WEBVTT - TechStuff Classic: How Metal Detectors Works 0:00:04.120 --> 0:00:07.160 Get in touch with technology with tech Stuff from how 0:00:07.200 --> 0:00:13.920 stuff Works dot com. Hey there, and welcome to tech Stuff. 0:00:13.960 --> 0:00:16.680 I'm your host, Jonathan Strickland. I'm an executive producer with 0:00:16.720 --> 0:00:20.360 How Stuff Works in love all things tech and back 0:00:20.440 --> 0:00:24.840 on October two thousand eleven, my co host Chris Paulette 0:00:24.840 --> 0:00:28.640 and I sat down in a tiny little alcove at 0:00:28.760 --> 0:00:36.360 the then headquarters of How Stuff Works in Buckhead, Georgia, Buckhead, Atlanta. 0:00:36.760 --> 0:00:39.640 I'm kind of glad we're not in that particular alcove 0:00:39.880 --> 0:00:41.680 now I'm in a much nicer studio. But we sat 0:00:41.680 --> 0:00:45.199 down to talk about how metal detectors work. What is 0:00:45.240 --> 0:00:49.279 the operating principle behind metal detectors, what's the science behind it. 0:00:49.640 --> 0:00:52.560 So you're about to enjoy this classic episode of tech 0:00:52.600 --> 0:00:54.800 Stuff how metal detectors work, And I'll talk to you 0:00:54.840 --> 0:00:58.080 again in just a moment. So today we are going 0:00:58.120 --> 0:01:00.280 to talk about this. You know what, This was a 0:01:00.360 --> 0:01:04.320 topic that I don't know that anyone has ever requested. Um. 0:01:04.360 --> 0:01:08.080 It came to me actually as I was looking through 0:01:08.200 --> 0:01:11.960 stuff in my basement and went metal detectors. How should 0:01:11.959 --> 0:01:14.880 talking about We've never talked about metal detective Actually, we've 0:01:14.920 --> 0:01:17.880 sort of talked about metal detectors, because metal detectors use 0:01:17.920 --> 0:01:21.400 a lot of the technology we talked about before, especially 0:01:21.720 --> 0:01:26.800 the relationship of magnetism to electricity. Yeah, um, but yeah, 0:01:26.800 --> 0:01:30.000 I mean it's something that we run into very often, 0:01:30.120 --> 0:01:32.679 especially if we travel and walk through the metal detectors 0:01:32.680 --> 0:01:35.680 at the airport. If we're not getting back scattered or uh, 0:01:36.040 --> 0:01:38.680 you know, dropping stuff that you can't find, losing your 0:01:38.720 --> 0:01:43.400 wedding ring and the malts outside. Yikes, that's good stuff. 0:01:43.440 --> 0:01:46.520 I've done that. I still have it, so there you go. 0:01:46.680 --> 0:01:50.840 I've never lost my wedding ring. All right, Well it 0:01:50.920 --> 0:01:54.920 was only temporary. So anyway, metal detectors talk about what 0:01:54.960 --> 0:01:58.120 they are. We're mostly going to be talking about the 0:01:58.200 --> 0:02:01.160 kind that you would you would care you with you 0:02:01.160 --> 0:02:03.520 you know, the portable metal detectors that you would use 0:02:03.560 --> 0:02:07.520 when looking for say, loose change on the beach, or 0:02:07.920 --> 0:02:12.960 you know, searching for that rare civil war uh bullet 0:02:13.440 --> 0:02:16.640 or a gun that might be part of you know, 0:02:16.680 --> 0:02:19.120 in an area that you knew the battle happened here, 0:02:19.160 --> 0:02:21.880 so there may very well be stuff here. Yeah. We 0:02:21.880 --> 0:02:24.120 we should definitely talk about some of the applications of 0:02:24.160 --> 0:02:26.639 the technology. Um, and I would like to point out 0:02:26.639 --> 0:02:29.000 that we have an excellent article on how stuff works 0:02:29.000 --> 0:02:32.519 dot com if you're interested in learning more, um, how 0:02:32.639 --> 0:02:35.400 metal detectors work. Yeah, it should be pretty easy for 0:02:35.440 --> 0:02:38.400 people to find, written by Jeff Tyson, and it is 0:02:38.440 --> 0:02:43.240 a very good article and very uh simple to follow, 0:02:43.320 --> 0:02:46.400 easy to understand. I would say this is this is 0:02:46.440 --> 0:02:49.320 one of those really great how stuff works articles. Yeah. 0:02:49.480 --> 0:02:51.079 You know, by the time you get through it and 0:02:51.120 --> 0:02:55.040 you're like, oh, yeah, no, that totally makes sense, especially 0:02:55.080 --> 0:02:57.080 if you have a little bit of