Physics
Electricity & Magnetism fields
Okayama University
Year 1986
New technique for producing a strong
multi-pole magnet
Takayoshi Nakata∗
N. Takahashi†
G. Kawashima‡
K. Fujiwara∗∗
∗ Okayama
University
University
‡ Sumitomo Bakelite Coporation Limited
∗∗ Sumitomo Bakelite Coporation Limited
This paper is posted at eScholarship@OUDIR : Okayama University Digital Information
Repository.
† Okayama
http://escholarship.lib.okayama-u.ac.jp/electricity and magnetism/51
IEEE TRANSACTIONS ON MAGNETICS, VOL. MAG-22, NO. 5 , SEPTEMBER 1986
1072
NEW TECHNIQUE FOR PRODUCING A STRONG MULTI-POLE MAGNET
T.Nakata*
,
N,Takahashi',
G,KawashimaYY a n d L F u j i w a r a "
ABSTRACT
new technique for producing s t r o n g multi-pole
magnet is developed,
A cylindrlcal magnet oriented
with i t s easy a x i s of magnetization perpendicular to
the cylinder a x i s is magnetized by a
multi-pole
magnetizer. This procedure results in a multi-pole
magnet w i t h a flux density almost sixty percent greater
than t h e flux density produced by a multi-pole magnet
which is n o t oriented, The technique is especially
e f f e c t i v e for producing small cylindrical magnets w i t h
many poles and agreement of a theoretical a n a l y s l s with
experimental r e s u l t s is v e r y good, with deviations of
no more t h a n a f e w percent,
A
*oil
F1g.l Electromagnet f o r orientation.
motors a n d o t h e r electrical machines
employ cylindrical magnets w i t h many poles and w i t h
high flux densities, I n such magnets it 1 s desirable
that t h e particular easy axes be o r i e n t e d in the
d i r e c t i o n s of their respective fluxes, Radial or p o l a r
orientations have been customarily used in rnultipoled
structures. Radial orientation i s diffrcult to obtain
when the a x i a l length of the magnet is much greater
t h a n its diameter and when t h e number of poles is large
for t h e s i z e of t h e magnet, This is because it then
becomes d i f f i c u l t to a p p l y a magnetizing coil of
sufficient cross sectional area and c u r r e n t capaclty
far t h e necessary flux.
Moreover, these conditions
necessitate more complex inlection tools and r e s u l t in
lower y i e l d s and h i g h e r costs,
Accordingly, a simpler method for t h e production
of s t r u n g multi-poled magnets was developed i n which
a l l magnetization vectors are aligned or a n t r a l i g n e d
to a single axis of orientation[ll,
Because this
technique employs a simple injection tool t h a t affords
multi-cavity molding, y i e l d s a r e Increased and costs
lowered, I t is the purpose of this paper to describe
the rationale of the new technique, to discuss the
results of a numerical analysis thereof and to compare
t h e results
of
the
theoretical
analysis
with
experimental data.
Stepping
2,
Department of Electrical Engineering,
Okayarna University, okayama 7 0 0 , Japan,
**
Fig-2 Model of a multi-pole
magnetizer.
,measured
alculated
0.1
MULTI-POLE MAGNETIZATION
In the course of fabrication the cylindrical
magnet is orlented with its easy axis transverse to the
cylinder axis as shown in Figureel,
It is t h e n
magnetized by an e l e c t r i c coil whose elemnts are
alternately
parallel
and
antiparallel
to
the
cylindrical a x i s as shown I n F i g u r e 2.
The yoke is
made of carbon s t e e l and t h e magnet to be magnetized is
polymer bonded, Figure 3 shows the r e s u l t m g f l u x
d e n s i t y on t h e s u r f a c e of the magnet as a function of
the azimuthal angle. T h e amplitude of the flux density
is s e e n to be approximately 0,08(T) as compared to the
0,05(T) obtained with t h e same magnetizing coil in
isotropic magnets of the same dimensions,
The sixty
percent increase c l e a r l y illustrates the advantage of
orientation,
*
I
Amagasaki Laboratary,
Sumitorno Bakelite Co.,
Amagasaki 661,
Japan,
Ltd.#
-0.4-
Fig.3
Distributions of radial component
of f l u x density along the s u r f a c e
of magnet
3 . METHOD O F ANALYSIS
The field distribution i n
equation(23
a i3A d a A
-(v--->+---(v--}=-J--vo
ax
ax
ay
ay
the
magnet
aMy d M x
(---
ax
)
the
obeys
(1)
ay
where v andVO a r e the reluctivities of iron and a i r , A
is t h e magnetic vector p o t e n t i a l , J is t h e exciting
current density and Mx and My a r e the components of
magnetization, Flgure 4 illustrates t h e dependence of
f l u x density on magnetizing field[33,
Mx and M y in
equation ( 1 ) are obtained from the magnetization and
demagnetization c u r v e s .
