How Thermal Imaging Works

writing and recording these episodes that much more difficult. I feel like if I'm jazzed about it, it just comes more easily. But once in a while, I'll see either an interesting article or a video, or sometimes just a headline, and that makes me think I should probably cover that technology. And that's what happened to me on the morning of April six, twenty twenty, which is the morning that I

wrote this sentence right here. Now, um, I'm recording this on April, so there's a lot of time shifting going on here. But the headline I saw was on tech Crunch and it read Chinese startup ro kid pitches COVID nineteen detection glasses in US, and I know we've had a lot of talk about COVID nineteen, but that's not what this episode is really going to be about. See, those detection glasses don't magically pick up that someone has

been infected by the coronavirus. It's not like they see the coronavirus crawling on the person or anything that would really be a trick. No, these are thermal imaging glasses with some added bells and whistles, like the ability to take photos or record video. That's not necessarily part of thermal imaging cameras or sensors. But really, these glasses don't tell you if someone has COVID nineteen. They might tell

you if someone has an elevated body temperature. Now, keeping in mind that some folks might be contagious with COVID nineteen and not have any symptoms, that means these glasses are helpful but not a perfect way to screen people. The glasses wouldn't indicate that an asymptomatic person is a threat, for example, and other people might have an elevated body temperature. You know, people with immuno compromise systems frequently have this problem,

but they may not necessarily have COVID nineteen. So what I'm saying is that critical thinking and a broad spectrum approach to taking precautions is necessary, and that putting all our eggs in one basket is always a bad idea, And I would usually save that stuff for the end, but times being what they are, I felt it was important to address that first. Anytime anyone claims that they have a solution that solves a really complicated problem, it's

good to take a closer look. But I want to talk about thermal imaging technology in general because it does work, it's incredibly precise, and it's super awesome stuff. Now, in a past episode, I covered how night vision works, and that can include normal imaging, but we typically think of a different kind of approach with night vision. You know, all the television shows and movies tend to show that kind of green vision, that green video where stuff is

super bright. Well, that's really called image enhancement, and that method takes all available light that's in an environment and then amplifies the signal from that light to create a video with an intensity that is easier for us to perceive. Thermal imaging is different from that, So thermal imaging has to do with infrared light, which in turn, we cannot see with our eyeballs. It is invisible to us, but

we can still sense it because it's heat. All objects in the universe omit some level of infrared radiation as long as those objects are above absolute zero. Some of them do it a lot more than others, you know, like stars and stuff. They emit way more infrared radiation. But we emit infrared radiation too. We humans were kind of like infrared light bulbs. I mean, granted, so is a light bulb and every other object to some extent.

The visible spectrum of light, you know, the stuff that we can perceive with our eyes is bordered on either side of the electro magnetic spectrum by bands of light that are beyond our ability to see. At frequencies higher than visible light. So that means the wavelengths of these light waves are shorter. That would be ultra violet light or UV. At frequencies lower than visible light, or longer wavelengths of light, you get infrared. Now there's other stuff

that goes beyond those bands as well. For example, if you keep going to higher frequencies and shorter wavelengths, you run into X rays and gamma rays, and if you keep going toward the longer wavelengths and lower frequencies, you'll hit microwaves and radio waves. The first recorded discovery of infrared light comes to us courtesy of smarty pants extraordinaire, Sir William Herschel. This guy is what you would call of von der Kind. First of all, he was born

in Germany, so the word I use is linguistically appropriate. Secondly, he was a composer, he was an astronomer and just generally a scientifically minded guy. And he's the guy who discovered uranus the planet. And yes, I'm going to pronounce it that way, because to do it the other way makes it sound juvenile. He was also the grandfather of another William Herschel, who would go on to establish fingerprints as a means of authenticating documentation, but I've covered that

