Faculty Publications
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Item Influence of filler on dielectric properties of silicone rubber particulate composite material(Elsevier Ltd, 2020) Mathias, K.A.; Hiremath, H.; Manohar Shankar, B.S.; Kulkarni, S.M.This paper deals with the development of silicone rubber particulate composites filled with strontium titanate to improve dielectric properties of neat silicone rubber. The composite material is prepared by a solution casting method with three different volume percentages of the filler. The composite samples prepared are tested for dielectric properties as per standards. The influence of filler on dielectric properties of composite material is studied by testing for dielectric permittivity, loss tangent, and ac conductivity. The dielectric permittivity experimentally obtained is compared with the available empirical models. The dielectric permittivity, loss tangent, and ac conductivity of silicone rubber composite increased with the increase of volume percentage of strontium titanate. Compared to neat silicone rubber the dielectric permittivity, loss tangent, and ac conductivity of the silicone rubber composite filled with 10% volume of strontium titanate is increased by 66%, 117%, and 267% respectively. Further, the empirical models confirmed that dielectric permittivity obtained is within the limit. The microscopic study reveals that the improved dielectric properties attributed to the stronger bond between the silicone rubber and the strontium titanate particles. © 2019 Elsevier Ltd. All rights reserved.Item Influences of dielectric and conductive fillers on dielectric and mechanical properties of solid silicone rubber composites(Springer London, 2019) Manohar Shankar, B.S.; Kulkarni, S.M.Dielectric elastomers are materials being used for electromechanical transduction applications. Their electromechanical response depends on permittivity, Young’s modulus and electric breakdown strength. A factor that limits its application is high operating voltages that can be reduced through improvement in permittivity. One of the methods is by incorporating high permittivity fillers into polymer matrix to obtain dielectric–dielectric composites (DDC).These composites show high permittivity at the cost of reduced flexibility. An alternative solution is development of composites by incorporating organic or inorganic conductive fillers into polymer matrix. These composites show high permittivity with high dielectric loss and low breakdown strength. To overcome both the above limitations both dielectric and conductive fillers are incorporated into dielectric polymer matrix to obtain conductor–dielectric composites (CDC). In this study, high temperature vulcanized solid silicone rubber as matrix has been used to prepare DDC composites with barium titanate (BT) filler and CDC composites with both BT as dielectric and ketjenblack as conductive fillers, using Taguchi design of experiments. The effect of factors such as amount of fillers and curing agent, mixing time in roll mill and curing temperature on the dielectric and mechanical properties are reported. Lichtenecker model predicts the permittivity of the DDC composite more accurately. For the CDC composites permittivity increased by 390%, effective resistivity decreased by 80%, Young’s modulus increased by 368% and Shore A hardness increased by 90% as compared to those of reference matrix. Important interaction effects are observed among both the fillers that are uniformly dispersed without any aggregation. © 2019, Iran Polymer and Petrochemical Institute.Item Influence of conductive and dielectric fillers on the relaxation of solid silicone rubber composites(Institute of Physics Publishing helen.craven@iop.org, 2019) Manohar Shankar, B.S.; Hiremath, S.; Kulkarni, S.M.Flexible dielectrics possessing high permittivity and low loss are desirable for many electromechanical transduction applications. Solid silicone rubber composites are promising materials for electromechanical applications. These composites are fabricated using high-temperature vulcanization process, with various amounts of conductive, dielectric and conductor-dielectric filler and processing parameters. Dielectric and conductivity relaxations of these composites are investigated using dielectric spectroscopy in the 20 Hz-2 MHz frequency range at room temperature. Dielectric relaxations of dielectric filler composites show different behaviour compared to conductive and conductive - dielectric filler composites even with the same filler loading. All composites show increased