relevance in practice as it relates approximately to the treatment of foodstuffs with microwaves.
This is because most foodstuffs have a relatively high effective loss factor εe″, which results in a
rapidly decaying electric field and justifying the assumption made above which is inherent in the
derivation of eqn.[5] Whether a finite slab or a semi-finite slab is considered, the electric field has
decayed to a very small value within a very short distance of the air/dielectric interface.
Finite slab: Unless the dielectric properties of the processed material are very high, the
assumptions made in the previous paragraph do not hold for a finite slab and the electric field is
given by the general solution of eqn. 3:
Ez=Re {[Ae-γy
+ Be+γy
]ejωt
} [6]
where A and B are constants that fit the appropriate boundary conditions. It is not justifiable now
to set B = O in this case because the slab has medium to low loss factor value and the second
term may be of the same order as the first term in eqn.[6]. The electric field in this case does not
decay exponentially and more elaborate solutions ought to be found when y is set equal to the
slab width.
Heating in the standing wave electric field: The analysis of the semi-infinite slab has been
applied to a dielectric material placed inside a multimode oven applicator for approximate
calculations of the electric field and other parameters. This is justified only if the dielectric loss
factor is fairly high, as is the case with most foodstuffs, resulting in a rapidly decaying field. With a
medium to low loss dielectric the electric field no longer decays exponentially and more rigorous