U.S. patent application number 13/209336 was filed with the patent office on 2012-08-30 for tuning electromagnetic fields characteristics for wireless energy transfer using arrays of resonant objects.
Invention is credited to Chunjie Duan, Koon Hoo Teo, Bingnan Wang, William S. Yerazunis.
Application Number | 20120217817 13/209336 |
Document ID | / |
Family ID | 46718469 |
Filed Date | 2012-08-30 |
United States Patent
Application |
20120217817 |
Kind Code |
A1 |
Wang; Bingnan ; et
al. |
August 30, 2012 |
Tuning Electromagnetic Fields Characteristics for Wireless Energy
Transfer Using Arrays of Resonant Objects
Abstract
A system for exchanging energy wirelessly includes an array of
objects, wherein each object is electromagnetic (EM) and
non-radiative and generates an EM near-field in response to
receiving the energy. Each object in the array is electrically
isolated from the other objects and arranged at a distance from all
other objects. An energy driver provides the energy to the array of
objects. A receiver, at a relative position with respect to the
array receives the energy via resonant coupling of evanescent
waves. The system can tunes characteristics of the EM near-field
depending on a relative position of the receiver with respect to
the array. The tuning can affect frequency, phase and amplitude of
the energy field.
Inventors: |
Wang; Bingnan; (Boston,
MA) ; Yerazunis; William S.; (Acton, MA) ;
Duan; Chunjie; (Brookline, MA) ; Teo; Koon Hoo;
(Lexington, MA) |
Family ID: |
46718469 |
Appl. No.: |
13/209336 |
Filed: |
August 12, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61447599 |
Feb 28, 2011 |
|
|
|
Current U.S.
Class: |
307/104 |
Current CPC
Class: |
H04B 5/0081 20130101;
H02J 50/12 20160201; Y02T 90/167 20130101; H02J 50/40 20160201;
H02J 7/025 20130101; H02J 50/20 20160201; Y02T 10/7072 20130101;
H02J 50/70 20160201; B60L 53/65 20190201; H04B 5/0087 20130101;
Y02T 90/16 20130101; Y02T 90/12 20130101; Y04S 30/14 20130101; H02J
50/05 20160201; B66B 7/00 20130101; H02J 5/005 20130101; Y02T 10/70
20130101; H04B 5/0037 20130101; Y02T 90/169 20130101; Y02T 90/14
20130101 |
Class at
Publication: |
307/104 |
International
Class: |
H02J 17/00 20060101
H02J017/00; H03J 7/08 20060101 H03J007/08 |
Claims
1. A system for exchanging energy wirelessly, comprising: an array
of objects, wherein each object is electromagnetic (EM) and
non-radiative and generates an EM near-field in response to
receiving the energy, wherein each object in the array is
electrically isolated from the other objects and arranged at a
distance from all other objects; an energy driver configured to
provide the energy to the array of objects; a receiver, at a
relative position with respect to the array, to receive the energy
via resonant coupling of evanescent waves; means for tuning
characteristics of the EM near-field depending on a relative
position of the receiver with respect to the array.
2. The system of claim 1, wherein the characteristics include a
desired frequency for all relative position of the receiver with
respect to the array to obtain a highest energy transfer efficiency
at all positions for a highest energy transfer efficiency for all
positions.
3. The system of claim 1, wherein the means for tuning further
comprises; a detection and feedback module configured to detect
feedback information; a controller configured to processes the
feedback information and generating a frequency tuning message for
the energy driver.
4. The system of claim 3, wherein the feedback information includes
an amount of reflected energy from the array, and the frequency
tuning message obtains a lowest reflected energy.
5. The system of claim 3, wherein the feedback information includes
the position of the receiver.
6. The system of claim 1, wherein the tuning is dynamic.
7. The system of claim 6, wherein the receiver is moving.
8. The system of claim 1, wherein the means for tuning further
comprises; a detection and feedback module configured to detect
feedback information; a controller configured to processes the
feedback information and generating a phase tuning message for a
tunable phase shifter connected to the array at two or more feed
points.
9. The system of claim 8, wherein an energy distribution on the
array is determined by a superposition of patterns of the EM
near-field at all feed points.
10. The system of claim 8, wherein the feedback information
includes an amount of reflected energy from the array, and the
phase tuning message obtains a lowest reflected energy.
11. The system of claim 8, wherein the feedback information
includes an amount of energy received by the receiver.
12. The system of claim 8, wherein the feedback information
includes the position of the receiver.
13. The system of claim 1, wherein the characteristics include a
desired frequency and a desired phase for all relative position of
the receiver with respect to the array to obtain a highest energy
transfer efficiency at all positions for a highest energy transfer
efficiency for all positions.
14. The system of claim 1, wherein a resonant frequency of the
receiver is tuned for best coupling at a desired frequency of the
system.
15. The system of claim 14, wherein the receiver includes a
varactor.
16. The system of claim 1, wherein the resonant frequency is tuned
by a micro-electro-mechanical system device in the receiver.
17. The system of claim 1, wherein the resonant frequency is tuned
by ferroelectric material at the receiver.
18. The system of claim 6, wherein the generates an amplitude
tuning message for a tunable phase shifter connected to the array
at two or more feed points.
19. A method for exchanging energy wirelessly, comprising the steps
of: distributing energy to an array of objects, wherein each object
is electromagnetic (EM) and non-radiative and generates an EM
near-field in response to receiving the energy, wherein each object
in the array is electrically isolated from the other objects and
arranged at a distance from all other objects; receiving the energy
in a receiver at a position relative to the array via resonant
coupling of evanescent waves; tuning characteristics of the EM
near-field depending on the relative position of the receiver with
respect to the array.
20. The method of claim 19, wherein the characteristics include
frequencies of the EM near-field.
21. The method of claim 19, wherein the characteristics include
phases of the EM near-field.
