WEBVTT - How Thermal Imaging Works 0:00:04.400 --> 0:00:07.760 Welcome to Text Stuff, a production from I Heart Radio. 0:00:12.240 --> 0:00:15.160 Hey there, and welcome to Text Stuff. I'm your host, 0:00:15.360 --> 0:00:18.960 Jonathan Strickland. I'm an executive producer with I Heart Radio, 0:00:19.000 --> 0:00:22.080 and I love all things tech. And you know, there 0:00:22.120 --> 0:00:25.079 are times when I sit down to choose a topic 0:00:25.280 --> 0:00:28.960 for Text Stuff and I just come up empty. Either 0:00:29.120 --> 0:00:32.600 I'll only come across stuff that I've already covered in 0:00:32.640 --> 0:00:36.080 the past, or I'll see stuff that just doesn't really 0:00:36.120 --> 0:00:40.080 ignite my curiosity. And honestly, that just makes researching and 0:00:40.120 --> 0:00:43.479 writing and recording these episodes that much more difficult. I 0:00:43.800 --> 0:00:47.000 feel like if I'm jazzed about it, it just comes 0:00:47.040 --> 0:00:50.840 more easily. But once in a while, I'll see either 0:00:51.000 --> 0:00:55.080 an interesting article or a video, or sometimes just a headline, 0:00:55.280 --> 0:00:58.800 and that makes me think I should probably cover that technology. 0:00:59.120 --> 0:01:01.120 And that's what happened to me on the morning of 0:01:01.200 --> 0:01:04.920 April six, twenty twenty, which is the morning that I 0:01:04.959 --> 0:01:09.560 wrote this sentence right here. Now, um, I'm recording this 0:01:09.600 --> 0:01:13.759 on April, so there's a lot of time shifting going 0:01:13.800 --> 0:01:16.679 on here. But the headline I saw was on tech 0:01:16.760 --> 0:01:21.600 Crunch and it read Chinese startup ro kid pitches COVID 0:01:21.720 --> 0:01:26.039 nineteen detection glasses in US, and I know we've had 0:01:26.040 --> 0:01:28.760 a lot of talk about COVID nineteen, but that's not 0:01:29.000 --> 0:01:32.920 what this episode is really going to be about. See, 0:01:32.959 --> 0:01:36.959 those detection glasses don't magically pick up that someone has 0:01:37.000 --> 0:01:40.000 been infected by the coronavirus. It's not like they see 0:01:40.040 --> 0:01:43.520 the coronavirus crawling on the person or anything that would 0:01:43.560 --> 0:01:48.360 really be a trick. No, these are thermal imaging glasses 0:01:48.440 --> 0:01:51.280 with some added bells and whistles, like the ability to 0:01:51.320 --> 0:01:55.320 take photos or record video. That's not necessarily part of 0:01:55.440 --> 0:01:59.400 thermal imaging cameras or sensors. But really, these glasses don't 0:01:59.400 --> 0:02:03.080 tell you if someone has COVID nineteen. They might tell 0:02:03.160 --> 0:02:06.800 you if someone has an elevated body temperature. Now, keeping 0:02:06.800 --> 0:02:09.520 in mind that some folks might be contagious with COVID 0:02:09.600 --> 0:02:13.440 nineteen and not have any symptoms, that means these glasses 0:02:13.480 --> 0:02:16.880 are helpful but not a perfect way to screen people. 0:02:17.360 --> 0:02:21.720 The glasses wouldn't indicate that an asymptomatic person is a threat, 0:02:21.960 --> 0:02:25.920 for example, and other people might have an elevated body temperature. 0:02:25.960 --> 0:02:30.520 You know, people with immuno compromise systems frequently have this problem, 0:02:30.560 --> 0:02:33.920 but they may not necessarily have COVID nineteen. So what 0:02:33.960 --> 0:02:37.400 I'm saying is that critical thinking and a broad spectrum 0:02:37.440 --> 0:02:41.320 approach to taking precautions is necessary, and that putting all 0:02:41.400 --> 0:02:44.919 our eggs in one basket is always a bad idea, 0:02:45.080 --> 0:02:47.639 And I would usually save that stuff for the end, 0:02:48.000 --> 0:02:49.920 but times being what they are, I felt it was 0:02:49.960 --> 0:02:53.760 important to address that first. Anytime anyone claims that they 0:02:53.800 --> 0:02:57.919 have a solution that solves a really complicated problem, it's 0:02:57.919 --> 0:03:00.000 good to take a closer look. But I want to 0:03:00.000 --> 0:03:03.760 talk about thermal imaging technology in general because it does work, 0:03:04.080 --> 0:03:08.320 it's incredibly precise, and it's super awesome stuff. Now, in 0:03:08.360 --> 0:03:11.840 a past episode, I