Biomedical Engineering Reference
In-Depth Information
14.8 cm
28.7 cm
Exciting
slot
Exciting
slot
2H
14.3 cm
3H
20.7 cm
Exciting
slot
Exciting
slot
5H
4H
19.6 cm
28.5 cm
19.6 cm
19.7 cm
FIGURE 8.5
Contact flexible microstrip applicators, types 3H, 4H, and 5H. On the right the size of the applicator is indicated. (From Kok, H.P.,
Correia, D., De Greef, M., Van Stam, G., Bel, A., Crezee, J.,
Int J Hyperthermia
26, 2010.)
common edges of the elements are perpendicular or parallel to
the direction of impressed current (see Figure 8.4).
on their operating frequency. In Europe the CFMA for super-
ficial hyperthermia operates at 434 MHz. The two active elec-
trodes are excited by the feeding pin of the coaxial cable as a
plane dipole-like microstrip antenna (5 mm spacing between the
electrodes). A short circuit is positioned at about ¼λ from the
exciting slot [54]. The orientation of the principal E-field direc-
tion is across the slot and perpendicular to the lines indicated on
the surface of each applicator. Bending is only possible around
the axis perpendicular to the exciting slot. The whole applicator
is incorporated in a rubber frame in which a thin rubber water
bolus is integrated. The surface of the rubber frame is covered
with 5 mm high lugs to prevent collapse of the water bolus. The
thickness of the water bolus is 1 cm measured from the highest
rim of the rubber frame. A special feature of the CFMA is that it
can be bent around the axis perpendicular to the exciting slot in
order to follow the curvature of the body.
Following the successful use of the single element applica-
tors, SRPC “Istok” developed the CFMA-12, consisting of 12
capacity-type mini-antennas [55]. The 12-element microstrip
applicator array adds spatial control of the energy distribution
by amplitude modulation for each element (see Figure 8.6). The
Advantages: robust applicator with reliable performance;
effective field area approaches aperture size;
spatial power control in array; H-field energy
coupling; uniform performance between
applicators; versatile use over all body parts.
Disadvantages: power output limited by self-heating of the
applicator, cooling required; rigid applicator;
applicator mounting system required.
8.5.1.1.3 Contact Flexible Microstrip Applicators (CFMA)
Contact flexible microstrip applicators (see Figure 8.5) have been
designed by Gelvich et al. [53]. They are available as single ele-
ment applicators with different sizes: 2H: 14.8 × 14.3 cm
2
; 3H:
28.7 × 20.7 cm
2
; 4H: 19.6 × 19.6 cm
2
; and 5H: 28.5 × 19.7 cm
2
.
The applicators are available from SRPC “Istok” in Moscow,
Russia. The CFMA consist of two active, coplanar electrodes
and a shield electrode. The electrodes are mounted on a sub-
strate of fluoroplastic with a thickness of 0.5−1.5 mm depending
30 cm
FIGURE 8.6
Twelve-element contact flexible microstrip applicator, type CFMA-12. On the right an example of the measured relative SAR distri-
bution at 1 cm depth in a muscle-equivalent phantom with elements activated as indicated [55].
