Magnet Design Guide – Learn How to Make Your Magnets

Magnet Design Guide

Designing your magnets can be an overwhelming task without the right information. It does not matter the type of magnet design you want –  it is critical to consider possible shapes, materials, magnetic performance characteristics, and uses among others.

Once you understand these 4 principles for magnets design, the process will be seamless and straightforward.

Step 1: Know the Magnet Design or Shape

First, you must know the magnet design shape you want. In most cases, the applications will determine the magnet shape.

Of course, there are those we consider “standard” while others are custom designs. Whenever you have magnet design ideas, consider the following:

Magnet Shape Design Importance/Features
Cylinder Magnets
  • Magnetization occurs either across their diameters or through the length
  • Applications: making medical equipment, sensors, switching systems
  • They have a magnetic field with a longer reach
Bar magnets
  • Most common shapes available
  • Their shapes resemble a “bar metal” with poses on two opposite sides
  • Applications: making fridge magnets and compass
  • A good example of a bar magnet is the rectangular bar magnet
Horseshoe magnet
  • These magnets are identified by the “U” shape
  • Usually, the poles point in one direction
  • Applications: picking objects due to the strong poles or lifting equipment
Ring magnets
  • They have a hollow center with a circular shape
  • Applications: making sensors, speakers, motors, etc.
Disc magnets
  • They have a wide flat surface
  • Characterized by large pole area
  • Known for their effective strength and ease of pole modification
  • They are round but without holes at the center
  • Applications: making models, crafts, and DIY projects
Sphere magnets
  • Their shape resembles that of a ball, hence at times referred to as ball magnet
  • Applications: electrical parts, toys, hobby products, etc.

Types of magnet designs

Types of Magnets – photo courtesy: Vecteezy

Although these are some of the most common magnet design shapes, you can also choose custom options for your project design. However, working with standard design will make the entire magnet design process easier and simple.

Step 2: Choosing Magnet Material

Whichever magnet design ideas you have, knowing the right magnetic material is paramount.  Some popular magnetic materials for your personalized magnets include:

Magnet Material Characteristics of Magnetic Material
NdFeB (Neodymium-iron-boron)
  • It is a rare earth metal
  • The strongest magnet
  • The composition is Nd2Fe14B
  • Their use started in the 1980s
SmCo (Samarium-cobalt)
  • Available in two compositions Sm1Co5 and Sm2Co17
  • The material was developed in the 1960s
Ferrite or Ceramic
  • The composition is mainly SrFe2O3 or BaFe2O3
  • Popular for their low cost
  • Materials have been in use since the 1950s
Alnico (Aluminum-nickel-cobalt)
  • Composition is mainly Al-Ni-Co
  • Material has been in use since the 1930s

Depending on the specific requirements, the magnet design engineer will advise on the right magnetic material.

All these magnetic materials vary in magnetic strength, magnetizing force, working temperature, and magnetic flux density, among other critical variables.

Therefore, you will choose these variables depending on your personalized custom magnet design requirements. They will determine how to use the magnets.

Remember, they are available in different material grades for specialized applications.

Magnetic material summary

Magnetic Material Summary – Photo courtesy: Science Direct

More resources:

Step 3: Understanding Magnetic Parameters

How to make a magnet requires careful understanding and analysis of various magnetic parameters. That is, you must evaluate all the intended environmental conditions and working parameters.

To design your magnets, you should consider the following key variables:

1. Finite Element Analysis (FEA)

FEA is modeling criteria that help you arrive at a suitable magnet design. Through various simulations, you can analyze the magnets:

  • Flux density
  • Torque
  • Magnetic forces

These magnetic design software will help you develop information on:

  • Flux paths
  • Vector magnetic potential
  • Flux density

Usually, working closely with magnet design engineers will help you get accurate parameters from the simulation process.

2. Understand the B-H Curve Characteristics

This magnet curve illustrates the relationship between:

  • Magnetic flux density; is usually denoted by B;
  • Magnetizing force; is denoted by H.

When it comes to the magnet design guide principle, you must evaluate the B-H curve/hysteresis loop.

