Page - 3 - in Adaptive and Intelligent Temperature Control of Microwave Heating Systems with Multiple Sources

1.1. DevelopmentofMicrowaveHeating heating of the intermediate medium, especially for high tempera- ture applications [TC99]. Because of the unique volumetric heat- ing ability, there is no need to spend additional time in the surface heating and the heat transfer process. Moreover, the heating rate to the insideof thematerial isnot limitedbytheslowheat transfer process, but mostly determined by the microwave power. In prin- ciple, themicrowaveheatingisabletoprovideanydesiredheating rateas longasthemicrowavepowerissufficient,whichlargelyre- duces theoverallheatingtime[LM03]. 2. Selectiveandcontrollableheating When a product consisting of different materials is heated in a mi- crowave cavity, different heating rates are achieved due to differ- ent properties of individual materials. This selective heating phe- nomenon is desired in many applications, especially in the mi- crowave chemistry area. For example, in the applications intro- ducedby[ZQY14], temperaturegradientsatdifferent locationsare requiredtoenhancedifferent local chemical reactions. In conventional heating, it is slow and clumsy to control the heat- ingrate. Incomparisontotheconventionalheating, therateofmi- crowave heating can be immediately controlled by adjusting the microwave power. In applications where multiple stages with dif- ferent heating rates are required, i.e. sintering of ceramics [Kat92] or curing of composite materials [LLG14], microwave heating is preferredbecauseof its controllableandquickresponse. Due to above mentioned advantages, considerable research has been performed on microwave heating since the 1950s. Nowadays, there are a large number of successful applications of microwave heating in different industries, including food, rubber, pharmaceutical, poly- mers, plastics and textiles [oED07]. During the last 10 to 15 years, more and more interests have been drawn to the emerging domain of fabricatingcarbonfiberreinforcedpolymer(CFRP)compositemateri- als using microwave heating. CFRP composite material is one kind of advanced high-performance (AHP) composite materials that increas- inglyattractsbothcommercialandresearchattentions[Cor01]. Dueto itsexcellentmechanicalproperties,suchasthefatigueresistance, light weight and extraordinary high-temperature characteristics [LLG14], CFRPhasbeenwidelyappliedinautomotive, renewableenergy,aero- 3