grounding in the 0:02:57.120 --> 0:03:04.360 way electromagnetism works and conductors and inducers. Right, So we'll 0:03:04.440 --> 0:03:06.400 we'll cover that. I mean, we've talked about an in 0:03:06.400 --> 0:03:09.440 previous podcast, but we'll we'll do a quick brush up 0:03:09.440 --> 0:03:12.600 so that we can explain it. Um, so you wanna, 0:03:12.800 --> 0:03:15.399 let's let's talk about the the Jeff does a great 0:03:15.480 --> 0:03:19.840 job at breaking down what the typical portable metal detector, 0:03:19.919 --> 0:03:23.400 the four main parts of one, what they would be. Yeah, 0:03:23.440 --> 0:03:26.160 I mean, if you've ever seen people walking around with 0:03:26.639 --> 0:03:28.600 a metal detector, you you sort of know what they 0:03:28.600 --> 0:03:31.720 look like. They have a round dish part that's used 0:03:31.800 --> 0:03:34.040 close to the ground, right, that's a that's called the 0:03:34.040 --> 0:03:39.119 coil um then yes, And then you have the stabilizer um, 0:03:40.240 --> 0:03:42.600 which is the part that you actually hold onto, that 0:03:42.800 --> 0:03:45.160 holds onto europe, that that you see on your arm 0:03:45.160 --> 0:03:48.360 because you know, frankly, having used a metal detector, it's 0:03:48.400 --> 0:03:51.440 not the lightest thing, right. This this helps, This helps 0:03:51.480 --> 0:03:54.640 distribute the weight somewhat so that you're not you don't 0:03:54.680 --> 0:03:57.600 feel like you're carrying around a you know, ten pound 0:03:57.680 --> 0:04:01.440 brick the whole time, because without that then you would 0:04:01.440 --> 0:04:04.120 get very tired very quickly. Yeah. And the the ten 0:04:04.240 --> 0:04:07.120 pound the aforementioned ten pound brick, which probably isn't ten pounds, 0:04:07.120 --> 0:04:09.120 but it certainly can feel that way after a while. 0:04:09.360 --> 0:04:12.200 That's the control box, uh, And you've got all your 0:04:12.280 --> 0:04:17.880 your electronics in there. And and then the the connecting bit, yes, 0:04:18.279 --> 0:04:21.320 the long skinny part that's the shaft. Yes, it connects 0:04:21.360 --> 0:04:24.279 the coil at the base to the part that you're holding, 0:04:24.400 --> 0:04:26.760 and the of course the control box. So those are 0:04:26.800 --> 0:04:30.599 your four basic parts of your basic metal detector. Yes. 0:04:30.800 --> 0:04:34.120 And then you know you have your headphones because this 0:04:34.200 --> 0:04:37.000 is one of our episodes of stuff that beeps and 0:04:37.040 --> 0:04:39.440 stuff what beats? Stuff? What beeps and it it does 0:04:39.520 --> 0:04:43.040 in fact deep Yeah, there's usually some sort of audible 0:04:43.080 --> 0:04:47.680 alert that you have in fact detected metal and now 0:04:47.720 --> 0:04:50.880 and more sophisticated UH, metal detectors will tell you a 0:04:50.880 --> 0:04:53.800 lot more often with uh, well sometimes with with an 0:04:53.839 --> 0:04:56.800 audible tone, but also with a visual uh, some kind 0:04:56.800 --> 0:05:00.040 of visual analysis. We can get into that to in 0:05:00.040 --> 0:05:05.159 a minute. So there are three main types of metal detectors, 0:05:05.320 --> 0:05:09.960 the ones at work, the three three main approaches to 0:05:09.960 --> 0:05:13.960 to metal detection. Let's say, Uh, there's UM, there's the 0:05:14.200 --> 0:05:18.080 very low frequency which is probably the most um, the 0:05:18.120 --> 0:05:21.040 most popular or the most common type of MEL detector, 0:05:21.040 --> 0:05:25.080 at least for the portable metal detectors. UM. Yeah. When 0:05:25.160 --> 0:05:26.960 we get into this, you'll you'll see that each of 0:05:27.000 --> 0:05:30.440 these different types has its own strengths and weaknesses. And 0:05:30.520 --> 0:05:33.560 you might say, well, the VLF detector sounds great, why 0:05:33.600 --> 0:05:35.800 would you use the others? We'll get into that. Yeah. 0:05:35.880 --> 0:05:42.120 The other two are pulse induction and beat frequency oscillation. Yeah. 0:05:42.320 --> 0:05:50.039 I I knew a beat frequency oscillator once. He was awesome. Anyway, 0:05:50.040 --> 0:05:51.640 I think there was something else I guess, So, yeah, 