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The Use of Radar Methods to Determine Moisture Content in the Vadose Zone

Description: The objective of our three-year research project is to determine the optimal way to use radar methods to obtain information about moisture content in the vadose zone. In our research we will focus on two specific aspects of the link between radar images and moisture content. The first aspect or question we address is: Can we use a measure of the dielectric constant of a volume of the subsurface to determine the moisture content of that volume? The second question we address is involved specifically with the issue of spatial heterogeneity. Rather than using radar data to get estimates of moisture content at specific locations, can we use the radar data to directly obtain information about the way in which the level of moisture content varies spatially?
Date: June 1, 2000
Creator: Knight, Rosemary
Partner: UNT Libraries Government Documents Department

The Use of Radar Methods to Determine Moisture Content in the Vadose Zone

Description: Moisture content is a critical parameter affecting both liquid-phase and vapor-phase contaminant transport in the vadose zone. The objective of our three-year research project is to determine the optimal way to use of radar methods--both surface and borehole--as a noninvasive means of determining in situ moisture content. In our research we focus on two specific aspects of the link between radar images and moisture content. The first question we address is: Can we use a measure of the dielectric constant of a volume of the subsurface to determine the moisture content of that volume? The second question we address is: Can we use the radar data to characterize the spatial variability in moisture content?
Date: June 1, 2001
Creator: Knight, Rosemary
Partner: UNT Libraries Government Documents Department

A Collection of Complex Permittivity and Permeability Measurements

Description: We present the results of measurements of the complex permittivity and permeability over a frequency range of 0.1-5.1 GHz for a range of microwave absorbing materials used in a variety of accelerator applications. We also describe the automated measurement technique which uses swept-frequency S-parameter measurements made on a strip transmission line device loaded with the material under test.
Date: February 1, 1993
Creator: Barry, W.; Byrd, J.; Johnson, J. & Smithwick, J.
Partner: UNT Libraries Government Documents Department

Influence of magnetic fields on structural martensitic transitions

Description: We show evidence that a structural martensitic transition is related to significant changes in the electronic structure, as revealed in thermodynamic measurements made in high-magnetic fields. The magnetic field dependence is considered unusual as many influential investigations of martensitic transitions have emphasized that the structural transitions are primarily lattice dynamical and are driven by the entropy due to the phonons. We provide a theoretical framework which can be used to describe the effect of magnetic field on the lattice dynamics in which the field dependence originates from the dielectric constant.
Date: January 1, 2009
Creator: Lashley, J C; Cooley, J C; Smith, J L; Fisher, R A; Modic, K A; Yang, X- D et al.
Partner: UNT Libraries Government Documents Department

Proof-of-principle Experiment of a Ferroelectric Tuner for the 1.3 GHz Cavity

Description: A novel tuner has been developed by the Omega-P company to achieve fast control of the accelerator RF cavity frequency. The tuner is based on the ferroelectric property which has a variable dielectric constant as function of applied voltage. Tests using a Brookhaven National Laboratory (BNL) 1.3 GHz electron gun cavity have been carried out for a proof-of-principle experiment of the ferroelectric tuner. Two different methods were used to determine the frequency change achieved with the ferroelectric tuner (FT). The first method is based on a S11 measurement at the tuner port to find the reactive impedance change when the voltage is applied. The reactive impedance change then is used to estimate the cavity frequency shift. The second method is a direct S21 measurement of the frequency shift in the cavity with the tuner connected. The estimated frequency change from the reactive impedance measurement due to 5 kV is in the range between 3.2 kHz and 14 kHz, while 9 kHz is the result from the direct measurement. The two methods are in reasonable agreement. The detail description of the experiment and the analysis are discussed in the paper.
Date: January 1, 2009
Creator: Choi,E.M.; Hahn, H.; Shchelkunov, S. V.; Hirshfield, J. & Kazakov, S.
Partner: UNT Libraries Government Documents Department

