Discussion Forum

Hello fellow COMSOL users,

I am relatively new to COMSOL and I've tried to build a gradiometer with 2D axial-symmetry in the Magnetic Fields physics with a time-dependent study. Eventually I want to check the response of magnetic particles at different distances from the coils, but first I want to be able to measure the response without magnetic particles.

The setup consists of 2 identical excitation coils (counter wound, 100 turns, driven by 500[mA]*sin(2*pi*1[kHz]*t)) and 1 detection coil. The detection coil is positioned exactly in between the two excitation coils, so the fields of the coils are cancelled at position of the detection coil. Around the coils I’ve made a relative large air domain in which the coils are made up from copper. I've attached the file.

However, the voltage I measure with the detection coil is not 0 V, but in the mV range. Moreover, when I change the position of the coil setup (coil position relative to each other remains the same) the voltage in my detection coil changes seemingly random (for example 25e-7 V at position 0mm and -12e-6 V at position 40mm).

I’ve tried the following options to get rid of this disturbance:
Extremely fine mesh (0.01mm for the coils),
Extremely large air domain around the coils,
Small tolerances (1e-6 for absolute, relative and event tolerances).

But all these changes did not improve the results.
Does anyone know how to fix this problem?

Thanks in advance.

Kind regards,
Daniël