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Figure 1. There are numerous options for a contactless data link,
including 2.45-GHz RF, but power links are for now best achieved
using inductively coupled power transfer
approach.
As mentioned, a separable connection
provides a separate connection
between two elements of an electronic
system
without
unacceptable
degradation
of
performance.
The separable connection and
unacceptable performance depend
on the connector application and
its electrical and environmental
application. Factors to consider when
choosing a connector include:
Power distribution:
Joule
heating, which is proportional to the
connector resistance, can result in
increases in the connector operating
temperature, a major factor in
connector
degradation.
Both
magnitude and stability of contact
resistance are critical for power
connectivity. Arcing is also significant
in power applications, especially
where there are hazardous gas
environments.
Signal distribution:
Signal
distribution requirements center
around maintaining the integrity of
the signal waveform. For high-data-
rate systems, this may involve
controlled-impedance
connector
designs and careful attention to
signal-to-noise ratios. The magnitude
of the required connector resistance
is strongly dependent upon the
devices in the circuitry the connector
must interconnect. For many devices,
high connector resistance - hundreds
of milliohms - can be tolerated.
E n v i r o n m e n t a l
considerations:
Harsh
environments, such as deep ocean or
vibration sensitive surroundings, may
constrain the traditional connector
application and design. There may
also be harsh and safety-critical
applications, such as gaseous
environments, which limit the
application of contact technology.
Corrosion:
Corrosion occurs in
many forms and can be classified by
the cause of the chemical deterioration
of a metal. The most common form of
corrosion is rust or ferric oxide.
Galvanic corrosion, or dissimilar metal
corrosion, occurs when two different
metals are located together in a
corrosive electrolyte.
Movement:
Cabled solutions are
generally constrained in their
movements. Wear and tear on cables
coupled to motor-driven, rotating
subsystems, such as robotic arms,
can lead to downtime, severely
affecting productivity. A classic
example is a robotic arm, which may
have to move along multiple axii.
Traditionally, rotation with reliable
connectivity is achieved using slip
rings that are connected to stationary
rings via brushes. Cables are used to
position these copper rings in close
proximity to enable physical contact
with carbon brushes.
Mating cycles:
The connector
may be designed to meet specified
mating frequency and cycles from a
few hundred to thousands. Cycle-life
requirements affect the design and
materials used in manufacturing the
connector.
Other factors:
Cost, size,
efficiency and the ability to transmit
over certain distances may also be
Data Link
Pro
Challenges
Capacitive coupling Low EMI. Also suit-
able for ring struc-
tures
Requires significant
plate area, challeng-
ing for tiny rotating
couplers, sensitive to
changes of material/
fluids
RF, 60 GHz (OOK,
ASK, QAM)
Large bandwidth
(>1Gbps), low laten-
cy (nanoseconds)
Should generate a
circular polarized
wave to support rota-
tion
RF, 2.4/5 GHz (e.g.
GFSK, MSK, ASK)
Easy near field an-
tenna design (simple
loop), RF solutions
widely available
No high bandwidth
without OFDM, but
that increases la-
tency
RF, sub GHz (e.g.
FSK)
Easy near field an-
tenna design (simple
loop), RF solutions
widely available
Low bandwidth (sub
Mbps)
Via ICPT power link No separate antenna
needed
Low bandwidth (10-
100kbps)
Optical
Very high bandwidth
possible (>10Gbps)
Sensitive to dust and
dirt, precision optics
& lenses needed
Sensors
Special Edition
54 l New-Tech Magazine Europe