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APUSNCURSINRSM.2017.8072845

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A Novel Efficient Multiple Input Single Output RF
Energy Harvesting Rectification Scheme
O. Björkqvist, C. I. Kolitsidas, Student Member IEEE, O. Dahlberg, G. Silver, M. Mattsson and B.L.G Jonsson
KTH Royal Institute of Technology
School of Electrical Engineering
Department of Electromagnetic Engineering
SE 100 44 Stockholm, Sweden
e-mail: oskarbjo@kth.se
Abstract—In this work an implementation of an ambient radio
frequency harvesting system utilizing multiple input single output
approach is demonstrated. Measurements of typical ambient
radiation have been conducted with respect to power levels
and frequency to determine which communication signals are
suitable for harvesting. The measurement campaign showed that
the WiFi frequency band at 2.45 GHz is a good candidate for
indoors applications. A Greinacher voltage doubler is used for
the rectification. A multiple input single output - MISO scalable
scheme approach is implemented that is able to provide a DC
differential output voltage. Simulated and experimental results
proved the MISO rectenna to be an efficient scheme for RF
harvesting.
I. I NTRODUCTION
The automation and digitalization of society has resulted
in more functionality than ever being carried out using electronics and wireless communication systems. Optimizing and
making systems more efficient is in constant focus and electric
control systems can be found in anything from automotive
control to systems that regulate the temperature in buildings.
Automation of a system requires that the system is able to
provide information about itself and its current physical state.
This makes sensing circuits play a significant role in modern electric systems. Sensors provide the translation between
physical and digital information and can give measurements of
physical quantities such as temperature, position, acceleration
and much more. An ideal sensor should provide this translation
in a seamless manner by being easy to use, environmentally
friendly and having a small need of maintenance. In the case
of a stand-alone sensor that does not need to be in constant
use, an appealing solution to all these problems is to power
the sensor entirely with energy that is available in the physical
vicinity of the sensor, and RF energy is abundant in a modern
environment.
The idea to capture and store microwave energy is commonly referred to as radio frequency (RF) harvesting and
has gained an increasing amount of attention in recent years.
Several studies, [1], [2], have been made on the topic and
it has been proved that the approach of harvesting ambient
microwave energy is a viable approach.
978-1-5386-3284-0/17/$31.00 ©2017 IEEE
II. A SCALABLE M ULTIPLE I NPUT S INGLE O UTPUT RF
HARVESTING SCHEME
A scalable MISO approach is utilized for the full system.
This is illustrated in Fig. 1. This design also makes it possible
to combine any number of antennas and input signals to a
single output signal. The full rectification circuit has two inputs
that can receive signals from two different sources. By utilizing
two antennas, the total gain of the antenna system is doubled
and more energy will be captured. This, in contrast to just
using one antenna and dividing the power, [3], to the two
ports, provides twice the amount of energy given that the
two antennas receive similar signals. This is further exploited
by combining two antenna ports to a full wave voltage
doubling Greinacher circuit. Combining the DC outputs in
series of every rectifier utilized in the system the DC voltage
is multiplied. The two Greinacher circuits are connected in a
topology where positive and negative rectification happens in
different branches forming a differential DC output.
Fig. 1. The proposed scalable MISO approach.
III. R ECTENNA DESIGN AND IMPLEMENTATION
The RF harvester is aimed for indoors application and is
going to be placed in a rich scattering and polarization envi-
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AP-S 2017
ronment. An X-shaped slot has been introduced to the patch
layout for miniaturization. The patches are dual polarized to
accommodate the expected rich scattering environment. The
layout of the patch antenna is illustrated in Fig. 2 and the
constructed antennas in Fig. 3. A foam material, Rohacell
51HF is used with a thickness of 6 mm, dielectric constant
r = 1.075 and tan δ = 0.0002 - properties that are close to
resembling the characteristics of air - is used as a substrate.
Fig. 2. A suggested setup of two patch antennas and a detail of the patch
antenna layout.
50Ω to match the simulation setup. The deviations from
the simulations are mainly due to the manufacturing of the
antennas.
The rectifiers are designed on a very low loss PTFE Teflon
substrate with dielectric constant r = 2.53. The simulated
and measured results are presented in Fig. 5 where a good
agreement between simulations and measurements is achieved.
In Fig. 5 the developed rectifier layout and the constructed one
are depicted as well. The down shift of the rectifier is due to
the diode soldering.
Fig. 5. Simulated and measured S(1,1) of the proposed rectifier where in
picture the layout and the realized circuit are visible.
IV. C ONCLUSION
In this work a novel MISO RF harvesting system is proposed where two antennas are utilized to yield one differential DC voltage output. The system can become scalable
and multifunctional where different frequency bands can be
covered making and combined in series as voltage outputs. The
scalability of the system stems that it can easily be extended
in array or the array can consists of different frequency scaled
versions of this realization. All the DC voltage outputs will
combine again in series in the same point for maximizing the
voltage output. The frequency bands selected when the system
is scaled are depended in the available environmental RF bands
where the harvester will be placed.
Fig. 3. The constructed patch antennas.
ACKNOWLEDGEMENT
The authors would like to thank the Department of Electromagnetic Engineering at KTH Royal Institute of Technology
as well as Malmes Stiftelse foundation for the financial support to complete the project. This project was also partially
financially supported by the VINN Excellence Center, Chase
stage IV.
R EFERENCES
Fig. 4. Simulated and measured S(1,1) and the E-plane of the proposed
antenna.
Simulated and measured results of the patch antennas are
illustrated in Fig. 4. A slight shift is observed at the S(1,1)
but is still operable in the required bandwidth. The simulated
and measured E-plane of the antenna is also depicted in
Fig. 4 and and an excellent agreement between the two is
observed. The measurements are performed with the near
field scanner RFexpert. During the measurement process all
the non measured ports of the system where terminated with
[1] C. Song, Y. Huang, J. Zhou, J. Zhang, S. Yuan, and P. Carter, “A highefficiency broadband rectenna for ambient wireless energy harvesting,”
IEEE Transactions on Antennas and Propagation, vol. 63, no. 8, pp.
3486–3495, Aug 2015.
[2] V. Marian, B. Allard, C. Vollaire, and J. Verdier, “Strategy for microwave
energy harvesting from ambient field or a feeding source,” IEEE Transactions on Power Electronics, vol. 27, no. 11, pp. 4481–4491, Nov 2012.
[3] U. Olgun, C. C. Chen, and J. L. Volakis, “Efficient ambient wifi energy
harvesting technology and its applications,” in Antennas and Propagation
Society International Symposium (APSURSI), 2012 IEEE, July 2012, pp.
1–2.
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