Sarin Sukumar A wrote:
> Hi,
> Again One problem for me...
> I am designing some metal detection circuit. I am using an FPGA. My coding
> has done and the hardware is working perfectly.
> But i need an antenna of 1kHz to 3MHz, i think i can make it using loop
> antenna, but i dont know the parameters.
> I just got some idea from googling about this , some kind of loop antenna
> will do this.
> But any body know anything about this?
> YOurs SaRIn....
>   
1kHz seems unlikely.
It's very rare to have more than 10:1 on an Aerial and loops are much 
narrower band, Maybe 3:1.

As Russell says you need to explain what the principle of operation is 
and also what is connecting to the loop.

The  main methods I know are
1) Two identical oscillators a few 100Hz apart. The detection coil is  
tuned circuit of one,  and the two are mixed to give audio beat. 
Typically 450KHz
2) Similar to (1) but with differential detector coils separated by a 
few metres.
3) Some method of measuring inductance of a loop. Brass, copper, 
Aluminium will reduce and Iron, Steel, etc increase inductance.
4) Ground penetrating radar.
5) Ultra sound

Since RF based metal detectors are essentially transmitters with loop 
aerial, most countries have certain bands and power restrictions. In 
some countries they may not be legal other than for finding wires and 
pipes.
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