A proof-of-principle experiment of the ferroelectric tuner for the 1.3 GHz gun cavity

Description: A novel ferroelectric frequency tuner was developed by the Ornega-P company and was tested at the Brookhaven National Laboratory on a 1.3 GHz RF cavity at room temperature. The tuner is based on the ferroelectric property of having a permittivity variable with an applied electric field. The achievable frequency tuning range can be estimated from the reactive impedance change due to an applied voltage via a S{sub 11} measurement at the tuner port. The frequency shift can be measured directly with a S{sub 21} measurement across the gun cavity with the tuner connected and activated. The frequency change due to an applied 5 kV obtained from the two methods is in reasonable agreement. The reactive impedance measurement yields a value in the range between 3.2 kHz and 14 kHz, while 9 kHz is the result from the direct measurement. The detail description of the experiment and the analysis will be discussed in the paper.
Date: May 4, 2009
Creator: Hahn,H.; Choi, E.; Shchelkunov, S. V.; Hirshfield, J.; Kazakov, S. & Shschelkunov, S.
Partner: UNT Libraries Government Documents Department

Linear and nonlinear wave propagation in negative refractionmetamaterials

Description: We discuss linear and nonlinear optical wave propagation in a left-handed medium (LHM) or medium of negative refraction (NRM). We use the approach of characterizing the medium response totally by a generalized electric polarization (with a dielectric permittivity {tilde {var_epsilon}}(w, {rvec k})) that can be decomposed into a curl and a non-curl part. The description has a one-to-one correspondence with the usual approach characterizing the LHM response with a dielectric permittivity {var_epsilon}<0 and a magnetic permeability {mu}<0. The latter approach is less physically transparent in the optical frequency region because the usual definition of magnetization loses its physical meaning. Linear wave propagation in LHM or NRM is characterized by negative refraction and negative group velocity that could be clearly manifested by ultra-short pulse propagation in such a medium. Nonlinear optical effects in LHM can be predicted from the same calculations adopted for ordinary media using our general approach.
Date: May 29, 2003
Creator: Agranovich, V.M.; Shen, Y.R.; Baughman, R.H. & Zakhidov, A.A.
Partner: UNT Libraries Government Documents Department

Domain evolution and polarization of continuously graded ferroelectric films

Description: A thermodynamic analysis of graded ferroelectric films demonstrates that in the equilibrium state the films are subdivided into a single-domain band and a polydomain band which consists of wedge-shape domains. Polarization under an external electrostatic field proceeds through an inter-band boundary movement due to growth or shrinkage of the wedge domains. It is shown how the domain structure and evolution are determined by the principal characteristics of the film: the distribution of the spontaneous polarization and dielectric constant. Graded films exhibit a sharp increase of polarization with the field for weak fields, with a drop of the dielectric constant when the field is increasing. A general approach to finding the dependence of the displacement and the wedge-domain shape on the field as well as analytical solutions for the p{sup 4} Landau-Devonshire and parabolic potentials are presented.
Date: January 1, 2008
Creator: Roytburd, A. & Roytburd, V.
Partner: UNT Libraries Government Documents Department

Exp6-polar thermodynamics of dense supercritical water

Description: We introduce a simple polar fluid model for the thermodynamics of dense supercritical water based on a Buckingham (exp-6) core and point dipole representation of the water molecule. The proposed exp6-polar thermodynamics, based on ideas originally applied to dipolar hard spheres, performs very well when tested against molecular dynamics simulations. Comparisons of the model predictions with experimental data available for supercritical water yield excellent agreement for the shock Hugoniot, isotherms and sound speeds, and are also quite good for the self-diffusion constant and relative dielectric constant. We expect the present approach to be also useful for other small polar molecules and their mixtures.
Date: December 13, 2007
Creator: Bastea, S & Fried, L E
Partner: UNT Libraries Government Documents Department

