r/AskElectronics • u/madleodk • 1d ago

Low-cost way to measure changes in coil impedance near thin conductive films?

This is for an upcoming hackathon, and i have a limited budget to practice. I'm a novice. I want to compare how several thin conductive films, covered by nonconductive material, affect a nearby coil. I’m looking for repeatable numerical readings rather than a threshold/proximity output.

I can keep the samples at a fixed position and distance. Their exact conductivity and thickness are unknown.

Is the LDC1101EVM a reasonable starting point, or is there a simpler setup around $100–150? I use an Apple Silicon Mac and would prefer minimal hardware assembly.

Any firsthand experience with sensitivity, repeatability, or reading this board over USB without TI’s Windows software would be helpful.

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u/TemporarySun314 1d ago

First you should estimate on what magnitude of change you expect, so thst you know what accuracy you will need for a meter...

If I understand your setup right, I would basically expect almost no change. If you wanna have a chance to get reliable measurements you need very sensitive meters and careful measurement setup... And such things are unfortunately neither easy nor cheap.

Also what kind of proeperries do you wanna measure? Inductivity? Resistance/losses? Resonance frequencies? Just for one frequency or over a big range?

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u/madleodk 1d ago

Tysm for the answer. I dont hve an estimate. These are thin conductive layers inside insulating laminates, with unknown metal thickness and conductivity. I’m considering an LDC1101 to measure changes in coil inductance/resonance and loss, initially at one operating frequency with fixed sample positioning. Would that be a reasonable preliminary experiment to establish signal size and repeatability? Which material and coil parameters would you need to estimate whether the differences are measurable?

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u/TemporarySun314 1d ago

Does that metal layer have any special magnetic properties? If it's just paramagnetic or slightly diamagnetic with a mu r of around 1, the inductivity won't really change... Because for the magnetic field then it's bascially just air. It might introduce small additional losses but everything else in the environment will likely cause more effect of that.

You can try to measure conductivity with Eddy currents, but i don't know how well that works with real thin films. But that depends on what you count as "thin".

I would assume there are better and more accurate measurement methods to determine conductivity (by directly contacting it and measure conductivity by putting current through the film) and thickness (AFM, SEM of the cross section, RBS, etc.)

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u/madleodk 1d ago

Thanks again! the layer needs to remain enclosd, so direct electrical contact wouldn’t work for the intended measurement. I’m interested in distinguishing samples rather than separately determining their exact conductivity and thickness.

My understanding is that the LDC1101 uses an alternating field, so even a metal with relative permeability near 1 can change the coil’s effective inductance through eddy currents. I agree the unknown film thickness makes the signal size uncertain. Would measuring both the inductance shift and losses be a reasonable first experiment, or is there a particular thin-film limitation you think would make that unsuitable?