0:05:51.680 --> 0:05:56.560 that's the beat boxer frequency oscillator. That the uh, the 0:05:56.640 --> 0:06:00.400 VLF metal detector is the type that I have. UM, 0:06:00.440 --> 0:06:06.320 and uh the the basic differences, uh, and these is 0:06:06.600 --> 0:06:09.599 you know, you'll see those really in the coils. To 0:06:09.680 --> 0:06:13.440 be honest, because the VLF has two different coils. One 0:06:13.720 --> 0:06:18.880 transmits um and and the other is basically an antenna 0:06:18.960 --> 0:06:21.760 to pick up the signals, so they're shielded from one another, 0:06:21.800 --> 0:06:24.840 so it doesn't pick up because otherwise you turned it on, 0:06:24.920 --> 0:06:27.040 you would just have the receiver saying, oh my gosh, 0:06:27.120 --> 0:06:31.960 there's metal everywhere. Holy crap, you're rich, even up in 0:06:31.960 --> 0:06:35.680 the air. It's it's literally everywhere. Yeah, that would that 0:06:35.720 --> 0:06:38.120 would not be very useful. And taking this back to 0:06:38.200 --> 0:06:41.000 the store where I bought it. It's a detector detector. 0:06:41.120 --> 0:06:43.360 This does not do me any good. It's a detected 0:06:43.680 --> 0:06:50.920 or it's a detected or where's perry? So the the 0:06:50.920 --> 0:06:55.120 the transmitter coil um it's it think of a circle, 0:06:56.000 --> 0:06:59.360 all right. It's the circular part at the base of 0:06:59.440 --> 0:07:02.680 the male detector. And if you were to take it apart, 0:07:02.720 --> 0:07:05.280 which I do not recommend you do, you would see 0:07:05.279 --> 0:07:08.039 that there is a warrant point your warranty and it 0:07:08.080 --> 0:07:10.440 may not work anymore. You will have a there's a 0:07:10.480 --> 0:07:14.600 coil of wire that goes around the perimeter of this circle. 0:07:14.680 --> 0:07:17.240 Like it's it's wrapped around. So the circle itself is 0:07:17.400 --> 0:07:19.120 let's say it's like a quarter of an inch thick, 0:07:19.560 --> 0:07:21.640 and you've got this coil of wire that's that's coiled 0:07:21.640 --> 0:07:24.040 around this quarter of an inch all the way around 0:07:24.040 --> 0:07:27.560 the perimeter of this circle. When you run electricity through 0:07:27.560 --> 0:07:30.720 this coil of wire, what happens besides the fact that 0:07:30.800 --> 0:07:35.040 electrons are moving through because of the nature of electricity 0:07:35.080 --> 0:07:40.480 and magnetism, Well, when you run electricity around a coil 0:07:40.560 --> 0:07:43.480 like that, it generates a magnetic field. That's right, It 0:07:43.600 --> 0:07:46.720 does generate a magnetic field, and it generates a magnetic 0:07:46.720 --> 0:07:50.280 field perpendicular to the direction of the electricity. It's just 0:07:50.320 --> 0:07:53.800 the nature of electromagnetism. It's amazing, it's awesome. That's what 0:07:53.960 --> 0:07:57.920 how electro magnets work and UH dynamo's work in UH 0:07:58.560 --> 0:08:02.240 and sort of using this reverse um. So you've got 0:08:02.240 --> 0:08:06.640 electricity flowing through these coils, and that generates the magnetic field. Well, 0:08:06.680 --> 0:08:10.080 it doesn't just the electricity. Electricity doesn't just flow in 0:08:10.160 --> 0:08:13.200 one direction, no, it it goes back and forth. It 0:08:13.280 --> 0:08:17.120 alternates very very very fast, almost as fast as I 0:08:17.160 --> 0:08:18.920 waffle back and forth on what I want to eat 0:08:18.920 --> 0:08:24.560 for lunch. And that means that the magnetic field also alternates. 0:08:24.600 --> 0:08:29.000 The direction of the magnetic field changes. Uh And if 0:08:29.040 --> 0:08:31.520 you think of it in terms of the disc, the 0:08:32.120 --> 0:08:35.600 the coil disc being towards the ground, you can think 0:08:35.640 --> 0:08:38.360 of it as the magnetic field occasionally is pushing against 0:08:38.520 --> 0:08:41.960 or pulling the ground in general. That just think of 0:08:41.960 --> 0:08:43.880 it that way. That's the direction of the magnetic field 0:08:43.880 --> 0:08:46.280 while the electricity is going around and around in a circle, 0:08:46.360 --> 0:08:49.520 back and forth and in the various directions, and that 0:08:49.720 --> 