IEC TR 63239:2020
(Main)Radio frequency beam wireless power transfer (WPT) for mobile devices
Radio frequency beam wireless power transfer (WPT) for mobile devices
IEC TR 63239:2020 presents the surveyed technologies, product development trends, international standards, and regulation trends of RF beam WPT. This report can be used for the research and analysis of projects that apply small-output remote WPT to mobile devices, such as smartphones, Internet of Things (IoT) devices, and ultra-small sensors.
General Information
Standards Content (Sample)
IEC TR 63239
®
Edition 1.0 2020-02
TECHNICAL
REPORT
Radio frequency beam wireless power transfer (WPT) for mobile devices
IEC TR 63239:2020-02(en)
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IEC TR 63239
®
Edition 1.0 2020-02
TECHNICAL
REPORT
Radio frequency beam wireless power transfer (WPT) for mobile devices
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 29.240.99 ISBN 978-2-8322-7869-7
Warning! Make sure that you obtained this publication from an authorized distributor.
® Registered trademark of the International Electrotechnical Commission
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– 2 – IEC TR 63239:2020 © IEC 2020
CONTENTS
FOREWORD . 3
1 Scope . 5
2 Normative references . 5
3 Terms and definitions . 5
4 Introduction to RF beam WPT . 5
4.1 Overview of the RF beam WPT type . 5
4.2 Requirements for RF beam WPT . 6
4.2.1 General . 6
4.2.2 Power transfer system design of RF beam WPT . 7
4.2.3 Available candidate frequencies of RF beam WPT . 8
4.2.4 Operating principle of omnidirectional RF beam WPT . 8
4.2.5 Operating principle of directional RF beam WPT . 9
4.3 Operating scenario of RF beam WPT . 11
4.3.1 Possible requirement for RF beam WPT . 11
4.3.2 Operating scenario of omnidirectional RF beam WPT . 12
4.3.3 Operating scenario of directional RF beam WPT . 12
5 Trends in standards, regulations, and technologies related to RF beam WPT . 14
5.1 Trends in standards related to RF beam WPT . 14
5.2 Trends in regulations related to RF beam WPT . 15
5.3 Trends in global products related to RF beam WPT . 19
6 Summary . 22
Figure 1 – TX and RX structures of RF beam WPT . 7
Figure 2 – Beam pattern diagram of omnidirectional RF beam WPT . 8
Figure 3 – Example of high-output omnidirectional RF beam WPT in the space . 9
Figure 4 – Beam pattern diagram of directional RF beam WPT . 9
Figure 5 – Electromagnetic wave transmission/reception at each pattern antenna of
directional RF beam WPT . 10
Figure 6 – Direction RF beam WPT (a) description on delay generation at each pattern
antenna (b) delay adjustment method to transmit desired signals. 10
Figure 7 – Example of beam pattern formation by the delay and direction adjustment
of the transmission signals of each antenna . 11
Figure 8 – Expected operating scenario of omnidirectional RF beam WPT . 12
Figure 9 – Expected operating scenario sequence of directional RF beam WPT – Pilot
signal transmission from the single RX in case of an obstacle . 13
Figure 10 – Expected operating scenario sequence of directional RF beam WPT –
Directional WPT to the single RX in case of an obstacle . 13
Figure 11 – Expected operating scenario sequence of directional RF beam WPT –
Directional WPT from multiple TXs to multiple RXs in case of an obstacle . 14
Table 1 – Overview of the RF beam WPT type . 6
Table 2 – Characteristics of candidate frequencies for RF beam WPT . 8
Table 3 – Activities of domestic/overseas standardization organizations related to RF
beam WPT . 15
Table 4 – Major recommendations and regulations of standardization organizations
related to WPT for mobile devices. 16
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IEC TR 63239:2020 © IEC 2020 – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
RADIO FREQUENCY BEAM
WIRELESS POWER TRANSFER (WPT) FOR MOBILE DEVICES
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
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The main task of IEC technical committees is to prepare International Standards. However, a
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example "state of the art".
IEC TR 63239, which is a Technical Report, has been prepared by technical area 15: Wireless
power transfer, of IEC technical committee TC 100: Audio, video and multimedia systems and
equipment.
The text of this Technical Report is based on the following documents:
Draft TR Report on voting
100/3212/DTR 100/3317/RVDTR
Full information on the voting for the approval of this Technical Report can be found in the
report on voting indicated in the above table.
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.
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The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to
the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct understanding
of its contents. Users should therefore print this document using a colour printer.