When the oriented magnet is magnetized in the
manner described above, most regions are exposed to
001&-9464/g6/0900-1072$0f.0001986 IEEE
1073
applied magnetizating f i e l d s w i t h directions ditterent
from t h e easy axis orientation, It is assumed t h a t any
resulting magnetization will be along t h e orientation
axis o n l y and t h e effective magnetizing field would
then be B1cos$ as shown in Figure 5, where B' is the
field applied by t h e coil and QI is its arientation with
respecL to the axis of alignment of the magnet,
Although the effective magnetizing
field
becomes
smaller with increasing 9 it is apparently s u f f i c i e n t
to magnetize t h e material even for v a l u e s of fl very
close to n / 2 .
These considerations are illustrated in
F i g u r e s 6 to 10,
Because the fields
from
the
individual coil loops become smaller and increasingly
interfere with each other as one approaches t h e c e n t e r
of the magnet, magnetization for small r a d i i
is
negligible as shown in F i g u r e 9 and, effectively, one
is left with the magnetization p a t t e r n of Figure 10.
Figure 13 shows the f l u x p a t t e r n arising from the
magnetization distribution of Figure 10, Here we have
a visual confirmation of t h e remarkable constancy of
flux amplitude with $. This is a consequence of how
t h e magnetic poles are distributed on t h e surface and
on t h e magnetization reversal boundaries,
As
increases t h e pole density on the boundaries decreases
n
h
B
e
Fig.7 Calculated and measured flux densities.
+
1.0
-
n
+
W
CLI
dernagnetiza
curves
rnagnetlzation
curve
Fig.4
Magnetlzing process of a magnet.
0.5
* 0.5
0.5
Fig-8 Distribution of flux density,
Fig.5 Magnetization in the direction
different from orientation,
magnetization
Q
( a ) Magnet
- p (b)
- 6 :Dirichlet boundary
analyzed region
*
7
Fig.6 Magnet model,
(A=O)
Fig.9
Distribution of magnetization,
1074
maqne t
Fig.11
Flux distribution,
170O(V), After magnetization t h e flux density along
the surface is measured w i t h a H a l l probe and t h e good
agreement with t h e o r y is shown in Figure 3 .
4,CONCLUSIONS
A new technique has been developed
for
producing
small, h l g h f l u x density, multi-pole magnets w i t h more
than 100 poles. A t present, there is no o t h e r way to
accomplish t h i s .
Work is now in progress to produce
e v e n stronger magnets of similar configuration,
ACKNOWLEDGEMENTS
The a u t h o r s t h a n k Mr, Koshida, t h e
Amagasaki Laboratory of Sumitorno Bakellte
f o r permission to publish this work,
manager of
Co.,
Ltd,#
REFERENCES
113 T.Nakata, N.Takahashi, G,Kawashima and K,Fujiwara:
"Multi-pole Magnetlzation of Permanent Magnet w i t h Only
One E a s y D i r e c t i o n of Magnetization",
Papers
of
Technical Meeting on Magnetxs, MAG-85-120, I E E of
Japan ( 1 9 8 5 )
[ 2 ] T.Nakata and N.Takahashi: " F i n i t e Element Method i n
Electrical Engineering", Morikita Publishing Co,,Tokyo
{ 1982)
[ 3 ] T-Nakata, N.Takahashi,
K.Fujiwara
a n d 1,Hayase:
"Numerical Design Method f o r Magnetizers", Journal of
Magnetlsm a n d Magnetic Materials, 41, 1-3, 418 (1984)