in a different episode. So Billy Herschel the first was pontificating about the nature of light, and it was obvious that light carried heat with it. When you step out of the shade into the sunlight, you feel it. So Herschel was working with different types of colored glass. He was experimenting with different telescopes that he might be able to use to observe the Sun, because the Sun's rays are far too bright to stare at without the risk of injury. We all know this. You don't stare at

the sun. So by using glass of different colors, he was hoping to reduce the amount of light coming in through the telescope so that he could still take a closer look at the Sun and make observations safely. But you discovered that some colors of glass seemed to reduce the amount of heat that was passing through his telescope, and others seemed to allow a great deal of heat to come through, including enough heat to potentially cause an injury, but this time due to heat rather than to the

intensity of light damaging his eye. And he knew about how light could pass through a prism and would break apart into the different colors of light, and collectively those colors make up white light. What he wondered was if those colors carried different amounts of heat. So he set up an experiment and he used a prism to break light into the different bands of colors, and then he used a thermometer with the bulb end blackened by ink, and he used that to measure the temperature within each

band of color. And he noticed as he measured the violet end of the spectrum, the temperature readings were lower, and towards the red end they were higher, and he decided to also test the area just beyond the red end. There was no visible light at that section, but he observed that it was at that area where the thermometer was registering the highest temperature. And this is the earliest recording of someone figuring out that there was something beyond

the rainbow, so to speak. And yeah, I know, I misquoted a song just to make that reference. Herschel referred to this area beyond visible light as the thermometric spectrum. In early days, some would refer to it as dark heat or invisible rays. The term infrared wouldn't really come around until the other end of the nineteenth century, and there are no reliable records that indicate who actually coined the term, but whomever was responsible, it became the standard

way to refer to this specific band of radiation. So I've used the term thermal imaging in this episode, and the reason I have is that it implies when we use these technologies that were not somehow magically seeing infrared radiation. Right, We're not able to suddenly see infrared light through this tech. Instead, what we're doing is we're using technology to detect infrared radiation or heat, and then using some sort of process

to convert that data into a visual representation. For example, with thermal glasses, we'd see different colors that different intensities to indicate varying degrees of heat between objects. Typically we use colors like bright yellows, oranges, and reds to indicate hot surfaces, and greens and blues to indicate cooler surfaces, which is nice because that also corresponds to how much

heat energy those bands of light carry. Not in a one to one scale, mind you, but the general principle remains, and we kind of grasp it, right, We say, Okay, this red thing is definitely hotter than that blue thing. But to be able to do all this, we first have to be able to detect and measure the heat coming from an object in a reliable way in the first place. Right. So, one of the cool things about physics is how seemingly unrelated factors are actually tied together.

From the macro scale. That being the world that you and I live in most of the time. Anyway, some of you may have been having Honey I Shrunk the Kid's Adventures, and I'm all for it. But on the rand scale, it's not necessarily intuitive. But temperature can have a big impact on other stuff, such as electrical properties

like conductivity and resistance. So just a reminder, conductivity describes a material's ability to act as a conduit for an electric charge, to allow an electric charge to pass through it. Resistance is the flip side of that coin. It's a material's tendency to resist an electrical charge. We can think of it kind of in terms of friction. If you have a very smooth floor that's been recently waxed, there's very little friction there, and you might slide all over it,

perhaps without even intending to do so. But if you're on something like a rough concrete surface, there's a lot of friction and your attempts to slide would be met with a lot of resistance. Well, the electrical world, that's kind of analogous to conductivity and electrical resistance. Heat can change these properties. For example, even a good conductor has saw electrical resistance just like we can't entirely negate friction,

even with our smoothest materials. But if you cool that conductor down, like way down, like colder than the depths of space, you can reduce its resistance, and depending on the material, you can reduce it all the way down to nothing. At that point you've got what's called a super conductor. Likewise, a conductive material will increase in resistance as it heats up, so temperature and electrical resistance have

this kind of relationship. Now, the whole reason I went down that apparent bunny trail is that it brings us to an important component that would play a huge role in thermal sensors, and that's the bolometer. Now, when I first read this word, which is spelled b O l O m e t e R, I had not heard anyone pronounce it, and as many of us know, sometimes that means in our heads we have a very different pronunciation.

