Conference Session Electrical Engineering A8 Paper # 2336
Chris Roberts (cjr54@pitt.edu), Jennifer Franco (jlf117@pitt.edu)
Abstract— In today’s world, MEMS (micro electromechanical systems) play a vital part in almost every aspect of life. Finding a way to adequately supply power to these extremely small devices has been an ongoing problem.
To meet this ever increasing demand, engineers must constantly investigate new and improved methods to power these devices. A popular solution to this issue has become piezoelectric energy harvesters or scavengers. PEHD’s reuse the wasted energy that is expelled from their surroundings through the piezoelectric effect, which is the ability of certain types of materials to generate electricity when they are subjected to a mechanical stress or heat [1].
These properties make piezoelectric materials an extremely valuable resource, as they can supply power where batteries or other external power sources are impossible or unrealistic. We will discuss the energy transfer applications of PEHD’S in MEMS [2] and also the use of piezoelectric devices to harvest wasted energy in MEMS[3]. To conclude this paper we will introduce some future applications that are currently being developed.
Key Words — MEMS, piezoelectric device, piezoelectric effect, piezoelectric energy harvesting, piezoelectric material, PZT
Thanks to the piezoelectric effect these materials can be inserted into MEMS such as wireless sensory nodes and supply power to the system from ambient vibrations from the system’s surroundings. This would make piezoelectric devices a great alterative to batteries in these types of applications because they do not need to be changed constantly. With piezoelectric devices installed people would no longer have to waste time constantly monitoring power levels on these sensory nodes and can use this extra time more efficiently by focusing on more important tasks.
The same concept can be applied to MEMS where energy is lost in the form of heat or motion. The piezoelectric device will respond to the heat or motion by generating electricity through the MEMS thereby making it much more efficient.
To begin to understand how and why these piezoelectric materials can be used in various MEMS along with how well they will work, a more detailed description of the piezoelectric effect must be provided.
T HE P IEZOELECTRIC E FFECT
I
NTRODUCTION
In MEMS a constant goal for designers is to increase efficiency in the circuits they are creating. One way to make
MEMS more efficient is to recycle wasted energy which would cut down MEMS power consumption. Piezoelectrics are ideal for this task in the form of piezoelectric energy harvesters. As the name implies, these devices can be used to recycle the otherwise wasted energy in a circuit.
Piezoelectric devices become even more important to
MEMS when the circuit has to function wirelessly. In wireless circuits, piezoelectric devices can be the main power source for certain wireless MEMS devices. Due to their energy harvesting and wireless power capabilities, these piezoelectrics are very appealing for MEMS design.
The piezoelectric effect is the reason piezoelectric devices are able to supply power to these systems. The piezoelectric effect is the ability of certain materials to generate electricity when they are subjected to a mechanical stress or heat. The opposite is true were if a piezoelectric device experiences an electrical charge it will respond with a mechanical stress or motion. Both responses will be discussed in a more detailed fashion in the next section which is based solely on piezoelectric effect.
According to Nader Jalili, author of a book on piezoelectric based vibration control, Pierre and Jacques Curie were the first to discover the piezoelectric effect in 1880 [1]. Jalili goes on to explain that in the Curie brothers’ experiments they found when a piezoelectric material is subjected to a mechanical pressure the material’s crystal structures become electrically charged. This voltage will be applied in the opposite direction of the applied force [1]. In addition to its direction being determined by the applied force, the voltage that is induced is dependent on the magnitude of the stress that is applied to the material as well. A higher stress will induce a larger voltage through the material. As stated before, if a piezoelectric material is placed in an electric field the opposite effect will occur. It will stretch and compress along its various axes with the magnitude of the stretching and compressing forces depending on the strength of the electric field. These special properties are what make piezoelectric materials so unique and important in certain applications for MEMS where most other energy sources may simply not be an option or are impractical to use.
The reason the piezoelectric effect occurs in these materials has to do with the crystal structures of the material.
As Jalili explains, when these materials are above a specific temperature, known as the Currie Temperature, their crystal structures are a symmetric cubic structure. When a piezoelectric material drops below the Currie Temperature the material’s structure changes and takes on the form of a
