Electroactive Actuators Research Articles

Towards fully polymeric electroactive micro actuators with conductive polymer electrodes

The performance of micro devices actuated using electroactive polymers is often limited by the high stiffness of metallic electrodes, which prevents the polymeric components extension. In this work we report on an approach allowing to reduce the use of metals to a minimum by incorporating softer conductive polymer electrodes. A multilayered actuator incorporating polyimide (PI) substrate and a thin electroactive polymer (EAP) layer of P(VDF-TrFE-CFE) squeezed between polyaniline (PANI) electrodes was fabricated and characterized. The PANI layer was electrodeposited on the electroactive structures using cyclic voltammetry. Our results show that while the use of conjugate conductive polymer electrodes is feasible, the influence of the thin metallic seed layers required for electro-deposition is significant. The proposed electro-deposition based polymeric process is highlighted by its simplicity and relatively low cost, compared to common Physical Vapor Deposition processes, and can be extended to other polymers.

Elastic characteristics of a strip-like electro-active elastomer actuator

Electro-active elastomer actuators have been widely studied, and many applications have been proposed for them. However, nearly all studies are focused on driving principle, structures, and control, and investigations on the mechanical properties and efficiency are insufficient. Using a strip-like actuator as a model case, this study revealed the maximum deformation, the relationship between driving force and deformation, and the maximum efficiency to provide a basic guide for the design of such actuators. First, the strains without mechanical constraints were studied, and the maximum strain was discussed under a linear assumption. Second, the displacement and driving force were analyzed considering the effects of electrodes and the margins of dielectric elastomer, and the results were compared. Finally, the electromechanical efficiency was investigated, and the approaches for improving efficiency were discussed.

Layer-by-Layer Assembly of Free-Standing Nanofilms by Controlled Rolling.

A water surface not only provides a habitat to many living organisms but also opens up new possibilities to develop state-of-the-art technologies. Here, we show a technology for the layer-by-layer assembly of free-standing nanofilms by controlled rolling. The water surface is exploited as an ideal platform for rolling a nanofilm, allowing adhesion control and frictionless feeding. The nanofilm floating on the water surface is attached to a tube by van der Waals adhesion and is rolled up by the rotation of the tube. This method can assemble diverse film materials including metals, polymers, and two-dimensional materials, with an easy control of the number of layers. Furthermore, heterogeneous and spiral structures of the nanofilm are achieved. Various applications such as a stretchable tubular electrode, an electroactive polymer tube actuator, and a superelastic nanofilm tube are demonstrated. We believe this work can potentially lead to a breakthrough in the nanofilm assembly processes.

3D printed soft parallel actuator

This paper presents a 3-dimensional (3D) printed soft parallel contactless actuator for the first time. The actuator involves an electro-responsive parallel mechanism made of two segments namely active chain and passive chain both 3D printed. The active chain is attached to the ground from one end and constitutes two actuator links made of responsive hydrogel. The passive chain, on the other hand, is attached to the active chain from one end and consists of two rigid links made of polymer. The actuator links are printed using an extrusion-based 3D-Bioplotter with polyelectrolyte hydrogel as printer ink. The rigid links are also printed by a 3D fused deposition modelling (FDM) printer with acrylonitrile butadiene styrene (ABS) as print material. The kinematics model of the soft parallel actuator is derived via transformation matrices notations to simulate and determine the workspace of the actuator. The printed soft parallel actuator is then immersed into NaOH solution with specific voltage applied to it via two contactless electrodes. The experimental data is then collected and used to develop a parametric model to estimate the end-effector position and regulate kinematics model in response to specific input voltage over time. It is observed that the electroactive actuator demonstrates expected behaviour according to the simulation of its kinematics model. The use of 3D printing for the fabrication of parallel soft actuators opens a new chapter in manufacturing sophisticated soft actuators with high dexterity and mechanical robustness for biomedical applications such as cell manipulation and drug release.

Modelling and Control of Ionic Electroactive Polymer Actuators under Varying Humidity Conditions

In this work, we address the problem of position control of ionic electroactive polymer soft actuators under varying relative humidity conditions. The impact of humidity on the actuation performance of ionic actuators is studied through frequency response and impedance spectroscopy analysis. Considering the uncertain performance of the actuator under varying humidity conditions, an adaptable model using the neural network method is developed. The model uses relative humidity magnitude as one of the model parameters, making it robust to different environmental conditions. Utilizing the model, a closed-loop controller based on the model predictive controller is developed for position control of the actuator. The developed model and controller are experimentally verified and found to be capable of predicting and controlling the actuators with excellent tracking accuracy under relative humidity conditions varying in the range of 10–90%.

