What is an inductor?

Electromagnetic induction is a phenomenon caused by a magnetic field and generates an electric current. An area delimited by a given conductor undergoes variation in the flow of magnetic induction. An electromotive force (emf) or voltage is created between its terminals. If its terminals are connected to an electrical device, it will generate current, called induced current. Inductance is the physical quantity related to inductors, represented by the letter L and measured in Henry (H). It is a parameter that relates the voltage induced in the magnetic field and the current responsible for the appearance of this field. The voltage at the inductor terminals is proportional to the current flowing through it.

The inductor, also called a solenoid or coil, is a passive electrical device, capable of storing energy created in a magnetic field formed by an alternating current (AC). This component is used in electrical, electronic, and digital circuits, to store energy through a magnetic field. Inductors are used to prevent variations in electrical current, to form a transformer and also in filters that exclude high-frequency signals, low pass filters.

Upon reading these definitions, we conclude that inductors and capacitors have in common the ability to store energy. Like capacitors, inductors are opposed to alternating current. Also in comparison to capacitors, we say that:

  1. The faster the current changes over a period of time, the more the voltage at the inductor terminals;
  2. Sudden variations in current are not accepted;


Inductors are generally constructed as a coil of conductive material, such as copper. A ferromagnetic core, which increases inductance by concentrating the lines and buds of the magnetic field that flow through the conductive turns.

With the application possibilities, inductors can be built for a specific situation, for example, in integrated circuits. In this case the conductive material is usually aluminum.

Small inductors designed to be used at high frequencies can be made with a wire passing through a ferrite cylinder.

Types of inductors

Inductors can differ in the construction characteristics of each model. See the main types of inductors below:

Types of inductors.

  • Air core:

In air core inductors, the ferromagnetic material is not used in the core, as previously mentioned. This has low losses, which results in a high frequency. Low inductance and used for high frequencies.

  • Ferromagnetic core:

In these models, the core is made of a ferromagnetic material, which results in a much higher inductance, however, it also causes losses. The greater inductance is due to the material, as it is able to concentrate the magnetic field better.

  • Laminated core:

Used in low-frequency inductors and transformers. The core is made of sheets of steel-silicon material, surrounded by insulating varnish. These compounds are not chosen for anything. The varnish prevents losses due to eddy current, and the silicon added to the steel causes the hysteresis in the material to be reduced.

  • Ferrite core:

These inductors are made of a type of ferromagnetic ceramic, which performs better at high frequencies, where they are most used. They have no eddy currents other than low hysteresis.

  • Toroidal coils:

The toroidal core is usually made of ferrite and is thread-shaped. Thanks to this format, a path through which the magnetic field circulates is created. This type of core is used in rod-shaped coils. In this case, the magnetic field suffers losses when circulating from one end to the other, through contact with air. That is why this nucleus was designed to make a path to this field, avoiding the number of losses.

The energy stored in the inductor (measured in joules) is equal to the amount of work required to establish the flow in the inductor, that is, the magnetic field.