With the B-H curve, it is easier to characterize various magnet materials. You will learn all the fundamental aspects during the magnets design process. It is a closed loop showing:

  • Magnet saturation phase
  • Demagnetization phase
  • Magnet saturation (thou in the opposite demagnetization)
  • Demagnetization phase

Theoretically, you can experience this under the influence of an external force. You can see this illustrated in the Cartesian plane below for the B-H curve:

Hysterisis loop

Hysteresis Loop – photo courtesy: Electrical Academia

Usually, the 2nd quadrant in the Cartesian plane of the B-H curve is always very critical. Usually, it represents practical situations where you can use a magnet. The curve is usually called the demagnetization curve.

Therefore, unless you subject the magnet to unique working conditions – in most cases the working characteristics will remain within the demagnetization curve.

Even as you analyze the hysteresis loop/B-H curve (refer to the curve above), you should note the following:

Points where the Curve Crosses the B-H axes

Usually, we have:

  • Residual induction (Br)
  • Coercive force (Hc)

You can characterize residual induction by:

  • Zero magnetization
  • Hysteresis curve meets the y-axis (B axis)
  • Maximum flux output

On the other hand, the coercive force is characterized by:

  • Magnetic material can withstand external magnetic field
  • There is zero demagnetization due to the external magnetic field

Additionally, you must take note of B and H being maximum. It is also called BHmax. It is the point where the product of B and H is maximum.

As a basic magnet design guide principle, a small magnet volume still implies the product of BHmax is high.

To calculate the B:

When analyzing magnet total flux, consider:

  • Flux as a result of the magnetizing field
  • The magnetic material’s ability to produce more flux which depends on the domain alignment.

After designing your magnets, ideally, the characteristics will be in the 2nd quadrant of the hysteresis loop curve.

From the above figure, you can see the value of H is negative while B is positive.

For purposes of your custom magnet design, it is important to note the following:

  • Intrinsic coercive force, that is when the curve intersects the horizontal axis (H-axis)
  • A high intrinsic coercive force is an indication of a stable magnetic material
  • Normal curves are suitable for designing permanent magnets and static magnets. Assuming there are zero external magnetic fields.
  • Use both intrinsic curves and normal curves when designing magnets that are subjected to external magnetic force.

3. Important Calculations in Magnet Design

There are many magnet simulation software for the design process. Of course, they all depend on certain mathematical modeling to get possible magnet designs and requirements.

In this section, we shall explore some fundamental equations that will help you design the magnets.

Calculating: Magnet Length, Pole Area, and Permeance Coefficient

Let’s look at these equation courtesies of Magnetshop.com:

Magnet Equation

Magnet Equation – Courtesy: Magnet Shop

Assuming there is no coil to excite the magnet, you can determine both length and poles using equations (1) and (2) above. Furthermore, if you want to determine the permeance coefficient, you use equation (3). You will get equation (3) by combining (1) and (2) above.

The following is the meaning of the abbreviations or symbols in the equations for your magnet design characteristics:

Abbreviation or Symbol Meaning
Bm Flux density (at the point of operation)
Hm A force of magnetization (at the point of operation)
Ag Area of an air gap
Lg Length of the air gap
Bg Gap flux density
Am Magnet pole area
Lm Magnet length
µ Permeability
k A constant for reluctance and possible leakages
Pci intrinsic permeance coefficient (Bi/H)
Pc normal permeance coefficient (B/H)

 

Although the calculations are based on a magnet operating on the 2nd quadrant of the B-H curve, we give H a positive number.

Putting this into perspective:

This is a fundamental principle you must remember when designing magnets. Here are some 4 examples of magnet designs:

Example of Magnet Designs Main Characteristics
Alnico 5 ·         High flux density which performs well in electromechanical devices

·         It has low coercively

Alnico 8 ·         A high magnetizing force implies a small length

·         Low flux density thereby the need for a large magnet area

Rare earth Magnets ·         Flux density depends on the magnetizing force – from medium to extremely high values

·         Magnet length can be short with a small volume

Ceramic or Ferrite Magnets ·         Most low flux density

·         A magnet will have a large pole face area

Magnet Flux Density Calculation

The key variable to magnetic flux density calculation is:

  • Different magnet shape designs and configurations
  • Magnet central line

You can use this formula courtesy of magnetshop.com.

