wireless power transmission based on resonant electrical...
TRANSCRIPT
Wireless power transmission based
on resonant electrical coupling
Ricardo Fernandes,
João Matos, Nuno Carvalho
Department of Electronics, Telecommunications and Informatics, IT, University of Aveiro
Abstract
A novel technique for wirelessly
transferring power over non-
negligible distances is shown in
this poster. This technique is
based on resonance and electrical
coupling. Preliminary
experimental results have shown
that this technique can be used
for wireless power transfer (WPT)
purposes. So far an efficiency of
approximately 40% was obtained
at a distance of 5 meters using a
prototype measuring 16 by 16 cm
by 3.7 cm at most. In this case the
ratio between distance and
maximum dimension of the
prototypes is therefore
approximately 30. The efficiency
of the power transfer remains
stable even if the relative
orientation between the
transmitter and the receiver is
significantly altered.
Some years ago, in 2007, a team of researchers at the Massachusetts
Institute of Technology (MIT) made a substantial contribution to the state of
the art of WPT. They proposed a system composed of 4 copper coils (largest
diameter of 60 cm, wire cross sectional radius of 3 mm). Using this system
they were able to wirelessly light up a 60 W incandescent light bulb across a
2 m gap with an efficiency of 40% (see Fig. 1). The attention given to this
demonstration by both the scientific community and the media was
remarkable. It was shown that a very interesting trade-off between power
transfer capability, efficiency, maximum range, size of the devices involved,
complexity and cost was possible. Previous WPT proposals were, in general,
either very large and expensive or severely limited in terms of maximum
range (see Fig. 2). In this technique the efficiency of the power transfer relies
on the strong magnetic coupling formed between coils with very high Qs
(quality factors) at resonance. The first coil, a single turn loop, is connected to
a power source. The second coil, a multi turn, is placed near the loop on the
same axis. A capacitor is added to the loop in order to make it resonant
precisely at the self-resonant frequency of the multiturn coil. The receiver is
defined identically, except that the loop is connected to the load. The loops
are magnetically coupled to the nearby multi turn coils because of the close
physical proximity. The multiturn coils are magnetically coupled to each other
because the very high Qs counteract the effect of distance. Such high Qs are
only achievable at resonance.
Resonant magnetic coupling (RMC) is now a well established WPT
technique, however, the possibility of a dual technology - resonant electrical
coupling (REC) - was never considered.
The principal objective of this research is to investigate the feasibility of REC
as a novel method for transferring power wirelessly across non-negligible
distances with high efficiency.
Several encouraging results were already achieved:
1) A circuit model which exhibits a very specific behavior (see Figs. 3 and 4)
previously observed only in RMC was found;
2) An efficiency of approximately 40% across a gap of 5 m was obtained in
the laboratory using prototypes with dimensions of 16 by 16 cm by 3.7 cm
at most (see Figs. 5, 6, 7 and 8).
Conclusions
The REC concept was presented for the first time in the 2014 edition of the
IEEE Wireless Power Transfer Conference that took place in Jeju, South
Korea, from May 8 to May 9, 2014. It was considered the best paper in the
conference. Regarding intelectual property, a patent for this technology was
filed in March 14, 2014.
References
Fernandes R. D.; Matos J. N.; Carvalho N. B., “Behavior of resonant electrical
coupling in terms of range and relative orientation”, 2014 IEEE Wireless
Power Transfer Conference (WPTC), 8-9 May 2014.
Fig 3 / Circuit model proposed for resonant
electrical coupling.
Fig 4 / Theoretical behavior of the proposed circuit
model.
Fig 8 / Experimental S21 behavior observed with
the proposed prototype.
Fig 6 / Experimental setup (proposed prototypes,
polystyrene supports and a vectorial network
analyzer).
Fig 7 / Behavior of the S21 parameter considering
the distance between devices shown in the
experiental setup.
Fig 5 / Proposed prototype, measuring 16 by 16
cm by 3.7 cm at most.
Fig 2 / The power toothbrush, a well known
example of wireless charging based on magnetic
coupling (non resonant).
Fig 1 / The first public demonstration of resonant
magnetic coupling (carried out by MIT researchers,
in 2007).