Any sufficiently advanced technology is indistinguishable from magic.
Arthur C Clarke, Hazards of Prophecy: The Failure of Imagination
The search for gold, for buried treasure, is woven into the genetic fabric of Australians. It is responsible for much of the nation’s wealth; it lingers in the collective imagination of every red-blooded adventurer.
We caught up with Philip Beck, General Manager of Engineering and Operations at Minelab, to find out a bit more about just how metal detectors work. He has been with the company for two decades developing metal detecting technology, which puts him at the forefront of a global industry.
What do you do at Minelab?
I’m responsible for the engineering team, the design, the development, putting into manufacture all our new products. I’m an electronic engineer. I’ve been with Minelab for about 20 years now. I started getting involved with designing metal detectors in the early days, through to now, running the team that does.
How does a metal detector work?
The transmitter generates a varying magnetic field, and this varying magnetic field sets up what we call eddy currents in the target. So any conductive target will then have the electrons moving within that target, creating current, and then that current creates its own magnetic field, which the receiver for the metal detector listens for.
With a very sensitive receiver, you can see that magnetic field. So, essentially, a varying magnetic field creates current in the target, and then that current in the target creates its own magnetic field, that’s then perceived by the receiver.
I like to use the demo of an aluminium tube. You drop a piece of steel down it; it drops through quite quickly with gravity. But, if you drop a magnet through an aluminium tube, it drops through quite slowly.
The moving magnet creates eddy currents in the aluminium tube, the eddy currents then create their own magnetic field, which is in opposition to the moving magnetic field of the magnet dropping. This actually suspends the magnet, so it descends very slowly through the tube.
Are there different kinds of metal detectors for different kinds of treasure?
Yes, they’re trying to do different things. So, with a gold machine, we’ll actually pulse that field on and off. And that gives us the best response in gold fields, where we’re looking for really small targets, in what we call mineralised ground, where the ground itself starts to look like the target.
Whereas we’ll use a sinusoidal varying magnetic field in a coin and treasure machine, because that will give us really good discrimination. So you can tell whether you’re about to dig up a $1 coin or a $2 coin.
Do you find that gold detecting is the most popular type of detecting, considering there are so many gold fields here?
Traditionally, it absolutely has been. Particularly in Victoria, where the gold fields are so accessible. A lot of people journey to Western Australia, particularly over the cooler period and will take their holidays there for a month and look for gold.
Coin and treasure detecting has become more popular over recent years. We’ve got a guy in Adelaide who we talk to a lot, who goes through the parks and he finds old cricket buckles from touring teams, and relatively old coins, for Australia. So he has quite an exciting time doing that.
A lot of people don’t understand the amount of research that goes into detecting. In Australia, beaches are largely opportunistic.
You’ll find old house sites, or old towns, even where people used to gather. You’ll find signs of where people used to gather in towns and urban centres; it takes a lot of research, looking at old maps etc., and can be an occupation all by itself.
What kind of budget does one need to get into metal detecting?
Again, it depends on gold versus coin and treasure. Gold, generally you can get into for a bit over a grand for a gold machine, but it’s not going to be as satisfying as if you spend a bit more.
If you spend about $4,500 for an SDC2300, that’s going to give you a good chance of finding gold in most locations because it’ll work in more mineralised ground.
There are two effects; there’s salt and there’s mineralisation. Generally, the SDC will deal well with the mineralisation. Salt is not a problem with that detector. You’ll find half-gram nuggets, 0.2-gram nuggets, even nuggets so small that you can’t measure their weight.
The good thing about being able to find small gold is that there’s so much of it around. It’s a lot easier to go out and find a piece of small gold, or ten pieces of small gold, than it is to go and find a one ounce piece.
You can go out with a Gold Monster, but in a lot of places in Australia, the ground is a little bit too mineralised. And so you need to invest a little bit more to get that better detector for the local conditions.
I think that metal detecting is a lot like fishing. I’ve met two types of guys on charter boats; one of them has spent $800 to be there, so he wants to take home $800 worth of fillets, whereas the other guy has spent the same and wants to make sure he has $800 worth of fun.
Honestly that latter guy always has a better experience, and I suspect metal detecting is much the same. If you’re having a good time doing it, and you’re enjoying the hunt, then that $4,500 is paid back really quickly.
Yes, exactly. I’ve got a video on YouTube of a couple of guys and it goes from them getting their first signal, through to them pulling a ten ounce piece out of the ground. And these guys, they look a bit hardcore, but they’re dancing around, singing, and they would have been equally happy with a two-gram piece as well.
What about for the coin and treasure detectors, what kind of cost is associated with them?
You can get started a lot cheaper. You can buy an Equinox for $1,000 in Australia, but you can go as low as $300-$400 for a Vanquish, which will work really well on the beach, or in parks or an old house site etc. And one of the good things about the current crop of metal detectors is they’re a lot easier to use than those from the past.
To take a step back, what are Minelab doing in the future, R&D wise? Where are you guys looking to go?
We work in three areas. We work in the counter mine arena, where we’re looking for land mines. We’ve recently in the last 12 months released a model in that category that’s a combined ground penetrating radar and metal detector.
We’re looking at putting that metal detecting technology into a new land mine detector and creating a metal detector only model that will be for militaries and NGOs. NGOs will be clearing minefields around the world.
In the coin and treasure side, we put out a new technology three years ago now that’s a simultaneous multi frequency technology that had been used a little bit up until then, but the way we’ve used it, we’ve used a lot more signal processing from what has been done before, so we’re able to collect so much more information about the target and ground that allows a lot better discrimination in a lot more circumstances.
There’s always somewhere for the technology to go. Somewhere like gold detection, you’re a lot closer to the basic physics, so that becomes a lot harder to get significant improvements. The biggest step most recently that we’ve put out is the GPZ7000, which increases depths of targets significantly, and that really pushes the bounds of the physics.
The thing we’ve got going for us is that we’ve got PhD physicists looking for new insights. We’re really lucky with the size of the team that we can throw at these problems just gives as fantastic technology and performance that we wouldn’t have even thought about years ago, and ease of use. You get the power and you get the ease of use that’s so important.
We’ve got a mantra internally about changing people’s lives, and watching our customers’ success stories becomes really fulfilling for us.