EMlLight Hybrid Energy Harvesting with Directional Dipole Antenna for loT Sensor In-June Hwang, DukSoo Kwon, Dong-Jin Lee, Jong-Won Yu Department of Electrical Engineering
Wang-Sang Lee Dept. of Electr. Eng'/Engineering Research Institute (ERI)
Korea Advanced Institute of Science and Technology (KAIST)
Gyeongsang National University
Daejeon, South Korea
Jinju, South Korea
[email protected]
[email protected]
Abstract-A hybrid electromagnetic (EM) and light energy
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harvester is proposed for autonomous loT sensor. The hybrid energy harvester is comprised of dipole rectenna in 91SMHz ISM band and flexible photovoltaic film . The photovoltaic film is integrated on metal surface at a certain distance from dipole antenna, which plays a role as a reflector. This integration has little effect on antenna performance and increase of antenna gain.
A prototype of loT sensor with proposed harvester is fabricated.
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The proposed hybrid energy harvester obtains DC power from
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both of energy sources which and can be used with loT sensor.
I. INTRODUCTION
Drive Dipole
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Recently, energy-harvesting technologies and studies on au
Photovoltaic Film as a Reflector
tonomous devices have increased with the entrance to concept such as Internet of Things (loT). The energy harvesting is a process to produce the power for operation of wireless sensors
DC-DC
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from external environment source, such as electromagnetic
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(EM), solar, thermal, and vibration. However, the amount of capturable energy from each sources is very limited. Therefore,
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the hybrid energy harvesting methods, which can obtain the
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Photovoltaic �
of power.
Fig. 1.
In this paper, a main interest is power capturing from both EM and light source. There were some concerns about
PV
D,
D2
Structure of the proposed hybrid energy harvesting circuit
Fig. 1 shows the proposed hybrid energy harvesting circuit
to obtain compact integration and minimize the effects of the cell on antenna performance. Earlier studies
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II. DESIGN OF THE HYBRID ENERGY HARVESTER
realization of EM/light hybrid energy harvesting. One is how
(PV)
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energy from different sources, is necessary to enough supply
photovoitaic
loT Sensor Application
with directional dipole antenna operating at 91SMHz ISM
cells are attached on the weak field
band. The proposed directional dipole antenna is composed
region of the antenna structure. The other is the DC power
of a dipole antenna and a parasitic element with a flexible
combining circuit which is necessary for combining energy
photovoltaic film. The dipole antenna and parasitic plate are
have proposed the
implemented in a FR4 substrate of 1.6mm thickness. This plate
obtained from EM, solar, or both [1-3]. The proposed hybrid energy harvester is demonstrated as in
acts as a reflector of the dipole, and the photovoitaic film is
PV
the following. It is shown that an flexible photovoitaic film is
attached on this plate. This arrangement of dipole and
placed at a metal plate with a certain spacing from dipole
can minimize the interaction of them and increase the antenna
cell
antenna. This arrangement is an effective and synergistic
directivity and gain of dipole.
method for minimizing effect on the antenna performance and
The dimensions of the proposed directional antenna with
increasing the antenna gain compared to a simple dipole. The
photovoitaic-combined reflector are Ll =71.Smm, L2=82mm,
metal plate with photovoltaic film works by a reflector of the
WI =9mm, ant W2=3Smm. The length L2 of parasitic plate is
dipole antenna, and overall structure have a form of Yagi-Uda
longer than of dipole length L1, then the impedance of plate
antenna. And, an loT sensor applied EM/light energy harvester
is inductive which act as a reflector. The prototype of loT sensor applying hybrid energy har
is fabricated. The increase of obtained power through the use of hybrid harvesting is verified.
978-1-4799-781S-1/15/$31.00 ©2015 IEEE
vester is implemented. The output power of rectenna and
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PV
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D/ ./ ,,",'V ,-,:;j ,A'" ,A' EM Energy Transmitter
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1m
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o~~~.-~~_.~~~~~~~~~ 100 110 120 130 140 150 160 170 180 190 200 Distanee (em)
Fig. 5.
Fig. 2. Measured received power by spacing between the dipole and reflector
cell is combined at energy storage capacitor which capaci tance is SOmF. The obtained energy drives the bluetooth low energy chip and sensors such as temperature, humidity, and illuminance.
Measured wakeup time for operating proposed loT sensor
and reflector, has effect on return loss and antenna gain. The optimized distance D, which has minimal effect on antenna performance and higher directivity than single dipole, is determined by 6Smrn. The reflection coefficient of the proposed antenna is mea sured with Protek A333 Vector Network Analyzer. Fig. 3
III. MEASURED AND SIMULATED RESULTS Fig. 2 shows the received power at 1m from the EM energy transmitter with a signal of 3W EIRP in 91SMHz. The received power PR of the structure with a reflector is varied with the distance D. This figure also shows the effect of attached PV film on antenna when the light illuminated on PV film, or not. The measured values of these two conditions have small differences. The antenna performance is not affected by the operation of PV film. Change in the parameter D, the gap between the dipole O ,-------�--__,
shows measured return loss. -10 dB bandwidth is 149MHz at SI9-96SMHz, and can covers 91SMHz ISM band. Fig. 4 demonstrates simulated absolute radiant gain at 91SMHz. The gain of main lobe in 6.31dBi increased by about 4dB from 1.97dBi of single dipole. Note that the proposed arrangement of a reflector with PV film can obtain the minimal effect on each energy harvester and synergistic effect by increasing antenna gain. The loT sensor, which obtains drive energy from proposed hybrid energy harvester, operates with charged power on the capacitor. The wakeup times with distance between EM energy transmitter and loT sensor, which the operating period of loT sensor, are measured and represented in Fig. S. The obtained power is in inverse proportion to wakeup time. It is verified
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that the hybrid energy harvesting with EM and light gets power over the case of single EM source. IV. CONCLUSION This paper presented hybrid energy harvesting circuit with efficient arrangement of an antenna and a PV film which
30
has a form of Yagi-Uda antenna. Proposed integration had no performance degradation of each harvesters, and improves 40+---�----r_--��L,�--�-- ,_--�--� 0.9
0.8
0.7
1.0
1.1
Frequency (GRz)
Fig. 3.
Simulated and measured return loss with/without reflector
antenna directivity. The proposed circuit can obtain the driving energy from EM and light source, and transmit the sensed environment information. REFERENCES
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