U.S. patent application number 11/960072 was filed with the patent office on 2009-06-25 for wireless energy transfer.
This patent application is currently assigned to NOKIA CORPORATION. Invention is credited to Harri Heikki Tapani ELO.
Application Number | 20090160261 11/960072 |
Document ID | / |
Family ID | 40547460 |
Filed Date | 2009-06-25 |
United States Patent
Application |
20090160261 |
Kind Code |
A1 |
ELO; Harri Heikki Tapani |
June 25, 2009 |
WIRELESS ENERGY TRANSFER
Abstract
An apparatus comprising monitoring circuitry configured to
monitor a resonant frequency of a supply source, a receiving
component, and a control unit configured to vary a resonant
frequency of said receiving component, wherein the apparatus is
configured to vary the resonant frequency of said receiving
component in dependence of the resonant frequency of said supply
source.
Inventors: |
ELO; Harri Heikki Tapani;
(Helsinki, FI) |
Correspondence
Address: |
Locke Lord Bissell & Liddell LLP;Attn: IP Docketing
Three World Financial Center
New York
NY
10281-2101
US
|
Assignee: |
NOKIA CORPORATION
Espoo
FI
|
Family ID: |
40547460 |
Appl. No.: |
11/960072 |
Filed: |
December 19, 2007 |
Current U.S.
Class: |
307/104 |
Current CPC
Class: |
H02J 7/025 20130101;
H01F 38/14 20130101; H02J 50/90 20160201; H02J 50/40 20160201; H02J
50/12 20160201 |
Class at
Publication: |
307/104 |
International
Class: |
H01F 27/42 20060101
H01F027/42 |
Claims
1. An apparatus comprising: monitoring circuitry configured to
monitor a resonant frequency of a supply source; a receiving
component; and a control unit configured to vary a resonant
frequency of said receiving component, wherein the apparatus is
configured to vary the resonant frequency of said receiving
component in dependence of the resonant frequency of said supply
source.
2. An apparatus according to claim 1, wherein the receiving
component is adapted to receive energy Tirelessly from the supply
source by resonant inductive coupling.
3. An apparatus according to claim 2, wherein the apparatus further
comprises a plurality of electrical components, and the apparatus
is configured to supply electrical energy to at least one of these
electrical components.
4. An apparatus according to claim 3, further comprising a battery
for supplying electrical energy to at least one of the electrical
components when energy is not being received from the supply
source.
5. An apparatus according to claim 1, wherein the receiving
component comprises an adaptive receiving component having a
variable resonant frequency.
6. An apparatus according to claim 1, wherein the apparatus is
configured to match the resonant frequency of said receiving
component with the resonant frequency of said supply source.
7. An apparatus according to claim 1, wherein a voltage is induced
in the receiving component by a magnetic field generated by the
supply source, and the control unit is configured to vary the
resonant frequency of the receiving component to match the resonant
frequency of the supply source.
8. An apparatus according to claim 1, wherein the apparatus
comprises a portable electronic device.
9. An apparatus according to claim 1, wherein the apparatus
comprises a mobile telephone.
10. An apparatus according to claim 1, wherein the apparatus
comprises a personal digital assistant (PDA).
11. An apparatus according to claim 1, wherein the apparatus
comprises a laptop computer.
12. An apparatus comprising: means for detecting a presence of a
supply source; means for monitoring a resonant frequency of said
supply source; and means for varying a resonant frequency of a
receiving component in dependence of the resonant frequency of said
supply source.
13. An apparatus comprising a receiving component having variable
resonance characteristics for receiving energy wirelessly from a
supply source, wherein the resonance characteristics of the
receiving component may be varied to match resonance
characteristics of the supply source to increase the efficiency at
which energy is received from the supply source.
14. An apparatus according to claim 13, further comprising
monitoring circuitry for detecting and monitoring the resonance
characteristics of the supply source.
15. An apparatus according to claim 13, wherein the receiving
component comprises an adaptive receiving component having variable
resonance characteristics and the apparatus further comprises: a
control unit configured to automatically vary the resonance
characteristics of the adaptive receiving component to match the
resonance characteristics of the supply source.
16. An apparatus according to claim 13, wherein the apparatus
further comprises one or more electrical components and the
receiving component is coupled to power supply circuitry to supply
power to at least one of these electrical components.
17. An apparatus according to claim 16, further comprising a
battery for supplying electrical energy to at least one of the
electrical components when energy is not being received from the
supply source.
18. An apparatus according to claim 13, wherein the apparatus
comprises a portable electronic device.
19. An apparatus according to claim 13, wherein the apparatus
comprises a mobile telephone.
20. An apparatus according to claim 13, wherein the apparatus
comprises a personal digital assistant (PDA).
21. An apparatus according to claim 13, wherein the apparatus
comprises a laptop computer.
22. A system comprising: a supply source; and an apparatus
comprising: monitoring circuitry configured to monitor a resonant
frequency of the supply source; a receiving component; and a
control unit configured to vary a resonant frequency of said
receiving component, wherein the apparatus is configured to vary
the resonant frequency of said receiving component in dependence of
the resonant frequency of said supply source.
