Top PDF Effective behavior of dielectric elastomer composites

Effective behavior of dielectric elastomer composites

Effective behavior of dielectric elastomer composites

The class of electroactive polymers has been developed to a point where real life applications as “artificial muscles” are conceivable. These actuator materials provide attractive advantages: they are soft, lightweight, can undergo large deformation, possess fast response time and are resilient. However, widespread application has been hindered by their limitations: the need for a large electric field, relatively small forces and energy density. However, recent experimental work shows great promise that this limitation can be overcome by making composites of two materials with high contrast in their dielectric modulus. In this thesis, a theoretical framework is derived to describe the electrostatic effect of the dielectric elastomers. Numerical experiments are conducted to explain the reason for the promising experimental results and to explore better microstructures of the composites to enhance the favorable properties. The starting point of this thesis is a general variational principle, which character- izes the behavior of solids under combined mechanical and electrical loads. Based on this variational principle, we assume the electric field is small as of order ε 1 2 , assume
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Dielectric Elastomer Composites: Macroscopic Behavior and Instabilities

Dielectric Elastomer Composites: Macroscopic Behavior and Instabilities

estimates for the effective response of two-phase DECs with random particulate mi- crostructures. Our results show that the addition of highly dielectric yet stiff particles can enhance the electromechanical response of DECs, for appropriate choices of the relevant microstructural parameters. This is not a trivial result since the addition of highly dielectric but stiff particles to the dielectric elastomer matrix increases both the overall permittivity and the stiffness of the DEC. While a higher overall permit- tivity leads to an increased attractive force between the electrodes, the higher stiffness limits the overall electrostrictive strains that can be achieved. Consistent with the early theoretical results for electrostriction (Landau et al. 1984, Shkel & Klingenberg 1998), the framework developed in this work expresses the effective electromechanical coupling of the composite in terms of the derivative of the permittivity with respect to the strain, also incorporating the effect of particle rotations. In addition, it ac- counts for dipolar interactions between particles, as well as for the nonlinear coupling between the electric and mechanical fields. For these reasons, the new framework is expected to produce more accurate estimates than earlier estimates (Li & Rao 2004, Rao & Li 2004), especially when the field fluctuation in the matrix phase become significant (Li et al. 2004). On the other hand, while the framework developed in this work should be equivalent to the recently developed homogenization framework of Tian et al. (2012), the alternative expression for the electromechanical coupling in terms of the strain-dependent permittivity (instead of third moments of the elec- tric and mechanical fields) has allowed the computation of such coupling constants for composites with general distributions of ellipsoidal inclusions, which is something that has not yet been possible with the formulation of Tian et al. (2012).
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Miniaturization Methods for Modular Robotics: External Actuation and Dielectric Elastomer Actuation

Miniaturization Methods for Modular Robotics: External Actuation and Dielectric Elastomer Actuation

Module design is an active area of research, as there are numerous design trade- offs. The module complexity ranges from independently mobile units to systems that are simply active material (e.g. a magnet). It is apparent that module complexity typically decreases with the size of the module for practical reasons. For robotic applications, increased module complexity can increase system functionality. How- ever, it is not clear what the appropriate level of module functionality should be to achieve cost effective, reliable, high performance systems. Techniques such as collec- tive actuation seem promising in order to maintain force output using robots with smaller, weaker modules. Projects that focus on reconfigurable self-assembly appli- cations typically use simple units actuated by sophisticated external systems. As the goal of this thesis is module miniaturization, we design low complexity modules and experimentally determine if they reliably achieve self-reconfiguration or desired robotic behavior.
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Highly Anisotropic Dielectric Elastomer Composites.

Highly Anisotropic Dielectric Elastomer Composites.

