"Radiofrequency-Field Exposure Facility

Two different exposure systems were used during the course of the study: a system designed to simulate a far-field exposure condition during the last 4 days of pregnancy through weaning of the pups at 23 6 2 days old and a near-field, principally head-only exposure system used from day 35 (of age) through 2 years. The exposure systems used in these studies at 1.62 GHz were based on proven designs used for similar studies at 836.55 MHz (6). However, some modifications to the exposure chamber, electronic components, and restraint system were made to achieve the required SAR values at 1.62 GHz as well as to facilitate animal handling and reduce the cost of equipment. The Iridium signal modulation uses differentially encoded quaternary phase shift keying (DEQPSK), a frame length of 90 ms with 11 data slots per frame [For more information on digital telephony signal transmission formats, see ref. (21)]"

"1. Simulated far-field system

The design for simulated far-field prenatal and neonatal exposure at 1.62 GHz used a horizontal beam orientation in a flared plate design to produce an SAR of 0.16 W/kg in the brains of rat fetuses in the pregnant dams (22). The parallel-plate enclosure was 2.48 m long and was lined with copper foil on the top and bottom plates. The sides of the plate system were covered with pyramidal anechoic material as described (22). Animal cages were located approximately 12 wavelengths from the source in a 1.45 3 2.40 3 1.60-m box covered on five of the interior walls with pyramidal (normal to the wavefront) or grooved (parallel to the wavefront) anechoic material. The cages were placed with their front surfaces in the plane of the parallel plate aperture, with 18 standard rat cages (45.7 3 24.1 3 20.3 cm) arranged in three rows of six cages per row. RF illumination (23 dB beam width) at the cage position provided exposure in an area 2.11 3 1.11 m, with a uniformity of better than 62.6 dB. A Motorola Iridium source operating at 1.62 GHz was used to control a preamplifier and signal generator (HP 8780A Vector, Hewlett Packard, Cupertino, CA). RF-field power was fed to the parallel-plate enclosure by a coaxial to waveguide adapter (WR-510) that provided for illumination of the 18 animal cages at a distance of 3 to 3.5 m from the antenna. Power for the exciter was provided by a 400-W linear power amplifier (Microwave Power Equipment, Inc., Brentwood, NY). Forward power and voltage standing wave ratio (VSWR) was monitored by a power meter (HP E4418B) and power sensor (HP 8481H) connected to the coupled output of the directional coupler. A sham system was also constructed for sham exposure. The sham system was installed in an adjoining room.

During the short far-field exposure portion of the study, animals in field exposure groups were exposed at a calculated brain SAR of 0.16 W/kg. In the subsequent (near-field exposure) portion of the study, these two groups were separated, with one receiving 1.6 W/kg and the other receiving 0.16 W/kg. The use of the lower SAR for both groups during the far-field exposure was due to the limited power capacity of the farfield 400-W amplifier. During the far-field exposure portion of the study, the groups were not exposed in a blinded fashion. However, the animal groups were coded after the far-field exposure so that the near-field exposure and sham exposure was truly blind."

"Exposure Monitoring and Control

A computer-control system was used to monitor system performance and to record and store observations from the study. Interfacing of the exposure system to the computers was accomplished through National Instruments (Austin, TX) LabView Field Point equipment. This reliable modular interface system provided for multiplexing of input signals, analog to digital input data, as well as digital to analog conversion of control signals. The system automated data collection and recording and eliminated the need for strip chart recording and multiplexer use. In addition to the field sensors installed to sense and allow adjustment of the exposure fields, three other sensors are monitored by the data acquisition unit every 6 min. Identical combination temperature and relative humidity sensors (Omega Engineering, Model HX93V) were installed in the exposure and animal home cage rooms.

1. a.c. magnetic-field measurements

The a.c. magnetic-field flux density was determined at each carousel position in the animal exposure room (Room 194) using the three-axis EMDEX II (Enertech, Campbell, CA) magnetic-field meter. RF fields were energized during the measurements. The EMDEX II device has a detection limit of 1 mT and a 1-mT measurement resolution. The EMDEX II was used in the broadband mode that measures flux density in the frequency range between 40 Hz and 800 Hz. The a.c. magnetic fields at all but four carousel positions were determined to be nominally 1 mT.

2. Static (d.c.) magnetic-field measurements

The d.c. (geomagnetic) field measurements were made using the Bartington three-axis probe and pre-amplifier system at 14 positions in the exposure room (Room 194) and seven positions in the animal housing room (Room 192). The average d.c. RMS magnetic-field flux densities were 413 and 434 mT in the two rooms, respectively."

"Timed-pregnant rats were procured and palpated for pregnancy status. Thirty-six rats were randomly assigned to each of three treatments based on body weight and pregnancy status. Two groups were exposed to the far-field signal in a flared parallel-plate exposure system (22) at a nominal SAR of 0.16 W/kg. A third group was sham-exposed in a similar nonenergized system."

"To minimize the effect of any subtle variation in environmental factors in the animal room, such as temperature or light intensity, animal cages were rotated weekly within each rack and each rack was rotated within the room. To minimize any potential location or system differences during far-field exposure, the location of cages within the exposure system was rotated each week. During near-field exposures, rats were rotated through the six different carousel positions of the zone. In addition, the exposure time was rotated weekly through the three daily 2-h exposure shifts to randomize any potential effects due to time of day of exposure. The exposure groups were color coded so that study personnel did not know the exposure groupings during the study. The code was broken only after the pathology evaluation was complete."

P0, Fischer 344 rats, female - 2xFar-Field, Sham, Shelf Control

HAWC