Method rotates magnet about a wire loop of rectangular shape placed inside the pole tips and measures induced loop voltage with a wave analyzer. Quantitative field characteristics are determined from voltage induced at various harmonics of the rotation frequency

Lacey, R. F.

English

NASA Technical Reports Server

1972	 B72-10113 
NASA TECH BRIEF 
Goddard Space Flight Center 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Hexapole Magnet Field Analysis 
The problem: 
The measurement of a hexapole magnet field by the	 The voltage induced at the n'th harmonic is related to 
use of Hall effect magnetometers or flip coils is inaccurate 	 Bn by the expression: 
because their size is large compared to the magnet gap. 
The solution: 
A method was developed in which the field of the 
hexapole magnet is analyzed by rotating the magnet 
about a wire loop of rectangular shape placed inside the 
pole tips, and measuring the induced loop voltage with a 
wave analyzer. The quantitative characteristics of the 
field are then determined from this voltage induced at 
various harmonics of the rotation frequency. 
How it's done: 
The technique requires an analyzer, a loop, and the 
magnet. The two components of the magnetic field are 
determined from the following expressions: 
Br=Bn(r/ro)nl cos nO 
130 =_Bn(r/ro)nl sin nO 
where r0 is the radius of the magnet. 
For a symmetric hexapole magnet, Bn has non-zero 
values at n = 3, 9, 15. . ., with n = 3 producing the 
dominant term. The magnitude of Bn is determined by 
rotating the magnet about its axis and measuring the 
voltage induced in a rectangular pickup loop placed so 
that it is bisected by the magnet axis. In this arrangement, 
various harmonics of rotation frequency can readily be 
separated by the wave analyzer. Furthermore, the har-
monic number of the Bn can be unambiguously identified 
by measuring the rotation period with an electronic 
counter.
Vn(t)=2LrowBn(D/2ro)n cos nwt 
where L is the length of the loop, D its width measured 
between the centers of the wire, t is time, and w is the 
angular frequency at which the magnet is rotated. 
Applications for this technique are also useful in the 
design of hexapole magnets. For example, the effect of 
different pole tip shapes on the field can be measured, 
and the effect of different designs on the maximum 
field strength can be determined. 
Note: 
Requests for further information may be directed to: 
Technology Utilization Officer 
Goddard Space Flight Center 
Code 207.1 
Greenbelt, Maryland 20771 
Reference: T5P72-101 13 
Patent Status: 
No patent action is contemplated by NASA. 
Source: R. F. Lacey of
Hewlett-Packard Company 
under contract to
Goddard Space Flight Center
(GSC-10995) 
Category 03 
This document was prepared under the sponsorship of the National 	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States 	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States 	 will be free from privately owned rights.
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Hexapole magnet field analysis

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