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tetragonal structure [1]. This will result in microscopic dipoles forming in the crystal structure; however these electric dipoles are not strong enough to induce a macroscopic electric dipole. The randomness of the microscopic dipoles in the crystal structure result in the dipoles canceling each other out and leaving zero net polarization throughout the material. When a strong stress field is applied to a piezoelectric material below the Currie
Temperature, it causes the electric dipoles to align to causing a macroscopic electric dipole throughout the material [1].
This is how a mechanical stress or strain induces a charge through a piezoelectric material. To strengthen the electric properties of the material there are several things that can be done to make these piezoelectric materials better suited for
MEMS.
P
IEZOELECTRIC
M
ATERIALS
: N
ATURAL VS
.
M AN -M ADE
The experiments of the Curie brothers involved ten specially prepared natural crystals, including quartz, cane sugar, and
Rochelle salt (potassium sodium tartrate); quartz crystals are unique among all naturally occurring piezoelectric crystals, as its useful characteristics exhibit the following: structural rigidity, chemical stability, a strong piezoelectric response, and a very sharp resonance point[4]. Despite the exciting phenomenon revolving around the discovery of piezoelectric crystals, piezoelectric technology took a back seat to the rapidly developing science of electro-magnetism, due to the long time period it took to present the advances of the technology and extremely complicated mathematics required to understand this science. However, there was a wave of applications that emerged circa WWI, which included such technology as SONAR. Unfortunately, the materials available at this time limited device performance. There was a second wave of piezoelectric interest that occurred during and after WWII with the introduction of ceramic piezoelectric materials. Research groups discovered that this man-made option exhibited dielectric constants of up to
100x higher than common cut crystals. During this time ferroelectrics, which exhibited similar improvements, were also made. Some of the applications that evolved were: more powerful SONAR, piezoelectric ignition systems, and small sensitive microphones.
That second wave of interest has led us to today’s piezoelectric materials, which include: piezoelectric polycrystalline ceramics, piezoelectric single crystal materials, piezoelectric and electrostrictive polymers, and piezoelectric thin films [3]. We will provide equations and a table visualizing some thin film properties of ZnO (zinc oxide), AlN (aluminum nitride), and PZT (lead zirconate titanate) which are used in wireless applications as sensors and also in energy harvesting systems. These are most commonly used piezoelectric materials used due to low manufacturing costs and the variety of shaping possibilities available when compared to single crystalline
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Chris Roberts
Jennifer Franco piezoelectrics[5]. We will focus in more detail on PZT, as it will relate directly to the section addressing the applications of wireless sensory nodes. NKN films, which are another alternative material to PZT, will be introduced in the future applications section. These films are a lead-free alternative being explored and used in bio-medical applications today.
In order to choose the best material for a particular application, various equations are needed to compute the various necessary values that are crucial in making the proper decision. These equations are far too complex to describe in detail in this paper, so a brief overview will be provided. The following equations, referenced from N.
Bassiri-Gharb’s book Piezoelectric and Acoustic Materials for Transducer Applications, provide calculations to show how the electric displacement and stress/strain are related by a linear dependence at low fields [6]:
D i
  k d ik
 k and D i
  k e ik x k
(1)
(direct effect) x i
  k d ki
E k and
 i
   k e ki
E k
(2)
(converse effect) where the direct effect applies to when a stress is applied to the material and converse effect applies to when an electric field in applied to the material. displacement and E k
D i
is the electric
is the electric field tensor;
 k
and x k
are the stress and strain tensors, respectively, d ik
and e ik
are the piezoelectric coefficient tensors. Our focus will be towards piezoelectric thin films and the following equations, also from the referenced book of the above equations, reflect the use of effective piezoelectric coefficients for films [6]:
(3)
2
(4) where s ij
and c ij represent components of the elastic and stiffness tensor, respectively[6].
The following table lists piezoelectric thin film properties of ZnO, AlN, and PZT [6]:
TABLE I
Parameter ZnO AlN PZT(1-3µm) d
33 , f
(pm/V) e
31 , f
( C / m
2 ) e
31 , f

