Microwave Definition and 349 Threads

Microwave is a form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter corresponding to frequencies between 300 MHz and 300 GHz respectively. Different sources define different frequency ranges as microwaves; the above broad definition includes both UHF and EHF (millimeter wave) bands. A more common definition in radio-frequency engineering is the range between 1 and 100 GHz (wavelengths between 0.3 m and 3 mm). In all cases, microwaves include the entire SHF band (3 to 30 GHz, or 10 to 1 cm) at minimum. Frequencies in the microwave range are often referred to by their IEEE radar band designations: S, C, X, Ku, K, or Ka band, or by similar NATO or EU designations.
The prefix micro- in microwave is not meant to suggest a wavelength in the micrometer range. Rather, it indicates that microwaves are "small" (having shorter wavelengths), compared to the radio waves used prior to microwave technology. The boundaries between far infrared, terahertz radiation, microwaves, and ultra-high-frequency radio waves are fairly arbitrary and are used variously between different fields of study.
Microwaves travel by line-of-sight; unlike lower frequency radio waves they do not diffract around hills, follow the earth's surface as ground waves, or reflect from the ionosphere, so terrestrial microwave communication links are limited by the visual horizon to about 40 miles (64 km). At the high end of the band, they are absorbed by gases in the atmosphere, limiting practical communication distances to around a kilometer. Microwaves are widely used in modern technology, for example in point-to-point communication links, wireless networks, microwave radio relay networks, radar, satellite and spacecraft communication, medical diathermy and cancer treatment, remote sensing, radio astronomy, particle accelerators, spectroscopy, industrial heating, collision avoidance systems, garage door openers and keyless entry systems, and for cooking food in microwave ovens.

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  1. S

    Why does my canned chili splatter in 700 W microwave but not in 1000W?

    I am a truck driver. I have a 700 watt microwave in my truck that is powered by an inverter. At my house, I have a 1000 Watt microwave that just plugs into a regular wall outlet. I like to eat Campbell's Microwaveable Chili. Campbell's microwaveable chili comes in a can with a plastic lid...
  2. R

    I Does the use of microwave communication heat water particles?

    As microwave communication systems send designated frequencies through the atmosphere, are water particles within the path of these systems agitated enough to increase their temperature?
  3. K

    I Question about microwave reflections

    Hello! I have an experimental setup in which I need to send microwaves (MW). I would like to reduce the unwanted scattering of the MW as much as possible and I was wondering what materials are best for this (in vacuum). For example, if I make some holders of metal (e.g. aluminum or steel) I...
  4. G

    What do shunts in a microwave oven transformer do?

    I removed the high voltage secondary winding of a microwave oven transformer and replaced it with 9 turns of wire I need 2.1 vac 50 amps. Should I remove the shunts? I have a 100a bridge rectifier I need 3 vdc 50a for about 5 to 7 days. I don't think a MOT is 100% duty cycle so I plan to use...
  5. W

    B History of CMB, prediction of 1 in 100,000?

    Variations in the tamperatureo of the CMB are 1 part in 100,00. My understanding is that this was first measured by COBE, But was this value predicted? What were the ranges of estimates for its value before it was measured?
  6. Leo2024

    Optimal thin absorber of electromagnetic energy

    Hi, I am a material engineer and have a question about a formula derivation relative to microwave absorption. I really cannot figure it out after days of trying. This should be simple for a specialist. In this attached paper, how could one derive Eq(10) based on Eq (8) and (9)? Is k_2 in Eq...
  7. H

    B Wi-Fi Interference: How Microwaves Can Affect Your Wireless Connection

    I have noticed that every time my microwave is ON, my Wi-Fi connection freezes. It comes back as soon as the microwave stops. Is it normal?
  8. nav888

    Microwave standing wave calculations (max/min Intensity, Wavelength)

    I have tried to subtract the two values of y for the minimum intensities to find half the wavelength but I am really stuck. Any help would be appreciated thanks
  9. hilbert2

    Receiving High Freq Signals via Passive Downconverter

    I'm getting this type of device in mail, it is a passive microwave signal downconverter that converts a signal of up to 3.5 GHz to something that can be received with an RTL-SDR of upper frequency limit less than 1.5 GHz. Is it expected that I have to put the antenna-received high freq signal...
  10. D