23. A method comprising: detecting a presence of a supply source;
monitoring a resonant frequency of said supply source; and varying
a resonant frequency of a receiving component in dependence of the
resonant frequency of said supply source.
24. A method according to claim 23, further comprising: matching
the resonant frequency of said receiving component with the
resonant frequency of said supply source.
25. A method according to claim 23, further comprising: receiving
energy wirelessly at the receiving component from the supply source
by resonant inductive coupling.
26. A method according to claim 23, wherein said receiving
component comprises an adaptive receiving component having a
variable resonant frequency and the method further comprises:
inducing a voltage in the adaptive receiving component using a
magnetic field generated by the supply source; and varying the
resonant frequency of the adaptive receiving component to match the
resonant frequency of the supply source.
27. A method according to claim 23, further comprising supplying
electrical energy to an electrical apparatus.
28. A method according to claim 23, further comprising: receiving
energy at the receiving component from the supply source by
resonant inductive coupling; supplying energy received by resonant
inductive coupling to at least one component of an electrical
device; and supplying energy to at least one component of an
electrical device from a battery when energy is not being received
at the receiving component from the supply source.
29. A computer program product comprising a computer-readable
medium having computer-readable program code embodied in said
medium, comprising: a computer-readable program code configured to
detect a presence of a supply source; a computer-readable program
code configured to monitor a resonant frequency of said supply
source; and a computer-readable program code configured to vary a
resonant frequency of a receiving component in dependence of the
resonant frequency of said supply source.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to wireless energy transfer,
particularly, but not exclusively, to wireless energy transfer
between a supply source and a receiving component.
BACKGROUND OF THE INVENTION
[0002] It is common practice for a portable electronic device, for
example a mobile telephone or a laptop computer, to be powered by a
rechargeable chemical battery. Generally speaking, such a battery
is releasably connected to the body of a portable device.
[0003] The use of a battery for supplying power to a portable
electronic device is not ideal because the energy storage capacity
of a chemical battery is limited. As such, it is necessary for the
chemical battery to be recharged at regular intervals.
[0004] In order to provide a means for recharging the battery, the
portable device is normally supplied with a charging means for
allowing electrical energy to flow from a mains power supply to the
rechargeable battery. The charging means is usually in the form of
a charger unit, which conventionally comprises an electrical plug
for connecting to a mains power supply socket and an electrical
cable for connecting the electrical plug to the portable
device.
[0005] This is disadvantageous because, if there is no convenient
mains power supply socket, as is the case in most outdoor and
public environments, the rechargeable battery will run out of power
and the portable device will need to be switched off.
[0006] The use of such a charger unit is further disadvantageous in
that it requires a physical connection between the portable device
and a mains power supply socket. This severely restricts the
movement of the portable device during charging, thereby negating
the portability of the device.
[0007] Another type of charger unit makes use of the principle of
conventional, short-range inductive coupling, which involves the
transfer of energy from a primary inductor in a charger unit to a
secondary inductor in the portable device. Such charger units are
commonly used, for example, for charging rechargeable batteries in
electric toothbrushes.
[0008] Chargers utilising this type of conventional inductive
coupling are able to transfer power wirelessly and hence do not
require a physical connection between the mains supply and the
portable device. However, the maximum distance over which effective
power transfer can be achieved is limited to distances of the same
order of magnitude as the physical dimensions of the inductors. For
portable electronic devices, the dimensions of the inductor are
limited by the size of the portable electronic device. Accordingly,
in general, at distances of anything greater than a few
centimetres, the efficiency of energy transfer between primary and
secondary inductors is too small for this type of power transfer to
be viable.
[0009] Therefore, as with the electrical cable discussed above,
power transfer using conventional inductive coupling requires the
charger unit and the portable device to be in very close proximity,
meaning that the movement of the portable device is severely
restricted.
[0010] In addition to the above problems associated with
recharging, the use of a chemical battery as a power supply
presents a number of further disadvantages. For example,
rechargeable chemical batteries have a limited lifespan and tend to
experience a decrease in their maximum storage capacity as they get
older. Furthermore, chemical batteries are relatively heavy,
meaning that the inclusion of a chemical battery in a portable
device generally adds a significant percentage to the device's
overall weight. If the device's reliance on the chemical battery
could be reduced, then it would be possible for portable electronic
devices such as mobile telephones to become significantly
lighter.
SUMMARY OF THE INVENTION
[0011] According to a first example of the invention, there is
provided an apparatus comprising monitoring circuitry configured to
monitor a resonant frequency of a supply source, a receiving
component, and a control unit configured to vary a resonant
frequency of said receiving component, wherein the apparatus is
configured to vary the resonant frequency of said receiving
component in dependence of the resonant frequency of said supply
source
[0012] The receiving component of the apparatus described in the
immediately preceding paragraph may be adapted to receive energy
wirelessly from the supply source by resonant inductive
coupling.
[0013] The receiving component of the apparatus described in either
of the immediately preceding paragraphs may comprise an adaptive
receiving component having a variable resonant frequency.
[0014] The apparatus described in any of the three immediately
preceding paragraphs may be configured to match the resonant
frequency of said receiving component with the resonant frequency
of said supply source.
