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Santa Clara, CA, United States

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Lean M.H.,QEDone LLC | Chu W.-P.L.,QEDone LLC
Journal of Polymer Science, Part B: Polymer Physics | Year: 2015

Bipolar charge injection and field-dependent mobility transport through nanocomposite film comprised of ferroelectric ceramic nanofillers in an amorphous polymer matrix is simulated using a 3D particle-in-cell model which extends the classical electrical double layer by substitution of a dipolar core for the nanofiller. The stability criterion of the explicit algorithm conforms to the Courant-Friedrichs-Levy limit. Simulation results for BaTiO3 nanofiller in amorphous polymer matrix indicate that antiparallel polarization results in the highest leakage conduction and lowest level of charge trapping in the interaction zone. Theoretical considerations validated simulation prediction in identifying a size range of 80 to 100 nm to minimize attachment and maximize conduction. The largest difference is in attached charge in the antiparallel case where fractions go from 2.2 to 97% as nanofiller size is decreased from 150 to 60 nm. Computed conductivity of 0.4 × 10-14 S/cm is in agreement with published data for PVDF. © 2015 Wiley Periodicals, Inc.


Lean M.H.,QEDone LLC | Chu W.-P.L.,QEDone LLC
EIC 2014 - Proceedings of the 32nd Electrical Insulation Conference | Year: 2014

This paper describes a rapid and robust axisymmetric hybrid algorithm to simulate divergent field experiments on layered polymer film. The hybrid algorithm uses a source distribution technique based on an axisymmetric boundary integral equation method (BIEM) to solve the Poisson equation and a 4 th order Runge-Kutta (RK4) method with an upwind scheme for time integration. Iterative stability is assured by satisfying the Courant-Friedrichs-Levy (CFL) stability criterion. The model computes dynamic temporal and spatial charge distributions assuming bipolar charge injection using Schottky emission and/or Fowler-Nordheim tunneling and field-dependent mobility while allowing for charge recombination and bulk and interfacial trapping/de-trapping. This model may be used to identify failure mechanisms such as charge packets, gaseous voids, and electroluminescence. Charge packets cause substantial increase of electric stress and could accelerate the breakdown of polymeric capacitors. Conditions for the creation of charge packets are identified and numerically demonstrated for a combination of impulsive step excitation, high charge injection, and discontinuous interface. Enhanced anisotropic interface conduction is shown to reduce charge accumulation, thus reducing E field contrast. © 2014 IEEE.


Lean M.H.,QEDone LLC | Chu W.-P.L.,QEDone LLC
COMPEL - The International Journal for Computation and Mathematics in Electrical and Electronic Engineering | Year: 2014

Purpose - The purpose of this paper is to describe a rapid and robust axisymmetric hybrid algorithm to create dynamic temporal and spatial charge distributions, or charge map, in the simulation of bipolar charge injection using Schottky emission and Fowler-Nordheim tunneling, field-dependent transport, recombination, and bulk and interfacial trapping/de-trapping for layered polymer films spanning the range from initial injection to near breakdown. Design/methodology/approach - This hybrid algorithm uses a source distribution technique based on an axisymmetric boundary integral equation method (BIEM) to solve the Poisson equation and a fourth-order Runge-Kutta (RK4) method with an upwind scheme for time integration. Iterative stability is assured by satisfying the Courant-Friedrichs-Levy (CFL) stability criterion. Dynamic charge mapping is achieved by allowing conducting and insulating boundaries and material interfaces to be intuitively represented by equivalent free and bound charge distributions that collectively satisfy all local and far-field conditions. Findings - Charge packets cause substantial increase of electric stress and could accelerate the breakdown of polymeric capacitors. Conditions for the creation of charge packets are identified and numerically demonstrated for a combination of impulsive step excitation, high charge injection, and discontinuous interface. Originality/value - Metallized bi-axially oriented polypropylene (BOPP) dielectric thin film capacitor with self-clearing and enhanced current carrying capability offer an inexpensive and lightweight alternative for efficient power conditioning, energy storage, energy conversion, and pulsed power. The originality is the comprehensive physics and multi-dimensional modeling which span the dynamic range from initial injection to near breakdown. This model has been validated against some empirical data and may be used to identify failure mechanisms such as charge packets, gaseous voids, and electroluminescence. The value lies in the use of this model to develop mitigation strategies, including re-designs and materials matching, to avoid these failure mechanisms. © Emerald Group Publishing Limited.