    Help with understanding of RF theory-Kinetic inductance parametric amp

    So this might be long question that requires some literature review but I will try condense it as much as possible such that hopefully I can get some help without the reader having to review the related paper. So I will start off by saying that I am involved in a honours thesis in which I need...
  11. M

    Measuring wavelength of microwave radiation using double slits

    For this problem, The solution is, However, when they found the angle, they did not account for the uncertainty. I guess this is allowed still since the sine of the angle will still be greater than 1, correct? Many thanks!
  12. M

    I Blocking microwave auditory effect / Frey effect?

    Microwave auditory effect / Frey effect: https://en.wikipedia.org/wiki/Microwave_auditory_effect Hypothetically, if someone could send "v2k" to a person's brain, how could this v2k be blocked, practically? A tin foil hat? The EMF shielding fabric?
  13. M

    I Cosmic Microwave Background Surveys

    If I understand correctly, by reference say here, the results seem to relate to a survey of the Milky Way. 1. Is the Milky Way a 'closed' system? 2. Whether or not, were the surveys based on data from the visible Universe, or restricted in all or part to the data form 'within' the Milky Way.
  14. T

    I Microwave background radiation - temperature at recombination

    The commonly called value of the temperature at recombination is 3000 K. According to this reference the process of recombination can be described by the Saha equation: 3.1. Recombination and the formation of the CMB Recombination happens quickly (i.e., in much less than a Hubble time t ~...
  15. NTL2009

    Microwave Oven door attenuation in dB?

    I recently made a repair to the door switches/bracket on our microwave oven (MWO). All is well, but later, after reinstalling a trim piece and checking the fit, I noticed that with the door closed and latched, that there was a bit of play (1/8"?) - I could push the door a bit further closed, and...
  16. P

    B Does Microwave Energy Transfer Depend on Contents Inside?

    I've got no real physics education but I am interested in it from a popular science and layperson level. If anyone is able to help with this thought experiment. My question is, on a given microwave power setting and a fixed duration, is the heat transferred to the contents largely constant...
  17. B

    B What's the reason microwave oven frequencies are at 2.45 Ghz?

    Hi, A little background before my question: I read that microwave oven frequencies are at 2.45 Ghz, or about a 12cm wavelength. Lately, 5G is using frequencies called millimeter waves, and these frequencies can be as high as 40Ghz. So, linguistically to me, it seems as microwave oven waves...
  18. PainterGuy

    I Some questions about Cosmic Microwave Background radiation

    Hi, I have some questions about cosmic microwave background radiation, CMB, and I thought it's better to ask them together. I have combined all related content for each question to make the question clearer, understandable, and to provide proper context for any person like who stumbles upon...
  19. PainterGuy

    I Blackbody radiation and the cosmic microwave background

    Hi, The following is my basic understanding of blackbody radiation spectrum. The important sections are in boldface. Source: https://en.wikipedia.org/wiki/Black-body_radiation#Spectrum Question 1: The quote above says that at room temperature (let's say 20 C or 293 K) the emission is in the...
  20. wnvl2

    I Applying Reisenbach Transf. to EM Wave in Microwave Oven

    There is no possible measurement, no matter how clever, that can measure the one way speed of light. It is a synchronization convention. In this topic I would like to apply this idea on a specific case. I have a microwave oven with width L. In this oven I have a standing wave. $$E(t,x)=E...
  21. maayan_aloni

    I Exploring Oscillating Electric Fields for Dipolar Molecules

    Hi all! I was wondering, Is it possible, given a specific dipolar molecule, to create the perfect oscillating electric field so as to heat it and not, i.e. the water around it? What I'm basically asking is could there exist a specific microwave just for X and not all dipolar molecules without...
  22. G

    Power inside a microwave oven due to reflections

    That is how much more power would it consume if one was to try and produce the same amount of heating power with just the waveguide holes and no walls, so no reflections?
  23. J

    I How Does a CMB Photon Travel Through Expanding Universe?

