ISSN(Print) 1975-0102
ISSN(Online) 2093-7423
J Electr Eng Technol Vol. 7, No. 6: 954-958, 2012
http://dx.doi.org/10.5370/JEET.2012.7.6.954
Flexible Patch Rectennas for Wireless Actuation of Cellulose
Electro-active Paper Actuator
Sang Yeol Yang*, Jaehwan Kim† and Kyo D. Song**
Abstract – This paper reports a flexible patch rectenna for wireless actuation of cellulose electroactive paper actuator (EAPap). The patch rectenna consists of rectifying circuit layer and ground layer,
which converts microwave to dc power so as to wirelessly supply the power to the actuator. Patch
rectennas are designed with different slot length at the ground layer. The fabricated devices are
characterized depending on different substrates and polarization angles. The EAPap integrated with the
patch rectenna is actuated by the microwave power. Detailed fabrication, characterization and
demonstration of the integrated rectenna-EAPap actuator are explained.
Keywords: Microwave power transmission, Patch rectenna, Flexible substrate, Wireless actuation,
Electro-active paper
characteristics, these materials have advantages and
disadvantages, for example, high actuation voltage for
electronic EAP materials and wetness requirement for ionic
EAP materials. Recently, cellulose has been discovered as
a smart material that can be used as sensors, actuators and
smart devices. The newly discovered material is termed as
electro-active paper (EAPap) [12], which has merits in
terms of light weight, flexible, dryness, biodegradable, low
electrical power consumption and low price. To overcome
the durability and low actuation performance of EAPap at
low humidity condition, many attempts have been made
including a polypyrrole and ionic liquid nanocoating on the
cellulose EAPap [13].
Once the MPT technology is integrated with the
cellulose EAPap, a ultra-lightweight actuator can be
developed since the integrated device does not need to
carry battery so it can be a wirelessly-driven ultralightweight actuator. This paper aims at demonstrating a
rectenna integrated EAPap actuator. However, there are
technical challenges for the integration of rectenna and
EAPap actuator. Firstly, the rectenna should be flexible so
as to be integrated on the cellulose EAPap. Conductive
antenna layer for the rectenna should be fabricated on the
cellulose membrane and the Schottky diode should be
soldered on the antenna. Secondly, the rectenna should be
polarization independent with respect to the microwave
antenna. Generally, dipole rectenna has high conversion
efficiency while patch rectenna has low efficiency. However
dipole rectenna is sensitive to its polarization: once its
polarization is not matched with the microwave transmitting
antenna, its efficiency is low [14]. Thus, a patch rectenna
that has dual polarization is used in this research. This patch
rectenna is insensitive to the polarization. The configuration,
fabrication process and characterization of the patch
rectenna are addressed, and the integrated rectenna-cellulose
EAPap actuator is demonstrated.
1. Introduction
Wireless power transmission is a promising technique
for the long-term power supply of wireless applications. A
wireless means of actuator excitation, communication, and
sensor interrogation has many benefits such as fast
inspection, less downtime, labor cost reduction, etc. Since
microwave power transmission (MPT) has been first
initiated from the concept of solar power satellites [1], it
has been used and proposed for various applications such
as a microwave-powered helicopter [2], a solar power
satellite that converts solar energy to microwaves and
beams down to the earth [3, 4], a 4.5 m wingspan airplane
powered only by microwave energy [5], and a microwavepowered smart material actuator [6]. The key component
for this type of wireless power transmission is rectenna.
Rectenna is a combination of a rectifying circuit and an
antenna. Rectenna converts microwave or RF power to dc
power. The antenna receives the electromagnetic power
and the rectifying circuit converts it to dc power. The
rectifying circuit consists of a Schottky barrier diode, an
inductor, and a capacitor. There are several types of
rectennas, such as patch, dipole, bow-tie and slot [7-9].
Recently, a dual-polarized rectenna was developed that can
produce a 50-V output voltage and can be used for driving
smart material actuators [10].