So when I first read it, I thought it might be a bolo meter, and then I immediately second guess myself because I'm pretty sure a bolometer would be a device for measuring Texas neckties. So no, it's a bolometer. Now, to understand a bolometer. It helps if we also understand what a wheat Stone bridge is, and it's not an architectural thing. This is a type of circuit and its purpose is to measure the unknown electrical resistance of a material.

It was first implemented in eighteen thirty three by Samuel Hunter Christie and later refined by Sir Charles Wheatstone in the eighteen forties. This is a little tricky to describe without the use of visual aids, but I'm going to give it a shot. All right, Imagine you have a perfect square. Now turn that perfect square forty five degrees so that it's a Diamond's got a top, left, right, and bottom point. And those four corners of this diamond

present points of electric potential. And let's let's name the top point is A, the bottom point is B, so they're opposite each other. The left point is C, the right point is D, so they're opposite each other. Now, let's also imagine that C and D connect to each other with a horizontal line that cuts right through the middle of this diamond. So you've got a path going from C to D, as well as the uh the straight lines of the diamond from A to c A to D and then C two B and D two

B the sides of the diamond. Those lines that I just mentioned connecting the points represent resistors. And here's the key when using a wheat stone bridge. You know the electrical resistance for three of those resistors. Those are ones that you have put in place. So you've got three resistors where you know the electrical resistance. The fourth resistor represents the material you're actually testing. You don't know its

electrical resistance. So in our little amount engineering wheat stone bridge, let's say that the line between point D, which is the one that's on the right side of the diamond, and point B, which is on the bottom side of the diamond, that represents the resistor we're interested in. We're trying to figure out what is its electrical resistance. Now, another important point is that on the opposite side of the circuit, the line that's representing C the point on

the left, and B on the bottom. So the other bottom leg that one is a resistor that we can actually adjust the electrical resistance. We can fine tune it. It's like a radio dial. You can just fine tune that electrical resistance by applying a difference of voltage between A at the top and BE at the bottom. We allow current to flow through this circuit, and if current can flow from point C on the left to point D on the right, or vice versa, it means the

bridge is unbalanced. That means there's more resistance on one side of the circuit than the other. So we slowly start to find t that one leg that C B resistor, and we continue to fine tune it until no current is passing between points C and D. That would mean that the wheat stone bridge is in balance. It also means the ratio of resistance represented by the left side of the circuit has to be equal to the ratio of resistance on the right side. And we know the

electrical resistance of three of those four resistors. So by knowing the ratio on one side and knowing half of the ratio on the other side, we can figure out the variable. Right. It's just a simple algebra problem. So you just solve for X and boom, you found the electrical resistance of that material you were testing. Why is all of that important, Well, it's because the bolometer is built upon the premise of the wheat stone bridge. In

Pokemon terms. It would be an evolution. I'll explain in just a moment, but first let's take a quick break. Before the break, I described the wheat stone bridge circuit and how it allows researchers to determine the electrical resistance of a material. Now it's time to talk about bolometers and Samuel Pierre Pont Langley what a name. It's sp Langley's how he was typically referred to, Professor S. P. Langley. Langley was a lot of things. He wasn't just a professor.

