Waveguide

Waveguide (English: wave guide), called an inhomogeneous medium as a wave bundles by its physical nature, that it is out there.

• 2.1 optics
• 2.2 sound 2.2.1 waveguide effect in the ocean
• 2.2.2 corded phone
• 2.2.3 stethoscope

Waveguide for electromagnetic waves

Shape of the Cable

Symmetrical in form of a ribbon cable consisting of two wires or rigid wires, partly in the same screen, or asymmetrically in the form of a coaxial cable. These cables are for transmission of high frequencies in the VHF ( Very High Frequency ) - suitable and UHF ( decimeter ) range. Conductor cross-section and insulating affect the attenuation per length. The thinner the wire is, the higher the attenuation in the rule. Kinks and bruises, which change the cable geometry, cause reflections or radiation.

Application: antenna cable for radio transmitters and receivers, transmission of high- frequency powers up to the FM band; customary to 1 GHz, between 1-10 GHz depending on the application, then about waveguide.

Single-wire waveguide

Even on a single wire which an electromagnetic wave can propagate. In an area of approximately 1/2 wavelength at the line but must not contain any damping or conductive materials. The line should have no creases. Therefore, these very low-loss mode of transmission is limited to a few applications: Previously supplied to remote places with such, leading through the whole settlement line and enabled at low transmission power television reception - the participants had to bring in the vicinity of this line only their antennas. For this purpose, was ideally a powerful receiving system on a suitable elevated location. From this then the actual reception area was supplied with a Goubau line over several kilometers. The power supply and also the reflection-free completion of such a line is performed with a coaxial Exponentialtrichter, but which can also consist of several bars in skeleton construction.

Tube shape

Waveguide metal pipes are without inner conductor with a rectangular or circular cross section. They are used for high frequencies and power. The inner cross section has to have certain minimum dimensions, depending on the largest wavelength to be transmitted. Metallic objects therein cause a mismatch, thereby even a damage to the inner walls can be caused by arcing. Metallic waveguide can be fed with a coaxial cable, the inner conductor extends into the waveguide. The shafts are hollow metal body "trapped" and may spread along the conductor from the coupling to the exit loss and without influence from or to the outside. However, there are dielectric " waveguide " in which the shaft is guided as in a fiber optic cable.

Metallic hollow conductors are used in the SHF frequency range for high performance. Therefore, a magnetron is usually responsible for the supply, which is often even already has a waveguide flange.

The width of a rectangular waveguide must be greater than λ / 2, so that it can propagate electromagnetic waves over long distances. With a circular cross-section roughly is that the amount must be greater than the wavelength λ. This also limits the usability of coaxial cables at very high frequencies, because can then unwanted waveguide modes occur. Most common application: radar, microwave oven.

Stripline

Waveguides can also planar ( flat ) as a strip line (english stripline, microstrip line ) to be executed, such as microstrip or Koplanarleiter. This thin metal films on non-conducting (dielectric ) materials are applied. Such lines can be found for example on printed circuit boards for high frequencies (eg in satellite receivers ( LNBs ) ) and are used in strip -line antennas (also known as panel antenna or flat panel antenna called ) and some helical antennas.

More waveguide

Optics

Fiber Optic (FO ) or fiber-optic cables are used for data transmission, as a fiber laser for flexible propagation of laser radiation or illumination or decorative purposes. There are also on the integrated optic waveguide to the substrate materials, which are produced by doping, for example.

Sound

Waveguide effect in the ocean

In the ocean, does that sound speed minimum, which occurs in the subpolar regions of about 200 m, in subtropical in depth about 1200 m, as a waveguide. This is for example used for the acoustic data transmission (See SOFAR channel). In physical oceanography to use this fact to measure temperature profiles or currents ( see Acoustic tomography).

Also in the ocean, the equator is a waveguide that propagate along which to equatorial Kelvin waves. This example plays an important role in the El Niño phenomenon.

Corded phone

The corded phone uses longitudinal body sound waves.

Stethoscope

When stethoscope or in pipes with funnels on playgrounds sound waves are guided in pipes and hoses.

Waveguide effect in the atmosphere

In the atmosphere over distances of ultra-short waves are known to be caused by inversion layers. The radio waves propagate in these as in a waveguide.

In a broader sense can also be the way Herreflexion of medium and short waves between the earth's surface and the ionosphere to be construed as a waveguide. Such radio waves reach in this manner around the earth. In the region between Earth's surface and ionospheric D- layer ( less than 90 km altitude), low frequency waves ( less than 30 kHz) as performed in a waveguide ( ionospheric wave guide ).