BRADY MICHAEL BARRY CLIVE (GB)
| CH483705A | 1969-12-31 | |||
| GB783494A | 1957-09-25 | |||
| SU693447A1 | 1979-10-25 | |||
| DE842817C | 1952-07-03 |
| 1. | A magnetic circuit arrangement comprising three Cshaped magnets, the free ends of which are each attached to a respective sideface of one of a pair of axially spaced triangular shaped pole pieces. |
| 2. | A magnetic circuit arrangement according to claim 1 in which the magnets are each formed from two blocks of magnetic material connected by a strap. |
| 3. | A magnetic circuit arrangement according to Claim 1 or 2 in which the pole pieces are of an equilateral triangle shape. |
| 4. | A magnetic circuit arrangement according to Claim 2 or 3 in which the blocks of magnetic material are of rectangular box like shape. |
| 5. | A magnetic circuit arrangement as claimed in any preceding claim disposed about a magnetron. |
Conventionally when producing a magnetron one of the main cost constraints lies in the magnetic circuit. A well known magnetic circuit comprises four generally
horseshoe or C-shaped magnets clustered around a pair of axially spaced cube
shaped iron pole pieces. Each horseshoe magnet is provided by a pair of rectangular magnetic blocks connected by an iron strap. Surprisingly, we have found that reducing the number of magnets can increase the available magnetic field strength. It is believed that this is because the size of the iron pole piece can then be reduced and that this reduces the consequential magnetic leakage losses.
Accordingly, this invention provides a magnetic circuit arrangement comprising three C-shaped magnets, the free ends of which are each attached to a respective side face of one of a pair of axially spaced triangular shaped pole pieces.
By employing the invention it is possible to provide a magnetic circuit which not only has improved performance as compared to the above mentioned prior art arrangement, but which is also cheaper to manufacture, lighter and more compact.
In order that the invention may be better understood, an embodiment thereof
will now be described with reference to the accompanying diagrammatic drawings, in
which;
Figure 1 is a plan view of a magnetic circuit arrangement of the invention; and
Figure 2 is a cross-sectional view along line A-A of Figure 1.
A magnetron 1 , shown in dotted outline, is of cylindrical shape having an axis 2. In order to produce an axially extensive magnetic field, indicated by flux lines 3, a magnetic circuit arrangement comprises three generally C-shaped magnets 4 clustered around a pair of axially spaced iron pole pieces 5. Each magnet 4 is formed from a pair of ferrite blocks 6 of rectangular box like shape magnetically connected by an iron strap 7. The blocks may be formed from another magnetic material such as Neodinium Boron iron.
According to the invention, the pole pieces 5 are of an equilateral triangle shape when seen in the plan view of Figure 1 and each side face 8 is attached to a respective free end face 9 of a magnet 4. An axial hole 10 is present in each pole
piece to reduce flux leakage losses.
In an example using identical ferrite magnets it was found that a magnetic field strength of 4700 Gauss could be produced from an arrangement of the invention as compared to only 4200 Gauss when four such C-shaped magnets each attached to a pair of cube shaped pole pieces were used.
It is to be understood that the invention is not limited to the use of a strictly geometrical triangle, for example the corners may be rounded or removed. The straps for the three magnets may be connected to one another as in a sleeve-like arrangement. Alternatively, the magnets may each include an integrally formed strap
magnetically connecting the poles.