Latest patent from Minelab

[Qiaozhi]

Metal Detector for Salt Soils ->

[Teleno]

The subject matter can't hardly get any more obfuscated than this. In the end it's the good old linear combination of delayed samples that's being claimed.

[0080] The averaged outputs of the post first, second and fourth synchronous demodulation signals (the output of the averagers 141, 143 and 183 respectively) will then be linearly combined with different coefficients by the processing electronics 145 to produce an indicator output signal 137 indicative of the presence of a metallic target in the soil. The coefficient to be applied to the output of the averager 183 can be determined in a similar way to that of the methods described above.

[Koala]

Gave up and got board after the first few paragraphs. Same with most patents I have read recently.

[Ferric Toes]

The definition of a soil is 'the upper layer of earth in which plants grow, a black or dark brown material typically consisting of a mixture of organic remains, clay, and rock particles'. The Minelab patent appears only to deal with land soils that are salty enough to give a conductive signal in addition to any superparamatic iron mineral signal. To my knowledge these salty soils are very few and far between and the resulting conductivity has no effect on a PI unless you are using ultra short delay times i.e. much less than 10uS, or exciting huge volumes with a very large coil.

A wet saltwater sand or shingle beach cannot be classified as a soil and, unless I missed it, this patent make no mention of this application, or indeed underwater diver held PI detectors for searching in the sea. On a beach you have a conductive half space situation but as soon as you submerge the coil it becomes more and more a conductive full space as you dive deeper, depending on the coil size. In the patent only a soil is mentioned in relation to having a conductive half space.

Cancelling out the salt seawater signal for beach and and diver held detectors would be very beneficial, as we could then detect those very fine gold chains that I am often asked about.

Does the fact that all references are to a 'soil' that has conductive and magnetic properties, mean that this patent cannot apply to beach, shallow water, and diver use?

Eric.

[Qiaozhi]

According to the Unified Soil Classification System, sand is actually a type of soil known as 'coarse grained'.
https://en.wikipedia.org/wiki/Unifie...ication_System

[Davor]

A thing which is new for Minelab patents is approximating salt response with t^(-x), but in the patent x is flipping between 3/2 in paragraph 0052, and 5/2 in paragraph 0058. Reasoning for such approximation is perhaps for the simplification of calculation. It is easier if everything is calculated in log-log domain. And the salt response is a relevant contributor only for a very short time, so any approximation may do.
Reasons for diving closer to a transition moment is perhaps because their new toys are not PI-s in a traditional sense, but instead step voltage devices. The high voltage part is connected to a high voltage source of a sort. It enables a transition that is not time limited with a Tx coil flyback. This way they are able to sample immediately, and in theory pick fly$hit gold. In practice the salts became also very much visible, and there you have it. You suddenly need a VLF kind of GB. Multifrequency-style.
I'm not sure this t^(-x) estimate would also work as patented on a salty beach, but the mechanism they described seem capable of adopting to salt water as well.

[Qiaozhi]

A thing that's not new for Minelab patents is the painful legalese, and the constant repetition. It's as if you're not expected to get to the end of the document before falling asleep. It's definitely hard work.

Presumably the coefficients of the synchronously demodulated periods are adaptive, but how well this method will work in practice remains to be seen.

[Davor]

It will work. Multifrequency devices work, so it should work too.
So far it seem harmless for the hobbyists or the rest of the industry, as long as everyone keeps from copying the exact procedure, which to me seem pointless. There are many more combinations at hand if you ever need to go this close to transition. I like the log time way of presenting the scheme though.

[Koala]

Makro Racer seems to work wet sand and single frequency. Must all be done on software somehow ?

Not that I have tried one myself.

[Davor]

The whole point is not any more in finding a single ground solution, but simultaneously eliminating two interferers or more.
The end game is an idiot-proof device built for a blond without any detecting experience.

[Dutchie]

In the Minelab patent US20170299753A1.pdf they make a broad claim.
It raised a few questions.
My impression is that the claim restricts high voltage to a maximum of 400 V.
is that correct? and if so would it be an option to use the same broad claim an restrict it to the range of 401 to 4000V.
(Vallon uses 400 V (part of the cycle) for charging the Tx coils according to post on the Forum.... so this is not new either)

Further I have the impression that the claim is limited to devices with a detector perpendicular to the pulse-emitting device -
so anything they claim here could be used for one coil or coplanar multicoils without infringment on this patent.
Perpendicular setup of coils is not new either (youtube shows this for quite some time)

[Davor]

I think you give far too much credit to patents. 400V is an arbitrary value set by limitations of the components. There is nothing magical about it.

About the patent wording - get used to it if you wish to read more of them. It is 90% legal vs 10% technical. In reality, it is a marriage of impossible partners, so everything goes.

Infringement only happens when you copy a unique part of the technical solution, or ... wait for it ... if you use the same (legal) terminology to describe it. For that reason you'll find distinguishable company lingo in every patent around. Minelab has a particularly convoluted lingo. Guess it helps triggering their search engines for plagiarism/infringement. In a way it is OK to get flayed at court if you are stupid enough to copy other people's patents wording.

Live by the patent, die by the patent.

There are other less excruciating ways to protect your work.

[Dutchie]

Hi Davor,

Thanks for your reply!

I am not in the business of designing detectors for commercial purpose.
As a newby who has not done any serious programming or electronic work for over 30 years I am not wanting (or able) to issue any patent-application regarding detectors myself.
The text of this patent was in my impression not a valid claim because there was nothing in it that was not available before published on the geotech or other forums or visible in youtube films. My thought that this patent is a fake claim - and - maybe a claim regarding the higher voltage domains could preserve this for the diy hobby world so boards can be produceds for other hobbyist without the risk of a legal threat for copy right infringment.

Dutchie

[Davor]

Well, I hope you won't torture yourself with patenting anything. But hey, there are soooo many patents out there.

The ju-ju of the patent is not in Tx side, as much as in the Rx side, where a mechanism that already works on viscous soils is employed to fix the salt response problem. Most probably there is a new machine rolling on, and most probably it will be in a mid range. And few months before the launch you'll see some marketing pamphlets covering it with unicorn poo and technical pixie dust.