[0015] A voltage may be induced in the receiving component of the
apparatus described in any of the four immediately preceding
paragraphs by a magnetic field generated by the supply source, and
the control unit may be configured to vary the resonant frequency
of the receiving component to match the resonant frequency of the
supply source.
[0016] The apparatus described in any of the four immediately
preceding paragraphs may further comprise a plurality of electrical
components, and the apparatus may be configured to supply
electrical energy to at least one of these electrical
components.
[0017] The apparatus described in the immediately preceding
paragraph may further comprise a battery for supplying electrical
energy to at least one of the electrical components when energy is
not being received from the supply source.
[0018] The apparatus described in any of the preceding paragraphs
may comprise a portable electronic device.
[0019] The apparatus described in any of the preceding paragraphs
may comprise a mobile telephone, personal digital assistant (PDA)
or laptop computer.
[0020] According to a second example of the invention, there is
provided an apparatus comprising means for detecting a presence of
a supply source, means for monitoring a resonant frequency of said
supply source, and means for varying a resonant frequency of a
receiving component in dependence of the resonant frequency of said
supply source.
[0021] According to a third example of the invention, there is
provided an apparatus comprising a receiving component having
variable resonance characteristics for receiving energy wirelessly
from a supply source, wherein the resonance characteristics of the
receiving component may be varied to match resonance
characteristics of the supply source to increase the efficiency at
which energy is received from the supply source.
[0022] The apparatus described in the immediately preceding
paragraph may further comprise monitoring circuitry for detecting
and monitoring the resonance characteristics of the supply
source.
[0023] The receiving component of the apparatus described in either
of the two immediately preceding paragraphs may comprise an
adaptive receiving component having variable resonance
characteristics and the apparatus may further comprise a control
unit configured to automatically vary the resonance characteristics
of the adaptive receiving component to match the resonance
characteristics of the supply source.
[0024] The apparatus described in any of the three immediately
preceding paragraphs may further comprise one or more electrical
components and the receiving component may be coupled to power
supply circuitry to supply power to at least one of these
electrical components.
[0025] The apparatus described in the immediately preceding
paragraph may further comprise a battery for supplying electrical
energy to at least one of the electrical components when energy is
not being received from the supply source.
[0026] The apparatus described in any of the five immediately
preceding paragraphs may comprise a portable electronic device.
[0027] The apparatus described in any of the six immediately
preceding paragraphs may comprise a mobile telephone, personal
digital assistant (PDA) or laptop computer.
[0028] According to a fourth example of the invention, there is
provided a system comprising a supply source, and an apparatus
comprising monitoring circuitry configured to monitor a resonant
frequency of the supply source, a receiving component, and a
control unit configured to vary a resonant frequency of said
receiving component, wherein the apparatus is configured to vary
the resonant frequency of said receiving component in dependence of
the resonant frequency of said supply source.
[0029] According to a fifth example of the invention, there is
provided a method comprising detecting a presence of a supply
source, monitoring a resonant frequency of said supply source, and
varying a resonant frequency of a receiving component in dependence
of the resonant frequency of said supply source.
[0030] The method described in the immediately preceding paragraph
may further comprise matching the resonant frequency of said
receiving component with the resonant frequency of said supply
source.
[0031] The method described in either of the two immediately
preceding paragraphs may further comprise receiving energy
wirelessly at the receiving component from the supply source by
resonant inductive coupling.
[0032] The receiving component of the method described in any of
the three immediately preceding paragraphs may comprise an adaptive
receiving component having a variable resonant frequency and the
method may further comprise inducing a voltage in the adaptive
receiving component using a magnetic field generated by the supply
source, and varying the resonant frequency of the adaptive
receiving component to match the resonant frequency of the supply
source.
[0033] The method described in any of the four immediately
preceding paragraphs may further comprise supplying electrical
energy to an electrical apparatus.
[0034] The method of the immediately preceding paragraph may
further comprise supplying energy to at least one component of an
electrical device from a battery when energy is not being received
at the receiving component from the supply source.
[0035] The method of the paragraph six paragraphs above this one
may further comprise receiving energy at the receiving component
from the supply source by resonant inductive coupling, and
supplying energy received by resonant inductive coupling to at
least one component of an electrical device.
[0036] According to a sixth example of the invention, there is
provided a computer program stored on a storage-medium which, when
executed by a processor, is arranged to perform a method comprising
detecting a presence of a supply source, monitoring a resonant
frequency of said supply source, and varying a resonant frequency
of a receiving component in dependence of the resonant frequency of
said supply source.
BRIEF DESCRIPTION OF THE DRAWINGS
[0037] In order that the invention may be more fully understood,
embodiments thereof will now be described by way of illustrative
example with reference to the accompanying drawings in which:
[0038] FIG. 1 is a diagram showing a flow of energy from a feeding
device to a portable electronic device.
[0039] FIG. 2 is a circuit diagram of primary and secondary RLC
resonator circuits with coupling coefficient K.
[0040] FIG. 3 is a circuit diagram of an equivalent transformer
circuit for the first and second RLC resonator circuits shown in
FIG. 2.
