Design Considerations

Material and Grade Selections

Selecting the correct permanent magnet material and grade is critical in any magnet design.  There are a few key parameters to be carefully considered when evaluating the right material selection for your application:
  • Maximum Operating Temperature: Determine what the maximum operating temperature is for your applications. Different permanent magnet materials have various operating temperature limits.
  • Maximum Energy Product: Select the permanent magnet material that best "fits" your application requirements. Increased energy product will typically reduce the maximum operating temperature.
  • Intrinsic Coercivity (Resistance to demagnetization): Permanent magnet material will demagnetize if the intrinsic coercivity is too low for the application.  Be careful to select a material that will perform in your application’s environment.
Max Operating Temp Max Magnetic Energy Product (MGOe) Coercivity (Resistance to demagnetization)
Alnico 540°C 10 MGOe Low
UHT SmCo 550°C 18 MGOe High
SmCo 300°C 34 MGOe High
Ceramic 300°C 4 MGOe Low
NdFeB 70 °C 52 MGOe Medium

Handling Magnetic Materials

Working with magnetic material is difficult and can be dangerous.  Careful consideration of the characteristics below will help with safe and effective handling of magnetic materials.
  • Orientation: Most magnets have a definite orientation, or North and South Pole.  It is a good idea to know how the magnet is oriented—in what direction does it most want to draw to something like steel or another magnet?  A steel paperclip or polarity checker can be very useful.
  • Cleanliness: A magnetized magnet will attract to steel, other magnets, and will attract to itself particles and dust that are magnetic.  A clean magnet is safer to handle than a magnet that has dust or debris on it.  In a safe area use a malleable putty to pull dust and debris off magnet surfaces before critical handling is performed.
  • Mechanical Strength: Most magnet material is very brittle and can chip or crack if not handled appropriately.  If magnets are allowed to suddenly impact a hard surface or each other, chips and sharp pieces can fly off the surface.  Beyond the obvious eye hazard, these sharp objects can stick or land on surfaces where splinters can be picked up.  And loss of material may also affect magnetic properties or the fit of the magnet in an assembly.
  • Magnetic Fields: There are devices specifically designed using strong magnets to disrupt and scramble electronics.  Be aware of the proximity of strong magnets to all electronics, credit cards, data storage devices, analog watches, and even pacemakers.
  • Corrosion: Due to the iron content of most magnets, there is potential for corrosion, especially with NEO magnets.  Handling magnets with gloves should be an option to avoid moisture from hands and fingers.  Storage with a desiccant, after cleaning the surfaces with Acetone or Isopropyl Alcohol, is recommended.

Finite Element Analysis

At Electron Energy, our engineering team works closely with customers to provide a virtual in-house magnet technology resource when it comes to prototype design and fabrication. We use 2D and 3D Finite Element Analysis to solve the most demanding engineering problems. Also, our in-depth knowledge of magnetic materials and decades of practical magnet and magnet assembly experience enable us to provide innovative solutions for our customers and ensure that their precise magnetic requirements are met.

Why Use Finite Element Analysis?

FEA offers many advantages over traditional trial-and-error prototyping, helping you bring your product to market faster:
  • FEA is more cost effective than making prototypes
  • FEA can provide faster solutions than prototyping
  • Using FEA, the design can be optimized
  • More  alternative designs can be examined to improve quality, increase product life and customer satisfaction
At Electron Energy, we have applied our design expertise to electric motors, generators, magnetic bearings, magnetic couplers, magnetic seals, guidance systems, mixers, traveling wave tubes, and medical devices for private sector customers and government agencies. We strive to be a perfect extension of our customers’ engineering departments. Our strong engineering capabilities have made us the industry leader worldwide, and we are continually developing new products to meet changing customer needs. Following are some examples of our magnetic designs:

Motors and Generators

EEC conducted FEA for the design and performance prediction of various PM rotating machines (e.g. brushless DC/AC motors, brushed DC motors, interior PM motors, and synchronous motors). FEA enables us to evaluate new topologies to meet the desired power requirements, torque profile with low torque ripple, back EMF waveform, and other motor performance characteristics. Currently EEC has designed a brushless interior PM motor with high saliency ratio for a NASA SBIR Phase II program. A variety of generator designs also have been analyzed at EEC using 3D FEA, including axial and radial field generators.

Magnetic Bearings

Magnetic bearings technology is considered to be an enabling technology for new advanced engine designs. It eliminates the need for lubrication and increases machine reliability. A magnetic bearing can be designed via iterative search employing 3D finite element based electromagnetic field simulations. FEA can provide the force-current relationships, maximum load capacity of the bearings, required saturation flux levels, losses, etc. Optimization of weight, performance and cost can be achieved by skillful numerical analysis. Currently, an ultra-high temperature magnetic bearing is being designed and built to produce 500 lbs of force at 538°C by EEC and Texas A&M University for a NASA SBIR Phase II program, as shown in figure 1. magnetic-bearings

Magnetic Couplers

Rotary magnetic couplings are commonly designed in two configurations: co-axial and face-to-face. The torque characteristics of a magnetic coupler can be investigated and optimized by FEA using 3D electromagnetic field solver. The coupling torque is related to magnetic performance of permanent magnets, number of poles, air gap, and the magnetic circuits. For fixed air gap magnetic coupler, FEA can help determine the best magnetic circuit design options. Figure 2 shows a conventional 12 pole co-axial PM coupler model. magnetic-couplers

Traveling Wave Tubes

Traveling wave tubes (TWTs) amplify radio frequency waves by converting electron beam energy into microwave energy. We have used FEA to design the magnet stacks to achieve pre-determined axial filed profiles. Figure 3 shows a typical axial field profile of the magnet stacks for TWT applications. traveling-wave-tubes

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