He was almost the inventor of the airplane. A couple of upstarts called the Right Brothers beat him to it. He was also an astronomer, and like Sir William Herschel nearly a century earlier, he wanted to find ways to study the solar energy that made it from the Sun to the Earth, And in eight seventy eight he invented an apparatus that could be used to measure the amount of infrared energy hitting a specific point. And this was

the bolometer. So remember the wheat stone bridge I described earlier, Well, now imagine you've got the same sort of layout, except this time you know the electrical resistance of every leg in this circuit, so you're not you're not trying to figure out the electrical resistance You already know what it's supposed to be for all parts of this wheat stone

bridge style circuit. However, the material you're using is very sensitive to changes in heat, which in turn changes the electrical resistance of those resistors like super super sensitive, even the shift of just one thousand of a degree celsius will make a change in its electrical resistance, So the

electrical resistance of the materials changes. So rather than tuning in to find a specific electrical resistance as you would with a traditional wheat stone bridge, a volometer monitors the electrical resistance of a circuit, and the changes in resistance indicate a change in temperature. A bigger change in electrical resistance indicates a higher intensive of infrared radiation, meaning a bigger change in temperature. Langley invented an incredibly sensitive thermal detector.

It was able to pick up incredibly small changes in heat from an enormous distance. Reportedly, with one of his refined thermal sensors using a bolometer, he could detect the body heat of a cow from four hundred meters away. The bolometer was that sensitive and would pick up the infrared energy coming off that cow, indicating that there was something in that spot that was generating more heat than

the surrounding objects in that environment. So by measuring the changes in electrical resistance, you could work back to understand

the intensity of the infrared radiation hitting that sensor. And this was really good for detecting differences in temperature, right, not necessarily getting an exact read out of the temperature of an object, but rather getting the difference between one object and say it's environment or another object, and hotter things give off more intense infra red radiation, so you can build up your knowledge base this way. There's a

bit more to it than that. When we talk about modern bolometers, those get pretty complicated, and honestly, it gets to a point where I don't think I can really tackle an explanation that will mean anything without the use of visual aids. But the basic principle measuring infrared radiation through monitoring electrical changes remains the same. So again, this was sort of an indirect way to detect heat, right.

I mean, the changes in temperature would affect the electrical resistance in the bolometer, and that's what we were actually measuring. We're not measuring heat, We're measuring electrical resistance that changes as a result of infrared radiation or heat, and then a meter measuring that resistance would indicate what was going on. But this meant researchers had to spend time to refine what that actually meant. They had to match the changes

in electrical resistance to the differences in temperature. And this is a part of science and engineering that just blows my mind, not just that super smart people had to take some known phenomena and then make use of it, but then later refine that so that the use is more practical. We'd see a lot of further steps build

upon this foundation. Bilometers could indicate changes in temperature, but it would take a lot more work and technology to use that data and then convert it again into something that could be presented visually as a thermal image or

thermographic display. So with a bolometer based thermal imager, you've got infrared radiation which hits a thermal sensor, which changes its electrical resistance as a result, which a meter detects, which sends this metric to a processor which interprets that data and then converts it into a different type of information that can be displayed on a screen. This is

what amazes me. So the bolometer would become a really important tool for astronomers, but it would take a bit longer to play a role in thermal imagers, though not too much longer. According to multiple sources, the first person to create a thermal television camera was the Hungarian born Kalman to Hanji in nineteen nine. He built it for Britain to use as part of their anti aircraft technologies

after World War One. I wish I could tell you more about the technology of his device, but honestly, there's not much information I could find about how it actually worked. There's a general agreement that this is the first thermal imaging camera, though all of that could ultimately be pulling the information from a single source, which makes it less reliable.

But I couldn't find much information on what the actual implementation to Hanyi used in his invention, and in a few sources, I found his device confused with a later thermographic camera that would be reportedly based off his invention, but was its own distinct thing. So while it appears The first thermal imaging camera dates to nine nine, and it was all about live images. I can't tell you a whole lot about it, and I'm sure there are patents out there for it, but my patent searches were

not terribly fruitful. I couldn't find anything all the way back at nine that match the description. However, one thing I can say is that for the first few decades of thermal imaging, almost all the research and development for

that technology fell to militaries around the world. Thermal detection in general was a big area of research, and engineers were trying to incorporate thermal sensors and stuff like missiles and torpedoes, and later on in rifle scopes and headsets, the idea being that this could be part of a guidance system to help an explosive projectile lock into a target. I mean a lot of military targets are also sources of considerable amounts of heat, such as warships, submarines, tanks,

