US 200900 15075A1

(19) United States

(12) Patent Application Publication (10) Pub. No.: US 2009/0015075A1
Cook et al. (43) Pub. Date: Jan. 15, 2009
(54) WIRELESS ENERGY TRANSFER USING (21) Appl. No.: 11/775,168
COUPLED ANTENNAS
(22) Filed: Jul. 9, 2007
(75) Inventors: Nigel P. Cook, El Caion, CA (US);
Paul Meier, Hamilton (NZ); Lukas Publication Classification
Sieber, Olten (CH); Marc Secall, (51) Int. Cl.
Fribourg (CH), Hanspeter H02. I7/00 (2006.01)
Widmer, Wohlenschwil (CH) (52) U.S. Cl. ........................................................ 307/149
Correspondence Address:
Law Office of Scott C Harris Inc (57) ABSTRACT
PO Box 1389 A power transmission system produces a magnetic field at a
Rancho Santa Fe, CA 92.067 (US) source that is wirelessly coupled to a receiver. Both the source
and receiver are capacitively coupled LC circuits, drivenator
(73) Assignee: Nigel Power, LLC a SOaC.

TRANSIMITTER
- 150RECEIVER
(ENERGY SOURCE) YYY (ENERGYSINK)
152

160
LOAD
(RECTIFIER AND
REGULATOR)
Patent Application Publication Jan. 15, 2009 Sheet 1 of 9 US 2009/0015075A1

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Patent Application Publication Jan. 15, 2009 Sheet 2 of 9 US 2009/0015075A1

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Patent Application Publication Jan. 15, 2009 Sheet 3 of 9 US 2009/0015075A1

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Patent Application Publication Jan. 15, 2009 Sheet 4 of 9 US 2009/0015075A1

418 415

410

505

FIG. 5
Patent Application Publication Jan. 15, 2009 Sheet 5 of 9 US 2009/0015075A1

700

705

706
FIG. 6

FIG. 7
Patent Application Publication Jan. 15, 2009 Sheet 6 of 9 US 2009/0015075A1
Patent Application Publication Jan. 15, 2009 Sheet 7 of 9 US 2009/0015075A1

s
Patent Application Publication Jan. 15, 2009 Sheet 8 of 9 US 2009/0015075A1

CH1S 11 log MAG 10dB/ REF0 dB 1-28.676 dB

13.907 000 MHZ
BW 083 288 MHZ
0 Cent: 13.905322 MHZ
1 loss-28.676 de''

CENTER 13.907 000 MHz

| | | 2 | | | | SPAN 400 000 MHZ

FIG 10A
Patent Application Publication Jan. 15, 2009 Sheet 9 of 9 US 2009/0015075A1

