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Modeling of Multilayer Perforated Electrodes for Dielectric Elastomer Actuator ApplicationsAuthor: Seshadri Reddy Nagireddy Date: 2020-09-26 Report no: IIIT/TH/2020/96 Advisor:Aftab M Hussain AbstractSoft robotics is a sub-branch of robotics in which nature is an inspiration to develop robots with physically flexible bodies to mimic the movements of living organisms and their complex structures. All soft robots require an actuation system to generate forces that allow for the movements. In the field of soft robotics and its applications, Dielectric Elastomer Actuators (DEAs) are becoming popular as biomimetic (pseudo-muscular) actuators. The key working principle of DEAs is actuation based on the electrostatic pressure experienced due to applied voltage. Since the DEAs are electromechanical transducers, they must contract and stretch along with the polymer. Thus, the electrodes should be complaint. To get this desired stretch-ability, stretchable electrodes based on carbon nanotube (CNT) are used so that even at large strains, the electric conductivity of the electrode is retained. The high driving voltage of 0.3-4kV is one of the main drawbacks of DEAs. In order to reduce the operating voltage of the actuator, the relative permittivity can be increased without reducing the thickness. On the other hand, the thickness can be decreased to reduce the driving voltage, and a multiple-layered structure can be used to have the same actuation force. CNT based thin film electrode consists of a mesh of extensive network of interwoven CNTs. These networks of CNTs slide on each other when they get strained, increasing the dimensions of the thin film. However, this interwoven structure of CNTs does not resemble a continuous thin film but resembles a perforated one. This perforated thin film-like structure can lead to intricate patterns and distribution of the electric field, especially for multilayered DEAs. Since DEAs are inherently capacitors, they can be represented in the capacitor/resistor model. In the following work, the study of the electrostatics of such multilayered structures is carried, focusing on screening or lack of screening of electric fields generated by adjacent capacitors and the corresponding effect it has on the overall capacitance of the multilayered system. From the result of theoretical analysis, it has been observed that for a multilayered interdigitated structure with uniaxial perforation of the thin film electrode, the capacitance of such a system can be calculated by the following equation: πΆπ = πΆ0 [π β 2(π β 1)π½ + 2(π β 2)π½ 2 β β― + 2(βπ½) πβ1] Where Co is the capacitance of all solid electrode single layer system, Ξ² is the constant dependent on the perforation ratio of electrode, and n is the number of layers of the structure. Further, the result from the above theoretical analysis is verified by modeling the structures in 2D and 3D space using Finite Element Analysis (FEA). Further to get the multilayered structure, the analysis is carried by modeling them as an interdigitated structure, and the corresponding capacitance is obtained. From further analysis and their results, it has been discovered that Ξ², which is a constant dependent on the perforation ratio, is independent of the number of layers of the structure. This acquired data closely matches the results of theoretical analysis obtained for normalized capacitance. Normalized capacitance is determined to show the change of percentage with that of an all-solid electrode-based capacitor. The loss of the electric field due to the discontinuity caused by perforations of the electrode in an interdigitated structure is minimal for a reasonable coverage area. Further, it can even be neglected for coverage of more than 90% in the area. The above analysis and the corresponding modeling give an estimate on the impact due to perforations and is essential for the development and manufacturing of reliable and robust CNTs based DEA structures. Full thesis: pdf Centre for VLSI and Embeded Systems Technology |
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