wireless power transmission based on resonant electrical...

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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).

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Page 1: Wireless power transmission based on resonant electrical ...uaonline.ua.pt/upload/med/joua_m_2969.pdfWireless power transmission based on resonant electrical coupling Ricardo Fernandes,

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).