(M)HEJM0d

DISTANCE (INCH)
FIG. 10B

39 0.006
0.008

USABLE
RANGE

FIG 10C
US 2009/00 15075 A1 Jan. 15, 2009

WIRELESS ENERGY TRANSFERUSING that the efficiency and amount of power is Superior for a
COUPLED ANTENNAS system which uses a single, Substantially un-modulated sine
wave. In particular, the performance is Superior to a wide
BACKGROUND band system which attempts to capture the power contained in
0001. It is desirable to transfer electrical energy from a a wideband waveform or in a plurality of distinct sinusoidal
Source to a destination without the use of wires to guide the waveforms of different frequencies. Other embodiments may
electromagnetic fields. This wireless transfer of energy has use less pure waveforms, in recognition of the real-world
been attempted historically by many electromagnetic field characteristics of the materials that are used.
experts—most notably Nikola Tesla in the early 20th century. 0015 Techniques are described herein which enable small
A difficulty of these previous attempts has been low efficiency resonant antennas with relatively high Q factors. The Q of a
together with an inadequate amount of power delivered. resonant device is the ratio of the resonant frequency to the
so-called “three dB or “half power” bandwidth of the reso
SUMMARY nant device. While there are several “definitions, all are
Substantially equivalent to each other, to describe Q in terms
0002 The present application teaches a wireless electrical of measurements or the values of resonant circuit elements.
energy transfer, and teaches specific techniques for that 0016. A basic embodiment is shown in FIG. 1. A power
energy transfer. transmitter assembly 100 receives power from a source, for
0003 Aspects describe the specific antennas, and specific example, an AC plug 102. A frequency generator 104 is used
types of coupling between the transmitter and receiver. to couple the energy to an antenna 110, here a resonant
BRIEF DESCRIPTION OF THE DRAWINGS antenna. The antenna 110 includes an inductive loop 111,
which is inductively coupled to a high Q resonant antenna
0004. These and other aspects will now be described in part 112. The resonant antenna includes a number N of coil
detail with reference to the accompanying drawings, wherein: loops 113 each loop having a radius R. A capacitor 114, here
0005 FIG. 1 shows a block diagram of a magnetic wave shown as a variable capacitor, is in series with the coil 113,
based wireless power transmission system; forming a resonant loop. In the embodiment, the capacitor is
0006 FIG. 2 illustrates circuit diagrams of the circuits in a totally separate structure from the coil, but in certain
the FIG. 1 diagram; embodiments, the self capacitance of the wire of forming the
0007 FIG. 3 illustrates an exemplary near field condition coil can form the capacitance 114.
plot; (0017. The frequency generator 104 can be preferably
0008 FIGS. 4-8 illustrate exemplary transmit antennas; tuned to the antenna 110, and also selected for FCC compli
0009 FIG. 9 illustrates an exemplary receiving antenna; aCC.
and
0010 FIGS. 10A-10Cillustrate data plots of that receiving 0018. This embodiment uses a multidirectional antenna.
antenna.
115 shows the energy as output in all directions. The antenna
