Low loss ferrites

Details Low loss ferrites Low loss ferrites

2000-06-19

2002-08-20

Koslow, C. Melissa (Department: 1755)

Compositions

Magnetic

Iron-oxygen compound containing

C252S062620

Reexamination Certificate

active

06436307

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to low loss ferrites and especially to ferrites used at high, very high and ultra-high temperatures (of 1.5 MHz to 500 MHz) and more particularly materials that show low magnetic losses under high applied power values. The particular features of these materials are firstly their low sintering temperature (T<1000° C.) and secondly their low magnetic losses at high, very high and ultra-high frequencies. The ferrites described in the present invention are particularly suitable for making low-loss magnetic cores for high power (100 to 1000 W) applications, very wide frequency band applications or integrated electronic applications in the radiocommunications frequency range.
2. Description of the Prior Art
The development of electronic equipment is linked to the miniaturization of the passive and active components. Among these components, the bulkiest are the passive components which fulfill the resistor, inductor and capacitor functions and, more particularly, the passive inductive or inductance components. In the “high-level” applications, which implement high electrical power values, the losses of the inductive component are determined essentially by the total losses of the magnetic material used to make the core. In the high frequency range (f>1.5 MHz), nickel-zinc ferrites are used because of their appropriate magnetic properties and high electrical resistivity.
The “low loss” ferrites designed for high frequency applications (f>1 MHz) are generally nickel-zinc ferrites with the chemical formula Ni
x
Zn
y
Fe
2
O
4
with x+y=1. They are used as magnetic cores having a variety of forms (torus, pot, rod and other cores) enabling the making of inductors or wound transformers, the winding part being made by means of enamelled copper wire or coaxial conductors.
The performance characteristics of these components are often limited by the total losses of the ferrite which, therefore, determine the dimensions of the component and the permissible incident power.
FIG. 1
indicates the performance characteristics of a commercially available nickel-zinc ferrite optimized for applications of this type. It represents the variation of the total losses measured at 1.5 MHz as a function of the induction and at ambient temperature. The measurement is made on a wound torus using an enameled copper wire. The initial static permeability of the ferrite is equal to 125.
FIG. 2
shows the variation of the total losses of the same material as a function of the frequency and for a frequency/induction product equal to 37.5 MHz.mT, these conditions corresponding to the operation of the wideband power transformers. It must be noted that the losses diminish when the frequency is increased because the induction in the material diminishes. The total losses as a function of frequency and the induction may be estimated according to the relationship: p (f, B)=cste. B
&agr;
. f
&agr;
where &agr;≧2 and &bgr;≧1. They increase monotonically when the frequency increases.
The known types of ferrites have high losses at high frequencies and at high power values.
The invention seeks to obtain ferrites that can be used to overcome this drawback.
SUMMARY OF THE INVENTION
The invention therefore relates to a ferrite material based on nickel, copper and zinc having the following formula:
Ni
x
Zn
y
Cu
z
Co
&egr;
Fe
2±&dgr;
O
4
in which:
x+y+z+&egr;=1±&dgr;
&dgr;≦0.05
0.04≦&egr;
0.05≦z≦0.35
0≦y≦0.65
The invention also relates to a component applying the ferrite material, the component comprising at least one ferrite core.


REFERENCES:
patent: 3032503 (1962-05-01), Sixtus et al.
patent: 5748013 (1998-05-01), Beauclair et al.
patent: 6071430 (2000-06-01), Lebourgeois et al.
patent: 6120916 (2000-09-01), Delvinquier et al.
patent: 0 800 183 (1997-10-01), None
patent: 8-133826 (1996-05-01), None
patent: 9-232124 (1997-09-01), None

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