covered how night vision works, and 0:03:11.919 --> 0:03:16.120 that can include normal imaging, but we typically think of 0:03:16.160 --> 0:03:19.120 a different kind of approach with night vision. You know, 0:03:19.160 --> 0:03:21.919 all the television shows and movies tend to show that 0:03:22.040 --> 0:03:26.040 kind of green vision, that green video where stuff is 0:03:26.240 --> 0:03:31.320 super bright. Well, that's really called image enhancement, and that 0:03:31.360 --> 0:03:34.800 method takes all available light that's in an environment and 0:03:34.840 --> 0:03:38.600 then amplifies the signal from that light to create a 0:03:38.760 --> 0:03:42.480 video with an intensity that is easier for us to perceive. 0:03:42.960 --> 0:03:47.160 Thermal imaging is different from that, So thermal imaging has 0:03:47.200 --> 0:03:50.680 to do with infrared light, which in turn, we cannot 0:03:50.720 --> 0:03:53.400 see with our eyeballs. It is invisible to us, but 0:03:53.960 --> 0:03:58.360 we can still sense it because it's heat. All objects 0:03:58.440 --> 0:04:02.720 in the universe omit some level of infrared radiation as 0:04:02.760 --> 0:04:06.760 long as those objects are above absolute zero. Some of 0:04:06.800 --> 0:04:09.840 them do it a lot more than others, you know, 0:04:10.280 --> 0:04:14.160 like stars and stuff. They emit way more infrared radiation. 0:04:14.240 --> 0:04:18.800 But we emit infrared radiation too. We humans were kind 0:04:18.800 --> 0:04:22.440 of like infrared light bulbs. I mean, granted, so is 0:04:22.560 --> 0:04:25.880 a light bulb and every other object to some extent. 0:04:26.400 --> 0:04:28.520 The visible spectrum of light, you know, the stuff that 0:04:28.600 --> 0:04:32.159 we can perceive with our eyes is bordered on either 0:04:32.240 --> 0:04:35.800 side of the electro magnetic spectrum by bands of light 0:04:35.880 --> 0:04:39.799 that are beyond our ability to see. At frequencies higher 0:04:39.960 --> 0:04:43.520 than visible light. So that means the wavelengths of these 0:04:43.640 --> 0:04:47.240 light waves are shorter. That would be ultra violet light 0:04:47.440 --> 0:04:52.000 or UV. At frequencies lower than visible light, or longer 0:04:52.080 --> 0:04:56.080 wavelengths of light, you get infrared. Now there's other stuff 0:04:56.120 --> 0:04:59.280 that goes beyond those bands as well. For example, if 0:04:59.279 --> 0:05:02.680 you keep going to higher frequencies and shorter wavelengths, you 0:05:02.760 --> 0:05:05.400 run into X rays and gamma rays, and if you 0:05:05.480 --> 0:05:09.240 keep going toward the longer wavelengths and lower frequencies, you'll 0:05:09.320 --> 0:05:13.880 hit microwaves and radio waves. The first recorded discovery of 0:05:13.920 --> 0:05:18.279 infrared light comes to us courtesy of smarty pants extraordinaire, 0:05:18.480 --> 0:05:22.480 Sir William Herschel. This guy is what you would call 0:05:22.520 --> 0:05:24.920 of von der Kind. First of all, he was born 0:05:24.920 --> 0:05:29.200 in Germany, so the word I use is linguistically appropriate. Secondly, 0:05:29.440 --> 0:05:32.400 he was a composer, he was an astronomer and just 0:05:32.640 --> 0:05:36.400 generally a scientifically minded guy. And he's the guy who 0:05:36.480 --> 0:05:40.400 discovered uranus the planet. And yes, I'm going to pronounce 0:05:40.480 --> 0:05:42.760 it that way, because to do it the other way 0:05:42.839 --> 0:05:46.320 makes it sound juvenile. He was also the grandfather of 0:05:46.400 --> 0:05:50.240 another William Herschel, who would go on to establish fingerprints 0:05:50.279 --> 0:05:54.480 as a means of authenticating documentation, but I've covered that 0:05:54.600 --> 0:05:58.479 in a different episode. So Billy Herschel the first was 0:05:58.520 --> 0:06:02.120 pontificating about the nature of light, and it was obvious 0:06:02.200 --> 0:06:05.000 that light carried heat with it. When you step out 0:06:05.040 --> 0:06:08.240 of the shade into the sunlight, you feel it. So 0:06:08.320 --> 0:06:11.960 Herschel was working with different types of colored glass. He 0:06:12.000 --> 0:06:14.960 was experimenting with different telescopes that he might be able 0:06:14.960 --> 0:06:18.159 to use to observe the