Description
RELATED APPLICATION
[0001] The present invention claims priority to U.S. Provisional
Patent Application 61/447,599, "Wireless Energy Transfer Using
Array of Resonant Objects," filed by Wang et al. on Feb. 28, 2011,
and is related to U.S. patent application Ser. No. 13/209,297,
"Wireless Energy Transfer Using Arrays of Resonant Objects,"
co-filed herewith by Wang et al. on Aug. 12, 2011, and U.S. patent
application (MERL-2429) Ser. No. 13/______ "System and method for
automatically optimizing wireless power, co-filed by Yerazunis et
al, on Aug. 12, 2011, all incorporated herein by reference, all
incorporated herein.
FIELD OF THE INVENTION
[0002] The present invention relates generally to transferring
energy wirelessly, and more particularly to transferring energy
using arrays of resonant objects.
BACKGROUND OF THE INVENTION
[0003] Wireless Energy Transfer
[0004] Inductive coupling is used in a number of wireless energy
transfer systems, such as a cordless electronic toothbrush, or
vehicle batteries. In coupled inductors, such as transformers, a
source, e.g., a primary coil, generates energy as an
electromagnetic field, and a sink, e.g., a secondary coil, subtends
that field such that the energy passing through the sink is
optimized, e.g., the energy generated by the sink is as similar as
possible to the energy of the source. To optimize the energy, a
distance between the source and the sink should be as small as
possible, because over greater distances the inductive coupling
method is highly ineffective.
[0005] Resonant Coupling System
[0006] FIG. 1 shows a conventional resonant coupling system 100 for
transferring energy from a source 110 to a sink 120. In resonant
coupling, two resonant electromagnetic objects, i.e., the source
and the sink, interact with each other under resonance
conditions.
[0007] A driver 140 inputs the energy into the source to form an
oscillating electromagnetic field 115. The excited electromagnetic
field attenuates at a rate with respect to the signal frequency at
the driver or self-resonant frequency of the source and sink in a
resonant system. However, if the sink absorbs more energy than is
lost during each cycle, then most of the energy is transferred to
the sink. Operating the source and the sink at the same resonant
frequency ensures that the sink has low impedance at that
frequency, and that the energy is optimally received.
[0008] The energy is transferred, over a distance D, between
resonant objects, e.g., the source has a length L.sub.1 and the
sink has a length L.sub.2. The driver connects a power provider to
the source. The sink is connected to a power consuming device,
e.g., a resistive load 150. Power is supplied by the driver to the
source, transferred wirelessly and non-radiatively as energy from
the source to the sink. The rate of energy transfer powers the
load. The wireless non-radiative energy transfer is performed using
the field 115, e.g., the electromagnetic field or an acoustic field
of the resonant system. For simplicity of this description, the
field 115 is an electromagnetic field. During the coupling of the
resonant objects, evanescent fields 130 are propagated between the
source and the sink.
[0009] However, the resonant coupling transfers energy from the
source to the sink over a mid-range distance, e.g., a few times of
the resonant frequency wavelength, is inefficient when the distance
becomes larger. It is thus desirable to extend the range of
efficient wireless energy transfer.
SUMMARY OF THE INVENTION
[0010] The embodiments of the invention are based on a realization
that an array of strongly coupled resonant objects extends the
range of efficient wireless energy transfer and facilitates an
efficient energy transfer to receiving objects moving over a large
distance.
[0011] Embodiments of the invention are based on another
realization that, if the energy is provided to at least one object
of an array of strongly coupled resonant objects, the energy
oscillates among all objects in the array with reasonable losses.
If the energy is provided to at least one object in the array, the
energy is distributed from the object to all other objects in the
array. Thus, the sink can receive energy wirelessly from any object
of the array. Accordingly, the embodiments of the invention provide
a novel way to store and distribute energy for subsequent wireless
retrieval of the energy at any desired direction and distance from
the energy driver.
[0012] In conventional energy distribution systems, the energy is
transmitted over a closed loop to return the unused energy back to
the source or to other specially designed energy storages. That was
not considered as a problem, but rather as a fact of the energy
transfer. The embodiments of the invention eliminate this
requirement allowing arbitrarily arrangements of the objects and
thus, arbitrarily configuration of energy distribution
topography.
[0013] In one embodiment, a system configured to transfer energy
wirelessly between a transmitting device and a receiving device is
provided. The system comprises a source, which is formed by an
array of resonant objects, to generate evanescent electromagnetic
(EM) field. The system further comprises an energy driver for
providing the energy to at least one object in the array, such
that, during an operation of the system, the energy is distributed,
e.g., oscillated, from the object to all other objects in the
array.
[0014] In one variation of this embodiment, the system further
comprises a sink at a distance from the source for receiving energy
wirelessly from the source via coupling of evanescent EM fields.
The sink can be resonant or non-resonant structures. The energy
transfer can be achieved from any resonant object in the array of
the source.
[0015] Another embodiment discloses a system configured to exchange
energy wirelessly, comprising: an source comprising a first array
of objects; an sink comprising a second array of objects, each
object in the source and sink has a resonant frequency, is
electromagnetic (EM) and non-radiative, and is configured to
generate an EM near-field in response to receiving the energy; an
energy driver for providing the energy at the resonant frequency to
at least one object in the source, such that, during an operation
of the system, the energy is distributed from the object in the
source to all other objects in the source; and a load from
receiving the energy from the sink, wherein each object in the
first and the second arrays is arranged at a distance from all
other objects in, respectively, the first and the second arrays,
such that upon receiving the energy the objects in the first and
the second arrays are strongly coupled to, respectively, at least
one other object in the first and the second array, via a resonant
coupling of evanescent fields, and wherein the sink is arranged to
receive energy wirelessly from the source via the resonant coupling
of one or many objects in the first array with one or many objects
in the second array.