0:08:55.320 alternation is happening hundreds of times per second. So you've 0:08:55.320 --> 0:08:59.400 got this magnetic field that's that's just oscillating essentially right 0:08:59.400 --> 0:09:02.800 there against the ground. When it comes to contact with 0:09:03.200 --> 0:09:06.000 something that is metal, well, the metal will start to 0:09:06.240 --> 0:09:10.000 that magnetic field will cause a a weaker magnetic field 0:09:10.320 --> 0:09:13.760 to generate around the metal object. Yeah. Basically induces a 0:09:13.800 --> 0:09:17.600 magnetic field in a metal object in the ground. So 0:09:17.679 --> 0:09:23.280 let's say, uh, um, you drop a screw and when 0:09:23.320 --> 0:09:25.880 you're trying to build something outside and you're trying to 0:09:25.920 --> 0:09:27.680 find it with your metal detector so that you don't 0:09:27.679 --> 0:09:29.520 step on it with a bare foot, and you know, 0:09:29.760 --> 0:09:33.360 need a trip to the hospital and a technis shot. Um. 0:09:33.400 --> 0:09:35.960 So as soon as you run the coil of the 0:09:35.960 --> 0:09:38.040 field and you're not trying to touch the ground with it, 0:09:38.080 --> 0:09:41.600 you really just need it close to the ground. Um, 0:09:41.640 --> 0:09:44.640 it will find the screw. The screw will basically start 0:09:44.679 --> 0:09:50.080 inducing a It will metal detect detector will generate a field, 0:09:50.120 --> 0:09:53.080 and that will cause the screw to generate its own 0:09:54.000 --> 0:09:56.839 a weaker magnetic Yeah, yeah, considerably weaker, but it will 0:09:56.960 --> 0:10:01.599 the metal detector, Uh, the antenna coil and the transmitter 0:10:01.640 --> 0:10:03.760 coil will say, oh, look there's something right there that 0:10:03.880 --> 0:10:07.520 is generating a magnetic field. It's right here. Chris and 0:10:07.520 --> 0:10:09.320 I have a lot more interesting things to say about 0:10:09.360 --> 0:10:12.120 metal detectors, but first let's take a quick break to 0:10:12.240 --> 0:10:22.280 thank our sponsor. So, if you have a coil of 0:10:22.360 --> 0:10:26.480 wire and you introduce it into a fluctuating magnetic field, 0:10:26.520 --> 0:10:29.480 that will induce the flow of electricity within the wire. 0:10:30.240 --> 0:10:32.960 Just as electricity and the wire will create generate a 0:10:32.960 --> 0:10:37.000 magnetic field, a magnetic field will induce electricity to run 0:10:37.040 --> 0:10:40.760 through wire fluctuating magnetic field. It can't just be just 0:10:40.800 --> 0:10:46.319 a magnetic field. So when the weak magnetic field from 0:10:46.360 --> 0:10:49.920 the mental object hits that that the wire in the 0:10:49.920 --> 0:10:55.680 the the the receiver coil that generates electricity which then 0:10:55.760 --> 0:10:59.880 alerts the control box and that that's what. Then when 0:10:59.880 --> 0:11:03.360 the control box gets an electric signal from the receiver coil, 0:11:04.040 --> 0:11:09.320 that says beep, something is here, stuff, what beeps? Yep? Stuff? 0:11:09.400 --> 0:11:14.000 What beeps? So yeah, that's the basic uh way that 0:11:14.120 --> 0:11:19.120 a VLF metal detector works. It shoots out this magnetic field. 0:11:19.320 --> 0:11:24.080 The polarization is alternating the same as the the flow 0:11:24.120 --> 0:11:28.160 of electricity around the the the transmitter coil, and then 0:11:28.320 --> 0:11:31.880 the receiver coil picks up any magnetic fields generated by 0:11:31.960 --> 0:11:34.080 metal objects that are under the surface of the ground. 0:11:35.120 --> 0:11:38.120 It's pretty cool and generally it will go more or 0:11:38.240 --> 0:11:42.360 less about a foot. Yeah, you're not gonna find you know, 0:11:42.480 --> 0:11:46.120 the Earth's core. Yea with a metal detect and the 0:11:46.559 --> 0:11:50.840 depth of what the depth of the The effectiveness of 0:11:50.880 --> 0:11:53.160 this metal detector is also going to be dependent on 0:11:53.280 --> 0:11:57.520 other factors, like the nature of the metal object itself, 0:11:57.840 --> 0:12:00.440 because some some metal objects are going to generate a 0:12:00.440 --> 0:12:04.640 stronger magnetic field than others, like iron. Uh. It will 