What does a magnet do?
Magnets do the following things:
- Attract certain materials – such as iron, nickel, cobalt, certain steels and other alloys;
- Exert an attractive or repulsive force on other magnets (opposite poles attract, like poles repel);
- Have an effect on electrical conductors when the magnet and conductor are moving in relation to each other;
- Have an effect on the path taken by electrically charged particles traveling in free space.
Based on these effects, magnets transform energy from one form to another, without any permanent loss of their own energy. Examples of magnet functions are:
- Mechanical to mechanical – such as attraction and repulsion.
- Mechanical to electrical – such as generators and microphones.
- Electrical to mechanical – such as motors, loudspeakers, charged particle deflection.
- Mechanical to heat – such as eddy current and hysteresis torque devices.
- Special effects – such as magneto-resistance, Hall effect devices, and magnetic resonance.
What are permanent magnets made of?
Modern permanent magnets are made of special alloys that have been found through research to create increasingly better magnets. The most common families of magnet materials today are ones made out of aluminum-nickel-cobalt (Alnico), strontium-iron (Ferrites, also known as Ferrites), neodymium-iron-boron (neo magnets, sometimes referred to as “super magnets”), and samarium-cobalt. (The samarium-cobalt and neodymium-iron-boron families are collectively known as the Rare Earths).
How are magnets made?
Modern magnet materials are made through casting, pressing and sintering, compression bonding, injection molding, extruding, or calendering processes.
How permanent is a magnet’s strength?
If a magnet is stored away from power lines, other magnets, high temperatures, and other factors that adversely affect the magnet, it will retain its magnetism essentially forever.
Will magnets lose their power over time?
Modern magnet materials do lose a very small fraction of their magnetism over time. For samarium cobalt materials, for example, this has been shown to be less that 1% over a period of ten years.
What might affect a magnet’s strength?
The factors can affect a magnet’s strength:
- Strong electrical currents in close proximity to the magnet
- Other magnets in close proximity to the magnet
- (Neo magnets will corrode in high humidity environments unless they have a protective coating.)
Shock and vibration do not affect modern magnet materials, unless sufficient to physically damage the material.
How does a magnet’s strength drop off over distance?
The strength of a magnetic field drops off roughly exponentially over distance.
Here is an example of how the field (measured in Gauss) drops off with distance for a Samarium Cobalt Grade 18 disc magnet which is 1” in diameter and 1/2 “ long.
|Distance, x||Field at Distance x|
What is the governing equation for field strength relative to distance?
For a circular magnet with a radius of R and Length L, the field at the centerline of the magnet a distance X from the surface can be calculated by the following formula (where Br is the Residual Induction of the material):
Can a magnet that has lost its magnetism be re-magnetized?
Provided that the material has not been damaged by extreme heat, the magnet can be re-magnetized back to its original strength.
Can I make a magnet that I already have any stronger?
Once a magnet is fully magnetized, it cannot be made any stronger – it is “saturated.” In that sense, magnets are like buckets of water: once they are full, they can’t get any “fuller.”
How do you measure the strength or power of a magnet?
Most commonly, Gaussmeters, Magnetometers, or Pull-Testers are used to measure the strength of a magnet. Gaussmeters measure the strength in Gauss, Magnetometers measure in Gauss or arbitrary units (so its easy to compare one magnet to another), and Pull-Testers can measure pull in pounds, kilograms, or other force units.
If I have a neo magnet with a Br of 12,300 Gauss, should I be able to measure 12,300 Gauss on its surface?
No. The Br value is measured under closed circuit conditions. A closed circuit magnet is not of much use. In practice, you will measure a field that is less than 12,300 Gauss close to the surface of the magnet. The actual measurement will depend on whether the magnet has any steel attached to it, how far away from the surface you make the measurement, and the size of the magnet (assuming that the measurement is being made at room temperature). For example, a 1” diameter Grade 35 Neo magnet that is 1/4“long, will measure approximately 2,500 Gauss 1/16” away from the surface, and 2,200 Gauss 1/8” away from the surface.
What are Magnetic Poles?
Magnetic Poles are the surfaces from which the invisible lines of magnetic flux emanate and connect on return to the magnet.
What are the standard industry definitions of “North” and “South” Pole?
The North Pole is defined as the pole of a magnet that, when free to rotate, seeks the North Pole of the Earth. In other words, the North Pole of a magnet seeks the North Pole of the Earth. Similarly, the South Pole of a magnet seeks the South Pole of the Earth.
Can a particular pole be identified?
Yes, the North or South Pole of a magnet can be marked if specified.
How can you tell which is the North Pole if it is not marked?
You can’t tell by looking. You can tell by placing a compass close to the magnet. The end of the needle that normally points toward the North Pole of the Earth would point to the South Pole of the magnet.
What are the different types of magnets available?
There are 2 types of magnets: permanent magnets and electromagnets.
Permanent magnets emit a magnetic field without the need for any external source of power. Electromagnets require electricity in order to behave as a magnet.
There are various different types of permanent magnet materials, each with their own unique characteristics. Each different material has a family of grades that have properties slightly different from each other, though based on the same composition.
What are Rare Earth Magnets?
Rare earth magnets are magnets that are made out of the rare earth group of elements. The most common rare earth magnets are the neodymium-iron-boron and samarium cobalt types.
Which are the strongest magnets?
The most powerful magnets available today are the rare earths types. Of the rare earths, neodymium-iron-boron types are the strongest. However, at elevated temperatures (of approximately 150 C and above), the samarium cobalt types can be stronger than the neodymium-iron-boron types (depending on the magnetic circuit).
What does ‘orientation direction’ mean?
Most modern magnet materials have a “grain” in that they can be magnetized for maximum effect only through one direction. This is the “orientation direction”, also known as the “easy axis”, or “axis”.
Unoriented magnets (also known as “isotropic magnets”) are much weaker than oriented magnets, and can be magnetized in any direction. Oriented magnets (also known as “anisotropic magnets”) are not the same in every direction – they have a preferred direction in which they should be magnetized.