Multitran.com: Free online dictionary in English, German, French, Spanish. 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). The experiments P126.96.36.199 and P188.8.131.52 show that many of the properties of microwaves are comparable to those of visible light. The diffraction of microwaves at an edge, a single slit, a double slit and an obstacle are investigated. Additionally, the refraction of microwaves is demonstrated and the validity of Snell s law of refraction is confirmed.
- Microwave Diffraction Therapy
- Microwave Diffraction Method
- Microwave Diffraction Sensor
- Microwave Diffraction Effect
- Microwave Diffraction
Radio waves and microwaves are very important to us for communication.
(And for heating up left over pizza.)
When microwaves are transmitted from a dish the wavelength must be small compared to the dish diameter to reduce diffraction – the spreading out of the beam. The dish is made of metal because metal reflects microwaves well. Mobile phones use microwave signals. Experimental results of the near zone diffraction field of circular and elliptical apertures and of the infinite slit are presented. The investigations were made on apertures which were illuminated by a plane polarized electromagnetic wave and whose characteristic dimensions were varied over a considerable range with respect to the wavelength of the incident radiation.
They are both on the long wavelength end of the Electromagnetic Spectrum:
- Radio waves have wavelengths of 1 m up.
The frequency at 1 m is 300 MHz.
- Microwaves have wavelengths of 1 mm (millimeter) to 1 m.
The frequency at 1 mm is 300 GHz.
(Note: some people say microwaves are just a type of radio wave, so for them radio waves have wavelengths of 1 mm up.)
We can create radio and microwaves, and they are also produced by the Sun and many other natural sources.
We use radio and microwaves to communicate without wires. This is great, as we can move around and live our lives while still being in touch.
Transmitting and Receiving
Transmit ... and Receive on a device
Radio waves are produced by a vibrating electric current in an antenna ...
... the electromagnetic waves then spread out ...
... and are then received by a small antenna inside your device, that detects the very small amount of current created by the radio waves.
Your device can then decode the signal, and you can watch or listen to what was sent out.
Radio waves are good at broadcasting (sending out to lots of receivers) and that is how we get to listen to radio and TV broadcasts.
TVs (and radios!) can receive broadcast signals using antennas.
Radio waves are good at bending around buildings and hills by diffraction (see below also).
Microwave ovens use electromagnetic waves at a frequency of 2.45 GHz (wavelength about 12 cm) that make water molecules vibrate fast and heat up.
Microwaves are created by the Magnetron,
are sent in different directions by the stirrer,
bounce off metal surfaces,
and are absorbed by the water in food.
Microwaves can travel through glass and plastic and penetrate about a centimeter into food (depending on the food), but bounce off metal surfaces.
There must always be something to absorb the microwaves, such as food or a glass of water.
So basically you are cooking by heating up the water in the first cm or so of the food. That is why many recipes say to leave the food stand for a while (to let the heat spread evenly).
Microwaves can also heat us up and can damage our cells. Keep the door closed when on, and never use a damaged microwave oven.
Wave diffraction into a bay
Diffraction is very important for radio communications!
Diffraction is when waves bend around the corner of an obstacle.
Medium gap: some diffraction, but mostly straight
Microwave Diffraction Therapy
Gap of wavelength size: most diffraction
The maximum effect is when the gap and wavelength are about the same size.
Radio waves with wavelengths of kilometers diffract
over hills and through valleys so you can easily get reception.
But microwaves with wavelength of centimeters tend to go straight.
So radio waves are good at 'broadcasting' to many people, but microwaves are good at point-to-point communication.
And for microwaves the transmitter and receiver must be 'line of sight' (they can see each other).
A typical microwave antenna is a parabolic dish of about 0.3 m to 3 m in diameter, like on this building:
The ionosphere is an electrically charged layer of the upper atmosphere that is between 75 and 1000 km above the ground.
It is very important for radio and microwave communication!
Low to medium frequency radio waves get reflected off the ionosphere, so it is possible to receive radio signals from far away that have bounced their way to us.
