Various forms of inductors are available depending on sizes and ratings. Their sizes differ due to the material used in their manufacturing. There are several forms of inductors based on the key core material used. The core material of the inductor plays a major role in the efficiency of the inductor. Based on cores, the types of inductor include:

Air-core Inductor

A core is lacking in this form of inductors. These inductors give strong reluctance path and hence less inductance to the magnetic flux. These types of inductors have larger coils for producing higher flux densities. By comparing these inductors with other types with core, it must contain much more number of turns. Ceramic inductors are typically labelled as air-core inductors. 

Applications:  

• Used in high-frequency applications such as in TV and radio receivers.
• Used in filter circuits and snubbers circuits.
• It is also used to ensure a lower peak inductance and for constructing RF tuning coils.

Iron-core inductor

As the name suggests, the core in this form of an inductor is constructed from iron. These core inductors have high inductance property owing to their greater magnetic permeability. These are high-power inducers but are restricted in higher frequency capacity because of the loss in hysteresis and eddy current. However, their high-frequency capability is minimal. 

Applications: 

• Iron core inductors are usually used in devices involving higher power levels yet low-frequency power rates such as audio equipment, power conditioning and inverter systems.
• Used in the filter circuit for smoothing out the ripple voltage.
• It is often used as a filter choke in fluorescent tube display, industrial power supply and inverter systems. 
• Can be used at low power frequency (50Hz) for building surge voltage and at an audio frequency (20Hz – 20 kHz) choke for tone control.

Toroidal core inductors

In these types of core inductors, the leakage of flux is very low, and the coil is wounded on a toroid circular former. These types of core inductor contain more inductance per turn as compared to the solenoid with the core of the same material and size. They can hold a larger amount of current and sometime ferrite core is also used to decrease the loss. 

Applications:

• Toroid core inductors have a wide range of uses in telecommunication techniques, industrial controls, electronics clutches and brakes and also in aerospace and nuclear fields.
• They have much application in medical devices and can also be used as an output filter (SMPS). 
• Other applications include noise filtering for switching regulators, power supplies, power amplifiers and triac control circuits.

Ferrite Core Inductors

Ferrite is one of the most commonly used cores for a number of inductor forms. Ferrite is a metal oxide ceramic formed on a mixture of Ferric Oxide Fe2O3 and either manganese-zinc or nickel-zinc oxides which are extruded or forced into the required shape. These are the various forms of inductors that give benefits of reduced costs and small core losses at high frequencies. 

Applications:

• It is used in switching circuit and for radio interference suppression.
• It can be used at low and large frequencies.
• Can be used as filter chokes and also Pi filters.