or aircraft. So a missile or torpedo that has a thermal sensor on it would be able to hone in on the heat source pretty easily. But by the nineteen fifties, other disciplines were also interested in making use of this technology, such as in medicine. There were some doctors who were hoping to use thermal imaging to help them do stuff like identify potentially cancerous tumors. The idea being that a cancerous tumor would likely consist of cells replicating at a

faster rate than normal cells. Thus they would have a higher metabolic rate, and you would think that that would mean they would be generating more heat than healthy tissue. A device sensitive to minute differences in temperature and capable of displaying that information on a screen, particularly if you could do it in real time, would be handy if

that hypothesis were to hold true. Now, I want to add that this particular approach isn't proven to be the most effective means for detecting a tumor, and that other methods such as mammograms are far moral liable and likely to catch cancer at earlier stages. But at the time there were doctors hoping that it might be a helpful technology. However, for most part, thermal imaging remained in the domain of

the military around this time. So we're going to skip forward a bit to the development of a different kind of heat sensor. This one is based off pyroelectric materials. Pyro Electricity refers to a certain set of crystals that have large electric fields and that generate a voltage when they undergo changes in temperatures. This is similar to, but distinct from piezo electricity or piezo electricity if you prefer. Those are crystals that accumulate an electric charge after those

crystals have been subjected to a mechanical stress. They also will vibrate if they are subjected to an electric charge. So the quartz crystal in a you know, classic watch is a piezoelectric crystal. Pyro electric is slightly different. This is in changes in temperature. That's where you get the voltage. Pyro Electric crystals generate voltages upon those temperature changes, but after a while, if the temperature remains constant, the voltage

will decrease and eventually disappear. These aren't typically used in thermal sensors for cameras. They can be, but they're not typically used that way. They're commonly found in stuff like light switches that automate lights when they detect someone's in

the area. We often think of these as motion sensors and I'm sure some of you out there have stories of being in, say I don't know, a bathroom when the lights automatically go out, and then you have to find creative ways to get the sensors to pick up on the fact that you're still in there and you're still attending to your dark business. Typically these aren't motion sensors. They can be, but they're not always. They often are

heat sensors. So moving around isn't getting picked up by some sort of optical element, at least not in the visible spectrum, but rather you are generating a lot more infrared radiation as you're moving around, getting head up, and thus the sensor picks up this infrared radiation says, whoops, somebody's still in here, and then the light cell come on so that that warm body inside that bathroom can

get down to business. Then there are thermo couples. Breaking down the name, we can figure out this has something to do with heat and it has to something or others, right, a couple. So in this case, the couple the something or others are strips of two different types of metal. The metals have to be specific types that will generate a voltage when the temperature of the two metals doesn't match, so the temperature of one metal is higher than the

temperature of the other metal. So when infrared energy hits the strips of metal, the strip one of them is painted black that one will absorb more energy it heats up faster. The change in temperature causes a voltage to apply across the circuit and current flows. Typically you create a big collection of thermo couples into what is called

a thermopile to do anything useful with it. All of these approaches rely on physical materials generating some sort of detectable and measurable response to changes in temperature, and over the decades, these sort of components would play a part in sensors in general and thermal imaging in particular. In nineteen sixty three, an engineer at the company Texas Instruments named Kirby Taylor invented a technology called forward looking Infrared

or f l I R. FLEAR. Okay, so before f l I R, most thermal imaging systems used a single line of sensors. So just think of a line of these things, a vertical line or a horizontal line, and you would sweep that line of sensors across an area to pick up differences of temperatures, you would physically move the sensors across this area. The military would use these kind of sensors mounted on planes to do this. The planes could fly over an area and scan the area below.

