Remanence, surface magnetism and magnetic flux are three very easy to confuse concepts, here to clarify
Remanence is an essential property of materials. On the premise that self-demagnetization does not occur, the remanence of a magnet is constant, which is determined by the product raw material formula and preparation technology, and its test is carried out in a completely closed state.
Surface magnetism is the magnetic induction value of the measured location (a small area) when the magnet or magnetic component is in an open or semi-open state. The surface magnetic is a vector with direction. The surface magnetic data on different surfaces of the magnet varies greatly. We usually say that the surface magnetic value is perpendicular to the magnetic pole plane. The highest surface magnetic value of a single magnet is one half of the remanent magnetic value. Note that it is "single magnet". In some magnetic components and magnetic arrays, special magnetic circuit design can be used to improve the surface magnetic value of the magnet, and the value can even exceed the remanent magnetic value.
Magnetic flux is a measurement of the overall magnetic size of a magnet through coil testing. Usually magnetic components are not suitable for testing magnetic flux. Magnetic flux also has direction requirements by default. Of course, the total magnetic flux value can also be measured by using three-dimensional Helmholtz coil in actual measurement. Special attention should be paid to the testing direction when measuring surface magnetic flux and magnetic flux.
Magnetic Circuit
Magnetic circuit refers to a component composed of one or more permanent magnets and magnetic conductive materials in a certain shape and size to form a magnetic field with a specific working air gap. In the magnetic circuit, the magnetic conductive material plays a role in controlling the flux direction, increasing the local magnetic induction intensity, preventing or reducing magnetic leakage, and improving the mechanical strength of the entire component.
Usually, the magnetic state of a completely independent single magnet (no magnetic materials and other permanent magnet materials caused by magnetic circuit change) is called open circuit state. The most typical is to place a magnet on a platform without magnetic attraction, without any magnetic materials and other magnet influence around, then the magnet is open circuit state.
If the magnetic path of the magnet is completely locked in a built-in space and no magnetism is displayed externally, then the magnet is in a closed-circuit state. The most typical one is the magnet under the demagnetization curve measurement, which almost does not show magnetism externally.
Above in addition to open and closed state, the rest can be called semi-open.
