IB coil positioning

[eluong1]

I was looking at the many guides available for building an induction balance metal detector, and noticed that many of them use an overlapping design for the two coils. I was wondering what the reasoning for doing this was. I sort of need the center to be hollow, so the coil should just be circular, but unfortunately this does not seem to be possible.

Thanks,
- Eli

[Carl-NC]

Probably because DD coils are simple to make. But for any IB detector design,
you can use any IB coil design. Take a look at Dave Emery's article on building concentric coils here.

- Carl

[Max]

I was looking at the many guides available for building an induction balance metal detector, and noticed that many of them use an overlapping design for the two coils. I was wondering what the reasoning for doing this was. I sort of need the center to be hollow, so the coil should just be circular, but unfortunately this does not seem to be possible.

Thanks,
- Eli

Hi Eli,
as Carl say, DD are simple to make. Also field shape is different to e.g. concentric :

- concentric have more central depth advantages and good pinpointing
- DD have a central close-to-elliptical area of major sensitivity--> means they are easy in cancelling gnd signal, with good sensitivity too but less easy pinpointing than concentric

There are other kind, examples are:
- four rx and one central tx (like AN/PSS11)
- figure-8 RX
- rectangular 1 TX, 2 RX (like some east-european / russian)
- elliptical shape, 2 RX round , 1 elliptical TX
- pcb square tx and rx

and many others. Every configuration have pros and cons!

One have to chose one for best operations.

Best regards,
Max