Question 1: What are the magnetic shielding materials? In low-frequency (DC to 100KHz) magnetic shielding, the most critical factor in designing a low-cost shield is a thorough understanding of magnetic shielding. The purpose is to reduce the specified magnetic field so that it does not pose a threat to the shielded device or system. Once this goal is determined, some basic design factors should be considered that will affect the low-cost design of the shield. These include: material selection, key design parameters and processing techniques. 2. Material selection: For shielding, the type of material selected has a great impact on its performance and cost. When designing shields it is important to have a thorough understanding of the properties of the different shielding alloys commonly used. Understanding these different properties allows you to select the appropriate materials to meet your target requirements. Magnetic shielding materials should be selected according to their respective characteristics, especially magnetic permeability and magnetic saturation properties. High permeability materials (such as the 80% nickel alloy Mumetal, a high permeability iron-nickel alloy) are often used as shielding materials due to their effectiveness in changing the direction of low-frequency magnetic fields. These alloys meet the requirements of MIL-N-14411C Part 1 and ASTM A753-97 Style 4. It is available in relatively thin thicknesses of 0.002 to 0.125 inches and is easily machined by experienced shield fabricators. These alloys are typically used when a magnetic field needs to be reduced in a very small space. These materials are often chosen when there is a need to provide greater shielding than required, or when the magnetic field strength (more typical at higher field strengths) requires materials with higher saturation values. Ultra-low carbon steel (ULCS) may be the best choice when the shielding target requires only a slight reduction in field strength (1 to 1/4), or when the field strength is sufficient to saturate a high-permeability shield. These lower cost materials typically have less than 0.01% carbon content; they have higher magnetic permeability and excellent saturation properties compared to other steels. These materials are less flexible and easier to fabricate than silicon steel, which allows for easy installation in large-area shielding projects and the ability to machine smaller components in the same way. ULCS can be used with high permeability materials to create an optimal shield where high saturation protection and high attenuation levels are required. For low-temperature shields, Cryoperm10 (a registered trademark of Vaccumschmelze GmbHg, Germany) is the best choice. Like Mumetal, Cryoperm10 is a high permeability nickel-iron alloy that is specially processed to provide increased permeability at lower temperatures. Standard shielding alloys (such as Mumetal) lose most of their magnetic permeability at low temperatures. But Cryoperm10 can increase the magnetic permeability by 10 times at 77.3 to 4.2°K. Table 1 shows a comparison of the permeability saturation values ??of the most commonly used shielding materials. Saturation permeability material (Gaussian) μ (maximum) μ (40)
Amumetal (80 Nickel)
8,000
400,00
p>
60,000
Amunickel (48 Nickels)
15,000
150,000
12,000
Cryoperm10
9,000
250,000
65,000
Ultra-low carbon steel
22,000 4,000
1,000
Question 2: What material can shield the magnetic field? The problem of field shielding is an issue that has both practical and theoretical significance. Depending on the conditions, electromagnetic field shielding can be divided into three types: electrostatic shielding, static magnetic shielding and electromagnetic shielding. These three conditions are both qualitatively different and intrinsically related and cannot be confused.
Electrostatic shielding
In the state of electrostatic equilibrium, whether it is a hollow conductor or a solid conductor; no matter how charged the conductor itself is, or whether the conductor is in an external electric field, it must be an equipotential body. Its internal field strength is zero, which is the theoretical basis of electrostatic shielding. Because the electric field in a closed conductor shell has typical and practical significance, we take the electric field in a closed conductor shell as an example to discuss electrostatic shielding.
(1) The electric field inside a closed conductor shell is not affected by the charge or electric field outside the shell.
If there is no charged body inside the shell but there is charge q outside the shell, electrostatic induction will charge the outer wall of the shell. There is no electric field in the shell during electrostatic equilibrium. This does not mean that the electric charge outside the shell does not generate an electric field inside the shell, a root electric field. Since charges with different signs are induced on the outer wall of the shell, the combined field strength of them and q excited at any point in the space inside the shell is zero. Therefore, the inside of the conductor shell will not be affected by the charge q or other electric fields outside the shell. The induced charge on the outer wall of the shell plays an automatic adjustment role. If the above-mentioned cavity conductor shell is grounded, the positive charges induced on the shell will flow into the ground along the ground wire. After electrostatic equilibrium, the cavity conductor is at the same potential as the earth, and the field strength in the cavity is still zero. If there is charge in the cavity, the cavity conductor is still at the same potential as the ground, and there is no electric field in the conductor. At this time, there is an electric field in the cavity because there are induced charges with different signs on the inner wall of the cavity. This electric field is generated by the charges inside the shell, and the charges outside the shell still have no effect on the electric field inside the shell.
From the above discussion, it can be seen that the internal electric field of a closed conductor shell is not affected by the charge outside the shell, regardless of whether it is grounded or not.
(2) The external electric field of a grounded closed conductor shell is not affected by the charges inside the shell.
If there is a charge q in the cavity inside the shell, due to electrostatic induction, the inner wall of the shell carries an equal amount of charges with different signs, the outer wall of the shell carries an equal amount of charges with the same sign, and there is an electric field in the space outside the shell. This electric field can be said It is indirectly generated by the charge q in the shell. It can also be said that it is directly generated by the induced charge outside the shell. But if the shell is grounded, the charge outside the shell will disappear, and the electric field generated outside the shell by the charge q inside the shell and the induced charge on the inner wall will be zero. It can be seen that if the charge inside the shell is to have no effect on the electric field outside the shell, the shell must be grounded. This is different from the first case.
