Applications of fixed and variable frequency microwave (VFM) facilities inpolymeric materials processing and joining

Microwave processing of materials is a relatively new technology advancemen t alternative that provides new approaches for enhancing material propertie s as well as economic advantages through energy savings and accelerated pro duct development Factors that hinder the use of microwaves in materials pro cessing are declining, so that prospect for the development of this technol ogy seem to be very promising [Ceram. Bull. 68 (2) (1989) 376]. The two mec hanisms of orientation polarisation and interfacial space charge polarisati on, together with DC conductivity, form the basis of high frequency heating . Clearly, advantages in utilising microwave technologies for processing ma terials include penetrating radiation, controlled electric field distributi on and selective and volumetric heating. However, the most commonly used fa cilities for microwave processing materials are of fixed frequency, e.g. 2. 45 GHz. This paper presents a stare-of-the-art review of microwave technolo gies, processing methods and industrial applications, using variable freque ncy microwave (VFM) facilities. This is a new alternative for microwave pro cessing. The technique is geared towards advanced materials processing and chemical synthesis. It offers rapid, uniform and selective heating over a l arge volume at a high energy coupling efficiency. This is accomplished usin g a preselected bandwidth sweeping around a central frequency employing fre quency agile sources such as travelling wave tubes as the microwave power a mplifier. Selective hearing of complex samples and industrial scale-up are now viable. During VFM processing, a given frequency of microwaves would on ly be launched for less than 1 ms. (C) 2001 Elsevier Science B.V. All right s reserved.