Sun, because the Sun's rays 0:06:18.240 --> 0:06:20.719 are far too bright to stare at without the risk 0:06:20.760 --> 0:06:23.040 of injury. We all know this. You don't stare at 0:06:23.080 --> 0:06:26.960 the sun. So by using glass of different colors, he 0:06:27.000 --> 0:06:29.640 was hoping to reduce the amount of light coming in 0:06:29.680 --> 0:06:32.320 through the telescope so that he could still take a 0:06:32.360 --> 0:06:36.240 closer look at the Sun and make observations safely. But 0:06:36.279 --> 0:06:39.440 you discovered that some colors of glass seemed to reduce 0:06:39.560 --> 0:06:42.240 the amount of heat that was passing through his telescope, 0:06:42.600 --> 0:06:45.480 and others seemed to allow a great deal of heat 0:06:45.520 --> 0:06:50.600 to come through, including enough heat to potentially cause an injury, 0:06:50.680 --> 0:06:52.919 but this time due to heat rather than to the 0:06:52.960 --> 0:06:57.000 intensity of light damaging his eye. And he knew about 0:06:57.120 --> 0:07:00.480 how light could pass through a prism and would break 0:07:00.480 --> 0:07:04.560 apart into the different colors of light, and collectively those 0:07:04.600 --> 0:07:08.320 colors make up white light. What he wondered was if 0:07:08.360 --> 0:07:12.200 those colors carried different amounts of heat. So he set 0:07:12.280 --> 0:07:15.800 up an experiment and he used a prism to break 0:07:15.920 --> 0:07:18.800 light into the different bands of colors, and then he 0:07:18.880 --> 0:07:22.679 used a thermometer with the bulb end blackened by ink, 0:07:23.280 --> 0:07:26.119 and he used that to measure the temperature within each 0:07:26.240 --> 0:07:28.800 band of color. And he noticed as he measured the 0:07:28.880 --> 0:07:32.440 violet end of the spectrum, the temperature readings were lower, 0:07:32.720 --> 0:07:35.320 and towards the red end they were higher, and he 0:07:35.400 --> 0:07:38.840 decided to also test the area just beyond the red end. 0:07:39.360 --> 0:07:42.280 There was no visible light at that section, but he 0:07:42.320 --> 0:07:45.760 observed that it was at that area where the thermometer 0:07:45.920 --> 0:07:49.240 was registering the highest temperature. And this is the earliest 0:07:49.320 --> 0:07:52.400 recording of someone figuring out that there was something beyond 0:07:52.440 --> 0:07:54.840 the rainbow, so to speak. And yeah, I know, I 0:07:54.960 --> 0:07:58.520 misquoted a song just to make that reference. Herschel referred 0:07:58.560 --> 0:08:03.480 to this area beyond visible light as the thermometric spectrum. 0:08:03.520 --> 0:08:06.280 In early days, some would refer to it as dark 0:08:06.360 --> 0:08:10.600 heat or invisible rays. The term infrared wouldn't really come 0:08:10.600 --> 0:08:14.360 around until the other end of the nineteenth century, and 0:08:14.480 --> 0:08:18.040 there are no reliable records that indicate who actually coined 0:08:18.160 --> 0:08:22.080 the term, but whomever was responsible, it became the standard 0:08:22.080 --> 0:08:26.080 way to refer to this specific band of radiation. So 0:08:26.400 --> 0:08:29.440 I've used the term thermal imaging in this episode, and 0:08:29.480 --> 0:08:32.600 the reason I have is that it implies when we 0:08:32.679 --> 0:08:39.120 use these technologies that were not somehow magically seeing infrared radiation. Right, 0:08:39.400 --> 0:08:44.280 We're not able to suddenly see infrared light through this tech. Instead, 0:08:44.320 --> 0:08:47.839 what we're doing is we're using technology to detect infrared 0:08:48.080 --> 0:08:51.880 radiation or heat, and then using some sort of process 0:08:52.200 --> 0:08:56.560 to convert that data into a visual representation. For example, 0:08:56.720 --> 0:09:01.120 with thermal glasses, we'd see different colors that different intensities 0:09:01.280 --> 0:09:05.800 to indicate varying degrees of heat between objects. Typically we 0:09:05.920 --> 0:09:09.120 use colors like bright yellows, oranges, and reds to indicate 0:09:09.160 --> 0:09:13.760 hot surfaces, and greens and blues to indicate cooler surfaces, 0:09:13.920 --> 0:09:16.520 which is nice because that also corresponds to how much 0:09:16.559 --> 0:09:19.880 heat energy those bands of light carry. Not in a 0:09:19.960 --> 0:09:24.079 one to one scale, mind you, but the general principle remains, 0:09:24.160 --> 0:09:27.319 and we kind of grasp it, right, We say, Okay, 0:09:27.360 --> 0:09:31.240 this red thing is definitely hotter than that blue thing. 