Thermal Therapy - RF/Microwave Interaction with Biological Tissues - page 148

and
millimeter

-

γ -ray

Å Å

• X-ray therapy
• Heavy particle
radiation therapy
• Neutron capture
therapy
• Synchrotron orbital
radiation

•
•

• RF ablation
• RF hyperthermia

• Microwave
coagulation
therapy
• Microwave
hyperthermia

• Laser thermia

•

FIGURE 4.1 Thermal therapy and frequency.

applicator and the inductive heating applicator . In this chapter, the heating
principles of each applicator are described theoretically.

4.2.1 Foundations of Dielectric Heating Principle

Dielectric heating is based on the principle of generating heat for dielectrics
(insulators) such as plastic or rubber by applying an alternating electric field.
Generally, the particles such as the atoms or the molecules which construct
the dielectric are mutually bound by intermolecular force. When the alter-
nating electric field is applied to the dielectric, these particles exhibit a kind
of resistance due to intermolecular force. Accordingly, when the alternating
electric field is applied to the dielectric, it causes energy loss. As a result,
the dielectric is causing heat generation. This phenomenon is related to the
polarization in the dielectric material. To explain it in more detail, let us first
consider the case of one atom when an electrostatic field is applied to it, as
shown in Figure 4.2. Usually, protons in this case are surrounded by electrons
in the form of central-point symmetry, as shown in Figure 4.2 a .
If an electrostatic field is applied to the atom, the electrons slightly shift in
the direction opposite to the electrostatic field, as shown in Figure 4.2 b . Con-
sequently, the atom forms a kind of electric dipole, as shown in Figure 4.2 c .
This is called electronic polarization because the electrons themselves are
shifted, and this movement creates an electric dipole. As a special case, there
is a state where the electric dipole is naturally formed without applying an
electrostatic field, as seen in hydrogen chloride (HCl) and water (H 2 O), as
shown in Figure 4.3. This is because the molecular structure does not have a