(Not to scale!)
But microwaves can cut right through the ionosphere so they are good for communicating with satellites.
Signal and Noise
Information can be in analog or digital form.
Information can be put onto a wave by altering its height or wavelength a little:
A wave has a signal of this picture put into it.
As the wave travels it gets noise (random changes) added by other electrical activity around it:
Microwave Diffraction Method
When we try to recreate the image the result is not perfect!
But with digital we expect only certain values, such as 0s or 1s. So noise (if not too big) can be overcome.
Even with noise we still know every 0 and 1 and get a perfect image.
neutron [wave] diffraction - дифракция нейтронов [волны]
Новый большой англо-русский словарь. 2001.
Смотреть что такое 'diffraction' в других словарях:
Microwave Diffraction Sensor
Diffraction — La diffraction est le comportement des ondes lorsqu elles rencontrent un obstacle qui ne leur est pas complètement transparent ; le phénomène peut être interprété par la diffusion d une onde par les points de l objet. La diffraction se… … Wikipédia en Français
diffraction — [ difraksjɔ̃ ] n. f. • 1666; du lat. diffractus, p. p. de diffringere « mettre en morceaux » ♦ Phys. Phénomène optique de déviation des rayons lumineux, au voisinage de corps opaques. ⇒ déflexion, dispersion. Par ext. Phénomène analogue pour d… … Encyclopédie Universelle
Diffraction — Dif*frac tion, n. [Cf. F. diffraction.] (Opt.) The deflection and decomposition of light in passing by the edges of opaque bodies or through narrow slits, causing the appearance of parallel bands or fringes of prismatic colors, as by the action… … The Collaborative International Dictionary of English
diffraction — 1670s, from Fr. diffraction (17c.) or directly from Mod.L. diffractionem (nom. diffractio), noun of action from pp. stem of L. diffringere break in pieces, from dis apart (see DIS (Cf. dis )) + frangere to break (see FRACTION (Cf. fraction)) … Etymology dictionary
Diffraction — des Lichts, s. Beugung des Lichts … Herders Conversations-Lexikon
diffraction — DIFFRACTION. sub. fém. Terme d Optique. Inflexion ou détour que subissent les rayons de lumière en rasant la surface d un corps … Dictionnaire de l'Académie Française 1798
diffraction — ► NOUN Physics ▪ the process by which a beam of light or other system of waves is spread out as a result of passing through a narrow aperture or across an edge. DERIVATIVES diffract verb diffractive adjective. ORIGIN Latin, from diffringere break … English terms dictionary
diffraction — [di frak′shən] n. [ML diffractio < L diffractus: see DIFFRACT] 1. the breaking up of a ray of light into dark and light bands or into the colors of the spectrum, caused by the interference of one part of a beam with another, as when the ray is … English World dictionary
Diffraction — Computer generated intensity pattern formed on a screen by diffraction from a square aperture … Wikipedia
Diffraction X — Diffractométrie de rayons X La diffractométrie de rayons X (DRX, on utilise aussi souvent l abréviation anglaise XRD pour X ray diffraction) est une technique d analyse basée sur la diffraction des rayons X sur la matière. La diffraction n ayant… … Wikipédia en Français
diffraction — /di frak sheuhn/, n. Physics. 1. the phenomenon exhibited by wave fronts that, passing the edge of an opaque body, are modulated, thereby causing a redistribution of energy within the front: it is detectable in light waves by the presence of a… … Universalium
- Diffraction and Spectroscopic Methods in Electrochemistry, Jacek Lipkowski. This ninth volume in the series concentrates on in situ spectroscopic methods and combines a balanced mixture of theory and applications, making it highly readable for chemists and… ПодробнееКупить за 21080.71 рубэлектронная книга
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- Modern Diffraction Methods, U. Welzel. The role of diffraction methods for the solid-state sciences has been pivotal to determining the (micro)structure of a material. Particularly, the expanding activities in materials science… ПодробнееКупить за 15598.63 рубэлектронная книга