To study the application of Higuchi's fractal dimension as a nonlinear measure to evaluate the effect of external periodic stressor (microwave exposure) on electrical oscillations in the brain of 14 participants (2124 years old, seven males, seven females).
Exposure  Parameters 

Exposure 1:
450 MHz
Modulation type:
pulsed
Exposure duration:
1 min on  1 min off, for 10 cycles (20 min)


Frequency  450 MHz 

Type  
Exposure duration  1 min on  1 min off, for 10 cycles (20 min) 
Modulation type  pulsed 

Duty cycle  50 % 
Repetition frequency  40 Hz 
Measurand  Value  Type  Method  Mass  Remarks 

power density  0.16 mW/cm²  spatial average  estimated    +/ 0.02 at the left side of the head 
power density  0.025 mW/cm²  spatial average  estimated    +/ 0.01 at the right side of the head 
power density  0.08 mW/cm²  spatial average  estimated    +/ 0.01 above the head 
power density  0.8 mW/cm²  spatial average  estimated    +/ 0.2 at the left side of the neck and the left shoulder 
power density  0.03 mW/cm²  spatial average  estimated    +/ 0.01 at the right side of the neck and the right shoulder 
SAR  0.303 W/kg  peak value  calculated  1 g   
The data of fractal dimension values averaged over a group detected a small (12%) but statistically significant increase with exposure in all EEG channels. The fractal dimension was increased for 12 participants, decreased for one, and was constant for one subject. The fractal dimension showed the most remarkable effect in temporal and parietal regions of the left hemisphere where the microwave field was maximal. Changes of fractal dimension in these regions of the right hemisphere were much higher than expected in accordance with the electromagnetic field distribution.
In conclusion, the data showed that the weak periodic electromagnetic field exposure caused an increase of fractal dimension of the recorded EEG signals. The effect was mild but statistically significant in all EEG channels.
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