In alternating electrical circuits, the voltage changes polarity up to 60 times per second with each terminal changing from positive to negative and back again. Normally, such rapid changes in voltage would produce power fluctuations. An inductor is a component that produces an electromagnetic field in response to electrical current flowing through a coiled wire. The strength of an inductor depends on the current being applied, the core of the inductor, and the number of turns in the wire coil forming the inductor. An air core inductor is a wire coil with no solid core inside the coil.
Air has a low electrical conductivity, and so produces the weakest of all magnetic fields in opposition to current flow. The formula for inductance of a single layer air core inductor can be expressed as d2n2/18d+40z. D represents the diameter of the coil, n represents the number of turns in the coil, and z represents the length of the inductor. All units are expressed in inches. The inductance is measured in microhenries, or μH.
One of the biggest advantages of an air core inductor is the minimal signal loss that occurs at higher magnetic field strengths. With ferromagnetic cores such as iron, the core can become magnetically saturated when the magnetic field is too strong. This leads to a loss in inductance, but an air core inductor has no such problem. An air core inductor can carry electromagnetic frequencies up to 1 GHz, but ferromagnetic core inductors tend to experience loss when the frequency exceeds 100 MHz.
There are also disadvantages inherent to air core inductors: the main disadvantage is the number of turns in a coil necessary to achieve the same inductance that would occur in a solid-core inductor. The low electrical conductivity of air translates to low magnetic permeability and therefore lower inductance. They also pick up and transfer electromagnetic interference more easily because there are no closed magnetic pathways in air core inductors.
Radio transmitters make the most use of air core inductors to minimize the harmonic vibrations resulting from electromagnetic waves traveling across them. Hi-fi stereo speakers also include them to ensure minimal sound distortion occurs. Smaller air-core inductors are seen on printed circuit boards for electronic components because there are generally low voltages and low currents traveling along those pathways.