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IEC TR 63239:2020 © IEC 2020 – 5 –
RADIO FREQUENCY BEAM
WIRELESS POWER TRANSFER (WPT) FOR MOBILE DEVICES
1 Scope
This Technical Report presents the surveyed technologies, product development trends,
international standards, and regulation trends of RF beam WPT. This report can be used for
the research and analysis of projects that apply small-output remote WPT to mobile devices,
such as smartphones, Internet of Things (IoT) devices, and ultra-small sensors.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1
IoT
Internet of Things
service-based facilities to provide advanced services by connecting the various things of the
physical world and the virtual world based on information communication technology
Note 1 to entry: Infrastructure computing devices for realizing ubiquitous space are embedded in environments and
things to make them intelligent and to expand the machine-to-machine (M2M) concept, which is capable of intelligent
communication between humans and things or between things to the internet.
Note 2 to entry: The concept has evolved into a concept that interacts with all the information of reality and the
virtual world as well as things. The major technologies of IoT include sensing technology, wired and wireless
communication and network infrastructure technology, IoT interface technology, and service technology through IoT.
3.2
Wi-Fi
Wireless-Fidelity
certification mark provided to products compatible with the regulations determined by the
wireless LAN (WLAN) specifications (IEEE 802.11b) using 2,4 GHz
Note 1 to entry: Among the products manufactured in accordance with these specifications, the ones that passed
the test of the Wireless Ethernet Compatibility Alliance (WECA), a group founded by wireless-network-related
companies, can have this mark.
4 Introduction to RF beam WPT
4.1 Overview of the RF beam WPT type
RF beam WPT performs remote WPT using omnidirectional or directional antenna beam
patterns. This type is divided into the omnidirectional type, in which electromagnetic waves are
radiated in all directions to achieve constant radiation intensity in any direction, and the
directional type, in which radio waves are transmitted in a certain direction. Table 1 shows the
Overview of the RF beam WPT type.
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Table 1 – Overview of the RF beam WPT type
Electromagnetic waves
Omnidirectional Directional
Representative figure
Operating principle Electromagnetic wave radiation
Pt Pt X Gt
Electric field intensity
(Pt: transmitting power) (Gt: Antenna Gain by beamforming)
Small in proportion to Gt compared to Large in proportion to Gt compared to
Efficiency
directional RF beam WPT omnidirectional RF beam WPT
Long distance
Long distance
Transfer distance
(transfer up to the ~m unit is possible if
(up to ~m)
Line of Sight (LOS) is secured)
Mobility Possible Possible
There are issues on human safety. There are issues on human safety.
Safety
Human body protection should be Human body protection should be
considered. considered.
RF RF
Used frequency
(Hundred MHz, Several GHz) (Hundred MHz, Several GHz)
Standardization trend No standard No standard
4.2 Requirements for RF beam WPT
4.2.1 General
RF beam WPT radiates electromagnetic waves and is significantly different from the two
following two non-beam types in the operating principle for transferring power. The magnetic
induction and magnetic resonance types use non-radiation WPT and transfer power between
TX(Transmitter) and RX(Receiver) in close proximity using the magnetic lines of force and
resonance generated by alternating current (AC). On the other hand, RF beam WPT can
transfer power by radiating electromagnetic waves through an antenna as in wireless
communication. TX transmits the power of an electromagnetic wave oscillator using a
directional antenna while RX receives microwaves using an antenna and converts it to a direct
current (DC) power source through a rectifier to obtain power.
While RF beam WPT has a benefit in the charging distance because it enables remote charging
for multiple devices at the same time, it may affect the human body and exhibits very low power
efficiency. The recent technology achieved the power efficiency of very low power at the
distance of several meters, but studies to verify and avoid its effects on human health are
considered essential for the commercialization of RF beam WPT in the future. It is important to
note that the beam WPT needs to arrange conditions for sharing the frequency with existing
radio stations because it has the property of radiating the beam into space and transmitting
power. In this Subclause 4.2, the system design of the RF beam type, candidate frequencies,
and the operating principles of the omnidirectional and directional RF beam types are discussed.
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IEC TR 63239:2020 © IEC 2020 – 7 –
4.2.2 Power transfer system design of RF beam WPT
Figure 1 – TX and RX structures of RF beam WPT
Figure 1 shows the TX and RX circuit diagrams of RF beam WPT. In a WPT system, TX consists
of a microwave power source, a waveguide circulator, a waveguide adaptor, and a tuner and
directional coupler. The microwave power source generates an amplified signal for signal
control. The waveguide circulator and adaptor are required to generate specific required
frequencies such as GHz through signal response and adjustment. The tuner and directional
coupler filters unrequired frequencies as well as noise and matches the transmitter impedance
for the transmitting antenna.