Voltage-driven torsion of electroactive thick tubes reinforced with helical fibers

This work studies the voltage-driven torsional deformation of a thick-walled circular cylindrical tube composed of a dielectric elastomer (DE) reinforced with a family of helical fibers. The Helmholtz free energy of the DE composite tube involves separate DE matrix and fiber contributions. Upon the application of an electrical voltage difference on its inner and outer surfaces, the DE matrix contracts through the thickness and expands in cylindrical surfaces due to the Maxwell stress. Since the composite is stiffened along the fiber direction, it preferentially expands in the direction orthogonal to the fiber within the cylindrical surfaces. As a result, voltage-driven torsional deformation will occur in the helical fiber-reinforced DE tube. Although membrane theory was usually adopted to model fiber-reinforced thin DE membranes, the finite deformation theory is utilized in the present work to model relatively thick DE composite tubes. It is found that the bending effect plays an important role in the voltage-driven torsional deformation. The reorientation of the fibers and the distribution of the stress carried by the fibers in the tubes are discussed in detail so as to provide an interpretation to some new voltage-driven torsional behaviors. The theoretical model and physical insights provided in this work will aid the design and optimization of soft electroactive actuators and soft robotics.

Effect of porosity and tortuosity of electrodes on carbon polymer soft actuators

This work presents an electro-mechanical model and simulation of ionic electroactive polymer soft actuators with a porous carbon electrode, polymer membrane, and ionic liquid electrolyte. An attempt is made to understand the effects of specific properties of the porous electrodes such as porosity and tortuosity on the charge dynamics and mechanical performance of the actuator. The model uses porous electrode theory to study the electrochemical response of the system. The mechanical response of the whole laminate is attributed to the evolution of local stresses caused by diffusion of ions (diffusion-induced stresses or chemical stresses). The model indicates that in actuators with porous electrode, the diffusion coefficient of ions, conductivity of the electrodes, and ionic conductivity in both electrodes and separator are altered significantly. In addition, the model leads to an obvious deduction that the ions that are highly active in terms of mobility will dominate the whole system in terms of resulting mechanical deformation direction and rate of deformation. Finally, to validate the model, simulations are conducted using the finite element method, and the outcomes are compared with the experimental data. Significant effort has been put forward to experimentally measure the key parameters essential for the validation of the model. The results show that the model developed is able to well predict the behavior of the actuator, providing a comprehensive understanding of charge dynamics in ionic polymer actuator with porous electrodes.

A new electroactive polymer based on carbon nanotubes and carbon grease as compliant electrodes for electroactive actuators

In this article, the novel type of dielectric elastomer made of polydimethylsiloxane, multi-walled carbon nanotubes, and carbon grease is presented. The aim of the study was the development of compliant electrodes with ability for large deformation under applied voltage. The largest deformation of 47% was obtained for electrodes made of 2 wt% of multi-walled carbon nanotubes and 20 wt% of carbon grease. Electrical conductivity achieved for this material was 4.8 S/m. Good dispersion of conductive fillers within silicone matrix was obtained by calendaring technique. It was found that electrical percolation threshold for the compound was below 0.05 wt%. The structure of the material and its mechanical properties were determined. It was described that both properties, electrical conductivity and stiffness of the nanocomposite, have a significant influence on the extent of the electrode deformation. Two actuator designs are presented as the examples of application of developed material.

Synthesis of novel ladder-type polydiaryldibenzo[1,5]diazocines for electroactive molecular actuator

Novel ladder-type polymers with diazocine units, namely polydiphenyldibenzo[1,5]diazocine (PBD) and polydimethoxyphenyldibenzo[1,5]diazocine (PMBD), were successfully prepared for molecular actuator by one-pot polymerization method. The structure of polydiaryldibenzo[1,5]diazocines was confirmed by NMR and FTIR. The molecular weights and molecular weight distributions of the polydiaryldibenzo[1,5]diazocines were characterized by GPC analysis. Cyclic voltammogram (CV) studies revealed that the redox behavior be reversible in one-electron transfer process. Moreover, molecular conformation calculations using the density functional theory method (DFT) showed that both PBD and PMBD prefer to display zigzag conformation and further suggest that the average percent dimensional change is 14.6 in the one-electron transfer process. These polymers with ladder-type structure show good solubility, which are very different from conventional ladder-type polymers, such as polypyrrole and polythiophene. Both of them can be dissolved well in common organic solvents, such as CHCl3, and THF. Studies of the polymers will afford us with novel materials to fabricate device using an electrochemical actuator.

