RF InductorTechnical Terms


This is the ratio between the magnetic flux flowing through a circuit and the current which is producing the magnetic flux.
In the case where the magnetic flux which indicates the size of the electromagnetic induction is produced by the current of the circuit itself is called self-inductance, and when produced by the current of other circuits is called mutual inductance, and inductance is used in meaning of self-inductance in many cases.


The Q (Quality factor) of the coil indicates the characteristics of the coil.
The higher Q indicates the lower amount of resistance, if the frequency and inductance are fixed.
This is expressed by the following formula.

Choke coil

This is an electronic component to suppress the flowing through of high frequency currents.

DC resistance

This is the resistance value when measuring with a DC signal. When the resistance value is large, the power loss becomes larger.

  • * It is more effective to have a lower "DC resistance" in each in each inductor for resonance, impedance matching and chokes.

Self resonance frequency

This is the frequency which resonates between the distributed capacity of the inductor and the inductance.
It does not function as an inductor beyond the resonance frequency.

  • * It is more effective to have a "self-resonant frequency" in each inductor for resonance, impedance matching and chokes larger than the frequency being used.

Direct current superposed characteristics

This is the fluctuation of the characteristics value when a DC current is applied.

Allowable current/Rated Current

This is the maximum value of the DC current which can flow through the inductor. When the allowable current is exceeded, the heating value becomes larger and the quality cannot be guaranteed.

  • * The "allowable current" in the inductor for chokes, must be larger than the maximum current of the circuit to be used.

Operating temperature range

This is the allowable range of ambient temperature when using an inductor. Self-heating is not included in the operating temperature range.

  • * The "operating temperature range" in each inductor for resonance, impedance matching and chokes must be compatible to the operating temperature range of the set.


This is the general term of ceramics which use iron oxide as the main component.

Magnetic shield

The magnetic shield refers to the insulation against electrostatic, magnetic or electromagnetic waves from other electronic equipment, by covering the electronic equipment or a portion of the equipment with a conductor, conductive material or magnetic material.

Magnetic saturation

Magnetic flux occurs when a magnetic field is applied to a magnetic material, such as ferrite.
The inductance value of the inductor is determined according to the occurrence level of this magnetic flux.
When the magnetic field becomes larger, the level of increase in the magnetic flux to the magnetic field is decreased, and even though the magnetic field is increased, the magnetic flux will not increase. This is a phenomenon called the magnetic saturation of the magnetic material.
When considering from the level of the inductor component, when the current flowing to the inductor is increased, the magnetic field will also increase which generates the magnetic saturation of the magnetic material. As a result, the inductance value drops.
The magnetic saturation characteristics of the inductor are influenced by the type and structure of the magnetic material used by the inductor, and a large current flows through the inductor used in power supply systems, therefore, it is important to confirm if magnetic saturation tends to be generated. In order to confirm the level of this tendency, the DC superimposing characteristics of the inductor are used as a reference.

Magnetic coupling

Magnetic coupling refers to the interactive status of the effect in the magnetic flux created in other circuits.

Leakage flux

The magnetic flux generated in the inductor does not only remain within the magnetic material, such as the ferrite, and leaks into a portion of the external space. This leaked magnetic flux is called leakage flux. It is necessary to pay attention as the magnetic flux distribution of the inductor may change when magnetic materials, such as structural components approach the portion with the leakage flux, which changes the performance. Also, when interference occurs with the leakage flux of other components, a jump transfer may occur by the magnetic coupling of the signal. In order to reduce leakage flux, there are inductors that are protected by a magnetic shield structure.