Lean M.H.,QEDone LLC | Chu W.-P.L.,QEDone LLC
IEEE Transactions on Dielectrics and Electrical Insulation | Year: 2014

This paper describes a hybrid algorithm for the solution of the drift-diffusion equations for bipolar charge transport in layered polymer films. Dynamic charge mapping is achieved using a source distribution technique for the solution of the Poisson equation and time-integration using a fourth order total variation diminishing Runge-Kutta scheme that satisfies the Courant-Friedrichs-Levy stability criterion. An integral equation formulation allow conducting and insulating boundaries and material interfaces to be represented by equivalent free and bound charge distributions that collectively satisfy all local and far-field boundary conditions. This hybrid technique solves the drift-diffusion equations that simulate charge injection, field-dependent mobility transport, recombination, and trapping/de-trapping in the bulk and at material and physical interfaces. The resulting charge map is the taxonomy of the different charge types and their abundance; presenting a dynamic view of the temporal and spatial distributions. Results are discussed for single-layer and multi-layered samples with physical and material interfaces. Conditions for creation of charge packets and electroluminescence due to recombination are computed and discussed.


Lean M.H.,QEDone LLC | Chu W.-P.L.,QEDone LLC
IEEE Transactions on Dielectrics and Electrical Insulation | Year: 2015

This paper describes 3D particle-in-cell (PIC) simulation of charge injection and transport through ferroelectric semicrystalline polymer (e.g. PVDF) film comprised of nanocrystallites in an amorphous matrix with varying degrees of crystallinity. The classical electrical double layer (EDL) model for a monopolar core is extended (eEDL) to represent the nanocrystallite by replacing it with a dipolar core. Charge injection at the electrodes assumes metal-polymer Schottky emission at low to moderate fields and Fowler-Nordheim tunneling at high fields. Injected particles propagate via field-dependent Poole-Frenkel mobility. In the eEDL model, the initial attachment of charge particles forms the bound Stern-Helmholtz layer leading to Maxwell-Wagner-Sillars polarization. Subsequent waves of charge particles are repelled by the attached charge resulting in the diffuse Gouy- Chapman transport layer. The simulation algorithm uses a boundary integral equation method (BIEM) for solution of the Poisson equation coupled with a second-order predictorcorrector scheme for robust time integration of the equations of motion. The stability criterion of the explicit algorithm conforms to the Courant-Friedrichs-Levy (CFL) limit assuring robust and rapid convergence. The model is capable of simulating a wide dynamic range spanning leakage current to pre-breakdown levels. Simulation results for semicrystalline film with varying degrees of crystallinity indicate that charge transport behavior depends on nanoparticle polarization with anti-parallel orientation showing the highest conduction and therefore lowest level of charge trapping in the interaction zone. Charge attachment to nanocrystallites increase with vol% loading or degree of crystallinity, and saturates at 40 vol% for the set of simulation parameters. The eEDL model predicts the intuitive meandering pathways of charge particle trajectories, which get progressively more inclined from normal incidence with increasing vol% loading. © 1994-2012 IEEE.


Lean M.,QEDone LLC | Wolak M.,U.S. Navy | Mackey M.,Case Western Reserve University | Baer E.,Case Western Reserve University
IEEE Transactions on Dielectrics and Electrical Insulation | Year: 2014

Multilayer polymer films comprising alternating layers of polycarbonate (PC) and polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) show enhanced dielectric strength relative to single component films of either source polymer. Previous failure analysis on films subjected to breakdown under divergent field conditions revealed that multilayer films produced distinct surface treeing patterns whereas monolithic films did not. The choice of surface layer (PC or PVDF-HFP) contacted by a needle electrode influenced the nature of these treeing patterns. Additionally, damage within the film was largely localized to the interfaces between layers. To help explain these empirical results, we model the divergent field based on the geometry of our experimental setup and calculate the internal electric field distribution using the boundary integral equation method (BIEM). All fundamental charges, including: free, bound, trapped, and space charges are accounted for in the calculations, based on current and voltage data recorded during prior breakdown measurements. The calculations show that when PC is used as the surface layer in contact with the needle anode, there is significant field intensification in the top PC layer, in excess of 2000 V/μm. This is many times higher than the measured dielectric strength of monolithic PC and is at least partially due to charge injection from the needle anode. In contrast, the PVDF-HFP sub-layer in this configuration has very low field. These observations are consistent with breakdown occurring near the surface of the film, resulting in large-range surface treeing. When PVDF-HFP is the top layer, field intensification occurs deeper in the film, which is again consistent with the observed optical and FIB/SEM imaging results where less surface treeing and more internal damage is observed. The calculations suggest that the large contrast in field between adjacent layers generates a nexus for localized breakdown at the layer interfaces, again consistent with large internal voids formed by layer delamination in films subjected to divergent field breakdown. © 1994-2012 IEEE.