Electro-Active Polymer (EAP) materials are able to offer
a range of performance and characteristics that are
promising for biologically inspired actuators. Many EAP
materials have been so far developed [11]. Due to their
†
Corresponding Author: Centre for EAPap Actuator, Department of
Mechanical Engineering Inha University, Korea. (jaehwan@inha.ac.kr)
* Centre for EAPap Actuator, Department of Mechanical Engineering Inha
University, Korea. (blackhole97@hanmail.net)
** Engineering Department, Norfolk State University, Norfolk, VA
USA. (k.d.song@larc.nasa.gov).
Received: July 8, 2011; Accepted: April 20, 2012
954
Sang Yeol Yang, Jaehwan Kim and Kyo D. Song
substrates. Thus, two different fabrication processes were
provided: an etching process was conducted for the FPCB
substrate and a silk screen printing process for the cellulose
membrane. Fig. 2 shows the fabrication processes.
2. Experimental
2.1 Design of patch rectenna
Fig. 1 shows a schematic diagram of the patch rectenna
that consists of a ground layer with slot and a rectifying
circuit layer with an independent rectifying circuit for each
of two orthogonal polarizations. A dielectric substrate
separates these two layers. The cross section of the
rectenna is shown in Fig. 1(b).
Rectenna Design
Make a
Mask Pattern
Photoresist Film
Lamination on FPCB
Spreading photoresist
on Silk Stencil
Photoresist Coating on
Silk Stencil
(a) Rectifying circuit layer
UV Expose through to
Mask Pattern
Cu or Ag
(b) Cross section
Developing
Cu or Ag
Etching
Spreading Electrode &
Squeezing
Strip Photoresist
Hardening Electrode
FPCB Rectenna
Cellulose Rectenna
(c) Grounding layer
Fig. 1. Schematic of patch rectenna.
Fig. 2. Rectenna fabrication process.
The patch rectenna was made on two different substrates
for their performance comparison: flexible printed circuit
board (FPCB) and cellulose EAPap [15]. FPCB is a
polyimide membrane on which copper layers are laminated
on both sides. Thickness of the polyimide layer of FPCB is
20 um and the copper layer is 18 um thick. Thickness of
the cellulose membrane is 19 um (±5%). Relative dielectric
constant of the polyimide is 3.48 at 2 GHz and the
cellulose membrane is 14.0 over 1 MHz. Two layers in
terms of the ground layer and the rectifying circuit layer
are separated with the polyimide for the FPCB and the
regenerated cellulose for the cellulose membrane. The
rectifying circuit consists of Schottky diodes and
microstrip line as a transmission line. An independent
rectifying circuit for each of two orthogonal polarizations
is made to mitigate its polarization sensitive behavior of
the rectenna. The schottky diode characteristic is one of
important parameters to decide performance of the
rectenna. We used MA2054-1141T model Schottky diode
of M/A-COM that has upper 250 mV of forward voltage, 3
V of breakdown voltage and 10 mA of reverse current.
Initially designed slot length and width are 7 mm x 0.8 mm.
At first, mask patterns were prepared from the CAD
designed patterns for the ground layer and the rectifying
circuit layer. For the etching process, a photoresist layer
was coated on one side of the FPCB and a UV light
exposed on it through the ground layer mask pattern. After
turning back, the same process was followed except the
rectifying circuit layer mask pattern. After stripping out the
photoresist layers, two patterned layers on both sides of the
FPCB can be obtained. For the cellulose membrane, the
same mask patterns were used to produce silk screens: two
silk screens were produced for the ground layer and the
rectifying circuit layer. Production process of the silk
screens is similar to the etching process. A silver paste
(CSP-3163, Chang Sung Corp.) was spread on the
patterned silk screen and squeezed through the silk screen
to the cellulose membrane. After drying the printed silver
paste pattern, the other side was also screen printed with
the other silk screen. The same drying process was
followed on it. Fig. 3 shows photographs of patch
rectennas fabricated on the FPCB (a) and the cellulose
membrane (b). Also SEM images of patch rectenna
fabricated on each substrate were taken at the surface and
cross section as shown in Fig. 4. The boundary of copper
layer is clear meanwhile the boundary of silver paste is
blurry. Thicknesses of polyimide and the copper are 15 um
2.2 Fabrication of patch rectenna
Patch rectennas were fabricated on two different
955
Flexible Patch Rectennas for Wireless Actuation of Cellulose Electro-active Paper Actuator
and 5 um, respectively, and these values of the cellulose
and the silver layer are 14 um and 7 um.
was located 10 cm far from the horn antenna and
displacement sensor was located on the opposite side.