0:09:32.000 --> 0:09:33.840 But to be able to do all this, we first 0:09:33.880 --> 0:09:36.560 have to be able to detect and measure the heat 0:09:36.679 --> 0:09:39.120 coming from an object in a reliable way in the 0:09:39.160 --> 0:09:42.640 first place. Right. So, one of the cool things about 0:09:42.760 --> 0:09:48.160 physics is how seemingly unrelated factors are actually tied together. 0:09:48.880 --> 0:09:51.680 From the macro scale. That being the world that you 0:09:51.760 --> 0:09:54.720 and I live in most of the time. Anyway, some 0:09:54.800 --> 0:09:56.520 of you may have been having Honey I Shrunk the 0:09:56.559 --> 0:09:59.880 Kid's Adventures, and I'm all for it. But on the 0:10:00.080 --> 0:10:04.400 rand scale, it's not necessarily intuitive. But temperature can have 0:10:04.440 --> 0:10:08.240 a big impact on other stuff, such as electrical properties 0:10:08.280 --> 0:10:13.320 like conductivity and resistance. So just a reminder, conductivity describes 0:10:13.360 --> 0:10:16.640 a material's ability to act as a conduit for an 0:10:16.640 --> 0:10:20.280 electric charge, to allow an electric charge to pass through it. 0:10:20.640 --> 0:10:23.440 Resistance is the flip side of that coin. It's a 0:10:23.440 --> 0:10:27.440 material's tendency to resist an electrical charge. We can think 0:10:27.440 --> 0:10:30.040 of it kind of in terms of friction. If you 0:10:30.080 --> 0:10:33.840 have a very smooth floor that's been recently waxed, there's 0:10:33.920 --> 0:10:36.679 very little friction there, and you might slide all over it, 0:10:36.760 --> 0:10:40.120 perhaps without even intending to do so. But if you're 0:10:40.160 --> 0:10:43.160 on something like a rough concrete surface, there's a lot 0:10:43.200 --> 0:10:46.080 of friction and your attempts to slide would be met 0:10:46.120 --> 0:10:49.880 with a lot of resistance. Well, the electrical world, that's 0:10:50.400 --> 0:10:54.880 kind of analogous to conductivity and electrical resistance. Heat can 0:10:55.000 --> 0:10:59.480 change these properties. For example, even a good conductor has 0:10:59.679 --> 0:11:04.440 saw electrical resistance just like we can't entirely negate friction, 0:11:04.760 --> 0:11:08.800 even with our smoothest materials. But if you cool that 0:11:08.880 --> 0:11:14.079 conductor down, like way down, like colder than the depths 0:11:14.120 --> 0:11:18.480 of space, you can reduce its resistance, and depending on 0:11:18.480 --> 0:11:21.040 the material, you can reduce it all the way down 0:11:21.080 --> 0:11:23.840 to nothing. At that point you've got what's called a 0:11:23.920 --> 0:11:29.200 super conductor. Likewise, a conductive material will increase in resistance 0:11:29.360 --> 0:11:33.200 as it heats up, so temperature and electrical resistance have 0:11:33.400 --> 0:11:36.720 this kind of relationship. Now, the whole reason I went 0:11:36.760 --> 0:11:39.720 down that apparent bunny trail is that it brings us 0:11:39.720 --> 0:11:42.760 to an important component that would play a huge role 0:11:42.920 --> 0:11:47.360 in thermal sensors, and that's the bolometer. Now, when I 0:11:47.480 --> 0:11:51.240 first read this word, which is spelled b O l 0:11:51.400 --> 0:11:55.040 O m e t e R, I had not heard 0:11:55.080 --> 0:11:59.760 anyone pronounce it, and as many of us know, sometimes 0:11:59.760 --> 0:12:03.040 that means in our heads we have a very different pronunciation. 0:12:03.160 --> 0:12:05.040 So when I first read it, I thought it might 0:12:05.040 --> 0:12:08.080 be a bolo meter, and then I immediately second guess 0:12:08.120 --> 0:12:11.080 myself because I'm pretty sure a bolometer would be a 0:12:11.120 --> 0:12:16.040 device for measuring Texas neckties. So no, it's a bolometer. Now, 0:12:16.040 --> 0:12:20.280 to understand a bolometer. It helps if we also understand 0:12:20.480 --> 0:12:23.959 what a wheat Stone bridge is, and it's not an 0:12:24.040 --> 0:12:27.360 architectural thing. This is a type of circuit and its 0:12:27.400 --> 0:12:31.480 purpose is to measure the unknown electrical resistance of a material. 