    Suppose we receive a cosmic microwave background (CMB) photon from space. According to the Big Bang model, this photon became free to travel when the universe was about 0.38 million years (Myr) old. At that time, it was about 42 million light years (Mly) away from our location. Because of the...
  24. J

    B Early Universe Radiation: Gamma to Microwave?

    Hi, Never done much cosmology but reading around I have found several sources saying the early universe (pre roughly 300,000 years) the early universe was full of gamma radiation. Since the universe has expanded this gamma radiation has been red shifted into the microwave region. Other sources...
  25. A

    Can moisture in a microwave cause ink to move on a mug?

    Hello. I was wondering if anyone could help me understand what just happened. I wrote a message ony mug, then microwaved water in it for coffee. I just noticed that a few letters are now duplicated below the message. It kinda looks like some moisture on the side lifted the ink up and ended up...
  26. Elsi b

    Microwave generator and a resonant cylindrical cavity

    I tried to fix this physics problem. But i think I’m using the wrong steps.
  27. jeffinbath

    A way to make the standing-wave patterns in a microwave oven visible

    Following on from the recent discussion on the gap size in the metal grill covering the door of a microwave oven, I thought up a way to actually enable one to see some of the standing microwave patterns going on in a typical oven . I bought a 20” x 20”cobalt chloride soaked cloth from Amazon...
  28. E

    Classical explanation for microwave door shielding

    What is the classical explanation for why the microwaves won't pass through the microwave door?
  29. G

    Invention of the microwave oven: Chocolate bar anecdote

    Hi. I've just read that microwave ovens were invented 75 years ago. The article mentions the following anecdote: Apparently, Percy Spencer discovered the heating effect of microwave radiation when a magnetron nearby melted a chocolate bar in his pocket. Is this story plausible, wouldn't you...
  30. R

    I How Does The Cosmic Microwave Background Show That The Universe is Expanding?

    I've been searching for weeks and still with the doubt. I just know scientist look the content of the CMB and with general relativity calculates the expansion rate today that is 73 km/s/Mpc, but nowhere does it say how exactly. What does the contents of the universe have to do with the...
  31. K

    Wireless routers vs. microwave ovens

    I believe most wireless router uses the same frequency as a microwave oven, yet microwave ovens heats up food while routers do not. If an energy of the light/radiation is only dependent on frequency, how is it that microwaves heats up food while wireless routers do not?
  32. Russ Edmonds

    Power absorbed and B vs H plot for microwave oven transformer

    A DI-149 data acquisition module was used to record a microwave oven transformer (MOT) primary voltage and current time histories. The secondary of the MOT was open. The DI-149 analog input specs are: +- 10 volts full scale, 5000 samples per second for each channel (assuming two channels being...
  33. D

    Quantum Help: Microwave Spectroscopy, C. H. Townes and A. L. Schawlow

    Hi, everyone: I tried to find the PDF or djvu for this book. Unfortunately, it failed to get it. Could you please so kind send me a link if you have? Thanks.
  34. L

    B Why don't the air atoms in the microwave warm up?

    The object you place in the microwave warm up because of the electromagnetic waves. How come the atoms of the air of the microwave do not warm up? Or do they only feel like they haven't warmed up, or do they not absorb the energy as much as the object you place in the microwave?
  35. PainterGuy

    B Questions about the cosmic microwave background radition and its discovery

    Hi, I have few questions about cosmic microwave background radiation (CMBD) and trying to find simple answer at a basic level. I really appreciate your help and time! The universe is almost 13.799 billion years old and currently has radius of around 46.5 billion light-years. It is said that...
  36. BlackPowder

    What is the difference between a waveguide/horn and regular metal pipes?

