They bought the patent in 2017, then let it lapse in 2023
The word patented is still on the brochure and still in the manual. The patent behind it was bought, renewed once late with a surcharge, reminded about in 2022, and then allowed to die with six years left to run. All of it is on the public file.
The AML Pro is sold on patented technology. Those words are on the product page, on the data sheet and in the manual, and none of those documents gives a patent number.
The patent that matches the described mechanism is US 7,898,456, and it has not been in force since 2023. It did not get challenged or invalidated. It was bought by SubSurface Instruments in April 2017, kept alive by one late payment in 2018, and then simply not renewed. The lapse was recorded on 3 April 2023, effective 1 March, with about six years still on the clock.
There is a smaller detail in the file that I think says more than the headline. On 17 October 2022 the patent office mailed a maintenance fee reminder. Somebody received it. Nothing was paid.
1The claim that is still being made
A patent does two jobs in a brochure. It tells a buyer an examiner agreed the thing was novel, and it tells them nobody else can sell the same thing. Both are reassuring when you are being asked for several thousand pounds for a handheld box.
“Find Buried PVC and All Other Plastic Pipes Using UHRF Advanced Digital Patented Technology & GPS Tracking”
“Patented, Radio Frequency Technology”
Neither the product page, nor the data sheet, nor the manual gives a patent number, a patent title or an inventor. The claim is asserted and the reader is left to take it on trust. So I went and checked it.
The claim is current, it is in three documents, and none of them names a patent.
2The search that hides the owner
This is worth a section on its own, because it is a trap I walked into myself while writing this piece, and it is the reason a casual check makes the situation look better for the seller than it is.
If you search Google Patents for patents assigned to Subsurface Instruments, you get almost nothing useful. It is tempting to conclude the company owns no relevant patent and that the marketing claim has no basis at all.
That conclusion is wrong. The assignee index keys on the original assignee, the one recorded at grant. A company that buys a patent after it is granted can own it outright and never appear in that field. The “current assignee” line on this patent still reads Prairielands Energy Marketing today, and Google itself warns on the page that its assignee list may be inaccurate.
The authoritative record is not the assignee field. It is the Legal Events table further down the same page, where assignments are recorded with a date and a reel and frame number. Read that instead, and the ownership is not ambiguous at all.
The fuller record makes the marketing claim look worse, not better. It is not that the company has no patent. It is that it had one, and stopped paying for it.
The assignee field hides post-grant buyers. Read the Legal Events table, which is where the truth is.
3The whole record, event by event
United States patents are not paid for once. They carry maintenance fees at roughly four, eight and twelve years, and if one goes unpaid the patent lapses. That schedule turns the file into a running statement, in cash, of what the owner thinks the invention is worth. Here is the whole of it.
| Date | Event on the file | What it means |
|---|---|---|
| 15 to 18 Mar 2009 | Assigned by Cloutier and Oehme to Prairielands Energy Marketing | The inventors sign it over |
| 1 March 2011 | Granted | The clock starts |
| 6 August 2014 | Fourth year fee paid | First renewal, on time |
| 18 April 2017 | Innovatum to Prairielands, and Prairielands to SubSurface Instruments, Inc. | Two assignments the same day. SSI now owns it. |
| 22 October 2018 | Maintenance fee reminder mailed | The eighth year fee is overdue |
| 1 November 2018 | Eighth year fee paid, plus a 7.5 year late surcharge | Paid late, inside the six month grace |
| 17 October 2022 | Maintenance fee reminder mailed | The twelfth year fee is due |
| 3 April 2023 | Lapsed for failure to pay maintenance fees | Effective 1 March 2023 |
| 22 August 2029 | The date it would have run to | About six years lost |
Status on the public record today: Expired, Fee Related. Entity status throughout: large entity, which is the higher fee band. Not challenged, not invalidated, not sold on. Simply not renewed.
Two renewals paid, the second one late, a reminder in 2022, and then nothing.
4April 2017, the day it changed hands twice
One line in that table deserves pulling out. On 18 April 2017 the file records two separate assignments, both effective the same day.
- Innovatum, Inc. to Prairielands Energy Marketing, Inc. Reel and frame 042040/0651.
- Prairielands Energy Marketing, Inc. to SubSurface Instruments, Inc., Wisconsin. Reel and frame 042040/0806.
Whatever the tidying-up behind that was, the outcome is not in doubt and it is not inferred. From 18 April 2017 the patent belonged to the company that sells the AML Pro. They did not license it from a stranger. They owned it.
SubSurface Instruments owned US 7,898,456 outright from April 2017.
That matters because it removes the most generous available explanation. If the marketing had been pointing at somebody else’s patent, a lapse would be somebody else’s decision and arguably none of their business. It was their patent and their decision.
