Alternate current will generate a magnetic field, and the change of the magnetic field will induce current; the ratio of their linear relation is called inductance.
But the inductor, through the mutual transformation of current and magnetic field, possesses the function of storing and releasing energy. The perfect inductor will not produce or consume energy.

Therefore, the inductor acts as a component to stabilize current, and matches phases; of course, there are various applications of the inductor such as filtering waves, storing energy, releasing energy, resonance, bypass, etc.

The aforementioned inductors are all perfect inductors, but it is impossible to produce a perfect inductor in the real world. Properties of passive components will be shown, regardless of resistors, capacitors, or inductors with better contribution in a certain frequency range of the equivalent circuit.
Since electronic products tend to be miniaturized, portable, and with dense component layout, surface mount components can be developed rapidly.

The elimination of electromagnetic interference for electronic products becomes the basic requirement of electronic products under the consideration of compatible electromagnetism. Every country establishes many laws for the restriction; only those complying with the regulations can be sold, which further increases the demand and application of the inductor.