33
/

0

33
(GV/m)
5.9
-1.0
-10.3
10.9
3.9-5.5
-1.05
-11.3
8.5-10.5
60 –130a
-8.0 to -17.7
-0.7 to -1.8
300-1,620
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tan

(1–10kHz,10 5 V / m ) 0.01-0.1 c
E
33 (GPa) 208
0.003
395
0.01-0.03
98
To end this section, we will introduce NKN films, the leadfree alternative to PZT. These alternatives are important in the bio-medical aspect of piezoelectric applications, as leadfree devices are being implanted directly into the human body. Experiments and results, as report by Kim, Koo,
Cheon, Yeom, Woo, and Ha [7], show that NKN films exhibit strong piezoelectric qualities, including clear switching characteristics in solutions similar to body fluids, making it bio-compatible for insertion MEMS applications[7]. They have found that although NKN may have somewhat worse overall properties when compared to
PZT, they exhibit enough similar traits to make it a strong candidate material for replacing lead-based films in biomedical applications [7].
M ANUFACTURING P ROCESSES
In this section we will introduce several types of manufacturing and fabrication processes that create piezoelectric components. Our focus will primarily be on the manufacturing of cantilevers which are a vital component in wireless applications as well as energy harvesting applications, both of which will be examined further in following sections. Graphics that depict several stages of the manufacturing process of a piezoelectric cantilever will also be displayed.
Some fabrication techniques of piezoelectric cantilevers include RF sputtering, pulsed laser deposition (PLD), chemical vapor deposition (CVD), metal organic decomposition (MOD), and sol-gel deposition. Among these methods, the convenient and low cost method of sol-gel deposition has attracted considerable interest because of many reasons, including: its better integration with circuit
(IC) fabrication, all of the starting chemicals are of a molecular level, composition of the multicomponent system is easily controlled, it has better reproducibility, and has a shorter fabrication cycle[8,9]. The following table provides information pertaining to various deposition methods:
TABLE II
Deposition +P r
(µC/cm 2 ) +E c
(kV/cm) Electric field
Methods (kV/cm)
Sputtering
MOCVD
15.1-22.0
21.5
MOD 11.4
Sol-gel 18-26
Mod. Sol-gel 22.2
65-81
33.8
57.9
28-77
30.7
+/- 200
+/- 150
+/- 200
+/- 150
+/- 250
P ARAMETERS OF V ARIOUS D EPOSITION M ETHODS [4] .
There are, however, some faults that occur with the conventional sol-gel process. Film cracking, device shortcircuiting and PZT diffusion to substrate (Pt/Ti/SiO
2
/Si) are the most common problems that cause low yield rate of
Chris Roberts
Jennifer Franco fabrication of piezoelectric devices [8]. To combat these problems, a modified sol-gel process has been developed as well as the use of a proof mass during manufacturing [8,10].
We will now describe cantilevers and how they are fabricated by Reilly and Wright [10]. The process flow is demonstrated in figure. If the crystalline quality were sufficient, then the films would be exposed to the first masking layer which patterned the surface. The PZT was
FIGURE 1
(1) F IRST MASKING STEP , DEFINITION OF DEVICE GEOMETRY :
( A ) CROSS SECTION AND ( B ) TOP DOWN .
(2) N EUTRAL A R ION MILLING TO
EXPOSE THE S I SUBSTRATE : ( A ) CROSS SECTION AND ( B ) TOP DOWN .
(3) S ECOND MASKING STEP , ELECTRON BEAM DEPOSITION OF THE