[0016] In another embodiment, a method of transferring energy
wirelessly between an source and an sink is disclosed. The method
comprises generating evanescent EM fields in an array of resonant
objects. The method further comprises transferring energy
wirelessly between the array of resonant objects and an sink. The
sink can be a resonant or non-resonant structure. In another
embodiment, the method further comprises transferring the energy
wirelessly between the array of resonant objects and another array
of resonant objects.
[0017] In another embodiment, characteristics of the
electromagnetic field are tuned dynamically depending on relative
positions between the source and the sink. The characteristics
include frequency and phase of the electromagnetic field.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a block diagram of a conventional resonant
coupling system;
[0019] FIG. 2 is a block diagram of a system with a sink beyond a
range of efficient wireless energy transfer according to
embodiments of the invention;
[0020] FIG. 3 is a block diagram of a system with a resonator array
as a source according to embodiments of the invention;
[0021] FIGS. 4A-D are schematics of an array of strongly coupled
resonant objects according to embodiments of the invention;
[0022] FIG. 5 is block diagram of a system for supplying energy
wirelessly to moving objects according to embodiments of the
invention;
[0023] FIGS. 6A-C are schematics comparing different
implementations of a sink;
[0024] FIG. 7 is a block diagram of a system with a resonator array
as the source and the sink according to embodiments of the
invention;
[0025] FIG. 8 is block diagram of a system for supplying energy
wirelessly to moving objects according to embodiments of the
invention;
[0026] FIG. 9 is a schematic of an array of spiral operating
resonators according to embodiments of the invention;
[0027] FIGS. 10A-E are graphs of transfer efficiency as a function
of frequency in the resonant array system and corresponding
resonant modes according to embodiments of the invention;
[0028] FIG. 11 is a schematic of a field intensity distribution
pattern;
[0029] FIG. 12 is a schematic of an example of one dimensional
system extended to two dimensional plane systems according to
embodiments of the invention;
[0030] FIG. 13 is a schematic of two circular loops in coordinate
system;
[0031] FIG. 14 is a graph of coupling coefficient of two coaxial
metallic loops as a function of distance, with an inset of a side
view of two loops with a distribution of the flux of the
electromagnetic field;
[0032] FIG. 15 is a graph of the coupling coefficient of two
laterally shifted coplanar metallic loops as a function of
distance, with an inset of a side view of two loops with the
distributions of the electromagnetic field;
[0033] FIG. 16 is an example of wireless energy transfer system
with an array of ten resonant objects and another resonant object
as receiver;
[0034] FIG. 17 is side view of the wireless energy transfer system
shown in FIG. 16, where the first object is excited by an external
source and the receiver is aligned with the last object in the
array, with different spacing between neighboring objects on top
and bottom Figs;
[0035] FIG. 18 is a graph of energy transfer efficiency as a
function of frequency, for the two cases shown in FIG. 17;
[0036] FIG. 19 is a side view of coupled resonant objects, when the
receiver is at different positions;
[0037] FIG. 20 is a side view of a wireless energy transfer system,
with a receiver moving from one end of the array to the other
end;
[0038] FIG. 21A is a graph of energy transfer efficiency as a
function of receiver position at a first frequency;
[0039] FIG. 21B is a graph of energy transfer efficiency as a
function of receiver position at a second frequency;
[0040] FIG. 21C is a second plot of energy transfer efficiency as a
function of receiver position (x-axis) and frequency (y-axis);
[0041] FIG. 22A is a graph of energy transfer efficiency as a
function of receiver position when the frequency is tuned to reach
maximum efficiency at each position;
[0042] FIG. 22B is a graph of corresponding frequency as a function
of receiver position;
[0043] FIG. 23 is a block diagram of a wireless energy transfer
system with an array of resonant objects, with resonant frequency
tuning of an electromagnetic field at source;
[0044] FIG. 24 is a block diagram of a wireless energy transfer
system with an array of resonant objects, with resonant phase
tuning of an electromagnetic field at a source;
[0045] FIG. 25 is a schematic of a phase controlled array with two
excitation ports;
[0046] FIG. 26 is a graph of energy transfer efficiency with two
excitations with no phase difference and two excitations with
90.degree. phase difference; and
[0047] FIG. 27 is a block diagram of a wireless energy transfer
system with an array of resonant objects, with resonant frequency
tuning of an electromagnetic field at a sink.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0048] Energy can be transferred wirelessly and efficiently between
coupled resonant objects at a resonant frequency. With the size of
resonant object is much smaller than the resonant wavelength, most
of the energy is stored inside the resonant object and does not
radiate into free space. The range of efficient wireless energy
transfer depends on the physical size of resonant objects. The
energy transfer is inefficient when the receiving object moves over
a large distance, compared to the size of resonant objects.
[0049] Thus, the resonant energy transfer system shown in FIG. 1 is
efficient when the distance D is on the order of the source size
L.sub.1 and the sink size L.sub.2. When D is much larger than
L.sub.1 or L.sub.2, the energy transfer system becomes inefficient.
Moreover, depending on the structure design of source 110 and sink
120, the system usually requires good alignment along one axis.
[0050] FIG. 2 shows an example when the wireless energy transfer
using source 210 and sink 220 is inefficient. The sink 220 is a
distance D in the x direction and a distance L in the y direction
from the source 210, where the distance L is much larger than
L.sub.1 and L.sub.2. Moreover, the sink 220 can move along a
direction 250. Thus, it is desirable to extend the range of
efficient wireless energy transfer and design a system to provide
energy wirelessly to mobile devices, such as elevators or electric
vehicles.
[0051] The embodiments of the invention are based on a realization
that an array of strongly coupled resonant objects extends the
range of efficient wireless energy transfer and facilitates an
efficient energy transfer to receiving objects moving over a large
distance.
