Practical method for air-core inductor design

Due to their characteristics of excellent linearity, high quality factor, absence of saturation and the losses typical of ferromagnetic cores, air-core inductors find numerous applications in various fields of electrical engineering. They are found in current limiters, damping networks in thyristorized converters, impedance equalizers, passive filters and for absorption of harmonic components, crossover networks in loudspeaker systems, etc. However, the absence of a ferromagnetic core of high permeability to contain the magnetic flux causes its dispersion. Thus, the inductance becomes a very complex function of the geometry, making it very difficult to design these components starting from the required value. Moreover, the information available in the specialized technical literature lacks a design approach. This paper presents a practical and easy-to-implement design routine, adapting it from the technical literature and supporting it with a practical example. The focus is limited to multilayer inductors with compact cylindrical coil development as they are the most commonly used.