The line of sensors were perpendicular to the planes travel, so the planes flying forward, the line is perpendicular to that forward uh direction, and this allowed it to scan across the ground underneath. This approach was incapable of producing real time two dimensional images. You were getting slices essentially, and it would be useful for reconnaissance, such as if you wanted to identify, I don't know, a possible Soviet missile silo in Siberia or something, but you weren't getting

a real time image of a heat map. Taylor worked on creating a forward looking thermal sensor, one that would use a scanning mirror to steer the sensors. So technically, what this mirror was doing was sweeping back and forth across the sensors, directing the infrared radiation coming in through the camera and in a coordinated way so that the processor on the other side of this could take the

information and make a two dimensional image from it. The scanning mirror achieved the same effect as moving a line of sensors across an area, but you didn't have to move the sensors because the mirror was doing the moving for them. Now, there are two branching forms of thermal imaging sensors that I should mention from this point. There

are uncooled detectors which can operate at normal temperatures. They don't require any special conditions apart from you know, the typical stuff like a source of power like a battery. Then there are cooled systems which require special cooling systems no big shock there to keep the sensors at a very low temperature. And these systems work with different types of infrared radiation. See, just like the visible light spectrum, infrared itself is a spectrum, but it's not just one

band of frequencies. Right, You've got near infrared on one side. That's the side of the band that's best buds of the visible spectrum. Right, you've got red light. The red light then gradually gives way to near infrared, which is invisible to us, but it is much closer to the wavelength of red light. Then on the other end of the infrared spectrum is what's called long wave infrared, in

between his midwave infrared. In general, uncooled detectors tend to work on the long wave infrared spectrum, while cooled detectors focus har har harror on the midwave spectrum. One thing that helped bring thermal imaging cameras out of the realm of the military, meaning it helped bring the cost down, was the development of micro bolometers. Now, a camera could have an array of micro bolometers acting like the pixels

in a digital camera. The camera would bring in infrared light just as it would light in a visible spectrum, and it would aim that light to an array of micro bilometers, just like it would an image sensor in a digital camera, and the microprocessor would take the information coming from these micro bolometers and interpret it as differences in temperature, which in turn could be communicated to the user as different colors and levels of brightness to indicate

which parts of an image were the warmest or coolest. I'll talk a bit more about cooled thermal detectors after the break. Cooled thermal cameras work on a different principle from the micro bilometers. Remember a bolometer describes the technology in which a component changes its electrical resistance in response to a change in temperature. Measuring that change in electrical resistance tells you how much infrared radiation the sensor has encountered.

Cooled thermal sensors respond to individual photons of infrared light. Yeah, just because we can't see it doesn't mean that the photons aren't there. So these sensors are sometimes referred to as photon counters. These are incredibly precise sensors that can detect single photons colliding with them. They might then generate what's called a t t L pulse. T t L stands for transistor to transistor logic. You can think of it as a little digit counter clicker. The sensor picks

up on a photon collision. There's a clique. It has a register to hit. In other words, if it registers many hits in a short amount of time, that can relate back to intensity, meaning you've found something pretty hot. It's super nifty stuff. Others might take a photon and generate an electron As a result, that electron would get stored in a capacitor and it honestly gets super duper technical and also gets beyond my level of familiarity pretty quickly.

Suffice it to say that this approach is not quite the same thing as using a bolometer. There are photon counters for all sorts of frequencies of light, not just the infrared spectrum, but obviously I are or infrared, that's what we're interested in for our topic, So let's get

back to these cooled thermal sensors. Cameras using the photon counting methodology have very short response times, which in turn allows for faster frame rates of video, so you get better video output than you would with an uncooled system. These cameras also have a greater level of sensitivity and can be more easily used to detect small differences in

temperature within the field of view. They're also better at detecting thermal output from small objects and depicting those small shapes on camera in an accurate way, as opposed to an uncooled system, where if it's a small object that's giving out heat, chances are you're just going to see an unidentifiable blob of color representing that smaller object. You

