Spelling suggestions: "subject:"[een] BREAKDOWN"" "subject:"[enn] BREAKDOWN""
11 |
Breakdown characteristics of nonuniform electric fields in crossflows /Hanby, David William, January 1993 (has links)
Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1993. / Vita. Abstract. Includes bibliographical references (leaves 92-94). Also available via the Internet.
|
12 |
An investigation into methods of modelling positive inhomogeneous-field breakdown and discharge process in SF6 with emphasis on the corona stabilisation phenomenonBhutt, Sanjeev 20 July 2016 (has links)
dissertatic,11 submitted to the Faculty of Engineering, University of the
Witwatersrand, Johannesburg, in fulfillment of the requirements for the degree of
Master of Science in Engineering,
I.:
Johannesburg, 1998 / Corona stabilisation is not a well understood phenomenon, consequently a rigorous
theoretical description of how the merhanism operates does not exist. Furthermore,
postulates on the prcJ'.tse physical processes that occur during corona stabilised
breakdown are varied and conflicting. 1t was thus essential to develop a qualitative
theory of how the mechanism operates around which a quantitative model could be
constructed. To this aim, a detailed analysis of available modelling methods and
empirical data from published works was carried out. This analysis together with
additional finite elements modelling done as part of this work, leads to a proposed
qualitative model which serves as a basis for a quantitative model developed to
simulate corona stabilized breakdown from a fixed panicle defect. There is a
favorable comparison between the predictions of the model and published
measurements, thus imbuing optimism in the proposed method. The problem of
measuring t: .;true charge deployed in a discharge is discussed and an experiment is
designed to circumvent this problem.
|
13 |
Two-carrier charge trapping and dielectric breakdown in thin silicon nitride films /Chang, Ko-Min January 1985 (has links)
No description available.
|
14 |
Unified Electron Emission and Gas Breakdown Theory Across Length, Pressure, and FrequencyAmanda M Loveless (9188939) 31 July 2020 (has links)
<p>As electronic device dimensions
decrease to micro and nanoscale, Paschen’s law (PL)—the standard theory used to
predict breakdown voltage (<i>V<sub>b</sub></i>)
governed by Townsend avalanche (TA)—fails due to ion-enhanced field emission
(FE). Analytic models to predict <i>V<sub>b </sub></i>at
these scales are necessary to elucidate the underlying physics driving
breakdown and electron emission in these regimes. Starting from a
previously-derived breakdown criterion coupling TA and FE, this dissertation
derives a universal (true for any gas) breakdown equation. Further simplifying
this equation using a matched asymptotic analysis, dependent on the product of
the ionization coefficient and the gap distance, yields an analytic theory for
dimensionless <i>V<sub>b</sub></i>. This
analytic model unifies the coupled FE/TA regime to a universal PL derived by applying
scaling parameters to the standard PL. This model enables parametric analyses
to assess the effects of different parameters (such as pressure, gap distance, and
field enhancement factor) on breakdown and quantify the relative contribution
of FE and TA to identify the transition to the universal PL. This dissertation
applies this general theory to experimental cases of different gap width, gap
pressure and electrode surface roughness before exploring unification across
electron emission regimes, validation with molecular dynamics simulations, and
extensions to alternating current (AC).</p>
<p> </p>
<p>One application of this theory to
experimental data used data from a collaborator at Xi’an Jiaotong University,
who used an electrical-optical measurement system to measure the breakdown
voltage and determine breakdown morphology as a function of gap width. An
empirical fit showed that the breakdown voltage varied linearly with gap
distance at smaller gaps as in vacuum breakdown. This dissertation demonstrates
that applying the matched asymptotic theory in the appropriate limits recovers
this scaling with the slope as a function of field emission properties. </p>
<p> </p>
<p>Pressure also plays a critical role
in gas breakdown behavior. This dissertation derives a new analytic equation
that predicts breakdown voltage <i>V<sub>b</sub></i>
within 4% of the exact numerical results of the exact theory and new
