Welcome to our educational section. We'll be adding to this section over a period of time with the aim of providing useful resources regarding magnets.
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The easiest way to identify the poles of a magnet is to use a digital pole identifier, or a magnet upon which the poles have already been identified. Should you not have access to either of the above, a compass will suffice.
When using a compass to identify the pole of a magnet it is important to remember that magnetic poles are attracted to their magnetic opposite. The needle of a compass is itself a small bar magnet and therefore has a north and a south pole. The north pole/north end of the compass will be attracted to the south pole of the magnet being testing.
The arrangement of magnetic poles can be seen by using magnetic viewing film, which will react to the magnetic field lines of the magnet beneath it. Dark areas on the viewing film denote a pole face and lighter areas denote the gap between the poles.
By measuring the gap between the field lines, the pole pitch (frequency) can be determined. However, the film will not indicate whether a pole is north or south.
Magnetic viewing film contains a colloidal solution of microscopic nickel flakes suspended in a viscous, oil-like substance. As nickel is a ferromagnetic, the flakes will react to a magnetic field. As they are suspended in a solution, they can rotate without obstruction when exposed to a magnetic field, allowing them to align themselves along the lines of magnetic flux, making the film appear lighter.
The terms 'Mag A' and 'Mag B' are used to denote opposing pole arrangements with flexible magnetic material.
Mag A has a central south pole, with a north pole on either side, followed by south poles, etc.
Mag B has a north pole at its centre and is the opposite of the Mag A pattern.
The pole pitch of both Mag A & B is 3.125mm. The central pole will sit on centre line of the profile, ensuring perfect alignment in both directions. In some circumstances, the width of the material being magnetised will result in a half pole as the outermost poles.
Material magnetised as Mag A above will directly align to a material magnetised as Mag B above due to the poles being opposite.
The easiest way to view a magnetic field is to use iron powder or filings. Scatter the powder or filings onto a sheet of paper and place a magnet beneath the paper. The powder or filings will move to align themselves with the magnet's magnetic field lines.
The difference between anisotropic and isotropic magnets relates to the alignment of the magnetic particles, or 'domains', within the magnet.
Anisotropic magnets have their magnetic domains aligned in a single direction during the manufacturing process by the application of an electromagnetic field that fixes the domains in a direction parallel to the applied electromagnetic field. This process optimises the magnetic characteristics of the magnetic domains, resulting in a stronger magnetic force. The direction in which the magnetic domains are aligned is known as the magnetic axis - the direction by which the magnet must be magnetised, referred to as the preferred direction of magnetisation. Attempts to magnetise across the magnetic axis will fail.
Isotropic magnets are formed by the same manufacturing process as their anisotropic counterparts, bar the application of an electromagnetic field. As a result, the magnetic domains remain unaligned or random and there is no preferred direction of magnetisation allowing for magnetisation to be applied equally in any direction.
In summary, anisotropic magnets exhibit stronger magnetic properties, yet are more expensive to produce and can only be magnetised in a single direction. Isotropic magnets have the benefit of accepting magnetisation along any axis and are generally less expensive to produce, but they will not perform as well magnetically as their anisotropic counterparts.
Magnetic fields consist of magnetic flux lines that are continuous closed loops. The number of magnetic flux lines that pass through an area at right angles to the direction of the flux lines denotes the density of the field at that point and is referred to as the 'magnetic flux density'.
The unit of measure for magnetic flux density is the gauss, after the renowned German mathematician and physicist Johann Carl Friedrich Gauss, and corresponds to the number of magnetic flux lines per square centimetre. Therefore, one line per square centimetre equals one gauss.
The other unit used to denote magnetic flux density is the tesla. With one tesla being equal to 10,000 gauss, teslas are usually used for very large magnetic fields such as those created by industrial electromagnets.
The gauss rating of a magnet does not alone fully specify its strength - the physical size of the magnet also has an effect. Therefore, the larger of two magnets with identical gauss ratings will always be stronger.
The N rating of a neodymium magnet relates to the stored energy within or the maximum energy product of the magnet, and is usually measured in units of megagauss-oersteds or MGOe. A higher N rating will, in general, mean a higher performing magnet.