ELASTIC / ELECTRODE METALLIC LAYER : ( A ) CROSS SECTION AND ( B ) TOP
DOWN .
(4) L IFT OFF TO THE ISOLATE TOP ELASTIC / ELECTRODE LAYER : ( A ) CROSS
SECTION AND ( B ) TOP DOWN .
(5) T HIRD MASKING STEP , DEPOSITION OF
PROOF MASS : ( A ) CROSS SECTION AND ( B ) TOP DOWN .
(6) R ELEASE FROM
THE SUBSTRATE ( A ) CROSS SECTION AND ( B ) TOP DOWN .[3] then etched using a Veeco neutral Arion milling machine.
The photoresist was stripped with an acetone bath, cleaned and baked, and the photoresist film was recoated to expose the second mask. The second mask served to cover the exposed Si substrate and expose the top electrode / elastic
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layer area. Electron beam evaporation was then used to deposit the top metallic electrode / elastic layer. A thin (10–30 nm) Cr adhesion layer was used to help delamination upon lift off. A composite metallic layer of 100 nm Au / 200 nm
Pd / 70 nm Au was deposited in sequence without breaking vacuum. The photoresist was again stripped and recoated for the third and final masking step. A small area of 100 μ m by
100 μ m, on the tip of the cantilever, was left exposed and
400 nm of Au was deposited again via electron beam evaporation to serve as the proof mass. The cantilevers were then released from the substrate using a gaseous XeF
2 etch.
A partially released cantilever is shown in figure and SEM images of cantilever beams in figure.
P
FIGURE 2
SEM OF THE PARTIALLY RELEASE CANTILEVER BEAM [3].
FIGURE 3
SEM IMAGE OF CANTILEVER BEAMS [3].
IEZOELECTRIC E NERGY H ARVESTING
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Piezoelectric energy harvesting devices can be of great use in MEMS. They can help to reuse wasted energy that would otherwise be lost to the environment. According to Jinhao
Qiu, author or a research article for Frontiers or Mechanical
Engineering in China, a piezoelectric energy harvesting system consists of a cantilever beam, piezoelectric element, electromagnet, and a rigid base [11]. Piezoelectric energy harvesters work by exploiting the piezoelectric effect.
Basically the piezoelectric element is attached to the root of the beam. When this beam is excited by the electromagnet underneath it, the beam will start to vibrate. This will cause the piezoelectric element to experience the vibration as well
4
Chris Roberts
Jennifer Franco which will generate a voltage. Energy generated by the piezoelectric material cannot be used directly by another device so an electrical interface must be added onto the piezoelectric energy harvester to ensure that the voltage is compatible with the load it is supplying energy to [11]. This interface setup will determine how much energy can be supplied to the load. While the original setup was not very effective, in recent years researchers have been able to design better interface circuits which make piezoelectrics a much more viable source for energy harvesters in MEMS.
Qiu and his colleagues tested several different circuit interfaces to determine how piezoelectric energy harvesting devices could be used more effectively [11]. They first tested the “classic interface” which merely takes the AC voltage from the piezoelectric element and converts it to a
DC voltage. They found through experimentation that the power is equal to the voltage supplied by the piezoelectric energy harvester squared divided by the resistance of the load that it is supplying the power to [11]:
P