0:12:32.000 --> 0:12:35.880 It was first implemented in eighteen thirty three by Samuel 0:12:35.960 --> 0:12:39.720 Hunter Christie and later refined by Sir Charles Wheatstone in 0:12:39.760 --> 0:12:43.080 the eighteen forties. This is a little tricky to describe 0:12:43.080 --> 0:12:45.400 without the use of visual aids, but I'm going to 0:12:45.440 --> 0:12:48.200 give it a shot. All right, Imagine you have a 0:12:48.200 --> 0:12:52.280 perfect square. Now turn that perfect square forty five degrees 0:12:52.320 --> 0:12:55.080 so that it's a Diamond's got a top, left, right, 0:12:55.160 --> 0:12:59.840 and bottom point. And those four corners of this diamond 0:13:00.080 --> 0:13:04.120 present points of electric potential. And let's let's name the 0:13:04.160 --> 0:13:06.960 top point is A, the bottom point is B, so 0:13:07.000 --> 0:13:09.840 they're opposite each other. The left point is C, the 0:13:09.960 --> 0:13:12.679 right point is D, so they're opposite each other. Now, 0:13:12.760 --> 0:13:16.080 let's also imagine that C and D connect to each 0:13:16.120 --> 0:13:18.319 other with a horizontal line that cuts right through the 0:13:18.360 --> 0:13:20.080 middle of this diamond. So you've got a path going 0:13:20.120 --> 0:13:22.920 from C to D, as well as the uh the 0:13:23.040 --> 0:13:26.360 straight lines of the diamond from A to c A 0:13:26.600 --> 0:13:29.320 to D and then C two B and D two 0:13:29.360 --> 0:13:32.520 B the sides of the diamond. Those lines that I 0:13:32.679 --> 0:13:37.360 just mentioned connecting the points represent resistors. And here's the 0:13:37.440 --> 0:13:41.280 key when using a wheat stone bridge. You know the 0:13:41.360 --> 0:13:45.520 electrical resistance for three of those resistors. Those are ones 0:13:45.559 --> 0:13:49.360 that you have put in place. So you've got three 0:13:49.400 --> 0:13:53.080 resistors where you know the electrical resistance. The fourth resistor 0:13:53.280 --> 0:13:56.600 represents the material you're actually testing. You don't know its 0:13:56.640 --> 0:14:01.520 electrical resistance. So in our little amount engineering wheat stone bridge, 0:14:01.679 --> 0:14:04.720 let's say that the line between point D, which is 0:14:04.720 --> 0:14:06.520 the one that's on the right side of the diamond, 0:14:06.800 --> 0:14:09.000 and point B, which is on the bottom side of 0:14:09.000 --> 0:14:12.360 the diamond, that represents the resistor we're interested in. We're 0:14:12.400 --> 0:14:16.280 trying to figure out what is its electrical resistance. Now, 0:14:16.280 --> 0:14:18.680 another important point is that on the opposite side of 0:14:18.679 --> 0:14:22.360 the circuit, the line that's representing C the point on 0:14:22.400 --> 0:14:24.720 the left, and B on the bottom. So the other 0:14:25.200 --> 0:14:28.400 bottom leg that one is a resistor that we can 0:14:28.440 --> 0:14:32.000 actually adjust the electrical resistance. We can fine tune it. 0:14:32.000 --> 0:14:34.760 It's like a radio dial. You can just fine tune 0:14:34.800 --> 0:14:39.400 that electrical resistance by applying a difference of voltage between 0:14:39.480 --> 0:14:41.960 A at the top and BE at the bottom. We 0:14:42.040 --> 0:14:45.360 allow current to flow through this circuit, and if current 0:14:45.400 --> 0:14:48.080 can flow from point C on the left to point 0:14:48.160 --> 0:14:50.960 D on the right, or vice versa, it means the 0:14:51.000 --> 0:14:55.360 bridge is unbalanced. That means there's more resistance on one 0:14:55.440 --> 0:14:58.960 side of the circuit than the other. So we slowly 0:14:59.000 --> 0:15:03.600 start to find t that one leg that C B resistor, 0:15:04.200 --> 0:15:07.280 and we continue to fine tune it until no current 0:15:07.480 --> 0:15:10.880 is passing between points C and D. That would mean 0:15:10.920 --> 0:15:13.880 that the wheat stone bridge is in balance. It also 0:15:13.960 --> 0:15:17.800 means the ratio of resistance represented by the left side 0:15:17.800 --> 0:15:20.360 of the circuit has to be equal to the ratio 0:15:20.480 --> 0:15:23.240 of resistance on