Plante et al. [161, 162] illustrated that by means of analytical and experimental studies of failure modes, D-EAP actuator can be designed to achieve their full potential in terms of deformation. Effect of four key parameters (pull-in failure, dielectric strength failure, viscoelasticity and current leakage) under different working conditions are proposed, evaluated with experiments and performance limits of D-EAP actuator are achieved. They modeled an idealized D-EAP actuator (both circular and diamond configurations) and used film prestretch during actuator fabrication, actuation voltage and stretch ratio as a function to predict their failure behavior .In order to characterize the viscoelastic properties, they used formulations proposed by Bergstrom-Boyce and for current leakage, [162] a first order model that includes both conductive and diffusive leakage properties are used. They concluded that the material strength failure effects are negligible when compared to dielectric strength and pull-in instability. They also reported that D-EAP actuators can operate reliably when used for short periods and at high stretch rate as the high stretch rates leads to high dielectric strength, whereas low stretch rates leads to pull-in stability which has more impact than the dielectric strength. Viscous dissipation reduces the actuation force as speed increases and large current leakage occurring at high extension and low speeds negatively affect the efficiency.
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Dielectric behavior of ceramic–graphene composites around the percolation threshold

Dielectric behavior of ceramic–graphene composites around the percolation threshold

effect on the matrix grains by graphene sheets induces a local decrease (at the grain boundaries) of the effective graphene concentration and, therefore, a decrease in the composite conductivity. Finally, the conductivity of the composites increases again for concentrations over 0.45 %. Analogously to the conductivity, the dependence of the average grain size with the graphene content has a direct influence on the real permittivity values of the composites. For this magnitude, the percolation theory predicts a non-intuitive behavior. According to the work of Efros [6], a near percolated system with conductive inclusions embedded in an insulator matrix should present a sharp maximum of the permittivity. The phys- ical interpretation of this phenomenon can be rational- ized as around the percolation threshold, conductor particles are very close between them, but completely
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Structural and Dielectric Properties of BST-BLT Composites

Structural and Dielectric Properties of BST-BLT Composites

KEYWORDS: Dielectric Constant, Barium Strontium Titanate, Barium Lanthanum Titanate, composites etc. ----------------------------------------------------------------------------------------------------------------------------- ---------- Date of Submission: 12-05-2018 Date of acceptance: 28-05-2018 ----------------------------------------------------------------------------------------------------------------------------- ----------

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Structural And Dielectric Properties Of Ppy/Zno Composites

Structural And Dielectric Properties Of Ppy/Zno Composites

ZnO. The surface morphology has been studied by scanning electron micrograph (SEM) and structure by X-ray diffraction technique. The SEM images of composites showed agglomeration of particles. The XRD pattern of the composites revealed the composites to be largely noncrystalline. The dielectric properties were measured at room temperature for the frequency range from 100Hz to 1MHz. Dielectric constant and loss decreased with increase in frequency. AC conductivity increased with frequency and ZnO concentration. Conductivity contains both frequency dependent and independent contributions, Conduction in these composites can be attributed to free as well as trapped charges.
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Control-focused, nonlinear and time-varying modelling of dielectric elastomer actuators with frequency response analysis

Control-focused, nonlinear and time-varying modelling of dielectric elastomer actuators with frequency response analysis

Electro-Active Polymers (EAPs) are a rapidly developing class of ‘smart’ material that produce actuation through deformation in response to an applied electric field [1]. EAPs combine a set of promising, desirable properties for actuation including large actuation strains, low mass, high response speed and compliance [2]. Dielectric elastomer actuators (DEAs) are a class of EAP, akin to a compliant capacitor, which show great potential in the replacement of conventional hard actuators for many applications, including robotics [3–5], orthotics and prosthetics [6, 7], and healthcare [8]. The nonlinearity and time-variation in DEA dynamics necessitates the need for advanced control algorithms before their potential in applications can be fully realised [5, 9, 10]. A crucial step therefore, is the development of techniques for control-focused modelling and analysis, which is the subject of this paper.
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Microstructure and dielectric properties of biocarbon nanofiber composites

Microstructure and dielectric properties of biocarbon nanofiber composites

BC fiber is an extracellular product excreted in the form of pellicles. It is structured in a web-like network by self-assembly of continuous nanofibers about 10 nm thick and 50 nm wide [12]. Each nanofiber is a bundle of cellulose microfibrils, each of which is about 4 nm thick and 4 nm wide. The web-like network leads BC to be homogenously dispersed in the matrices [13], and its composites have significant mechanical strength and ex- tremely low thermal-expansion coefficients [14,15]. After carbonization under a nitrogen atmosphere, BC was converted into a kind of carbon nanoribbon and the cor- responding TEM images are presented in Figure 2. As shown in Figure 2a, the carbonization at temperature of 800°C did not break the pristine structure, and the web- like networks were very well preserved. The carbonized bacterial cellulose networks can be described as a three- dimensional web built of entangled and interconnected cel- lulose ribbons. The width and thickness of the nanoribbons are in the order of tens of nanometers and a few
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DIELECTRIC AND AC CONDUCTIVITY OF POLYSTYRENE/OIL SHALE COMPOSITES

