Hi Everyone,

I have a quick question. I understand in a series RLC circuit that at resonance, the reactances of the inductor and capacitor cancel out. Therefore, the current through the circuit is dependent upon the driving voltage as well as the series resistance, which includes any series resistors as well as the intrinsic resistance of the inductor.

In my setup, there is no series resistor, so the series resistance is just intrinsic inductor resistance.

When I attach my inductor (an RFID coil) to an LCR meter to measure the resistance, I have the option of selecting the frequency. So my question is: does the intrinsic resistance of the inductor vary with driving frequency? I thought that resistance was a DC characteristic, so I'm a little confused.

Thanks for the help,

Austin

 

The resistance of a wire can vary with frequency due to the skin effect which cause the majority of the current to flow in the outer portion of the wire. The wire thus exhibits more apparent resistance because the current is not flowing uniformly in the whole wire diameter.

 

The "skin effect" generally is only of consequence at the higher frequencies. I am not sure just when it begins to cause a problem. I believe it could be when the "apparent resistance" begins to degrade the "Q" or quality of a resonant circuit enough to affect desired operation
It can be reduced by using a special type of wire or wiring called a "Litz wire" if I recall correctly. It is basically a number of smaller cross-sectional area wires which are insulated from each other and wound together to replace the one larger wire.
At the problem frequency then the "skin effect" is spread over the small wires and reduces the overall effect.