Similarly, the construction of the core
material can also affect the level of losses
the inductor incurs. Choosing the right core
material can also impact other crucial factors
such as weight, operating temperature
and size of the finished inductor. Design
engineers must consider these factors when
choosing their core material.
FERRITE CORE
One of the most common types of core,
ferrite cores are typically made from iron
and its alloys. These cores were traditionally
created in response to the need for inductors
to operate at higher frequencies. However, as
applications began to demand frequencies
higher than 20 kHz, the traditional laminated
core design became less and less effective.
Traditional laminated cores were made using
thin sheets of iron coated in an insulating
material and stacked together to form a core.
This method provided an effective means
of reducing losses such as eddy currents
compared to solid cores.
For higher frequency applications, ferrite
cores are created using iron powder mixed
with an insulator and binder material and
compressed under high pressure. The
resulting core has a distributed air gap where
the energy is stored in tiny air gaps that
occur between the small particles of iron in
the substrate.
This means that the core delivers a high
permeability with a uniform temperature
and performance curve. It also means
that the losses are distributed across the
material. Producing ferrite cores in this
manner is relatively cheap but is reserved for
relatively low frequency applications and are
only practical to manufacture to a diameter
of around 140 mm. In an amorphous core, the atoms are
arranged in a non-uniform manner. For
design engineers, amorphous metals offer
the best of both worlds, offering very low
losses at very high frequencies of 300kHz
while retaining a high permeability.
NANOCRYSTALLINE CORE REO UK has made strides in developing
usable inductors and chokes made from
both nanocrystalline and amorphous core
materials. We’ve made it easier for design
engineers by constructing the components
to avoid damage to the core or altering
its physical structure and achieve superior
inductance performance with very low stray
values.
Although nanocrystalline cores are
ostensibly similar in appearance to ferrite
cores, typically taking a donut-shaped form,
they are made from thin ribbon-like strips of
nanocrystalline material. Although they are
still made from iron, the grain size is much
smaller, typically 10 nm in size — hence the
name, nanocrystalline.
This type of core is annealed during its
manufacture, where a heat treatment
process is used to achieve a uniform atomic
structure and significantly improve the
magnetic permeability of the material,
usually by a factor of 10–20. However,
design engineers should take care with this
material because the annealing process can
leave the core brittle, so insulators should
be used to reinforce the core’s structural
strength.
AMORPHOUS CORE
Recent advances in metallurgy have
made once exotic core materials more
accessible for use in components such
as inductors. Also referred to as metallic
glass or glassy metal an amorphous core is
made by heating and rapidly cooling the
ferromagnetic material to produce a thin foil
with a non-crystalline structure.
With a background specialising in wound
components, REO UK also offers the
flexibility of building components with an
ingress protection rating of IP66 and water-
cooling where required.
As clean energy applications begin to
take the market by storm, semiconductor
materials will continue to get smaller,
and operate at higher frequencies. In this
environment, it’s important that design
engineers continue to keep pace with
market requirements by specifying the right
material for the job.
For more information visit
www.reo.co.uk.
Issue 39 PECM
75