The effects of exposure to extremely low frequency magnetic fields on magnetophosphene perceptions should be investigated.
A total of 81 volunteers (18-55 years) were divided into the following groups: exposure to a magnetic field of 1) 20 Hz (n=20), 2) 50 Hz (n=21), 3) 60 Hz (n=20) and 4) 100 Hz (n=20). Each subject was tested in 11 exposure periods. The magnetic flux density ranged from 0 to 50 mT with 5 mT increments, and each exposure period was followed by 5 seconds of rest without exposure. The order of the exposures was randomly assigned by a computer program. The volunteers were sitting in the dark (adaptation time = 5 min) with eyes closed and they used a button-press to report magnetophosphene perception.
| Exposure | Parameters |
|---|---|
|
Exposure 1:
20 Hz
Exposure duration:
11 x 5 seconds
|
|
|
Exposure 2:
50 Hz
Exposure duration:
11 x 5 seconds
|
|
|
Exposure 3:
60 Hz
Exposure duration:
11 x 5 seconds
|
|
|
Exposure 4:
100 Hz
Exposure duration:
11 x 5 seconds
|
|
| Frequency | 20 Hz |
|---|---|
| Type | |
| Exposure duration | 11 x 5 seconds |
| Exposure source | |
|---|---|
| Chamber | participants were sitting in the dark (adaptation time = 5 min) with the eyes closed |
| Setup | exposure system consisted of two 99-turn coils (11 turns of 9 layers), made with square copper wire cooled with circulating water, the coils had a 356 mm inner diameter and a 501 mm outer diameter and were arranged in a Helmholtz coil-like manner, enabling the generation of a homogenous MF (± 5%) over the head; a motorized non-magnetic lift enabled vertical movement of the coil system such that the participant's eyes could be centered between the coils |
| Measurand | Value | Type | Method | Mass | Remarks |
|---|---|---|---|---|---|
| magnetic flux density | 0 mT | effective value | measured | - | lowest magnetic flux density |
| magnetic flux density | 50 mT | effective value | measured | - | highest magnetic flux density |
| Frequency | 50 Hz |
|---|---|
| Type | |
| Exposure duration | 11 x 5 seconds |
| Exposure source |
|
|---|
| Measurand | Value | Type | Method | Mass | Remarks |
|---|---|---|---|---|---|
| magnetic flux density | 0 mT | effective value | measured | - | lowest magnetic flux density |
| magnetic flux density | 50 mT | effective value | measured | - | highest magnetic flux density |
| Frequency | 60 Hz |
|---|---|
| Type | |
| Exposure duration | 11 x 5 seconds |
| Exposure source |
|
|---|
| Measurand | Value | Type | Method | Mass | Remarks |
|---|---|---|---|---|---|
| magnetic flux density | 0 mT | effective value | measured | - | lowest magnetic flux density |
| magnetic flux density | 50 mT | effective value | measured | - | highest magnetic flux density |
| Frequency | 100 Hz |
|---|---|
| Type | |
| Exposure duration | 11 x 5 seconds |
| Exposure source |
|
|---|
| Measurand | Value | Type | Method | Mass | Remarks |
|---|---|---|---|---|---|
| magnetic flux density | 0 mT | effective value | measured | - | lowest magnetic flux density |
| magnetic flux density | 50 mT | effective value | measured | - | highest magnetic flux density |
Results showed frequency-dependent thresholds for initial perception of 2.51 T/s at 20 Hz (group 1), 6.28 T/s at 50 Hz (group 2), 7.54 T/s at 60 Hz (group 3), and 12.57 T/s at 100 Hz (group 4) and for the 50% detection rate 4.73 T/s at 20 Hz, 8.83 T/s at 50 Hz, 10.55 T/s at 60 Hz, and 33.46 T/s at 100 Hz.
The authors conclude that magnetophosphene perception sensivity was greater at lower frequencies of magnetic field exposure.
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