V 2
DC
(5)
R
L
(Power for “classic interface”)
They found that the highest power achievable was with a medium sized resistor value for the load as very high or low resistor values gave low power results [11]. The second configuration used was a voltage doubler interface. By using the voltage doubler there was a noticeable improvement over the classic interface in terms of power supplied at higher load resistances, but it performed worse than the classic interface at low load resistances.
After these two types of interfaces they moved on to the newer types of interfaces which involve a technique called synchronous charge extraction (SCE). Qin summarizes the technique and circuit as follows. “The idea behind it is to build up a charge on a capacitor C by using the energy o supplied by the piezoelectric energy harvester. There is also a switch S and an inductor L that are in series with the switch turned off while the capacitor is charging. Once the capacitor is done charging the switch turns on and the capacitor discharges into the inductor causing a high current to be induced in the inductor. When this happens basically all of the stored energy is transferred to the inductor after which the switch is turned off again. The current will then flow into another capacitor C r and the electric load R
L
”
[11]. This switch will only be turned on for approximately
1/50 of the vibration period of the PEHD. The average power supplied by the PEHD is now much higher and is represented by the following equation [11]:
P

2

2

* U *
* C o

2
(6)
(Power for SCE interface)
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Where alpha is the force factor of the vibration, U is the displacement of the beam tip, omega is the frequency at which the PEHD vibrates at, and C is the charge on the o capacitor near the PEHD as stated above.
The final interface that was analyzed is known as the synchronized switch harvesting on the inductor (SSHI). Qin describes this configuration as follows. “utilizes a nonlinear processing circuit connected to the electrodes of the piezoelectric element and the input side of the rectifier bridge. The nonlinear processing circuit is very simple, consisting of an inductor and a switch The nonlinear processing circuit can increase the voltage amplitude on the capacitor of the piezoelectric element, due to a voltage inversion process. The switch S is turned on when the voltage V on capacitor C of the piezoelectric element o reaches a maximum or a minimum. At these triggering instants, an oscillating electrical circuit is established between L and C o
and the voltage V on C o
is inversed.
The switch S is turned off again after the voltage inversion process is finished. Due to voltage inversion, the voltage V on C increases with time because electric charges are o generated by mechanical strains” [11]. The power delivered to the load is expressed by the following equation [11]:
P

4
( R
L

* C o
2
*

*

2
* U
( 1

2 e
 
* R
L
/ 2 * Q
)
 
)
2
(7)
(Power for SSHI interface)
When all interfaces were compared with each other Qin received the following results.
Chris Roberts
Jennifer Franco
There are other ways to improve the efficiency of PEHD besides changing the interface. As shown by Meiling Zhu, a member of the Department of Materials at Cranfield
University, the value of the resistive load can change the voltage output of a PEHD while the devices geometry can change its power output [2]. He designed three experiments to test these different factors. In the first test Zhu tested the effect of the variable load resistance. He hooked up a piezoelectric energy harvesting device to a variable load board where he then began to increase the load in increments of 25 k

[2]. As the resistive load increased, the voltage measured at the devices resonance frequency increase as well [2]. The devices resonance frequency also increased as well with the increase in load resistance [2]. While both resonance frequency and voltage increased with the load resistance, the power output from the piezoelectric energy harvesting device did not because they measured it using the power equation [2]:
P
2

V
2 R
(8)
While the resistive load was unable to change the power output, the geometry of the device was able to change it.
Using coupled piezoelectric-circuit finite element model software Zhu was able to determine that the device would be affected by its size and found that the optimum volume was
1 cm
3
[2]. Using this knowledge and the results from the first part of the experiment he was able to optimize the voltage and power output for the piezoelectric energy harvesting device. The max power output from the piezoelectric energy harvesting device was 370

