56 / 84
coupled power-transfer system is
shown (Figure 2). It consists of a
transmitter coil L1 and a receiver
coil L2. Both coils form a system of
magnetically coupled inductors. An
alternating current in the transmitter
coil generates a magnetic field,
which induces a voltage in the
receiver coil. The efficiency of the
power transfer depends on the
coupling (k) between the inductors
and their quality, defined as their Q
factor.
The coupling is determined by the
distance between the inductors (z)
and the ratio of D2/D. The shape
of the coils and the angle between
them further determines the
effective coupling.
The performance of a wireless
power link can be improved using
resonant
inductive
coupling.
Resonance of a circuit involving
capacitors and inductors occurs
because the collapsing magnetic
field of the inductor generates an
electric current in its windings that
charges the capacitor, and then
the discharging capacitor provides
an electric current that builds the
Figure 3. A complete contactless connectivity design integrates ICPT for power transfer and
2.45GHz wireless for data transmission, all within an M30-type form factor. [Image courtesy of TE
Connectivity]
Figure 4. Implemented in an M30-type connector, the near-field
loop antenna design for a contactless connectivity-based data
link is symmetrical to allow for rotation. [Image courtesy of TE
Connectivity]
through of how it works is useful in
understanding its utility as a wireless
power-transfer mechanism.
Faraday's law of induction states
that the induced electromotive
force in any closed circuit is equal to
the rate of change of the magnetic
flux enclosed by the circuit, or
mathematically as:
Where is the electromotive force
(EMF) and ΦB is the magnetic flux.
The basic principle of an inductively
Sensors
Special Edition
56 l New-Tech Magazine Europe