Development of a Low Loss, High Dielectric Strength Microwave Substrate

Description: This work describes a comparison of two candidate materials for pulse forming line fabrication with respect to bulk dielectric breakdown, frequency response of relative permittivity and dielectric loss. One material is a commercially available microwave substrate material that can be procured in sheet form without a high voltage specification while the other is a newly developed material that also comes in sheet form that can also be cast between the electrodes.
Date: June 5, 2006
Creator: Sanders, D; Sampayan, S; Caporaso, G; Rhodes, M; Watson, J; Slenes, K et al.
Partner: UNT Libraries Government Documents Department

CHARACTERIZATION OF A HIGH CURRENT INDUCTION ACCELERATOR ELECTRON BEAM VIA OPTICAL TRANSITION RADIATION FROM DIELECTRIC FOILS

Description: Traditionally, thin metal foils are employed for optical transition radiation (OTR) beam diagnostics but the possibility of shorting accelerator insulating surfaces and modifying accelerating fields are concerns. The successful utilization of dielectric foils in place of metal ones could alleviate these issues but necessitates more understanding of the OTR data for inferring desired beam parameters because of the dielectric's finite permittivity. Additionally, the temperature dependence of the relevant foil parameters due to beam heating should be accounted for. Here, we present and discuss sample synthetic diagnostic results of Kapton OTR spot-size measurements from the Flash X-Ray (FXR) accelerator which studies these and sightline effects. These simulations show that in some cases, the observed spot-sizes and radii are noticeably larger than the beam radii.
Date: June 13, 2007
Creator: Tang, V; Brown, C & Houck, T
Partner: UNT Libraries Government Documents Department

Calculations of precursor propagation in dispersive dielectrics.

Description: The present study is a numerical investigation of the propagation of electromagnetic transients in dispersive media. It considers propagation in water using Debye and composite Rocard-Powles-Lorentz models for the complex permittivity. The study addresses this question: For practical transmitted spectra, does precursor propagation provide any features that can be used to advantage over conventional signal propagation in models of dispersive media of interest? A companion experimental study is currently in progress that will attempt to measure the effects studied here.
Date: August 1, 2003
Creator: Bacon, Larry Donald
Partner: UNT Libraries Government Documents Department

Quantum optics mini-program on fast light, slow light, and metamaterials.

Description: The topic of electromagnetic propagation in dielectric media has been enlivened in the past decade by a number of remarkable experimental results showing the technical ability to control the speed of light propagation in exotic ways. Light pulses have been observed travelling faster than c, or slowed by many orders of magnitude, or even stopped completely. All of thcse results require careful interpretation, and a variety of theoretical interpretations have been proposed and/or published, not all agreeing with each other. At the same time, in a lower frequency range than optical, rapid development of so-called meta-materials or double-negative materials has occurred. These materials are characterized by electric permittivity and magnetic permeability with very unconventional values, both quantities negative in some cases. Such unusual properties, especially when leading to a negative value for the group velocity, clearly indicate another possibility for control of light. Such materials are being improved rapidly, but independent of their implementation in the laboratory, their theoretical properties have led to dramatic predictions such as the existence of a perfect lens, Le., a finite lens (actually even planar-flat rather than parabolic) that can deliver an ideally sharp focus unaffected by diffractive effects. There are strong contentions currently being published that such predictions are erroneous
Date: January 1, 2002
Creator: Milonni, Peter W.
Partner: UNT Libraries Government Documents Department

Electric Field Penetration in Au/Nb:SrTiO3 Schottky Junctions Probed by Bias-Dependent Internal Photoemission

Description: Electric field penetration into the metallic side of a Schottky junction is in principle a universal phenomenon, the magnitude of which increases with the semiconductor permittivity. Here, we quantitatively probe this effect using bias-dependent internal photoemission spectroscopy at the Schottky junction between a large dielectric permittivity semiconductor SrTiO{sub 3} and gold. A clear linear reduction of the barrier height with increasing interface electric field was observed, highlighting the importance of field penetration into the gold. The interfacial permittivity of SrTiO{sub 3} at the interface is reduced from the bulk value, reflecting intrinsic suppression at the interface.
Date: August 15, 2011
Creator: Hikita, Y.
Partner: UNT Libraries Government Documents Department

Localized temperature stability in Low Temperature Cofired Ceramics (LTCC).

