SYSTEMS DESIGN INTERCONNECTION
then soldered, crimping involves
material being deformed to lock the
termination together using a special
crimping tool.
Electromagnetic interference
Electronic equipment is sensitive to
electromagnetic interference (EMI)
and connectors are no exception,
according to Jakub Kosinski, a
product manager at PEI Genesis.
“EMI is a serious concern
for engineers in almost every
application, but especially situations
where signal integrity is vital —
such as mission critical military
communications, fly-by-wire avionics
and medical applications. In
those situations, EMI can cause
orders, control adjustments and
medical data respectively to be
miscommunicated, with potentially
fatal consequences.”
The most important aspect of
EMI resistance is the enclosure,
according to Kosinski, both in terms
of it material and topology.
“The enclosure material is the
first line of defence against EMI.
Conductive metallic enclosures
are ideal here, because any
electromagnetic waves incoming
or outgoing induce a current in the
enclosure which saps the energy
away from the waves. As a result,
they act as an insulating shield, as
opposed to other non-conductive
enclosures, including plastic ones,
which are transparent to EMI and
allow the interference to pass
through unimpeded.”
Enclosure material is critical,
even the slightest change can make
a big difference. Traditional EMI
resistant enclosures have been
plated with cadmium to reduce
corrosion. This thin plated layer also
works to increase the opacity of the
material to EMI.
Unfortunately, cadmium has toxic
effects on the kidneys as well as the
skeletal and respiratory systems.
“Recently, however, more and
more enclosures are being plated
with zinc-nickel to make them
Restriction of Hazardous Substances
(RoHS) compliant - zinc-nickel offers
similar EMI shielding and corrosion
resistance but without using any
cadmium, with its associated
negative health impacts.”
The second line of defence is the
topology, or shape, of the connector
enclosure.
“Imagine a rectangular enclosure
for example. Here, sharp edges act
as weak points for EMI to leak in
and out of the connector, and flat
faces create impromptu waveguides
where the EMI is trapped and
interferes with itself, creating even
more electromagnetic noise,”
explains Kosinski.
“So, with a topologically smooth,
zinc-nickel-plated, stainless-steel
enclosure, it is possible to severely
limit EMI flux either emitted or
absorbed by the connector.
“Backshells like the Amphenol
M85049, Polamco 35 Series and
Sunbank M85049 are specifically
designed to give a 360 degree
connection with the cable braid,
which offers the best EMI protection
for the wire itself.”
This way there’s nowhere for
EMI to leak out of the connection,
but what about EMI generated by or
already present in the wiring itself?
“This can be addressed from two
angles,” suggests Kozinski. “The first
is to use braided coaxial cabling. Like
the conductive connector enclosures,
coaxial cables include a conductive
sheath to protect the signal wire from
EMI. For the best protection, the
coaxial sheath should be grounded
to the backshell of the connector to
allow an escape route for the EMI
induced current.
“The second approach is to
include filtering components in the
connectors which are tuned to pass
power and signal frequencies, but
remove EMI frequencies. Using filters
is quite convenient because they
can easily be retroactively applied
to typically noisy networks with little
to no reworking or redesigns of
equipment needed.”
Design early, design once
“One of the biggest mistakes I see
manufacturers make is considering
connector design too late in the
design process of their product. This
often means that a product’s time to
market is delayed while the design is
reworked,” points out Lokhandwalla.
“It’s important to remember that
your connector may have physical
design constraints like a minimum
wire-gauge or number of contacts,
so it’s vital to consult with your
connector supplier early in the
process. At PEI-Genesis, we are able
to offer customers a 3D wire model
of the connector that customers can
drop into their design to see if it fits.
“If it doesn’t, our engineering
team can help refine or redesign
the existing design, or propose
a different connector entirely,
that meets the specification. This
includes changing features like
threaded, bayonet and friction
fittings, or accessories like
backshells, or something simple like
a dust cap.”
“One of
the biggest
mistakes I see
manufacturers
make is
considering
connector design
too late in the
design process of
their product.”
Ammar
Lokhandwalla
www.newelectronics.co.uk 9 February 2021 23
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