permittivity at lower frequencies. The maximum permittivity of 46, 5.8 and 46 at 20 Hz was attained for the conductive, dielectric and conductive-dielectric composites respectively at similar filler loadings. The composites follow the AC universality law with exponents in the range of 0.82 to 1.02. The conductive filler is more reinforcing than dielectric filler as seen from the variation of Young's modulus with filler type. Uniform dispersion of fillers is observed for all the three composites. © 2019 IOP Publishing Ltd.Item Experimental investigation on performance of disposable micropump with retrofit piezo stack actuator for biomedical application(Springer Verlag service@springer.de, 2019) Mohith, S.; Karanth P, P.N.; Kulkarni, S.M.Extensive researches are being conducted to develop miniaturized pumping systems to fulfill the need for accurate delivery of fluids at required rates, particularly in the biomedical field. This paper presents the design, fabrication, and testing of novel valveless micropump actuated through an amplified piezo actuator. The proposed model of the micropump pump has the unique feature of a disposable chamber and employs low-cost polymeric materials, conventional molding and machining operations for fabrication. The disposable part of the pump consists of a laser-cut pump chamber with nozzle/diffuser made of Polymethyl methacrylate (PMMA) and conventionally molded silicone rubber diaphragm. The retrofit part includes the amplified piezo actuator and support structures build from PMMA. Systematic characterization of the pump was carried with water and blood mimicking fluid to understand the effect of operating parameters such as driving frequency and actuation voltage on flow rate and back pressure of the micropump. Experimental results show that the proposed design was capable of pumping 3.3–3.4 ml/min of dye solution and 1.7–1.75 ml/min of blood mimicking fluid at a driving frequency of 5 Hz and actuation voltage of 150 V. The corresponding computed volume resolution/stroke of the pump was found to about 5.75 µl and 11.25 µl of blood mimicking fluid and dye solution, respectively. The proposed pump was found to work effectively against a maximum back pressure of 156 Pa with blood mimicking fluid and 250 Pa with the dye solution as the working fluid under the same operating condition of 5 Hz and 150 V. © 2019, Springer-Verlag GmbH Germany, part of Springer Nature.Item Performance analysis of valveless micropump with disposable chamber actuated through Amplified Piezo Actuator (APA) for biomedical application(Elsevier Ltd, 2020) Mohith, M.; Karanth P, N.; Kulkarni, S.M.The precise manipulation of fluid through pumping systems has been the technological challenge in microfluidic applications. The biomedical applications call for precise and accurate delivery of fluid through miniaturized pumping systems. This paper presents a novel valveless micropump for biomedical applications operated by the Amplified Piezo Actuator. Integrating the disposable chamber and reusable actuator with the proposed micropump allows the actuator to be reused and eliminates the possibility of infection or contagion. The micropump was fabricated using low-cost polymeric materials like Polymethylmethacrylate (PMMA), Silicone rubber through CNC milling, Laser Cutting, conventional moulding operation. The micropump chamber, nozzle/diffusers, and a bossed diaphragm constituted disposable part and Amplified Piezo Actuator with structural support formed the reusable part of the micropump. The bossed diaphragm of the pump chamber consists of a central cylindrical protrusion to reduce the force of adhesion on the diaphragm and transmit force required for micropump actuation. A theoretical analysis was performed to assess the effect of diaphragm thickness and the bossed region on the effective stiffness of the diaphragm, which in turn influences the deflection achieved. Besides, an analytical approach has been presented to address the effect of adhesive force on the diaphragm surface due to the residual fluid and chamber depth. The experimental characterization of the micropump was carried out to determine the optimal performance parameters with water, fluids mimicking blood plasma, and whole blood. Based on the experimental results, the pumping rate and head developed by the micropump have been significantly affected by factors such as bossed ratio, diaphragm thickness, depth of the micropump chamber, and viscosity of the fluid. The optimum configuration of the micropump cosidered silicone rubber diaphragm with thickness of 0.20 