experimental results at subatmospheric pressure for gap distances from 1-25
. At atmospheric pressure, <i>V<sub>b</sub></i> transitions to PL near the product of pressure and
gap distance, <i>pd</i>, corresponding to
the Paschen minimum; at lower pressures, the transition to PL occurs to the
left of the minimum. We further show that the work function plays a major role
in determining whether <i>V<sub>b</sub></i> transitions from the coupled FE/TA
equation back to the traditional PL to the right or the left of the Paschen
minimum as pressure increases, while field enhancement and the secondary
emission coefficient play smaller roles. These results indicate that
appropriate combinations of these parameters cause <i>V<sub>b</sub></i> to transition to PL to the left of the Paschen
minimum, which would yield an extended plateau similar to some microscale gas
breakdown experimental observations. </p>
<p> </p>
<p>Finally, the importance of
electrode surface structure on microscale gas breakdown remains poorly
understand. This dissertation provides the next step at assessing this by
applying the asymptotic theory to microscale gas breakdown measurements for a
pin-to-plate electrode setup in air at atmospheric pressure with different
cathode surface roughness. Multiple discharges created circular craters on the
flat cathode up to 40 μm deep with more pronounced craters created at smaller
gap sizes and greater cathode surface roughness. The theory showed that
breakdown voltage and ionization coefficient for subsequent breakdown events
followed our earlier breakdown theory when we replaced the gap distance <i>d</i> with an effective gap distance <i>d<sub>eff</sub></i> defined as the sum of
cathode placement distance and crater depth. Moreover, the theory indicated
that <i>d<sub>eff</sub></i> could become
sufficient large to exceed the Meek criterion for streamer formation, motivating
future studies to assess whether the cathode damage could drive changes in the
breakdown mechanism could for a single electrode separation distance or the
Meek criterion requires modification at microscale. </p>
<p> </p>
<p>We next unified field emission with
other electron emission mechanisms, including Mott-Gurney (MG), Child-Langmuir
(CL), and quantum space-charge-limited current (QSCL) to develop a common
framework for characterizing electron emission from nanoscale to the classical
PL. This
approach reproduced the conditions for transitions across multiple mechanisms,
such as QSCL to CL, CL to FE, CL to MG to FE, and microscale gas breakdown to
PL using a common nondimensional framework. Furthermore, we demonstrated the
conditions for more complicated nexuses where multiple asymptotic solutions
matched, such as matching QSCL, CSCL, MG, and FE to gas breakdown. A
unified model for radiofrequency and microwave gas breakdown will be compared
to experimental results from Purdue University to elucidate breakdown
mechanism. </p>
<p>The results from this dissertation
will have applications in microscale gas breakdown for applications including
microelectromechanical system design, combustion, environmental mitigation,
carbon nanotube emission for directed energy systems, and characterizing
breakdown in accelerators and fusion devices.</p>
|
15 |
A Comparative Study of Laser Induced Breakdown Spectroscopy and Spark Induced Breakdown Spectroscopy for Rapid Analysis of Mercury in SoilsSrungaram, Pavan Kumar 15 December 2012 (has links)
Elevated concentrations of mercury in soils are quite hazardous to flora and fauna and water bodies near these soils. This makes continuous monitoring of mercury very essential. This work compares two potential spectroscopic methods LIBS and SIBS at their optimum experimental conditions for mercury monitoring. The experimental conditions for Hg measurements with LIBS and SIBS were determined and calibration was developed. The limits of detection (LODs) of Hg in soil were calculated from the Hg calibration curves. The LOD for mercury (Hg) in soil calculated using LIBS and SIBS are 483 parts-per-million and 20 parts-per-million, respectively. The present study indicates that SIBS is more efficient with powder samples in a low concentration region for quantification of mercury in soils while LIBS is efficient in the region of higher concentrations using pellet samples. Both these techniques can be further investigated and improved for in-situ analysis of soils.