the right side. And we know the 0:15:23.240 --> 0:15:28.040 electrical resistance of three of those four resistors. So by 0:15:28.080 --> 0:15:32.360 knowing the ratio on one side and knowing half of 0:15:32.400 --> 0:15:34.280 the ratio on the other side, we can figure out 0:15:34.320 --> 0:15:37.760 the variable. Right. It's just a simple algebra problem. So 0:15:37.840 --> 0:15:40.600 you just solve for X and boom, you found the 0:15:40.600 --> 0:15:45.280 electrical resistance of that material you were testing. Why is 0:15:45.320 --> 0:15:48.600 all of that important, Well, it's because the bolometer is 0:15:48.640 --> 0:15:52.280 built upon the premise of the wheat stone bridge. In 0:15:52.360 --> 0:15:56.080 Pokemon terms. It would be an evolution. I'll explain in 0:15:56.120 --> 0:15:58.880 just a moment, but first let's take a quick break. 0:16:06.440 --> 0:16:09.640 Before the break, I described the wheat stone bridge circuit 0:16:09.760 --> 0:16:13.040 and how it allows researchers to determine the electrical resistance 0:16:13.080 --> 0:16:16.440 of a material. Now it's time to talk about bolometers 0:16:16.440 --> 0:16:21.040 and Samuel Pierre Pont Langley what a name. It's sp 0:16:21.240 --> 0:16:25.640 Langley's how he was typically referred to, Professor S. P. Langley. 0:16:25.920 --> 0:16:28.280 Langley was a lot of things. He wasn't just a professor. 0:16:28.640 --> 0:16:31.520 He was almost the inventor of the airplane. A couple 0:16:31.560 --> 0:16:33.800 of upstarts called the Right Brothers beat him to it. 0:16:34.200 --> 0:16:37.320 He was also an astronomer, and like Sir William Herschel 0:16:37.480 --> 0:16:40.560 nearly a century earlier, he wanted to find ways to 0:16:40.640 --> 0:16:43.680 study the solar energy that made it from the Sun 0:16:43.920 --> 0:16:47.440 to the Earth, And in eight seventy eight he invented 0:16:47.480 --> 0:16:50.400 an apparatus that could be used to measure the amount 0:16:50.480 --> 0:16:54.000 of infrared energy hitting a specific point. And this was 0:16:54.080 --> 0:16:58.400 the bolometer. So remember the wheat stone bridge I described earlier, Well, 0:16:58.440 --> 0:17:01.200 now imagine you've got the same sort of layout, except 0:17:01.240 --> 0:17:04.440 this time you know the electrical resistance of every leg 0:17:04.760 --> 0:17:07.040 in this circuit, so you're not you're not trying to 0:17:07.080 --> 0:17:09.800 figure out the electrical resistance You already know what it's 0:17:09.840 --> 0:17:13.280 supposed to be for all parts of this wheat stone 0:17:13.320 --> 0:17:19.080 bridge style circuit. However, the material you're using is very 0:17:19.119 --> 0:17:23.159 sensitive to changes in heat, which in turn changes the 0:17:23.200 --> 0:17:28.440 electrical resistance of those resistors like super super sensitive, even 0:17:28.520 --> 0:17:31.920 the shift of just one thousand of a degree celsius 0:17:31.960 --> 0:17:36.879 will make a change in its electrical resistance, So the 0:17:36.920 --> 0:17:41.399 electrical resistance of the materials changes. So rather than tuning 0:17:41.440 --> 0:17:44.920 in to find a specific electrical resistance as you would 0:17:44.960 --> 0:17:48.800 with a traditional wheat stone bridge, a volometer monitors the 0:17:48.800 --> 0:17:52.800 electrical resistance of a circuit, and the changes in resistance 0:17:52.920 --> 0:17:57.280 indicate a change in temperature. A bigger change in electrical 0:17:57.320 --> 0:18:03.000 resistance indicates a higher intensive of infrared radiation, meaning a 0:18:03.040 --> 0:18:09.600 bigger change in temperature. Langley invented an incredibly sensitive thermal detector. 