A lot of people are opining on this lawsuit without even knowing what the lawsuit is about. The patent in question (US7579839) basically says:
"A metal detector with a switched-voltage transmitter (basically all multifrequency designs) with synchronous demodulators (basically all metal detectors) whereby the user can change frequencies."
The Legend likely infringes this patent, but then so does the Garrett Apex, XP Deus II, White's V3. and probably models from AKA and Rutus. A question comes to mind: why sue NM and not the others? Possibly because NM has made a significant dent in Minelab sales, possibly because they are perceived as being an easier target, or possibly this is a warm-up for the other companies.
The V3 is an interesting case because it would be the first detector to infringe this patent -- the DFX did not, nor did the Fisher CZ, as neither had selectable frequencies. Yet Minelab did not sue White's; they did not even send a cease-&-desist letter (the normal step before filing a lawsuit), I was there at the time. Patent '839 was filed during the development of the V3 and that was in the days of "first to invent" rules, meaning that if White's could show they knew of the concept before the patent was filed, they would be in the clear. And, indeed, that was the case; I recall a development document written by Mark Rowan that predates the patent. If Garrett inherited this document then they can probably fend off a lawsuit as well.
Other companies (like NM) may not be so lucky. If they choose to fight the suit they will have to directly challenge the patent, which ain't easy or cheap. But there's loads of prior art to look at, not only metal detectors but eddy flaw detectors, vending machines, and even slot machines. You'd be surprised at what's been patented that uses the exact same technology as hobby detectors. And then there is the question as to whether '839 even rises to patentability based on whether there was an inventive step or lack of obviousness. And I think that last one would be a winner, as synchronous demodulation that follows the frequency selection has been around for decades. But it may be cheaper for NM to simply agree to a licensing deal with Minelab, especially since the patent expires in 2 years.
- Minelab has been fairly successful in lawsuits, and they now have a boatload of patents to pick from. Some are really good patents, some are really weak.
- Two of the successes came on patent US7310586 (the use of wireless technology in metal detectors) vs White's & XP. It's one of those patents that should have never gotten by the examiner based on obviousness. This is a key problem with the US patent office: examiners who have no idea what they are looking at. It's why prescription drugs cost so much.
- I don't recall that Minelab sued Fisher. The story I heard is they sent a cease-&-desist letter to Fisher, and Fisher replied with evidence that the CZ did not infringe. Minelab went away, no lawsuit.
- The Legend is not a copy of the Equinox. It may imitate the Equinox in many ways but that's been the story of hobby detectors since 1960. All of the Equinox's secrets are in software and NM engineers had to figure out a lot of things in order to get even close to an Equinox. The fact that they did so well in their inaugural MF release is simply incredible.
- Fisher did not invent the concept of MF, neither did Minelab. There is a Westinghouse MF patent from 1972, and another one even earlier than that (don't recall it offhand).
- I don't recall that White's & Garrett sued each other over VLF motion disc, which was invented by George Payne while he was at Bounty Hunter.
- White's sued Payne when he left to create Teknetics, and they lost on a technicality: they failed to have Payne sign a second no-compete agreement when he was re-hired from Bounty Hunter.
- About 2/3rds of Minelab's revenue is from metal detection, and about half of that is from hobby & gold. So, no, it's not a sideline.