0:12:04.679 --> 0:12:08.599 also depend on the composition of the soil. Yes, so 0:12:08.760 --> 0:12:11.520 the soil has a lot of elements in it that 0:12:11.559 --> 0:12:14.280 would create a magnetic field, you're gonna get a lot 0:12:14.280 --> 0:12:19.360 of interference, yeah, or or an environment where uh that 0:12:19.360 --> 0:12:22.960 that would conduct electricity more readily, Like if you were 0:12:23.000 --> 0:12:26.760 trying to look for something and say saltwater, you might 0:12:26.840 --> 0:12:29.360 have more difficulty than if you were looking, you know, 0:12:29.520 --> 0:12:33.319 on on a different type of soil. UM. Now there 0:12:33.400 --> 0:12:37.440 is something to uh called phase shifting, Yes, and that's 0:12:37.440 --> 0:12:40.199 how it's able to tell what sort of metal, what 0:12:40.320 --> 0:12:43.600 sort of metal it is, UM. And it really has 0:12:43.640 --> 0:12:47.000 to do with the the inductance and the resistance of 0:12:47.200 --> 0:12:49.760 the object that you're looking for. Now, the inductance is 0:12:50.080 --> 0:12:55.000 um the objects ability to conduct electricity UM. And if 0:12:55.040 --> 0:12:58.400 it's inductive, it will be able to to conduct electricity easily, 0:12:58.480 --> 0:13:04.280 but it's slow to react to changes in the electrical current. UM. 0:13:04.320 --> 0:13:07.160 If it's resistive, it doesn't conduct electricity is easily, but 0:13:07.280 --> 0:13:10.080 it is quick to react to those those changes. And 0:13:10.360 --> 0:13:13.920 a sophisticated metal detector will be able to tell you, well, 0:13:13.960 --> 0:13:18.720 that's I think that's gold or based upon that phase shift, 0:13:18.760 --> 0:13:21.160 because the face shift for a particular element is going 0:13:21.200 --> 0:13:24.880 to remain constant, you know. That's that's why if it 0:13:24.880 --> 0:13:27.800 didn't remain constant, then this wouldn't matter at all because 0:13:27.800 --> 0:13:30.000 it wouldn't you know, we wouldn't know, you know, It's 0:13:30.040 --> 0:13:32.160 like we just know something is down there, we wouldn't 0:13:32.200 --> 0:13:34.840 know have any way of guessing what it is. But 0:13:35.000 --> 0:13:39.800 because it's an inherent property of this particular material and 0:13:39.840 --> 0:13:42.960 it's really dependent upon the molecular composition of whatever that 0:13:43.000 --> 0:13:46.920 material is, UM, then we can make start making guesses 0:13:47.000 --> 0:13:50.280 based on that phase shift. UM. And it's yeah, the 0:13:50.280 --> 0:13:52.240 face shift, you know, with it being that difference in 0:13:52.280 --> 0:13:57.000 timing between the transmitters frequency uh and the frequency of 0:13:57.040 --> 0:14:01.680 the magnetic wave that's generated by the object. Um. You know, 0:14:01.760 --> 0:14:06.240 it's these are sort of ranges, right like if it 0:14:06.600 --> 0:14:09.280 if it's a certain range there, then the male detector 0:14:09.320 --> 0:14:13.160 can give a best guess as to what that material maybe. 0:14:13.400 --> 0:14:17.959 So there's never necessarily a guarantee that whatever it is 0:14:18.000 --> 0:14:22.040 you've detected is specifically going to be you know, aluminum 0:14:22.160 --> 0:14:25.040 versus goal or whatever. But it's a it's an indicator, 0:14:25.120 --> 0:14:28.520 so that uh, it gives you at least the idea 0:14:28.520 --> 0:14:31.000 of you know, is that you measure risk versus reward, 0:14:32.280 --> 0:14:36.560 the risk of exhausting yourself digging up useless junk versus 0:14:36.560 --> 0:14:40.440 the reward of possibly finding something that is of true value. 