Metal Detecting Depth - A Deep Subject

This sucker goes deep!

One of the most contentious issues I've ever run into in the metal detecting hobby is how deep will a metal detector go? More than 6 - miles down, at least (their eyes widen) IF I toss it overboard, just above the 7-mile deep Marianas Trench in the Atlantic Ocean. All smart ass responses like that aside, what they really want to know is how deep can the electromagnetic field go in finding treasure...et al.

Well, in context, a metal detector's target sensing depth, (Verly Low Frequency or Pulse machine) depends on the size and makeup of the search coil (Concentric or Wide-Scan or Monoloop), the conductivity of the ground (wet or dry), the amount and type of local electromagnetic interference (power lines), the amount of mineralization in the immediate environment (salt water), the presence of iron or "hot-rocks" in the immediate vicinity, the amount of power (sensitivity and gain controls) reaching the search coil and the frequency of the magnetic field(s) emanating from the search coil, any "masking" effects of more than one target under the coil simultaneously, plus the size and makeup of the target itself, all have a vote in that. And modern VLF machines are calibrated to coin-sized targets. So usually, when someone asks you how deep does a certain metal detector go, the best response is "DEPENDS..."and not the ones in the box at the drug store, unless you are my age. Onward!

I'm kinda' tired today, so I'm not going into a detailed explanation for the millionth time concerning these factors, but for those that don't know, I would suggest reading some of the basic books on metal detecting and treasure hunting by Charles Garrett, Dick Stout, Andy Sabisch, Gary Drayton and others that can get you into the wilds of metal detector basics and advanced operations.

I will say, a basic tenet in metal detecting is that max power usually leads to max headaches in the field. Try shining your headlights on "BRIGHT" into fog while driving in the deep woods and then we can talk at the hospital later, while they are patching you up, why the BRIGHT lights made it harder, or impossible, to see that now-dead deer wedged in your shattered windshield. Visible light rays are also, believe it or not, in the same electromagnetic spectrum your metal detector search field operates in...just at a much higher wavelength. And at high settings, the waves scatter and reflect off everything, without a very accurate target response, with more falsing than finding.

My ire, I think, has been raised on this subject mainly because every end-of-the-year holiday season, the time for the new metal detector models, aka, the "deeper" metal detectors to come out, the claims of increased depth begin. After over 50-years in the hobby with almost every kind of metal detector, I sometimes look at the new, seasonal "...deeper!" claims the same way I view some dark figure in an alleyway going "Pssst...wanna' buy a Rolex?" 

Strangely enough, while I was working on this blog subject, Dick Stout in his Stout Standards blog beat me to it with his "brainfarts" column talking about the same subject; detector depth. So I had to delay this a few months. From my perspective analog VLF/TR machines (as opposed to digital VLF nowadays) of the early days (60's,70's,80's) were no slouches in the depth department either, and I used to dig silver coins regularly at 8" to 12" deep in the 70's and 80's.

So, as far as I am concerned, electromagnetic-based Very Low Frequency hobby machines have probably gone about as far as they are going to go depth-wise, unless a major paradigm shift occurs in Physics, which I doubt. But then again...