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Xerxeskingofkings

kinda? we just call them microwave wavelength radar.


LondonParamedic

I know we can produce images by processing microwave data, such as the picture of the cosmic microwave background. Can we do something analogous to that and a camera, showing real-time video like with a thermal camera?


AdarTan

The smallest detail you can distinguish are approximately the size of the wavelength that you are using. Microwaves have wavelengths measured in centimeters vs. the tenths of a micrometer scale for visible or infra-red light


Quynn_Stormcloud

Being reminded of the size of these waves always gets me to wonder why they got the moniker “microwave.” They’re really big waves!


Bensemus

They are tiny compared to radio waves though.


ComesInAnOldBox

Microwaves *are* radio waves. Just really high frequency ones.


2FightTheFloursThatB

Microwaves and radio waves are just two types of electromagnetic waves. I don't think it is precise to say Microwaves are just high frequency radio waves.


TheJeeronian

Microwaves are indeed just one subset of radio waves. The term "radio waves" is inherently imprecise as the umbrella is huge, but the statement is fully and absolutely accurate.


Maxnwil

Technically, they’re also under the umbrella of “infrared”! (Source: IR astronomer who uses microwave/radio telescopes)


Zelcron

Gamma radiation, too, falls in the broader category of EM waves. On the other end are the extremely long wavelengths the Navy uses to communicate with submarines. In order to penetrate the water, the wavelengths are in meters. The messages are extremely low bandwidth, so typically a message might be only a few letters signifying a pre determined command code.


ComesInAnOldBox

What's the range of the telescope?


ComesInAnOldBox

By definition, radio waves are frequencies within the electromagnetic spectrum between 3 Hz and 300 GHz. Microwave frequencies are between 300 MHz and 30 GHz, well within the range of radio.


gordonjames62

> I don't think it is precise to say Microwaves are just high frequency radio waves. We call certain kinds of energy RF (radio frequency). According to the wikipedia page on [Radio frequency](https://en.wikipedia.org/wiki/Radio_frequency#RF_energy) we see that . . . >**Radio frequency (RF)** is the oscillation rate of an alternating electric current or voltage or of a magnetic, electric or electromagnetic field or mechanical system in the frequency range from around 20 kHz to around 300 GHz. **This is roughly between the upper limit of audio frequencies and the lower limit of infrared frequencies** It is part of the definition of [microwave](https://en.wikipedia.org/wiki/Microwave) that >**Microwave is a form of electromagnetic radiation with wavelengths** shorter than other radio waves (as originally discovered) but longer than infrared waves. Its wavelength ranges **from about one meter to one millimeter**, corresponding to **frequencies between 300 MHz and 300 GHz**, broadly construed.


ComesInAnOldBox

"Micro" just means small, and they are indeed small when compared to most other forms of radio waves. The wavelength of your regular FM radio stations is between 2.74 and 3.41 meters. The AM band goes between (roughly) 176 and 555 meters. 12.5cm is pretty dang small in comparison.


badr3plicant

Historical reasons, I suspect. When radio started, we were working in the kHz frequencies, which is where AM radio still lives. 


Defleurville

Minicomputers are the size of a refrigerator and microcomputers are the size of a backpack. Because computers used to be the size of a football field.


wosmo

Fun fact - the original allocation for amateur radio (in the US) was everything above 1500kHz (200metres) because it was at the time believed that such short waves weren't commercially useful. So microwaves are really short compared to this definition of shortwave.


PuzzleheadedDebt2191

Well they are in micro(meter) scale. It just so happens that kicrometer range wavelenghts are not all that short.


reichrunner

Where are you getting that micro and meter are analogous? Micro is usually a prefix meaning 1 millionth (10^-6). Does it mean something different here?


superbob201

'Radio' generally means that the wave is created by/interacts with electronics. Microwaves are radio waves that interact with microscopic electronic devices.


defeated_engineer

They are often called millimeter waves in academia if it makes you feel better.


Quynn_Stormcloud

That *does* ease a great burden from my mind.


manofredgables

A normal indoor photo at full resolution would probably not need to be more than a few hundred pixels to capture all information possible lol


ackermann

A couple centimeters resolution should be good enough for photos of landscapes, cityscapes, buildings, etc


PrateTrain

Ah so do electron microscopes use gamma rays or something?


