Simulation Aids First Online Monitoring of

Simulation Aids

(continued)

approximated as a solid dielectric. The default time step was

being used in

2.0964 picoseconds in the main grid and 0.420 picoseconds in

experiments. The

the subgrid. Each simulation ran for 9550 time steps.

parallel orientation,

on the other hand,

provides two orders

Validating the Model

of magnitude larger

SAR than when

To test the validity of the XFDTD model, the numerically

the filter is located

computed electric field (E) and magnetic flux density (B) within

at the B field

the waveguide, with the cell perfusion apparatus removed,

maximum. This is

were compared

because the E field

with well-known

is much stronger

waveguide theory

in this orientation

based on measured

and the E field is

values of forward and

Distribution of the Specific Absorption

coupled into the

reflected power. The

Rate in Watts/kg in the region containing

filter according

magnitudes of E and

the biological cells. Here the biological

to the tangential

B at their maxima

cells were assumed to be evenly

boundary

in the standing

distributed over the entire glass fiber

condition. In

wave pattern in

filter. Results are from XFDTD for an input

this orientation,

the waveguide at

power of 0.5W into the waveguide and

homogeneity

a frequency of 1

a frequency of 1 GHz, and are imported

within 30% is

GHz showed good

into SigmaPlot for plotting and analysis.

achieved over

agreement for

83% of the filter

forward powers in

area. The simulation demonstrated that this configuration

the range 0.5-5 W,

and this configuration alone provides the high and consistent

with a maximum

SAR needed to evaluate the exposure of chromaffin cells for

Numerical mesh of the cell perfusion

difference of 8.5%.

identifying RF

apparatus created by XFDTD.

This difference can

field effects on

likely be attributed

catecholamine

to the fact that the computations based on waveguide

release. The

theory utilized values of power measured by a wattmeter

simulation also

having a manufacturer specified accuracy of 5% and that the

provided detailed

waveguide theory computations did not take into account field

SAR values

disturbances caused by the probe launch and waveguide slots.

over the filter.

Knowing the

Determining the Optimal Cell

SAR distribution,

Perfusion Apparatus Position and

together with

Orientation

ability to

determine the

The next step was simulating the waveguide with the cell

location of cells

perfusion apparatus in order to determine a position and

on the glass fiber

orientation for the RF exposure of the cells. The researchers

filter at the end

Figure 5: Distribution of the Specific

first used XFDTD to predict SAR distribution with the cell

of the experiment

Absorption Rate in Watts/kg in the region

perfusion chamber located at the maximum in B. This

by staining the

containing the biological cells. Here the

position with the E field perpendicular to the plane of the

cells with a

same number of biological cells as used in

glass filter provided a very low SAR, on the order of 10-2 W/kg

dye , provides

generating the results shown in Figure 4 were

across the filter. The overall SAR on the filter is small because

the researchers

assumed to be evenly distributed over a small

of the low value of the E field at the maximum of B in the

with important

circular region of diameter 1 cm at the center

standing wave pattern and the E field, being normal to the

information to

of the glass fiber filter. Results are directly

plane of the filter, provides little coupling. Computation of

interpret their

plotted in XFDTD for an input power of 0.5W

the SAR distribution across the filter with the E field parallel

experimental

into the waveguide and a frequency of 1 GHz.

to the plane of the glass fiber showed higher SAR values but

results.

with relatively higher variation of SAR within the filter.

1. T. Hagan, I. Chatterjee, D. McPherson and G.L. Craviso, "A Novel

Researchers next changed the XFDTD model to position the

Waveguide-based Radio frequency/microwave Exposure System for

cell perfusion chamber at the E field maximum. When the

Studying Nonthermal Effects on Neurotransmitter Release Finite-

cell perfusion apparatus was oriented so that the filter was

difference Time-domain Modeling," IEEE Transactions on Plasma Science,

perpendicular to E, the SAR distribution showed dramatic

Vol. 32, August 2004, pp. 1668-1676.

differences that also precluded this configuration from

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