Dual-band electromagnetic energy harvester with resistance compression network
Apostolos Georgiadis1*, Ana Collado1š, and Kyriaki Niotaki1Ã
1
Centre Tecnologic de Telecomunicacions de Catalunya (CTTC), 08860 Castelldefels (Spain)
* ageorgiadis@cttc.es, š acollado@cttc.es, à kniotaki@cttc.es
Abstract
This work presents the design of a dual-band rectenna operating at 915 MHz and 2.45 GHz. The design of the
rectifier is based on the concept of dual-band resistance compression network as the impedance matching network of
the circuit. The 915MHz/2.45GHz rectifier exhibits a low sensitivity at different load and input power variations.
Additionally, a dual-band antenna is designed and fabricated to operate at the same frequency bands. The
electromagnetic energy harvester is evaluated for different power densities, showing a DC voltage of 293 mV and 79
mV for a load value of 1 kΩ and a power density of 1uW/cm2 at 915 MHz and 2.45 GHz, respectively.
1. Introduction
RF energy harvesting plays a key role for the design of autonomous Wireless Sensor Networks (WSNs) due to
the emergence of the Internet of Things (IoT) and smart cities [1]. The concept of battery-less WSNs is based on their
ability to collect and store the energy that is available in the environment. Since the availability of the harvested power
depends on the application scenario and the operating frequency, the design of dual-band/broadband rectennas is a
fundamental task for maximizing the amount of harvested power. Multiband and broadband energy harvesters have
already been proposed in the literature [2-5].
In this work, a dual-band energy harvester operating at 915 MHz and 2.45 GHz is presented. Initially, a dualband antenna and a dual-band rectifier are designed and fabricated. The design of the dual-band rectifier is based on the
concept of resistance compression networks (RCNs) as the impedance matching network of the circuit [6-7]. The dualband resistance compression networks are designed to operate at 915 MHz and 2.45 GHz. The proposed rectenna is
evaluated for different power density values ranging from 0.05 uW/cm2 to 1 uW/cm2. A DC voltage of 293 mV and 79
mV is obtained at 915 MHz and 2.45 GHz for a power density of 1uW/cm2.
In Section 2, the design of a 915MHz/2.45GHz antenna is presented. Section 3 concerns the design of a dualband rectifier operating at the same frequencies. Section 4 includes the performance evaluation of the rectenna for
various power density levels. Finally, Section 5 summarizes the conclusions of this work.
2. Dual-Band Antenna
Initially, a dual-band antenna is designed in a commercial simulator (Ansys HFSS). The design is based on a
series fed printed dipole pair antenna [8]. The desired operating frequencies are 915 MHz and 2.45 GHz. The final
dimensions of the antenna are 8 cm x 19 cm. The antenna is fabricated in Arlon 25N 20 mil substrate that is
characterized with permittivity of 3.38 and loss tangent of 0.0025. Fig. 1 shows the measured reflection coefficient of
the antenna versus frequency. The antenna exhibits a gain of 4 dB and 4.8 dB at 915 MHz and 2.45 GHz, respectively.
0
S11 (dB)
-5
-10
-15
-20
0.5
1
1.5
2
Frequency (GHz)
2.5
3
Figure 1. Measured reflection coefficient (S11) of the antenna versus frequency.
978-1-4673-5225-3/14/$31.00 ©2014 IEEE
3. Dual-Band Rectifier
A dual-band rectifier is designed to operate at 915 MHz and 2.45 GHz. The simulated topology consists of two
rectifying devices (Skyworks SMS7630 Schottky diode). The impedance matching network for the maximization of
power transfer from the source to the diodes is based on a dual-band resistance compression network.
A resistance compression network is used as the matching network of the circuit in order to reduce the sensitivity
of the rectifier at the load and input power variations during its operation [6]. Thus, large variations at the input power
and load values result in small variation at the input impedance of the diode and thus, to a better impedance matching. A
resistance compression network operating at a single frequency (f1) consists of two branches that exhibit equal but
opposite phase response (φ1) at f1 [6]. The operating principles of a single frequency resistance compression network
are shown in Fig. 2(a). A dual-band resistance compression network uses Composite Right/Left-Handed (CRLH) unit
cells to achieve this phase condition at two operating frequencies.
