A compact electroactive polymer actuator suitable for refreshable Braille display

Available online at www.sciencedirect.com

Sensors and Actuators A 143 (2008) 335–342

A compact electroactive polymer actuator suitable for refreshable Braille display Kailiang Ren a , Sheng Liu a , Minren Lin b , Yong Wang a , Q.M. Zhang a,b,∗ a

Department of Electrical Engineering, The Pennsylvania State University, University Park, PA 16802, United States b Materials Research Institute, The Pennsylvania State University, University Park, PA 16802, United States Received 5 April 2007; received in revised form 18 October 2007; accepted 29 October 2007 Available online 13 November 2007

Abstract The large strain, high elastic modulus, and easy processing of poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) (P(VDF-TrFECFE)) electrostrictive terpolymer make it very attractive to replace low strain piezoceramics and piezopolymers in many applications with much improved performance. In this paper, a compact polymer actuator is developed utilizing the electrostrictive terpolymer, which is suitable for full page Braille display and graphic display. Key issues related to the reliability of electroactive polymers used in the compact actuators and for the mass fabrication of these polymer actuators are investigated. Making use of a recently developed conductive polymer, a screen printing deposition method was developed which enables direct deposition of very thin conductive polymer electrode layer (<0.1 ␮m) with strong bonding to the terpolymer surface and short fabrication time. It was observed that the thin conductive polymer electrodes lead to the self-healing of the polymer after electric breakdown. An electroactive polymer (EAP) compact Braille actuator was designed and fabricated with these terpolymer films wound on a spring core. The test results demonstrate that the EAP Braille actuator meets all the functional requirements of actuators for refreshable full Braille display, which offers compact size, reduced cost and weight. © 2007 Elsevier B.V. All rights reserved. Keywords: Electroactive polymers; Actuators; Braille display actuators; Conducting polymer electrodes; Electrode effect

1. Introduction Solid state actuators with large strain and high elastic energy density are attractive for a broad range of applications. One area where these actuators will have great impact is the refreshable Braille display, where the piezoelectric ceramic actuators are currently used. Due to the small transverse strain level of the piezoceramics (<0.05%), the actuator is in the bimorph configuration to “amplify” the actuation to reach required Braille dot displacement (>0.5 mm), as schematically shown in Fig. 1(a), which results in a large Braille cell size (see Fig. 1(b)) [1,2]. The bulky size and fragility of the piezoceramic bimorph actuator and high cost of each actuator for the refreshable Braille display limit the development of a practical full page refreshable Braille display and graphic display. To circumvent this difficulty associated with the piezoceramic bimorph actuators, several alternative actuation methods ∗

Corresponding author. E-mail address: [email protected] (Q.M. Zhang).

0924-4247/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.sna.2007.10.083

have been investigated, such as the pneumatic and thermopneumatic actuators, to realize full page refreshable Braille display with size, weight, and cost acceptable to the user community [3–5]. However, various shortcomings associated with these new technologies prevent them to be practical for the full page display. In 2000, a wheel-based Braille display was reported which can significantly reduce the number of actuators to move the dots in a refreshable display and hence, can reduce the cost of the Braille display markedly [6]. However, the moving wheel display seems not to be accepted by the user community. Recently, we reported a class of electrostrictive polymers, i.e., P(VDF-TrFE) based relaxor ferroelectric terpolymers and high energy irradiated P(VDF-TrFE) copolymers, with electromechanical responses substantially higher than the traditional piezoceramics and piezopolymers. For instance, an electrostrictive P(VDF-TrFE-CFE) terpolymer can exhibit strains higher than 5% with high elastic energy density (>0.5 J/cm3 ) [7–9]. These high performance electroactive polymers (EAPs) provide an opportunity to develop compact Braille actuators, which can directly replace the bulky piezoceramic bimorph actuators, as

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films, it is inevitable that the films contain weak spots, causing electric breakdown. It was found that the thin conductive polymer electrodes, due to its low melting point and the chemistry, can lead to self-healing, which also requires much lower electric energy to burn out the breakdown spot in comparison with aluminum electrodes. In this investigation, EAP films were wound on a thin spring to form compact Braille actuators. For the standard Braille display, the dot displacement and dot spacing are 0.025 inch (0.635 mm) and 0.1 inch (2.54 mm), respectively. There are 32 or 20 cells with eight dots per cell in the commercial product [12]. Test results to be presented in this paper indicate that the actuator performance exceeds the requirements for the Braille actuator. In the following, the experimental details of the electroded terpolymer films will be presented. Then, the results related to the self-healing, which are crucial for reliable operation, will be discussed, followed by the Braille actuator fabrication and characteristics. The key points related to the EAP Braille actuator will be summarized at the end. 2. Experimental and the influence of electrodes on the EAP strain response

