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How to build a flat inductor?
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ro0ter:
Hello all,

I`m struggling to build a flat inductor for one of my projects that should harvest power from a RFID field.
I use a very thin copper wire (0.2mm) and I don`t really have any clue on how these coils are actually built..

A colleague showed me the inductor inside an access card, but I can`t really extract it since there`s plastic poured allover it..

How are these inductors made? Anyone has any clue?

How can someone make a diy, in-house flat inductor? (not necessarrily 1 turn per level, maybe 2~3, but the end result should be under 0.5mm... I`ll epoxy it later on.

Thank you all!
Ian.M:
You either need a dismantleable  former that constrains the wire to a single layer as you wind it, (e.g. two rigid disks with nonstick surfaces, bolted together at their centers, with a washer between them slightly thicker than the wire diameter, one of the disks slotted or drilled for the tail at the center end of the winding), and apply a suitable 'dope' to the wire as you wind it,  or for a one-off you could try laying down the coil on thin double sided sticky tape, with a large washer or similar as a former for the first turn, remove the washer and coat the coil with epoxy and a layer of fine glasscloth or kraft paper for strength, and let cure under pressure,  then strip off the double sided tape, solvent clean the coil surface and epoxy coat and reinforce it as you did the other side.
RoGeorge:
An adapter for 3D printers can do flat coils:  https://hackaday.com/2018/06/16/delta-printer-morphs-into-cnc-flat-coil-winder/
chemelec:
You could design it as a PCB, than Etch it.
SiliconWizard:
Some manufacturers make flat wire coils. It's a dead cause to make one yourself unless you have very specific reasons to IMO.
Still, you can use this as a design helper: http://www.tesla-institute.com/!app/sim/fscic.php

A lot of RFID cards or tags use flat coils etched on PCB as traces. You can use this for approximate values: http://www.circuits.dk/calculator_planar_coil_inductor.htm
Be aware that those are meant to harvest very little power.

You said you want to "harvest power" but didn't give any figures. The solution to use depends on the power you want to harvest and target size.
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