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. Greg Bernhardt

    Microwave Engineering by David M. Pozar

    Author: David M. Pozar Title: Microwave Engineering Amazon Link:https://www.amazon.com/dp/0470631554/?tag=pfamazon01-20 Prerequisities: Contents:
  2. M

    Is the Cosmic Microwave Background an Absolute Frame of Reference?

    I heard sometime ago that the cosmic microwave background may be a candidate for an absolute frame of reference. Did this idea ever get any credence?
  3. S

    Microwave Optics Lab Experiment - PSU Manual

    Homework Statement We're working through the first Microwave Optics lab described in the following PASCO Scientific manual: intro.phys.psu.edu/class/p457/experiments/html/pasco_microwave_optics_WA-9314B.pdf We're using a slightly modified version of this setup, with a voltmeter hooked...
  4. S

    What's the bandwidth of the Cosmic Microwave Background radiation?

    What's the bandwidth of CMB and what was the bandwidth of CMB when it was emitted (at the moment when the Universe was 379,000 years old)?
  5. S

    For how long the Cosmic Microwave Background was emitted?

    When the Universe was 379,000 years old, the radiation could travel into space. From that point in time the CMB started to be emitted in form of visible light. Am I correct? my question is: for how long the CMB was emitted? Or is it still emitted today? If the CMB was emitted for 10...
  6. I

    Air-popped Popcorn vs Microwave Popcorn vs Oil-popped Popcorn

    Which of the three do you prefer? Air-popped popcorn is obviously the healthiest but how much healthier is it really? And is microwaved popcorn really that much worse than say oil-popped popcorn?
  7. Spinnor

    Microwave photons, when do they become real?

    A microwave oven produces microwaves that can heat food. Can we consider the electromagnetic energy leaving the magnetron and traveling in the waveguide virtual photons and when the electromagnetic energy leaves the waveguide the electromagnetic energy "becomes" real photons? Or are they...
  8. Astronuc

    Microwave Engineering by David Pozar

    Author: David M. Pozar Title: Microwave Engineering, 4th ed Amazon Link: https://www.amazon.com/dp/0470631554/?tag=pfamazon01-20 Prerequisities: Calculus/Engineering Mathematics (introductory complex analysis and linear analysis), Introductory Physics, Circuit Theory, Electromagnetic...
  9. JimiJams

    Microwave ovens versus WiFi signals

    Hi, just a simple question. We've always been told that microwave ovens are dangerous and to not stand near them when they're on, obviously because they have the ability to heat up water molecules. I just read that the microwave frequencies they emit are 2.45 GHz. Wifi signals consist of 2.4...
  10. C

    Refractive Index of Gold at Microwave Frequencies

    Hi, can anyone help me out with the refractive index of pure gold at microwave freguencies? (Specifically something close to 2.4 GHz, or your average household microwave oven) Much obliged!
  11. T

    Why is there no fibre for microwave (or other) frequencies?

    Optical fibre communication depends on total internal reflection at the core-cladding boundary. Why not use the same principle for other portions of the spectrum? After all, total internal reflection occurs at all frequencies.
  12. F

    Cosmic microwave background radiation

    Homework Statement The cosmic microwave background radiation has a blackbody type spectrum. Determine its max frequency and the correspondent wavelenght. Verify if found frequency is a microwave frequency and compare with the following curve: Homework Equations Using the...
  13. E

    Knowing the Refractive Index of a Prism using Microwave Transmitter

    Homework Statement A prism of 90-45-45 was placed between a microwave receiver and transmitter. What steps should I take to know the index of refraction of the prism given that its material is not transparent to microwave? I positioned the prism so that a side of the prism is perpendicular to...
  14. D

    Experiment: Microwave Faraday Cage & WIFI Hotspot

    So I tried out a small, fun experiment of putting my cell phone in the microwave (not turning it on, of course) to see if the WIFI Hotspot capabilities were hindered by the Faraday cage that insulates the microwaves. I had heard that microwave cages will hinder If not completely block 802.11...
  15. B

    Microwave oven at relativistic speed

    Imagine a microwave oven on some kind of track such that it can reach speeds approaching c. If the microwave was switched on and shot past us at a speed so that as it traveled away from us, the relativistic doppler effect shifted the emitted microwaves into the visible spectrum - What would we...
  16. H

    How efficient is a microwave oven

    This site was at the top of the Google results for "How efficient is a microwave oven" I can't restart the old discussion, so I'll start a new thread. Previous posters came up with numbers from 99% to 46%. The Wikipedia page offers only this: "A microwave oven converts only part of its...
  17. J

    Cosmic microwave background question.

