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

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Fig. 2.  Computer-generated drawing (SolidWorks, Concord, MA) of (top)

the cell perfusion apparatus showing (bottom) an exploded view of the filter

holder and its components. Component manufacturers and dielectric properties

are listed in Table I.

amount of catecholamine released by high-performance liquid

Fig. 1. Photographs of (a) RF/MW exposure system for experiments

conducted at the  field maximum of the standing wave pattern and (b) a close

chromatography. During experiments, the temperature of the

up of the cell perfusion apparatus.

BSS entering and exiting the cell perfusion apparatus as well as

the ambient temperature inside the waveguide is monitored and

logged continuously by a fluoroptic thermometer3 interfaced to

et al. [14], are immobilized on a filter within a plastic filter

a computer.

holder to allow continuous perfusion of the cells with a bal-

anced salt solution (BSS). The cell perfusion apparatus, which

B. Waveguide Exposure Setup

is constructed entirely of nonmetallic components, is placed in

a waveguide (Fig. 1). The specific components of the cell per-

The exposure system is based on a WR-975 rectangular wave-

fusion apparatus include: a Millipore Swinnex filter holder, two

guide4 terminated with a shorting plate5 at one end to create a

Luer injection fittings, silicone rubber tubing, and a Plexiglas

standing wave. The other end is connected to a computer-con-

stand (Fig. 2). Inside the filter holder are three nylon filters sand-

trolled RF/MW signal generator6 and amplifier7 via a coax-to-

wiching a single glass fiber filter on which the chromaffin cells

waveguide adapter8 containing a probe launch (Figs. 1 and 3). A

are located. The two halves of the filter holder, each with a sili-

circulator9 is inserted between the amplifier and the waveguide

cone rubber gasket, screw into each other, thereby compressing

to reroute the reflected power to a 50- load. A wattmeter10 pro-

the filters. However, there is sufficient separation between the

vides an indication of both forward and reflected power with a

two sections of the filter holder so that once loaded onto the

manufacturer-specified accuracy of 5%.

glass fiber filter, the chromaffin cells are not crushed and the

The aluminum waveguide has undergone a chromate conver-

BSS spreads out uniformly across the entire filter during perfu-

sion process to prevent corrosion. It is equipped with rectangular

sion. Dental putty fills the dead space of each side of the filter

nonradiating slots (2.54  0.95 cm) at the top, bottom, and sides

holder, leaving only a central flow channel having a diameter of

through which perfusion tubing and temperature probes gain

1.8 mm for the BSS to pass through. A Luer injection fitting at

access. The distances of the slots from the shorting plate were

both the top and bottom of the filter holder allows entry of fluo-

carefully designed for positioning the cell perfusion apparatus

roptic temperature probes1 into the BSS flow path at each point.

at either the  field or magnetic flux density

maxima in the

For the experiments, 4­8 million chromaffin cells are gravity

frequency range of interest (0.75­1.12 GHz). With this design,

fed onto the glass fiber filter located in the filter holder. Then,

a specific pair of top and bottom slots can be used to insert the

they are perfused with temperature-controlled (36 C) BSS at

3Luxtron

model 790, Santa Clara, CA.

a flow rate of 1.2 ml/min. A fraction of the effluent runs into a

4Space

Machine & Engineering Corporation, St. Petersburg, FL.

computer-interfaced electrochemical detector2 for online mon-

5Space Machine & Engineering Corp.

itoring of catecholamine release. The remaining effluent flows

6Agilent model 8648A, Palo Alto, CA.

into a fraction collector for later quantification of the precise

7Instruments for Industry model SMV300, Ronkonkoma, NY.

8Space Machine & Engineering Corp.

1Luxtron

9UTE Microwave model CT-1541-N, Asbury Park, NJ.

model SFW-2, Santa Clara, CA.

2Bioanalytical

10Bird Electronics model 4931A, Cleveland, OH.

Systems model LC4C, West Lafayette, IN.