W , the maximum voltage was 15.5 volts, the optimal resistive load was 325 k

, and the operating frequency was 87 Hz [2].
As Zhu himself pointed out, these are very promising numbers that show piezoelectric energy harvesting devices could potentially be used in a much wider spectrum than some previously believed [2]. This is especially true when it comes to MEMS because MEMS, as the name implies, does not require huge amounts of energy for them to properly function. The fact that piezoelectric energy harvesters do not require regular maintenance or care while being able to run off of little or no power supply other than vibrations or heat makes them a very appealing product for the future.
C URRENT A PPLICATIONS
FIGURE 4
P OWER VS .
R ESISTANCE G RAPH [11]
From the results in figure [4] it is easy to see the SSHI configuration is far better than any of the others that had been used previous. With this new interface working with the standard PEHD it would drastically improve its performance and make it a very appealing option for use in
MEMS, especially in a wireless setting.
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In addition to the devices that were mentioned and described in the previous section, we will introduce some of the other current applications of piezoelectric devices used today.
Piezoelectrics are used in a variety of everyday items, some of which are commonly known and some that are unusual and not well known. For example, piezoelectric elements are used in the probe tip of atomic force microscopy (AFM) as actuators and sensors, simplifying the force-sensing system, as the laser alignment procedure can be complicated [6].
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Piezoelectric cantilever actuators have a place in computers as well, specifically in servo systems for data access in hard drive disks [6]. Piezoelectric sensors are utilized by the transportation industry and integrated into our vehicles in multiple ways. They are used knock sensors. Knock sensors are placed near the engine in order to detect irregular combustion [12]. They are also used in the parking sensors via ultrasonic transducers which measure distance and assist with the parking of a vehicle [12]. Fuel injection systems benefit from piezoelectric stack actuators because of their faster response time and as a result they have reduced fuel consumption [12]. Some consumer applications include uses in cigarette lighters, speakers, disc drives, inkjet printers and cell phones. Unusual uses include those in the sports industry. Sports equipment has been designed with piezoelectric components to improve function. We will briefly introduce two such pieces of sports equipment: skis and tennis racquets. In skis, piezoelectric sensors and an actuator control system has aided to the performance of skis by eliminating unwanted vibrations that compromise ski stability [13]. The use of piezoelectric ceramics in skis is a prime example of how a stress placed on the piezoelectric element will in turn develop an electrical charge. The electrical charge that was created is fed back into a circuit that combats the unwanted vibrations. These circuits cancelled out unwanted vibrations, which caused the skis to lose contact with the snow, leaving a much greater portion of the ski in contact with the snow, hence improving performance [13]. Similarly to skis, tennis racquets also endure an extreme overload of unwanted vibrations.
Vibrations caused by a tennis ball’s impact are converted into electrical energy. This energy is then captured and released at a specified time, usually with in milliseconds, as determined by an imbedded chip in the racquet [14]. This action creates a cancelling counter vibration to provide dampening effects [14]. Again, as with the skis, this enhances performance of the equipment. Figure [5,6] illustrates the integration of piezoelectric fibers in a tennis racquet.
FIGURE 5
P IEZOELECTRIC T ENNIS R ACQUET
[15].
Chris Roberts
Jennifer Franco
FIGURE 6
P IEZOELECTRIC T ENNIS R ACQUET [16].
F
UTURE
A
PPLICATIONS
As seen in the previous sections, piezoelectric devices in
MEMS have a significant role in our everyday lives. Many items we use daily contain this type of technology. With the ongoing research and development in the piezoelectric field, new and innovative applications are being investigated.
Needs for flexible piezoelectric substrates have been in demand as well, especially in the medical field. A band-aid type device to detect a pulse on a victim would significantly assist in the triage and care of patients. This band-aid device would contain a piezoelectric transducer that would accurately detect a patients pulse by first-responders, aiding them in the split second decision of whether or not to begin external defibrillation [17]. An image of this proposed device is shown in figure.
