# Inductance and frequency relationship

### Relationship between Frequency, Inductance and Resistance | All About Circuits We can rewrite the above equation for inductive reactance into a more familiar form Where: ƒ is the Frequency and L is the Inductance of the Coil and 2πƒ = ω . Generally speaking the higher the frequency, the greater the reactance if the inductance stays the same. What is the relation between a current and frequency in a inductive circuit? What is the difference between inductance and inductive reactance in a circuit?. An inductor, also called a coil, choke, or reactor, is a passive two-terminal electrical component .. For inductors with magnetic cores, the above equation is only valid for linear regions of the magnetic flux, at currents below Above the self-resonant frequency the capacitive reactance is the dominant part of the impedance.

In this field, they are more commonly referred to as reactors. Inductors have parasitic effects which cause them to depart from ideal behavior. They create and suffer from electromagnetic interference EMI. Their physical size prevents them from being integrated on semiconductor chips. So the use of inductors is declining in modern electronic devices, particularly compact portable devices. Real inductors are increasingly being replaced by active circuits such as the gyrator which can synthesize inductance using capacitors. A ferrite "bead" chokeconsisting of an encircling ferrite cylinder, suppresses electronic noise in a computer power cord. Large 50 Mvar three-phase iron-core loading inductor at an Austrian utility substation An inductor usually consists of a coil of conducting material, typically insulated copper wirewrapped around a core either of plastic to create an air-core inductor or of a ferromagnetic or ferrimagnetic material; the latter is called an "iron core" inductor.

Since power inductors require high induction levels, high permeability and low saturation points in the core materials are not ideal. Low frequency inductors are constructed like transformers, with cores of electrical steel laminated to prevent eddy currents. Inductors come in many shapes. Some inductors have an adjustable core, which enables changing of the inductance.

### Impedance vs frequency (video) | Khan Academy

Inductors used to block very high frequencies are sometimes made by stringing a ferrite bead on a wire. Small inductors can be etched directly onto a printed circuit board by laying out the trace in a spiral pattern. Some such planar inductors use a planar core. Small value inductors can also be built on integrated circuits using the same processes that are used to make transistors.

Aluminium interconnect is typically used, laid out in a spiral coil pattern. However, the small dimensions limit the inductance, and it is far more common to use a circuit called a gyrator that uses a capacitor and active components to behave similarly to an inductor.

Regardless of the design, because of the low inductances and low power dissipation on-die inductors allow, they're currently only commercially used for high frequency RF circuits. Shielded inductors[ edit ] Inductors used in power regulation systems, lighting, and other systems that require low-noise operating conditions, are often partially or fully shielded.

Air-core inductor[ edit ] An antenna tuning coil at an AM radio station. It illustrates high power high Q construction: The term air core coil describes an inductor that does not use a magnetic core made of a ferromagnetic material. The term refers to coils wound on plastic, ceramic, or other nonmagnetic forms, as well as those that have only air inside the windings. Air core coils have lower inductance than ferromagnetic core coils, but are often used at high frequencies because they are free from energy losses called core losses that occur in ferromagnetic cores, which increase with frequency.

A side effect that can occur in air core coils in which the winding is not rigidly supported on a form is 'microphony': Radio-frequency inductor[ edit ] Collection of RF inductors, showing techniques to reduce losses. The three top left and the ferrite loopstick or rod antenna,     bottom, have basket windings. At high frequenciesparticularly radio frequencies RFinductors have higher resistance and other losses.

In addition to causing power loss, in resonant circuits this can reduce the Q factor of the circuit, broadening the bandwidth. In RF inductors, which are mostly air core types, specialized construction techniques are used to minimize these losses.

The losses are due to these effects: 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, the interior portion of the wire may carry little current, effectively increasing its resistance. Proximity effect Another similar effect that also increases the resistance of the wire at high frequencies is proximity effect, which occurs in parallel wires that lie close to each other.

The individual magnetic field of adjacent turns induces eddy currents in the wire of the coil, which causes the current in the conductor to be concentrated in a thin strip on the side near the adjacent wire.

Like skin effect, this reduces the effective cross-sectional area of the wire conducting current, increasing its resistance. Dielectric losses The high frequency electric field near the conductors in a tank coil can cause the motion of polar molecules in nearby insulating materials, dissipating energy as heat. So coils used for tuned circuits are often not wound on coil forms but are suspended in air, supported by narrow plastic or ceramic strips. Parasitic capacitance The capacitance between individual wire turns of the coil, called parasitic capacitancedoes not cause energy losses but can change the behavior of the coil. Each turn of the coil is at a slightly different potential, so the electric field between neighboring turns stores charge on the wire, so the coil acts as if it has a capacitor in parallel with it.

At a high enough frequency this capacitance can resonate with the inductance of the coil forming a tuned circuitcausing the coil to become self-resonant. High Q tank coil in a shortwave transmitter left Spiderweb coil right Adjustable ferrite slug-tuned RF coil with basketweave winding and litz wire To reduce parasitic capacitance and proximity effect, high Q RF coils are constructed to avoid having many turns lying close together, parallel to one another.

## Inductance

This relationship is stated by the formula: As shown in the equation, any increase in frequency, or "f," will cause a corresponding increase of inductive reactance, or "XL. As you can see, the higher the frequency, the greater the inductive reactance; the lower the frequency, the less the inductive reactance for a given inductor.

This relationship is illustrated in figure Increasing values of XL are plotted in terms of increasing frequency. Starting at the lower left corner with zero frequency, the inductive reactance is zero. As the frequency is increased reading to the rightthe inductive reactance is shown to increase in direct proportion.

Effect of Frequency on Capacitive Reactance In an a. Because the capacitor "reacts" to a changing voltage, it is known as a reactive component. The opposition a capacitor presents to a.

### Inductance - Wikipedia

The opposition is caused by the capacitor "reacting" to the changing voltage of the a. The formula for capacitive reactance is: That is, the lower the frequency, the greater the capacitive reactance; the higher the frequency, the less the reactance for a given capacitor. As shown in figurethe effect of capacitance is opposite to that of inductance. Remember, capacitance causes the current to lead the voltage by 90 degrees, while inductance causes the current to lag the voltage by 90 degrees. Any change of frequency changes the reactance of the circuit components as already explained.