I've been looking at a metal detection circuit. As I understand, it depends on changes in the magnetic field in a coil: when metal comes close from the coil, the circuit can detect that metal is nearby.

My question is: what will happen if I cover the coil with a 3mm thick plastic layer? Will this plastic affect the response of the circuit, or will the circuit continue to operate correctly?

Here is a picture of the circuit:

Picture of metal detector

  • \$\begingroup\$ Normally the coil is separate from the board, making it easier to use. Those usually have plastic cases, so it shouldn't make a difference in your case (pun intended) \$\endgroup\$ – crocboy Jun 8 '15 at 20:29
  • \$\begingroup\$ I would agree with crocboy that it shouldn't matter. You could always take a piece of metal and detect it with no plastic housing. Take the metal further away until it stops detecting. Then put plastic housing on and see if you get the same distance detection. \$\endgroup\$ – I. Wolfe Jun 8 '15 at 20:31

Ordinary (that is, not loaded with carbon or with ferrite or metal particles etc.) plastic will have no effect whatsoever on the magnetic fields.

It will work the same as it does without the plastic there (which may or may not be 'well').

  • \$\begingroup\$ which may or may not be 'well' is that means this circuit may be cant detect metal ?? \$\endgroup\$ – lookaaz Jun 8 '15 at 20:01
  • \$\begingroup\$ It may not be quite in the same league as a $600 state-of-the art metal detector. I have little doubt it will detect metal to one degree or another. \$\endgroup\$ – Spehro Pefhany Jun 8 '15 at 20:10

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