[0041] FIG. 4 is a circuit diagram of a reduced circuit of the
equivalent transformer circuit shown in FIG. 3.
[0042] FIG. 5 shows the impedances of the individual components of
the equivalent transformer circuit shown in FIG. 3.
[0043] FIG. 6 is a graphical illustration of the relationship
between the efficiency of power transfer between two resonators and
the difference between the resonators' resonant frequencies.
[0044] FIG. 7 is an illustration of a wireless transfer of energy
from a feeding device to a portable electronic device at mid-range
using conventional inductive coupling.
[0045] FIG. 8 is an illustration of a wireless transfer of energy
from a feeding device to a portable electronic device at mid-range
using resonant inductive coupling.
[0046] FIG. 9 is a schematic diagram of a portable electronic
device, including a reactance and monitoring circuitry.
[0047] FIG. 10 is a schematic diagram showing components of a
wireless power transfer apparatus in a portable electronic
device.
[0048] FIG. 11 is a schematic diagram showing an adaptive receiving
component in a wireless power transfer apparatus of a portable
electronic device.
[0049] FIG. 12 is a flow diagram showing steps associated with the
initiation of wireless power transfer by resonant inductive
coupling.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0050] Referring to FIG. 1, a feeding device 100 comprises a supply
source 110 for supplying power wirelessly to a portable electronic
device 200. The supply source 110 comprises a primary reactance,
for example comprising a primary inductor 111, adapted to receive
an electrical current from an electrical circuit 112. The
electrical circuit 112 may be optionally connected to a power
supply, for example comprising a mains power supply 300, for
supplying electrical current to the electrical circuit 112. The
primary inductor 111 has an inductance L.sub.111, Q-factor
Q.sub.111 and resonant frequency f.sub.0(111).
[0051] As will be understood by a skilled person, a flow of
electrical current through the primary inductor 111 causes a
magnetic field 400 to be created around the primary inductor 111.
As is shown by FIG. 1, the magnetic field 400 created around the
inductor 111 penetrates the exterior of the feeding device 100,
meaning that the effects of the magnetic field 400 may be
experienced in the surrounding environment. For instance, the
magnetic field 400 may be used to induce a voltage in a receiving
component comprising a secondary reactance, such as a secondary
inductor in an electrical device. This is the principle upon which
wireless energy transfer through conventional short-range inductive
coupling is based. However, efficient wireless energy transfer by
such conventional short-range inductive coupling is limited to
distances of the same order of magnitude as the physical dimensions
of the inductors involved in the energy transfer.
[0052] As is fully described below, the portable electronic device
200 is adapted to receive energy wirelessly by an alternative type
of inductive coupling. This alternative type of inductive coupling
will be referred to as resonant inductive coupling.
[0053] Using resonant inductive coupling, is it possible to
efficiently transfer energy over longer distances than over those
possible with conventional inductive coupling. This means that
resonant inductive coupling provides a greater degree of freedom
and flexibility than conventional inductive coupling when used for
the transfer of energy. As is described in more detail below,
resonant inductive coupling is based on inductive coupling in which
the resonant frequency f.sub.0 of a supply source and the resonant
frequency f.sub.0 of a receiving component are equal to one
another.
[0054] More specifically, if the resonant frequency f.sub.0
associated with a primary reactance, for example the resonant
frequency f.sub.0(111) associated with the inductor 111 in the
feeding device 100, is equal to the resonant frequency f.sub.0
associated with a secondary reactance, for example a receiving
component comprising a secondary inductor in a portable electronic
device 200, placed in a magnetic field generated by the primary
reactance, efficient wireless energy transfer between the primary
and secondary reactances can be achieved at longer ranges than is
possible with conventional inductive coupling.
[0055] For example, wireless energy transfer with an efficiency of
tens of percent may be achieved by resonant inductive coupling over
distances at least one order of magnitude greater than the physical
dimensions of the inductors being used for the transfer.
[0056] A general example of wireless energy transfer between two
inductors by resonant inductive coupling is given below.
[0057] Referring to FIG. 2, there are shown primary and secondary
RLC resonator circuits 500, 600. The primary RLC circuit 500
comprises a first inductor (L.sub.1) 510, a first capacitor
(C.sub.1) 520 and a first resistor (R.sub.1) 530. The secondary RLC
circuit 600 comprises a second inductor (L.sub.2) 610, a second
capacitor (C.sub.2) 620 and a second resistor (R.sub.2) 630. In
this example, L.sub.1=L.sub.2 and C.sub.1=C.sub.2.
[0058] The primary RLC circuit 500 is connected to a power source,
comprising a time-dependent current source (i.sub.SUPPLY(t)) 540.
The time-dependency of the current source 540 is such that the
current may take the form of a sine wave, tuned to the resonant
frequency
f 0 = 1 2 .pi. L 1 C 1 = 1 2 .pi. L 2 C 2 ##EQU00001##
of both the first and second RLC circuits 500, 600.
[0059] The second RLC circuit 600 is connected to a load,
represented in FIG. 2 as a DC current source (i.sub.LOAD) 640. The
current from the DC current source 640 is zero when energy is not
being transferred between the first and second RLC circuits 500,
600.