DIELECTRIC AND AC CONDUCTIVITY OF POLYSTYRENE/OIL SHALE COMPOSITES

The electrical properties of prepared polystyrene/oil shale composites with different concentration: 0, 5, 10, 20, 30 wt. % of oil shale were studied in this paper, under various measuring conditions including filler content and applied electric field frequency. The dependence of AC-electrical properties of polystyrene/oil shale composites on filler content and frequency were studied using the AC impedance technique. The impedance measurements were performed in the frequency range (100 kHz - 1.5 MHz) at room temperature (30 o C). Impedance, dielectric constant and AC-conductivity showed frequency and filler content dependencies. The relaxation time was determined for different filler concentrations .The study includes application of some models to explain the observed results. The universal power law of the AC conductivity behaviour is satisfied for different concentration.
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Cerebellar inspired algorithm for adaptive control of nonlinear dielectric elastomer based artificial muscle

Cerebellar inspired algorithm for adaptive control of nonlinear dielectric elastomer based artificial muscle

Figure 1. Dielectric elastomer actuators (DEAs) are difficult to control. (a) Sketch of DEA operation. Voltage applied to the electrodes produces electrostatic pressure that squeezes and expands the elastomeric film between them. When the voltage is switched off, the film returns to its original shape (cf. [6]). (b) Time course of displacement response to a step change in voltage (ordinate shows voltage prior to amplification by a factor of 800). The time course can be approximated by a single exponential, with time course in this case of approximately 100 ms [7]. The responses shown in this and the subsequent panels were obtained from DEAs made of acrylic elastomer (3M VHB 4905) with conductive layers of carbon grease as the electrode plates [7,8] (further details in Methods.). The schematic response shown here is derived from the nonlinear Hammerstein model developed by Wilson et al. [7] that accounts for 96 – 98.8% of the variance in the responses of six DEA samples to filtered white noise. (c) The top trace shows the coloured-noise voltage input ( prior to amplification, cf. panel b) over a 30 min period of stimu- lation. The bottom trace shows the corresponding displacement response of a DEA sample. The response gradually changes (‘creeps’) over the 30 min period. (d) Data from panel c replotted to show displacement as a function of voltage for successive time periods as indicated by the colour scale. The displacement response is nonlinear, displays hysteresis, and varies over time (from fig. 1e of [8]).
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Optimisation of silicone based dielectric elastomer transducers by means of block copolymers – synthesis and compounding

Optimisation of silicone based dielectric elastomer transducers by means of block copolymers – synthesis and compounding

Soft elastomers such as silicones, acrylates and polyurethanes have been studied extensively for use in artificial muscle technology [1,2]. Electroactive polymers, known as EAPs, are elastomers that exhibit a change in size or shape when stimulated by an external electrical field [3]. EAPs can be divided into ionic and electronic, with the former requiring low driving voltages and an electrolyte and deforming due to the diffusion of ions in the material in the presence of an electrical field. Electronic EAPs, on the other hand, require high driving voltages and can be operated in the air. Additionally, they possess higher electrical energy than ionic EAPS and come complete with large actuation forces, rapid response times and long lifetimes [1]. Their drawback is that they require high driving voltages, between 500 V to 10 kV, to actuate [2,4]. Polymer electrets [5–7], electro-strictive graft elastomers [8], ionic polymer gels [9] and dielectric elastomers [10–12] are examples of electronic EAPs. Among all of the mentioned electronic EAPs, dielectric elastomers are the most favourable in actuation, due to high actuation speeds, large strains, high work densities and a high degree of electromechanical coupling [1].
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Development of a Refreshable Prototype Actuator using Silicone Dielectric Elastomer Actuator (DEA).

Development of a Refreshable Prototype Actuator using Silicone Dielectric Elastomer Actuator (DEA).

