What are Air Core Inductors?

What is an Air Core Inductor? What are its properties and applications?

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- everything RF

Aug 11, 2023

An Air Core Inductor is a type of inductor that uses the self-inductance of a wire coil to store energy in a magnetic field instead of using a ferromagnetic core material like iron or ferrite. As the name suggests the core in this inductor can be air. These inductors are used in applications where low inductance & high frequency are required.

Structure of an Air Core Inductor

An air core inductor consists of a coil wound around a non-magnetic core - usually air but can also be plastic, ceramic, or another non-conductive material. The inductance of an air core inductor is dependent on the number of turns in the coil, the wire's diameter, and the coil's physical dimensions. The coils are generally produced with copper material insulated wire with stripped and non-stripped ends and tinned or bare ends. The coil leg orientation includes radial, opposed, axial and other special orientations.

When current flows through the coil, a magnetic field is generated around it, resulting in self-inductance. Unlike inductive components with ferromagnetic cores, air core inductors do not experience magnetic saturation, making them suitable for applications that involve high-frequency signals or where low losses are crucial.

An air core ensures a lower peak inductance, however, it also decreases the energy losses associated by means of ferrite inductors. The lack of core losses permits air core inductors to function at higher frequencies. These types of inductors are utilized whenever the amount of inductance required is less and they do not have a core loss because there is no core. However, the number of turns in this inductor is more as compared to other inductors which have a magnetic core.

Generally, ceramic inductors are frequently called air-core inductors. These inductors provide efficient solutions especially for switch mode magnetic requirements when focusing on high frequency, high linearity & reduced core loss.

The inductance (L) of an air core inductor is directly proportional to the square of the number of turns (N) in the coil, the cross-sectional area (A) of the coil, and inversely proportional to the length (l) of the coil:

L ∝ (N^2 x A) / l

Advantages of Air Core Inductors:

High-Quality Factor (Q): Air core inductors typically exhibit low resistance, which leads to high Q factors. The Q factor represents the efficiency of an inductor, and higher Q values mean less energy loss, making air core inductors suitable for applications requiring high performance and minimal losses.

No Magnetic Saturation: Since air does not saturate magnetically, air core inductors can handle high currents and intense magnetic fields without losing inductance. This characteristic makes them ideal for use in high-power applications.

Low Interference: Unlike inductors with magnetic cores, air core inductors do not produce significant electromagnetic interference (EMI) or electromagnetic radiation, making them preferable for sensitive electronic circuits and RF applications.

High Self-Resonant Frequency: Air core inductors can achieve higher self-resonant frequencies compared to inductors with magnetic cores. This property is beneficial in radio frequency and high-frequency applications.

Disadvantages of air core inductors:

  • These Inductors are large in size.

  • High inductance values of these inductors are not possible.

  • The number of turns required within a coil is more to attain the same level of inductance as a solid-core inductor.

  • The lower electrical conductivity of the air core converts to low magnetic permeability & then lower inductance.

Applications of Air Core Inductors

RF Circuits: Air core inductors find extensive use in RF circuits, such as radio transmitters and receivers, filters, impedance-matching networks, and oscillators. Their high self-resonant frequency and low interference make them ideal for such applications.

Wireless Power Transfer (WPT): Air core inductors play a vital role in wireless power transfer systems, where they are used in both the transmitter and receiver coils. The absence of a magnetic core prevents losses associated with hysteresis and eddy currents, improving the efficiency of power transfer.

High-Frequency Transformers: Air core inductors are employed in high-frequency transformers, which are crucial components in power inverters, switch-mode power supplies, and renewable energy systems.

RFID Systems: Radio frequency identification (RFID) systems rely on air core inductors in their antennas and readers to facilitate wireless communication and identification in various applications like access control, inventory management, and contactless payments.

Inductive Heating: In certain industrial applications, air core inductors are used for inductive heating processes, where alternating currents generate heat in conductive materials without direct contact.

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