100 is non-radiative, in the sense that much of the output of
DETAILED DESCRIPTION the antenna is not electromagnetic radiating energy, but is
rather a magnetic field which are more stationary. Of course,
0011. The present application describes transfer of energy part of the output from the antenna will in fact radiate.
from a power Source to a power destination via electromag 0019. Another embodiment may use a radiative antenna.
netic field coupling. Embodiments describe techniques for (0020. A receiver 150 includes a receiving antenna 155
new coupling structures, e.g., transmitting and receiving placed a distance Daway from the transmitting antenna 110.
antennas. The receiving antenna is similarly a high Q resonant coil
0012 A preferred embodiment is shown in which the main antenna 151 having a coil part and capacitor, coupled to an
coupling occurs via inductive coupling, using primarily a inductive coupling loop 152. The output of the coupling loop
magnetic field component. In the embodiment shown in FIG. 152 is rectified in a rectifier 160, and applied to a load. That
1, for example, energy is formed as a stationary magnetic load can be any type of load, for example a resistive load Such
wave in the area of the transmitting antenna. The energy that as a light bulb, or an electronic device load Such as an elec
is produced is at least partly a non-radiative, stationary mag trical appliance, a computer, a rechargeable battery, a music
netic field. The produced field is not entirely magnetic, nor player or an automobile.
entirely stationary, however at least a portion is. Unlike a 0021. The energy can be transferred through either elec
traveling electromagnetic wave, which would continue trical field coupling or magnetic field coupling, although
propagating into space and have its energy wasted, at least a magnetic field coupling is predominantly described herein as
portion of the stationary magnetic wave remains in the area of an embodiment.
the transmitting antenna and is rendered usable by the dis 0022 Electrical field coupling provides an inductively
closed techniques.
0013. Other embodiments may use similar principles of loaded electrical diode that is an open capacitor or dielectric
the embodiments are equally applicable to primarily electro disk. Extraneous objects may provide a relatively strong
static and/or electrodynamic field coupling as well. In gen influence on electric field coupling.
eral, an electric field can be used in place of the magnetic 0023 Magnetic field coupling may be preferred, since it
field, as the primary coupling mechanism. has a weak influence on any extraneous objects and many
0014. One aspect of the embodiment is the use of a high extraneous objects have the same magnetic properties as
efficiency via increasing the so-called Q factor of the cou 'empty' space.
pling structures (primarily the antennas) at the self-resonant 0024. The embodiment describes a magnetic field cou
frequency used for the sinusoidal waveform of the electro pling using a capacitively loaded magnetic dipole. Such a
magnetic field, voltage or current used. We have discovered dipole is formed of a wire loop forming at least one loop or
US 2009/00 15075 A1 Jan. 15, 2009

