Magnetic measurement basics

Magnetic measurement refers to the measurement of magnetic fields and magnetic materials, and the measurement of other physical quantities through magnetic measurement. The basic measurands include magnetic flux Φ, magnetic induction intensity B, magnetic field intensity H, magnetization M and so on. In 1785, Coulomb discovered Coulomb's law and magnetic Coulomb's law of the force between charges and magnetic poles, which opened the prelude to the history of magnetic measurement. From 1819 to 1820, Oersted discovered the magnetic effect of current and Ampere et al. discovered Ampere's law of force on the magnetic interaction between currents. A comprehensive and essential understanding of macroscopic magnetic phenomena led to the beginning of the Gaussian system of units in 1832, and true magnetic measurements were made possible.

Physical Basis:

Magnetic law is the relationship between various magnetic quantities or between magnetic quantities and other physical quantities in space, matter, materials and objects. Some relationships are qualitative, some are quantitative, and some of the more basic relationships can often be accurately expressed with simple mathematical formulas.

The scope of the magnetic law is constantly expanding with the expansion of people's understanding of magnetic phenomena, and it is developed around different aspects of the magnetic law. These magnetic laws include the basic macroscopic magnetic laws and magnetic units, the laws of material magnetism, the laws of magnetization of ferromagnetic materials, the laws of sample magnetization and the magnetic effect of materials.

Magnetic laws are the physical basis for correct and effective magnetic measurements. First of all, the basic magnetic quantities such as magnetic field intensity, magnetic moment, magnetization intensity and magnetic induction intensity can only be measured after the basic macroscopic magnetic laws are discovered and their definitions and units are given at the same time; for various specific magnetic fields, also They can only be measured if the corresponding specific magnetic laws are mastered and the magnetic quantities reflecting their characteristics are defined. That is to say, the object of magnetic measurement and the definition of the measured magnetic quantity come from the magnetic law, which should be the basis of magnetic measurement. Secondly, in order to realize the correct measurement of the measured magnetic quantity, the principle of the measurement method used should be correct, and these principles are basic or relatively basic magnetic laws. For example, the principles of two major types of magnetic measurement methods, namely the magnetic force method and the induction method, are the aforementioned magnetic Coulomb's law, Ampere's law of force and Faraday's law of electromagnetic induction, which are all basic magnetic laws.

The instruments used in various magnetic measurements must be able to measure the magnetic quantities defined by the magnetic laws with the specified accuracy. The various operating procedures to achieve magnetic measurement are also restricted by various magnetic laws, and must meet the requirements put forward by the magnetic laws. Some basic magnetic laws have already been established, but the level of magnetic measurement, even for basic magnetic quantities, is still improving. This is the comprehensive result of the continuous development of science and technology, including the ability to apply basic magnetic laws. improvement. The role of basic magnetic laws in specific magnetic measurement is often gradually recognized by people, and some more specific magnetic laws can only be discovered through practice. This understanding and discovery will play an important role in the development of magnetic measurement technology. .

Principle:

When a sample is placed in a single magnetic field, a magnetic moment is induced. The sample is placed in the pick-up coil of the vibrating sample magnetometer. When vibrating, a voltage signal will be induced in the detection coil due to the change of the magnetic flux passing through the sample. This signal is proportional to the magnetic moment, so a vibrating sample magnetometer can be used to measure the magnetic properties of a material. Magnetic fields can be generated by electromagnets or superconducting magnets, so the magnetic moment and magnetization can be measured as parameters of the magnetic field. As a parameter of temperature, a sample of a superconducting magnet can be induced to induce a magnetic moment when placed in a single magnetic field at a temperature lower than normal. The sample is placed in the pick-up coil of the vibrating sample magnetometer. When vibrating, a voltage signal will be induced in the detection coil due to the change of the magnetic flux passing through the sample. This signal is proportional to the magnetic moment, so a vibrating sample magnetometer can be used to measure the magnetic properties of a material. Magnetic fields can be generated by electromagnets or superconducting magnets, so the magnetic moment and magnetization can be measured as parameters of the magnetic field. As a parameter of temperature, a VSM system of superconducting magnets or a system with a cryogenic Dewar electromagnet or a VSM system with a cryogenic Dewar electromagnet can be used when the temperature is lower than normal. Above normal temperature, a system with a heating furnace is available. Above normal temperature, a VSM system with a furnace can be used. Because the selection of ferromagnetic materials is mainly determined by their magnetization and hysteresis loop, so the system. Because the selection of ferromagnetic materials is mainly determined by their magnetization and hysteresis loops, a common function of VSM systems is to measure the magnetic properties of ferromagnetic materials.

Classification:

Static magnetism refers to the magnetism of magnetic materials in a steady and constant magnetic field, including basic magnetization [1] curves, hysteresis loops and various parameters defined by them, such as saturation magnetization M; or saturation magnetic induction, residual magnetization Or residual magnetic induction, various magnetic susceptibility or permeability, etc. Fundamentally, the above parameters are determined by measuring the magnetization or magnetic induction under a certain magnetic field. Dynamic magnetic properties refer to the magnetic properties of magnetic materials in alternating magnetic fields.

The magnetic properties of magnetic materials in alternating magnetic fields are called AC magnetization properties. Different from static magnetic properties. The dynamic magnetic properties of a substance are not only related to the magnetic properties of the substance itself, but also to the frequency, amplitude, waveform and other factors of the excitation current.

The area of the static hysteresis loop is the static hysteresis loss, and the area of the dynamic hysteresis loop is the total loss, including three parts: hysteresis loss: refers to the inherent loss of ferromagnetic material as a magnetic medium under a certain excitation magnetic field (the loss generated in the process of converting electrical energy into magnetic energy); Eddy current loss: When the magnetic flux changes, the iron core generates an induced electromotive force and then an induced current. The induced current is in the shape of a vortex. Eddy current loss; residual loss: loss other than hysteresis loss and eddy current loss, so the area of dynamic hysteresis loop is always larger than that of static hysteresis loop.