Air core inductors – wound on a non-magnetic core or on no core at all – are the choice when a design must be free of core saturation, immune to high-frequency core losses, and perfectly linear at high current. They are used in RF circuits, high-power switching supplies, and measurement applications where magnetic cores would introduce loss or distortion. This guide explains how air core inductors work, their key specifications, and how to select one for your design.
What Is an Air Core Inductor?
An air core inductor is an inductor whose magnetic path is air (or a non-magnetic material such as plastic or ceramic). Because there is no ferromagnetic core, the inductor never saturates, has essentially no core loss, and its inductance is constant regardless of the current flowing through it. The winding can be a simple solenoid, a flat spiral, or a toroidal shape wound on a plastic or ceramic former. Air core inductors are used where frequencies are high, currents are large, or linearity and stability are critical.
How Air Core Inductors Work
A current through the winding creates a magnetic field in the surrounding air. Since air has a permeability of 1, there is no material to concentrate the flux – so air core inductors need more turns or larger dimensions to reach a given inductance than ferrite or powdered-iron inductors. The advantage is that the inductance is set purely by the geometry of the winding, so it is extremely stable over temperature and current, and the inductor cannot saturate no matter how much current flows. Energy storage and filtering behave exactly as for a cored inductor, but without nonlinearity and hysteresis losses.
Key Specifications of Air Core Inductors
Inductance: Determined by the number of turns, coil diameter, length, and spacing; typically from tens of nanohenries to hundreds of microhenries.
Current rating: Limited by winding wire size and self-heating rather than core saturation – there is no Isat to respect.
Q factor: The ratio of reactance to resistance at the operating frequency; high Q means low loss, critical in RF and resonant circuits.
Self-resonant frequency (SRF): The frequency where parasitic winding capacitance resonates with the inductance; operate well below SRF.
DC resistance (DCR): Copper loss of the winding; lower is better for power applications.
Temperature stability: Inductance drift over temperature is near zero because there is no magnetic material.
Form and shielding: Solenoid, spiral, or toroidal; self-shielding toroids reduce radiated fields versus open solenoids.
How to Choose an Air Core Inductor
Decide the required inductance and the operating frequency, then choose the geometry – solenoid for simple RF tanks, flat spiral for low-profile PCB designs, toroidal for self-shielding with a compact field. Size the wire for the RMS current and acceptable temperature rise, and check the Q factor and self-resonant frequency against your frequency band. Because there is no saturation limit, air core inductors shine in high-current and high-frequency applications, but the larger size needed for high inductance is the trade-off – evaluate whether a powdered-iron or ferrite design would be more compact for your requirement. Shaanxi SiRui Technology Co., Ltd manufactures air core inductors – solenoid, spiral, and toroidal, through-hole and SMD – under ISO 9001:2015 quality management with RoHS and REACH compliant materials.
Applications of Air Core Inductors
RF circuits and antennas, LC filters and impedance matching, high-power induction heating, high-frequency switching power supplies, snubber and damping circuits, current-sensing coils, tesla coils and experimental equipment, and instrumentation where linearity is essential.
FAQ
Why use an air core inductor instead of a ferrite one?
Air core inductors do not saturate, have no core loss, and are perfectly linear and temperature stable – ideal for high frequency, high current, and precision applications. The cost is lower inductance per size, needing more turns or space.
Can an air core inductor carry high current?
Yes – because there is no core to saturate, the only limit is wire heating. This makes them excellent for large DC and AC currents, provided the size is acceptable.
What is the self-resonant frequency?
The frequency at which the inductor’s parasitic winding capacitance resonates with its inductance, making it behave like a parallel resonant circuit. Above the SRF the inductor becomes capacitive, so designs operate well below it.
Do you supply custom air core inductors?
Yes. Shaanxi SiRui Technology Co., Ltd supplies custom air core inductors – geometry, inductance, wire, and termination – from samples to volume production with full test documentation.
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