turn of a coil, in series with a capacitor that electrically loads 0034. In addition, the capacitors should be able to with
the antenna into a resonant state. stand high Voltages, for example as high as 1000 V. Since the
0025 FIG. 2 shows an equivalent circuit for the energy resistance may be small in relation to the capacitive reactance.
transfer. The transmit circuit 100 is a series resonant circuit A final important feature is the packaging: the system should
with RLC portions that resonate at the frequency of the high be in a small form factor. The Q factor can be expressed as:
frequency generator 205. The transmitter includes a series
resistance 210, and inductive coil 215, and the variable
capacitance 220. This produces the magnetic field M which is
shown as magnetic lines of force 225.
0026. The signal generator 205 has an internal resistance
Q- V.
that is preferably matched to the transmit resonator's resis
tance at resonance by the inductive loop. This allows trans C = Cself + Ced
ferring maximum power from the transmitter to the receiver R – Riad + Ross
antenna.
0027. The receive portion 150 correspondingly includes a
capacitor 250, transformer coil 255, rectifier 260, and regu 0035. Where:
lator 261, to provide a regulated output Voltage. The output is
connected to a load resistance 265. FIG. 2 shows a half wave 0036. The value L represents the inductance of the reso
rectifier, but it should be understood that more complex rec nator. This inductance is given by the geometry of the reso
tifier circuits can be used. The impedance of the rectifier 260 nator and its antenna.
and regulator 261 is matched to the resistance of the receive 0037. The value C represents capacitance, including an
resonator at resonance. This enables transferring a maximum inherent capacitance which stores energy in the electric field.
amount of power to the load. The resistances take into account Both the self capacitance of the inductor, as well as an exter
skin effect/proximity effect, radiation resistance, as well as nal capacitor form part of the total capacitance.
both internal and external dielectric loss.
0028. A perfect resonant transmitter will ignore, or mini 0038. The value R represents the resistance of the resona
mally react with, all other nearby resonant objects having a tor, formed by the coil resistance of the inductor, and the
different resonant frequency. However, when a receiver that radiation resistance. These collectively lower the Q of the
has the proper resonant frequency encounters the field of the resonator as Rincreases.
transmitting antenna 225, the two couple in order to establish 0039 All of these values together form the Q or quality
a strong energy link. In effect, the transmitter and receiver factor of the resonator. Q represents in general how well the
operate to become a loosely coupled transformer. resonator generates and receives magnetic energy. By keep
0029. The inventors have discovered a number of factors ing C and R low, the L of the coil may be the most predomi
that improve the transfer of power from transmitter to nant factor.
receiver.
0030 Q factor of the circuits, described above, can assist 0040. It is desirable to increase the Q as much as possible
with certain efficiencies. A high Q factor allows increased in an embodiment. Accordingly, certain values should be
considered.
values of current at the resonant frequency. This enables
maintaining the transmission over a relatively low wattage. In 0041 As previously described, high resistance brings
an embodiment, the transmitter Q may be 1400, while the down the Q, since the Q is inversely proportional to R. R has
receiver Q is around 300. For reasons set forth herein, in one two parts, the radiation resistance, as well as an ohmic loss
embodiment, the receiver Q may be much lower than the process.
transmitter Q, for example /4 to /s the transmitter Q. How 0042. For a loop antenna, the radiation resistance equals
ever, other Q factors may be used.
0031 High Q has a corresponding disadvantage of narrow
bandwidth effects. Such narrow bandwidth have typically
been considered as undesirable for data communications.
However, the narrow bandwidth can be used in power trans
fer. When a high Q is used, the transmitter signal is suffi
ciently pure and free of undesired frequency or phase modu where r represents the radius of the coil.
lation to allow transmission of most of its power over this 0043. Therefore, the radiation is dependent on frequency
narrow bandwidth.
0032 For example, an embodiment may use a resonant to the fourth power, radius to the fourth power, and the num
frequency of 13.56 MHz and a bandwidth of around 9 kHz. ber of turns Squared.
This is highly usable for a substantially un-modulated funda 0044 Loss resistance can be evaluated as
mental frequency. Some modulation on the fundamental fre
quency may be tolerated or tolerable, however, especially if
other factors are used to increase the efficiency. Other N filo
embodiments use lower Q components, and may allow cor Ros = 3. O. 2.7 ra: (1 + C)
respondingly more modulation on the fundamental.
0033. An important feature may include use of a fre
quency which is permitted by regulation, such as FCC regu Note that this is dependent on the square root offrequency, the
lations. The preferred frequency in this exemplary embodi wire dimensions and material, and the so-called proximity
ment is 13.56MHz, but other frequencies may be used as well. effect.
US 2009/00 15075 A1 Jan. 15, 2009