PetrasSukys

There is a hint in the title... electron microscopes use, you guessed it, electrons to "light up" the thing and detect what is reflected.


PrateTrain

Ah weird I had always assumed they were called that because that's what they could look at


PetrasSukys

On the contrary, they can't really look at/see electrons... :D but atoms and molecules - sure.


PrateTrain

Fascinating, thank you


ghostowl657

Interestingly electron microscopes are used because at any given input energy electrons have much smaller wavelengths than photons (because they have mass). Which makes them much more practical for imaging.


bigblackcat1984

Like the name suggest, they use electron beam.


Angdrambor

The main problem here is that microwaves are big. Microwaves are about 100,000 times bigger than light that humans can see, or about the size of your hand. That means that pixels in a microwave camera also need to be big. This means that your camera sensor is gigantic, and you can only fit a few pixels on it, so you can't get good resolution. For an example of how many pixels you can fit, check out the [https://en.wikipedia.org/wiki/AN/APG-81](https://en.wikipedia.org/wiki/AN/APG-81) . Its a big radar array for military aircraft, but it can only fit 1,676 pixels. Normal cameras usually have more than 10,000,000 pixels to collect light with. To be clear, the AN/APG-81 doesn't use it's pixels like a camera. It uses them to aim it's microwave beam, and it builds up a picture over time by scanning that beam back and forth.


Sjoerdiestriker

To add to this, it's not just that the pixels have to be big. It's also that the details you'd be imaging have to be big. Basically, you can never resolve details smaller than about the wavelength, because of wave diffraction. So if you'd want to image some object, you'd inherently get a really, really blurry image for regular sized objects, basically blurred over a distance the size of the wavelength.


Angdrambor

Well that's fine. There are plenty of things to see in the world with details bigger than 10cm. If you built a camera sensor the size of a house, you probably wanted to use it to look at big stuff anyway.


thewerdy

Sort of. Since microwaves are so much bigger than visible light or IR, resolutions are pretty limited considering realistic sizes of receivers. You'd need a really big aperture to get a similar resolution to a typical optical images. However, with a moving collection platform you can create a sort of synthetic large aperture and get a high resolution image out of that. See [Synthetic Aperture Radar](https://en.wikipedia.org/wiki/Synthetic-aperture_radar) for more information.


dont_say_Good

Yeah it's called a radar


Drusgar

My phone can "see" other wavelengths. So can my popcorn, kinda.


nun_gut

Instructions unclear, just microwaved my phone.


Aberdolf-Linkler

Fully charged?


Adventurous_Use2324

Pardon?


FromTheOrdovician

So what does RCWL 0516 do exactly


Zouden

It's a single "pixel" and senses a whole room at once.


BaconReceptacle

We definitely have sensors that can detect microwaves in detail however displaying them on a screen like you would a video or photograph would require a heavily processed image. Just like many of the images we have of planets, stars, and galaxies are not actually what they look like if you were to see them up close with a human eye. This is because the data that represents those non-visible wavelengths is processed so that we can see it. You might configure the software that processes it to represent any data that is 2.6 to 2.7 Ghz is colored blue and 2.8 to 3.0 Ghz is purple.


Other_Mike

Most deep sky objects are photographed in visible light, unless you're specifically using an instrument that uses other wavelengths. The only difference between an amateur astrophoto and looking at an object with a telescope is that it's bright enough to see detail and color. The color was always there (unless you're shooting specific narrowband to highlight some feature), it's just that it isn't bright enough when you look at it to trigger the cone cells in your eyes. (One noteworthy exception in my case was seeing the Whirlpool Galaxy through a large telescope under dark skies; I could clearly see the blue in its spiral arms.)


floznstn

Yes and no… it’s not a camera as such, but still an RF visualizer https://hackaday.com/2023/03/04/inspect-the-rf-realm-with-augmented-reality/ here’s another AR visualizer for RF https://hackaday.com/2019/01/09/smartphone-app-uses-ar-to-visualize-the-rf-spectrum/


sharkowictz

This should be pinned as the answer, these are great visualizer projects. 👍🏻


mks113

Yes, we call them weather radars. The standard 2400 MHz frequency used by a microwave oven is chosen because it is absorbed and reflected by water. If you send out signals with a very directional antenna, and have a similar setup to receive the pulses, you have a camera (actually more of a scanner) that creates a picture of where water is ahead of you. There are array antennas but I don't think they really act like a camera, just a means of focusing the signals from one very specific direction.


