Electromagnets vs. Permanent Magnets
When it comes to the design of devices and systems, engineers face many challenges. One of the most complex and vital choices is deciding which type of magnet they should incorporate into their application: Permanent magnets or electromagnets?
In this article, we will take a closer look at both permanent magnets and electromagnets, and provide details to help you determine which is most suitable for your design.
What Are Permanent Magnets?
A permanent magnet is defined as any material that retains its magnetic properties in the absence of an inducing field or current. They are referred to as “permanent” since the magnetic properties are generated by the structure of the material.
This inherent property allows for diverse usability across various industries and products, such as:
- Sensors and Encoders
- Brushless Motors
- Plasma Confinement
- Couplings and Clutches
- Magnetic Resonance Imaging
Permanent Magnet Materials
A wide variety of magnetic materials are available. Choosing the right one to support your application is essential. The wrong selection would result in poor product performance.
Such materials can include:
- Ceramic Hard Ferrite
- Neodymium Iron Boron
- Bonded Neodymium Iron Boron
- Samarium Cobalt
- Flexible Magnet Sheets
Permanent Magnet Considerations and Advantages
When choosing the right magnet for a product or magnet-based system, manufacturers should consider the following criteria:
- Simplified design requirements
- The system requires a continuous magnetic field but has limited access to a continuous power source of having one is not practical
- Limited or constrained space requirements
- Lowered price point
- Restricted or limited access
- Stray Fields
- Field continuously present versus on-demand field generation
What Are Electromagnets?
Electromagnets usually consist of wire wound into a coil. A current through the wire creates a magnetic field that is concentrated in the hole in the center of the coil.
Some examples are:
- Electric bells and buzzers
- Transformers and inductors
- Induction Motors
- Recording heads in audio, video, and data storage equipment
- Beam focusing and deflection
- Plasma confinement
The common electromagnet is actually composed of two components:
- a copper coil ti
- asoft magnetic materials.
Soft magnetic materials are those materials that are easily magnetized and demagnetized and are used primarily to enhance and/or channel the flux produced by an electric current. The coil is tightly wound around the soft magnetic material, commonly referred to as the core.
The types of applications for soft magnetic materials fall into two main categories: DC (direct current) and AC (alternating current).
In DC applications the material is magnetized in order to perform an operation and then demagnetized at the conclusion of the operation, e.g. an electromagnet on a crane at a scrap yard will be switched on to attract the scrap steel and then switched off to drop the steel. While AC applications the material will be continuously cycled from being magnetized in one direction to the other, throughout the period of operation, e.g. a power supply transformer. A high permeability will be desirable for each type of application, but the significance of the other properties varies.
For DC applications the main consideration for material selection is most likely to be the permeability. For example, this would be the case in shielding applications where the flux must be channeled through the material. Where the material is used to generate a magnetic field or to create a force then the saturation magnetization may also be significant.
For AC applications the important consideration is how much energy is lost in the system as the material is cycled around its hysteresis loop. The energy loss can originate from three different sources:
- Hysteresis loss, which is related to the area contained within the hysteresis loop
- Eddy current loss, which is related to the generation of electric currents in the magnetic material and the associated resistive losses
- Anomalous loss, which is related to the movement of domain walls within the material
Hysteresis losses can be decreased by the reduction of the intrinsic coercivity, with a consequent reduction in the area contained within the hysteresis loop. Eddy current losses can be reduced by decreasing the electrical conductivity of the material and by laminating the material, which has an influence on overall conductivity and is important because of skin effects at higher frequency. Finally, the anomalous losses can be reduced by having a completely homogeneous material, within which there will be no hindrance to the motion of domain walls.
Electromagnet Considerations and Advantages
Electromagnets can have an integral role in a magnetic system or product, so choosing the appropriate one can directly tie into enhanced performance and even product lifespan.
Some considerations when choosing an electromagnet can include:
- The type of core material
- Strength of the current passing through the core
- Size and shape of the core
- The number of turns the wire on the core has
When compared to permanent magnets, electromagnets can yield many advantages for manufacturers of magnetic systems and products:
- Dynamically controllable field strength
- Can be turned off (safety, reduce power consumption)
- Can feasibly achieve higher strengths
- Assembly of the device is safer
- Electromagnets don’t risk demagnetization the way permanent magnets do
Soft magnetic materials include:
- Iron-Silicon Alloys
- Amorphous & Nano-Crystalline Alloys
- Nickel-Iron Alloys
- Soft Ferrites
Unlike permanent magnets, electromagnets don’t require rare earth materials, but in special cases, the unique core material can be added to the electromagnet if a higher field output is required.
Electromagnets vs. Permanent Magnets: Which One Do You Need?
While both provide magnetic fields that can be leveraged in many similar ways, it’s fair to say that the differences between permanent magnets and electromagnets can lead to vastly different applications.
Perhaps the most significant differences between the two lie in their permanent versus on-demand magnetic fields, access to a power source, and their lifespan, If a permanent magnet is demagnetized (which can occur as a result of high temperatures), it is essentially rendered useless and will have to be replaced. Electromagnets, on the other hand, have no such risk and can be switched on and off in order to provide better product safety and energy consumption.
When choosing between the two, it’s essential to discuss your needs with the right magnet supplier who can guide you through the benefits of each and assist you in making the right decision. Based on your application requirements, and project expectations, a magnet expert can help your company in making the most efficient choice.
As the global leader in electromagnetic and permanent magnet solutions, Dexter Magnetic Technologies is here to assist your company in making the optimal choice for your new application.
From providing unique electromagnetic designs to suit your need to create a full magnetic system, our team is ready to assist you with everything your project needs.
The Dexter Difference
Dexter Magnetic Technologies works with a skilled team of engineers and support staff to help our clients access innovative technological solutions designed to get them the very best results.
If you want to learn more about our services or tap into our expertise, contact us today.