[0052] Coupled Resonator Array
[0053] FIG. 3 shows a system 300 according to embodiments of the
invention. Instead of using one resonant object as the source, an
array of at least three resonant objects 311 having the same
resonant frequency is used as the source 310. Each object is
electromagnetic (EM) and non-radiative, and configured to generate
an EM near-field in response to receiving the energy. The array 310
can be any arrangement of the objects 311. The objects 311 in the
array are arranged at a distance from each other, i.e., not
physically connected, such that upon receiving the energy the
object is strongly coupled to at least one other object in the
array via resonant coupling of an electromagnetic field 360.
[0054] The type of resonant coupling in the array can be an
inductive coupling, a capacitive coupling, or combination thereof.
An energy driver 330 is used to provide energy to one or more
objects in the array 310. The resonant coupling distributes the
energy to all the objects in the array 310. The energy distribution
in the array is achieved by the excitation of the evanescent fields
360 that propagate along the objects of the array due to the
resonant coupling. The evanescent field is localized within the
near-field of the resonant objects and does not radiate to free
space. In one embodiment, to reduce the loss during the process,
resonant objects with high quality factor (Q-factor, Q>100) are
selected.
[0055] A sink 320 is a distance D away from the array. The sink can
be constructed as a resonant object or a non-resonant object. The
energy is transferred from the source 310 to the sink 320 via
coupling of evanescent fields 370. The coupling can occur between
one or more objects in the source and the sink. The sink receives
energy wirelessly from the source and provides energy to a load
340. The sink can be at different positions along the direction
350. Different objects in the source 310 are coupled to the sink
320 when the sink is at different positions.
[0056] Embodiments of the invention are based on a realization that
if the energy is provided to at least one object of an array of
strongly coupled resonant objects, the energy oscillates among all
objects in the array with reasonable losses. Thus, the sink can
receive energy wirelessly from any object of the array.
Accordingly, the embodiments of the invention provide a way to
store and distribute energy for subsequent wireless retrieval of
the energy at any desired direction and desistance from the energy
driver.
[0057] In conventional wired energy distribution systems, the
energy is transmitted over a closed loop to return unused energy to
the source or to other specially design energy storages. That was
not considered as a problem, but rather as a fact of the energy
transfer. The embodiments of the invention eliminate this
requirement and allow arbitrarily arrangements of the objects and
thus, arbitrarily configuration of energy distribution
topography.
[0058] Array Configurations
[0059] The resonant object 311 in the resonant array 310 can take
any physical shape depending on the application. For example, the
resonant object can be self-resonant coils, spirals, and dielectric
resonators.
[0060] In one embodiment as shown in FIG. 4A, the resonant object
has the form of a planar spiral 411. The resonant object can form
different arrangement forming the array of different shapes. An
array 410 is formed by linearly arranging multiple resonant
objects. The spiral object 411 is made of conducting wires and is
self-resonant at the resonant frequency. The sink can include one
or more objects constructed with resonant or non-resonant
structures. In one embodiment, the sink is constructed as the
spiral 420, and arranged on top of one of the objects of the array
410. In another embodiment, the sink is movable between a current
and another position 430. In yet another embodiment, multiple sinks
420 and 430 are used at different positions.
[0061] FIGS. 4B-D show more complex shapes of the array. FIG. 4B
shows an array 440 of resonant objects arranged a curve. In another
embodiment as shown in FIG. 4C, the resonant objects are arranged
along a circle 450. In yet another embodiment as shown in FIG. 4D,
the resonant objects can be arranged in two dimensions in a plane
460. In various embodiments, the sink is a resonant object having
the resonant frequency for receiving the energy wirelessly.
EXAMPLE APPLICATIONS
[0062] The embodiments of the invention can be applied to various
applications to provide energy wirelessly to mobile devices, or
wirelessly charge batteries on different devices. The devices
include, but are not limited to, electric vehicles, elevators,
robots, electronic devices such as cell phones, laptops.
[0063] FIG. 5 shows a system 500 for providing the energy
wirelessly to an elevator car 550. The source is formed by an array
510 of resonant objects 511, and is installed at an elevator shaft.
A driver 530 is used to provide energy to one or more objects in
the array 510. The driver 530 is connected to a power grid. The
sink 520 is a resonant object, and connected to a load 540 of the
elevator for powering the elevator car. The sink 520 receives
energy wirelessly from the source, and provides energy to the load
540. Both the sink 520 and the load 540 are positioned outside of
the elevator car 550. Impedance matching networks and other
components (not shown) can be used to control and optimize the
peifonnance of the elevator system. The system can be adapted to
other applications such as wireless charging of electric
vehicles.
[0064] Resonator Array as Sink
[0065] Some embodiments of the invention use the sink formed by an
array of resonators. FIGS. 6A-6B show examples of systems 610 and
620 having different sink configurations. In both systems, the
source is constructed by spirals aligned in a linear array. A loop
antenna is used at the driver to provide energy to the resonant
spiral at one end of the array. In the system 610, the sink is an
identical spiral resonator and is aligned coaxial with the resonant
spiral at the other end of the array. The sink is 0.5 m away from
the plane of the array. A loop antenna is used to extract energy
from the sink. In system 620, the sink is constructed by an array
of identical spirals. A loop antenna is aligned coaxial with the
spiral at one end of the array.
[0066] FIG. 6C shows the transfer efficiency 625 of the system 620
is better than the transfer efficiency 615 in the system 610. The
distance between he sink and load is 0.1 m.
[0067] Two Coupled Resonator Arrays
[0068] FIG. 7 shows a system 700 including a pair of resonator
arrays, i.e., a first array 710 and a second array 720, for
wireless energy transfer. The energy oscillating at resonant
frequency is provided to the source 710 from the drive 730. The
energy can be provided wirelessly. The source 710 and the sink 720
are arrays of resonant objects 711 and 721. Mutual coupling between
the resonant objects in the source and the sink redistributes the
wireless energy in the system according to the resonant arrays
configuration. Typically, the distance between objects of,
respectively, the first and the second arrays, is less than a
distance between the source and the sink.
