Page - 15 - in Adaptive and Intelligent Temperature Control of Microwave Heating Systems with Multiple Sources

2. Introductionof HEPHAISTOS In this chapter, the distributed microwave heating system HEPHAIS- TOS will be introduced in detail. In the beginning, the principles of electromagnetic heating is addressed. Then the components of HEP- HAISTOS, including the microwave heating system, the process con- trol system and the temperature measurement system, are explained onebyone. 2.1. ElectromagneticHeating Almosteverythingintherealworld,exceptaperfectconductororper- fect insulator, canbeheatedwithinanelectromagneticfield. Basedon different kinds of materials, the electrical heating techniques can be dividedintoseveraldifferentclasses, includingohmicheating, induc- tionheatinganddielectricheating. 2.1.1. OhmicHeating Ohmic heating, also known as Joule heating [GC99], is a basic electri- calheatingmechanism. Whenadirectcurrent(DC)oralternatingcur- rent (AC) flow passes through a conductor or semiconductor, a frac- tion of the electrical energy is transformed into thermal energy due to electrical resistance, and therefore the heat is generated. The amount of heating powerPohmic is proportional to the square of the current I, suchas Pohmic= I ·V = I2 ·R= V 2 R , (2.1) 15