Nagireddy Seshadri Reddy received his MS-Dual Degree in Electronics and Communication Engineering. His research work was supervised by Dr. Aftab M Hussain.
Here’s a summary of Seshadri’s M.S thesis, Modelling of Multilayered Perforated Electrodes for Dielectric Elastomer Actuator Applications as explained by him:
Dielectric Elastomer Actuators (DEAs) are emerging as pseudo-muscular actuators in the field of soft robotics. DEAs work on the principle of actuation due electrostatic pressure. Since the DEAs are electromechanical transducers they must contract and stretch along with the polymer. Thus, the electrodes should be complaint. In order to achieve this stretchability carbon nanotube (CNT) based electrodes are used to retain conductivity even at large strains. One of the main drawback of DEAs is their high driving voltage of 0.3-4 kV. In order to reduce the actuation voltage the without reducing the thickness the relative permittivity can be increased 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 thin film consists of a mesh of large number of interwoven CNTs.
When they undergo strain the CNTs merely slide on each other increasing the dimensions. However, this interwoven structure of CNTs does not resemble a continuous thin film but resembles a perforated one. This can create complex electric field patterns especially for multilayered DEAs. Since DEAs are inherently capacitors they can be represented in capacitor/resistor model. In this work, we tried to study the electrostatics of such multi-layered structures focusing on screening or lack of screening of electric fields created by ad-joint capacitors and the effect it has on the observed capacitance of the system. Under theoretical treatment, it has been found that for an n-layered interdigitated structure with uniaxial perforation the capacitance of the system can be estimated by the equation:
?? = ?0 [? − 2(? − 1)? + 2(? − 2)? 2 − ⋯ + 2(−?) ?−1 ]
where n is the number of layers, β is the constant dependent on perforation ratio, Co is the capacitance of single layer with all solid electrodes. Further the above theoretical model is verified using Finite Element Analysis (FEA) in both 2D and 3D space. The perforated electrode is modelled as a charged metallic electrode with gaps in between in 2-dimensional case and a metallic sheet with circular holes in 3-dimensional case. Further the analysis is carried on an interdigitated structure to obtain capacitance of multilayered structure. The electric field is seen to briefly fringe very close to the perforations as there is discontinuity in charge at these points. At large distances from the perforations, the electric field is approximately constant. From the results it’s been found that β is independent of number of layers and is dependent only on perforation ratio. The obtained data closely matches the theoretical analysis results for normalized capacitance. Normalized capacitance is calculated to show the percentage change with that of a capacitor with solid electrodes. The drop in normalized increases as the perforation ratio increases also the normalized capacitance decreases with increase in number of layers but saturates afterwards. The loss of electric field due to perforations in the electrode system is limited for a reasonable area coverage and can even be neglected for area coverage of more than 90%.