detector to detect objects at close range

[zeph]

Hi, I am trying to build a metal detector that will be able to detect small objects (3mm by 20mm) at close range (1cm or less). I am making the maximum diameter of the search probe/coil to be around 10 to 15mm. I was wondering if someone could recommend a circuit schematic to follow. I've looked at pulse induction and continuous wave technologies. I'm trying to detect stainless steel objects, which has a high resistivity and dissipates the eddy currents induced into the object quickly, and if using pulse induction, the frequency would need to be high. I was wondering if users on this forum can comment about the feasibility of such as small detector. Only the coils need to be restricted to such a small size.

Thanks.

 

[Digger]

I don't know of any schematics available. But, several small detectors (referred to as electronic pinpointers or pocket probes) may perform the task you are describing. My VibraProbe 560 is a larger diameter than you describe. However, it is a Pulse Inductive detector, capable of detecting very small items at close range. Even those with a high resistance and low retentivity, as you mentioned. The beauty of the VibraProbe is that it detects targets at the tip area only. As an example, it will detect a penny at around one inch. So, detecting your targets at less than 1 cm shouldn't be a problem. New ones are around $100. But, you might consider buying a used one, tearing it apart, and rebuilding the core to fit your application. HH Randy

 

[zeph]

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