0:14:41.240 --> 0:14:44.160 So that's really the whole purpose of this anyway. It's 0:14:44.200 --> 0:14:46.600 just you know, to kind of tune in on that 0:14:46.720 --> 0:14:49.400 beep and make it more meaningful so that you know, 0:14:49.440 --> 0:14:53.480 you don't waste your time digging up uh little pull 0:14:53.560 --> 0:14:58.680 tabs from soda cans. Yeah. Now, yeah, if you have 0:14:58.720 --> 0:15:02.480 a higher inductance, it's going to create a larger phase shift, 0:15:02.520 --> 0:15:06.040 and lower inductance has a smaller phase shift. Now, Uh, 0:15:06.200 --> 0:15:12.800 metal detectors use a phase demodulator to read this, and uh, 0:15:12.880 --> 0:15:18.040 what that creates is discrimination. Yeah, yeah, I know it's terrible, 0:15:18.160 --> 0:15:21.680 but oh no, not that. Within metal detectors, it's okay, Yeah, 0:15:21.720 --> 0:15:25.080 because the thing is a good metal detector will allow 0:15:25.120 --> 0:15:29.200 you to filter out stuff that you don't want because 0:15:29.920 --> 0:15:32.040 the metal detector, if you said it at a certain 0:15:32.120 --> 0:15:35.280 setting and say, you know, I'm really looking for metals 0:15:35.320 --> 0:15:38.680 that fall within this range, yeah, perhaps gold. I've actually 0:15:38.840 --> 0:15:43.000 seen uh, metal detector booths and they'll have like this 0:15:43.080 --> 0:15:47.320 giant jar of class rings that people have lost, which 0:15:47.360 --> 0:15:49.720 is sort of a you know reminder that you know, hey, 0:15:49.800 --> 0:15:51.840 you you can find stuff if you just take your 0:15:51.840 --> 0:15:54.800 metal to of course, people look at you funny, but yeah, 0:15:55.520 --> 0:15:57.480 that way. That way. Let's say that you're out there 0:15:57.480 --> 0:16:00.840 looking for something specific. You can you know, meld detectors 0:16:00.880 --> 0:16:03.440 have settings where you can, uh you can tell the 0:16:03.480 --> 0:16:07.320 meld detector to ignore anything outside of a particular range 0:16:07.320 --> 0:16:09.960 of frequencies. So in other words, you're saying, you might say, 0:16:10.000 --> 0:16:14.240 I'm only interested in finding silver. Let's say, so what 0:16:14.320 --> 0:16:16.200 I'll do is I'll set my meld detector so that 0:16:16.280 --> 0:16:20.360 it'll it'll only uh activate, it will only alert me 0:16:20.880 --> 0:16:26.280 if something that generates a magnetic frequency similar to that 0:16:26.360 --> 0:16:29.720 of silver is encountered by the metal detector. So in 0:16:29.760 --> 0:16:31.640 other words, what you might you might pass over a 0:16:31.680 --> 0:16:35.080 gold deposit and nothing happens. But as soon as you 0:16:35.440 --> 0:16:38.120 go over that that silver half dollar but ink, and 0:16:38.160 --> 0:16:40.080 then you dig it up and you like, hey, look 0:16:40.120 --> 0:16:43.600 I'm rich. I Meanwhile, the gold guy behind you was like, sucker. 0:16:45.040 --> 0:16:47.640 Well that's that. That can be called notching. Basically, you 0:16:47.680 --> 0:16:51.000 set it for a if you imagine a scale, uh 0:16:51.000 --> 0:16:53.680 you know, he's one notch on that scale. Or some 0:16:53.720 --> 0:16:56.120 of the more sophisticated metal detectors will allow you to 0:16:56.160 --> 0:16:58.840 set more than one notch r So that way you 0:16:58.880 --> 0:17:01.080 could look for both silver on gold and you'd say, 0:17:01.120 --> 0:17:06.200 ha ha, Mr smarty gold pants. Um, now that's that's 0:17:06.240 --> 0:17:11.720 the VLF. The post induction metal detector a little bit different. Yeah, 0:17:11.760 --> 0:17:14.679 it uses only a single coil, or it can use 0:17:14.760 --> 0:17:17.480 multiple coils working at the same time. Yeah, but they're 0:17:17.800 --> 0:17:20.359 these are these are coils that haven't that don't have 0:17:20.440 --> 0:17:23.439 that shielding. It's not like you have a transmitter coil 0:17:23.520 --> 0:17:27.080 and then a receiver coil, and all of these coils 0:17:27.080 --> 0:17:33.400 are generating very quick bursts of electricity, which of course 0:17:33.480 --> 0:17:38.160 creates a very sharp magnetic wave. And uh so it's 0:17:38.200 --> 0:17:40.560 just a really quick spike and then what will happen 0:17:40.680 --> 0:17:43.439 is that magnetic wave if it encounters a metal object again, 0:17:43.640 --> 0:17:45.680 that metal object will have to will generate its own 0:17:45.720 --> 0:17:50.440 magnetic wave, and the metal detector will pick up on that. 0:17:50.520 --> 0:17:52.800 And it's all it's kind of like an echo, right, 0:17:53.400 --> 0:17:56.040 It's kind of like an echo, right, thank you. So 0:17:57.160 --> 0:17:59.679 if you think about it that way, it's it's like 0:18:00.359 --> 0:18:03.440 sending out a signal and waiting for