0045. The values for capacitance are: 0054) At the 13.56 MHz frequency, the exposure must be
kept below 60 dBuA/m express in W/m2 instead of dBuA/
m. Another objective, therefore, requires maintaining this
2. r. b. so value or less at 10 m.
CeClt =
p p 2 0055 Another important issue is attributable to the spe
Hi, + (g) - 1 cific antenna type.
0056 FIG. 4 illustrates a first embodiment that uses a
Cit circular loop on a wooden frame. The loop is connected to a
self - N capacitor 400, which may be a variable capacitor with a
varying part 405, in series with the main loop 410. This may
beformed of one or several loops of wire, preferably, coaxi
Note that this is also dependent on the physical dimensions of ally wound. The coil is mounted to a wooden frame 415, by
the wires, as well as the number of turns. mount devices 418.
0046 For a plate capacitor, the external capacitance is 0057 This antenna was demonstrated to have a Q of
approximately equal to around 90 at 3 MHz. It has high losses due to its small copper
Surface.
0.058 FIG.5 illustrates a solenoidantenna which can oper
&o & A ate between 9 and 15 MHz, and has been demonstrated to
Cert =
have a Q of 1300. The Q may be greatly increased, for
example up to 2200, if suspended in air via insulating strings
which is dependent on the area of the plates, as well as the away from solid objects. The loop portion of this antenna 500
distanced between the two plates. induces power into the solenoid portion 505. The solenoid
antenna of FIG. 5 may produce the best performance in cer
0047 Finally, the inductance tain circumstances.
0059 A rectangular loop antenna is shown in FIG. 6. This
antenna is formed of a loop portion 700, capacitive portions
plot. N°. r 705,706, which may be variable capacitors. This antenna has
0.9. A + i. a Qof about 700, over its tunable range of 12 to 14 MHz. Note
that both the inducing part and the regular loop are substan
which is dependent on number of turns squared and radius tially coplanar, and hence that this form factor is usable in a
Squared. laptop computer, for example.
0060 FIG. 7 illustrates a shielded flat-panel antenna,
0048. As explained above, the high Q may create high formed by a number of separate loops 700, 702, 704 all held
Voltages, e.g., up to 5 KV. These reactive Voltages may be together. Each loop 700 has a corresponding variable capaci
evaluated according to: tor 706. This antenna produced a Q of about 100 between 8
U,-O-PR and 10 MHz. While it may have a low L/C ratio due to the
capacitance of the coax cable, it has other packaging advan
0049. An important feature of an embodiment is based on tages.
the relationship between the power source, e.g., the transmit 0061 An unshielded flatbed antenna is shown in FIG. 8
ter, and the load, e.g. the receiver. The efficiency of the cou comprising the inductive loop 800, and the flat-panel antenna
pling between source and load is based on the Q factors of the 805 formed of a single loop 805, in series with capacitor 810.
circuits, mechanical characteristics of the circuits (mostly, This has a Q of about 450, and is tunable between around 9
wire sizing), and the distance therebetween. and 15 MHZ.
0050 For an efficiency p less than 0.3, the efficiency can 0062 Based on all of these tests and experiments, appli
theoretically be expressed as cants have concluded that wireless power coupling using
antennas of this type allows a transfer efficiency of 10% or
greater for short range application, less than 2 m. At the same
ri.2 ra.
.2
Q, Q, K, K, time, the transferable power under the legal exposure con
11(d) s 166 straints is less than 5 W. For a given Q factor, the transfer
efficiency becomes independent offrequency. However, there
may be an optimum frequency for each antenna form factor.
0051. Note that this is proportional to the Q, inversely 0063. An embodiment showing a receive antenna is shown
proportional to the sixth power of distance, and positively in FIG. 9. It is a very small manually tunable antenna on a
proportional to the radius. 40x90 mm flat panel. The antenna has multiple coils of wires,
0052 For energy transfer in the near field, a special kind of in series with two variable capacitors 900, 902. Other analo
analysis must be considered. The inventors found that usable gous sizes may also be used—for example, another embodi
power can be harvested from the stationary wave that is set up ment describes a small antenna of 60x100 mm, flat-panel,
in the near field of an RF coil. For purposes of this embodi manually tunable. Yet another is a medium antenna 120x200
ment, the near field is considered to be W2 for the frequency mm, flat-panel, manually tunable. A large antennais240x310
of interest. FIG.3 illustrates how the near field for 13.56 MHZ mm, also manually tunable.
extends approximately 3.5 m from the center of the transmit 0064 FIGS. 10A-10C illustrates graphically the actual
antenna. results for use with the FIG. 9 antenna. FIG. 10A illustrates
0053 Another constraint may be imposed by radiation the measured resonance frequency of 13.9 MHZ. FIG. 10B
exposure limits. illustrates how this antenna has a 3 dB point at about 1 foot.
US 2009/00 15075 A1 Jan. 15, 2009