    What is the difference between those horns/waveguides and regular metal pieces with a same geometry? Why the microwave companies sell those parts at hundreds and thousands dollars? Why we cannot buy some metal sheets or pipes on McMaster-Carr with very low price and make some microwave...
  37. I

    Running a microwave oven empty

    So I know it's generally not a good idea, but I wondered what actually is the limiting factor. Does the magnetron heat up much more quickly? - and if so what's the physics going on that's causing it to heat up - is it increased current in the resonant cavities ? Also is it bad for the cathode...
  38. A

    Permeability of copper in the microwave frequency range

    Relative DC permeability of copper is 1. Conductors are considered dispersive and therefore the permeability should change with frequency. Where can I find data or how can I calculate permeability of copper in Ghz frequency range?
  39. A

    The simulation of a microwave antenna made of nanofilm Ti3C2 (Mxene)

    Hello! I am a student of the radio engineering faculty and now I am engaged in master's work. The purpose of my work is to find application for Ti3C2 in antenna technology. I found a lot of information from article http://advances.sciencemag.org/content/4/9/eaau0920 But I can't understand how...
  40. berkeman

    Help with a strange microwave oven behavior please

    The last couple days at work, one of the microwave ovens in the kitchen has been acting strangely. Today it seemed to get potentially dangerous, so I marked it "Out of Order" for now, and would like to figure out if it is hopeless, or if it can be recovered easily. I first noticed a couple...
  41. nmsurobert

    I Cosmic microwave background observations

    If my understanding is correct... From Earth the cmb is fairly uniform around us. From a galaxy that is 12 billion light years away, would they also see a uniform distribution of the cmb? to add to that question, would the radiation be less redshifted. From my understanding on why we aren't...
  42. Charles Bagwell

    How can I calculate the efficiency of my microwave oven for steam production?

    I am working at retrofitting a microwave oven to produce steam for my 3 HP steam engine/generator. I have read estimates of 50-70% efficiency, but I am trying to verify those figures. Can anyone point me in the direction of calculating the efficiency myself?
  43. S

    Reaction or Reactionless -- Acceleration force on a microwave antenna

    A microwave transmitter, bouncing the microwaves off a parabolic dish, should have a small amount of acceleration due to the reaction of the microwaves against the dish. Would an arrangement of two dipole antennas, 1/4 wave apart and phase shifted by 90 deg., creating a cardioid pattern...
  44. S

    I Microwave photons and microwave oven doors

    Photons are point-like particles with no size, but they have different frequencies. Photons with certain frequencies (like microwave photons) can not pass through the holes of the mesh on a microwave oven, so this confuses me. Photons seem to act like they have size at low frequencies. I have...
  45. wirefree

    Can a microwave VSWR meter be used to measure Power?

    G'day. Recently we conducted an experiment in the microwave engineering lab where we were tasked to measure power in, what's called, a Directional Coupler. Here you'll find much on it. My concern with the setup is that we took our measurements on a VSWR meter by noting off the db scale. So...
  46. jim hardy

    Appliances Microwave Oven - Magnetron End Cap Replacement

    Question of you radar guys.. My 14 year old Panasonic Microwave Oven suffered a magnetron end cap failure it commenced arcing and melted off a corner. I noticed it's not sealed, brand new ones have a hole in the end ... so I'm wondering just what does the endcap do ? I find plenty of...
  47. T

    How Do Microwave transmitters work without physical connections?

    So I recently picked up 40 of 10.525 GHz Microwave RADAR transmitters: I opened up one out of curiosity and had something like this (image attached) . I noticed some parts of the PCB aren't even connected to anything. How do the different shapes and sizes of the PCB interact with each-other...
  48. C

    I Cylindrical Microwave Cavity Resonator: Speed of Light Dependency?

    Does the operation of a cylindrical microwave cavity resonator as described here, https://en.wikipedia.org/wiki/Microwave_cavity, depend on the speed of light being isotropic along the cylinder axis?
  49. S

    How do microwave plasmas work?

    I'm new to PF, I have an engineering background, but am trying to understand how microwave plasmas are generated. I'm trying to work out if a tuned microwave waveguide can create a plasma in a specific point in the waveguide say over 30 seconds as the microwave energy heats up the waveguide thus...
  50. G

    Why Do Arcs Form Between Fork Tines in a Microwave Oven?

    Some fireworks in our microwave from peeling paint got me thinking... If you place a fork inside, arcs will form between the tines. Why? Presumably the EM field is inducing different potentials on each tine, and the pointiness concentrates the field enough to exceed the breakdown voltage there...
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