wouldn't be able to see what the thing was. You would have a rough idea of how warm or cold it was with respect to the other things in the environment. But that's about it. The cooled cameras come with some this advantages. First of all, they tend to be more expensive than uncooled systems, so that's a downside. And also that has to do partly with the fact that you've got a sensor that has to remain cryogenically cooled, and that in term requires special considerations and often a good

deal of energy. It makes the cooled systems unsuitable for certain use cases like normal glasses, because I don't know about you, but I'm not too eager to put on a cryogenically cooled headset anytime soon. In a little film called Predator came out and it taught us that I don't got time to bleed, Okay. In that movie, a group of mercenaries, including the iconic Arnold Schwarzenegger, although I

just I just quoted the equally iconic Jesse the body Ventura. Anyway, they end up becoming the targets of a planet trotting big game hunter alien, the titular Predator, and we get treat did to Predator vision a few times where we see the world from the perspective of this alien, and that includes heat vision. Schwarzenegger helps avoid the predator at one point by coating himself in mud to disguise his

heat signature. That would only work for a short while because the thermal sensors initially would just pick up on the temperature of the mud, not the person under it, but your body heat would gradually raise the temperature of the mud to your own temperature, so soon you would just be a muddy, warm mess, and then shortly after

that you'd become predator trophy material. Thermal cameras can see through stuff like smoke pretty effectively, and firefighters have used thermal cameras when entering smoke filled areas to help rescue people from dangerous situations. Uh, thermal cameras don't work so well in fog and rain because water droplets can scatter infrared radiation makes it harder to get a clear image.

That being said, in certain rainy can sans they can be more effective than visible light sensors, so while it's not ideal, it's still an improvement over other methods in several cases. On top of that, you've got glass. Glass is highly reflective for light in the infrared range. Visible light can pass through transparent glass no problem, so you can see on the other side of a transparent pane of glass, but infrared light bounces off that glass like

it's a mirror. So if you take a thermal image of someone who's wearing glasses, you'll see that the lenses are just these solid shapes of color. You can't see through them. You will be able to see the person's eyes because of that reflectivity. Highly reflective surfaces in general are a problem. Shiny metal can reflect infrared radiation, which means it can be hard to use thermal sensors if you want to monitor, say, machinery for signs of overheating.

One cool thing you can do, and there are great photos of people doing this online, is take a photo of something warm, like I don't know, your foot inside an opaque plastic bag, I mean still attached to you. Don't don't remove your foot, but like put a plastic bag like a garbage bag or a bin liner, as my buddies across the pond would say, around your foot. So this is opaque. You cannot see through it, as long as that plastic isn't too thick. However, the infrared

light will pass right through. Visible light gets blocked so you can't see your foot, but that infrared radiation passes straight through the bag, and a thermal imaging camera can still see your foot just fine. Inside of it. You also get this kind of nifty halo effect too. The Predator film helped bring thermal imaging cameras into the mainstream consciousness, but the equipment was still pretty expensive, so you weren't likely to find it outside of some limited commercial uses,

and in the military, firefighters were using it. Heavy industry was starting to use it. It would take a while for the price to come down enough for inspectors to be able to use it, for example. But these days thermal cameras and smartphone thermal camera accessories are far more accessible than the early days of thermal imaging. It's still

a relatively expensive technology. You're typically looking at a few hundred dollars for a basic thermal imaging camera, probably more than a thousand for something of really decent quality, and far more than that if you want something of professional quality. But that's still an incredible step down in price from what it used to be, and when you think about everything that has to happen to make thermal imaging possible, from detecting heat to measuring intensity to translating that into

something we can see, all in real time. It's a heck of a thing. One thing I wanted to close this with is the concept of active I R sensors. I've really been talking about passive I R sensors, which detect, measure, and display thermal information from the environment. It's coming from the environment itself, but there are also active thermal sensors which both detect and project infrared radiation. So why do

they do that? Well, think of it kind of like using a flashlight, except the light you're giving off is in the infrared spectrum, so we humans can't see that light unaided. So you might use something like this and say, I don't know, a nighttime military operation, so that no one would be the wiser, and you have people snooping around using these infrared flashlights and infrared sensors to be