[0069] The mutual coupling between the arrays 710 and 720 supports
the wireless energy transfer through the near field 750 over
mid-range, e.g., several resonant object dimension size. The energy
is transferred from the source to the sink via coupling of one or
more resonant objects in the source with one or more resonant
objects in the sink. The overall filed distribution due to the
mutual coupling forms a coupled mode of the two resonator arrays of
a single system.
[0070] In various embodiments, the resonant objects 711 and 721 are
of different shape and geometry. The resonant frequency can vary
between the source and the sink. However, one embodiment maintains
the same resonant frequency for both resonant objects 711 and 721
in order to achieve the optimum energy transfer efficiency.
[0071] In various embodiments, a size of the first array is less,
greater, or equal a size of the second array. The first and the
second arrays can be of the same or different dimensions. The first
and the second arrays can have the same or different degrees of
freedom. In one embodiment, the second array has at least one
degree of freedom.
[0072] In some embodiment, the driver can provide energy to one or
to several resonant objects concurrently. Also, in one embodiment,
a driver feeding position 731 can move. The system resonating
frequencies and the resonant mode for each resonant frequency are
fixed after the system configuration, i.e., the objects of the
source and the sink, are determined. The driver 730 can provide
energy to the system at any resonator object 711 in the source
710.
[0073] Similarly, in one embodiment, the load energy extraction
position can move. The energy can be extracted from any resonant
object 721 of the sink. In variation of this embodiment, the load
740 can extract energy from more than one object in the array of
the sink, e.g., at different positions 741, 742, 743 and 744.
[0074] In some embodiments, multiple drivers in the system 700 can
be used to provide energy to the source array 710 at different
positions. Similarly, multiple loads 740 and 745 can be used to
extract energy from the sink 720 at different positions.
[0075] Moving Device
[0076] FIG. 8 shows a system 800 for supplying energy wirelessly to
a moving devices, such as elevator cars. The source is an array 860
of resonant objects 880. The source is installed at an elevator
shaft and receives energy 815 from an energy driver 810. The energy
driver can be connected to a power grid and supply energy to the
source, e.g., inductively. The resonator array is configured to
generate electromagnetic evanescent fields in the specified
resonant mode at specified resonant frequency.
[0077] The elevator car 850, i.e., the load, is connected
wirelessly to the sink formed by a resonator array 820. The sink
can have less, more or the same number of resonant objects as the
resonator array of the source.
EXAMPLE
[0078] FIG. 9 shows another example embodiment. Spiral resonators
910 resonating at 27 MHz form the resonator arrays of the source
920 and the sink 930. For example, both resonator arrays have six
spiral elements separated by a distance D1. Two loop antennas with
R radius are used as the energy driver 940 and the load 950. The
separation between driver/load and source array/sink array is D2.
The distance between the source and sink array is D.
[0079] For example, the energy is provided to the energy driver 940
via wired cable and then provided to the source via, e.g.,
inductive coupling at resonant frequency. The specified resonant
mode is excited in the system and the energy redistributed over the
whole system according to the resonant mode. The load 950 extracts
the energy wirelessly from the sink 930. When the energy is
extracted from the system, energy balance of the system is
disturbed and more energy is provided from the driver 940 to
maintain the balance. Accordingly, the energy transferred from
drive 940 to load 950 continues as long as the resonant mode is
maintained in the system.
[0080] Because the resonant mode of the system is frequency
dependent, the transfer efficiency is also frequency dependent, as
shown in FIG. 10A. The energy transfer efficiency 1030 has multiple
peaks in the system which is the result of the multiple resonator
configurations.
[0081] Different peaks in the energy transfer efficiency curve,
1011 to 1014, correspond to different corresponding resonant modes
1021 to 1024 as shown in FIGS. 10B-10E. When the resonant mode
common to the whole system is excited, the energy is confined
within the system with little radiation.
[0082] In particular, the highest energy transfer efficiency from
the driver to the load is at the resonant mode where the energy is
evenly distributed over the all system, which is the peak 1014.
[0083] FIG. 11 shows the corresponding mode 1110. Each resonator in
the source 920 and the sink 930 are excited in this resonant mode,
and the energy is evenly distributed oscillating along and between
the two arrays,
[0084] Two-Dimensional Resonant Arrays
[0085] FIG. 12 shows how the array of resonant objects can be of
different dimensions, e.g., a two-dimensional (2D) array of the
resonant objects. The 2D arrays extending in both the x and y
direction, and is used as the source 1240 and the sink 1230. The
energy driver 1260 provides 1250 the energy to the source at the
resonant frequency. Due to the mutual coupling, 1270-1273, between
the resonant objects in the source, wireless energy redistributed
over the system in both direction. The mutual coupling 1274 between
the resonant objects in the sources and the resonant objects in the
sink results in the wireless energy transfer from the source 1240
to the sink 1230. The corresponding resonant mode of the overall
system is excited through the providing energy at the resonant
frequency. At the corresponding resonant mode, the energy in the
system 1200 is redistributed in 3 directions. Particularly, the
energy is transferred wirelessly in the z direction.
[0086] Coupling of Two Loops of Metallic Wires
[0087] Coupling of electromagnetic (EM) fields is essential in
wireless energy transfer based on inductive coupling and resonant
coupling. It is important to understand the coupling behavior
between EM objects to better design a wireless energy transfer
system.