[deleted]

[удалено]


ZachTheCommie

Microwaves work through dielectric heating of certain molecules, and that sounds a lot like resonance of some kind.


Obliterators

Resonance has nothing to do with dielectric heating. Any wavelength would work on water and microwave ovens heat up fats and sugars as well, they even work on glass with some preheating. [Water has a very broad microwave absorption spectrum](https://i.imgur.com/ieTBSiK.png). Household microwave ovens were allocated a 2.45 GHz industrial, scientific, and medical (ISM) band to reduce interference with radar and radio. It's also offers reasonable heating penetration and power requirements. Some industrial microwave ovens use 915 MHz instead for more uniform heating.


ZachTheCommie

So a microwave is basically just a box filled with very bright invisible light? Not arguing. I'm genuinely trying to understand the principles of this. Also, what frequencies would *not* work for a microwave? And how does interference matter if a microwave is a self-contained Faraday cage?


Obliterators

>So a microwave is basically just a box filled with very bright invisible light? Kind of. Microwaves are photons just like visible light but with much longer wavelengths. But the mode of heating is not the same. Dielectric heating works because polar molecules want to align themselves with an electric field. In an oscillating electric field, like when a microwaves pass through food, the molecules try to flip back and forth and that creates heat. This works on any polar molecules and is not dependent on any resonant effects; water just works best because of it's small size, high polarity, and abundance in food. >Also, what frequencies would not work for a microwave? What works and doesn't is a continuum. 10-300 GHz would be the optimum if you wanted to maximize energy absorption. However, higher frequencies penetrate shorter distances into the food so you'd end up only heating a very thin layer on the surface. 2.45 GHz has a penetration depth of a few centimetres which works well for typical microwaved foods. At much higher frequencies (>1-10 THz) the electric field switches too quickly for the molecules to respond and the heating mode switches to more conventional heating of excitation by photon absorption. Lower frequencies penetrate deeper and heat more evenly but have problems heating smaller quantities of food and require more power and larger devices. >And how does interference matter if a microwave is a self-contained Faraday cage? Microwave ovens do leak some amount of microwave radiation, mostly through the door. This is most noticeable with turned-on microwave ovens being able to cause disruptions to Wi-Fi since they operate on the same frequency. The older the oven the less lax the emissions regulations were at the time. The 2.45 GHz band was chosen in the late 1940s when microwave ovens were in their infancies and that band was unused. [Here's an FCC report from 1947:](https://web.archive.org/web/20130621164400/http://transition.fcc.gov/Bureaus/Mass_Media/Databases/documents_collection/annual_reports/1947.pdf) >[Laboratory Division's] chief activity during 1947 was in establishing standards procedures for reducing interference from diathermy[i.e. microwave ovens] and industrial heating equipment. >In one instance the industry had proposed the join use of frequencies by diathermy, industrial heating and radar. Field tests indicated that such operation would result in a hazardous condition, since the operation of diathermy and industrial heating equipment on the same frequency as radar equipment could blank certain sectors of the radarscope and thus endanger vessels and aircraft. 2.45-2.70 GHz was designated to industrial, scientific and medical devices in the International Radio Conference of 1947.


ZachTheCommie

I figured that higher frequency photons would be better for a dialectic effect since they have higher energy, but that makes sense about longer wavelengths having a more penetrative depth. Thanks for the informative answer.


