Study type: Medical/biological study (experimental study)

Thresholds of microwave-evoked warmth sensations in human skin med./bio.

By: Blick DW, Adair ER, Hurt WD, Sherry CJ, Walters TJ, Merritt JH
Published in: Bioelectromagnetics 1997; 18 (6): 403-409
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Aim of study (acc. to author)

To measure thresholds for microwave-evoked skin sensations of warmth at five different frequencies (2.45, 7.5, 10, 35, and 94 GHz). In the same subjects, thresholds of warmth evoked by infrared radiation were also measured for comparison.

Endpoint

Exposure

Exposure Parameters
Exposure 1: 2.45 GHz
Exposure duration: intermittent: 10 s exposure in 1 min intervalls
Exposure 2: 7.5 GHz
Exposure duration: intermittent: 10 s exposure in 1 min intervalls
Exposure 3: 10 GHz
Exposure duration: intermittent: 10 s exposure in 1 min intervalls
Exposure 4: 35 GHz
Exposure duration: intermittent: 10 s exposure in 1 min intervalls
Exposure 5: 94 GHz
Exposure duration: intermittent: 10 s exposure in 1 min intervalls

General information

additional experiments were done with infrared irradiation of 0 - 30 mW/cm²

Exposure 1

Main characteristics
Frequency 2.45 GHz
Type
Charakteristic
Exposure duration intermittent: 10 s exposure in 1 min intervalls
Exposure setup
Exposure source
Distance between exposed object and exposure source 0.84 m
Chamber 90 cm x 90 cm x 180 cm testing chamber consisting of 5 cm thick polystyrene sheets placed inside an anechoic chamber
Setup MW or IR applied through a circular aperture in one wall with a diameter of 20.4 cm; long axis of the test peron parallel to the E-vector of the electromagnetic field
Sham exposure A sham exposure was conducted.
Parameters
Measurand Value Type Method Mass Remarks
power 500 W maximum calibration - -
power density 63.1 mW/cm² spatial average measured - ± 6.7 mW/cm²

Exposure 2

Main characteristics
Frequency 7.5 GHz
Type
Charakteristic
Exposure duration intermittent: 10 s exposure in 1 min intervalls
Exposure setup
Exposure source
Distance between exposed object and exposure source 570 mm
Sham exposure A sham exposure was conducted.
Parameters
Measurand Value Type Method Mass Remarks
power 300 W maximum calibration - -

Exposure 3

Main characteristics
Frequency 10 GHz
Type
Charakteristic
Exposure duration intermittent: 10 s exposure in 1 min intervalls
Exposure setup
Exposure source
Distance between exposed object and exposure source 720 mm
Sham exposure A sham exposure was conducted.
Parameters
Measurand Value Type Method Mass Remarks
power 250 W maximum calibration - -

Exposure 4

Main characteristics
Frequency 35 GHz
Type
Charakteristic
Exposure duration intermittent: 10 s exposure in 1 min intervalls
Exposure setup
Exposure source
Distance between exposed object and exposure source 2 m
Sham exposure A sham exposure was conducted.
Parameters
Measurand Value Type Method Mass Remarks
power 70 W maximum calibration - -

Exposure 5

Main characteristics
Frequency 94 GHz
Type
Charakteristic
Exposure duration intermittent: 10 s exposure in 1 min intervalls
Exposure setup
Exposure source
Distance between exposed object and exposure source 2 m
Sham exposure A sham exposure was conducted.
Parameters
Measurand Value Type Method Mass Remarks
power 50 W maximum calibration - -
power density 4.5 mW/cm² spatial average measured - +/- 0.6 mW/cm²

Exposed system:

Methods Endpoint/measurement parameters/methodology

Investigated system:
Time of investigation:
  • during exposure

Main outcome of study (acc. to author)

Sensitivity increased monotonically with frequency throughout the range of microwave frequencies tested. The threshold at 94 GHz (4.5 +/- 0.6 mW/cm²) was more than an order of magnitude less than at 2.45 GHz (63.1 +/- 6.7 mW/cm²), and it was comparable to the threshold for infrared radiation (5.34 +/- 1.07 mW/cm²).

Study character:

Study funded by