[0060] The Q-values associated with the first and second resonator
circuits 500, 600 are represented by the first and second resistors
530, 630. As is explained in more detail below, the magnitude of
the Q-values of the resonator circuits 500, 600 is proportional to
the efficiency of energy transfer between the circuits 500,
600.
[0061] In this general example, the inductors 510, 610 are
separated by a distance approximately one order of magnitude
greater than the physical dimensions of the inductors 510, 610
themselves. At this range, the coupling coefficient K between the
inductors 510, 610 is small, for example 0.001 or less, meaning
that any attempt to transfer energy between the resonator circuits
500, 600 by conventional inductive coupling would be extremely
inefficient.
[0062] FIG. 3 shows an equivalent transformer circuit for the first
and second RLC resonator circuits 500, 600. When the frequency of
the time-dependent current source 540 is not equal to the resonant
frequency f.sub.0 of the second RLC resonator circuit 600, the
second resonator circuit is bypassed due to negligible inductance
LK. As such, very little or no power is transferred to the load.
However, when the conditions for resonant inductive coupling are
met, this situation is reversed as is explained below.
[0063] A first condition for energy transfer by resonant inductive
coupling is that the Q-values (represented by the resistors 530,
630) of the resonator circuits 500, 600 are very high, for example
one hundred or more. A second condition for energy transfer by
resonant inductive coupling is that the resonant frequencies
f.sub.0 of the circuits 500, 600 are equal to one another. When
these conditions are met, and current is supplied by the current
source 540 at
f 0 = 1 2 .pi. L 1 C 1 , ##EQU00002##
current in the first inductor 510 is routed via the second inductor
610. Under these conditions, the inductance LK in the equivalent
transformer circuit shown in FIG. 3 is tuned with the secondary
resonator circuit. As such, the equivalent transformer circuit
shown in FIG. 3 can be reduced to the circuit of a single
electrical resonator, as shown by FIG. 4. There is no limit on the
number of secondary resonator circuits which could receive current
from a primary resonator circuit in this way.
[0064] The impedances of the individual components of the
equivalent transformer circuit shown in FIG. 3 are shown in FIG. 5.
The impedance Z of the reduced circuit can thus be calculated as
follows:
Z = j.omega. L K Z secondary j.omega. L K + Z secondary
##EQU00003##
[0065] Assuming the Q-value of the secondary resonator circuit 600
is high, Z.sub.secondary may be written as:
Z secondary = j.omega. L ( 1 - K ) + 1 / j.omega. C .thrfore. Z = j
.omega. L K ( j.omega. L ( 1 - K ) + 1 / j.omega. C ) j.omega. L K
+ ( j.omega. L ( 1 - K ) + 1 / j.omega. C ) = j.omega. L K (
j.omega. L ( 1 - K ) - j.omega. L ) j.omega. L K + ( j.omega. L ( 1
- K ) - j.omega. L ) = j.omega. L K ( - j.omega. L K ) j.omega. L K
- j.omega. L K ##EQU00004##
.thrfore.|Z|.fwdarw..infin. as the conditions for resonant
inductive coupling are reached.
[0066] In this way, a secondary resonator circuit may be tuned so
as to receive energy by resonant inductive coupling from any
primary resonator circuit.
[0067] FIG. 6 illustrates a general relationship between the
efficiency of wireless energy transfer .eta. through inductive
coupling between primary and secondary reactances separated by a
distance one order of magnitude larger than the physical dimensions
of the reactances. The efficiency of wireless energy transfer .eta.
is plotted on the vertical axis using a logarithmic scale, and the
difference in resonant frequency f.sub.0 between the reactances is
plotted on the horizontal axis. This relationship is applicable to,
for example, wireless energy transfer between the primary inductor
111 of the feeding device 100 and a secondary inductor 211 of a
portable device 200 shown in FIG. 7.
[0068] As can be seen, the efficiency of wireless energy transfer
.eta. between the reactances is at a maximum when the resonant
frequencies f.sub.0 associated with the reactances are equal to one
another. Moreover, the efficiency of wireless energy transfer .eta.
between the reactances decreases markedly as the difference between
the resonant frequencies f.sub.0 associated with the reactances
increases. Accordingly, as discussed above, in order to transfer
energy at the maximum possible efficiency it is preferable for the
reactances to have resonant frequencies f.sub.0 which are as close
to each other as possible. Ideally, the resonant frequencies
f.sub.0 should be identical.
[0069] In addition, as previously discussed, the efficiency of
energy transfer between primary and secondary reactances is
proportional to the magnitude of the Q-values associated with the
reactances; for a high efficiency of energy transfer, the magnitude
of the Q-values should be large. For example, in the case of the
primary and secondary inductors 111, 211 discussed above in
relation to the transfer of energy from the feeding device 100 to
the portable device 200, efficient energy transfer may be achieved
with Q-values Q.sub.111, Q.sub.211 in the order of 100.
