WIRELESS POWER TRANSMISSION IN URSI

Naoki Shinohara

Research Institute for Sustainable Humanosphere, Kyoto University, Gokasho, Uji, Kyoto, Japan

shino@rish.kyoto-u.ac.jp

Keywords: Wireless Power Transmission, Energy Harvesting, Rectenna, Beam Forming, Phase Array

Abstract: In URSI, Inter-Commission Working Group on Solar Power Satellites (SPS) was established in 2002 and

the URSI Board has been working on writing and reviewing an URSI White Paper on SPS, which was

published on June 2007, because the SPS is one of huge application of radio science. One of important

application of the radio science on the SPS is a wireless power transmission (WPT) via microwave

(microwave power transmission ; MPT). At first, the WPT walked along with the SPS. But now we have

some kinds of the WPT and its commercial applications. One of important application of the WPT is an

energy harvesting. The other is MPT for the SPS. Some important researches are done as URSI activities in

Japan. It is high efficiency rectenna development at low power and at wide band frequency. It is also high

efficiency and low cost phased array for the MPT and the SPS. Some of them were published in URSI

conference. In this paper, I will show mainly present status of the WPT in Japan and in the world and will

also show a relationship between the WPT and the URSI activities.

1 INTRODUCTION

In URSI, Inter-Commission Working Group on

Solar Power Satellites (SPS) was established in 2002

and the URSI Board has been working on writing

and reviewing an URSI White Paper on SPS because

the SPS is one of huge application of radio science.

The White Paper on SPS was published on June,

2007(SPS White Paper, 2013). One of important

application of the radio science on the SPS is a

wireless power transmission (WPT) via microwave

(microwave power transmission ; MPT). The MPT

researches walked along the SPS researches from the

end of 1960s(Brown, 1984)(Matsumoto, 2002). The

SPS was one and only application of the MPT

because the commercial or industrial MPT system,

especially antennas, theoretically become larger than

that imagined by users. But in 21

century, some

new WPT systems arise to be applied for the

commercial or industrial uses(Shinohara, 2011). One

is called a resonance coupling WPT which was

established by MIT’s group in 2006. The other is

called an energy harvesting which includes

rectifying technologies from weak broadcasting

radio waves and power generations from vibration,

heat, and light, etc. Technologies for the energy

harvesting from radio waves and for the MPT are the

same. Difference is only that the energy harvesting

is a passive system only with a rectenna, rectifying

antenna, against that the WPT is an active system

with a power transmitter (Fig.1). The energy

harvesting is supported by low power device

technologies and is applied for ubiquitous sensor

network or simple wireless communications. On

contrary, we can transmit power and information

simultaneously on the WPT system. The URSI can

support to make new theory of the MPT including

the energy harvesting and the SPS and can advance

its commercialization. In this paper, I will show

mainly present status of the WPT in Japan and in the

world and will also show a relationship between the

WPT and the URSI activities.

Shinohara N.

WIRELESS POWER TRANSMISSION IN URSI.

DOI: 10.5220/0004785100490053

In Proceedings of the Second International Conference on Telecommunications and Remote Sensing (ICTRS 2013), pages 49-53

ISBN: 978-989-8565-57-0

Energy Harvesting

Transmitter

・We need only a part of transmitted

power (which is wasted as wireless

communications)

・Wide band because we transmit an

information

Transmitter

Transmitted

Power

Receiver

→Power

・We need almost all transmitted

power

・Very narrow band because we use

carrier (pure)

・Simultaneous transmission of power

and information is available.

.Conversion efficiency is important.

Receiver

→Power

Only Carrier for WPT

Time and Space

Information

Frequency

Very Narrow

Wide

Electric Power

to User

Electric Power

to User

Receiver

→Power

Transmitted

Power

Transmitted

Power

Transmitted

Power

Frequency

Time and

Space

Transmission efficiency is important.

Microwave Power Transmission

Figure 1 Microwave Power Transmission and Energy Harvesting

2 ENERGY HARVESTING

An energy harvesting is most hopeful wireless

power application recently because there have been

no allowed frequency for a wireless power

transmission in the world. The energy harvesting

does not require special frequency because the

system is passive and the wireless power is

harvested from broadcasting radio waves or waves

of wireless communications. There are a lot of

researches and developments of the energy

harvesting systems in the world(Sample,

2009)(Collado, 2012)(Visser, 2013)(Popovic, 2013).

Some of them are researches based on RF-ID

technologies and some of them are that based on the

energy harvesting from the other power source like

vibration or solar.