|
16 |
THEORETICAL ANALYSIS OF MICROWAVE BREAKDOWN FOR MICROSCALE GAPSShivani Mahajan (16640952) 25 July 2023 (has links)
<p>Dielectric breakdown in gases is an important criterion for device reliability when designing various electronic devices such as sensors, medical plasma jets and fusion applications. As devices become smaller and more compact, microscale gap distances need to be considered and Paschen’s law, which dictates typical breakdown behavior when electron avalanche dominates, fails. The stronger electric fields for microscale gaps induce field emission, which generates additional electrons that further enhance the electric field at the cathode and the resulting secondary emission to reduce breakdown voltages below those predicted by Paschen’s law. Field emission is governed by the Fowler-Nordheim equation, which mathematically describes the quantum tunneling that occurs. Many studies have examined breakdown voltage in the Paschen’s and field emission regimes but recent theories have unified the two regimes for DC gas breakdown at microscale gaps [A. L. Garner, A. M. Loveless, J. N. Dahal, and A. Venkattraman (2020)]. However, although microwave and RF fields are used in many microelectronics systems and microplasmas, they have been less studied. This thesis derives a breakdown condition that unifies avalanche and field emission for RF fields. The derivation includes analysis of potential secondary emission representations for AC fields. The breakdown condition is then benchmarked to simulations that accounts for both avalanche and field emission for user-defined AC fields.</p>
<p>We use a modified version of XPDP1, which is a one-dimensional in space and three-dimensional in velocity (1D/3v) particle-in-cell (PIC) code that incorporates field emission. The resulting breakdown depends on several parameters, most notably gap size d, pressure p and frequency f. We determine breakdown voltages in terms of d and pd scalings for 1-10 𝜇m gap distances, 10-1000 GHz frequencies, and 180-760 Torr pressures. Additional scalings that were studied include the work function, field enhancement factor, secondary emission, and ionization coefficients. PIC demonstrated that the breakdown voltage varied linearly with gap distance up to ~4 𝜇m from DC to 10 GHz for a secondary electron emission coefficient 𝛾𝑆𝐸=0.05. For DC fields, the breakdown voltage decreases with increasing gap distance; the breakdown voltage increases with increasing frequency, approaching linearly with increasing gap distance.</p>
|
17 |
The Breakdowns of BiCGStab.Graves-Morris, Peter R. January 2002 (has links)
No / The effects of the three principal possible exact breakdowns which may occur using BiCGStab are discussed. BiCGStab is used to solve large sparse linear systems of equations, such as arise from the discretisation of PDEs. These PDEs often involve a parameter, say . We investigate here how the numerical error grows as breakdown is approached by letting tend to a critical value, say c, at which the breakdown is numerically exact. We found empirically in our examples that loss of numerical accuracy due stabilisation breakdown and Lanczos breakdown was discontinuous with respect to variation of around c. By contrast, the loss of numerical accuracy near a critical value c for pivot breakdown is roughly proportional to |¿c|¿1.
|
18 |
The effect of processing conditions on the morphology and electric strength of polyethylene blendsGreenway, Giles R. January 2000 (has links)
No description available.
|
19 |
Two-dimensional device simulation of junction termination structures for determination of breakdown behaviorTan, Leong Hin, 1957- January 1989 (has links)
In this work, we have investigated numerical techniques to determine the breakdown behavior of complex semiconductor devices using two-dimensional simulation. In particular, we have augmented the device simulator SEPSIP with a capability for handling single and multiple floating field rings, and for handling devices with slanted edges. We have furthermore improved the grid width selection algorithm in SEPSIP. A capability for plotting equi-field contours was added to the code. Finally, all system dependencies were removed from the SEPSIP code, and a new version of SEPSIP (Version 2.0) was generated which can be executed on any PC/XT, PC/AT, or PC/386 compatible computer. This eliminates the need for transfering files back and forth between the PC, which had formerly been used as an I/O processor, and the VAX, which was used for numerically intensive computations. It also makes the code more accessible to scientists and engineers who are working in this important research area.
|
20 |
Corona suppression on high voltage direct current systemsBoudjelthia, H. January 1989 (has links)
No description available.
|
Page generated in 0.0489 seconds