Note, unexpectedly, however, that below 10 inches, the computer Such as a workstation. The computer may be an
received power value goes down, not up. This is because the Intel (e.g., Pentium or Core 2 duo) or AMD based computer,
receiving antenna, being in the near field of the transmitting running Windows XP or Linux, or may be a Macintosh com
antenna actually interacts with the transmitting antenna field puter. The computer may also be a handheld computer. Such
by detuning the transmitter. An important feature, therefore, as a PDA, cellphone, or laptop.
is to maintain this detuning within a determinate limit and 0071. The programs may be written in C or Python, Java,
design the system intending to maintain the distance between Brew or any other programming language. The programs may
and transmitter and receiver far enough apart so that the be resident on a storage medium, e.g., magnetic or optical, the
antenna can avoid or minimize undesired de-tuning. How computer hard drive, a removable disk or media Such as a
ever, the antenna systems are intentionally allowed to have memory stick or SD media, wired or wireless network based
both maximum and minimum usable distances. FIG. 10C or Bluetooth based Network Attached Storage (NAS), or
shows a chart with values, thereby illustrating the usable other removable medium. The programs may also be run over
range within which these exemplary antennas can be used. a network, for example, with a server or other machine send
Here that distance range is between approximately 0.15 to 0.2 ing signals to the local machine, which allows the local
m (6-8 inches) and 0.5 m (20 inches). However, with other machine to carry out the operations described herein.
antenna pairs, the minimum distance may be as low as 0.05 m 0072. Where a specific numerical value is mentioned
(2 inches), or as high as 0.3 m (12 inches). herein, it should be considered that the value may be
0065. The general structure and techniques, and more spe increased or decreased by 20%, while still staying within the
cific embodiments which can be used to effect different ways teachings of the present application, unless some different
of carrying out the more general goals are described herein. range is specifically mentioned. Where a specified logical
0066 Although only a few embodiments have been dis sense is used, the opposite logical sense is also intended to be
closed in detail above, other embodiments are possible and encompassed.
the inventors intend these to be encompassed within this What is claimed is:
specification. The specification describes specific examples 1. A method of transmitting power wirelessly, comprising:
to accomplish a more general goal that may be accomplished driving a series resonant antenna at a value near its resonant
in another way. This disclosure is intended to be exemplary, frequency to produce a magnetic field output, said non
and the claims are intended to cover any modification or radiative antenna formed of a combination of resonant
alternative which might be predictable to a person having parts, including at least an inductive part formed by a
ordinary skill in the art. For example, where a variable capaci Wire loop, and a capacitor part that is separate from a
tor is mentioned, a fixed capacitor may be substituted. material forming the inductive part; and
0067. The preferred implementation described here uti maintaining at least one characteristic of said antenna Such
lizes a single, dipole series resonant antenna for the sake of that its usable range has a minimum usable distance over
simplicity, but in general an array of multiple antennas may be which power can be received, which minimum distance
used to shape or direct most of the electromagnetic power in is set by a detuning effect when a receiver gets too close
the wave towards the receive antenna and not towards to said antenna.
'empty space. 2. A method as in claim 1, further comprising receiving the
0068 Methods for control of directionality via adjustment magnetic field in a receiving antenna, said receiving antenna
of sinusoidal wave phase and amplitude in each antenna is also having a series resonant part, and producing usable
well known to those skilled in the other embodiments may power from said receiving antenna, and coupling said usable
optionally make use of the completely different process that power to a load.
we call “sniffing to determine where the receiver is located 3. A method as in claim 1, wherein said minimum useable
before transmitting full power to it. Before full power flow is distance is between 6 and 8 inches.
established, we turn on the transmitter for limited time inter 4. A method as in claim 1, wherein said minimum usable
vals to Scan the space Surrounding the transmitter by means of distance is between 2 and 4 inches.
directive beam for the purpose of determining the presence 5. A method as in claim 1, further comprising setting the
and location of a receiver, if any. resonant frequency to a value of approximately 13.56 MHz.
0069. Furthermore, when comparing the techniques of 6. A method as in claim 1, wherein said non-radiative
generating an intentionally partially evanescent wave vs. the antenna has a Q value of approximately 1400.
technique of generating a partially non-evanescent wave, in 7. A method as in claim 1, further comprising using a
many configurations there may be little practical difference capacitor part which is capable of withstanding at least 1000
between the two results. Partly because portions of near field V.
are evanescent even when the design intent is to produce a 8. A method as in claim 1, further comprising using a signal
non-evanescent wave. Therefore, the mere presence of eva generator to produce said driving, and matching an imped
nescent waves in a portion of the space near the transmit ance of the signal generator to a resistance of the antenna at
antenna is a historically well-known phenomenon and does SOaC.
not imply that we are utilizing the properties of evanescent 9. A method as in claim 1, wherein said antenna has a
waves in any particular way. substantially round outer form factor.
0070 Also, the inventors intend that only those claims 10. A method as in claim 1, wherein said antenna has a
which use the words “means for are intended to be inter Substantially rectangular outer form factor.
preted under 35 USC 112, sixth paragraph. Moreover, no 11. A method as in claim 1, wherein said antenna is a dipole
limitations from the specification are intended to be read into that includes a first inductive part, coupled to receive said
any claims, unless those limitations are expressly included in driving, and a second part, which is physically separated from
the claims. The computers described herein may be any kind said inductive part, said second part formed of at least one
of computer, either general purpose, or some specific purpose loop of wire in series with said capacitor.
US 2009/00 15075 A1 Jan. 15, 2009