0:18:10.440 --> 0:18:13.480 It was able to pick up incredibly small changes in 0:18:13.560 --> 0:18:17.359 heat from an enormous distance. Reportedly, with one of his 0:18:17.480 --> 0:18:21.719 refined thermal sensors using a bolometer, he could detect the 0:18:21.760 --> 0:18:25.800 body heat of a cow from four hundred meters away. 0:18:26.240 --> 0:18:29.159 The bolometer was that sensitive and would pick up the 0:18:29.200 --> 0:18:32.399 infrared energy coming off that cow, indicating that there was 0:18:32.440 --> 0:18:35.200 something in that spot that was generating more heat than 0:18:35.400 --> 0:18:39.639 the surrounding objects in that environment. So by measuring the 0:18:39.720 --> 0:18:43.440 changes in electrical resistance, you could work back to understand 0:18:43.480 --> 0:18:48.520 the intensity of the infrared radiation hitting that sensor. And 0:18:48.600 --> 0:18:52.600 this was really good for detecting differences in temperature, right, 0:18:52.720 --> 0:18:56.720 not necessarily getting an exact read out of the temperature 0:18:56.760 --> 0:19:00.360 of an object, but rather getting the difference between one 0:19:00.400 --> 0:19:04.639 object and say it's environment or another object, and hotter 0:19:04.760 --> 0:19:08.040 things give off more intense infra red radiation, so you 0:19:08.040 --> 0:19:11.080 can build up your knowledge base this way. There's a 0:19:11.119 --> 0:19:12.960 bit more to it than that. When we talk about 0:19:13.080 --> 0:19:17.000 modern bolometers, those get pretty complicated, and honestly, it gets 0:19:17.040 --> 0:19:18.600 to a point where I don't think I can really 0:19:18.640 --> 0:19:22.120 tackle an explanation that will mean anything without the use 0:19:22.160 --> 0:19:26.600 of visual aids. But the basic principle measuring infrared radiation 0:19:26.720 --> 0:19:31.120 through monitoring electrical changes remains the same. So again, this 0:19:31.160 --> 0:19:34.280 was sort of an indirect way to detect heat, right. 0:19:34.320 --> 0:19:37.040 I mean, the changes in temperature would affect the electrical 0:19:37.080 --> 0:19:40.560 resistance in the bolometer, and that's what we were actually measuring. 0:19:41.040 --> 0:19:45.400 We're not measuring heat, We're measuring electrical resistance that changes 0:19:45.560 --> 0:19:50.080 as a result of infrared radiation or heat, and then 0:19:50.119 --> 0:19:53.400 a meter measuring that resistance would indicate what was going on. 0:19:53.840 --> 0:19:56.360 But this meant researchers had to spend time to refine 0:19:56.440 --> 0:19:59.360 what that actually meant. They had to match the changes 0:19:59.400 --> 0:20:03.120 in electrical resistance to the differences in temperature. And this 0:20:03.200 --> 0:20:05.760 is a part of science and engineering that just blows 0:20:05.800 --> 0:20:08.240 my mind, not just that super smart people had to 0:20:08.760 --> 0:20:12.240 take some known phenomena and then make use of it, 0:20:12.280 --> 0:20:14.960 but then later refine that so that the use is 0:20:14.960 --> 0:20:18.199 more practical. We'd see a lot of further steps build 0:20:18.359 --> 0:20:22.080 upon this foundation. Bilometers could indicate changes in temperature, but 0:20:22.119 --> 0:20:24.359 it would take a lot more work and technology to 0:20:24.440 --> 0:20:27.080 use that data and then convert it again into something 0:20:27.119 --> 0:20:30.160 that could be presented visually as a thermal image or 0:20:30.440 --> 0:20:35.960 thermographic display. So with a bolometer based thermal imager, you've 0:20:35.960 --> 0:20:40.280 got infrared radiation which hits a thermal sensor, which changes 0:20:40.320 --> 0:20:43.960 its electrical resistance as a result, which a meter detects, 0:20:44.000 --> 0:20:47.720 which sends this metric to a processor which interprets that 0:20:47.840 --> 0:20:50.359 data and then converts it into a different type of 0:20:50.400 --> 0:20:52.919 information that can be displayed on a screen. This is 0:20:52.960 --> 0:20:56.000 what amazes me. So the bolometer would become a really 0:20:56.040 --> 0:20:58.800 important tool for astronomers, but it would take a bit 0:20:58.840 --> 0:21:02.520 longer to play a role in thermal imagers, though not 0:21:02.680 --> 0:21:08.000 too much longer. According to multiple sources, the first person 0:21:08.119 --> 0:21:12.119 to create a thermal television camera was the Hungarian born 0:21:12.440 --> 0:21:16.720 Kalman to Hanji in nineteen nine. He built it for 0:21:16.760 --> 0:21:21.119 Britain to use as part of their anti aircraft technologies 0:21:21.320 --> 0:21:24.359 after World War One. I wish I could tell you 0:21:24.400 --> 0:21:28.560 more about the technology of his device, but honestly, there's 0:21:28.600 --> 0:21:32.320 not much information I could find about how it actually worked. 