Furthermore, the relative difference between the resonant
frequencies f.sub.0(111), f.sub.0(211) associated with the
inductors 111, 211 should be less that the reciprocal of their
associated Q-values. At relative differences greater than the
reciprocal of the Q-values, the efficiency of energy transfer
decreases by 1/Q.sup.2.
[0070] FIGS. 7 and 8 illustrate the difference between conventional
inductive coupling and resonant inductive coupling when the
distance between reactances, for example the primary and secondary
inductors 111, 211, is one order of magnitude greater than the
reactances' physical dimensions. Referring to FIG. 7, with
conventional inductive coupling, i.e. when the difference between
the resonant frequencies associated with the inductors 111, 211 is
outside of the limits discussed above, only a negligible amount of
energy in the magnetic field 400 is passed from the primary
inductor 111 to the secondary inductor 211 in the portable device
200. In contrast, referring to FIG. 8, when the resonant
frequencies f.sub.0 associated with the inductors 111, 211 are
matched, energy is able to tunnel by resonant inductive coupling
from the primary inductor 111 in the feeding device 100 to the
secondary inductor 211 in the portable electronic device 200 via
the magnetic field 400.
[0071] For the purposes of simplicity and clarity, the above
example discusses the transfer of energy from a primary inductor
111 to a single secondary inductor 211. However, alternatively,
energy can be transferred from the primary inductor 111 to a
plurality of secondary inductors 211 all being associated with the
same resonant frequency f.sub.0, potentially enabling multiple
portable devices 200 to receive energy wirelessly from a single
feeding device 100.
[0072] In this way, feeding devices 100 are able to supply energy
to portable electronic devices 200 over mid-ranges, for example
several metres, in environments in which it is not convenient to
install mains power sockets. As an example, in a similar manner to
the installation of wireless LANS in cafes and restaurants, a
network 700 of feeding devices 100 could be installed throughout a
public space to provide members of the public with a power supply
for their portable electronic devices 200. Such a public space
could be, for example, a cafe, restaurant, bar, shopping mall or
library. Alternatively, feeding devices may be installed in private
spaces such as, for example, the interior of a person's car or
home.
[0073] In order to maximise the potential of such a network 700 of
feeding devices 100, it is preferable that the feeding devices 100
have the capacity to supply energy to as many portable devices 200
as possible. One way in which this could be achieved is to
implement a degree of standardization in the properties of the
reactances, for example the primary and secondary inductors 111,
211, used in the feeding devices 100 and portable electronic
devices 200. In particular, it would be preferable if the resonant
frequency f.sub.0 associated with the primary reactance in each
feeding device 100 of the network 700 was the same. This would
enable manufacturers of portable devices 200 and other electrical
devices to equip their devices with secondary reactances associated
with the same standardized resonant frequency f.sub.0.
[0074] A skilled person will appreciate, however, that due to
manufacturing tolerances, the mass production of inductors to a
degree of accuracy in which all the inductors are associated with
exactly the same resonant frequency f.sub.0 may be difficult to
achieve. This will lead to variations in both the resonant
frequencies f.sub.0 of feeding devices 100, and to variations in
the resonant frequencies f.sub.0 of portable devices 200.
Furthermore, even if feeding devices 100 and portable devices 200
can be manufactured with identical resonant frequencies f.sub.0 in
free space, the resonant frequencies f.sub.0 of each individual
unit will be affected when in use by other inductors in the unit's
surrounding environment. The amount by which the resonant frequency
of each unit is altered will depend on the number and proximity of
other inductors.
[0075] Thus, even when attempts have made to standardize the
resonant frequencies f.sub.0 of feeding devices and portable
devices, manufacturing intolerances and environmental conditions
still have the potential to cause problems for energy transfer by
resonant inductive coupling.
[0076] One way to alleviate this problem is to provide portable
electronic devices 200 with a wireless energy transfer apparatus
210 for altering the resonant frequency f.sub.0 associated with
their secondary inductors 211 post-manufacture in dependence of the
properties of a nearby feeding device 100. This provides portable
electronic devices 200 with the ability to tune their inductor's
resonant frequency f.sub.0 to match that associated with the
primary inductor 111 in a nearby feeding device 100 and thus
receive energy wirelessly by resonant inductive coupling.
[0077] An exemplary embodiment of a portable electronic device 200
adapted to receive energy wirelessly by resonant inductive coupling
is given below. Referring to FIG. 9, the portable electronic device
200 comprises a wireless energy transfer apparatus 210, comprising
a power supply unit (PSU), for receiving energy from a magnetic
field and supplying electrical energy to electrical components 240
of the portable device 200. Alternatively, as discussed below,
electrical energy may be supplied to a rechargeable chemical
battery 250 of the portable electronic device 200.
[0078] In the example discussed below, the magnetic field will be
referred to in the context of the magnetic field 400 created by
current flowing through the primary inductor 111 in a feeding
device 100. However, a skilled person will appreciate that the
magnetic field could alternatively correspond to a magnetic field
created by another feeding device, or any other suitable magnetic
field source.
