Electrical conductor

A conductor is a material in physics, the different types of energy or particles can be transported between different locations. There are conductors of electricity, heat, light and magnetism. A non-conductive material is called an insulator.

• 3.1 RF and microwave waveguide
• 3.2 Waveguide
• 3.3 light

Electrical conductor

An electrical conductor is a medium having free charge carriers and thus can be used for the transport of charged particles; this transport is called electric current. The Equivalent but archaic term for an electrical conductor, konduktor, in the narrower sense, one made ​​of metal charge collector in the form of a can or ball in electrostatic devices.

For practical embodiment of metallic interconnect conductors refer to electrical conduction.

Head of 1st class

Metals, graphite and some other chemical compounds, such as niobium ( II) oxide are the so-called first -class conductors. The conductivity of metals (for example, measured as specific resistance) is not based on the number of electrons in its outer shell ( valence ), it is defined primarily by the lattice structure. Metals form a crystal lattice structure in which the electrons are only weakly bonded and can be considered as electron gas; That is, the electrons are more or less freely movable.

The best electrical conductor is silver; as a cheaper alternative but is used in a rule which is also very good conductive copper. If one wants to keep the head small mass about overhead lines, aluminum is used.

The conductivity also depends on the material temperature. For metals, the resistivity slightly increases with increase in temperature (see # Electrical conductivity temperature dependence ); coal and semi-conductors, the resistance may also decrease with increase in temperature.

For some ( partly insulating ) materials can jump at very low temperatures, the resistivity to zero. This condition is called superconductivity.

Head first class experience through the electrical line no material change.

• Note: a conductor 1st class or 2nd class should not be confused with the conductor grades 1 to 6, which are standardized in electrical engineering.

Quantum mechanical view

When metals quantum mechanically considered ( Bloch wave function, Fermi -Dirac statistics ) shows that the electrons can not assume any energy, but can only exist in certain energy bands - the shape of these bands will depend on the crystal lattice of the material.

The Fermi energy ( the energy of the most energetic electron at the temperature of 0 Kelvin ) makes a distinction:

• Insulator when the energy gap between the valence band and the conduction band is large compared to the thermal energy;
• Otherwise it is a semiconductor.

Semiconductors are a special form: In their pure state crystal lattice can build stable electron bonds. The electrons can ascend to a conduction band at higher temperature; therefore derived semiconductors compared to metals at higher temperatures better.

An interesting effect in semiconductors is the holes line ( also voids line ): The Ascended into the conduction band electron leaves a hole in the binding, which behaves similarly to an electron with a positive charge and also contributes to the conductivity.

In semiconductors even foreign atoms can be introduced - this is called doping. The impurity atoms serve either to introduce additional electrons - this is called n-type doping (eg nitrogen in silicon crystal) - or contain fewer electrons to introduce holes, which is called p- doping ( eg, boron in silicon crystal ).

• Drude theory
• Sommerfeld theory
• Bloch theory

Superconductivity

Superconductivity can occur at low temperatures. The resistance of the superconducting material below a limit temperature jumps to zero, which can be explained by quantum mechanics. This limiting temperature is dependent on the alloy: While the first investigated superconducting temperatures near absolute zero required today, so-called high temperature superconductors are known in which this effect is just as occurs at higher temperatures. It however still involves very low temperatures in the popular sense ( below -130 ° C).

• For highly sensitive sensors for electromagnetic fields
• To reduce the resistive losses in electrical systems
• Lossless transport of electricity

Head of 2nd class

So-called ion conductors are conductors 2nd class. The conductivity is caused by dissociation ( splitting ) of the ( ionic ) crystal lattice structure with the formation of electrically charged mobile ions in the so-called electrolyte. This can be done by melting by dissolving in a polar solvent (such as water ) or not.

A classic example are salt solutions. Soluble salts are solvated in the dissolution process (ambient as the solvent ), positive and negative ions decomposed; this effect the conductivity. The positive ions move it toward the negative cathode and are called cations; the negative anions migrate toward the positive anode. At the electrodes the respective ions are discharged by electron transfer. Can be used ( sodium chloride ) or for the electrolysis of water to hydrogen and oxygen, for example, for the electrolytic deposition of metal, release of chlorine.

The charge conduction in the conductor class 2 of this material is changed by chemical reactions.

At higher temperatures ( above about 600 ° C) glass (also ) be electrically conductive as the ion conductor. This is used, for example, in respective furnaces in that after conventional heating, the glass melt then directly through electrodes are immersed, - heated - that is, by the current flow.

Heat conductor

The heat pipe is one of three mechanisms, in which thermal energy may be transported. ( The two other options are radiation and convection ( flow ). )

In solids, the heat transport through the spread of lattice vibrations. A good spread option for this stimulating vibrations provide conduction electrons, therefore, are electrical conductors, especially metals, also good conductors of heat ( Wiedemann - Franz law ). The treatment of this phenomenon is usually conveniently in the model of a free or quasi-free electron gas (ie electrons, which can move to a good approximation almost free in the solid state, comparable to the mobility of a gas ( Drude theory, Sommerfeld theory ) ). Since, in this line, the electrons are moved and a current flow is produced ( the Seebeck effect).

In electrical insulators, the heat is mainly transferred by lattice vibrations ( phonons). Therefore, the thermal conductivity depends on the speed of sound.

In semiconductors, both effects occur.

Good heat conductors: metals. Poor conductors of heat: wood, plastics, salts.

Contrary to popular assumption, water is a poor conductor of heat. Significant contribution to the heat transport supplies here, unlike solids, convection.

Other models: Einstein model of the solid

An electromagnetic waveguide

High frequency and microwave conductor

A well-known waveguide for high-frequency electromagnetic waves is the coaxial cable.

The waveguide for microwave exploits that the waves induce currents. They consist generally of a metallic tube ( round or rectangular), whose diameter is slightly greater than half the wavelength of the wave to be transported.

Waveguide

→ Main article: waveguide

A waveguide is a waveguide for electromagnetic waves, mainly in the centimeter wave region ( 3-30 GHz). As a waveguide is called round or rectangular metal pipes in which they can transfer such high frequencies in contrast to very low loss cables.

Light

The optical waveguide is available in two designs:

• One-dimensional: One example is serving as an optical waveguide fiber. With conventional glass fibers, the light guide is effected by means of total reflection. In some modern versions, the light is guided with the help of photonic crystals.
• Two-dimensional: An example is a planar waveguide. They are used, for example, in semiconductor lasers.

Magnetic Head

The magnetic conductivity, and magnetic permeability ( μ ) referred to, is a measure of the permeability of magnetic fields. It is closely related to the magnetic susceptibility. Permeability is the ratio of the magnetic flux density B to the magnetic field strength H.

The magnetic constant μ 0 is a physical constant (exactly 4π · 10-7 · Vs / Am) for the magnetic permeability of the vacuum. The relative permeability μ r, formerly referred to as relative permeability, μ is the ratio of the magnetic field constant μ 0

For the vacuum, thus resulting in a relative permeability of 1 The dimensionless quantity μ r is related to the magnetic susceptibility χ together on the formula.

The complete impermeability of superconductors for magnetic fields is called Meissner effect.