Minelab Equinox

Here is a interesting writeup I came accross...


As we get closer to the Minelab Equinox reveal, I thought it would be fun to get really esoteric about it and discuss what it might be and what the implications are. This might be a rehash of conversations you've seen elsewhere online, but we haven't really discussed it here.

Here's what we know so far, based on this advert

Reveal Date: September 16, 2017"Makes single frequency VLF obsolete""New technology"

So on the 16th of this month we'll be introduced to a new machine that boasts a new technology that will make single-frequency VLF obsolete. Personally, I think single-freq VLF is already obsolete, but whatever. What else can we possible find out?

Well, based on this trademark filing, we can assume that the new machine is called Equinox. It's funny that the Equinox is being released on September 16th when the equinox this year is actually September 22nd. Too bad the stars didn't align on this one.

It's possible that this name is a hint at the "dual" nature of the machine, as the equinox is the time of year when both day and night are of equal length. Given that Minelab has completely moved away from single-freq - and how the advert specifically calls out single-freq - maybe this means it's a dual frequency machine? Honestly, I'd be surprised if that's the implication; BBS, FBS, and FBS2 machines already use pairs of frequencies in a wide range. Plus, machines like the Nokta and the Deus can switch between multiple frequencies on the fly. It would be crazy to release a tw-freq machine. I am almost certain that, if this is a hint at duality, it doesn't mean "two frequency VLF".

What else do we know? Thankfully, patent filings are public records, and many people believe THIS PATENTdescribes the Equinox's new technology. Here is the abstract:

A method for detecting a target in a soil using a metal detector, including: generating a transmit magnetic field for transmission into the soil based on a transmit signal; receiving a receive magnetic field; providing a receive signal induced by the receive magnetic field; processing the receive signal for producing a set of data which has effects of signals from the soil reduced therein or removed therefrom; producing at least two components of a form of at least one time constant spectrum based on the set of data; and producing, at least one indicator output signal based on the at least two components for indicating the presence and/or identity of the target when the target is within, an influence of the transmit magnetic field.

On it's own, this isn't very exciting, although it makes much more sense after reading the whole document. Someone wrote up a post on a blog about how the new technology is "a magnetic field", which is really silly. That's what detectors use now! Whoever wrote that either didn't read the whole thing or simply doesn't understand the patent or metal detectors. If you doubt this, read the second paragraph in "Background" (emphasis mine):

These metal detectors usually, but not necessarily, consist of transmit electronics generating a repeating transmit signal cycle of a fundamental period, which is applied to an inductor, for example a transmit coil, which transmits a resulting varying magnetic field, sometimes referred to as a transmit magnetic field.

This is talking about metal detectors that are currently on the market now. They send a signal through an inductor (the search coil) to generate a magnetic field. That's the same technology used in this new machine. Nothing new here. Further down in "background", the author describes two type of detectors that are common today:

Time domain metal detectors typically include pulse-induction (“PI”) or pulse-induction like metal detectors, and rectangular current-pulse metal detectors, wherein the receive processing includes sampling of the receive signal and/or synchronous demodulation over selected periods, which may include gain weighting of the samples or synchronous demodulation periods.

Frequency domain metal detectors typically include single or multi-frequency transmission, or pulse transmission with either sine-wave weighted synchronous demodulation, or unweighted synchronous demodulation with pre synchronous demodulation band-pass and/or low-pass filtering.

These are PI machines and VLF machines, respectively. PI and VLF are two wildly different machines with their own pros and cons. We've discussed them at length on this sub. The next lines discuss discrimination, and at first I didn't understand the significance and the reference they were making.

It is known to demodulate receive signals of a metal detector for processing to characterise the receive signals in terms of time constants. WO/2011/011820 discloses that discrimination of a target to a certain degree can be achieved by analysing the spread of the time constants. Mu-Hsin Wei, Scott, W. R., McClellan, J. H., “Estimation and application of discrete spectrum of relaxations for electromagnetic induction responses,” Geoscience and Remote Sensing Symposium, 2009 IEEE International, IGARSS 2009, vol. 2, no pp. II-105, II-108, 12-17 Jul. 2009 discloses that by identifying each of the main frequency components (inversely proportional to time constant) of the received signals, it is possible to enhance discrimination. Mu-Hsin Wei, Scott, W. R., McClellan, J. H., “Landmine detection using the discrete spectrum of relaxation frequencies,” Geoscience and Remote Sensing Symposium (IGARSS), 2011 IEEE International, vol., no., pp. 834, 837, 24-29 Jul. 2011 discloses a pre-screener to ignore cases where substantial soil signals are present.

And the next line gives us the reason behind this new patent:

The invention disclosed herein offers an alternative to the prior art for target discrimination.

Taken with the reference to "electromagnetic induction responses" above, it appears that researchers have discovered a new way to identify metals based on their reaction to pule induction signals, and Minelab is leveraging that technology to make a PI machine capable of discrimination. At this point in my initial read, I assumed it was a new PI machine with DISC. This is confirmed further along:

With these representations, we can define the response of a metallic object by specifying a discrete time constant spectrum. That is, a set of amplitudes-time constant pairs. The time constant spectrum of a metallic object depends on its shape, conductivity, and permeability. Thus, an accurate estimation of the time constant spectrum of a metallic object can be used as a means of distinguishing one type of metallic object from another, and from clutter objects. In the following we explicitly omit the determination of the a0 term of the time constant spectrum.

This is talking about using the newly-discovered time constant measurement in order to determine target size, shape, and composition. It goes on to say that the new method of discrimination allows a target to be better identified regardless of the target orientation or its proximity to other targets. The rest of the document gives the specific equations and the numbers of channels and yadda yadda yadda. It's a lot to read and if you're into this sort of thing, I recommend you check it out.

Going back to the "dual" nature of the name Equinox - I originally thought that this was a VLF/PI hybrid, due to the amount of times the patent talks about VLF, but now I'm not quite sure. It might be that the machine can use mono-polar and bi-polar PI signals. Or it might be totally meaningless.

I'll wrap it up because I've written too much so tl;dr - I think this is a new Pulse Induction detector with discrimination or possibly a hybrid between multi-freq VLF and this new PI technology.

What a load of crap, this changes nothing, single frequency machines have a dedicated purpose and all detectors put out a magnetic field, all it means is that it can do multiple things and just how well it can do them is unknown, some multipurpose machine do well others don't.