12. A method as in claim 11, wherein said an inductive part 25. A system as in claim 24, further comprising a receiving
and said second part have different outer form factors. antenna, also having a series resonant part that has a corre
13. A method as in claim 11, wherein said inductive part sponding resonance to said resonant frequency of said
and said outer part have substantially the same outer form antenna, and has a connection outputting usable power to a
factors. load.
14. A method as in claim 11, wherein said second part is 26. A system as in claim 25, wherein said minimum bound
electrically connected to said capacitor part. useable distance is between 6 and 8 inches.
15. A method as in claim 13, wherein said capacitor part is 27. A system as in claim 24, wherein said minimum usable
a variable capacitor. distance is between 2 and 4 inches.
16. A method, comprising: 28. A system as in claim 24, wherein the resonant fre
transmitting a magnetic field using a first resonant trans quency is set to a value of approximately 13.56 MHz.
mission part; 29. A system as in claim 24, wherein said antenna has a Q
receiving said magnetic field in a second resonant trans value of approximately 1400.
mission part; and 30. A system as in claim 24, wherein said capacitor part is
in said second resonant transmission part, using power capable of withstanding at least 1000 V.
from the magnetic field. 31. A system as in claim 24, further comprising signal
17. A method as in claim 16, further comprising using said generator that drives said antenna, said signal generator hav
power in said second resonant transmission part to drive a ing an impedance of the signal generator that is matched to a
load. resistance of the non radiative antenna at resonance.
18. A method as in claim 16, further comprising detuning at 32. A system as in claim 24, wherein said antenna has a
least one of said transmitting or said receiving when said substantially round outer form factor.
second resonant transmission part gets closer than a prede 33. A system as in claim 24, wherein said antenna has a
termined amount to said first resonant transmission part. Substantially rectangular outer form factor.
19. A method as in claim 16, wherein said transmitting 34. A system as in claim 24, wherein said antenna is a
comprises using a capacitively loaded magnetic dipole for dipole that includes a first inductive part, coupled to receive
transmitting the magnetic field. said driving, and a second part, which is physically separated
20. A method, comprising: from said inductive part, said second part loop, formed of at
forming a magnetic field using a first part; least one loop of plural coils of wire in series with said
coupling said magnetic field to a second part that forms a capacitor.
loosely coupled transformer with said first part, where 35. A system as in claim 34, wherein said an inductive part
said second part is further than 6 inches from said first and said second part have different outer form factors.
part; and 36. A system as in claim34, wherein said inductive part and
in said second part, recovering power from the coupled said outer part have Substantially the same outer form factors.
magnetic field. 37. A system as in claim 34, wherein said second part is
21. A method as in claim 20, further comprising using said electrically connected to said capacitor part.
power in said second part to drive a load. 38. A system as in claim 13, wherein said capacitor part is
22. A method as in claim 20, further comprising detuning at a variable capacitor.
least one of said transmitting or said receiving when said 39. A system, comprising:
second part gets closer than a predetermined amount to said a first resonant transmission part formed of a capacitively
first part. loaded magnetic dipole antenna;
23. A method as in claim 20, wherein said transmitting a second resonant reception part, tuned to have similar
comprises using a capacitively loaded magnetic dipole for resonant characteristics to said first resonant transmis
transmitting the magnetic field. sion part, receiving a magnetic field therefrom, and pro
24. A system comprising: ducing a power output from the magnetic field.
a series resonant antenna; 40. A system, comprising:
a driving part for said series resonant antenna, driving said a first LC circuit, connected to receive a signal that forms a
antenna at a value near its resonant frequency to produce magnetic field; and
a magnetic field output, said antenna formed of a com a second LC circuit that forms a loosely coupled trans
bination of series resonant parts, including at least an former with said first LC circuit, where said second part
inductive part formed by a wire loop, and a capacitor part is further than 6 inches from said first part, and has a
that is separate from a material forming the inductive connection for recovering power from the coupled mag
part, and netic field.
wherein said series resonant antenna has at least one char 41. A system as in claim 40, wherein said first LC circuit
acteristic Such that its usable range has a minimum includes a capacitively loaded magnetic dipole for transmit
usable distance over which power can be received, ting the magnetic field.
which minimum distance is set by a detuning effect c c c c c
when a receiver gets too close to said antenna.