detailed understanding difficult, it also holds the promise of unexplored avenues and fruitful discoveries. Thus, we attempt in this paper to provide a fundamental basis for the understanding of these devices with the anticipation that such a basis will stimulate new ideas and further progress in the field. We discuss atomic and molecular energy levels, excitation and inversion mechanisms, chemical processes, existing devices, fundamental considerations, and avenues of inquiry that seem especially attractive.