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FIGURE 7
A RTIST
’
S RENDERING OF AN ACOUSTIC BAND AID FOR PULSE DETECTION BY
FIRST RESPONDERS .
Another innovative technology currently under investigation is the ability capture ambient energy from external sources, such as thermal, wind, solar, and hydrodynamic [18]. One such application, as described by William Hobbs and David
Hu, is tree-inspired piezoelectric energy harvesting [18].
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Chris Roberts
Jennifer Franco
This tree mimics swaying in the wind, which create a uniform flow of vibrations that are captured by piezoelectric elements. One issue they are facing is how to optimize the circuitry for varying wind speeds [18]. The details of these experiments are far too complex for this paper, but the information provided allows us to visualize the use of this type of technology in various other applications that mimic nature.
In the future, we hope to see this technology develop on a larger scale. The idea of harvesting wasted or excess energy in simple actions such as walking or capturing vibrations from a roadway would be a major achievement. A method to successfully capture and store this energy on a large scale must be developed, as well as a method to efficiently return this energy to another circuit. With the ability to implement piezoelectric devices and energy harvesters into everyday actions, we will be able to steer away from fossil fuels and nuclear power as sources for energy. This fact shows how piezoelectric devices are beneficial to many other aspects of life than just those dealing with MEMS.
R
EFERENCES
[1] N. Jalili. (2010). Piezoelectric-Based Vibration Control: From Macro to
Engineering in China.
[Online article]. 4(2), pp. 153-159. Available: DOI
Micro/Nano Scale Systems.
[Online book]. Springer Science + Business
10.1007/s11465-009-0031-z
[12] J. Nuffer, T. Bein. (2006, October). “Application Of Piezoelectric
Media, LLC. New York, NY. Available: DOI 10.1007/978-1-4419-0070-8
[2] M. Zhu, E. Worthington. (2009). “Design and Testing of Piezoelectric
Materials In Transport Industry.”
Global Symposium on Innovative Solutions for the Advancement of the Transport Industry 4.-6. [Online]. Available:
Energy Harvesting Devices for Generation of Higher Electric Power for
Wireless Sensor Networks.” IEEE Sensors 2009 Conference.
[Online article]. pp. 699-702. Available: DOI 10.1109/ICSENS.2009.5398559 http://www.inmar.info/press/InMAR_Reliability_TRANSFAC_2006.pdf
[13] B. Nash. (2002, March 30 th ). “Engineering a Smooth Ride: Creating the Perfect Ski Through Shaping and Vibration Control.”
Illumin . Vol. IV,
[3] H. Kim, Y. Tadesse, S. Priya. (2009). “Piezoelectric Energy Harvesting”
Issue III. [Online article]. Available: http://illumin.usc.edu/11/engineeringin Energy Harvesting Technologies.
[Online book chapter] Springer Science a-smooth-ride-creating-the-perfect-ski-through-shaping-and-vibration-
+ Business Media, LLC. New York, NY. pp. 3-39. Available: DOI
10.1007/978-0-387-76464-1_1 damping/
[14] J. Yoshida. (2002). “Piezoelectric rackets and professional oomph.”
[4] C. S. McGahey. (2009). “Harnessing Nature’s Timekeeper: A History of
EE/Times: News and Analysis.
[Online article]. Available: the Piezoelectric Quartz Crystal Technological Community (1880-1959). http://www.eetimes.com/electronics-news/4043462/Piezoelectric-rackets-
Ph. D. Dissertation, Georgia Institute of Technology.
Available: add-professional-oomph http://proquest.umi.com/pqdlink?did=1814779271&Fmt=2&clientId=17454
&RQT=309&VName=PQD
[15][Onlineimage].Available: h ttp://www.bing.com/images/search?q=piezo
[5] R. Ballas. (2007). “Piezoelectric Materials” in Piezoelectric multilayer electric+tennis+racquets&view=detail&id=916469AB1600F53BFDFD3DC beam bending actuators: Mictrotechnology and MEMS.
[Online book
EB32CE53F0A609BF8&first=0&FORM=IDFRIR chapter]. Springer Science + Business Media, LLC. New York, NY. pp. 17-
[16][Onlineimage].Available:http://www.bing.com/images/search?q=piezoe
30. Available: DOI 10.1007/978-3-540-32642-7_2 lectric+tennis+racquets&view=detail&id=9AAB5C87B5512332FA644F71
[6] N. Bassiri-Gharb. (2008). “Piezoelectric MEMS: Materials and
Devices” in
Piezoelectric and Acoustic Materials for Transducer
F2088CE290D2C9F9&first=0&FORM=IDFRIR
[17] S. Trolier-McKinstry, F. Griggio. C. Yaeger, P. Jousse, D. Zhao, S.
Applications. [Online book chapter] Springer Science+ Business Media,
LLC. New York, NY. pp. 412-430. Available: DOI 10.1007/978-0-387-
