Study type: Medical/biological study (experimental study)

Characteristics of microwave evoked body movements in mice med./bio.

By: Brown DO, Lu ST, Elson EC
Published in: Bioelectromagnetics 1994; 15 (2): 143-161
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Aim of study (acc. to editor)

To study microwave evoked body movements in mice.

Endpoint

Exposure

Exposure Parameters
Exposure 1: 1.25 GHz
Modulation type: pulsed
Exposure 2: 1.25 GHz
Modulation type: pulsed
Exposure 3: 1.25 GHz
Modulation type: pulsed
Exposure 4: 1.25 GHz
Modulation type: pulsed
Exposure 5: 1.25 GHz
Modulation type: pulsed
Exposure 6: 1.25 GHz
Modulation type: single pulse
Exposure 7: 1.25 GHz
Modulation type: single pulse
Exposure 8: 1.25 GHz
Modulation type: single pulse
Exposure 9: 1.25 GHz
Modulation type: single pulse
Exposure 10: 1.25 GHz
Modulation type: single pulse
Exposure 11: 1.25 GHz
Modulation type: single pulse

General information

Twelve different MW events including sham were tested in two series of experiments. The first series was designed to compare the twofold increase in the response rate (evoked body movements) by pulsed to gated CW (single pulse) MW (E1, E2, E3, E6, E7, E8). The second series was designed to supplement and to expand the dose-response curve of the first series (E4, E5, E9, E10, E11, and sham). Each mouse was exposed in three sessions, at least 24 h apart. Each session comprised six consecutive randomised MW events, the testing period for each event lasting 15 s. To evaluate thermal stimulation and hyperthermia, rectal and four subcutaneous cranial temperatures were measured in an anaesthetised mouse for five different MW exposures (E4, E5, E9, E10, E11) and eight replications. Positive controls were performed using 100-ms acoustic (104 dB SPL, 2.5-25 kHz noise) and tactile (40 psi air puff) stimuli using a procedure similar to the MW exposure.

Exposure 1

Main characteristics
Frequency 1.25 GHz
Type
Charakteristic
  • guided field
Modulation
Modulation type pulsed
Pulse width 10 µs
Repetition frequency 80 Hz
Additional info

train of 2 pulses and 25 ms duration
Exposure setup
Exposure source
Setup A mouse holder (10-cm metal tube with 2.5-cm acrylic liner) with a protruding nose cone was attached from outside to the center of the end-wall.
Parameters
Measurand Value Type Method Mass Remarks
power 200 kW peak value measured - -
power 160 W mean measured - -
SA 0.29 kWs/kg mean measured - mid-brain average
SA 0.18 kWs/kg mean calculated whole body dose 4 J
Additional parameter details

The tuning of the cavity was optimised for the pulsed MW source impedance. Therefore, two different mid-brain SAR values were used for the pulsed (73.7 W/kg per W) and the gated CW (96.0 W/kg per W) MW.

Measurement and calculation details

Incident and reflected powers were measured using crystal detectors and an oscilloscope. A network analyser was used for daily system calibration. The low-Q cavity was tuned for minimum reflection (-10 to -15 dB) before each series of experiments and daily in two steps using a 20-g muscle phantom and a live mouse. Local SAR was determined by a thermometric method inserting the temperature probe into the brain. The whole-body average SAR was calculated from the incident power and the body weight of the mouse resulting in an over-estimation due to the return loss (3-10%) and waveguide absorption (10-20%).

Exposure 2

Main characteristics
Frequency 1.25 GHz
Type
Charakteristic
  • guided field
Modulation
Modulation type pulsed
Pulse width 10 µs
Repetition frequency 80 Hz
Additional info

train of 4 pulses and 50 ms duration
Exposure setup
Exposure source
Parameters
Measurand Value Type Method Mass Remarks
power 200 kW peak value measured - -
power 160 W mean measured - -
SA 0.59 kWs/kg mean measured - mid-brain average
SA 0.36 kWs/kg mean calculated whole body dose 8 J

Exposure 3

Main characteristics
Frequency 1.25 GHz
Type
Charakteristic
  • guided field
Modulation
Modulation type pulsed
Pulse width 10 µs
Repetition frequency 80 Hz
Additional info

train of 8 pulses and 100 ms duration
Exposure setup
Exposure source
Parameters
Measurand Value Type Method Mass Remarks
power 200 kW peak value measured - -
power 160 W mean measured - -
SA 1.18 kWs/kg mean measured - mid-brain average
SA 0.73 kWs/kg mean calculated whole body dose 16 J

Exposure 4

Main characteristics
Frequency 1.25 GHz
Type
Charakteristic
  • guided field
Modulation
Modulation type pulsed
Pulse width 10 µs
Repetition frequency 80 Hz
Additional info

train of 16 pulses and 200 ms duration
Exposure setup
Exposure source
Parameters
Measurand Value Type Method Mass Remarks
power 200 kW peak value measured - -
power 160 W mean measured - -
SA 2.36 kWs/kg mean measured - mid-brain average
SA 1.45 kWs/kg mean calculated whole body dose 32 J

