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I have come across those requirements:

"The equipment shall not be susceptible to DC magnetic fields of up to 60 μT."

"The equipment shall not be susceptible to electric fields of up to 140dBuV/m between 400MHz and 10GHz"

My intuitive idea of how electric and magnetic fields impact a circuit is not enough, it seems.

  1. I know that current through a wire generates a magnetic field decreasing in 1/r, but I don't know if it makes sense to say that we can calculate the current induced in a wire from the magnetic field value and the distance from the source.
  2. Are there any other effect of a parasitic magnetic field on a circuit? Such as inaccuracies in hall effect sensors readings etc.
  3. As for electric fields, I assume it changes the values of the capacitors in the circuit, but I don't know how. I didn't find any answer during my research on internet.
  4. Are there any other effect of a parasitic electric field on a circuit?

I would like to understand those types of requirements (not only those particular ones), what they mean. I only have a vague idea of how magnetic and electric fields can impact a circuit, and clarification if possible with examples would be much appreciated.

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  • \$\begingroup\$ Distance is irrelevant. \$\endgroup\$ Commented May 1, 2015 at 17:25
  • \$\begingroup\$ The standard you're testing to should describe the conditions under which those specs must be met. \$\endgroup\$
    – Matt Young
    Commented May 1, 2015 at 17:39
  • \$\begingroup\$ @LeonHeller: I assume the downvote and close vote come from you then. You should know that this is much too short to be an answer, and in fact it does not answer my question in any way. Otherwise you should read the rules of the forum. \$\endgroup\$ Commented May 1, 2015 at 17:49
  • \$\begingroup\$ @MattYoung: so you do agree there is missing information if I consider these requirements without any other information? I updated my post to clarify the fact that I would mainly like to understand those requirements. I only have a vague idea of how magnetic fields and electric fields can impact an electronic circuit. \$\endgroup\$ Commented May 1, 2015 at 17:51
  • \$\begingroup\$ You really have two questions here. First, as I said, the missing information is the standard. The meaning of those specifications in the context of a standard is one question. How electric and magnetic fields effect a circuit is a second, larger, more interesting question. \$\endgroup\$
    – Matt Young
    Commented May 1, 2015 at 17:57

1 Answer 1

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I'm just answering the magnetic field part of the question: -

31.869 µT (3.2 × 10−5 T) is the strength of Earth's magnetic field at 0° latitude, 0° longitude so hopefully you can put that into context with the 60 µT requirement. I'd say that if the equipment were moving fast there could be induced voltages in cables of sensitive equipment but without knowing anything about the circuit I cannot say.

Anyway, motional emf = vBL

Where v is velocity in m/s, B is flux density and L is length of wire. This applies to an open circuit wire.

Here's my thoughts on the E-field side: -

It's really tricky to generalize how the E-field will affect a "general circuit". All I can say is that it can create a voltage in space of 10V/metre and across a gap of (say) 1mm is creates a voltage of 10mV RMS. But what is that "sort" of gap on a PCB and how "collapsable" is the field in the presence of a moderately low impedance across that 1mm. If I assumed that there is likely to be an accompanying H-field i.e. there is a proper electromagnetic field then I could argue that the impedance source is 377 ohms (impedance of free space) but then the accompanying H field will also induce a voltage so, I'm backing out of answering this part because it's beyond my skillset.

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    \$\begingroup\$ If you specify the earth's magnetic field with 5(!) significant digits you should also specify the date (and maybe the time of day too). In other words: it is changing en.wikipedia.org/wiki/… (this gif represents only the direction but also the absolute value is changing) \$\endgroup\$
    – Curd
    Commented May 1, 2015 at 19:36
  • \$\begingroup\$ @Curd value taken from en.wikipedia.org/wiki/Tesla_%28unit%29 - please feel free to suggest this to wiki page. As far as I am concerned the value is roughly the same order as the static field in the question and I'm hinting that virtually all normal circuits operate quite nicely without problem in this level of field. That is the important point. \$\endgroup\$
    – Andy aka
    Commented May 1, 2015 at 20:51
  • \$\begingroup\$ Thanks, that is indeed low. I'm however more interested in understanding how those fields can have any effect in the general case. If the circuit is not moving with respect to the magnetic field, is there any impact (mainly on inductors I assume?)? \$\endgroup\$ Commented May 1, 2015 at 21:06
  • \$\begingroup\$ If the field and circuit is not moving then there is no induced effect into wires. At that level of flux density there will be a 0.008% increase in the saturation of regular ferrite material i.e. nothing to worry about here. However if the apparatus is used to specifically measure magnetic flux then this static flux will have an effect! \$\endgroup\$
    – Andy aka
    Commented May 1, 2015 at 21:38
  • \$\begingroup\$ I'd like to accept this answer but it doesn't cover the electric field side... I've already +1'd, do you want to have a go at the electric field to make it complete? \$\endgroup\$ Commented Dec 1, 2015 at 17:31

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