Two recorded assignments on one day in 2017 put the patent in the seller’s own hands, six years before it died.
5The late payment, and then the one they did not make
The eighth year fee tells you something on its own. A reminder went out on 22 October 2018. The payment came on 1 November 2018 and it carried a 7.5 year late payment surcharge, which is what you pay when you have gone past the window and are inside the six month grace period.
So in 2018 the renewal nearly did not happen, a letter arrived, and somebody paid it, late and with the penalty. The patent survived that one.
Four years later the same thing happened again. A maintenance fee reminder was mailed on 17 October 2022. This time nothing was paid, the grace period ran out, and on 3 April 2023 the file records the lapse.
I want to be careful here, because there is an obvious uncharitable reading and I do not think the record supports it on its own. A company can miss a renewal for a dozen mundane reasons: a change of agent, a change of address, an unpaid invoice sitting in somebody’s tray. The file cannot tell you which, and neither can I.
What the file does establish is the sequence. Warned in 2018 and paid. Warned in 2022 and did not.
The same warning arrived twice. The first time it was paid with a penalty. The second time it was not paid at all.
6What an owner is saying when they stop paying
A maintenance fee is the cheapest decision a patent holder ever makes, and it is the only one they make in public. Renew and you are saying the exclusivity is still worth more than the fee. Stop, and you are saying it is not.
Two renewals, then a decision that a third was not worth it.
You can hold that thought alongside the marketing without either one settling the other. The device may work exactly as claimed and the patent may simply have stopped mattering commercially. But a buyer reading “patented technology” on the current brochure is reading a word that stopped being accurate three years ago, about a patent the seller owned and chose not to keep.
And there is a simple fix available to them, which is the same fix I asked for in the piece about the missing power figure. Print the number. If there is a live patent I have not found, one line in the brochure settles it and this page becomes wrong, which I would genuinely welcome.
Stopping the fee is a valuation. The marketing did not follow the patent into retirement.
7What I am not saying
I am not saying an expired patent means the device does not work. It does not mean that and it never has. Patent examination tests novelty, not efficacy, and plenty of excellent equipment is sold with no patent at all. Anyone quoting this page to argue otherwise has gone past the evidence.
I am not saying the lapse was deliberate or that anybody set out to mislead. I do not know why the fee went unpaid and the file does not say.
I am not saying anything against the inventors. Paul Cloutier is Professor Emeritus of Physics and Astronomy at Rice University, a NASA mission co-investigator, and the pair have been filing detection patents together since 1984, most of them magnetic instruments that work and are still sold today. The question here is about a renewal fee, not about them.
What I am saying is narrow, and it is four checkable things.
- The current sales material claims patented technology and names no patent number.
- SubSurface Instruments owned US 7,898,456 from 18 April 2017.
- They paid the eighth year fee late, with a surcharge, then did not pay the twelfth year fee after a reminder in October 2022.
- The patent lapsed on 3 April 2023 with about six years left to run, and the marketing did not change.
That is all it would take to settle it.
8Questions people ask
Who owned the AML Pro patent?
SubSurface Instruments, Inc. of Wisconsin owned it. US 7,898,456 was assigned to them on 18 April 2017 by Prairielands Energy Marketing, Inc., recorded at reel and frame 042040/0806. A Google Patents assignee search does not show this, because that index keys on the original assignee and a company that buys a patent after grant never appears in it. The authoritative record is the assignment event in the Legal Events table.
When did the AML Pro patent expire?
US 7,898,456 lapsed for failure to pay maintenance fees. The lapse was recorded on 3 April 2023 with an effective date of 1 March 2023. Had the twelve year fee been paid it would have run until 22 August 2029, so roughly six years were left on it.
Is the AML Pro still patented?
No. The patent that matches its described mechanism expired in 2023 for non payment of renewal fees and its status on the public record is Expired, Fee Related. It was not challenged, invalidated or sold. The marketing has continued to describe the technology as patented since then.
Did SubSurface Instruments let their own patent expire?
Yes. They acquired US 7,898,456 in April 2017, paid the eighth year maintenance fee on 1 November 2018 with a late payment surcharge, received a maintenance fee reminder on 17 October 2022, and did not pay. The patent lapsed on 3 April 2023 while under their ownership.
Does an expired patent mean the AML Pro does not work?
No, and it is important not to claim that it does. A lapsed patent says nothing about whether a device performs, and plenty of good equipment is sold with no patent at all. What a lapse does mean is that the exclusive right has ended, that anyone may now practise the invention, and that the owner judged the protection no longer worth the renewal fee.
This piece is only about the renewal record. The physics, the depth claims and the market test are set out elsewhere: the AML Pro in five minutes, the transmit power that is not published, the certificate and the machine named on it, or the full investigation.