Hui Meng, Guiping Tang, Abby Shen, Michelle Qian, Qifeng Wei, George Mizzell & Christina H. Chen

Published in Scientific Reports on 15 June 2021

http://www.nature.com/articles/s41598-021-91969-8

This investigation reveals the mystery of the cases where magnetic like poles attract each other, and unlike poles repel one another. It is identified that for two unequally sized like poles, the pole with a higher Pc (permeance coefficient) causes a localized demagnetization (LD) to the pole with a lower Pc. If the LD is large enough, the polarity of a localized area can be reversed, resulting in an attraction between these two like poles in the LD area in a small gap. Two unusual behaviors are observed: (1) an inflection point IP appears on the force vs gap curves of all the unequally sized like poles since they have different Pc. Normally, the like poles’ repelling force increases when the gap decreases, but this IP results in nonmonotonic curves, even an attractive force in a small gap; (2) for some NdFeB magnets with a low coercivity and nonlinear B–H curve in the 2nd quadrant, a repulsion can occur for these unequal sized unlike poles, after previously pairing with their like poles that left an unrecoverable LD and reversed polarity area. The relationship of the LD, the Pc ratio, and the B–H curve are also explored in this paper.

Hui Meng, Qifeng Wei, Guiping Tang, George Mizzell & Christina H. Chen

Presented on November 7th, 2019 MMM: 64th Annual Conference on Magnetism and Magnetic Materials

At: Las Vegas, USA

Click Here for the PPT File

Even though Gauss’ law for magnetic flux density (B-field) indicates there is no free magnetic charge, we can still define the effective bound magnetic charges from the magnetization of magnetic material [1]. The positive magnetic charge is what we usually called the “north pole”, and correspondingly, the negative magnetic charge is what we usually called the “south pole”. The interaction between the magnetic charges is governed by Coulomb’s law so that like poles repel and unlike poles attract [2]. However, experiment shows that when two permanent magnets with significantly different permeance coefficients Pc (say, a small one with dimension of D4mm*4mm and Pc of 3.46, and a big one with dimension of D24mm*2mm and Pc of 0.18) were put together, with their directions of magnetization (DOM) pointing against each other, instead of repelling, they will attract to each other, especially when the coercivity of the big magnet is relatively low. This phenomenon may lead people to think that Coulomb’s law for magnetic charges is not always right, and in some cases, like poles attract. In this work, we show that the above bizarre phenomenon is caused by the partial demagnetization in the low Pc magnet, rather than violation of Coulomb’s law. When the experiment is carried out using sintered NdFeB magnet of N50 grade, the working point for the stand-alone low Pc magnet is very near to the knee of its demagnetizing curve, so it’s very vulnerable to the external and its self-demagnetizing field. Finite Element Analysis (FEA) shows that demagnetization happens obviously in the central region of the magnet with low Pc, but the magnetization remains in the same direction all over the magnet. FEA also gives an attractive force when the above low Pc and high Pc magnets are close to each other and with opposite DOMs. Based on the magnetic charge model and Coulomb’s law, the numerical integration of Coulomb’s force is carried out, which gives almost the same attractive force as FEA.

Christina H Chen, Hui Meng, and Min Fan

Presented on Aug 2018 at 2018 International Conference on Rare Earth Permanent Magnets and Advanced Magnetic Materials and Their Applications (REPM 2018)

At: Beijing, China

The magnetic force of magnetic components can be determined by using the Maxwell magnetic force equation F = B^2 A/(2μ0), with A is the cross-section area and B is the flux density. However, in many practical cases it is difficult to determine the B, and the accuracy is usually unsatisfactory. This paper reports a simple equation F = Br^2 (aA^2 +bA), where remanence Br is a known value of a magnet, and A is the magnet’s polar area. The factors a & b are function of magnet’s thickness t. The equation is developed based on the large database generated by using 3D computer simulation for the rare earth magnets (rings /cylinders /rectangular blocks) interacting with steel plates, and the equation is effective to all the magnets with high load lines. The effect of load line on the magnetic force is tremendous. For the magnets with low load lines, the magnetic force vs the area cannot develop satisfactory equation as the force values are in a large range for a single area. This paper also reports the details, including simulation set up, data analyses, equation development, and the effect of load line. Based on the database a Force Calculator App has been established for all the rare earth magnets with the gaps to steel are from 0.01 to 15 mm.

