Microwave processing of materials is a relatively new technology advancement alternative that provides new approaches for enhancing material properties as well as economic advantages through energy savings and accelerated product development. Factors that hinder the use of microwaves in materials processing are declining, so that prospect for the development of this technology seem to be very promising (Sutton, W.H., 1989). The two mechanisms of orientation polarisation and interfacial space charge polarisation, together with dc. conductivity, form the basis of high frequency heating. Clearly, advantages in utilising microwave technologies for processing materials include penetrating radiation, controlled electric field distribution and selective and volumetric heating. However, the most commonly used facilities for microwave processing materials are of fixed frequency, eg 2.45 GHz. This paper presents a state-of-the-art review of microwave technologies, processing methods and industrial applications, using variable frequency microwave (VFM) facilities. This is a new alternative for microwave processing. The technique is geared towards advanced materials processing and chemical synthesis. It offers rapid, uniform and selective heating over a large volume at a high energy coupling efficiency. This is accomplished using a preselected bandwidth sweeping around a central frequency employing frequency agile sources such as travelling wave tubes as the microwave power amplifier. Selective heating of complex samples and industrial scale-up are now viable. During VFM processing, a given frequency of microwaves would only be launched for less than one millisecond. Two facilities were employed during the study. The VW1500 (Figure 1) with a maximum power output of 125 W generates microwave energy in the frequency range of 6–18 GHz and the other, Microcure 2100 Model 250 (Figure 2) operates at 6–18 GHz with a maximum power level of 250 W. The cavity dimension of VW1500 (Figure 1) was 250 mm x 250 mm x 300 mm and the Microcure 2100 model 250 has a cavity size of 300 mm x 275 mm x 375 mm. Successful applications of the VFM technology are in the areas of curing advanced polymeric encapsulants, thermoplastic matrix composite materials characterisation, adhesive characterisation, rapid processing of flip-chip (FC) underfills, joining reinforced thermoplastic matrix composites materials, and structural bonding of glass to plastic housing. However, there are a lot of factors that have to be considered before employing variable frequency microwave (VFM) irradiation for processing materials. Not all materials are suitable for microwave processing and one has to match the special characteristics of the process. Blind applications of microwave energy in material processing will usually lead to disappointment. On the other hand, wise application of the technology will have greater benefits than have been anticipated. Successful applications of these modern facilities by the authors include the characterisation of glass or carbon fibre reinforced thermoplastic matrix composites, eg 33% by weight glass fibre reinforced low density polyethylene [LDPE/GF (33%)], of primers eg two-part five-minute rapid araldite (LRA), and joining of the above mentioned composite materials with, or, without primers. Such applications are detailed in this paper.
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机译：材料的微波处理是一种相对较新的技术进步选择，它通过节能和加速产品开发，提供了增强材料性能和经济优势的新方法。阻碍在材料加工中使用微波的因素正在减少，因此该技术的发展前景似乎非常有希望（Sutton，W.H.，1989）。定向极化和界面空间电荷极化的两种机制，以及直流电。导电性，构成高频加热的基础。显然，利用微波技术处理材料的优势包括穿透辐射，受控的电场分布以及选择性和体积加热。但是，最常用的微波处理设备是固定频率的，例如2.45 GHz。本文介绍了使用变频微波（VFM）设施的微波技术，处理方法和工业应用的最新技术综述。这是微波处理的新选择。该技术适用于先进的材料加工和化学合成。它以高能量耦合效率在大体积上提供快速，均匀和选择性的加热。这是通过使用频率捷变源（例如行波管）作为微波功率放大器，使用围绕中心频率扫描的预选带宽来实现的。现在可以对复杂样品进行选择性加热并进行工业放大。在VFM处理期间，给定频率的微波只会发射不到一毫秒的时间。在研究过程中采用了两种设施。最大输出功率为125 W的VW1500（图1）产生6–18 GHz频率范围内的微波能量，而另一款Microcure 2100 Model 250（图2）在6–18 GHz上运行，最大功率为250W。VW1500（图1）的腔体尺寸为250 mm x 250 mm x 300 mm，而Microcure 2100型号250的腔体尺寸为300 mm x 275 mm x 375 mm。 VFM技术的成功应用包括固化高级聚合物密封剂，表征热塑性基体复合材料，表征粘合剂，快速处理倒装芯片（FC）底部填充，接合增强型热塑性基体复合材料以及玻璃与塑料的结构粘合住房。但是，在将可变频率微波（VFM）辐射用于处理材料之前，必须考虑许多因素。并非所有材料都适合微波处理，并且其中一种必须符合该过程的特殊特征。微波能量在材料加工中的盲目应用通常会令人失望。另一方面，明智地应用该技术将具有比预期更大的收益。作者对这些现代设备的成功应用包括玻璃或碳纤维增强的热塑性基体复合材料的表征，例如底漆（如两部分）的重量百分比为33％（玻璃纤维增强的低密度聚乙烯[LDPE / GF（33％）]）。分钟的快速钠长石（LRA），并使用或不使用底漆将上述复合材料连接起来。本文将详细介绍此类应用。
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