Obliterators

Here are a couple of figures to illustrate the penetration depth and frequency relationship: [Absorption coefficient vs frequency](https://i.imgur.com/vRwQGVE.png) [Penetration depth vs frequency](https://i.imgur.com/QbjcJ8f.png) Sources: [One](https://www.sfu.ca/phys/346/121/resources/physics_of_microwave_ovens.pdf), [Two](https://em.eecs.umich.edu/pdf/tb3.pdf)


ChipotleMayoFusion

Yes absolutely, but the resolution will be on the order of centimeters, whereas visible light has resolution on the order of a micrometer, so 10,000x smaller. There are absolutely far infrared cameras, basically thermal optics. The amount of microwaves emitted by typical materials at typical temperatures is so miniscule I can't think of an application we're you would want to build an imaging system for a human sized object. Cell towers have a sort of microwave imaging so they can determine the direction of a target and do beam steering. In that case the "image" the whole space around the tower within range.


GreenStrong

Microwaves are defined as the part of the electromagnetic spectrum with wavelength between one millimeter and one meter. Radar in the millimeter wave range is used for fire control on the [Longbow variant of the AH-64](https://www.northropgrumman.com/what-we-do/an-apg-78-longbow-fire-control-radar) We know that it produces images, but information is not available as to how much resolution it has. We do know that it can track 256 separate moving targets. Milimeter wave radar can see a human through a wall, but [the image is more of a point cloud than a "picture"](https://ksp-windmill-itn.eu/research/fmcw-mmwave-radars-can-see-through-walls/) [There is a company using AI to interpret those point clouds, and they claim to be able to see human outlines using only a consumer WiFi router as the emitter.](https://www.sify.com/technology/this-neural-network-uses-wifi-to-see-through-walls/) This is about as close as it comes to a camera. WiFi is 6 or 12cm wavelength, well within the microwave range.


the_other_Scaevitas

I have taken pictures of microwaves with my iphone. I just go to the kitchen with my phone and voila


grat_is_not_nice

Airport Security Scanners (the booths you stand in with your arms up) use *millimeter* radar to image the person and detect things under clothes. They have enough resolution to require blurring of genital regions. But they also have a large rotating antenna to capture that image. Microwaves in the centimeter range would capture significantly less detail and need larger antenna due to the longer wavelength. Using multiple antenna to monitor wifi signals, you can detect changes in signal patterns as people move around a room (i.e. static environment), but at very low resolution.


ApatheticAbsurdist

Beyond having a sensor. The issue is focusing such waves. The airy disk would be massive so you wouldn’t be able to resolve much detail. We can pick them up with antennas. But that’s unfocused.


manincravat

The microwave oven was literally developed as a side-effect of working on radar [https://en.wikipedia.org/wiki/Microwave\_oven](https://en.wikipedia.org/wiki/Microwave_oven) *In 1945, the heating effect of a high-power microwave beam was accidentally discovered by* [*Percy Spencer*](https://en.wikipedia.org/wiki/Percy_Spencer)*, an American self-taught engineer from* [*Howland, Maine*](https://en.wikipedia.org/wiki/Howland,_Maine)*. Employed by* [*Raytheon*](https://en.wikipedia.org/wiki/Raytheon) *at the time, he noticed that microwaves from an active radar set he was working on started to melt a* [*Mr. Goodbar candy bar*](https://en.wikipedia.org/wiki/Mr._Goodbar) *he had in his pocket. The first food deliberately cooked with Spencer's microwave oven was popcorn, and the second was an egg, which exploded in the face of one of the experimenters.* So if you have ever failed to cook an egg in a microwave know you are part of a long heritage


Independent-Pen-5333

Spectrum analyzer and a directional antenna to visualizethe presence of waves. If you could see the waves visually it would look like was everything was underwater everywhere. With constant static during the day.


Uporabik

You have. It isn’t a camera but a X-Y table with probe and spectral analyser. By scanning you can create image of different frequencies


rupertavery

We can't use normal camera sensors because of physics, i.e. the physical properties and the nature of light and electromagnetism. In order to detect a photon, we use a CCD or CMOS sensor. They are designed to detect photons, and has to do with how photons travel and interact with things. To detect radio wavelengths, we use antennas. They "couple" to the EM field and so any changes local to the antenna are induced as current changes in the antenna itself. Compared to a photon, microwave wavelengths are huge. So to take a "snapshot" of the EM field you would need an array of antennas.


LondonParamedic

Isn't the difference between a microwave photon and a visible light photon just its wavelength and energy level?