In Japan, there are also some trials of the energy

harvesting from broadcasting waves. One is carried

out by ATR (Advanced Telecommunications

Research Institute International). They evaluated an

energy harvesting system from an 800 MHz cellular

BS. For this system, they developed an 800 MHz

band twin-loop antenna and an RF-DC conversion

circuit. The antenna gain of 5.2 dBi and the RF-DC

conversion efficiency of 9 % at -20 dBm input

power were obtained. Experimental results showed

that a 1.0 F electric double layer capacitor was

charged up to 469 mV in 19 hours and drove a low

power LCD thermometer for 10 minutes using its

stored energy(Kitazawa, 2013).

The other group is Univ. of Tokyo. They

developed an energy harvesting system from UHF

(at 550MHz) broadcasting wave. They chose charge

pump rectifying circuit to charge the tank capacitor

to 1.8 and 3.0V are 38 and 70 micro-watts

respectively at 550 MHz. At a distance of 6.5km

from Tokyo TV tower, the energy harvesting circuit

charges up the 100uF charge tank to 2.9V in

3minutes making such a device ideal for battery less

operation of wireless sensors for remote

monitoring/sensing in most urban areas using just

the existing terrestrial TV broadcast infrastructure

for power(Vyas, 2012).

Kyoto University’s group focuses on development

of high efficiency rectenna at low power and at wide

band frequency. First of all, we, Kyoto University’s

group, developed high efficiency rectenna at 5.8GHz

with pure spectrum in a MPT system. We proposed

a concept of ‘Ubiquitous Power Source (UPS)’ with

the MPT technologies(Shinohara, 2005). In the UPS

system, we transmit a microwave power whose

microwave is not modulated and pure spectrum and

whose power is limited below 1mW/cm

, safety

regulation for human. We chose frequency of

2.45GHz or 5.8 GHz which are on ISM (Industrial,

Science, and Medical) band. We developed high

efficiency rectenna at low power with expectation of

Second International Conference on Telecommunications and Remote Sensing

application for the UPS and the energy harvesting. A

picture of the developed rectifying circuit of the

rectenna is shown in Fig.2. Target frequency is

5.8GHz continuous wave (CW). The circuit is based

on shingle shunt full wave rectifier whose theoretical

RF-DC conversion efficiency is 100% with one

diode only. As a rectifying theory, line length

between a diode and a capacitance (C2) must be λ/4

for 100% efficiency. However, we change the line

length between a diode and a capacitance to increase

the RF-DC conversion efficiency at 1mW. As a

result, we achieved approximately 50% of the RF-

DC conversion efficiency at 1mW, 1kΩ in 5.8GHz

CW(Fig.3).

LPF

DC cut capacitance

Diode

（HSMS285B）

：

capacitance for output filter 1

load

C3：capacitance

for output filter 2

LPF

DC cut capacitance

Diode

（HSMS285B）

：

capacitance for output filter 1

load

C3：capacitance

for output filter 2

Figure 2 Developed Rectenna for Rectifying of Low

Power

400 600 800 1000 1200

負荷抵抗

[

]

RF- DC変換効率

[

]

Connected Load (Ω )

RF-DC Conversion Efficiency (%) (Exp.)

Figure-3: Experimental Result of Load

Characteristics of RF-DC Conversion Efficiency at

1mW input microwave power (without Low-Pass

Filter)

For 2.45GHz system, we chose the other approach

to increase the RF-DC conversion efficiency of the

rectenna. Optimization of the line length between a

diode and a capacitance was the same. However, we

could not increase the efficiency enough with one

diode only. Therefore, we increased a number of the

diodes and put them like a charge pump rectifier

without capacitances (Fig.4). As circuit simulations,

we achieved 55.3% at 0.1mW, 8.2kΩ in

2.45GHzCW with type of 6EA (Fig.5). All

distributed lines and capacitances are optimized and

different in each circuit. Optimum connected loads

are also different in each circuit. This was

collaborative research with Kyoto University and

Mitsubishi Electric Corporation.

