THE BALLISTIC DEMAGNETISATION FACTOR OF CYLINDICAL BARS

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP78-04861A000400030024-0
• Release Decision: RIPPUB
• Original Classification: K
• Document Page Count: 20
• Document Creation Date: December 20, 2016
• Document Release Date: June 6, 2006
• Sequence Number: 24
• Publication Date: August 1, 1955
• Content Type: REPORT

Approved For Release 2007/10/23
CIA-RDP78-04861 A000400030024-0
THE BALLISTIC DEMAGNETISATION FACTOR
OF CYLINDRICAL BARS
K. Warmuth
Archiv fur Elecktrotechnik, 32 (1939) 747 - 763
(From German)
25X1
August, 1955
Approved For Release 2007/10/23: CIA-RDP78-04861A000400030024-0
 Approved For Release 2007/10/23: CIA-RDP78-04861A000400030024-0
25X1
THE.BALLISTIC DEMAGNETISATION FACTOR OF
CYLINDRICAL BARS
Archie fur E)ektrotechnik, ~2 (1939) 747-763
( From German)
SUMMARY
The ballistic demagnetisation factors of cylindrical bars are determined for dimension
ratios p < 10 down to P = 0 and for any susceptibilities 0 < K < OD. Furthermore, the
importance of the ballistic demagnetisation factor for the evaluation of magnetic measurements
is discussed in detail.
I. STATEMENT OF THE PROBLEM
In an earlier paper by the author [1]*, it was shown that by using the demagnetisation
factors of ellipsoids Nell it is possible, both for the limit case of infinitely high
susceptibility** K = oo and for the susceptibility K = 0, to derive. simple expressions for
the ballistic demagnetisation factor in the range p < 10 (p = ratio of length to diameter of
the cylindrical bar). The solution was there reduced to the determination of approximation
straight lines by the method of least squares.
In the following a method is given which leads in a different way, but likewise with
the use of the demagnetisation factor of ellipsoids, to simple derivations for the two limit
cases of the ballistic demagnetisation factor in the range 0 = p = 1W. It will also oe
shown that physically understandable results are obtained with the new formulae, and In
addition sufficient agreement with. experiment is obtained for ratios of practical interest.
Furthermore, for the range 0 < K,< oo and p < 10, which previously has not been
considered either theoretically or experimentally, an attempt is made to determine the
ballistic demagnetisation factor both by the method of approximation straight lines and
graphically.
Finally, the paper deals with a critical consideration of the importance of the
ballistic demagnetisation factor for the evaluation of magnetic measurements.
11. GENERAL PRINCIPLES
The premises previously made will also be retained for the present investigations,
i.e. the discussions are based in the first place on the fact that for p = 0, the demagnetisation
factor is equal to 47r, i.e.
[Nei l] p=0, . _ [No t K < Jr0 4 7r .
...... (1)
* Fbr references, see end.
K = ? 1 where ? is the permeability of material. This equation is a,numerical
equatron According to the new rules of the Archie f. Elektrotechn., this
expression as dimension equation would be
where P~o is the permeability of vacuum.
Approved For Release 2007/10/23: CIA-RDP78-04861A000400030024-0
 Approved For Release 2007/10/23: CIA-RDP78-04861A000400030024-0
47T _ P
Nell 1 - 1 /1 - A
Secondly, the mathematical assumption is made that the demagnetisation factor NO < K < 0) with
decreasing dimension ratios p approaches the limit value 47T steadily and monotonically, as is also
the case, furthermore, with the demagnetisation factor of the ellipsoid.
We shall now give the formulae which are necessary for the subsequent discussions. For
the susceptibility K = 0, E. Iussler [2] has developed the relationship
2 7r
NK= 0 p> 10 ......(2)
The case of infinitely high susceptibility K = oo may be reproduced by the following
interpolation formula of the author [3]:
NK = CD = 0.667. pp. 05 , Nel l , 10 = p = ...... (3)
The formula of Sthlein and Schlechtweg [4] gives the ballistic demagnetisation factor of
[5] :
cylindrical bars for dimension ratios A > 10 and susceptibilities 0 s K 1 ...... (6)
p2-1I/T32
cos 7i p] p < 1 ...... .(7)
III. THE BALLISTIC DEMAGNETISATION FACTOR OF
CYLINDRICAL BARS FOR DIMENSION RATIOS p 5 10
AND SUSCEPTIBILITIES 0 = K < co
i. NK=Ofor0 p