-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

H [A/cm]

typical ferrite

VITROPERM 500F

! = 80 000

! = 30 000

! = 20 000

VITROPERM 250F

! = 5000

[Seite 1/1]

E

100

1,000

10,000

100,000

0.001

0.01

0.1

1

10

frequency [MHz]

!'

!''

|!|

VITROPERM 500F, !=100 000

typical ferrite, !=5500

!'

!''

|!|

0.0

0.5

1.0

1.5

0.0

0.5

1.0

1.5

2.0

2.5

H [A/cm]

typical

ferrite

VITROPERM 500F

! = 80 000

! = 30 000

! = 20 000

VITROPERM 250F

! = 5000

Fig. 8b: Magnetization curve of VITROPERM 500F and VITROPERM 250F in comparison to

typical MnZn ferrite, showing noticeable differences in permeability

(slope of the curve) and saturation flux density (Bs)

Permeability

& magnetization curve

magnetization curve

The frequency dependence of the permeability, μ(f)

of VITROPERM 500F and ferrites differ fundamen-

tally. μ(f) of μ=5 000 ferrites offer a flat and linear

characteristic up to approximately 1 MHz (ferrites

with μ=10 000 range up to approximately 200 kHz).

In this flat range, the attenuation properties are de-

termined by μ’ and the impedance |Z| is dominated

by the inductance L. If the self resonance of the

choke is within this frequency range, the attenuation

curve is narrow-band and attenuation is primarily

caused by reflection of the interference signal.

Above 1 MHz (or 200 kHz) Re(Z) takes the major

share of attenuation and μ’’ becomes the dominant

factor. If the self resonance of the choke is in this fre-

quency range the attenuation characteristic beco-

mes increasingly broadband.

VITROPERM is basically similar in this respect. The

flat sector of μ(f) of VITROPERM 500F ranges (de-

pending on the initial permeability level) to frequen-

cies of several 10 kHz (20 kHz in this example), only.

Consequently, attenuation (or |Z|) is already domi-

nated by Re(Z) and is always broadband in the

whole EMC-relevant range above 150 kHz. In-

ductance plays a minor role and describes the atte-

nuation only partially. The determining factor is the

total impedance. The approximation |Z|=ωL is valid

for ferrite chokes. For VITROPERM chokes |Z|>>ωL

applies. Attenuation primarily does not result from a

reflection of the interference signal, but from its ab-

sorption.

It is only when these different characteristics are

taken into consideration that the design of optimized,

compact and low-cost nanocrystalline chokes is pos-

sible. However, VITROPERM 250F is an exception,

because the flat μ(f) sector range is similar to

μ=5 000 ferrites to frequencies of up to 1 MHz and

the attenuation is primarily inductive.

Fig.7:Differencesinthebalancebetweenμ’andμ’’forVITROPERMandferriteleadtodifferent

attenuation mechanisms

Fig. 8a: Hysteresis loops for various types of VITROPERM and typical MnZn ferrite.

NaNOcRysTallINE VITROPERM / EMc PROducTs

7