Electroionic Antagonistic Muscles Based on Nitrogen-Doped Carbons Derived from Poly(Triazine-Triptycene).

Electroactive soft actuators and bioinspired artificial muscles have received burgeoning interest as essential components in future electronic devices such as soft haptic‐feedback systems, human‐friendly wearable electronics, and active biomedical devices. However, important challenging issues including fast response time, ultralow input power, robust operation in harsh environments, high‐resolution controllability, and cost‐effectiveness remain to be resolved for more practical applications. Here, an electroionic antagonistic artificial muscle is reported based on hierarchically porous nitrogen‐doped carbon (HPNC) electrodes derived from a microporous poly(triazine‐triptycene) organic framework (PtztpOF). The HPNC, which exhibits hierarchically micro‐ and mesoporous structures, high specific capacitance of 330 F g−1 in aqueous solution, large specific surface area of 830.46 m2 g−1, and graphitic nitrogen doping, offers high electrical conductivity of 0.073 MS m−1 and outstanding volumetric capacitance of 10.4 MF m−3. Furthermore, it is demonstrated that a novel electroionic antagonistic muscle based on HPNC electrodes successfully displays extremely reliable and large bending deformations and long‐term durability under ultralow input voltages. Therefore, microporous polymer or covalent organic frameworks can be applied to provide significant improvements in electroactive artificial muscles, which can play key roles as technological advances toward bioinspired actuating devices required for next‐generation soft and wearable electronics.

Pentablock copolymer morphology dependent transport and its impact upon film swelling, proton conductivity, hydrogen fuel cell operation, vanadium flow battery function, and electroactive actuator performance

Ionomer composition and morphology impacts functional group distribution, water and ion-transport, and physical properties related to toughness, and degradation resistance. NEXAR MD9100 a pentablock copolymer (PBC) film morphology was dramatically altered when solution-cast into a film using tetrahydrofuran (THF) versus a cyclohexane: heptane (C:H) mixture. Film property and morphology changes were evaluated using Transmission Electron Microscopy (TEM), Small-Angle X-ray Scattering (SAXS), and electrochemical impedance spectroscopy. These changes were compared to Nafion 117 and Nafion 212. Average sulfonated inter-domain spacing through the film's thickness increased from 22.3nm (C:H cast) to 30.5nm (THF cast) that was estimated using SAXS. TEM revealed that PBC solution-cast films from C:H contained a random distribution of discrete sulfonated domains. An ordered PBC morphology consisting of lamella and hexagonally packed ion groups were created from a THF solution-cast film. These changes were attributed to favorable solvent-ionomer interactions during solvent evaporation and film densification. This ordered morphology led to increased conductivity (4.5mS/cm versus 47.8mS/cm), improved fuel cell power (19mW/cm2 versus 160mW/cm2), enhanced ionomer actuation (3.0cm versus 6.9cm), and modest self-discharge improvements for a vanadium redox-flow battery. This study demonstrates that morphology impacts ionomer physical properties, transport, and device function.

SELEMION CMV-BASED IPMC ACTUATORS’ DSP-ASSISTED BENDING CURVATURE OSCILLATION BEHAVIOR IN HUMIDITY-CONTROLLED ENVIRONMENTS