0:21:32.680 --> 0:21:35.560 There's a general agreement that this is the first thermal 0:21:35.640 --> 0:21:39.080 imaging camera, though all of that could ultimately be pulling 0:21:39.160 --> 0:21:42.399 the information from a single source, which makes it less reliable. 0:21:42.760 --> 0:21:45.600 But I couldn't find much information on what the actual 0:21:45.640 --> 0:21:49.560 implementation to Hanyi used in his invention, and in a 0:21:49.600 --> 0:21:53.280 few sources, I found his device confused with a later 0:21:53.440 --> 0:21:57.520 thermographic camera that would be reportedly based off his invention, 0:21:57.640 --> 0:22:01.240 but was its own distinct thing. So while it appears 0:22:01.280 --> 0:22:05.800 The first thermal imaging camera dates to nine nine, and 0:22:05.880 --> 0:22:09.119 it was all about live images. I can't tell you 0:22:09.160 --> 0:22:11.120 a whole lot about it, and I'm sure there are 0:22:11.119 --> 0:22:13.880 patents out there for it, but my patent searches were 0:22:13.880 --> 0:22:16.760 not terribly fruitful. I couldn't find anything all the way 0:22:16.800 --> 0:22:21.600 back at nine that match the description. However, one thing 0:22:21.640 --> 0:22:25.240 I can say is that for the first few decades 0:22:25.320 --> 0:22:29.280 of thermal imaging, almost all the research and development for 0:22:29.320 --> 0:22:33.720 that technology fell to militaries around the world. Thermal detection 0:22:33.760 --> 0:22:36.880 in general was a big area of research, and engineers 0:22:36.920 --> 0:22:40.760 were trying to incorporate thermal sensors and stuff like missiles 0:22:40.800 --> 0:22:45.520 and torpedoes, and later on in rifle scopes and headsets, 0:22:45.960 --> 0:22:48.560 the idea being that this could be part of a 0:22:48.600 --> 0:22:51.959 guidance system to help an explosive projectile lock into a target. 0:22:52.000 --> 0:22:54.560 I mean a lot of military targets are also sources 0:22:54.640 --> 0:22:59.240 of considerable amounts of heat, such as warships, submarines, tanks, 0:22:59.320 --> 0:23:02.919 or aircraft. So a missile or torpedo that has a 0:23:02.960 --> 0:23:05.560 thermal sensor on it would be able to hone in 0:23:05.680 --> 0:23:09.480 on the heat source pretty easily. But by the nineteen fifties, 0:23:10.040 --> 0:23:13.520 other disciplines were also interested in making use of this technology, 0:23:13.720 --> 0:23:16.800 such as in medicine. There were some doctors who were 0:23:16.840 --> 0:23:19.919 hoping to use thermal imaging to help them do stuff 0:23:19.960 --> 0:23:23.760 like identify potentially cancerous tumors. The idea being that a 0:23:23.800 --> 0:23:27.159 cancerous tumor would likely consist of cells replicating at a 0:23:27.200 --> 0:23:29.920 faster rate than normal cells. Thus they would have a 0:23:29.960 --> 0:23:33.880 higher metabolic rate, and you would think that that would 0:23:33.920 --> 0:23:37.160 mean they would be generating more heat than healthy tissue. 0:23:37.640 --> 0:23:41.520 A device sensitive to minute differences in temperature and capable 0:23:41.520 --> 0:23:44.480 of displaying that information on a screen, particularly if you 0:23:44.480 --> 0:23:47.639 could do it in real time, would be handy if 0:23:47.720 --> 0:23:50.919 that hypothesis were to hold true. Now, I want to 0:23:50.960 --> 0:23:53.960 add that this particular approach isn't proven to be the 0:23:53.960 --> 0:23:56.880 most effective means for detecting a tumor, and that other 0:23:56.960 --> 0:24:01.000 methods such as mammograms are far moral liable and likely 0:24:01.040 --> 0:24:04.439 to catch cancer at earlier stages. But at the time 0:24:04.600 --> 0:24:08.360 there were doctors hoping that it might be a helpful technology. However, 0:24:08.400 --> 0:24:11.359 for most part, thermal imaging remained in the domain of 0:24:11.440 --> 0:24:14.600 the military around this time. So we're going to skip 0:24:14.640 --> 0:24:17.480 forward a bit to the development of a different kind 0:24:17.640 --> 0:24:22.080 of heat sensor. This one is based off pyroelectric materials. 0:24:22.520 --> 0:24:26.359 Pyro Electricity refers to a certain set of crystals that 0:24:26.480 --> 0:24:30.480