Assuming you are designing magnets whose normal demagnetization curve is a straight line, with a distance say, X, Use these formulas:

For cylindrical magnet designs

Cylindrical magnet equation for flux density

Cylindrical Magnet

Rectangular Magnet Designs

Rectangle magnet flux density

Rectangle Magnet Flux Density

Ring magnet designs

Ring magnet flux density

Ring Magnet Flux Density

Apart from these magnet designs, there are certain situations where you may have special cases such as:

  • Designing magnets facing each other
  • Yoked magnet design

Calculating Magnet Force of Attraction

In most cases, you can use the formula:

Where:

  • F – force (pounds)
  • B – flux density (kilogauss)
  • A – pole areas (square inches)

At times, you may estimate the force using the formula:

In this case, you will have:

  • Br – residual flux density
  • A – pole areas (square inches)
  • Lm – magnet length

In short, personalized custom magnet designs require many calculations. It is the only way you can control all vital parameters that affect the magnet’s strength for any design.

4. Strive for Stability in the Permanent Magnet Design

Different shapes of magnet design have varying stability thresholds. Usually, during the magnet manufacturing process, the magnetization will align the poles in a specific direction.

Once that occurs, they are “locked” in that position. However, there is a certain phenomenon that can interfere with the normal operation of the magnet.

In the worst case possible, they may cause demagnetization.

Again, a principle magnet design guide dictates that the magnet should maintain its repeated magnetic performance. We refer to such a situation as magnet stability.

Magnetizing magnets

Magnetizing Magnets

Therefore, even as you design magnets, pay attention to:

Duration you Expect Magnet to Remain in Use

Electromagnets will remain magnetic as long as they are energized (availability of electric current).

However, permanent magnets will retain their magnetic force for a long time.

But again, after manufacturing magnets and subsequent magnetizations, they tend to lose a certain percentage of their magnetic strength. However, this loss is very small and cannot affect the normal working of the magnet.

In most instances, the magnet may have unstable domains. It is within these domains that these losses occur. A phenomenon called magnetic creep.

Once the number of unstable domains reduces, your magnet will retain the net magnetic effect for a very long time.

For some magnets such as samarium cobalt, the loss can be between 0% and 3% after nearly 10 years.

Effects of Temperature on the Magnet

The surrounding temperature where you intend to use the magnet also matters very important. Usually, the effects of temperature on magnetic properties may be reversible or irreversible.

However, for the irreversible losses, some you can recover, and some you may not. Well, that sounds interesting – you will learn more about that shortly.

Magnetic Material Curie Temperature (ºC) Maximum Temperature (ºC)
Ferritic or ceramic magnets 460 300
Neodymium 310 150
Samarium cobalt 750 300
Alnico 860 540

From this information, it is quite clear – if custom magnet designs are for high-temperature applications, then choose Alnico. For low-temperature applications, go for neodymium magnets. However, you must consider other factors such as resistance to corrosion, magnetic strength, ease of machinability, etc.

Temperature is just one variable.

Again in the table above, the maximum temperature refers to a range within which you can operate the magnet. The recommended working temperature.

The Curie temperature is a point where the magnet becomes completely demagnetized.

Now, let’s compare the various temperature conditions:

Classifying Temperature Situations in Magnets Effects of Temperature on Magnets
Reversible losses
  • Magnet retains its original property after temperature returns to normal condition
  • It varies depending on the magnetic material grade
Losses are irreversible however, you can recover the properties
  • It is partial demagnetization
  • You can restore magnetic properties through re-magnetization
  • Even if the magnet returns to normal temperature, it will not recover the magnetic properties by itself
Irreversible and unrecoverable losses
  • You cannot recover the lost magnetic properties through re-magnetization
  • At this stage, there are significant changes in the magnet’s metallurgical structure

With these in mind, how then does this contribute to designing a stable magnet?

  • Demagnetization may help achieve magnet stability. That is, you will expose the magnet to high temperatures thou the process must be controlled.
  • It will help achieve stabilized magnetism since magnet domains with low commitment will lose their magnetism
  • In stabilized magnets, the flux variation will be low.

Analyze Effects of External Magnetic Fields

Again, this comes to understanding where you will use the magnet. Remember, repulsive external magnetic fields can cause demagnetization.

Therefore, you should know the magnet’s coercive force. In most cases, rare earth magnets are difficult to demagnetize by an external magnetic field.

