How to Measure the Strength of a Magnet?

When we consider the "strength" of a magnet, there are several measurement methods that can affect the magnet's strength in different ways, which can often be confusing. It also depends on the meaning of strength, usually referring to both the pull strength and the magnetic field strength.

In this article, we will describe each property that contributes to improving magnet performance and answer the following question: How do we measure the strength of a magnet?

1.Maximum Magnetic Energy Product

The maximum magnetic energy product (MEP) of a magnet is measured in mega gauss-oersteds (MGOe) and is the primary indicator of magnet strength. Generally, the higher the MEP value, the greater the magnetic field produced by the magnet in a specific application.

The maximum energy product, also known as BHmax, is obtained by multiplying the remanence (BR) and coercive force (HC) of the magnet.

2. Magnet Remanence

Remanence (measured in Gauss) is the magnetic property that remains within a magnet after removing external magnetic force applied to magnetize it. When a material is magnetized, it has remanence because the magnetic field is induced by the external magnetic field to some extent.

3. Magnet Coercivity

The coercivity of a magnet is the energy required to demagnetize a magnetized object to zero, the saturation point. Essentially, it measures the magnetic material's resistance to demagnetization. The coercivity of magnetic materials is measured in oersteds.

The maximum magnetic energy product, remanence, and coercive force can only be measured using a hysteresis graph tester, which plots a second-quadrant hysteresis curve.

4. Magnet Flux Density

The magnetic field strength, measured in Gauss or Tesla (10000 Gauss = 1 Tesla), is also a common measure of magnet strength because it represents the magnetic field density produced by the magnet.

The magnetic field can be seen as magnetic lines of force. The magnetic field strength corresponds to the line density within a given region. The total number of magnetic lines of force through an area is called the magnetic flux density.

The remanence value of a magnet is the magnetic flux density that a magnet maintains in a closed circuit. After removing the magnet from the hysteresis tester, it is no longer in a closed circuit and is considered open. The magnetic field immediately drops to a lower level, which depends on the ratio of the surface area to its relative magnetic length. The open circuit flux density of a small and long magnet pole is higher than that of a large magnet pole with a relatively short magnetic length.

The open circuit flux density can be measured using a gauss meter and a Hall probe. The open circuit flux density of neodymium magnets rarely exceeds 6000 Gauss. However, because the demagnetization curve of NDM magnets is a straight line, the flux density increases when the magnet is immersed in a circuit, and the distance between the north and south poles can be reduced by introducing steel. Therefore, the flux density can rise from the open circuit value to almost the remanence value.

5. Magnet Pull Force

As neodymium magnets become more widely used, most manufacturers and suppliers provide the pull force of each magnet to indicate how much weight it can withstand. Pull force is the maximum holding force of a magnet, measured in kilograms.

It is the force required to remove a magnet from the surface of flat steel when the magnet and metal have complete direct surface contact. The grade of metal, surface condition, and pulling angle all affect the pull strength.

6. Magnet Tension Curve

The tension gap curve is plotted by directly contacting the magnet with a thick and flat steel plate and then steadily increasing the tension of the magnet within the air gap range. All magnets can be tested on various air gaps using a tension tester.

Therefore, the key to selecting a magnet is the magnet's maximum magnetic energy product.

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