[0088] We first describe the coupling of two loops of metallic
wires. FIG. 13 shows two coupled metallic loops. The positions and
geometrical parameters of them are defined in the coordinate
system. The mutual coupling of two metallic loops can be described
by
M = .PHI. / I 1 = .mu. 0 4 .pi. R 1 R 2 .intg. 0 2 .pi. .intg. 0 2
.pi. ( sin .phi. 1 sin .phi. 2 + cos .phi. 1 cos .phi. 2 cos
.theta. ) r .phi. 1 .phi. 2 , ##EQU00001##
where .PHI. is the flux of the e3lectromagentic field going through
the second loop due to the electric current I.sub.1 in the first
loop, and
r = x _ A - x _ B = ( R 1 cos .phi. 1 - R 2 cos .phi. 2 ) 2 + ( R 1
sin .phi. 1 - t - R 2 sin .phi. 2 cos .theta. ) 2 + ( d - R 2 sin
.phi. 2 sin .theta. ) 2 . ##EQU00002##
[0089] The self-inductance of the two loops are L.sub.1 and
L.sub.2. The coupling coefficient is defined as k=M/ {square root
over (L.sub.1L.sub.2)}. The self-inductance of a metallic loop with
radius R is calculated by
L = .mu. 0 R [ ln ( 8 R a ) - 2 ] . ##EQU00003##
[0090] With FIGS. 14 and 15, we describe two special cases of two
loops with identical size, with self-inductance L.sub.1=L.sub.2.
The flux 1401 of the corresponding electromagnetic field is shown
in the inset.
[0091] When the two loops are coaxial as seen in FIG. 14, with
distance d between the loops, the equations are simplified:
r = ( R 1 cos .phi. 1 - R 2 cos .phi. 2 ) 2 + ( R 1 sin .phi. 1 - R
2 sin .phi. 2 ) 2 + d 2 = R 1 2 + R 2 2 - 2 R 1 R 2 cos ( .phi. 1 -
.phi. 2 ) + d 2 , ##EQU00004## M = .mu. 0 4 .pi. R 1 R 2 .intg. 0 2
.pi. .intg. 0 2 .pi. cos ( .phi. 1 - .phi. 2 ) R 1 2 + R 2 2 - 2 R
1 R 2 cos ( .phi. 1 - .phi. 2 ) + d 2 .phi. 1 .phi. 2 .
##EQU00004.2##
[0092] The coupling coefficient is calculated numerically (arid
plotted as a function of distance in FIG. 14). The coupling
coefficient is very strong at short range, when the two loops are
close to each other. When the distance is equal to the radius of
loop, the coupling coefficient drops to about 0.05. When the two
loops are coplanar (as seen in FIG. 15), with distance d between
them, the equations are simplified:
r = ( R 1 cos .phi. 1 - R 2 cos .phi. 2 ) 2 + ( R 1 sin .phi. 1 - R
2 sin .phi. 2 - t ) 2 = R 1 2 + R 2 2 - 2 R 1 R 2 cos ( .phi. 1 -
.phi. 2 ) + t 2 - 2 t ( R 1 sin .phi. 1 - R 2 sin .phi. 2 ) ,
##EQU00005## M = .mu. 0 4 .pi. .intg. 0 2 .pi. .intg. 0 2 .pi. R 1
R 2 cos ( .phi. 1 - .phi. 2 ) R 1 2 + R 2 2 - 2 R 1 R 2 cos ( .phi.
1 - .phi. 2 ) + t 2 - 2 t ( R 1 sin .phi. 1 - R 2 sin .phi. 2 )
.phi. 1 .phi. 2 . ##EQU00005.2##
[0093] The coupling coefficient is calculated numerically and
plotted as a function of distance in FIG. 15. The coupling
coefficient is already very weak even when the two loops are
side-by-side. When the distance is equal to the radius of loop, the
coupling coefficient drops to less than 0.005.
[0094] The above analysis indicates that coupling coefficient for
two metallic loops is much weaker in coplanar case than in coaxial
case; and decreases rapidly with increasing distance in both cases.
The coupling coefficient is proportional to the amount of flux that
can go through the second loop due to the current in the first
loop. As shown in FIG. 14 and FIG. 15, much more flux 1401 goes
through the second loop in the coaxial case than in the coplanar
case. In wireless energy transfer system using inductive coupling
or resonant coupling, the receiver (or receivers) is usually
arranged in coaxial position with the transmitter instead of
coplanar with the transmitter to obtain higher energy transfer
efficiency and larger transfer distance.
[0095] For wireless energy transfer based on inductive coupling, a
high coupling coefficient (k>0.9) is usually required to achieve
high efficiency; thus good coaxial alignment and very small
distance between transmitter and receiver are required. For
wireless energy transfer based on resonant coupling, energy can be
transferred to receiver via many cycles of resonant exchange of
energy between them. Efficient energy transfer can be achieved even
without a high coupling coefficient, as long as the energy coupled
to the receiver is higher than the energy lost in the coupling in
each cycle.
[0096] Coupling in Array of Resonant Objects
[0097] In a wireless energy transfer system using an array of
resonant objects, two or more resonant objects are closely coupled
to provide energy to receivers. These objects are not physically or
electrically connected, but the energy is distributed between them
via resonant coupling of electromagnetic fields.
[0098] To obtain high transfer efficiency and larger transfer
distance, a receiver is preferably arranged such that the axis of
its plane is parallel to those of the transmitting objects
(coaxial, or coaxial with a lateral shift). The resonant objects in
the array need to be closely-coupled, in order to reduce energy
loss due to coupling. In general, when an array of resonant objects
is excited at one end the array, more energy is coupled to the
other end of the array when the coupling coefficient between
neighboring objects is higher. Moreover, due to the hybridization
of resonant coupling, the bandwidth is broader yielding a higher
coupling coefficient.