Multifunctional Elastomer rolls (MERs) were formed by rolling highly pretensioned planar DEA films onto a central compression spring [54, 65].These were described by the authors as multifunctional elastomer rolls (MERs). Those MERs with one degree of freedom perform as linear actuators and have demonstrated actuation maximum strokes of 5-7% of their active lengths and forces ranging up to 1N [33]. Those with higher Degree of Freedom (DOF) have the capability to perform multiple functions of load bearing, actuation, and sensing. They have demonstrated actuation in several ways through axial extension and bending through suitable electrode patterning on a single monolithic substrate. In one of the works [57], as shown in Fig.18, two acrylic films (3M VHB 4910) were pre- strained. Thereafter, the film was wound over the centrally compressed spring and in the process, the electrode areas were stacked on top of each other as shown in Fig.18 (b). Figs 18(c) and 18(d) indicate a rolled actuator using four 2 DOF MERs in the relaxed state and actuated state respectively [57].
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Loading system mechanism for dielectric elastomer generators with equi biaxial state of deformation

Loading system mechanism for dielectric elastomer generators with equi biaxial state of deformation

Dielectric Elastomers (DEs) are highly deformable non-conductive materials that can be employed as insulating layers to conceive variable capacitance transducers. DE transducers have been largely studied for actuation and sensing applications 1,2 . In the last decade, several researches have demonstrated that they can be successfully employed as electricity generators 3 . The working principle of DE Generators (DEGs) is based on a variable capacitor whose dielectric and conductive layers are deformed, resulting in large variations of its capacitance. Such a variable capacitor works as a charge pump and makes it possible to directly convert the introduced mechanical energy into usable electrical energy. A very promising application field for DEGs is the wave energy sector. At present, Wave Energy Converters (WECs) are based on hydraulic and mechanical components made of bulky, heavy, costly and corrosion-sensitive materials. DEGs show several positive attributes, that suit the requirements of the wave energy sector, such as: large energy densities, good energy conversion efficiency that is rather independent on cycle frequency, easiness in manufacturing and assembling, high shock resistance, silent operation and low cost. Introducing DE-based Power-Take-Off (PTO) systems, that directly convert oscillating mechanical energy into electricity, could largely simplify WEC technology. Several studies that focus on this particular application field of DEGs have already been conducted 4–8 .
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Dielectric Properties of 
                              BaTiO3/Nylon11/MgCl2/PANI composites

Dielectric Properties of BaTiO3/Nylon11/MgCl2/PANI composites

The piezoelectric materials can be divided in three classes viz. inorganic, organic and composites. In inorganic class there are ceramics and crystals having high dielectric constant, high piezoelectric coefficient, high electromechanical coupling but poor mechanical property and relatively high acoustic impedance restricting their use to only certain applications. In organic class there are polymers, such as Polyvinylidene Fluoride PVDF, having relatively low acoustic impedance, which could provide a good acoustic matching to water or tissues, but its piezoelectric coefficients are also relatively low as compared to ceramics. In composite class mainly there are ceramic:polymer composites having good piezoelectric and dielectric properties as compared to polymer and good mechanical properties as compared to ceramics. These composites have their use in many applications owing to their better and tunable properties.
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Structural and dielectric properties of polyaniline / TiO2 Nano-composites

Structural and dielectric properties of polyaniline / TiO2 Nano-composites

Electronic properties (Dielectric and Conductivity) were measured in pressed pellets in a press machine at 10 ton pressure in stainless steel die of 0.85 mm diameter and 0.5 mm thickness by using a two-point method in the frequency range 1MHz to 2.4GHz. The samples were connected to a Keithley 2400 electrometers and a current source electrometer. The dielectric constant of all the samples and reproducibility were checked. X rays powder diffraction analysis was carried out using an automated diffractometer, Panalytical X’ Pert PRO equipped with Cu Kα radiations (=1.54 A). The instrument was operated at 40 kV and 30 mA and diffraction patterns of PANI and PANI-TiO 2 Composites samples mounted on a
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Future MISFET gate dielectric: NiO/PVA Nanohybride composites