SBD:2コ

E1 E2

E2 E3

SBD

E1 E2

E2 E3

SBD

E1 E2

E2 E3

SBD

SBD:3コ

SBD

E1 E2

E2 E3

SBD

SBD:3コ

SBD

E1 E2

E2 E3

SBD

E1 E2

E2 E3

SBD

E1 E2

E2 E3

SBD

SBD:1コ

SBD:4コ

E1 E2

E2 E3

SBD

SBD RL

E1 E2

E2 E3

SBD

SBD:6コ

SBD

E1 E2

E2 E3

SBD

E1 E2

E2 E3

SBD

1EA

2EA

3EA

4EA

6EA

Figure-4 Proposed Rectifying Circuits in

2.45GHzCW (E : Distributed Line, C : Capacitance,

SDB : Shottky Barrier Diode)

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

ut Power

[

]

[

]

ode

EA Di

ode

4EA Di

ode

EA Di

ode

2EA Di

ode

1EA

▼

55.3％

3EA

2EA

1EA

4EA

6EA

with 8.2kΩ 3.9kΩ 3.9kΩ 1.8kΩ 1.8kΩ

Figure 5 Simulation Results of Proposed Rectifying

Circuits in 2.45GHzCW

Wireless Power Transmission in URSI

RF-DC conversion efficiency of these rectennas at

low input power is high. However, these are only for

continuous waves. We have to develop a rectenna

for modulated radio waves whose frequency range is

wide. Theoretically, it is difficult to increase RF-DC

conversion efficiency by modulated radio waves

because some high Q circuits like distributed lines

are used to increase the efficiency in a single shunt

rectifier. For an energy harvesting with high

efficiency, we, Kyoto University and NTT, proposed

new rectifying circuit based on the single shunt

rectifier in 2013(Shinohara and Hatano, 2013). It is

in 24GHz band. The experimental result is shown in

Fig.6. We put sector-type open stubs as resonators at

higher harmonics instead of a capacitance in a single

shunt rectifier. Compared with normal stubs as

resonators at higher harmonics, the frequency range

is expanded.

(a)

(b)

Figure 6 Simulation Result of RF-DC Conversion

Efficiency of Class-F Load Rectenna with Sector

Stubs(a) with Impedance Matching at 24GHz (b)

with Impedance Matching at All Frequencies

(Shinohara, 2013)

3 MICROWAVE POWER

TRANSMISSION

In URSI activities, we mainly focused on a MPT and

a SPS as a MPT application in Japan. Especially,

high efficiency beam forming in the MPT and the

SPS system is important work. It is not only a new

beam forming theoretical algorism but also a beam

forming algorism with considering a phased array

system.

For the SPS, phased arrays for the MPT were

historically developed (Shinohara, 2013). Magnetron

phased array developed in Kyoto University is one

of hopeful phased array for the SPS. We developed

phase controlled magnetron for the SPS. However,

one magnetron generates high microwave power, for

example, 1kW. For the SPS, the high output power

is a weak point because an output power from 1

antenna in the SPS will be less than 1 W. We have to

coexistent both beam forming without grating lobes

and high efficiency array. In order to coexistent both,

we consider two systems. One is a phased array with

power divider and sub-phase shifters whose loss are

small, between antennas and a magnetron

(Shinohara, 2002). We showed that we could keep

high beam collection efficiency at wider beam

scanning with magnetron phased array with sub-

phase shifter, comparing the simple magnetron

phased array. Based on the result, we developed

magnetron phased array with sub-phase shifters in

Kyoto University (Fig.7). The research results were

referred in URSI White paper on SPS.

Figure 7 Magnetron Phased Array with Phase

Controlled Magnetron through 1-bit sub-phase shifters

after 8-way power dividers

The other approach to coexistent both beam

forming without grating lobes and high efficiency

array, we proposed new random array to suppress

grating lobes and to increase beam collection

efficiency simultaneously (Shinohara, 2008)

(Shishkov, 2009)(Shishkov, 2011). In conventional

random array, we can suppress grating lobes with

large antenna spacing like a magnetron array.

However, energy of the grating lobes merges not to

main lobe but to side lobes. As a result, beam

collection efficiency of large spacing array with

grating lobes and random array without grating lobes

Second International Conference on Telecommunications and Remote Sensing

are the same and low. With our new proposed

element spacing algorism, grating lobes are

suppressed and beam collection efficiency is

increased simultaneously (Fig.8).

Figure 8 Beam Patterns of data3 (Proposed New

Positioning Algorism) and data2 (Conventional

Random Array), data1 (Uniform Array) for 1000

elements, average spacing

and uniform

excitation (Shinohara, 2008)

4 CONCLUSIONS

Radio waves can carry not only information but also

energy. A wireless power transmission is one of

important new radio scientific and technical region

in URSI. In this paper, I only show technical results

of the WPT and an energy harvesting. However,

propagation, plasma physics, EMC and biomedical

of the radio wave are also very important matters to

realize commercial WPT and the SPS. I hope fruitful

discussions will be in URSI.

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Wireless Power Transmission in URSI