Fabrication of a practical electroactive polymer-based actuator is one of significantly important topics in the material science field. It is expected that the electroactive polymer-based actuator motion is quite similar to the real muscle motion due to its innate softness. Therefore a number of scientists acknowledge that the electroactive polymer-based actuator could exhibit unprecedentedly fascinating performance as an electroactive actuator. IPMC (Ionic Polymer Metal Composite) is one of polymer-based actuators. The research’s main objective was to obtain, compute and analyze the actuator's dynamics and transfer functions for controlling purposes of the Selemion CMV-based IPMC actuators in humidity-controlled environments. This paper presents the DSP assisted Feedforward, Feedback and two-degree-of-freedom control applied to Selemion CMV – based IPMC actuator. Previously, the authors of this paper have noted that the dehydration treatment improves the electrical controllability of the bending curvature oscillations in Selemion CMV – based IPMC actuators. This was evident in the DSP assisted control systems. The bending curvature oscillations experiments were carried out during the winter season, where the relative humidity was 30% at a room temperature of 24°C. Prior to performing the experiments, actuator’s dynamics and transfer functions were obtained through a series of experiments and simulations. From the computed and derived transfer functions, the controllers were implemented. The three controllers performed quite well, with just slight deviations during the repeat experiments due to changes in electrical properties the actuators underwent

Characterization​ and ​analysis of ​m​otion ​m​echanism​ of electroactive​ chitosan-based actuator

In order to analyze the bending mechanism of the electroactive​ chitosan-based actuator, different amounts of poly(diallyldimethylammonium chloride) (PDAD) were incorporated in chitosan solution. The effects of PDAD concentration on electromechanical performance of chitosan actuator were investigated under various excitation voltages. With the incorporation of PDAD into chitosan solution, crosslinked chitosan film acts as an actuator showing a considerable displacement behavior. However it can be noted that higher incorporation of PDAD into chitosan solution decreased the performance of the actuators. Thermal, viscoelastic, and crystallographic properties of the chitosan films were examined by thermogravimetric analysis, dynamic mechanical analysis, and X-ray diffraction analysis, respectively. The effect of incorporation of PDAD in chitosan-based film on morphological properties of chitosan film was determined by scanning electron microscopy. It was observed that the films involving PDAD have larger pore size than the PDAD free film.

High-fidelity bioelectronic muscular actuator based on porous carboxylate bacterial cellulose membrane

Human-friendly electronic products, such as smart mobile phones, soft haptic devices, wearable electronics, and implantable or disposal biomedical devices, will require the use of high-performance durable soft electroactive actuators with eco-friendly, biocompatible, and biodegradable functionalities. Here, we report a high-fidelity bioelectronic muscular actuator based on porous carboxylate bacterial cellulose (CBC) membranes fabricated using the facile zinc oxide (ZnO) particulate leaching (PL) method. The proposed CZ-PL muscular actuator exhibits large deformation, low actuation voltage, fast response, and high-durability in open air environment. In particular, the CZ-PL membrane shows a dramatic increase in the ionic liquid uptake ratio, ionic exchange capacity, and ionic conductivity of up to 70.63%, 22.50%, and 18.2%, respectively, for CBC, resulting in a 5.8 times larger bending deformation than that of the pure CBC actuator. The developed high-performance CZ-PL muscular actuator can be a promising candidate for meeting the tight requirements of human-friendly electronic devices such as wearable devices, biomimetic robots, and biomedical active devices.

Electroactive Ionic Soft Actuators with Monolithically Integrated Gold Nanocomposite Electrodes

Electroactive ionic gel/metal nanocomposites are produced by implanting supersonically accelerated neutral gold nanoparticles into a novel chemically crosslinked ion conductive soft polymer. The ionic gel consists of chemically crosslinked poly(acrylic acid) and polyacrylonitrile networks, blended with halloysite nanoclays and imidazolium-based ionic liquid. The material exhibits mechanical properties similar to that of elastomers (Young's modulus ≈ 0.35 MPa) together with high ionic conductivity. The fabrication of thin (≈100 nm thick) nanostructured compliant electrodes by means of supersonic cluster beam implantation (SCBI) does not significantly alter the mechanical properties of the soft polymer and provides controlled electrical properties and large surface area for ions storage. SCBI is cost effective and suitable for the scaleup manufacturing of electroactive soft actuators. This study reports the high-strain electromechanical actuation performance of the novel ionic gel/metal nanocomposites in a low-voltage regime (from 0.1 to 5 V), with long-term stability up to 76 000 cycles with no electrode delamination or deterioration. The observed behavior is due to both the intrinsic features of the ionic gel (elasticity and ionic transport capability) and the electrical and morphological features of the electrodes, providing low specific resistance (<100 Ω cm-2 ), high electrochemical capacitance (≈mF g-1 ), and minimal mechanical stress at the polymer/metal composite interface upon deformation.