Future MISFET gate dielectric: NiO/PVA Nanohybride composites

This paper reports on the electrical and nanostructural properties of polymer-based materials in corporation with NiO (Nickel oxide) in weight concentrations of 0.2%, 0.4%, and 0.8% of PVA (polyvinyl alcohol) polymer. Nanocrystallite phases and properties were characterized by using X-ray diffraction (XRD), Fourier transfer infrared (FTIR) radiation, scanning electron microscopy (SEM), and atomic force microscopy (AFM) techniques. The dielectric constant of the samples has been calculated through measuring the capacity of the samples by application of GPS 132 A. Electrical property characterization was also performed with cyclic-voltameter (C-V) technique in TRIS solution; pH = 7.3, with the formula (HOCH 2 ) 3 CNH 2 .
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Effective Permittivity Tensor for a Metal-Dielectric Superlattice

Effective Permittivity Tensor for a Metal-Dielectric Superlattice

In this work, we have applied the homogenization theory developed in [9] to calculate the frequency-dependent effective local permittivity tensor of a metal-dielectric superlattice. We could also derive analytic expressions for the components of the permittivity tensor, describing both the regime, where Rytov’s formulas [4] are valid, and that found by Xu et al. [6] at very small metal filling fractions. Our results could be useful in designing metamaterials based on metal-dielectric 1D PC. ACKNOWLEDGMENT

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A study on synthesis, characterization and dielectric properties of PANI-NiO composites

A study on synthesis, characterization and dielectric properties of PANI-NiO composites

Polymer based conducting composites have gained much attention in the recent years due to their excellent optical, electrical and structural properties. Especially these composites have played important role in various applications like rechargeable batteries, electromagnetic interference shielding, electric catalysis and sensors. Out of all available conducting polymers, polyaniline (PANI) is the most popular due to its outstanding properties. Since it is a unique polymer it exhibits three stable oxidation states which are, fully reduced state: leucoemeraldine, fully oxidized state: pernigraniline form and partially oxidized state: emeraldine. Out of the three oxidation states, the first two states are poor conductors while emeraldine is most attractive owing to its tunable states, emeraldine base and emeraldine salt. Polyaniline is synthesized by many routes out of which solution blending, enzymatic polymerization and in situ polymerization techniques are the most popular ones. Initially it was synthesized by oxidation of aniline and later by subjected aniline to anodic oxidation at carbon electrode. Owing to its popularity many groups across the world are working on various aspects of polyaniline like polymerization, electronic conductance and electrostatic interactions. The important properties which make PANI attractive for molecular electronics are its ease of synthesis, high electrical conductivity and good environmental stability [1-4].
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Mechanical, Dielectric, and Spectroscopic Characteristics of “Micro/Nanocellulose + Oxide” Composites

Mechanical, Dielectric, and Spectroscopic Characteristics of “Micro/Nanocellulose + Oxide” Composites

We see from Fig. 5a, b that the dilatometric behavior of ΔL/L for the un-doped C0 sample was changed after heating and became like the dependencies described above for the other oxide-containing samples (Fig. 5a). Similarly, the coefficient of thermal expansion for the C0 sample was changed too that had resulted in similarity of the α(T) curves for the C0, C2, and C3 samples (Fig. 5b). At the same time, dilatometric characteristics and their temperature dependencies for the C1 sample appreciably differs from other dependencies. However, the C1 curve can be described as a superposition of the typical for all curves with a wide high-temperature peak near 95 – 97 °C and the abovementioned low-temperature sin- gularities (see Figs. 4b and 5b, C1 curve). It is interesting to analyze the behavior of the high-temperature peak intensity (comparing the data in Figs. 4b and 5b). These figures shows that, only for C0 after heating, the dilato- metric peak retains its intensity (about 250 – 300 1/°C), while for all other samples, the intensity of this peak de- creases of 1.5–2 times (560, 480, 420 1/°C before preheat- ing and 200, 300, 230 1/°C after preheating for the C1, C2, C3 samples, respectively). Besides, heating leads to de- crease of the low-temperature (30 – 60 °C) side of all the α ( T ) curves. Thus, we can state that several various mech- anisms determine the thermal expansion for both un- doped micro/nanocellulose and cellulose-oxide micro/ nanocomposite materials. Right now, there are not enough
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