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IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 32, NO. 4, AUGUST 2004

Computation of the standing wave patterns for the two

different positions of the cell perfusion apparatus (i.e., at the

and  ) showed a local suppression of the

maxima of

field across the glass fiber filter due to the conducting BSS.

However, the overall standing wave pattern was unaffected by

the presence of the cell perfusion apparatus.

1) SAR Distribution With the Cell Perfusion Chamber at the

Maximum in  :

a) Perpendicular orientation: With the cell perfusion

(18.90 cm from the

chamber located at the maximum in

shorting plate at 1 GHz), the SAR distribution across the glass

fiber filter in this orientation is fairly symmetrical (Fig. 7), going

through a smooth yet rapid transition from its 0 W/kg value at

the edge of the filter to a fairly uniform plateau covering a large

area of the filter. This variation does not include the two hot

spots on the associated surface plot or the rapid drop in SAR at

and near the center of the filter. The region from the edge of the

filter to the start of the plateau region can be further divided into

three distinct parts that are distinguished by the rate at which

the SAR distribution changes in the  direction [Fig. 7(a)].

The two distinct hot spots in the SAR distribution are directly

adjacent to the central region of low SAR and are diametrically

opposite to each other along the axis. These local peaks in the

SAR are attributed to the sharp edges of the central BSS flow

channel through the dental putty, which ends and restarts above

and below the glass fiber filter (Fig. 2). These results suggest that

tapering the flow channel or reducing its diameter should greatly

reduce the inhomogeneities. This has been borne out for the

case where the XFDTD model used a smaller channel diameter.

Thus, a minor modification of the original design of the cell

perfusion apparatus can significantly increase the homogeneity

of the SAR.

In this orientation, even though the glass fiber filter is at

the location of maximum inductive coupling, the SAR values

predicted by XFDTD were extremely low, on the order of

Fig. 7.  (a) Contour and (b) surface plot of the SAR distribution across the

10  W/kg across the filter. The overall SAR on the filter is

glass fiber filter (location of chromaffin cells) computed by XFDTD for the

small due to two contributing factors: 1) the low value of the

perpendicular orientation. Cell perfusion apparatus is at the maximum in  of

W, frequency

GHz.

the standing wave pattern. Forward power

field at the maximum of

in the standing wave pattern

field, being normal to the plane of the filter,

and 2) the

results in little coupling, as governed by boundary conditions.

center. Because homogeneity was not to within 30%, this orien-

Furthermore, the  field induced by  in the glass fiber filter

tation would not be acceptable for use in the experiments.

was small because the conductivity of the BSS saturated filter

2) SAR Distribution With the Cell Perfusion Chamber at the

Field Maximum:

was small (Table I). The overall shape of the SAR distribution

a) Perpendicular orientation: When the cell perfusion

field

across the filter was, therefore, similar to that of the

induced by  . From these results, the conclusion is that the

apparatus is oriented such that the plane of the glass fiber

filter is perpendicular to  , the SAR distribution across the

SAR is low but that the homogeneity achieved is to within 30%

filter shows dramatic differences (results not shown) that also

over 65% of the filter surface during exposure of the cells in the

preclude this orientation from being used in experiments. The

perpendicular orientation.

SAR is mainly concentrated at a small central region of the

b) Parallel orientation: Computation of the SAR distri-

filter. This region has a peak value of 14 W/kg that is due to

bution across the glass fiber filter for the parallel orientation re-

field into the BSS flow channel

the strong coupling of the

sulted in higher SAR values but with less homogeneity (results

located above and below the filter. The rest of the filter has a

not shown). In accordance with what would be expected from

SAR on the order of 0.001 W/kg. These results also are what

boundary conditions, there were distinct maxima and minima

along the  and  axes, respectively. Moving toward the center

would be expected from boundary conditions.

of the filter, where the main contribution to the SAR is due to

b) Parallel orientation: When the cell perfusion appa-

the  field that is tangential to the plane of the filter, the  field

ratus is oriented such that the plane of the filter is parallel to  ,

decreased progressively, reaching a value of almost zero at the

the SAR distribution over the region of the glass fiber filter is