Fig. 1. (a) Schematic diagram of a bimorph actuator and (b) schematic diagram of the commercial Braille cell using piezoelectric bimorph.

schematically shown in Fig. 2, for refreshable full page Braille display with compact size and much reduced cost. In this paper, we investigate the issues related to the electrostricitve polymers for a compact actuator, with the performance and size suitable for the full page Braille display. We examined various conductive polymers for the EAP film electrodes and developed a screen printing method, based on a unique conductive polymer, to deposit the patterned conductive polymer electrode to the terpolymer film surface with strong bonding and thinness, which can also easily scaled up to mass production. We also investigated self-healing of these EAP films after electric breakdown. In mass production of EAP actuator

Fig. 2. Schematic diagram of the proposed EAP Braille cell using the compact EAP Braille actuators.

P(VDF-TrFE-CFE) was synthesized by the suspension polymerization with an oxygen-activated initiator [13]. The terpolymer composition is 64.3/27.6/8.1 mol%. The polymer films were fabricated using the solution cast method, in which the polymer resins were dissolved in N,N-dimethylformamide (DMF) and solution cast from 20 ␮m to several hundred ␮m films, to meet the requirements for various tests. Following that, the film was uniaxially stretched to five times of the original length. The stretched film was annealed in two steps: first at 80 ◦ C for 2 h to release the mechanical stress induced during stretching and then annealed in 105 ◦ C for 4 h to increase the crystallinity of the film. Previous study has shown that such a two step annealing of stretched films can maintain the film stretching state under high temperature annealing [10]. For electroactive polymer films with large strain (>several% strain), metal electrodes as used in piezoceramic and piezopolymers will pose several problems. Firstly, the metal electrodes may have short lift time due to fracture under high strain. In addition, the high elastic modulus of the metal electrodes will also impose mechanical constraint to the active polymers which will reduce the strain level of the active polymer. In the past, we have developed several methods for depositing conductive polymer electrode layer on EAP films [14,15]. However, these early methods either take too long time to deposit electrodes, not suitable for mass production of EAP actuators or produces electrode layer not forming strong bonding with the EAP film surface. In this study, several conductive polymers as well as their deposition methods were investigated. It was found that a PEDOT Baytron S V2 conducting polymer (Bayer Corporation), which is an aqueous dispersion of poly(3,4-ethylendioxythiophene)poly(styrenesulfonate), can be easily screen printed on the surface of P(VDF-TrFE-CFE) terpolymer with strong bonding. No surface treatment of the terpolymer film is needed and the electrode layer can be very thin (∼0.1 ␮m). In order to produce

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Fig. 3. The image of the conductive polymer thin layer coated terpolymer films. The conductive polymer layers (top and bottom electrodes) are nearly transparent due to the thinness so we can see the text underneath the polymer films.

thin polymer film electrodes with different thickness, the commercial Baytron S V2 can be diluted by ethyl alcohol. In this study, the ratio of 1 to 1 between Baytron S V2 and ethyl alcohol was used. The electrode pattern on the screen printer was fabricated using a photolithography method. The electroded terpolymer films are nearly transparent as shown in Fig. 3 due to the thinness of the conductive polymer layers. The transverse strain (in-plane strain, defined in Fig. 4(a)) along the stretching direction of the electroded terpolymer films was characterized by a photonic sensor [16,17]. The data for the terpolymer films (8 ␮m film thickness) with 0.1 ␮m thick conductive polymer electrode layer is shown in Fig. 4. The transverse strain is 3.5% under 100 MV/m, which is similar to what has been measured earlier on thick films (>25 ␮m thickness) [9,16]. For such an EAP films to generate 1 mm Braille dot displacement, the actuator length is ∼3 cm (see Fig. 2). During the experiment, it was found that the electrode thickness has a critical effect in the strain of the terpolymer. As also shown in Fig. 4(b), the electromechanical strain becomes very small when the conductive polymer layer thickness is 2 ␮m, comparable to that of the terpolymer film. Since the elastic modulus of conductive polymer (>1 GPa) is higher than that of the terpolymer (∼0.5 GPa) and the thin terpolymer films

