Accouncing a new metal detector genre

[Thomas Scarborough]

Friends,

It might be of interest that I developed a new metal detector genre - implementations of which are being published in a number of magazines about now.

Instead of using search and reference oscillators as with BFO, or Tx and Rx coils as with IB, it uses two transmitters (search oscillators) with IB-style coil overlap, which influence each other through mutual induction.

The advantages of the concept are as follows:

It potentially offers the same sensitivity as IB, while using as little as three common components, plus coils. It offers high immunity to voltage and temperature variations. And it has a high degree of immunity to ground mineralisation, while offering good discrimination.

I have named the concept Beat Balance, or BB, and I have placed it in the public domain.

The first implementation of the concept was published in Servo magazine (USA) this month, and further implementations are scheduled to be published in Europe and worldwide in the coming months.

I have just designed an implementation which uses just two common components in the control box, plus an earpiece and the coils, clearly detecting an old Victorian penny (1" dia.) at 160mm in air.

With kind regards,
Thomas Scarborough.

[Beachcomber]

Where can we read more about this new concept as well as see diagrams?

n/t

[Beachcomber]

Re: Where can we read more about this new concept as well as see diagrams?

Also is 6.5 inches about as deep as this design is capable of on a 1" diameter coin or will refinements allow it to reach the capabilities of today's VLF's which are in the range of 12-16 inches (300-400mm) on a 1 inch diameter coin. How is the sensitivity to low conductive targets such as gold?

Thanks

HH

Beachcomber

[Thomas Scarborough]

Schematic sent to your e-mail. Feedback welcome.

Dear "Beachcomber", I have sent you a pre-publication schematic via e-mail. Feedback would be welcome. With kind regards, Thomas.

[proscan]

tell us more, seems it is not a fresh idea.

Seems you reinvented a detector patented in 1970s. The link is below.

Two generators coupled with a zero-mutual inductance coils.

What you say? Are you aware of the patent?

What's your advantage?

Give us some more info. Thanks.

proscan



Click Here

[Thomas Scarborough]

It is a fresh idea, and this is why.

Dear "proscan",

Thanks for the message.

I can see resemblances between my idea and the patent. However, there are crucial differences. The patent (US Patent 4,196,391) is very clever - a good piece of original thinking that I was excited to read. I shall describe a complete embodiment of my own concept below - but first a treatment of the differences.

The patent seeks (quote) "least interaction between the inductors", while my concept is almost entirely dependent on such interaction. A "significant novelty" of the patent is a gate oscillator, which my concept does not have. The patent uses dual difference frequencies, while my design uses a single difference frequency. The patent uses a dual variable capacitor for equalising frequencies in the transmitters, while mine uses a single variable capacitor to obtain a difference frequency. The "primary object" of the patent is binaural location, while the primary object of mine is to boost sensitivity through mutual coupling. The patent's main embodiment is relatively complex, using some 60 components and 8 building blocks. My design uses as few as 3 components, and 3 building blocks.

The patenter states that he is "surprised" to find "pronounced improvement" by alternating the signals in the ears. Why the expression of surprise? This is hardly scientific language. My hunch is that this pronounced improvement lay not in the ears, but in the coils, and so the patenter missed a significant breakthrough by a whisker.

Here then is one possible embodiment of my idea, and it can be described completely in a few lines. It could just as easily be done with a logic i.c. Do bear in mind that this is a pre-publication circuit I'm describing.

Take two coils with Faraday shields, 70 turns 30swg (0.315mm) wound on a 120mm diameter former. Take a TL074CN quad op.amp. Wire a coil across output and inverting input of each of two op.amps. Wire the non-inverting inputs to the outputs for stability. Wire a variable capacitor across the outputs. Take the outputs separately to the two inputs of a third op.amp, then a crystal earpiece from the third op.amp's output to 0V. Wire +12V to pin 4, 0V to pin 11. The circuit is now complete. The coils need to overlap to so as obtain a low tone in the earpiece. The only nuance is that the orientation of the coils makes some 20% difference to sensitivity. Get that right, and you should detect an old English penny at up to 160mm.

An early embodiment of my idea has been published in Servo magazine in the USA (Servo, January 2004). Further embodiments are scheduled for publication in Europe and worldwide in the near future.

I am placing my concept in the public domain, and would therefore be pleased to discuss it and share details. I have dubbed it beat balance or b.b., since it might be described as a hybrid of the two genres. Also, it matches the performance of many i.b. detectors, while offering cost advantages similar to b.f.o.

With kind regards,
Thomas.

[Beachcomber]

Re: Schematic sent to your e-mail. Feedback welcome.

Thanks!!! Hopefully I will be able to find a copy of Servo Magazine and read the entire article. The schematic is so simple and straightforward. When I get some free time I am going to build it.

Thanks Again!

HH

Beachcomber

[Mark Pauls]

Re: Schematic sent to your e-mail. Feedback welcome.

Hi Thomas

Could I please get the pre-schematic too.
It sounds very interesting and innovative.

Thanks.

Mark

[Carl-NC]

Re: Accouncing a new metal detector genre

Thomas,

Please post the schematic here, if the publication allows.

Speaking of, I know you've published quite a bit in EPE... do you ever submit a same article to a second magazine, such as Silicon Chip? I'm wondering if the publishers allow that, especially since there is virtually zero market overlap between EPE, SC, and in the US, Nuts & Volts.

- Carl

[Sean Goddard]

Re: Schematic sent to your e-mail. Feedback welcome.

Ah, but does it discriminate?

[Thomas Scarborough]

Yes, it discriminates.

Hello Sean,

Each coil has an opposite response to metal, but the overlapping segment in the middle discriminates.

With kind regards,
Thomas.

[Karl Harrar]

Re: Would like a schematic also?

Would love to build it and give you feedback.

Karl in AZ

[Al in NY]

Re: Schematic sent to your e-mail. Feedback welcome.

I would love to try and build it also. Please send the schematic and if you have a pcb layout send that as well.
Thanks, Al.

[Karl Harrar]

Just finished one and the thing works!

Now all I need to do is compare phase and amplitude to get it to discriminate.
Will test it on some black sand
tomorrow, by design it should
null it right out.

This design has great potential!

THANKS THOMAS,

will report soon,

Karl

[Thomas Scarborough]

Funny you didn't...

Funny you didn't question the originality of my design on the basis of your own web pages, Piotr. What a strange thing to do. It was Giorgio Obole of Torino who sent you my original design, which I previously sent only to technical editor John Becker. But there it is, my unseen design, which was known only to John Becker, and then to Giorgio, with those essential features which nobody saw, because eventually I withdrew it to do a revamped design as a full constructional article. However, forget the patents Piotr, I placed the design in the public domain long ago, for which there is independent evidence aplenty.

Thomas.