    So to detect the EM waves from this background, did the device that measured it focus on one single point in the sky, kinda like hubble, or did it do a full panoramic spherical measurement of the whole sky around it?
  18. G

    Why does the cosmic microwave background make a noise

    For about the 7th time I've been told the story of how Penzias and Wilson discovered a noise the source of which they could not detect. It turned out to be the CMB. Well, why should the cmb make a noise? It's just photons in the microwave spectrum.
  19. R

    Effect of CMB (cosmic microwave background) on objects at relativistic speeds

    A hypothetical question relating to 1) moving a physical object at a significant % of c. 2) interaction with the cosmic microwave background radiation Is it the case that doppler effect and time dilation means that the CMB is going to be physically damaging to the object? Further...
  20. R

    How many degrees of view is cosmic microwave background?

    Is it a section of sky or a full 100% 360 degree panoramic view? I am referring to the cosmic microwave background picture that can be found here: http://en.wikipedia.org/wiki/Cosmic_microwave_background_radiation
  21. L

    How Does a Magnetron Heat Your Food in a Microwave Oven?

    Hey everyone. I was wondering how a magnetron in a microwave works. I understand it emits microwaves and a fan pushes them in random directions to heat up food. Thanks.
  22. H

    Why are microwave waves bad for you?

    Well, my parents always told me to stay out of the microwave when it's running... I understand that well, of course if I were to go inside my water-based blood will boil and cook me thoroughly... but why are the waves that harmful for me? I mean, microwave wave lengths are even longer (fixed-...
  23. C

    How to get the frequency of microwave oven

    I had a phone interview. People asked me how to get the frequency of microwave oven if I do not know. I said measure it. They said, you are not allowed to use any measurement tools. Then I said, read product spec. They said, no, you do not have the spec. Finally I said I do not know. I think...
  24. S

    Microwave interactions with motion sensors

    Hello everyone here at the physics forum. Forgive me if I am not posting this question in the correct forum. I am not a physicist, but I do know my way around a little bit. Now on to my question. I am a security consultant who conducts security audits and specializes more specifically in...
  25. T

    'Density' of 2.73K Cosmic Microwave Background

    Never seen this addressed anywhere, and maybe it doesn't matter; but, regarding the cosmic background radiation, in any given instant, how many 2.73K (on average) photons are in a given volume ? See, we would measure the same background temperature with our instruments over a range of...
  26. 4

    Cosmic Microwave Background Radiation, why from 380,000?

    Hello, I just have a quick question about CMB. Why is it from 380,000 years after big bang? Why not before? Will you please tell me if my explantion is right? Before 380,000 years, the universe was too dense to have any neutral atoms (free electrons and protons / plasma). And...
  27. D

    Confusion in thermal radiation concepts - infrared, microwave, etc.

    Microwaves heating is often referred to as dielectric heating, but I'm not sure why this seems so special to specify of all the different thermal radiation frequencies. Doesn't infrared heat the dielectric material as well in a similar process? Isn't radiation heat transfer common for a wide...
  28. P

    Cosmic Microwave Background Radiation and Photography

    Hi firstly I am a photographer not a physicist, When taking photos there is always 'noise' in the image, especially at higher ISO. I presumed this is the same noise that we would hear on a radio, or see on a tv? Would it be possible to create a room that blocked out the background radiation...
  29. L

    Thermal Equilibrium - in a microwave?

    hi, i don't quite know how to pose this question but i'll try my best. if you have an object and heat one end of it, energy will move from an area of high energy, to an area of low energy. By this method, heat transfer will stop when all regions of the object are at the same temperature...
  30. Orion1

    Hawking radiation and cosmic microwave background radiation

    In order for the black hole to evaporate it must have a temperature greater than that of the present-day black-body radiation of the Universe. Cosmic microwave background radiation temperature: T_u = 2.725 \; \text{K} Hawking radiation temperature: T_H = \frac{\hbar c^3}{8 \pi G M k_B}...
  31. D

    What basics do I need to learn before diving into Microwave Engineering?

    I have taken an interest in microwave engineering. I found a great book: Microwave Engineering by David M. Pozar which I am going to read but I can't understand the mathematics in it. I have read nothing about physics, and I am up to a college algebra level in mathematics. My plan is to...
  32. C

    Modified microwave transformer- rneed advice for rectifiers and wire ratings.

    Modified microwave transformer- need advice for rectifiers and wire ratings. Hello everyone. I've been doing a lot of research as to how to go about purifying copper. There are two approaches I'm considering. Electrolysis and Smelting. The electrolysis method requires I have a DC output of low...
  33. Z

    What is the process called when metal is heated in a microwave oven?

    Recently I came across with one video in youtube where the guy in the video did experiment on microwave oven. He heat up aluminium foil in the oven and after a few second, the foil started to produce spark. This is my first time watching something like that. I never knew that when metal is heat...
  34. M

    Stopping Microwave Antenna Effect

    Currently I am working on a project which involves putting a metal shaft into a microwave which extends out of the microwave as well. After grounding the shaft I ran a test to look at the effect of microwave leakage out of the microwave due to an antenna effect from the shaft. There was...
  35. O

    Why metals spark in microwave ovens?