[0079] The wireless energy transfer apparatus 210 is controlled by
a microcontroller 220 and comprises a receiving component 211a,
comprising at least one reactance, for receiving energy wirelessly
from the magnetic field 400 by resonant inductive coupling. In this
example, the receiving component 211a comprises a secondary
inductor 211. The inductor 211 is associated with an inductance
L.sub.211, Q-factor Q.sub.211 and resonant frequency f.sub.0(211).
The microcontroller 220 may be integrated into the energy transfer
apparatus 210.
[0080] The wireless energy transfer apparatus 210 further comprises
monitoring circuitry 230 configured to detect a magnetic field 400
created by the primary inductor 111 in the feeding device 100, as
is described in more detail below. Upon detecting the magnetic
field 400, the monitoring circuitry 230 and microcontroller 220 are
further configured to detect and monitor the resonant frequency
f.sub.0(111) associated with the primary inductor 111.
[0081] The features of the monitoring circuitry 230 allow the
portable device 200 to wirelessly receive energy over mid-range
distances, for example distances at least one order of magnitude
greater than the physical dimensions of the primary and secondary
inductors 111, 211.
[0082] Referring to FIG. 10 in combination with FIG. 9, the
secondary inductor 211 of the wireless energy transfer apparatus
210 has a parasitic capacitance C and is connected to a plurality
of switched-mode power supplies (SMPSs) 212 via a diode-bridge 213
and LC filter 214. The purpose of the LC filter 214 is to ensure
that a constant reactive load is introduced to the secondary
inductor 211. If the inductor 211 were to be loaded resistively,
there would be a significant decrease in the Q-value Q.sub.(211)
associated with the inductor 211, which would in turn significantly
reduce the efficiency of the transfer of energy from the feeding
device 100, as previously discussed.
[0083] The diode-bridge 213 and LC filter 214 also protect the
inductor 211 from direct exposure to the strongly time-varying load
presented by the SMPSs 212, which are configured to supply power
received from the magnetic field 400 to various circuits of the
portable electronic device 200. The SMPSs 212 may be configured,
for example, to supply power to a rechargeable chemical battery 250
of the portable electronic device 200, as shown in FIG. 9, for
recharging.
[0084] Alternatively the SMPSs 212 may be configured to supply
power directly to electrical components 240 of the portable
electronic device 200, with the chemical battery 250 acting as a
reserve power source. For example, the chemical battery 250 may be
configured only to supply power to electrical components 240 of the
portable electronic device 200 when the wireless energy transfer
apparatus 210 is not receiving power by resonant inductive
coupling. If feeding devices 100 were to become widespread, the
inclusion of the rechargeable battery 250 in the portable device
200 could become unnecessary.
[0085] Referring to FIG. 11, in this example of the portable
electronic device 200, the receiving component 211a is adaptive.
This allows the resonance characteristics associated with the
secondary inductor 211 to be tuned to match the resonance
characteristics associated with the primary inductor 111 in the
feeding device 100. This provides the degree of tuneability
necessary for the resonant frequency f.sub.0(211) associated with
the secondary inductor 211 to be varied, should the resonant
frequency f.sub.0(211) not be identical to that associated with the
primary inductor 111 in the feeding device 100.
[0086] In more detail, as is shown by FIG. 11, the receiving
component 211a comprises the secondary inductor 211 optionally
coupled to an array of capacitors 215, each capacitor 215 having a
different capacitance to each of the others. For example, as shown
by FIG. 11, the capacitors 215 may comprise N capacitors with
capacitances C.sub.0, C.sub.0/2, . . . C.sub.0/2.sup.N-1. Each of
the capacitors 215 may be optionally coupled to the secondary
inductor 211 to affect the capacitance C.sub.211 of the receiving
component 211a, thereby varying the resonant frequency f.sub.0(211)
associated with the inductor 211 and providing a mechanism for the
portable device 200 to match the resonant frequency f.sub.0(211)
associated with the secondary inductor 211 with the resonant
frequency f.sub.0(111) associated with the primary inductor 111 in
the feeding device 100. It will be appreciated that the resonant
frequency f.sub.0(211) associated with the secondary inductor 211
could alternatively be varied by altering the inductance of the
receiving component 211a.
[0087] In this implementation, as is shown by FIG. 11, the array of
capacitors 215 is coupled to a control unit 216 in the
microcontroller 220 for automatically controlling the capacitance
C.sub.211 of the receiving component 211a in dependence of a
control signal from the monitoring circuitry 230. The
microcontroller 220 may comprise a memory and signal processing
means 217, for example including a microprocessor 218, configured
to implement a computer program for detecting and monitoring the
resonant frequency associated with the primary inductor 111 through
the monitoring circuitry 230 and analysing the control signal from
the monitoring circuitry 230 to vary the resonant frequency
associated with the secondary inductor 211 by connecting and
disconnecting the individual capacitors 215.
[0088] In this way, the control unit 216 is able to adapt the
resonant frequency f.sub.0(211) associated with the secondary
inductor 211 to make it equal to the resonant frequency
f.sub.0(111) associated with the primary inductor 111, thereby
initiating resonant inductive coupling between the primary inductor
111 and the secondary inductor 211.