Bending displacement was measured at the lower end of
the cellulose EAPap.
Fig. 3. Photographs of Patch Rectennas: (a) Fabricated on
the FPCB; (b) fabricated on the cellulose membrane.
Fig. 5. Schematic of microwave power transmission test
setup.
3. Results and Discussion
3.1 Output power of patch rectenna
The performance of patch rectenna should be tested
depending on the distances between the horn antenna and
the rectenna as well as its incidence side. Fig. 6(a) and (b)
show the dc voltage obtained from the FPCB retenna when
the microwave is incident on the ground layer side and the
rectifying circuit layer side. When the microwave is
incident on the rectifying circuit layer side, the MPT
performance is better than the other side. As increasing the
distance between the horn antenna and the rectenna, the dc
voltage of the rectenna decreases, which is inversely
Fig. 4. SEM images of patch rectennas: Surface image of
(a) fabricated on the FPCB; (b) cellulose membrane
and Cross section image of (c) fabricated on the
FPCB; (d) cellulose membrane.
0.8
2.3 Experimental stup
0 ;0°
Polarization
90
Polarization ; 90
(a)
0.6
5
Polarization ; 00 °
Polarization ; 90
90
(b)
°
4
°
Voltage (V)
An experimental setup for the MPT test of the patch
rectenna is shown in Fig. 5. The MPT test was performed
in an anechoic microwave chamber to protect against
ambient noise. Microwave power was generated from a
transmitter (ATV transmitter, GIE TV inc) and propagated
through a waveguide and fed to a horn antenna (U-3000L,
ED Laboratory) which gain is 15.13 ~ 17.82 dB depending
on the frequency from 8.2 to 12.4 GHz. The microwave
signal irradiated to the patch rectennas through the horn,
and a dc power was obtained due to the rectifying circuit. A
pulse signal analyzer (B&K 3560-B-030) was used to
measure its output voltage and current of patch rectenna
with 10 KΩ load resistor. The propagated microwave
power is 1.2 W with 10 GHz.
Fig. 5 also shows the bending actuation test setup to
demonstrate the possibility of the rectenna integrated
EAPap actuator as a microwave driven actuator. Since the
cellulose rectenna is made on cellulose EAPap, it can be
the rectenna integrated EAPap actuator. Cellulose rectenna
FCB
0.4
Ground Layer
Voltage (V)
Circuit layer
3
FCB
2
0.2
1
0.0
0
50
0
100
0
50
Distance(cm)
100
Distance (cm)
0.8
5
Polarization0 ; 0 °
(c)
Polarization90; 90
90
Polarization ; 90
°
4
Cellulose
Voltage (V)
Voltage (V)
Polarization0; 0 °
(d)
°
0.6
0.4
0.2
Cellulose
3
2
1
0.0
0
50
Distance (cm)
100
0
50
100
Distance (cm)
Fig. 6. Output voltages of patch rectennas with different
polarization angles and when microwaves are
incident to different sides: (a) ground layer of FPCB
rectenna; (b) rectifying circuit layer of FPCB
rectenna; (c) ground layer of Cellulose rectenna; (d)
rectifying circuit layer of Cellulose rectenna.
956
Sang Yeol Yang, Jaehwan Kim and Kyo D. Song
proportional to the distance. Note that the cellulose
rectenna shows higher dc voltage than the FPCB rectenna.
The slot size effect of the rectennas is investigated. Table 1
shows the slot length. Fig. 7(a) shows the output voltage of
FPCB rectenna with different slot length and polarization
angle, and (b) represents the cellulose rectenna results.
These patch rectennas are insensitive to their polarization.
The slot length does not have significant effect on the
performance of both rectennas. The cellulose rectenna
shows higher dc voltage than the FPCB rectenna.
dc power-on time is reduced from 2 minutes to 0.5 minutes,
its amplitude of the bending displacement decreases. To
autonomously activate the actuator, a control circuit may
be necessary that can control the signal and charge
accumulation on the actuator so as to mitigate slow
response. The addition of such control circuit may require
additional dc power from the rectenna.