mm having a bossed ratio of 0.33 and a chamber depth of 1.25 mm. With the optimal operating parameters of 150 V sinusoidal input of frequency 5 Hz, the proposed micropump was capable of delivering 7.192 ml/min, 6.108 ml/min, and 5.013 ml/min of water and blood plasma, whole blood mimicking fluid with the maximum backpressure of 294.00 Pa, 226.243 Pa, and 204.048 Pa respectively. The corresponding resolution, i.e., pumping volume/stroke of the micropump was about 23.972 µl, 20.358 µl, and 16.708 µl, respectively. © 2020 Elsevier LtdItem Effect of ketjenblack and barium titanate on the piezoresistive behaviour of silicone rubber particulate composites(IOP Publishing Ltd, 2021) Manohar Shankar, B.S.; Hiremath, H.; Kulkarni, S.M.In the present study, silicone rubber reinforced with ketjenblack and barium titanate were fabricated using high temperature compression molding method. These particulate composites are characterized for piezoresistive sensitivity. Ketjenblack and barium titanate are the conducting and dielectric fillers in the high temperature vulcanized silicone rubber matrix. The effects of ketjenblack and barium titanate fillers, filler loading, amount of curing agent, curing temperature and mixing time on the piezoresistive properties of these composites were investigated. The piezoresistive sensitivity recorded maximum values of 3.7(10-3) (kPa)-1 for dielectric and dielectric-conductive composites. The linear variation of normalized resistance change was observed for change in pressure up to 20 kPa. The dielectric composite sensitivity increases with reduction in dielectric filler and curing agent loadings, increasing with mixing time and curing temperature. The piezoresistive sensitivity for dielectricconductive composites depends on ketjenblack and barium titanate filler loading. These composites demonstrate interaction effects among the factors. © 2021 The Author(s). Published by IOP Publishing Ltd.Item Experimental studies on mechanical and dielectric behavior of Glycerol filled Silicone rubber composites(IOP Publishing Ltd, 2021) Mathias, K.A.; Hiremath, H.; Kulkarni, S.M.In this study, Silicone rubber composites are prepared with Glycerol filler in three different volume fractions. The samples developed are subjected to mechanical and dielectric testing. The tensile strength increases first and later decreases with Glycerol loading whereas compression strength decreases with Glycerol loading. Modulus of elasticity in tension and compression both decreases with the increase of Glycerol loading. Dielectric permittivity, dissipation factor and conductivity are increases with the increase of Glycerol loading. The Silicone Rubber (SR) composite with 15% volume of Glycerol filler shown a maximum reduction in modulus of elasticity of 29% (in tension) and 16.8% (in compression), and maximum improvement in the dielectric permittivity of 112% compared to neat silicone rubber. The reduction in modulus of elasticity with an increase in dielectric permittivity with an increase in Glycerol loading suggests that this material is a potential candidate for materials to be used in soft dielectric sensors and actuator applications. © 2021 IOP Publishing LtdItem Effect of fillers on the piezocapacitive behaviour of silicone rubber particulate composites(Institute of Physics, 2024) Manohar Shankar, B.S.M.; Kulkarni, S.M.Robotics and fluid dynamics applications have created demand for development of electronic skins with embedded pressure sensors. These applications require simple and low-cost fabrication processes with large area deployment. Both structured and unstructured material approaches to sensor development have been followed. Among the various sensing mechanisms, piezo capacitive transduction is superior. This paper reports the influence of fillers on the piezo capacitive characteristics of unstructured solid silicone rubber composites. Dielectric, conductive and conductive-dielectric fillers were incorporated into solid silicone rubber and fabricated using high temperature compression moulding to form dielectric-dielectric, conductive-dielectric and conductive-dielectric dielectric composites. The results reveal that piezo capacitive sensitivity varies with filler type, filler loading, curing agent loading, mixing time and curing temperature. The experiments reveal improved normalized capacitance with pressure characteristics of linearity and sensitivity of 3.9 × 10−3 (kPa)−1 in the 0-20 kPa range of pressure. These composites are thus candidate materials for flexible pressure sensing applications. © 2024 IOP Publishing Ltd