Fig. 4. The transverse strain of P(VDF-TrFE-CFE) film (6 ␮m thick) with screen printed PEDOT conducting polymer as the electrodes as a function of applied electric field. The two curves correspond to two thickness tm of the conductive electrode layer. Open circles, tm = 2 ␮m × 2 ␮m; triangle, 2 ␮m × 0.1 ␮m. There are two electrode layers for each polymer film. Data points are shown and curves are drawn to guide eyes.

are required in order to reduce the applied voltage, the electrode clamping effect must be considered in the design of the EAP Braille actuators. In the following, the mechanical clamping effect of the electrode layer on the strain response of the terpolymer films is examined. If there is no external mechanical stress and under an applied field E, the terpolymer film displays intrinsic transverse electrostrictive strains S10 and S20 , along and perpendicular to the film stretching direction, respectively (see Fig. 5(a)). Due to the electrode layer clamping effect, the strains will be reduced to S1

Fig. 5. The dependence of the strain ratio S1 /S10 on the electrode thickness for Au electrode (cross: +) and conductive polymer electrode (open circle: ) for two EAP film thicknesses (a) tp = 10 ␮m and (b) tp = 5 ␮m.

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and S2 : S1 = S2 =

p S10 + s11 T1 p S20 + s22 T2

p + s12 T2 p + s12 T1

(1)

where s11 and s22 are the elastic compliances of the EAP along p and perpendicular to the stretching direction, respectively. T1 p and T2 are the clamping stresses to the polymer film due to the electrode layers [11]. The transverse strains S1m and S2m in the electrode layer should be the same as S1 and S2 and the elastic equations for the strains in the electrode layer are,

To further simplify Eq. (8), we assume the Poisson’s ratios for terpolymer and electrode layer to be approximately 0.4 and 1/3, respectively [19]. One can also introduce B=

Yp sm = 11 Ym s11

where Yp and Ym are the Young’s moduli of the polymer film along the stretching direction and electrode layer and s11 = 1/Yp m = 1/Y . For the terpolymer, the elastic compliance s and s11 m 22 perpendicular to the stretching direction is about five times of elastic compliance s11 along the stretching direction [18]. Substituting these into Eq. (8), one can arrive

S1 1 = S10 1 + ((AB + 0.2) − 0.4(0.4 + 0.33AB))/(AB(AB + 0.2) − 0.33AB(0.4 + 0.33AB))

m T m + sm T m S1m = s11 1 12 2

(2)

m T m + sm T m S2m = s22 2 12 1

m and S m are the elastic compliances of the electrode where S11 22 m layer. T1 and T2m are the stresses exerted to the electrode layer from the polymer film. Because the clamping force to the polymer film and the stretching force to the electrode layer should be equal in magnitude with opposite sign, it can be derived that,

tp T1m T2m = −A p = p =− tm T2 T1

(3)

where tm and tp are the total thickness of the electrode layer, which is equal to the sum of the two electrodes on the two surfaces of the polymer film, and polymer layer, respectively. A is the thickness ratio between the polymer and electrode layers. p p Substituting T1m and T2m with T1 and T2 into Eq. (2) and for m m electrode layer s11 = s22 yields, p

p

p

p

m T A − sm T A S1m = −s11 12 2 1 m T A − sm T A S2m = −s11 2 12 1

(4)

In deriving Eq. (4), S20 = 0 was used since S20 is much smaller than S10 for the uniaxially stretched electrostrictive PVDF films [9,18]. Combining Eqs. (2) and (4) yields, p

p

m m m m m m T2 A − s12 T1 A = s22 T2 + s12 T1 −s11

(5)

Since p

T1 = −

m +s As11 22 p m T2 s12 + As12

(6)

it can be shown p

T2 =

m ((Asm As11 11

S1 m )) − sm A + s22 )/(s12 + As12 12

(7)

By combining these equations, one can arrive at the strain S1 of the polymer film under the constraints of the electrode layers

(9)

(10)

