Exposure to magnetic fields during a car journey
Comparison of exposure levels to the magnetic field before and after demagnetization of a vehicle’s tyres.
A few reminders about low frequency electromagnetic pollution when travelling by car
As soon as the motor is turned on, the driver as well as the front passenger are submitted to a weak intensity magnetic field which comes from the alternator. But then the vehicle’s speed will considerably increase the magnetic field, and this is the reason :
1// The alternator
As soon as the motor is turned on, the alternator continually produces a low frequency magnetic field. It produces a current which powers the vehicle’s electric circuits and recharges the battery. This pollution is practically constant whatever the speed of the motor. It normally only concerns the driver and the front passenger, the back-seat passengers are sufficiently far enough away from the alternator.
Warning: The batteries of some vehicle models are situated at the back at the level of the boot. As soon as the motor is turned on, the alternator which is at the front of the vehicle, permanently recharges the battery situated at the back. High intensity electric currents are permanently circulating from the front to the back, which in consequence generates very high-level magnetic fields of several thousand, or tens of thousands, of nT at the level of the seats both in the front and in the back.
Attention: some vehicle models have the battery integrated under the driver’s seat.
2// The tyres
They are by far the most important source of magnetic field radiation in the vehicle and this, as soon as you start moving. The tyres are equipped with steel reinforcements (ferromagnetic materials) which are magnetized during the manufacturing process. The turning of the wheel therefore produces a magnetic field of which the intensity strongly increases with speed. The magnetic field’s frequency is proportionate to the speed of the wheels (around 16 Hz at 130 Km/h). It is an intense source of magnetic field for the back-seat passengers. The back-seat passengers are effectively situated next to the back wheels where the magnetic field levels measured are extremely high (up to 6000 nT permanently on a motorway at 130 Km/h, close to the tyres). Only the middle back seat passenger is seated sufficiently far from the wheels and is practically not exposed at all.
Recording of magnetic field exposure values coming exclusively from the vehicles’s tyres using a NFA1000: maximum speed reached during journey - around 40 Mph
1// Before demagnetizing the vehicle’s tyres
An average permanent exposure limit of 879 nT recorded at the level of the front passenger’s feet coming principally from the right front wheel. You must subtract from this value about 70nT (frequence < 2Khz) coming permanently from the alternator.
Remark : the graphic below does not take into consideration exposure to the 50 Hz magnetic field coming from the high-voltage power lines along the route (57 nT recorded on average) and to the 16 Hz magnetic field coming from the Swiss electric train lines that were passed during the trip (81 nT recorded on average). If you take away the fixed magnetic field coming from the alternator (70 nT), you must subtract the magnetic field (in vector value). You then obtain just the magnetic field coming exclusively from the vehicle’s tyres. √ (879² – 70²) = 876 nT
Reminder : Bio-initiative Standard : 200 nT
Magnetic field intensity recorded before demagnetizing the tyres, produced by the vehicle during a journey of about one hour.
Permanent exposure at the level of the front passenger’s feet
The recording curve below also shows the exposure values of the 50 Hz magnetic field coming from the high-voltage electrified lines that we find all along the way (29 nT registered average) and the 16 Hz magnetic field coming from the Swiss electric train lines encountered during the trip. (25 nT average)
Herewith a summary of the magnetic field exposure values during a car journey in a vehicle with demagnetized tyres.
Front right tyre: 139 nT coming from the vehicle (vector sum of the magnetic field values coming from the front right tyre 120 nT as well as from the alternator 70 nT)
50 Hz from the electric line near the road: 29 nT
16 Hz from the Swiss electric trains near the road: 25 nT
Vector sum of the 3 fields : √ (139² + 29² + 25²) = 144 nT at feet level, which is quite acceptable
Reminder: Bio-initiative Standard : 200 nT (ideally 50 nT)
The magnetic field intensity recorded produced by the vehicle travelling for a period of about one hour after demagnetizing the tyres.
After demagnetizing the vehicle tyres
Permanent exposure at the level of the front passenger’s feet
The recording curve below also shows the exposure values of the 50 Hz magnetic field coming from the high-voltage electrified lines that we find all along the way (29 nT registered average) and the 16 Hz magnetic field coming from the Swiss electric train lines encountered during the trip. (25 nT average)
Herewith a summary of the magnetic field exposure values during a car journey in a vehicle with demagnetized tyres.
Front right tyre: 139 nT coming from the vehicle (vector sum of the magnetic field values coming from the front right tyre 120 nT as well as from the alternator 70 nT)
50 Hz from the electric line near the road: 29 nT
16 Hz from the Swiss electric trains near the road: 25 nT
Vector sum of the 3 fields : √ (139² + 29² + 25²) = 144 nT at feet level, which is quite acceptable
Reminder: Bio-initiative Standard : 200 nT (ideally 50 nT)
The DEMAG
The operation of demagnetizing the vehicle’s tyres is done with a specific device called DEMAG, originally developed by student engineers at the Haute Ecole Technique et Informatique at Bienne, in Switzerland.
Demagnetizing takes around 10 minutes per tyre. Once done, it will last the tyre’s lifetime. In Switzerland several garages offer this service.
Manufacturer email :
mut@mench-und-technik.ch
Hi there, I have an NFA1000, trying to replicate your result in a vehicle, I took the high pass filter off and left the filter set to M3D < 5Hz, not seeing these high readings in backseat ie 60 mG? Can you please let me know what I might be missing?
Very good post. I absolutely love this site. Thanks!