able to look at their environments in the dark. You would have the thermal sensor system, perhaps mounted in a head display. Inside that system would be the projector that sends out those infrared rays, and then the detector that picks up the reflected incoming infrared rays. It's just like visible light. When the infrared rays come out of the projector, when they hit something, they reflect off and then the sensor can pick up that reflection and then you get

the redoubt in your display or the visualization in your display. Uh. That would work pretty well unless the person you're snooping around also happens to have thermal imaging sensors, because then they would see that beam coming out from your system as if it were a flashlight beam. They would be picked up. Active i R systems are used in lots of applications, such as in robotics. Many robots have active i R sensors in them as a way to avoid

hitting obstacles. The projector sends out an infrared ray, and the sensor is looking out for infrared radiation in that same frequency band and above some sort of threshold. So not just like a tiny indicator has to hit above that for the robot to think, oh, there's something in my way. So when the sensor detects radiation at or above that threshold, it sends a signal that then gets

acted upon in some way by the robot. An easy example This is a robotic vacuum cleaner that starts to approach a wall, and then when it gets to a certain distance, it's close enough where the infrared radiation coming from its projector bounces off the wall and gets picked back up by the sensor that tells the robot to stop moving forward, to turn and move in a different direction.

Tuning stuff to a particular infrared frequency helps avoid interference, so not just like any infrared ray, but rather within this narrow band that's what it's looking for, so it's not likely to uh to misidentify another infrared source as being a problem. The Microsoft Connect Xbox per referral also uses a similar implementation of infrared active sensors to sense depth. This sensor includes a near infrared projector, so it's near

infrared beams. Those are the beams that are still invisible to us but are closer to the red side of the visible light spectrum, and they can be detected by standard digital camera sensors. So the projector and sensors work together to measure the time of flight. That it's the moment the light leaves the projector to the moment when a sensor picks it up and then working backward by knowing how long it took the light to go out

and come back. You know how far things are because you know about the constant of the speed of light. So the Microsoft system could determine how far away an object is, like the player from from the sensor. So this gives developers the option to include depth as a factor in games and applications that use the connect. So you wouldn't just have stuff that relies on movement within the two dimensional plane of up and down and left and right. It would also take in the third dimension

of closer to or further from the connect. Now, I want you guys to know there's a lot of super technical stuff that I skipped over in this episode. There are things we could talk about with focal plane arrays and various materials used over the years, and thermal sensors, but I felt the important part was to get the basic understanding down. I think that's pretty cool or hot.

I'm not sure which. I've misplaced my thermal glasses. And as for using them to screen people, as I said, it could be useful as a quick first pass for anyone who happens to have an elevated body temperature, but again that doesn't necessarily indicate a COVID nineteen infection. It's not enough of a precautionary measure all on its own. And that's not the fall of the technology. That tech

can be incredibly precise. It's rather that the risks go beyond those who may just have a fever and like that might not be someone with COVID nineteen, or you might be overlooking people who do have COVID nineteen because they don't actually have a fever. Yet that as long as you overlook these possible vectors, infection will continue, which is why we should never consider any one approach to be sufficient. We have to take a combination of approaches

if we want to put protective measures in place. As always, make sure you exercise critical thinking, give it a healthy dose of compassion, because without compassion, critical thinking is just cold and heartless. You gotta have both, and if you're able to apply both of them, then I think things will be okay. If you guys have suggestions for future episodes of tech stuff, whether it's a technology, a company, a trend in tech, anything like that, let me know.

Reach out to me. You can get in touch with me on Twitter or Facebook to handle for both is tech Stuff h s W and I'll talk to You again really soon. Tex Stuff is an I Heart Radio production. For more podcasts from My Heart Radio, visit the i Heart Radio app, Apple Podcasts, or wherever you listen to your favorite shows.