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.

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Status
Published
Publication Date
18-Feb-2020
Current Stage
PPUB - Publication issued
Completion Date
19-Feb-2020
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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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---------------------- Page: 2 ----------------------
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
---------------------- Page: 3 ----------------------
– 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

all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international

co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and

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The main task of IEC technical committees is to prepare International Standards. However, a

technical committee may propose the publication of a technical report when it has collected

data of a different kind from that which is normally published as an International Standard, for

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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– 4 – IEC TR 63239:2020 © IEC 2020

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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– 6 – IEC TR 63239:2020 © IEC 2020
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.
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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– 8 – IEC TR 63239:2020 © IEC 2020
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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– 10 – IEC TR 63239:2020 © IEC 2020
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
---------------------- Page: 12 ----------------------
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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– 12 – IEC TR 63239:2020 © IEC 2020
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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