Exposure 5

Main characteristics
Frequency 1.25 GHz
Type
Charakteristic
  • guided field
Modulation
Modulation type pulsed
Pulse width 10 µs
Repetition frequency 80 Hz
Additional info

train of 160 pulses and 2000 ms duration
Exposure setup
Exposure source
Parameters
Measurand Value Type Method Mass Remarks
power 20 kW peak value measured - -
power 16 W mean measured - -
SA 2.36 kWs/kg mean measured - mid-brain average
SA 1.45 kWs/kg mean calculated whole body dose 32 J

Exposure 6

Main characteristics
Frequency 1.25 GHz
Type
Charakteristic
  • guided field
Modulation
Modulation type single pulse
Pulse width 50 ms
Additional info

gated CW (wide pulse)
Exposure setup
Exposure source
Parameters
Measurand Value Type Method Mass Remarks
power 160 W peak value measured - -
power 160 W mean measured - -
SA 0.77 kWs/kg mean measured - mid-brain average
SA 0.36 kWs/kg mean calculated whole body dose 8 J
Measurement and calculation details

Incident and reflected powers were measured using power sensors and power meters.

Exposure 7

Main characteristics
Frequency 1.25 GHz
Type
Charakteristic
  • guided field
Modulation
Modulation type single pulse
Pulse width 100 ms
Additional info

gated CW (wide pulse)
Exposure setup
Exposure source
Parameters
Measurand Value Type Method Mass Remarks
power 160 W peak value measured - -
power 160 W mean measured - -
SA 1.54 kWs/kg mean measured - mid-brain average
SA 0.73 kWs/kg mean calculated whole body dose 16 J

Exposure 8

Main characteristics
Frequency 1.25 GHz
Type
Charakteristic
  • guided field
Modulation
Modulation type single pulse
Pulse width 200 ms
Additional info

gated CW (wide pulse)
Exposure setup
Exposure source
Parameters
Measurand Value Type Method Mass Remarks
power 160 W peak value measured - -
power 160 W mean measured - -
SA 3.07 kWs/kg mean measured - mid-brain average
SA 1.45 kWs/kg mean calculated whole body dose 32 J

Exposure 9

Main characteristics
Frequency 1.25 GHz
Type
Charakteristic
  • guided field
Modulation
Modulation type single pulse
Pulse width 200 ms
Additional info

gated CW (wide pulse)
Exposure setup
Exposure source
Parameters
Measurand Value Type Method Mass Remarks
power 98.6 W peak value measured - -
power 98.6 W mean measured - -
SA 1.89 kWs/kg mean measured - mid-brain average
SA 0.9 kWs/kg mean calculated whole body dose 19.7 J

Exposure 10

Main characteristics
Frequency 1.25 GHz
Type
Charakteristic
  • guided field
Modulation
Modulation type single pulse
Pulse width 800 ms
Additional info

gated CW (wide pulse)
Exposure setup
Exposure source
Parameters
Measurand Value Type Method Mass Remarks
power 28.6 W peak value measured - -
power 28.6 W mean measured - -
SA 2.2 kWs/kg mean measured - mid-brain average
SA 1.03 kWs/kg mean calculated whole body dose 22.7 J

Exposure 11

Main characteristics
Frequency 1.25 GHz
Type
Charakteristic
  • guided field
Modulation
Modulation type single pulse
Pulse width 3,200 ms
Additional info

gated CW (wide pulse)
Exposure setup
Exposure source
Sham exposure A sham exposure was conducted.
Parameters
Measurand Value Type Method Mass Remarks
power 7.2 W peak value measured - -
power 7.2 W mean measured - -
SA 2.21 kWs/kg mean measured - mid-brain average
SA 1.05 kWs/kg mean calculated whole body dose 23 J

Exposed system:

Methods Endpoint/measurement parameters/methodology

Investigated system:
Time of investigation:
  • during exposure

Main outcome of study (acc. to author)

No difference in response to pulsed and gated continuous wave stimuli of equal average power was observed.
The incidence of evoked body movements increased proportionally with specific absorption when the whole-body average specific absorption rate (SAR) was at a constant level (7300 W/kg). Under a constant average specific absorption rate, the response incidence reached a plateau at 0.9 kJ/kg. For higher doses (than 0.9 kJ/kg), response incidence was proportional to the specific absorption rate and reached a plateau at 900 W/kg.
Body movements could be evoked by a single microwave pulse.
The lowest whole-body specific absorption investigated was 0.18 kJ/kg, and the corresponding brain specific absorption was 0.29 kJ/kg. Bulk heating potentials of these specific absorptions were less than 0.1°C. For doses higher than 0.9 kJ/kg, the response incidence was also proportional to subcutaneous heating rate. The extrapolated absolute thresholds (0% incidence) were 1.21°C temperature increment and 0.24°C/s heating rate.
Data of this study should be considered in promulgation of personnel protection guideline against high peak power but low average power microwaves.

Study character:

Study funded by