Microwave Properties
Understanding microwaves and the Reverse Polymerization process is valuable for appreciating the advantages of this technology over other possible solutions. Microwaves are electromagnetic waves in the frequency band from 300 MHz to 300 GHz. Industrial microwave processing is usually accomplished at frequencies of 915 MHz or 2,450 MHz.
When an electric field, such as can be generated by microwave energy, interacts with a material, a number of responses can take place:
- In a material that is a conductor, electrons move freely in the material in response to an electric field and an electric current results. Unless the material is a superconductor, the flow of electrons will heat the material through resistive heating. Resistive heating is the process that is used in a typical electric heating element such as a stovetop.
- In an insulator, electrons do not flow freely, but re-orientation or distortions of induced, or permanent dipoles, can give rise to heating.
Microwaves penetrate materials and release their energy in the form of heat as the polar molecules (ones with positively and negatively charged ends - such as water) vibrate at high frequency to align themselves with the frequency of the microwave field. The microwaves interact directly with the object being heated. The interaction is related to the chemical properties of the object and it is possible to apply heat in ways that can not be achieved by conventional means (convection heating, conductive heating or radiant heating). For example, it is possible to heat up one object whilst another, close by, remains relatively cool. An example is a typical home microwave oven that will heat and cook the food, generally containing water, while the glass plate stays relatively cool. The water in the food links with the microwave energy while the plate is invisible to the microwaves. Any heating of the plate is caused by radiant heat transfer from the hot food. Microwave heating also heats the food relatively uniformly throughout while radiant or convection heating, raises the temperature from the outside inward. See the figure below for a comparison of the heating processes.
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