Lean M.H.,QEDone LLC | Chu W.-P.L.,QEDone LLC
IEEE Transactions on Dielectrics and Electrical Insulation | Year: 2014

This paper describes a modified dielectric breakdown model (mDBM), to predict breakdown pathways in polymer films taking into consideration trapped charge and gaseous voids. Modeling components include: (1) accurate boundary integral equation method (BIEM) based on Green function formulations for grid-less, non-orthogonal, Poisson growth; (2) treatment of kernel singularities; (3) matrix algebra for extensibility, reuse, and rapid iterative computation; and (4) Monte Carlo statistics with inverse probability integral for tree branch growth. 2D and 3D versions of mDBM have been successfully validated against known data and closed-form solutions, viz. charge and capacitance calculations with agreement to within 3% of the theoretical. The versatility of the models has been demonstrated by results of test cases for throughfilm breakdown in the presence of trapped charge, gaseous void, and combination of trapped charge and gaseous void. © 2014 IEEE.


Lean M.H.,QEDone LLC | Chu W.-P.L.,QEDone LLC
Journal of Applied Physics | Year: 2015

This paper describes 3D particle-in-cell simulation of bipolar charge injection and transport through nanocomposite film comprised of ferroelectric ceramic nanofillers in an amorphous polymer matrix. The classical electrical double layer (EDL) model for a monopolar core is extended (eEDL) to represent the nanofiller by replacing it with a dipolar core. Charge injection at the electrodes assumes metal-polymer Schottky emission at low to moderate fields and Fowler-Nordheim tunneling at high fields. Injected particles migrate via field-dependent Poole-Frenkel mobility and recombine with Monte Carlo selection. The simulation algorithm uses a boundary integral equation method for solution of the Poisson equation coupled with a second-order predictor-corrector scheme for robust time integration of the equations of motion. The stability criterion of the explicit algorithm conforms to the Courant-Friedrichs-Levy limit assuring robust and rapid convergence. The model is capable of simulating a wide dynamic range spanning leakage current to pre-breakdown. Simulation results for BaTiO3 nanofiller in amorphous polymer matrix indicate that charge transport behavior depend on nanoparticle polarization with anti-parallel orientation showing the highest leakage conduction and therefore lowest level of charge trapping in the interaction zone. Charge recombination is also highest, at the cost of reduced leakage conduction charge. The eEDL model predicts the meandering pathways of charge particle trajectories. © 2015 AIP Publishing LLC.


Lean M.H.,QEDone LLC | Chu W.-P.L.,QEDone LLC
Journal of Applied Polymer Science | Year: 2016

The effective permittivity and stored energy in nanocomposites incorporating dielectric and conducting nanofillers are computed by simulating bipolar charge injection, transport, attachment, and recombination through amorphous polymer using a self-consistent 3D particle-in-cell model with nanofillers treated as extensions to the classical electrical double layer. Effective permittivities computed using an energy conserving scheme is shown to have excellent agreement with the Lichtenecker, Bruggeman, and Maxwell-Garnett mixing rules especially at low volume fraction, low permittivity contrast, and small Clausius-Mossotti factor, and lie well within the Wiener bounds. The energy conserving scheme with Maxwell-Garnett E field interpolation combines the best of the Maxwell-Garnett and fundamental Lichtenecker rules and results in broad validity over the entire volume fraction range. Computed stored energies show monotonic increase with dielectric fillers and a peak at 25 vol % for conducting fillers, attributed to the competing effects of higher energy with increasing E field modification and lower energy with decreasing binder volume. © 2015 Wiley Periodicals, Inc.


Lean M.H.,QEDone LLC | Chu W.-P.L.,QEDone LLC
Journal of Physics D: Applied Physics | Year: 2014

This paper describes a hybrid algorithm to study the effect of a gaseous void on bipolar charge transport in layered polymer film. This hybrid algorithm uses a source distribution technique based on an axisymmetric boundary integral equation method to solve the Poisson equation and a fourth order Runge-Kutta (RK4) method with an upwind scheme for time integration. Iterative stability is assured by satisfying the Courant-Friedrichs-Levy stability criterion. Dynamic charge mapping is achieved by allowing conducting and insulating boundaries and material interfaces to be represented by equivalent free and bound charge distributions that collectively satisfy all local and far-field conditions. This hybrid technique caters to bipolar charge injection, field-dependent mobility transport, recombination, and trapping/de-trapping in the bulk and at material and physical interfaces. The resulting charge map is the taxonomy of the different charge types and their abundance, and presents a dynamic view of the temporal and spatial distributions. The paper is motivated by images of breakdown experiments that point to the role of gaseous void in delamination growth. For the test configuration, the high field at the edge of the gaseous void act as a sink first for positive and then negative charge. The net effect is to increase delamination stress at the edge leading to further growth of the defect and increasing the potential for partial discharge within the void. © 2014 IOP Publishing Ltd.

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