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I am aiming to measure the strength of an electric field at different positions in space. The electric field is generated by a coil, which is driven by an AC current. This work is based on this paper: https://pubmed.ncbi.nlm.nih.gov/25680320/

the following is a sketch of the probe I am using:

probe that holds wire to measure electric field

It is basically a wire wrapped as a triangle and plugged into a differential amplifying circuit(based on the INA 137). The center of the triangle is at the center of rotation of the probe. The probe is being moved around in space around two axis, here is a picture for illustration:

movement of the probe

My problem is the following: The probe measures different voltages at the same point depending of which side of the wire points towards the center of rotation.

here are two pictures to illustrate:

probe at Position A with end_1 of the wire pointing towards the center

probe at Position A with end_1 of the wire pointing towards the outside

I do not understand how this effect happens. I would expect the measured voltage to be the same for both configurations. I tried this with many diffident wires and probes and the effect still prevails. I am happy about any hints on how to interpret my results.

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Some thoughts. Does your probe get a charge from static electricity?

Are any metal parts near your probe? The coil might induce currents in them. If they are grounded, induced currents can flow to ground. That will affect the field differently than if ungrounded.

You are measuring small voltages. Any small error may be as big as your signal. Can you try a stronger field? More current? More turns in the coil?

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  • $\begingroup$ hi, thanks so much for your reply. I did not yet ground all the metal parts close to the probe, I will try that! I am measuring signals at around 30 mV with very little noise. If I look at the amplitudes of each oscillation for a given configuration, they are very consistent. That let me to believe the reason for my problem might not be noise. $\endgroup$
    – Fabian Pfeiffer
    Commented Jan 7 at 16:28

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