It is also important to note here:
① We say that grounding does not eliminate the charge outside the shell, but it does not mean that the outer wall of the shell must not be charged under any circumstances. If there is a charged object outside the shell, the outer wall of the shell may still be charged, regardless of whether there is a charge inside the shell.
②In practical applications, the metal shell does not have to be strictly and completely closed. Using a metal mesh cover instead of the metal shell can also achieve a similar electrostatic shielding effect, although this shielding is not complete and thorough.
③In electrostatic equilibrium, there is no charge flowing in the ground wire, but if the charge in the shielded shell changes with time, or the charge of the nearby charged body outside the shell changes with time, then This will cause current to flow in the ground wire. The shielding cover may also have residual charge, and the shielding effect will be incomplete and incomplete.
In short, whether a closed conductor shell is grounded or not, the internal electric field is not affected by the charge and electric field outside the shell; the electric field outside a grounded closed conductor shell is not affected by the charges inside the shell. This phenomenon is called electrostatic shielding. Electrostatic shielding has two meanings:
One is the practical meaning: shielding prevents instruments or working environments in metal conductor shells from being affected by external electric fields, and does not affect external electric fields. In order to avoid interference, some electronic devices or measuring equipment must implement electrostatic shielding, such as grounded metal covers or dense metal mesh covers on indoor high-voltage equipment covers, and metal tube shells for electronic tubes. Another example is a power transformer with full-wave rectification or bridge rectification. A metal sheet is wrapped between the primary winding and the secondary winding or a layer of enameled wire is wound around it and grounded to achieve a shielding effect. In high-voltage live operations, workers wear voltage-equalizing suits woven with metal wires or conductive fibers, which can shield and protect the human body. In electrostatic experiments, there is a vertical electric field of about 100V/m near the earth.
To exclude the effect of this electric field on electrons and study the movement of electrons only under the influence of gravity, eE The second is the theoretical significance: indirectly verifying Coulomb's law. Gauss's theorem can be derived from Coulomb's law. If the inverse square exponent of Coulomb's law is not equal to 2, Gauss's theorem cannot be derived. On the contrary, such as...gt;gt; Question 3: What material should I use to make a magnetic shield? Can aluminum be used? For static magnetic field shielding, please use magnetic shielding materials. Mumetal is commonly used, but iron or steel can also be used. Materials with high conductivity can be used to shield electromagnetic waves, such as commonly used aluminum, copper, etc. Question 4: Is there any material in the world that can shield magnets? Material: 0.5mm thick iron sheet, 10mm thick packaging foam Method: Two pieces of iron sheets are sandwiched with packaging foam to make a shielding plate. The six sides of the magnet are sealed with shielding plates, and the shielding effect reaches more than 90%. Question 5: What is magnetic shielding? What are the functions of magnetic shielding? 5 categories include electromagnetic waves For example, mobile phone signals are all electromagnetic waves Question 6: Which material is not attracted by magnets and has high magnetic permeability (strong magnetic shielding)) 30 points 1. Copper, tin, silver and gold 2. The problem with magnetic shielding is The magneto-preserving spacing and magnetic loop ensure that the external magnetic force is the weakest 3. It is recommended that the magnets form a loop and then form a magnetic shield through the spacing Question 7: Magnetic shielding material parameters and materials Divide? Magnetic shielding is made of magnetic materials. The parameter that measures the magnetic permeability of the material is magnetic permeability, which is usually expressed as a number to express the relative size. The vacuum magnetic permeability is 1, and the magnetic permeability of the shielding material ranges from 200 to 350,000; another important parameter of the magnetic shielding material is the saturation magnetization. Magnetic shielding materials are generally divided into three categories, namely high magnetic permeability materials, medium magnetic permeability materials and high saturation materials. The magnetic permeability of high saturation permeability materials is between 80000-350000, and its saturation field can reach 7500Gs after heat treatment; medium magnetic permeability materials are usually used together with high permeability materials, and their magnetic permeability The permeability value ranges from 12500-150000, and the saturation field is 15500Gs; the permeability value of high saturation field is 200-50000, and the saturation field can reach 18000-21000Gs. Question 8: What is the principle of magnetic shielding? The purpose of magnetic shielding is to prevent some high-frequency electronic devices from being interfered by external magnetic fields or causing electromagnetic interference to external communications. Usually the barbed wire mesh covers the parts that are sensitive to magnetic interference. The magnetic permeability of iron is quite high compared to air, about 5000 times that of air. When a magnetic field wants to pass through, it will be formed directly through the barbed wire mesh. The magnetic circuit does not pass through the part to be protected. For example, if the current flows through an almost zero conductor in parallel with an insulated circuit, the current will not flow through the insulator but directly through the conductor. This magnetically shields the part to be protected. Question 9: For magnetic shielding, is it better to use materials with higher magnetic permeability? Or is it better to use materials with lower magnetic permeability? The taller one, stupid thought, the lower one is made of plastic which is the lowest, easy to use, just add a plastic shell and it's cheaper.