Christina H Chen, Hui Meng, and Min Fan

Presented on 2018 IEEE International Magnetics Conference, at Singapore

Click Here For the details

The Maxwell magnetic force equation F = B^2*A/(2μ0) [1-6] can be used for determining the magnetic force of magnetic components, where F is the force in newton (N), B is the flux density in tesla (T), A is the area of cross-section in square meter (m^2), and μ0 is the permeability of the vacuum (4π×10−7 H/m). The formula can be converted to an easy to remember expression of F = 40B^2*A, in which the unit of A is cm^2. This equation says that if the field is 1T, and the area is 1cm^2, then the magnetic force is 40N or 4kgf. However, it is somehow difficult to determine the B value in many practical cases, and the accuracy is usually not satisfactory. Computer simulation using finite element method can determine the magnetic forces with various boundary conditions, but usually it is not convenient for industrial users. In this paper, we report several simple equations, which are established based on the large database generated by using 3D computer simulation. The users can use the equations to obtain the force by simply inputting the magnet’s Br, area and thickness. The effect of load line is also analyzed in this paper.

Toyota Motor Corporation has developed the world’s first neodymium-reduced, heat-resistant magnet. Neodymium magnets are used in various types of motors such as the high-output motors found in electrified vehicles, use of which is expected to increase rapidly in the future. The new magnet uses significantly less neodymium, a rare-earth element, and can be used in high-temperature conditions.

The newly developed magnet uses no terbium (Tb) or dysprosium (Dy), which are rare earths that are also categorized as critical materials(3) necessary for highly heat-resistant neodymium magnets. A portion of the neodymium has been replaced with lanthanum (La) and cerium (Ce), which are low-cost rare earths, reducing the amount of neodymium used in the magnet.

See details at:

http://www.autocarpro.in/news-international/toyota-magnet-electric-motors-slash-rare-earth-element-28145

Quadrant Magnetics Calculator is now available to download in Apple APP and Google play. Quadrant Magnetics Calculator provides a mobile APP to conveniently calculate the magnetic force F, the permeance coefficient Pc, and the demagnetizing factor N for various magnet shapes and dimensions. Quadrant Magnetics calculator uses computer simulation data of magnets interacting with steel plates (cold rolled steel CR1010) that are both thicker and larger than the magnets. Force in actual applications may vary significantly given different boundary conditions.

Contact www.quadrant.us for your specific needs.

This web has just launched the Magnetics calculator:

http://magnetnrg.com/calculator/

The calculator APP for mobile is also available to download
(email us at: contact@magnetnrg.com)

2018 International Workshop on Rare Earth Permanent Magnets & Their Applications will be held in Beijing, China

http://www.repm2018.org/

The workshop has a long history ever since Dr. Karl J. Strnat initiated the series of Workshops 42 years ago. In 1966, Dr. Karl J. Strnat and his colleagues at the U.S. Wright-Patterson Air Force Laboratory in Dayton, OH discovered the extremely high magnetocrystalline anisotropy in RE-Co alloys, which led to the development of modern permanent magnets.

The objectives are to bring together scientists and engineers working on rare-earth permanent magnets and their applications and to facilitate exchange of recent results and ideas on topics such as raw materials, resources, as well as processing and properties of rare-earth and future permanent magnets for innovative technologies.

The US Department of Energy’s (DOE) Advanced Research Projects Agency-Energy (ARPA-E) has announced $30 million in funding for 21 innovative projects as part of the Creating Innovative and Reliable Circuits Using Inventive Topologies and Semiconductors (CIRCUITS) program.

The program will use power converters based on wide bandgap (WBG) semiconductor technology like SiC or GaN to accelerate the development and deployment of innovative electric power converters that save energy.
….
Examples of selected CIRCUITS projects include Imagen Energy, which received $847,888 to develop a SiC-based compact motor drive system to efficiently control high power (greater than 500 kW), high performance permanent magnet electric motors operating at extremely high speed (greater than 20,000 rpm). Imagen Energy’s design seeks to address a major roadblock in operating electric motors at high speed, namely overcoming large back electromotive forces (BEMF). If successful, the project team will demonstrate a motor drive capable of handling large BEMF and increase motor system efficiency over a broad range of operating speeds.

​compoundsemiconductor.net/article/102313/ARPA-E_Awards_30M_to_develop_better_power_converters