In conventional thermal processing, energy is transferred to
the material through convection, conduction, and radiation of heat
from the surfaces of the material. In contrast, the microwave energy
is delivered directly to materials through molecular interaction
with electromagnetic field. In heat transfer, energy is transferred
as a result of thermal gradient between two points, but microwave
heating involves the transfer of electromagnetic energy to thermal
energy, and thus it is a kind of energy conversion rather than heat
transfer. This difference in the way energy is delivered can result
in many potential advantages to using microwaves for processing
of materials (Thostenson & Chou, 1999).