RX consists of an impedance matching and filter circuit, a coax-waveguide adaptor, and an RF-
DC converter. The impedance matching and filter circuit matches the receiver impedance for
the receiving antenna, and the coax-waveguide adaptor extracts specific required frequencies
through signal response and adjustment. Finally, the RF-DC converter converts the received
electromagnetic waves into DC power.
Since the purpose of RF beam WPT systems is to radiate power wirelessly, it is necessary to
design systems focusing on the transfer distance, spatial loss, power consumption of RX, and
RF-DC rectification efficiency. In RF beam WPT systems, the magnitude of the spatial loss of
power according to the distance is given by the Friis equation and its value is determined by
the three major elements, which are the used frequency, transferred power, and transfer
distance. Equation (1) shows the Friis equation.
2
λ
P = P G G ( (1)
RX TX TX RX
4πr
where P is the power input to the receiving module, P the power produced by the
RX TX
transmitting antenna of the transmission module, G and G the gains of the transmitting and
TX RX
receiving antennas, λ the wavelength of the used frequency, and r the distance between the
transmitting and receiving modules.
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4.2.3 Available candidate frequencies of RF beam WPT
Electromagnetic radiation technology uses GHz frequencies with short wavelengths for
long-distance wireless power transfer. Long-distance power transfer using high-output
electromagnetic waves in the industrial, scientific, and medical (ISM) bands such as 900 MHz,
2,4 GHz, and 5,8 GHz (900 MHz for the United States), may cause problems in terms of
efficiency and human health effects. Table 2 shows the characteristics of some candidate
frequencies for RF beam WPT. Whether RF beam WPT is ISM equipment or not is currently
being examined in ITU-R, and no conclusion has been obtained yet. Generally, in order to share
a frequency, coordination with radio stations that already use the frequency is required.
Table 2 – Characteristics of candidate frequencies for RF beam WPT
Candidate
Characteristics
frequency
More robust, less prone to interference
Pros
Lower attenuation, travels further through more obstacles
900 MHz
Cons Components are larger at lower frequencies
Wi-Fi facility can be used if possible
Pros
Components are smaller, cheaper
2,4 GHz
Congested band due to abundance of Wi-Fi, Bluetooth, microwaves, cordless phones
Cons
Attenuates much more quickly, will not pass through metal
Pros Less congested, few RF devices in this band
5,8 GHz
Low transmit power limitations
Cons
High attenuation in cables, requires very high gain antennas
4.2.4 Operating principle of omnidirectional RF beam WPT
Figure 2 – Beam pattern diagram of omnidirectional RF beam WPT
Figure 2 shows a brief diagram of a beam pattern diagram of omnidirectional RF beam WPT.
Omnidirectional RF beam WPT mainly transfers power to a remote distance by radiating
electromagnetic signals from a transmitting antenna to all directions through the air using the
electromagnetic waves of several GHz or higher. This type is capable of long-distance
transmission and reception because it uses high frequencies such as GHz and THz frequencies.
Its operating principle can be briefly introduced as follows. First, TX transmits electromagnetic
waves using a frequency with high energy. RX then receives the waves using a rectenna (in
which an antenna and a rectifier are combined) and converts them into DC power. If
approximately 5 W power is radiated from TX, RX receives only 2 mW to 4 mW of power (less
than 1 % efficiency). The power received by RX causes no human safety problem because it is
too small, but serious human safety problems may occur near TX with high output. Currently,
there is no efficient method capable of using this type, but technologies for high-output WPT
have been devised to be used in outer space in the future. Figure 3 shows an example of
high-output omnidirectional RF beam WPT in outer space.
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IEC TR 63239:2020 © IEC 2020 – 9 –
Figure 3 – Example of high-output omnidirectional RF beam WPT in space
4.2.5 Operating principle of directional RF beam WPT
Figure 4 – Beam pattern diagram of directional RF beam WPT
Directional RF beam WPT has the same effect as the spotlight shed on an actor on stage. In
an antenna array, the signals of each antenna are filtered or added depending on the
frequencies of adjacent signals. TX transfers power to limited targets by forming directional
beam patterns using constructive interference or destructive interference at certain angles.
Figure 4 shows a beam pattern diagram of directional RF beam WPT. Directional RF beam WPT
may occur at TX or RX to achieve spatial selectivity. It is different from omnidirectional
transmission and reception in that signals can be directional.
