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.
- 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.
- Are there any other effect of a parasitic magnetic field on a circuit? Such as inaccuracies in hall effect sensors readings etc.
- 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.
- 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.
Best Answer
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.