TDK Ferrites EE320x250x20 - Manual (Page 8)

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003-02 / 20101108 / e16_1.fm
• All specifications are subject to change without notice.
DIMENSIONAL RESONANCE
Dimensional resonance is a phenomenon which increases loss
and decreases magnetic permeability by electromagnetic standing
waves when the magnetic field of the core frequency is applied.
The phenomenon appears when the maximum dimension of the
cross section of the core perpendicular to the magnetic field is the
integral multiple of about half of the electromagnetic wavelength λ.
C: Electromagnetic wave speed in a vacuum(3.0
×10
8 m/s)
µ
r : Relative magnetic permeability
ε
r : Relative permissivity
f: Frequency of the applied magnetic field(electromagnetic wave)
As
µe decreases by inserting into the gap, using the same core
enables high frequency wave usage as indicated by the formula
above.
As dimensional resonance quickly decreases magnetic permeabil-
ity, design the actual frequency to avoid dimensional resonance.
In the case of possible dimensional resonance, it can be protected
against by dividing the core in the magnetic circuit direction and
bonding them.
RESONANCE DIMENSION vs. FREQUENCY
CHARACTERISTICS
GENERAL PRECAUTIONS WHEN USING FERRITE CORE
• When selecting the material/form of the ferrite core, while
considering the margins select from the range in the catalog
(product manual) display where factors such as inductance
value, maximum saturation flux density, core loss, temperature
characteristics, frequency characteristics and Curie temperature
are concerned.
• Select material that does not corrode or react in order to avoid
insulation failure or a layer short, and also be careful to avoid
loose winding of the core or causing damage to the wire.
• Be careful that the equipment and tools you use do not strike the
core in order to avoid core cracks.
• Please consider using cases, bobbins or tape for insulation
purposes.
• When using cases and bobbins, select those with a heat
expansion coefficient as close to that of the ferrite as possible.
• When laying out the case, bobbin, coil and the ferrite core,
create clearance between each part in order to prevent any core
cracks and to assure insulation.
• Please handle with care, since a ferrite core is susceptible to
shock.
• The outward appearance is determined according to the
standard of our company.
• Do not place close to strong magnets.
• Be careful not to cause shock by the use of equipment and tools.
• Be careful not to expose to rapid change in temperature, since it
is also susceptible to thermal shock.
• Careless handling may hurt your skin, since the corners of the
polished surface of the ferrite are very sharp, and in some
cases, burrs may have formed on the surface.
• Please be very careful when stacking and handling the
containers, since some ferrite cores are heavy, and can cause
injury, toppling or back pain.
• Where inner packaging is concerned, please be careful not to
damage the core when taking it out from the container since the
packing materials used in order to prevent damage during
transportation may make it difficult to take out.
• Do not reprocess the ferrite core as it can cause problems, such
as injury.
λ=
f × µ
r
ε
r ×
C
10 3
10 2
10 1
10 3 10 2 10 1
Frequency(kHz)
Resonant dimension
( mm
)
PE22
PC40