Fabrication and Performance of a Donut-Shaped Generator Based on Dielectric Elastomer Ran Hee Lee, 1 Utpal Basuli, 1 Min-Young Lyu, 2 Eun Soo Kim, 3 Changwoon Nah 1 1 BK-21 Plus Haptic Polymer Composite Research Team, Department of Polymer-Nano Science and Technology, Chonbuk National University, Jeonju 561–756, Republic of Korea 2 Department of Mechanical System Design Engineering, Seoul National University of Science and Technology, Seoul 139–743, Republic of Korea 3 Department of Electrical and Electronics Engineering, Jeonju University, Jeonju 560–759, Republic of Korea Correspondence to: C. Nah (E - mail: cnah@jbnu.ac.kr) ABSTRACT: Dielectric elastomers (DEs) have been suggested as generators to harvest electrical energy from natural mechanical energy sources, such as human movements and ocean waves. In this study, a donut-shaped DE generator (DEG) has been fabricated and its performance is characterized depending on the stretch deformation. A simple new stretchable electrode system using multi-walled car- bon nanotubes has been suggested. Measurements on the resistance, capacitance, and electrical power generation are made depending on the area expansion. The capacitance and harvested energy are parabolically increased with increased area expansions. The theoreti- cal prediction of energy harvesting is in good agreement with measured values of capacitance changes with stretching. FE analysis is also applied for calculation of strains for the DEG to figure out the distribution of strains. It is suggested that the DEG has promising applications in the field of designing an energy harvesting device depending on the type of energy available. V C 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40076. KEYWORDS: elastomers; rubber; sensors and actuators; stimuli-sensitive polymers Received 7 August 2013; accepted 13 October 2013 DOI: 10.1002/app.40076 INTRODUCTION Recently, there has been a greater interest in the issue of green and renewable electrical energies. Various attempts and relevant researches have been made for harvesting electrical powers with higher efficiency based on various materials, notably piezoelec- tric materials 1 and electroactive polymers (EAPs). 2 Dielectric elastomers (DEs), notably acrylic and silicone rubbers, is one class of EAP to be used as actuators and generators which can directly transform between the mechanical and electrical energy. 2–8 Comparing with other EAP materials such as electro- strictive polymers, conducting polymers, and polymer gels, DEs have many advantages of low cost, high deformation, no toxic- ity, high resistance to corrosion, quick response, high energy densities, and high conversion efficiency, which make them potentially well suited for development of power generators from natural energy sources such as ocean wave, heel-strike, winds, and waterfalls. 5,9–13 Thus the harvested energy is clean, unlimited, pollution-free, and environmentally friendly. 10,14,15 The DE generator (DEG) uses a very simple structure of sand- wiched elastomer sheet with compliant electrodes (Figure 1). This structure resembles conventional capacitors, where the capacitance is dependent on the area (A) and thickness between two electrodes (t), as is given below 10,15 : C5 ee 0 A t (1) where e and e 0 are the relative dielectric constant and permittiv- ity of free space (8.85 3 10 212 F/m), respectively. Since the unfilled elastomer vulcanizates show the Poisson’s ratio of 0.5, the volume is nearly constant during the stretch deformation. 6 If the sheet is expanded to be double (thickness reduces to be one half), the capacitance increases to four times higher. Thus the DE capacitor can be considered as a variable capacitor, since the capacitance is easily and efficiently controlled by changing the degree of stretch. When the stretched DEG is charged [high capacitance, Figure 1(a)] and it is allowed to contract due to elastic nature of elastomer [low capacitance, Figure 1(b)], the elastic stresses in the film works against the electric field pres- sure, thus increasing electrical energy. In this process, like charges are compressed together, while opposite charges are pushed farther apart. Electrically, this change raises the voltage of the charge. 3,5 Pelrine and coworkers proposed the harvesting energy calculation for the system as follows 10 : V C 2013 Wiley Periodicals, Inc. WWW.MATERIALSVIEWS.COM J. APPL. POLYM. SCI. 2014, DOI: 10.1002/APP.40076 40076 (1 of 7)