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Magnetic Field in the Car
May 7, 2018
9:35 am
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jclay
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Hi all, I cam across this forum because of my great concern about EMFs. I recently wanted to check what was the situation inside my car, an Audi A3 2008 Gasoline and was amazed to discover a quite high AC magnetic field of 300nT (below 20nT recommended).

The meter used is a Gigahertz Solutions 3840B (https://www.gigahertz-solution…..19/me3840b) and the reading was made on both front seats with the contact key turned on. More or less same values obtained with the engine on and while driving (50-70km/h).

The curious thing is that the AC electric field, is about only 2V/m (recommended below 10V/m).

My questions are:
1) why can I get a so high AC Magnetic field by having a low AC electric field?
2) how to reduce/cancel this AC Magnetic field?

Thank you all for your support.
Br,
JC

May 8, 2018
8:45 am
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Peter Williamson
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HI JC and welcome to the forum. Cars always seem to be a challenge. Normally a magnetic field is caused when an alternating current is flowing. Why should that happen in a car when the engine is not running, so presumably the alternator is not rotating? I can’t answer the question, but there is a document on cars in the Powerwatch library (http://www.powerwatch.org.uk/l…../index.asp) which might give you more information. The best documented magnetic field effect is probably from the rotating tyres when the car is moving (there’s a paper on this by Sam Milham) but this clearly does not apply in your case. If you search the main site here there are some articles on cars.

May 8, 2018
9:58 pm
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jclay
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Hi Peter and many thanks for the warm welcome.

The fact is, just by turning the ignition key, without starting the engine, magnetic field already jumps out nearly 300nT on the front seats. The value even exceed 1000nT when the meter is placed over the changing gear, just below the audio LCD system, always with the engine off.

Those levels are the same either when the engine is on or driving. Speed doesn’t look to have any impact on measured levels in my case.

The most strange thing to me is that the electric field is between 1-3V/m only. Could this low E field cause so high M field?

If I’m not wrong, following conversion can be done:
3V/m = 0.0001005 Gauss = 0.01005mT (milli Tesla) = 10.05nT (nano Tesla)

There’s clearly something wrong here because according my E reading, I should have approximately 10nT and not 300nT as it is on front seats.

Btw, I’ll check at powerwatch library and see if there’s some clue there.

(http://www.compeng.com.au/fiel…..alculator/)
(http://www.hkd.co.jp/english/unit_conv/)

May 9, 2018
11:33 am
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Peter Williamson
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Hi jclay
I can’t shed any more light on you carr issue. I’m also puzzled that there is a conversion from V/m (electric field) to Gauss (magnetic field) as I understood that they have different origins (current flow vs electric potential). (Unless it’s considering current flow through a fixed resistance, in which case there is a simple relationship. )
The conversion charts look useful – I’ve been looking for something like this for ages. Unfortunately they don’t seem to include conversion from V/M to DBm – unless it’s hidden under some different terminology. This would be useful because prof Trevor Marshall always quotes DBm and he’s done lots of interesting work on how very low field levels affect biology.

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