The signal radiation principle of directional RF beam type can be briefly summarized as
matching phases between the radiating signals of adjacent antennas. Each antenna offsets
signals in unwanted directions for radiating signals in a desired direction. Each antenna is
designed to control the direction of signals to obtain the antenna gain of the signals in a desired
direction. Figure 5 shows electromagnetic wave transmission/reception at each pattern antenna
of directional RF beam WPT. For example, each antenna pattern is designed to be a constant
pattern so that it could be half the used electromagnetic wave frequency. In this way, when
electromagnetic waves are transmitted, the delay between the transmitted signals becomes a
fixed value, making it possible to control the signals generated by all antennas. By adjusting
the phase of each antenna in this way, the transmission direction and magnitude of the entire
beamforming signals of an array antenna system can be controlled. Figure 6 shows the direction
RF beam WPT description on delay generation at each pattern antenna and Figure 7 shows an
example of beam pattern formation by the delay and direction adjustment of the transmission
signals of each antenna.
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Figure 5 – Electromagnetic wave transmission/reception
at each pattern antenna of directional RF beam WPT
a) b)
Figure 6 – Direction RF beam WPT (a) description on delay generation at each
pattern antenna (b) delay adjustment method to transmit desired signals
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IEC TR 63239:2020 © IEC 2020 – 11 –
Figure 7 – Example of beam pattern formation by the delay and direction adjustment
of the transmission signals of each antenna
4.3 Operating scenario of RF beam WPT
4.3.1 Possible requirement for RF beam WPT
In Subclause 4.3, the operating scenario of charging mobile devices using RF beam WPT is
discussed. The operating scenario of charging devices using RF beam WPT is described in this
Subclause 4.3. The environment assumed in the operating scenario is as follows.
a) Operating distance: 4 m (15 feet)
b) Charged devices: smartphone and wearable devices
c) Transmission power of each antenna: 23 dBm (transmission power used in wireless
communication; selected as it is considered harmless to human health)
d) Used frequency: 2,4 GHz or 5,8 GHz, which is used in Wi-Fi wireless communication
e) Charging method: RF beam WPT area at bus or subway stations
As described in the operating scenario of this document, the output of the transmitter installed
in the omnidirectional RF beam WPT area is considered harmless to human health because it
uses 23 dBm that satisfies human safety regulations. In addition, as power is radiated through
the RF beam type, more TXs can perform WPT to more RXs. The frequency used by TX shall
be determined after discussion with each device manufacturer. Frequencies of 2,4 GHz or
5,8 GHz, however, are considered for use with Wi-Fi, which is applied to all IoT devices. In this
case, there seems to be no problem with the sizes of the antennas included in each device.
Using these frequencies, however, may involve problems such as collision with communication
that uses the same frequency. Therefore, it is necessary to use WPT that does not cause
collisions with wireless communication, such as frequency occupancy (e.g. RF beam WPT using
the first or the last frequency band not used by wireless communication).
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4.3.2 Operating scenario of omnidirectional RF beam WPT
Figure 8 – Expected operating scenario of omnidirectional RF beam WPT
Figure 8 shows an expected operating scenario of omnidirectional RF beam WPT. When device
A possessed by a user having a smartphone arrives at a bus stop, it recognizes that it is in the
RF beam WPT area. The user activates the function of the TX of omnidirectional RF beam WPT
using an application. This process can be performed automatically under the assumption that
the user wants wireless power reception when the application is operating. For WPT between
the smartphone of the user and TX, first the required information (e.g. essential information for
safe power reception such as the rectifier voltage information of the device, desired voltage,
and battery status) is exchanged. When WPT is approved finally, TX radiates power in the form
of electromagnetic waves and RX finishes preparation for receiving power. Now, the RF beam
WPT area is activated, and if device B possessed by another user approaches the area, TX
determines whether power is also transmitted to device B through the same certification
procedure as that for device A. If device B does not want to receive power, device B can cut off
the circuit to receive the RF beam WPT because omnidirectional RF beam WPT is activated in
the area.
4.3.3 Operating scenario of directional RF beam WPT
Since directional RF beam WPT focuses power on a certain point or device using multiple
antennas, its operating scenario is somewhat different from that of omnidirectional RF beam
WPT. Although the output radiated by each antenna is identical due to human health problems,
technologies required to perform directional WPT with high efficiency are described.
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IEC TR 63239:2020 © IEC 2020 – 13 –
.
Figure 9 – Expected operating scenario sequence of directional RF beam WPT –
Pilot signal trans
...
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