something to bounce back. Yeah, 0:18:03.480 --> 0:18:05.760 but it's very fast. I mean the average is about 0:18:05.760 --> 0:18:09.960 a hundred pulses per second, which is yeah, fairly rapid, 0:18:10.040 --> 0:18:13.960 pretty quick, and then you're looking for the reflected pulse. Yes, 0:18:14.160 --> 0:18:17.480 which is what the the object that is under the 0:18:17.480 --> 0:18:22.680 ground or wherever. Uh, that's the the the pulse that 0:18:22.720 --> 0:18:25.520 it generates in response to the one that came from 0:18:25.560 --> 0:18:28.960 the MEL detector. Yeah. Now it uses a these these 0:18:28.960 --> 0:18:31.760 types of metal detectors use a sampling circuit basically trying 0:18:31.800 --> 0:18:35.600 to determine whether it's actually metal that you're finding or 0:18:35.680 --> 0:18:38.320 something else, some other type of magnetic field that is 0:18:38.359 --> 0:18:41.560 interfering with this signal. And it's basically judging that based 0:18:41.600 --> 0:18:48.120 on the amount of time it takes, uh too to reflect. Um. Yeah, 0:18:48.160 --> 0:18:49.960 that's another thing that we should point out is that 0:18:50.040 --> 0:18:53.679 MEL detectors can and encounter lots of different kinds of interference. 0:18:54.480 --> 0:18:56.880 Not just the composition of the soil. But let's say 0:18:56.880 --> 0:19:00.280 that you happen to cross over where in elector called 0:19:00.280 --> 0:19:04.400 cable has been buried. That could cause a problem. Your 0:19:04.440 --> 0:19:07.159 metal detector might think that, hey, look there's gold in 0:19:07.240 --> 0:19:11.119 them our hills, and truth, what you've hit is the 0:19:11.160 --> 0:19:13.720 power line, which you don't want to dig that up. No, 0:19:14.080 --> 0:19:18.680 it could result in everything from death, which is in 0:19:18.840 --> 0:19:22.960 the metal detection biz we call a bad thing, or 0:19:23.000 --> 0:19:27.080 it could result in or and or it could result 0:19:27.560 --> 0:19:33.000 in an entire region losing electricity. That's also a bad thing. 0:19:33.800 --> 0:19:36.080 That's that's a very good point. I mean, these these 0:19:36.080 --> 0:19:38.639 metal detectures are not only incredibly useful, they can be 0:19:38.640 --> 0:19:40.680 a lot of fun. A lot of hobbyists love them. 0:19:41.760 --> 0:19:44.520 But you do have to be very very careful. Um, 0:19:44.640 --> 0:19:47.520 and it's good to know your the territory. To quote 0:19:47.520 --> 0:19:50.399 a certain musical, but yeah, I mean, you need to 0:19:50.400 --> 0:19:53.639 know the territory. You gotta know where you're you're digging 0:19:54.119 --> 0:19:57.199 because you you really could get hurt. Hey, guys, it's 0:19:57.280 --> 0:19:59.760 Jonathan from the present day, butting in here. I was 0:20:00.160 --> 0:20:02.320 to want to talk to you for a second because 0:20:02.840 --> 0:20:06.280 my my, my AD detector is going off. Looks like 0:20:06.320 --> 0:20:17.200 we've got a sponsor read So we have an integrator 0:20:17.920 --> 0:20:22.320 on these on these pulse induction metal detectives, and that's 0:20:22.400 --> 0:20:25.480 reading the signals from the sampling circuit and converting them 0:20:25.480 --> 0:20:28.639 to d C. That's not current, yeah, not the district 0:20:28.640 --> 0:20:31.840 of Columbia. Yeah, not not a comic book publisher either. 0:20:32.080 --> 0:20:34.919 And that's feeding into the audio circuit and that is 0:20:34.960 --> 0:20:38.520 what beats. Yeah, that's the stuff what beats. The pulse indicator. 0:20:38.760 --> 0:20:42.359 The thing is, uh, these are very good at detecting metal, 0:20:42.480 --> 0:20:45.159 but they're not very good at discriminating between different types 0:20:45.200 --> 0:20:48.920 of metal. UM. So you're not going to get the 0:20:49.520 --> 0:20:52.320 level of precision that you would get with a VLF 0:20:53.080 --> 0:20:56.600 metal detector. But you know, they also you've got to 0:20:56.600 --> 0:20:59.280 remember that these different types of detectors, while some of 0:20:59.280 --> 0:21:02.080 them may work in conditions that others do not, there's 0:21:02.160 --> 0:21:06.800 there's also a price range here as well. Oh