HAGAN et al.: NOVEL WAVEGUIDE-BASED RF/MW EXPOSURE SYSTEM FOR STUDYING NONTHERMAL EFFECTS

1675

IV. CONCLUSION

A novel system for the in vitro exposure of chromaffin cells

for identifying RF/MW field effects on neurotransmitter release

has been designed. The combination of a standard waveguide

and a cell perfusion apparatus constructed of nonmetallic mate-

rials allows online monitoring of catecholamine release during

RF/MW exposure. A detailed characterization of this exposure

system using the FDTD method has allowed estimation of the

optimal design of exposure procedures that will provide the

most homogeneous SAR over the region containing the cells.

field max-

Positioning the cell perfusion chamber at the

imum provides a higher SAR than that which can be achieved

at the maximum of  for a given net input power into the wave-

guide. However, acceptable homogeneity is achieved only when

the  field is parallel to the plane of the glass fiber filter. These

modeling results clearly indicate that the orientations of the

plane of the glass fiber filter and the narrow BSS channel with

respect to the  field direction in the waveguide are strong fac-

tors in determining not only the magnitude of the SAR but also

its distribution in the region of the glass fiber filter.

In actual experiments, it will not be possible to control the

distribution of the cells on the glass fiber filter. However, the

FDTD results enable precise determinations of where field en-

hancements (electrical hot spots) occur. Knowing their locations

is important for two reasons. First, steps can be taken to mini-

mize them. For example, hot spots in SAR created by the exis-

tence of sharp corners and edges in the BSS flow channel in the

vicinity of the glass fiber filter can perhaps be greatly minimized

by modifying the geometry of the junction of the flow channel

in this region. Second, interpreting the outcomes of experiments

using the predicted knowledge of SAR distributions over the

filter will be facilitated. Because the location of the cells on the

glass fiber filter can be determined at the end of an experiment

by staining the cells with the dye neutral red, the magnitude of

Fig. 8. (a) Contour and (b) surface plot of the SAR distribution across the

any changes in catecholamine release can be correlated with the

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

density of cells in regions of high SAR.

parallel orientation. Cell perfusion apparatus is at the

field maximum.

Forward power

W, frequency

GHz.

ACKNOWLEDGMENT

The authors would like to thank M. Trakas, R. Dopf, and

fairly uniform (except for a very small region at the center) in

D. Bhakta for assistance in characterizing the different compo-

a large part of the filter (Fig. 8). The two electrical hot spots

nents of the cell perfusion apparatus. They also acknowledge

adjacent to the central region once again coincide with the loca-

the technical support of R. Brourman, Dr. R. Luebbers, and

tion of the narrow BSS flow channel joining the filter section of

C. Penney of REMCOM, Inc.

the cell perfusion apparatus. Thus, the SAR distribution has a

striking resemblance to that obtained when the glass fiber filter

is placed at the maximum in  with the  field perpendicular

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