A Composite Right/Left-Handed unit cell has a dual-band frequency response, providing a phase shift of -φ1 at
the low frequency (f1) and φ2 at the high operating frequency (f2) [9]. The phase response of a single CRLH unit cell is
shown in Fig. 2(b). A rearrangement of the CRLH unit cell exhibits equal but opposite phase response at the two
operating frequencies, as Fig. 2(c) shows. A phase shift of φ1 at the low frequency (f1) and -φ2 at the high operating
frequency (f2) is achieved. These properties of the CRLH unit cells are used to design a resistance compression network
operating at two arbitrary frequencies. Thus, by placing the conventional and the rearranged CRLH unit cell of Fig. 2(b)
and Fig. 2(c) at the two branches of a resistance compression network (Fig. 2(a)) a dual-band resistance compression is
achieved.
The simulated circuit topology of the dual-band rectifier is shown in Fig. 3. The simulation shows that a
maximum efficiency is achieved for the following component values: L1=8.7 nH, C1=27 pF, C2=0.8 pF and L2= 100 nH.
The rectifier is compared in simulation with a single diode dual-band rectifier operating at the same frequencies. Fig. 4
shows the RF-DC conversion efficiency of both circuits. It is shown that the proposed rectifier has an improved
performance. The simulated and measured reflection coefficient of the dual-band rectifier is shown in Fig. 5, showing a
good agreement between simulation and measurements.
RL
φ
(a)
(b)
-φ1 @ f1
RL
φ 2 @ f2
-φ
(c)
φ 1 @ f1
-φ2 @ f2
Figure 2. a) Resistance compression network operating at a single frequency, b) Composite Right/Left-Handed unit cell
and c) Rearranged Composite Right/Left-Handed unit cell.
L1 C1
C2
RF
input
L2
100
nH
120
pF
RL
100
nH
120
pF
Figure 3. Circuit topology of the dual-band rectifier (RL=1kΩ). The component values for each unit cells are L1=8.7
nH, C1=27 pF,C2=0.8 pF and L2= 100 nH.
4. Dual-Band Rectenna
The dual-band rectifier is placed together with the dual-band antenna as Fig. 6 shows. Initially, two identical
dual-band antennas are used to define the power density level for the measurements. Then, the rectenna is evaluated by
measuring the output DC voltage of the rectifier at different power densities. The measured DC voltage that is obtained
for different power density levels ranging from 0.05 uW/cm2 to 1 uW/cm2 is depicted in Fig. 7. It is shown that for a
power density of 1 uW/cm2 the circuit rectifies a DC voltage of 293 mV and 79 mV at 915 MHz and 2.45 GHz,
respectively.
a)
60
50
40
30
20
Single diode dual-band rectifier
Dual-band rectifier with RCN
10
00
1
2
RL (kΩ)
3
RF-DC Conversion Efficiency (%)
RF-DC Conversion Efficiency (%)
70
4
70
b)
60
50
40
30
20
Single diode dual-band rectifier
Dual-band rectifier with RCN
10
00
1
2
RL (kΩ)
3
4
Figure 4. Simulated RF-DC conversion efficiency of the proposed rectifier (solid line) and a dual-band single diode
rectifier operating for an input power of 0 dBm: a) at 915 MHz and b) 2.45 GHz.
0
S11 (dB)
-5
-10
-15
Simulation
Measurement
-20
-25
1
1.5
2
Frequency (GHz)
2.5
Figure 5. Simulated and measured S11 of the dual band rectifier versus operating frequency for RL=1 kΩ.
Figure 6. Measurement setup. The proposed rectenna consists of a series fed printed dipole pair antenna and a dualband rectifier based on resistance compression networks.
5. Conclusion
This work presents the design procedure of a dual-band rectenna operating at 915 MHz and 2.45 GHz. The
design of the rectenna circuit uses dual-band resistance compression networks as the matching network placed between
the source and the rectifying device. The dual-band electromagnetic energy harvester is tested for different power
density levels in the range of 0.05 uW/cm2 to 1 uW/cm2. A DC voltage of 293 mV and 79 mV is measured at 915 MHz
and 2.45 GHz for a power density of 1 uW/cm2.
300
915 MHz
2.45 GHz
DC Voltage (mV)
250
200
150
100
50
0
0.2
0.4
0.6
Power Density (uW/cm2)
0.8
1
Figure 7. Measured DC voltage for different power densities at 915 MHz and 2.45 GHz for RL=1 kΩ.
6. Acknowledgments
This work was supported by the Spanish Ministry of Economy and Competitiveness and FEDER funds through
the project TEC2012-39143, and the EU Marie Curie FP7-PEOPLE-2009-IAPP 251557. This work was also supported
by the COST Action IC1301 "Wireless Power Transmission for Sustainable Electronics (WIPE).
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