Table 1. Slot dimension of patch rectennas.
Flexible patch rectennas that are insensitive to their
polarization were designed and fabricated on the polyimide
substrate and cellulose membrane, The patch rectenna was
designed with the rectifying circuit layer and the ground
layer, in which a dielectric membrane separates these
layers. The rectifying circuit layer consists of Schottky
diodes and microstripline in such a way that the patch
rectenna is insensitive to the polarization. Two dielectric
substrates, namely FPCB and cellulose were used for the
flexible patch rectenna fabrication. The etching process and
the silk screening process were taken for these substrates.
The output power of the cellulose patch rectenna was
higher than the FPCB patch rectenna. The rectenna
integrated EAPap actuator was tested by actuating with
microwave. As the microwave power was on, the actuator
bent, and the maximum displacement of 2.2 mm was
obtained. This result shows the possibility of wireless
EAPap actuation using microwave power. More
investigation on the control circuit of the actuator is
necessary.
Substrate
FPCB
Cellulose membrane
Slot length (mm)
7
7.8
8.2
6.2
7
7.8
6.6
5.7
6
5
9
8.8
6
10kohm0
Polarzation
;0°
10kohm90
Polarzation ; 90 °
(a)
5
Polarzation
10Kohm0
;0°
10Kohm90 °
Polarzation
; 90
(b)
4
Voltage (V)
4
Voltage (V)
5. Conclusion
3
2
1
3
2
1
0
0
6.5
6.6
7.0
7.0
7.5 7.8 8.0 8.2
Slot Length (mm)
8.5
9.0
9.0
5.55.7 6.06.2 6.5
7.0
7.0
7.5 7.88.0
8.5 8.89.0
Slot Length (mm)
Fig. 7. Output voltages of patch rectennas (10 kΩ load
resistor) depending on different slot length and
polarization angle: (a) FPCB rectenna; (b) cellulose
rectenna.
3.2 Microwave driven eapap actuator
Fig. 8 shows the bending actuation test results of the
rectenna integrated EAPap actuator by time sequence. Fig.
8(a) shows the output voltage of the rectenna. A rising time
of the converted dc power at the patch rectenna is 1.6 sec,
which might be associated with parasitic inductance and
capacitance of the rectenna. Fig. 8(b) shows the bending
displacement of the rectenna integrated EAPap actuator.
The actuator moves to one direction when the power is on
and recovers to its original position after the power off.
When the power is on during 2 minutes, the maximum
displacement of 2.2 mm is obtained. As the duration of the
Acknowledgements
This work was supported by NRF/MEST under Creative
Research Initiatives (EAPap Actuator).
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Fig. 8. Performance of rectenna-integrated cellulose
EAPap actuator: (a) Output voltage of the rectenna;
(b) Bending displacement of the actuator depending
on on/off time interval
[4]
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Dr. Sang Yeol Yang He received his
B.E in electrical engineering in 2005,
MS in Advanced Precision Engineering
in 2007, and Ph.D. in mechanical
engineering in 2012 from Inha University, respectively. His research interests
are biomimetic actuators, wireless
power transmission technique, antenna
design.
Dr. Jaehwan Kim He received his
Ph.D. in engineering science and
mechanics from the Pennsylvania State
University, USA, in 1995. Since then
he joined mechanical engineering
department of Inha University and he is
now Inha Fellow Professor. His research interests are smart materials such as
piezoelectric materials, electro-active polymers, electroactive paper, and smart devices such as sensors, actuators,
motors, MEMS, and robotics.
Dr. Kyo D. Song He received MS in
Physics from Hampton University and
Ph.D. from the Center of Electro
Optics at University of Nebraska,
Lincoln. He has worked as a Research
Engineer at University of Washington,
Seattle, Washington, Korean Institute
of Aeronautical Technology, Seoul,
Korea and Source Tek, Inc., Virginia. Since then he joined
Norfolk State University in 1993 and Department of
Optical Engineering in 2002. His current areas of research
interests and publications are in the area of microwave
driven smart materials, nanomaterials and applications of
free electron lasers.
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