[0089] The monitoring circuitry 230 may be coupled to an output
from the LC filter 214 to detect signals from the secondary
inductor 211 and thus to detect when the portable electronic device
200 is in the presence of a magnetic field 400. For example, the
output of the LC filter 214 may be coupled to an input of an AD
converter 231, which may be integrated into the microcontroller
220, for sensing a voltage induced in the secondary inductor 211
and for supplying corresponding signals to the microcontroller 220
for calculating the resonant frequency associated with the primary
inductor 111. The resonant frequency associated with the secondary
inductor 211 may then be varied to match the calculated resonant
frequency of the primary inductor 111.
[0090] Alternatively, as shown by FIG. 9, the monitoring circuitry
230 may comprise a separate coil 232 for supplying induced voltage
signals to the AD converter 231.
[0091] The monitoring circuitry 230 is sensitive to very small
induced voltages, for example of the order of microvolts, and thus
is configured such that it is able to detect a magnetic field 400
even when the secondary inductor 211 is in a detuned state. The
monitoring circuitry 220 is thus able to detect the presence of a
primary inductor 111 even when then the resonant frequency
f.sub.0(111) associated with the primary inductor 111 is not equal
to the resonant frequency f.sub.0(211) set for the secondary
inductor 211 in the portable electronic device 200.
[0092] As shown by FIG. 11, the wireless energy transfer apparatus
210 may include a memory 219 for storing frequency values
corresponding to resonant frequencies f.sub.0 in different
environments, such that the resonant frequency associated with the
secondary inductor 211 can be automatically adjusted upon the
portable electronic device 200 entering a particular environment.
For example, such automatic adjustment could be prompted by a
control signal, received through an aerial of the portable device
200, indicating that the device 200 has entered a familiar
environment. The memory 219 may also be suitable for storing tuning
values between various life cycle states. The memory 219 may
comprise non-volatile memory in order that the various resonant
frequency values f.sub.0 stored in the memory 219 are not lost when
the device 200 is switched-off.
[0093] Steps associated with the initiation of a wireless energy
transfer between a supply source 110, for example comprising a
primary inductor 111, and the portable electronic device 200 in the
manner described above are shown in FIG. 12.
[0094] Referring to FIG. 12, as described above, the first step S1
is to detect the presence of the supply source 110 by detecting the
presence of its associated magnetic field 400 from an induced
voltage at the monitoring circuitry 230. The supply source 110 may
comprise a primary inductor 111 in a feeding device 100. The second
step S2 is to calculate and monitor the resonant frequency of the
supply source 110, and the third step S3 is vary the resonant
frequency of the receiving component 211a, comprising the secondary
inductor 211, in dependence of the resonant frequency of the supply
source 110. In order to initiate wireless energy transfer with the
highest possible efficiency, the third step S3 involves matching
the resonant frequency of the receiving component 211a with the
resonant frequency of the supply source 110. Upon completing these
steps, the fourth step S4 is to receive energy wirelessly from the
supply source 110 at the receiving component 211a by resonant
inductive coupling, and the fifth step S5 is to supply the energy
to one or more components 240 of the portable device 200.
[0095] If wireless energy transfer between the supply source 110
and portable device 200 stops, for example because the portable
device 200 moves out of range, then, as described above, the
chemical battery 250 may be configured to supply electrical energy
to the components 240 of the portable device 200 in step S6. As
shown by FIG. 12, in step S7, the supply of electrical energy from
the battery 250 is ceased when wireless energy transfer by resonant
inductive coupling is reinitiated.
[0096] The above example discusses the use of an adaptive receiving
component 211a to vary the resonant frequency associated with the
secondary inductor 211 in a portable electronic device 200 so as to
match the resonant frequency associated with the secondary inductor
211 to a detected resonant frequency associated with a primary
inductor 111 in a feeding device 100. However, it will be
appreciated that an adaptive component could alternatively be
employed in a feeding device 100 so as match the resonant frequency
associated with a primary inductor in the feeding device 100 to
that of a secondary inductor in a portable electronic device.
[0097] For example, a portable electronic device 200 may be
configured to supply a control signal to a feeding device 100 in
order to supply the feeding device 100 with the resonance
characteristics of the secondary inductor in the portable
electronic device. The feeding device 100 would then be able to
match the resonant frequency associated with its primary inductor
to the resonant frequency associated with the secondary inductor in
the portable device 200, thereby initiating wireless energy
transfer by resonant inductive coupling.
[0098] In another alternative, the supply source of a feeding
device may comprise a primary inductor driven by an amplifier, and
the microcontroller of the portable electronic device may be
configured to match a resonant frequency of the adaptive receiving
component to a detected frequency of a magnetic field associated
with the supply source.
[0099] In the example discussed above, the portable device 200
comprises a mobile telephone or PDA. However, it will be
appreciated that the portable device may alternatively comprise any
number of other devices, for example a laptop computer or digital
music player. It will further be appreciated that the invention is
not limited to the supply of power to portable electronic devices,
but may be used for powering a wide variety of other electrical
devices. For example, a network of feeding devices may be installed
in the home for supplying power to electric lamps and other
household appliances. The above-described embodiments and
alternatives may be used either singly or in combination to achieve
the effects provided by the invention.
* * * * *