Magnetic Core Characteristics and Applications

Magnetic components have been used in several power electronic devices for decades. They are used in a wide range of applications. In order to implement the designed magnetic components, it is essential to have a good understanding of magnetic materials and associated technology

In the previous article, we learned about the basic aspects of magnetic materials including their classification, core materials, and shapes. Read on to learn more about various core sizes, core assembly, choice of components, and applications of magnetic materials.

 

Core Sizes

The magnetic core is a specific design of magnetic material in a particular shape that possesses high magnetic permeability. It is employed to confine and guide the magnetic fields in electrical, electromechanical, and magnetic devices. 

The core is typically made of a ferromagnetic material like iron or of ferrimagnetic compounds such as ferrites. The idea behind using high permeability material for this purpose is to be able to have the magnetic field lines concentrated in the core material.

The size of the core varies for different applications based on the core material’s power or energy level. There are several standard sizes available off-the-shelf to cater to the needs, and also scope for customizing the sizes for specialized applications. 

The size of the coil former depends on the core size and needs to be chosen accordingly. The datasheets provided by the manufacturer come in handy for reviewing the standard sizes of the magnetic core and other related components.

 

Core Assembly

The entire core assembly comprises a coil former, core, and the mounting hardware [1]. Typically, the magnetic core is divided into two halves. They come as matched pairs that need to be assembled and used as a pair only. 

Manufacturer datasheets provide valuable information regarding temperature cycling needs and cleaning agents to facilitate optimum performance. Ferrite cores are most commonly used due to their high permeability and the wide range of accessible options for different power levels and applications. 

Standard gapping that enables precise values of inductance and standard mechanical dimension is a huge advantage as they in turn enable the right options for coil former and assembly hardware. The availability of a full range of commonly utilized core shapes like standard planar E and I cores helps facilitate rapid prototyping.

 

Choice of Components

The selection of ferrite core shapes depends on many factors. Each shape has some key advantages over the other based on the application at hand [2]. In most of the scenarios, there is no perfect choice and the decision is a compromise accounting for the must-haves. Along with the cores, it is equally crucial to order relevant accessories for the same like coil formers and the mounting hardware [3].

Another aspect to keep in mind during the design and implementation of the magnetic core is the aspect of the air gap. Cores with an air gap are useful for inductors and their applications. The variants in this type are based on the difference in air gap lengths. On the other hand, core without air gap is employed in transformer-based applications.

In the previous article, we discussed the details regarding the standard classification of magnetic materials. In terms of the choice of material based on specific applications in components and key performance characteristics, magnetic materials can be compared as in Table I [4]. These comparisons come in handy during the selection process and the datasheets can be referenced to gain this valuable information for other magnetic materials under consideration.

 

Material Hard Ferrite (HF) AlNiCo (AN) SmCo (SC) NdFeB (ND)
Adhesive Force Good Medium Strong Very strong
Maximum Working Temperature (in degrees C) 200 450 200 80
Corrosion Resistance Very good Very good Good Poor
Machinability Not possible Diamond cutting or grinding Not possible Not possible
Demagnetization Capability Moderate Easy

Extremely difficult

Difficult
Price Low High Very high

Moderate

Table I: Comparison among different magnetic materials
 

Applications of Magnetic Material

Magnetic materials find a multitude of applications in our daily lives ranging from electricity generation to electricity utilization. These include electric motors, transformers, and generators. They also play a key role in charging and storing equipment in various facets of data storage technology including hard disks and audio cassettes. They are also employed in telephones, CD players, television, loudspeakers, and video recorders.

 

Magnetic Core Characteristics and Applications
Figure 1: Sample applications of magnetic materials
 

In terms of the standard classification of magnetic materials, ferromagnetic materials are mostly used in permanent magnets and data storage applications. Ferrimagnetic materials are employed in the implementation of inductors, transformers, and related magnetic components. 

Superparamagnetic materials are used in the creation of recording tape for various audio and video applications. Some examples of applications of components with magnetic materials are showcased in Figure 1 [5].

 

Key references:

  1. L. Umanand, S.R. Bhat, “Design of Magnetic Components for Switched Mode Power Converters”, Wiley Eastern Limited.
  2. Marian K. Kazimierczuk, “High-Frequency Magnetic Components”, John Wiley and Sons, Ltd.
  3. TDK Databook on Ferrite cores-2, TDK Electronics Co. Ltd., Japan.
  4. Types of Magnetic Materials with Examples • Advanced Magnet Source
  5. Examples of applications using Neodymium Magnets – Magnets By HSMAG