Pengukuran Pada Frekuensi Tinggi

• Elemen rangkaian sangat dipengaruhi :– Induktansi – Kapasitansi – Skin efekBertambahnya frekuensi, nilai / harga berubah

-- An inductor (or reactor) is a passive (f) electrical component that can store energy in a magnetic field created by the electric current passing through it.-- An inductor's ability to store magnetic energy is measured by its inductance, in units of henries.

An inductor is usually constructed as a coil of conducting material, typically copper wire, wrapped around a core either of air or of ferromagnetic and ferrimagnetic(f) material. Core materials with a higher permeability than air increase the magnetic field and confine it closely to the inductor, thereby increasing the inductance.

The 'curves' here are all straight lines and have magnetic field strength as the horizontal axis and the magnetic flux density as the vertical axis.

Diamagnetic materials have a weak, negative susceptibility to magnetic fields, copper, silver, and gold.Paramagnetic materials have a small, positive susceptibility to magnetic fields. These materials are slightly attracted by a magnetic field and the material does not retain the magnetic properties when the external field is removed. magnesium, molybdenum, lithium, and tantalum

Permeability as representing 'conductivity for magnetic flux'; just as those materials with high electrical conductivity let electric current through easily so materials with high permeabilities allow magnetic flux through more easily than others. Materials with high permeabilities include iron and the other ferromagnetic materials. Most plastics, wood, non ferrous metals, air and other fluids have permeabilities very much lower: μ0.

• Just as electrical conductivity is defined as the ratio of the current density to the electric field strength, so the magnetic permeability, μ, of a particular material is defined as the ratio of flux density to magnetic field strength -

• μ = B / H

Stored energy

• The energy (measured in joules, in SI) stored by an inductor is equal to the amount of work required to establish the current through the inductor, and therefore the magnetic field. This is given by:

• where L is inductance and I is the current through the inductor.

• This relationship is only valid for linear (non-saturated) regions of the magnetic flux linkage and current relationship.

Skin effect: • The resistance of a wire to high frequency current is

higher than its resistance to direct current because of skin effect.

• Radio frequency alternating current does not penetrate far into the body of a conductor but travels along its surface. Therefore, in a solid wire, most of the cross sectional area of the wire is not used to conduct the current, which is in a narrow annulus on the surface. This effect increases the resistance of the wire in the coil, which may already have a relatively high resistance due to its length and small diameter.

Because of the influence of the skin effect upon inductance the resistance is frequency-dependent:

Skin depth

• Skin effect• In any case increased frequency of the same value of

field will always increase eddy currents, even with non-uniform field penetration.

• The penetration depth can be calculated from the following equation:

• [7] where: δ - penetration depth (m),[8] f - frequency (Hz), μ - magnetic permeability, σ - electrical conductivity (S/m)

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