    Hi, sorry for the childish title. But this problem is supposed to be solved quantitatively using Laplace's equation, so it's not so straightforward. Homework Statement (a) Explain why it is possible to keep a teaspoon in a cup of water heated in a microwave oven without spark formation, but...
  36. R

    Cosmic microwave background fits the blackbody radiation spectrum

    Homework Statement (a)The cosmic microwave background fits the blackbody radiation spectrum well with a temperature of 2.7 K and a corresponding peak wavelength at 1.9nm. Applying the relationship between the radiant emittance, i.e. the total power emitted per unit area, and the photon energy...
  37. L

    Rust from my microwave ruined a nice bowl of soup and also my day

    Hello all, Upon enjoying a nice hearty bowl of tomato soup, warmed conveniently in my microwave, I noticed a few mysterious specks of something dark floating around. On inspection it turned out that this was rust that had fallen from the roof of my microwave. Being a rather anxious person...
  38. F

    Layman's question on Cosmic Microwave Background

    Hi everyone, I'm a lowly computer programmer who has been interested in the CMB lately and recently became curious about one thing... As I understand it, the CMB is the left-over radiation from the Big Bang spread uniformly throughout the universe. Does this mean that this radiation is...
  39. S

    Infrared wave cooking vs microwave radiation

    I have learned that penetration ability increases with frequency. But why can microwave cook faster than infrared wave? Infrared gas a greater frequency so it should penetrate more and thus cook faster. So I'm not so clear about this. Thanks for the help
  40. W

    What is the role of resonance in the heating process of a microwave oven?

    hi , i have studied that thing to be heated in microwave oven have water contents -due to resonance of microwave and frequency of water molecules - water molecules start oscillating with larger amplitude thus thing gets heated. But how just ceramic without any water contents get heated and how...
  41. M

    What to study for high power microwave amplifiers?

    The kinds of devices I would like to be able to design are magnetrons, klystrons, gyrotrons, and maybe free electron lasers/masers. My goal is not to get a job in the field, but to just have enough knowledge to build some of these things myself. My first thought is plasma physics and EE, but I...
  42. G

    Explaining Electric Spark in Microwave with Foil-Wrapped Hamburger

    I put a hamburger(wrapped by foil) into microwave and pressed start. I noticed an electric spark near the foil's surface. How can we explain this incident? ps. sorry for my english
  43. G

    Radiation from microwave ovens

    Everybody seems to agree that when a microwave oven is opened, no radiation escapes. On a different thread, somebody said: "Microwave radiation is like light: it absorbs quickly into objects after the source is turned off." This analogy to light is often used to explain why no microwave...
  44. J

    Link between Universe mass density and Cosmic Microwave Background energy

    Present critical density of Universe rho_crit = 3 H^2 / 8 Pi G H = Hubble Constant = 2.2E-18 sec^-1 rho_crit = 8.6E-27 kg / m^3 What particle mass does this represent? The length scale associated with a quantum particle of mass m is the Compton wavelength lambda where lambda =...
  45. M

    Cooling in Cosmic Microwave Background

    I am a little confused about how exactly the CMB "works". At first hearing, it makes perfect sense that as time goes on and the universe expands radiation would decrese in frequence, but when I think about it a little more deeply I miss something. My thought is how exactly does the light...
  46. M

    How Do Chokes in Microwave Waveguides Function?

    Does anyone know how microwaves chokes work? Or have any references with simple explanations?
  47. I

    Radome pulsed microwave questions

    I would like to know about radome emissions. Radome in question is located on the west coast of Ireland. Its purpose is monitoring of international aircraft passing overhead. It has been described as Type 2. It emits at a power of 2.5 kW pulsed microwaves at a frequency of 1 GHz (according...
  48. H

    Using a Microwave Oven to Measure the Speed of Light

    For this lab, I'm supposed to use materials that heat up but doesn't allow heat to transfer. I've used raw spaghetti noodles already but I still a few more for more trials. So what materials are good for this lab? after heating up the material, I measure the distance between the "hot spots" so...
  49. S

    Rectenna Engineering? Microwave power? Is this possible?

    I want to power a device using microwaves. The microwave emitter will be about 1 meter away. I want the rectenna to be about a square meter in area and planar (not a dish). The rectenna will need to pass on about a kW of power. Is this possible? How do I design a rectenna like that? How much...
  50. S

    Can metal be placed in Microwave? Why or why not?

    I'm doing a physics project on microwave ovens. I've been researching online and some sites say that you can place metal in microwave ovens because nothing will happen, and some say that you can't because metal reflects microwaves. I'm curious as to what the correct answer is and why. Thanks!
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