Eq. (10) indicates that the degree of reduction in S1 is related to both the thickness ratio and the Young’s Moduli ratio between the polymer and electrode. Fig. 5 illustrates how the ratio of S1 /S10 changes with the total electrode thickness for the metal electrode (Au as an example, Y = 79 GPa) and conductive polymer electrode (Y = 1 GPa) for the terpolymer films with thickness of 5 and 10 ␮m, respectively. The elastic modulus of the terpolymer film along the stretching direction is 0.5 GPa [9]. The results show the advantage of using conductive polymer electrodes in reducing the electrode mechanical constraint effect to the EAP film strain responses. For the conductive polymer layer thickness in 0.1–0.2 ␮m range, the reduction of the strain of terpolymer films of 5–10 ␮m thick is quite small. However, when the conductive polymer layer thickness is comparable to that of terpolymer films, the strain reduction can be quite significant. These results are consistent with the experimental data. 3. Self-healing effect in PVDF-TrFE-CFE terpolymer films For EAP devices operated under high electric field, electric breakdown in EAP films is a concern. Such an electric breakdown may cause electroactive polymer film shorting between two electrodes and consequently catastrophic failure of the EAP actuators. For EAP Braille actuators, it is highly desirable to have self-healing or graceful failure after electric breakdown. That is, in an event of electric breakdown, the adjoining thin conductive electrodes evaporate and the defect thus becomes isolated, as schematically illustrated in Fig. 6. As a result, the EAP actuator will only lose very small portion of the film after the breakdown while maintaining the actuation function. In fact, in polymer film capacitor industry, self-healing has been used to remove the weak spots in the films prior to the assembly of the films into capacitors [20,21]. There are several methods that can be used to produce selfhealing or graceful failure in polymer films. One method utilizes the local heating at the breakdown spot, which can cause evaporation of the electrodes in the surrounding region and leave an

1 S1 = m + s ) − s (s + Asm ))/(Asm (Asm + s ) − sm A(s + Asm )) S10 1 + (s11 (As11 22 12 12 22 12 12 11 11 12 12

(8)

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Fig. 6. Schematic diagram of the electric breakdown process which produces self-healing (in the bottom figure, the electrodes are shown).

area around the breakdown spot without conductive electrodes [20]. Fig. 7 shows the thermal gravimetric analysis measurement of PEDOT film by using a TA Instrument SDT Q600. It shows that the decomposed temperature of PEDOT film is 350 ◦ C, which is much smaller than the melting temperature of Al (660 ◦ C). As will be shown later that thin conductive electrodes with low melting temperature makes it easier for the self-healing to occur (lower dissipated energy in the selfhealing breakdown). In most of the earlier works on self-healing, the electrode used is the aluminum, zinc, and zinc–aluminum alloy, because of their relatively low melting temperatures. The much lower decomposed temperature of the conductive polymer and the thin electrode layer developed here will lead to better self-healing behavior than these metal electrodes. In addition to the vaporization of the electrode layer in the self-healing process, it is also crucial that the polymer in the breakdown process decomposes to other gaseous by-products rather than graphite [20]. The formation of graphite will lead to increased conduction at the breakdown region of the polymer, which will result in the failure of EAP devices. In our experi-

Fig. 7. The percent weight loss of PEDOT film as a function of the temperature (TGA).

Fig. 8. An optic microscope image of a self-healing breakdown in the terpolymer film coated with conducting polymer electrode.

ment, it was observed that the presence of defect spots such as pits and pinholes in the film causes higher dielectric loss in the electroded films. Breakdown at these spots removes these defect spots as the electrodes evaporate around these spots, causing electric open around these spots (see Fig. 8). Therefore, the selfhealing after breakdown leads to terpolymer films with reduced dielectric loss and higher operation fields than that before the self-healing. Fig. 9 summarizes the change of the capacitance and dielectric loss measured by HP 4284A precision LCR meter (Hewlett Packard, Palo Alto, CA) for the terpolymer films with conductive polymer electrodes before and after breakdown. The data show a large reduction of the dielectric loss after the self-healing, indicating: (i) the defect spots in the films which contribute to the conduction loss have been removed through the self-healing breakdown process and (ii) the breakdown by-products are not conductive, i.e., no graphite formation. The data also show that there are reductions in the capacitance, which are due to the reduced area of the film samples after self-healing breakdown. The optical micrographs of the burn-out areas after self-healing breakdown are shown in Fig. 8. For some small film samples, these areas can be more than 10% of the total area as shown in Fig. 9. It is shown that the capacitance of the whole sample is reduced due to the reduction of the capacitor area. Meanwhile, the dielectric loss is also reduced since the burn-out of the defect spot. With improved film quality, the defect spots can be reduced markedly as in the commercial polymer film capacitors. The result here is consistent with the earlier results [20]. The dissipated energy during the self-healing process is an important parameter which was also characterized. A small energy for self-healing is highly desirable since it will cause less

