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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
Figure 2. In inductive coupling, the coupling is determined by the
distance (z) and the ratio of D2/D, while the efficiency of power
transfer between transmitting coil L1 and receiver coil L2 depends
on the coupling (k) between the inductors and their Q factor
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.
•
Environmental 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
Data Link
Pro
Challenges
Capacitive coupling
Low EMI. Also suitable
for ring structures
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 latency
(nanoseconds)
Should generate a cir-
cular polarized wave to
support rotation
RF, 2.4/5 GHz (e.g.
GFSK, MSK, ASK)
Easy near field antenna
design (simple loop),
RF solutions widely
available
No high bandwidth
without OFDM, but that
increases latency
RF, sub GHz (e.g. FSK) Easy near field antenna
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
New-Tech Magazine Europe l 31