I have an air core inductor whose inductance , as measured with LCR meter, is 45.1uH and quality factor is 4.4. When i place an Aluminum alloy (which is a Non-magnetic Material) as Load inside the coil, the Inductance of Coil=44.6µ H and Quality Factor=3.63. Why is the inductance decreasing when a non-magnetic material is placed in the coil. Or am i missing something.enter image description here


2 Answers 2


The hint is in the more drastic change which is the reduction in quality factor, indicating that the equivalent series resistance has increased.

As joseph h has pointed out, eddy currents are induced in the alloy, which cause resistive losses (hence the increased resistance) as well as oppose the original magnetic field (hence the reduced inductance). The alloy can be thought of as the secondary of a transformer connected to a resistor, with the inductor as the primary. The equivalent circuit is the original inductor with a resistor connected in parallel with some of its turns.

It would be interesting to see your results measured at different frequencies (which your LCR meter should be able to do). At higher frequencies, the equivalent resistance mentioned above would increase somewhat due to the skin effect, but not faster than the inductor reactance ($\omega L$) which is proportional to frequency. Because of this, the resistance should be more effective at partially "shorting" the inductor, so the alloy should cause a higher drop in inductance.


This is most likely due to the presence of Eddy currents.

Placing the Aluminum (which is a conductor, and is also typically nonmagnetic, or paramagnetic as you have stated) load inside the coil, causes Eddy currents to form in it. These currents create magnetic fields that oppose the initial magnetic$^1$ field caused by the coil, thereby resulting in a decrease to the total inductance of the coil.

$^1$This is an example of Lenz's law.


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