Types of magnetic fields

Types of Magnetic Fields – Source: Science Facts

Effects of Radiation on Magnets

Magnets such as Sm2Co17 can withstand radiation better than neodymium magnets. However, some magnets get demagnetized on exposure to a significant amount of radiation.

Mechanical Impact on Magnets

Mechanical impact range from vibration, shock, or stress. Again, this requires you to understand specific applications or where you intend to use the custom magnet design.

Although modern magnets can withstand a significant amount of shock, there are inherently brittle magnets.

For instance;

  • Thermal shock can damage samarium cobalt and ferrite magnets
  • Mechanical shock can break samarium cobalt magnets due to their fragility

Step 4: Understand the Manufacturing Magnet

Magnets manufacturing process

10 Magnets Manufacturing Process – Photo courtesy: SMD Magnetics

Magnet manufacturing is also an important factor to consider during the magnet design process.

We have a complete guide here on Different Ways to Manufacture Magnets. Remember, a manufacturing process can only be suitable for specific magnet designs.

Let’s summarize some important magnet manufacturing processes:

Magnet Manufacturing Technique Types of Magnet Designs
Sintering magnets
  • Rare earth magnets
  • Alnico magnets
  • Ferrite magnets or ceramic magnets
Injection molding magnets
  • Ceramic magnets or ferrite magnets
  • Rare earth magnets
Pressure bonding magnets
  • Rare earth magnets
  • Ceramic magnets or  ferrite magnets
Casting magnets
  • Alnico magnets
Extruding magnets
  • Neodymium magnets
  • Flexible magnets
Calendering magnets manufacturing
  • Flexible magnets

Therefore, even as you choose your magnets design, it is important to specify the recommended manufacturing process.

The manufacturing should cover every process, from material selection to magnetization and quality testing.

Remember, when it comes to evaluating the magnet’s manufacturing process, you must consider other factors such as:

  • Machining operations – these may involve grinding, cutting, or drilling to achieve certain surface finishes
  • Coating – some magnets may require coating for additional protection. This is to protect the magnet from corrosive environments that can cause rusting. For instance, neodymium magnets are not corrosion-resistant. Therefore, they require coating.
  • Magnet Assembly – you may use adhesive or fasteners to assemble magnets in various applications.

Quality Testing Magnet After Design and Manufacturing

Through quality testing, you can establish if you have a good design for your magnet or not. There are many ways of verifying magnet quality. Some common magnet quality testing includes:

  • B-H curves
  • Determining total flux
  • Measuring the flux density
  • Conducting pull-up tests

Step 5: Specify Uses of Custom Magnets

There are different shapes of magnet designs available for various applications. Remember, the magnet shape, material type, and performance characteristics determine specific magnet applications.

Generally, the available magnet designs perform 4 fundamental functions:

The function of a Magnet Examples of Applications
Mechanical to mechanical energy
  • Magnets either attract or repel certain components. The phenomenon can either be in a linear, rotary, or reciprocating motion.
Mechanical to electrical energy
  • They convert kinetic energy into electrical energy like in the case of generators
Converting electrical energy to mechanical energy
  • Some examples are magnetostrictive materials. Another example is the electric motors
Converting mechanical energy to heat energy
  • The hysteresis torque equipment and eddy current devices exhibit the conversion of mechanical energy into heat

Apart from these, there are certain instances where magnets may perform special functions such as:

  • Magneto resistance
  • Magnetic resonance
  • Hall effect

With these four steps, you can design and manufacture magnets easily. It doesn’t matter whether you are designing lifting magnets or sensor magnets. The fundamental principles remain the same.

Conclusion

As you can see, designing magnets is a rigorous process. You must know the material type, understand the magnet working parameters, choose a suitable magnet manufacturing process, and establish proper quality testing.

More Resources:

Designing Magnets – Source: MagnetShop

Principle of Designing Magnets – Source: Intemag

Magnetic Material – Source: JCBOSEUST

Principle to Design Magnets – Source: ICPTIAEA

Calculations for Designing Magnets – Source: Word Wide Science

Online Magnet Calculators – Source: MagnetShop

Magnetic Circuit Design Guide – Source: TDK

Design Considerations for Permanent Magnets – Source: Magnetic Mag

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