Superficial magnetic field, residual magnetism and magnetic flux

• Is the superficial magnetic field the magnetic force of a magnet? Is the magnet with higher magnetism better?
• Is there any difference and connection between superficial magnetic field, remanence and magnetic flux?
• Why are the values measured by a flux meter and a gauss meter different for the same magnet?

Recently, I have often been asked these questions in the background. In fact, these questions are related to the superficial magnetic field, remanence and magnetic flux of permanent magnets. Today we will introduce the similarities and differences and mutual relations of these three concepts.

Superficial magnetic field

Concept: Superficial magnetic field refers to the magnetic induction intensity at a certain point on the surface of the magnet (the Superficial magnetic field at the center and the edge is different), which is the value measured by the Gauss meter contacting a certain surface of the magnet, not the overall magnetic performance of the magnet.
Measurement: The superficial magnetic field for measuring magnets generally uses a Gauss meter, also called a Tesla meter. The Hall sensor elements on Gauss meters of different manufacturers are different, and the superficial magnetic field measured for the same magnet is also different. In addition, it should be noted that the Gauss meter measurement standards used in different countries are different.
The superficial magnetic field is related to the height-to-diameter ratio of the magnet (the ratio of the height to the diameter of the magnet). The larger the height-to-diameter ratio, the higher the superficial magnetic field, that is, the larger the surface area perpendicular to the magnetization direction, the lower the superficial magnetic field; the size of the magnetization direction The bigger, the higher the superficial magnetic field.

(common Gauss meter, the picture comes from the Internet)

Magnetic flux

Concept: In a uniform magnetic field with a magnetic induction intensity of B, there is a plane with an area S and perpendicular to the direction of the magnetic field. The product of the magnetic induction intensity B and the area S is called the magnetic flux passing through this plane, referred to as magnetic flux, and the symbol ” Φ”, the unit is Weber (Wb). Magnetic flux is a physical quantity that represents the distribution of the magnetic field. It is a scalar, but it has positive and negative values, which only represent its direction. Φ=B·S, when there is an angle θ between the vertical plane of S and B, Φ=B·S·cosθ.

(Schematic diagram of magnetic flux, the picture comes from the Internet)
The magnitude of the magnetic flux passing through a certain plane can be vividly illustrated by the number of magnetic lines of induction passing through this plane. In the same magnetic field, the greater the magnetic flux density, the denser the magnetic flux. Therefore, the larger the B and the larger the S, the larger the magnetic flux, which means that the number of magnetic lines passing through this surface is greater. If there are two magnetic fluxes in opposite directions across a plane, the resultant magnetic flux at this time is the algebraic sum of the magnetic fluxes in the opposite direction.
Measurement: Fluxmeter is an instrument for measuring magnetic flux, and it needs to be matched with a measuring coil (copper wire with a diameter of 0.1-0.5). In recent years, domestic permanent magnet manufacturers have widely used Helmholtz coils to detect bulk products (Helmhol The magnetic coil is a device that produces a uniform magnetic field in a small area. Due to the open nature of the Helmholtz coil, it is easy to put other instruments in or out, or directly perform visual observation, so it is often used in physics experiments Device. Named after German physicist Hermann von Helmholtz).

(Helmholtz coil and fluxmeter, the picture comes from the Internet)

Remanence

Concept: Residual magnetization refers to the magnetic induction retained in the ferromagnetic body when the external magnetic field is gradually reduced to zero after the external magnetic field is magnetized to a saturated state. Its full name is the residual magnetic induction intensity (Br represents). The remanence is determined by the characteristics of the magnet itself, and the remanence of the same magnet under certain conditions is constant and has a single value.
The relationship between remanence and Superficial magnetic field: Both are in Gaussian units, but there is no corresponding relationship between Superficial magnetic field and remanence, that is, two magnets with the same remanence, the size of Superficial magnetic field may not be the same, Superficial The magnetic field is affected by the shape, size, and magnetization of the magnet.

• 1) Two magnets with the same shape, performance and size, the higher the Superficial magnetic field, the stronger the remanence.
• 2) Two magnets with different shapes, performances and sizes cannot be judged simply by the level of the Superficial magnetic field.

The relationship between remanence and magnetic flux: When the magnetic circuit of the magnet is closed, a fluxmeter can be used to measure the magnetic flux and then calculate the remanence. Br=φ/n/s, where: φ represents the magnetic flux, n represents the number of turns of the coil, and s represents the cross-sectional area of the magnet.
Source: China Permanent Magnet Manufacturer – www.rizinia.com