[0099] FIG. 16 shows an example of an array of resonant objects and
a receiver 1601. The resonant objects are multi-turn square spiral
resonators. The array is made by ten such objects arranged in a
linear array. The receiver is also a multi-turn square spiral
resonator, arranged in parallel with the array and can move freely
along the plane formed by the array. The first object in the array
is excited by an external energy source; and energy is distributed
in all objects of the array via resonant coupling.
[0100] As shown in FIG. 17, two different spacing 1701-1702 for
positions of neighboring objects are used for the array. The energy
transfer efficiency, as a function of frequency, is can be
determined by simulations. In case 1, the spacing between
neighboring objects is 15% of the width of a resonant object. In
case 2, the spacing between neighboring objects is only 3% of the
width of a resonant object. The distance between the receiver and
the plane of the array is 50% of the width of a resonant
object.
[0101] FIG. 18 shows the energy transfer efficiency as a function
of the frequency for the two cases in FIG. 17. The efficiency is
higher for all frequencies and the bandwidth is much broader when
the array is closely arranged at positions.
[0102] Receiver at Different Positions
[0103] When a receiving object is at different positions, the
coupling between the receiving object and the array is different.
As shown in FIG. 19, the coupling from an array 1902 to a receiver
1901 is stronger when the receiver is aligned with one object in
the array. In comparison, when the receiver is in the middle of
neighboring objects, the coupling is weaker. The flux of the
electromagnetic field from the two neighboring objects may have
different directions, which cancels out the overall flux going
through the receiving object, and causing the coupling coefficient
even smaller. Due to the change in coupling coefficient, the energy
transfer efficiency changes correspondingly when the receiving
object is at different positions.
[0104] Moreover, the resonant mode and resonant frequency of the
system of the array and the receiver also changes when the receiver
changes its position. Working at resonant frequency of the system
usually leads to higher energy transfer efficiency than working at
other frequencies. So, as the receiver moves to different positions
different positions, the frequency for peak energy transfer
efficiency also varies. Hence, it is desired to tune the
frequencies depending on the relative positions of the array and
the receiver.
[0105] FIG. 20 shows a side view of an array of resonant objects
and a receiving object 2010 moving along the direction of the
array. The system design is shown in FIG. 16. The distance between
receiver and the array is 50% the width of a resonant object in the
array. The array is excited by an external source at the first
object in the array. The energy transfer efficiency as a function
of receiver position is shown in FIGS. 21A-21B.
[0106] The receiver position is in units of the period of the
array. Zero means the position of the receiver is aligned with the
first object in the array. The larger the number, the farther away
the receiver is from the first object.
[0107] FIG. 21A and FIG. 21B show plots at two different
frequencies. Both Figures show efficiency variation when the
receiver travels along the array. In FIG. 21A, the efficiency
varies from 85% to 60In FIG. 21B, the efficiency varies from 90% to
10%. The variation is more severe in FIG. 21B than in FIG. 21A,
which is due to different resonant modes at the two different
frequencies.
[0108] The energy transfer efficiency variation at different
frequencies when the receiver is at different positions is further
shown in FIG. 21C, where the energy transfer efficiency 2111 is
plotted as a function of both the receiver position and the
frequency. The frequencies for peak energy transfer efficiency
changes at different positions.
[0109] Therefore, it is desired ways to reduce the fluctuation for
wireless energy transfer using array of resonant objects.
[0110] Optimizing Electromagnetic Field Characteristics
[0111] The electromagnetic field has frequency and phase
characteristics. The embodiments of the invention enable the tuning
of these characteristics depending on relative positions of the
source with respect to the array. This can be done three ways.
[0112] Transmission Frequency Tuning
[0113] One way to improve the performance of a wireless energy
transfer system with an array of resonant objects is to tune the
frequency of the electromagnetic field depending on the relative
position of the receivers with respect to the array. When the
receivers are at different positions, the frequency for highest
energy transfer efficiency changes. If the frequency can be tuned
to this desired frequency for all positions, then the performance
of the system is improved.
[0114] FIG. 22A shows the energy transfer efficiency of the system
as shown in FIG. 16, as a function of receiver relative position
with respect to the array. In this embodiment the frequency is
tuned to the optimal frequency to obtain a highest energy transfer
efficiency at all positions. The efficiency is above 80% for all
positions, and the variation of efficiency is less than 10. Here,
the performance improvement is better when compared with the
performance shown in FIG. 21.
[0115] FIG. 22B shows the frequency for each receiver position.
[0116] FIG. 23 shows an embodiment of wireless energy transfer
system with an array of resonant objects 2310. Frequency tuning at
the source is used to generate the signal at a desired frequency.
An RF generator 2301 is connected to an amplifier 2302 to achieve a
desired power level, and a matching network 2305 for impedance
matching. Impedance matching maximize the power transfer and/or
minimize reflections.
[0117] The high-frequency energy is provided to the array of
resonant objects 2310. A receiver 2321 receives energy from the
array. The received RF energy passes through a rectifier 2322 and
regulator 2322 to power a device (load) 2324.
[0118] As used herein, power is the rate at which the energy is
converted to perform work.
[0119] To tune the operating frequency depending on the relative
position of the receiver with respect to the array for efficient
energy transfer, a detection and feedback module 2306 is used to
detect feedback and send the information to a controller 2304,
which then processes the feedback information and sends a frequency
tuning message 2303 to the high-frequency signal generator
2301.
[0120] Different information can be collected by the detection and
feedback system for frequency tuning. In one embodiment, an amount
of reflected energy from the array back to the RF source can be
monitored, and the frequency is tuned to obtain a lowest reflected
energy. The reflected energy depends indirectly of the position of
the receiver. In another embodiment, the transmitted energy level,
which also depends on the position, to the receiver can be
monitored, and the information is send back to the controller for
frequency tuning, until the highest energy is transmitted to the
receiver. Alternatively, the position of the receiver 2321 relative
to the array 2310 can be used directly to tune the frequency.
