Halbach array

Halbach array consisting of five permanent magnets. Arrows represent the magnetic orientation of each segment. The magnetic flux is greater below this array than above.

A Halbach array is a special configuration of permanent magnets . Such a configuration allows the magnetic flux on one side of the configuration to almost cancel, but increase on the other side. Such an arrangement is named after Klaus Halbach , then a scientist at the Lawrence Berkeley National Laboratory . In 1980, Halbach was the first to present a component (a 16-part quadrupole ) of this type. However, many specialist authors attribute the first publication to John C. Mallinson, who described this effect as early as 1973 under the name " one-sided flux ".

construction

To explain the function: On the upper side there is an increase in flow, on the lower side there is a decrease in flow

A Halbach array is composed of segments of permanent magnets, the direction of magnetization of which is tilted against each other by 90 ° in the direction of the longitudinal axis of the array. As a result, the field lines move closer together on the side in whose direction the director of the field is tilted, which causes an increase in the magnetic flux density . On the opposite side, the field lines are less close than in the undisturbed magnet, so the field is weakened even at a small distance or disappears completely, as the north and south poles alternate.

application

Symbolic explanation of function

The property that the magnetic flux on one side of the Halbach array is almost canceled out is of interest in various applications, such as magnetic levitation trains ( induct track ). Holding magnets (deco magnets on the refrigerator, magnetic wall) are often manufactured as Halbach arrays, as a significantly smaller amount of magnetic material achieves the same holding force.

When building generators and electric motors, ring-shaped Halbach arrays are interesting. The ring-shaped quadrupoles first examined by Halbach are used in particle accelerators. A relatively new application is the use of circular dipoles for NMR experiments.

Web links

Lawrence Livermore National Laboratory article on an induct track train with Halbach array ( Memento from September 20, 2008 in the Internet Archive )

literature

ZQ Zhu, D. Howe: Halbach permanent magnet machines and applications: a review . In: IEE Proceedings - Electric Power Applications . tape 148 , 2001, p. 299-308 , doi : 10.1049 / ip-epa: 20010479 .

Individual evidence

↑ K. Halbach: Design of permanent multipole magnets with oriented rare earth cobalt material . In: Nuclear Instruments and Methods . tape 169 , no. 1 , 1980, p. 1–10 , doi : 10.1016 / 0029-554X (80) 90094-4 ( PDF ).
^ J. Mallinson: One-sided fluxes - A magnetic curiosity? In: IEEE Transactions on Magnetics . tape 9 , no. 4 , 1973, p. 678-682 , doi : 10.1109 / TMAG.1973.1067714 ( PDF ).
^ H. Raich, P. Blümler: Design and construction of a dipolar Halbach array with a homogeneous field from identical bar magnets: NMR Mandhalas . In: Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering . 23B, no. 1 , October 2004, p. 16-25 , doi : 10.1002 / cmr.b.20018 .

[1] K. Halbach: Design of permanent multipole magnets with oriented rare earth cobalt material . In: Nuclear Instruments and Methods . tape 169 , no. 1 , 1980, p. 1–10 , doi : 10.1016 / 0029-554X (80) 90094-4 ( PDF ).

[2] J. Mallinson: One-sided fluxes - A magnetic curiosity? In: IEEE Transactions on Magnetics . tape 9 , no. 4 , 1973, p. 678-682 , doi : 10.1109 / TMAG.1973.1067714 ( PDF ).

[3] H. Raich, P. Blümler: Design and construction of a dipolar Halbach array with a homogeneous field from identical bar magnets: NMR Mandhalas . In: Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering . 23B, no. 1 , October 2004, p. 16-25 , doi : 10.1002 / cmr.b.20018 .