Bharadwaja, T. Jackson, S. Jesse, S. Kalinin, K. Wasa. (2011, September).
“Designing Piezoelectric Films for Micro Electromechanical Systems.”
76540-2_20
IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control.
[Online article]. 58 (9), pp. 1782-1792. Available: DOI
[7] S. Kim, C.Y. Koo, J-H. Cheon, J-H. Yeom. H-J. Woo, J. Ha. (2007).
“Lead-free Piezoelectric Thin Films for Bio-medical Applications.” [Online 10.1109/TUFFC.2011.2015 article]. pp. 858-860. Available: DOI 10.1109/ISAF.2007.4393428
[8] J. Xie, M. Hu, S. Ling, H. Du. (2006). “Fabrication and characterization on piezoelectric cantilever for micro transducers.” Elsevier: Sensors and
[18] W. Hobbs, D. Hu. (2012). “Tree-inspired piezoelectric energy harvesting.”
Journal of fluids and Structures.
[Online article]. 28 (2012) pp.
103-114. Available: DOI 10.1016/j.jfluidstructs.2011.08.005
Actuators A.
[Online article]. 126 (2006), pp. 182-186. Available: DOI
10.1016/j.sna.2005.09.019
[9] W. Dong, X. Lu, Y. Cui, J. Wang, M. Liu. (2007). “Fabrication and characterization of microcantilever integrated with PZT thin film sensor and actuator.” Elsevier: Thin Solid Films.
[Online article]. 515 (2007), pp. 8544-
8548. Available: DOI 10.1016/j.tsf.2007.03.138
[10] E. K. Reilly, P. K. Wright. (2009). “ Modeling, fabrication and stress compensation of an epitaxial thin film piezoelectric microscale energy scavenging device.” Journal of Micromechanics and Microengineering.
[Online article]. 19, 095014, pp. 1-11. Available: DOI 10.1088/0960-
1317/19/9/095014
[11] J. Qiu, H. Jiang, H. Ji, K. Zhu. (2008, Dec. 20). “Comparison between four piezoelectric energy harvesting circuits.”
Frontiers of Mechanical
A
DDITIONAL
R
ESOURCES
M. Bhaskaran, S. Sriram, S. Ruffell, A. Mitchell. (2010, December).
“Nanoscale energy generation characteristics of piezoelectric thin films.”
Optoelectronic and Microelectronic Materials and Devices.
[Online article]. pp. 149-150. Available: DOI 10.1109/COMMAD.2010.5699710
S. Bhuyan, J. Hu. (2007). “Wireless drive of piezoelectric plate by focused electric field.” Applied Physics Letters.
[Online article]. 91, 264101 (2007).
Available: DOI 10.1063/1.2824459
S. Bhuyan, K. Sivanand, S. Panda, R. Kumar, J. Hu. (2011). “Resonance-
Based Wireless Energizing of Piezoelectricv Components.” IEEE
University of Pittsburgh
Twelfth Annual Freshman Conference
Swanson School of Engineering
April 14, 2012
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Magnetics Letters . [Online article]. 2, 6000204 (2011). Available: DOI
10.1109/LMAG.2001.2167133
K. Cook-Chennault, N. Thambi, M. Bitetto, E.B. Hameyie. (2008).
“Piezoelectric Energy Harvesting: A Green and Clean Alternative for
Sustained Power Production.”
Bulletin of Science Technology & Society .
[Online article]. 28, pp. 496-509. Available: http://bst.sagepub.com/content/28/6/496
H. Hu, Y. Hu,. C. Chen, H. Wang. (2008, October). “A System of Two
Piezoelectric Transducers and a Storage Circuit for Wireless Energy
Transmission through a Thin Metal Wall.” IEEE Transactions on
Ultrasonics, Ferroelectrics, and Frequency Control.
[Online article]. 55
(10), pp. 2312-2319. Available: DOI 10.1109/TUFFC.930
Y. Li, W. Li, T. Guo, Z. Yan, X. Fu, X. Hu. (2009). “Study on structure optimization of a piezoelectric cantilever with a proof mass for vibrationpowered energy harvesting system.”
Journal of Vacuum Science and
Technolgoy, B.
[Online article]. 27 (3), pp. 1288-1290. Available: DOI
10.1116/1.3119677
P. Muralt, J. Conde, A. Artieda, F. Martin, M. Cantoni. (2009).
“Piezoelectric materials parameters for piezoelectric thin films in GHz applications.”
International Journal of Microwave and Wireless
Chris Roberts
Jennifer Franco
Technologies.
[Online article]. 1 (1), pp. 19-27. Available: DOI
10.1017/S1759078709000038
C. Pan, S. Tzou, R. Shiu. (2010). “A Novel Wireless and Mobile
Piezoelectric Micro Robot.”
International Conference on Mechatronics and
Automation.
[Online article]. pp. 1158-1163. Available: DOI
10.1109/ICMA.2010.5588196
S. Trolier-Mckinstry, P. Muralt. (2004). “Thin Film Piezoelectrics for
MEMS”. Journal of Electroceramics . [Online article]. 12, pp. 7-17.
Available: DOI 10.1023/B:JECR.0000033998.72845.51
R. Van Schaijk, R. Elfrink, T.M. Kamel, M. Goedbloed. (2008).
“Piezoelectric AlN energy harvesters for wireless autonomous transducer solutions.” IEEE Sensors 2008 Conference.
[Online article]. pp. 45-48.
Available: DOI 10.1109/ICSENS.2008.4716379
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CKNOWLEDGMENTS
We would like to thank Beth Newborg and Bert Cos for all their suggestions and help during this process.
University of Pittsburgh
Twelfth Annual Freshman Conference
8
Swanson School of Engineering
April 14, 2012