[0121] It is noted that the tuning can be dynamic, and in real-rime
as the receiver moves.
[0122] Transmission Phase Tuning
[0123] An array of resonant objects can be excited by external
sources at one or more resonant objects in the array through
different excitation ports. The phase and amplitude of each
excitation port can be dynamically tuned to achieve high efficiency
and reduce efficiency fluctuation when a receiver (o receivers) is
at different positions.
[0124] By tuning the phase and amplitude of excitation at each
port, the EM field distribution in the system of array (or arrays)
and receiver (or receivers) can be controlled. The coupling to a
receiver (or receivers) at different positions can be optimized by
the dynamic tuning.
[0125] Thus, optimal power transfer efficiency can be maintained. A
second advantage of multiple excitation ports is that losses in the
energy due to traversing multiple resonant objects are decreased.
With the proper excitation port design, it is possible to insert a
"null" area into the array, so that in that part of the array the
field strengths become vanishingly small, and receivers (whether
intentional or accidental) near that part of the array are not
coupled. Thus, one could "turn off' part of the array while it is
being serviced, such as in a wirelessly powered vehicle highway
network.
[0126] FIG. 24 shows how to improve the performance of a wireless
energy transfer system with an array 2404 of resonant objects by
varying the phase of the electromagnetic field depending on the
relative position of receiver 2405 with respect to the array, while
keeping the transmission frequency the same. Two or more feed
points 2400 are used to provide energy to the array. The energy
distribution on the array is determined by the superposition of
electromagnetic field patterns at all feed points.
[0127] The phase delay of one or more feed points in the array can
be tuned. By tuning the phase, the energy distribution along the
array 204 can be varied. When the receiver 2405 is at a position
with low energy and low energy transfer efficiency, tuning the
phase delay of one or more feed points increases the energy at that
position and improves the energy transfer to the receiver. If the
phase delay is tuned depending for the receiver at all positions
relative to the array, then the performance of the system can be
improved.
[0128] A high-frequency signal generator 2401 is used to generate
the signal at a desired frequency. The signal is fed to a power
amplifier 2402 for a desired level, and a matching network 2403 for
impedance matching. The high-frequency energy is provided to the
array 2404 of resonant objects at multiple feed points.
[0129] The phase delay of one or more feed points 2400 can be tuned
by a tunable phase shifter 2411 depending on a relative position of
the receiver 2405 with respect to the array. The receiver 2405
receives energy from the array 2404. The received RF energy passes
goes through the rectifier 2406 and regulator 2407, which is
converted to provide power to a device or load 2408.
[0130] To tune the phase depending on the receiver position for
efficiency energy transfer, a detection and feedback module 2409 is
used to detect information of the array system and send the
information back to a controller 2410. The controller processes the
feedback information and sends phase shift tuning message 2420 to
the tunable phase shifter 2411. The controller can also generate an
amplitude tuning message 2421.
[0131] Different information can be collected by the detection and
feedback system for phase shift tuning processing. In one
embodiment, the reflected energy from the array back to the RF
source can be monitored, and the phase is tuned to get lowest
reflected energy. The reflected energy depends on the position of
the receiver. In another embodiment, the energy received by the
receiver can be monitored, and the information is send back to the
controller for phase tuning, until the highest energy is
transmitted to the receiver. The position of the receiver relative
to the array can also be directly monitored.
[0132] FIG. 25 shows an example of a phase controlled array (Tx)
and a receiver (Rx). The array has two excitation ports (Tx). The
phase of each excitation is tuned to optimize energy transfer
efficiency.
[0133] FIG. 26 shows energy transfer efficiency for a receiver at
the same position. Two cases are considered in FIG. 26: two
excitations with no phase difference; and two excitations with
90.degree. phase difference. The efficiency is different for the
two cases. When the excitation frequency is fixed, the system can
be tuned by changing the phase angle of each excitation to optimize
the energy transfer.
[0134] Receiver Resonant Frequency Tuning
[0135] Another way to improve the performance of a wireless energy
transfer system with an array of resonant objects is to tune the
resonant frequency of a receiver for best coupling at the frequency
of the system.
[0136] FIG. 27 shows an embodiment of wireless energy transfer
system with array 2704 of resonant objects, with resonant frequency
tuning of a receiver 2705.
[0137] A high-frequency RF signal generator 2701 generates the
signal at desired frequency. The signal is fed to an amplifier 2702
to desired power level, and a matching network 2703 for impedance
matching. The high-frequency energy is provided to the array 2705
of resonant objects.
[0138] A tunable receiver 2705 receives energy from the array. The
received RF energy passes through the rectifier 2706 and regulator
2707 and is converted to power for the device 2708. The received
energy is monitored by a detector 2709. The information is then
sent to a controlling system 2710, which processes the information
and sends resonant frequency tuning message 2711 to the tunable
receiver. The process continues dynamically to achieve a highest
efficiency.
[0139] Different methods can be used to tune the resonant frequency
of a receiver. In one embodiment, a varactor 2712 is added to the
receiver and the capacitance of the varactor is controlled by a
biasing circuit. The resonant frequency of the receiver is tuned by
changing the capacitance of the varactor 2712.
[0140] In another embodiment, the capacitance, thus the resonant
frequency of the receiver can be controlled by a
micro-electro-mechanical system (MEMS) device. In yet another
embodiment, the capacitance, thus the resonant frequency of the
receiver can be controlled by a ferroelectric material.
[0141] It is noted that both the frequencies and the phases can be
optimized dynamically while the object is moving, as described
below.
[0142] Although the invention has been described by way of examples
of preferred embodiments, it is to be understood that various other
adaptations and modifications may be made within the spirit and
scope of the invention. Therefore, it is the object of the appended
claims to cover all such variations and modifications as come
within the true spirit and scope of the invention.
* * * * *