yes, yes, now, yeah, 0:21:06.800 --> 0:21:12.240 the beat frequency oscillator metal detectors can be uh fairly affordable. UM. 0:21:12.359 --> 0:21:14.960 They also used two coils, but one is in the 0:21:15.000 --> 0:21:17.000 search head and the other one is actually in the 0:21:17.000 --> 0:21:20.720 control box. UM. They're connected to an oscillator that as 0:21:21.720 --> 0:21:26.359 pulsing UM many many times per second, thousands of times 0:21:26.359 --> 0:21:30.080 per second UM. And and the and the frequency of 0:21:30.160 --> 0:21:32.480 the one that's inside the control box and the one 0:21:32.520 --> 0:21:36.880 that's inside the actual detector are slightly offset. They're not 0:21:37.080 --> 0:21:42.360 in sync or backstreet voice. Oh you got the other 0:21:42.359 --> 0:21:48.960 one I was gonna do so yeah, well, ironically enough 0:21:49.000 --> 0:21:52.800 to our our current part of the conversation. They create 0:21:52.920 --> 0:21:55.679 radio waves UM, and then the receiver in the control 0:21:55.720 --> 0:22:00.199 box UH picks that up and plays tones to you 0:22:00.280 --> 0:22:03.760 know when you're you're coming into range of metal, right, 0:22:03.800 --> 0:22:07.920 because what's happening is that when the metal encounters this 0:22:08.600 --> 0:22:12.959 uh this this this electromagnetic field that is going to 0:22:13.000 --> 0:22:17.040 alter that radio wave. And so what's really listening for 0:22:17.080 --> 0:22:20.600 our changes in the sound that you're hearing. The change 0:22:20.600 --> 0:22:24.240 in the sound indicates that you have encountered something that 0:22:24.440 --> 0:22:27.840 is generating this magnetic field. Because of the one you're generating, 0:22:28.119 --> 0:22:32.200 they know what they're going through. Um. So yeah, I 0:22:32.240 --> 0:22:36.560 mean detectors killed the radio star. But these these uh, 0:22:36.760 --> 0:22:40.160 like I said, these are a lot cheaper to manufacture. 0:22:40.200 --> 0:22:43.679 And therefore, if you are uh interested in getting your 0:22:43.720 --> 0:22:47.560 feet wet uh in the metal detector, the thing is 0:22:47.600 --> 0:22:49.880 a hobby, you might consider this, but they're they're far 0:22:49.960 --> 0:22:53.080 less accurate as in terms of being able to give 0:22:53.119 --> 0:22:58.240 you any kind of discrimination or any really any real control. Um, 0:22:58.760 --> 0:23:01.680 they actually use these are the types of metal detectors 0:23:01.720 --> 0:23:05.800 that you the handheld detectors that they use the airport. Um, 0:23:05.840 --> 0:23:08.280 you know if you walk through the scanner and and 0:23:08.280 --> 0:23:09.840 then yeah, that's the type they use in the one. 0:23:09.880 --> 0:23:13.359 Because they don't really need to know whether it's gold 0:23:13.480 --> 0:23:15.800 or iron. They just want to know what it is 0:23:15.840 --> 0:23:18.479 that you've got now once once, once something beeps, then 0:23:18.520 --> 0:23:20.800 they can say, all right, well let's see what that is. 0:23:20.960 --> 0:23:24.400 They don't, you know, necessarily need to know immediately. Yeah. 0:23:24.440 --> 0:23:27.960 And the metal detectors, the frames at the airport, they 0:23:28.119 --> 0:23:30.960 work on essentially the same principles we've talked about here. 0:23:31.400 --> 0:23:34.360 They're generating electromagnetic fields, which of course has brought up 0:23:34.400 --> 0:23:39.359 some concerns with people who may have uh devices like 0:23:39.400 --> 0:23:42.680 medical devices that could react to electromagnetic fields. That's why 0:23:42.720 --> 0:23:46.320 you'll occasionally hear about UH folks like that having to 0:23:46.440 --> 0:23:50.080 go through like a pat down security as opposed to 0:23:50.240 --> 0:23:52.600 a metal detector, just because of the concern that it 0:23:52.680 --> 0:23:56.720 could interfere with a medical device. Right right now, with 0:23:56.960 --> 0:23:59.960 with all of these um, what you're gonna find depends 0:24:00.200 --> 0:24:03.320 on the type of metal detector, the type of metal 0:24:03.440 --> 0:24:06.440 that you're looking for, about how big it is, the 0:24:06.520 --> 0:24:09.320