Electronic – Pancake Coil Magnetic Field Strength

accoilemffield-strengthmagnetic flux

I am trying to measure the magnetic field strength of a pancake (flat) coil. I know the turns, inner radius, current, and frequency from an AC input and am trying to measure the magnetic flux so I can use faraday's law to measure EMF output in a different coil. What equation/formula would I use to measure flux/field strength.

Thanks.

Best Answer

You definitely can do it! If you have an oscilloscope you can make quite accurate magnetic field strength measurements. Here is one paper, in which the procedure is explained and the properties of the probe antenna are also explained (page 4 to see the equation).

You just have to be careful which kind of probe you are using, so the cable doesn't capture power, only the loop. If you have a low frequency you can use twisted pair cable with a loop in the other end:

Do be careful to make the probe small enough, if it is too close to the antenna conductors the results will not be accurate.

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Electronic – Simulating a magnetic field in Spice

Model the change in field as a single ac voltage source. Add to this a resistance and inductance (pickup winding resistance and leakage inductance). For even better accuracy add some capacitance to model a bulk interwinding capacitance:

Lleakage 1 N1 <value>

Vac 2 N2 <func_of_time>

Rwinding 2 1  <value>

Cparasitic N1 N2 <value>

Electronic – Measure AC magnetic field strength between 100kHz and 300 kHz

As with any coil, induced voltage is N\$\dfrac{d\Phi}{dt}\$.

So, armed with the number of turns (N), the voltage, the frequency and the area of your loop, you can calculate the average magnetic flux density seen by the coil.

The coil should be measured open circuit and the fewer turns the better because coil parasitic capacitance can easily resonate the circuit and give big errors.

Best Answer

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Electronic – Simulating a magnetic field in Spice

Electronic – Measure AC magnetic field strength between 100kHz and 300 kHz

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