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Fig. 9. The changes of dielectric loss and the capacitance of the (PVDF-TrFE-CFE) films following the self-healing. Shaded bars: the dielectric properties before the self-healing breakdown; black bars: the dielectric properties after self-healing test. (a) Dielectric loss and (b) the capacitance (nF). The horizontal axis is the film sample numbers.

damage to the polymer film after breakdown. Shown in Fig. 10(a) is the current spike associated with a breakdown event in a terpolymer film and it is apparent that after breakdown, the film capacitor remains insulating under the high voltage. In order to prevent the air breakdown in these breakdown tests, the EAP films were dipped into the silicone oil momentarily to coat a thin insulation oil layer on the films prior to the breakdown tests.

The total charge associated with each breakdown event was also measured using a modified Sawyer–Tower circuit and a typical data is shown in Fig. 10(b), where the breakdown event causes a sudden increase in the charge density. The energy U consumed during the breakdown can be found from, U = ρq × A × V where ρq is the change of the charge density, A is total sample area, and V is the applied voltage. The dissipated energy during the self-healing event in Fig. 10(b) is about 0.21 mJ. The thickness of electrode and polymer film is about 0.1 and 16 ␮m, respectively. The total electrode area is about 4.11 cm2 for all the samples. Tests were conducted for many other polymer samples with the same conductive polymer electrode thickness and area. The dissipated energy during the self-healing process is in the range of 0.2–0.4 mJ, which is much lower than that for the polymer films using aluminum electrodes [20]. This is understandable because the aluminum electrodes have much higher melting temperature (∼660 ◦ C). The results here indicate the advantage of using conductive polymer electrodes for the EAP actuators. 4. The EAP Braille actuator

Fig. 10. (a) The current spike during the self-healing breakdown and (b) the charge density jump associated with a breakdown (DC voltage is 600 V and thickness of terpolymer film is 16 ␮m). The break in the curve at near −4 s is due to the electric breakdown in the film.

Terpolymers films with thin conductive polymer electrodes and after self-healing breakdown were wound around a prestressed thin spring to form a Braille actuator. A schematic diagram of the fabrication process is presented in Fig. 11. As shown in Fig. 4, the terpolymer film elongates under an electric field, which when combined with a pre-stressed spring core (compressive stress) will push the Braille dot up. Upon removing the electric field, the Braille dot returns to original position. A winding machine was designed and built for the fabrication of the EAP Braille actuator, which provides pre-stress in the spring core and better control of the fabrication process. In the current design, the EAP film thickness is ∼5–6 ␮m. To separate the two electrodes on the two faces of the EAP films in the wound actuator, the electroded polymer films were bonded together by employing the residual solvent in the films (the solvent DMF content is in 1–2% range) under high pressure and

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Fig. 11. Schematic diagram of fabrication process of the rolled EAP actuator for Braille display using the electrostrictive polymer thin films: (a) pre-strained spring core, (b) electroded polymer thin film, (c) the thin film is folded to form a bilayer to separate the positive and negative ends, and (d) the rolled actuator.

at an elevated temperature to form a bilayer (see Fig. 11(d)). In the thermal fusing process, the two thin EAP films were heated to 80 ◦ C under a 1000 lb force (3.6 MPa) for 20 min to bond the two layers together. To ensure the correct electric connection as well as good bonding, the capacitance and the total bilayer film thickness were measured. The total capacitance should be the sum of the capacitance of each layer. The bilayer film was wound on the spring core to form the Braille actuator. A commercial spring, spring probe ICT-100 (Interconnect Devices Inc., Kansas City, KS), was chosen as the core on which the EAP film is wound. The diameter of the spring core is 1.37 mm and the total length is 60 mm. The spring constant is about 225 N/m. After the winding, both ends of the EAP film are glued to the spring by 5 min epoxy. Care has to be taken in handling very thin polymer films in this fabrication process to ensure that the films are not damaged. The total length of active polymer film is about 34 mm and Fig. 12 presents a photograph of a finished actuator. The Braille actuator performance was characterized. The displacement of actuator is measured by a CCD camera. The strain data are shown in Fig. 13. That data shows that the total displacement of actuator is 1 mm under 100 MV/m, which corresponds to 3% strain in the EAP film and is consistent with the strain data in Fig. 4 (since the length of the active EAP film is 34 mm). The result indicates that the EAP film performs well in the Braille actuator configuration. For Braille display, the minimum dot displacement is 0.5 mm and hence, the compact Braille actuator developed here is more than adequate to meet the displacement requirement of the Braille dots. The force level of the finished actuator is also evaluated. Using a load cell, the force required to push back the actuator tip in 0.5 mm displacement, i.e., shorten the actuator length in Fig. 12 by 0.5 mm by applying a force at the tip is measured to 0.75 N. For a typical refreshable Braille display, the force level of the dots is in 0.1–0.5 N range. Therefore, the EAP Braille actuator meets all the functional requirements of refreshable Braille display, which also offers compact size, reduced cost and light weight.

