Frequency response of a target

[mikebg]

Are there published anywhere frequency responses of metal detected targets: different coins, rings, hot rocks, junk etc.? I can,t find in WEB even one frequency characterstic of target in complex (impedance) plane! Plese help! Mike. ***

 

[rmptr]

Boy would that be good info to have!
Too many variables...
Even the mfg's would wish for something definitive, like that.
Basically, it would probably take all the work out of detecting, as the holy grail could be built!

Good luck on your quest to quantify that information.

 

[Reg]

Hi,

Unfortunately, there is no specific frequency response of a target. Some will respond or have an ideal frequency for maximum detection depth and that can be determined but is of little value overall because the range of frequencies is extremely large.

So, the best we can hope for is to design a good detector that detects the desired targets we want to find as well as it can.

Your question is more aligned with a VLF so I have attached a link to something written by George Payne which has information that sort of answers your question in a general way. BTW, George Payne is one of the most noted designers of VLF detectors.

http://jb-ms.com/Baron/payne.htm

I hope this helps answer your question.

Reg

 

[mikebg]

Thanks boys for the answers. I find an explanation of frequency response made by Minelabs guru Bruce Candy. The paper is discussed above in the thread "A bit of light reading". That forced me to start writing a lesson explayng what Bruce Candy should to say. Soon i'll find an WEB classroom for the lesson. Mike.

 

[mikebg]

To all users of metal detectors and ham designers!
Despite my poor English, I'm writing for the forum a lesson explaying fundamental principles of induction sensor and target ID.
To understand "Candy's Gospel" and my lesson, to join in discussion and exercises, ham designers and users of metal detectors should read WEB resources of terms:
complex plane, frequency response, transfer impedance, lossless ferrite, lossy ferrite, super paramagnetism, magnetic viscosity, time constant.
After discussion, we will make many exercises and solve very interesting problems. To participate, you should download any free SPICE simulator and read WEB resources for terms:
decibel, Bode plot, cutoff frequency and other (they will arise gradually).
As introduction, I put now two questions:
The attached figure shows in complex plane the frequency response (transfer impedance) of lossless ferrite.
1. What is wrong in this plot if we decide to make transition from frequency domain in time domain?
2. Can we obtain such frequency response without any object close to sensor?
I will wait several days for your postings and then will post the lesson because it contain answers. Yours Mike.

 

[mikebg]

Sorry,
The attached figure is for lossy ferrite. I will plot the right figure.

 

[mikebg]

This is the frequency response of lossless ferrite.

 

[mikebg]

There is the Lesson:
Sorry. I can.t attach *.pdf files.
The lesson should be posted in Carl's forum, thread "Frequency response".

 

[MattR]

Hi there Mikebg....

You can produce such data, in a laboratory set-up, but to then usefully relate it to field work is not practical.

Your detector is calibrated for typical coins like a silver dollar etc. but that is just 'a rose by another name'.
As we are all aware, different targets of differing mass and conductivity can have the same 'singular identity'.

Minelab's excellent TWO DIGIT VDI was introduced to improve on the singular numeric display.

To me, the Explorer's 'Cartesian-like' display and digital numerics, are the finest contribution to the art of metal detecting.



Identifying targets is a complex function and not a perfect art, in as much as each situation is different.

The Explorer 2 is as close as you will get to you dream, for a dynamic analyser.

Despite these constraints, I'm with you 100% in your quest for understanding what makes it all tick.

Regardless of how limited our success, it is the willingness to try that is the measure of a man.....MattR.UK.