Improved electromechanical response in acrylic rubber by different carbon‐based fillers

Dielectric elastomers are materials often utilized for the fabrication of electroactive actuators. Acrylic rubber (ACM) is very widely used in dielectric elastomer actuators (DEAs). However, its overall good performance is limited by the high operating electric field required. In the present work, we compare the effect of different types of conventionally used carbon black (CB) as well as other carbon‐based fillers on the dielectric and actuation properties of ACM in order to show that performance of DEAs can be improved by the development of ACM composites. Indeed, addition of CB, carbon nanotubes (CNTs), and synthetic graphite leads to an increase in the relative dielectric permittivity of elastomeric material. Moreover, incorporation of nanodiamonds results in reduction of dielectric losses. Finally, actuation stress is remarkably improved by CNTs and different grades of CB. POLYM. ENG. SCI., 58:395–404, 2018. © 2017 Society of Plastics Engineers

Trade-Off Between Transport and Mechanical Properties in Ion-Containing Block Copolymers with Different Self-Assembled Morphologies: A Comparison Study Between Lamellar and Inverse-Hexagonal

Both transport and mechanical performances are required for ion-containing polymers to be successfully used in ion-conducting applications such as fuel cells, actuators and electrodialysis. Phase-separated structure with ion and non-ion domains has been proposed to meet this requirement because these two domains can accommodate the ion and solvent transport and provide mechanical support respectively. The self-assembling nature of block copolymers is therefore used to create ion-containing polymers with well-defined phase-separated morphologies. The morphologies with continuous ion-domain are usually designed to enhance ion transport (1), however more attention may be needed on the trade-off between transport and mechanical properties. We have found out that the mechanical property is poor for some morphologies with continuous ion domain even though the ion domain is still the minor phase compared to the non-ion domain. Due to the electrostatic ion interaction, ion-containing block copolymers display more complicated phase behaviors and generate morphologies beyond that of neutral copolymers (2). Among them, inverse-hexagonal (HEX) structures have been widely prepared (3-5). It has the major non-ion block form the ‘bulk-like’ cylinders residing in the ‘surface-like’ minor ion phase. Our experimental observation indicated that this inverse-HEX morphology may suffer from excessive water swelling when placed in liquid water environment. In our work, the ion-containing block copolymer under study was supposed to form lamellar morphology according to the block copolymer phase diagram, however it generated a mixture of lamellar and inverse-HEX morphologies when casting from a polar solvent. The formation of inverse-HEX was suppressed when adding a little nonpolar solvent for casting. These two morphologies were imaged by TEM as shown in Figure 1. They are both in principle ‘percolating’ structures for ion transport. Although the membrane with a mixture of lamellar and HEX structures did display higher ion-domain connectivity than the pure-lamellar one as per our preliminary dynamic tension test, its ion conductivity under low water activity (in water vapor) and its water vapor transport flux are very close to the pure-lamellar one. This inconsistency may be because of the larger ion to non-ion interface within the inverse-HEX structure, resulting in more interface resistance. Only under high water activities (more than 0.95), the one with inverse-HEX displayed larger conductivity than the pure-lamellar one, probably due to more effective swelling of the hydrophilic phase for the former. And if the water vapor transport was measured with liquid water contacting one side of the membrane, the one with inverse-HEX had larger flux. Water sorption experiment showed that the one with HEX morphology swell more than the pure-lamellar one. And we actually observed the HEX membrane broke apart after placed in liquid water for 2 month while the pure-lamellar one was still intact. Thermodynamic swelling model considering both interface energy and elastic energy is being developed to explain the difference between inverse-HEX and lamellar morphologies. (1) Arges, C. and Kambe, Y. et. al. Realizing the Potential of Micro-Phase Separated Block Copolymer Electrolytes: Ion Domain Connectivity Plays a Prominent Role in Ion Conduction. ECS Transactions. 2016, 75(14), 1013-1020 (2) Sing, C.; Zwanikken, J.; Cruz, M. D. La. Electrostatic Control of Block Copolymer Morphology. Nat. Mater. 2014, 13(7), 694–698 (3) Kim, O.; Shin, T. J.; Park, M. J. Fast Low-Voltage Electroactive Actuators Using Nanostructured Polymer Electrolytes. Nat. Commun. 2013, 4, 2208 (4) Mineart, K. P.; Lee, B.; Spontak, R. J. A Solvent-Vapor Approach toward the Control of Block Ionomer Morphologies. Macromolecules 2016, 49 (8), pp 3126–3137 (5) Zheng, W.; Cornelius, C. J. Solvent Tunable Multi-Block Ionomer Morphology and Its Relationship to Modulus, Water Swelling, Directionally Dependent Ion Transport, and Actuator Performance. Polymer. 2016, 103, 104–111 Figure 1