Fig. 12. An optic image of the EAP Braille actuator.

Fig. 13. The displacement of the tip (the Braille dot) of the Braille actuator as a function of applied field. The data show that to produce a 0.5 mm dot displacement, the required field is 60 MV/m.

5. Summary In conclusion, it was demonstrated that an actuator based on the electroactive terpolymer P(VDF-TrFE-CFE) can provide much better performance than the Braille actuator based on piezoceramics. In the development of the EAP Braille actuators, a screen printing conductive polymer electrode was developed, which can form thin (less than 0.1 ␮m thick) conductive polymer electrode with strong bonding to the EAP films, and suitable for mass production of the Braille actuators. It was further shown that the thinness, the low melting temperature of the conductive polymer, as well as the unique chemistry of the conductive polymer used, yield a self-healing of the EAP films after an electric breakdown. The self-healing electric breakdown pro-

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cess removes weak spots in the EAP films and the films after that can sustain high voltage and function properly. The final EAP Braille actuator generates a dot displacement of 1 mm with a force level more than 0.75 N. Acknowledgement This project was supported by NIH under Grant No. R21EY016799.

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Kailiang Ren received his BS from Tianjin University, China, in 1997, and MS and PhD degree in electrical engineering from Penn State University, University Park, PA, in 2005 and 2007, respectively. His research interests focus on fabrication and characterization of the various advanced materials (electrostrictive polymer, single crystal, 1-3 composite and shape memory polymer) for their applications, such as energy harvesting, transducers, polymer actuators and MEMS devices. Sheng Liu received the BS degrees in physics from Nanjing University, Nanjing, China, in 2003. He is currently working toward the PhD degree with Department of Electrical Engineering, Pennsylvania State University, University Park, PA. His research interests include high performance electroactive polymers & composites, solid state electromechanical devices such as artificial muscles, actuators and transducers. Dr. Minren Lin received his PhD at University of Missouri-St. Louis in 1990 major in organometallics and catalysis. Then he had worked in the department of chemistry at the Penn State University in the filed of catalytic system for methane conversion and polymerization as a research assistant and a senior research associate. He joined in Material Research Institute at the Penn State University in 2005, and has worked since then. Yong Wang was born in Jiangsu, China, on August 12, 1978. He received the BS and MS in Physics from Nanjing University, Nanjing, China, in 1999 and 2002 respectively. He also received the MS in electrical engineering from The Pennsylvania State University in 2006. He is currently working toward the PhD degree at the Department of Electrical Engineering, The Pennsylvania State University, University Park, USA. Dr. Qiming Zhang is a distinguished professor of electrical engineering and materials science and engineering of Penn State University. Dr. Zhang obtained PhD in 1986 from Penn State University. The research areas in his group include fundamentals and applications of novel electronic and electroactive materials. Research activities in his group cover actuators and sensors, transducers, dielectrics and charge storage devices, polymer thin film devices, polymer MEMS, and electro-optic and photonic devices. He has over 270 publications and 10 patents (2 pending) in these areas. His group has discovered and developed a ferroelectric relaxor polymer which possesses room temperature dielectric constant higher than 50, an electrostrictive strain higher than 7% with an elastic energy density ∼1 J/cm3 . His group also proposed and developed nano-polymer composites based on delocalized electron systems to raise the nano-polymeric composites dielectric constant near 1,000. More recently, his group demonstrated a new class of polar-polymer with electric energy density over 25 J/cm3 , fast discharge speed and low loss, attractive for high efficiency energy storage capacitors. He is the recipient of the 1999 Penn State Engineering Society Outstanding Research Award and a fellow of IEEE.