Electrochemical properties of bi-component bundle of coaxial polyacrylonitrile/ polyaniline nanofibers containing TiO2nanoparticles

Electroactive actuators including materials or devices can respond to an electric field, current, or voltage with a corresponding change in their size or shape. Recent researches show an emerging interest in the electroactive polymers actuating systems because of their proper electrochemical properties for actuators and artificial muscles. The current research involves fabrication of core–sheath polyacrylonitrile (PAN)–polyaniline (PANi) nanofibers containing up to 15% TiO2nanoparticles in core, as well as the investigation of the mechanical and electrochemical properties of the prepared nanofibrous bundles. In the first step, high electrical conductive PANi polymer was synthesized through the oxidative polymerization method. TiO2nanoparticles were added to the core of nanofibers to improve both mechanical and electrical properties of the produced nanofibrous bundles. Synthesized PANi was used to produce aligned nanofibrous bundles comprising PAN–TiO2(0–15%) as core and PAN–PANi as sheath with an average diameter of 199–350 nm. The structural and physical properties of nanofibrous bundles were studied by Fourier-transform infrared, scanning electron microscopy, and transmission electron microscopy techniques. Mechanical and cyclic voltammetric tests were performed on core–sheath PAN/PANi samples to evaluate the mechanical and electrochemical properties, respectively. According to the results, fabricated bundles of coaxial PAN–TiO2/ PAN–PANi nanofibers is highly recommended as a candidate for electroactive actuator because of high electrical conductivity. PAN/ PAN–PANi nanofibers demonstrate an oxidation/ reduction peak of 0.8 V with a maximum current of 14.0 × 10−5A related to PANi and PAN–TiO2(10%)/ PAN–PANi has a maximum current of 11.0 × 10−5A with a peak at 0.8 V because of the presence of PANi.

Soft electroactive actuators and hard ratchet-wheels enable unidirectional locomotion of hybrid machine

Combining synergistically the muscle-like actuation of soft materials and load-carrying and locomotive capability of hard mechanical components results in hybrid soft machines that can exhibit specific functions. Here, we describe the design, fabrication, modeling and experiment of a hybrid soft machine enabled by marrying unidirectionally actuated dielectric elastomer (DE) membrane-spring system and ratchet wheels. Subjected to an applied voltage 8.2 kV at ramping velocity 820 V/s, the hybrid machine prototype exhibits monotonic uniaxial locomotion with an averaged velocity 0.5mm/s. The underlying physics and working mechanisms of the soft machine are verified and elucidated by finite element simulation.

Digital Control of a High-Voltage (2.5 kV) Bidirectional DC--DC Flyback Converter for Driving a Capacitive Incremental Actuator

This paper presents a digital control technique to achieve valley switching in a bidirectional flyback converter used to drive a dielectric electroactive polymer-based capacitive incremental actuator. This paper also provides the design of a low input voltage (24 V) and variable high output voltage (0–2.5 kV) bidirectional dc–dc flyback converter for driving a capacitive incremental actuator. The incremental actuator consists of three electrically isolated mechanically connected capacitive actuators. It requires three high-voltage (HV) (2–2.5 kV) bidirectional dc–dc converters to accomplish the incremental motion by charging and discharging the capacitive actuators. The bidirectional flyback converter employs a digital controller to improve the efficiency and charge/discharge speed using the valley switching technique during both charge and discharge processes, without the need to sense signals on the output HV side. Experimental results verifying the bidirectional operation of a HV flyback converter are presented using a 3-kV polypropylene-film capacitor as the load. The energy-loss distributions of the converter are presented when 4- and 4.5-kV HV mosfet s are used on HV side. The flyback prototype with a 4 kV mosfet demonstrated 89% charge energy efficiency to charge the capacitive load from 0 V to 2.5 kV, and 84% discharge energy efficiency to discharge it from 2.5 kV to 0 V.