Description: The base dielectrics of commercial low temperature cofired ceramics (LTCC) systems have a temperature coefficient of resonant frequency ({tau}{sub f}) in the range -50 {approx} -80 ppm/C. In this research we explored a method to realize zero or near zero {tau}{sub f} resonators by incorporating {tau}{sub f} compensating materials locally into a multilayer LTCC structure. To select composition for {tau}{sub f} adjustment, {tau}{sub f} compensating materials with different amount of titanates were formulated, synthesized, and characterized. Chemical interactions and physical compatibility between the {tau}{sub f} modifiers and the host LTCC dielectrics were investigated. Studies on stripline (SL) resonator panels with multiple compensating dielectrics revealed that: 1) compositions using SrTiO{sub 3} provide the largest {tau}{sub f} adjustment among titanates, 2) the {tau}{sub f} compensation is proportional to the amount of SrTiO{sub 3} in compensating materials, as well as the thickness of the compensating layer, and 3) the most effective {tau}{sub f} compensation is achieved when the compensating dielectric is integrated next to the SL. Using the effective dielectric constant of a heterogeneous layered dielectric structure, results from Method of Momentum (MoM) electromagnetic simulations are consistent with the experimental observations.
Date: April 1, 2012
Creator: Dai, Steven Xunhu & Hsieh, Lung-Hwa.
Partner: UNT Libraries Government Documents Department

Method of inspecting dielectric materials at microwave frequencies

Description: A successful method of screening high-dielectric-constant, nonmagnetic, high-loss-factor materials at microwave frequencies was developed to provide material control by incoming inspection. This is accomplished by measuring the S parameters of the material---reliance on the manufacturer's permittivity data and x-ray examination for voids and inclusions is no longer necessary. Use of an automatic network analyzer makes 100% inspection economically feasible. (auth)
Date: November 1, 1973
Creator: O'Dell, G.D.
Partner: UNT Libraries Government Documents Department

Studies of ferroelectric heterostructure thin films and interfaces via in situ analytical techniques.

Description: The science and technology of ferroelectric thin films has experienced an explosive development during the last ten years. Low-density non-volatile ferroelectric random access memories (NVFRAMs) are now incorporated in commercial products such as ''smart cards'', while high permittivity capacitors are incorporated in cellular phones. However, substantial work is still needed to develop materials integration strategies for high-density memories. We have demonstrated that the implementation of complementary in situ characterization techniques is critical to understand film growth and interface processes, which play critical roles in film microstructure and properties. We are using uniquely integrated time of flight ion scattering and recoil spectroscopy (TOF-ISARS) and spectroscopic ellipsometry (SE) techniques to perform in situ, real-time studies of film growth processes in the high background gas pressure required to growth ferroelectric thin films. TOF-ISARS provides information on surface processes, while SE permits the investigation of buried interfaces as they are being formed. Recent studies on SrBi{sub 2}Ta{sub 2}O{sub 9} (SBT) and Ba{sub x}Sr{sub 1{minus}x}TiO{sub 3} (BST) film growth and interface processes are discussed.
Date: August 30, 1999
Creator: Auciello, O.; Dhote, A.; Gao, Y.; Gruen, D. M.; Im, J.; Irene, E. A. et al.
Partner: UNT Libraries Government Documents Department

CHARACTERIZATION OF AN AQUITARD AND DIRECT DETECTION OF LNAPL AT HILL AIR FORCE BASE USING GPR AVO AND MIGRATION VELOCITY ANALYSES

Description: Large quantities of non-aqueous phase liquids (NAPL), contaminate the near surface sediments at Operable Unit 1 (OU1), Hill Air Force Base (HAFB), Utah. In October 2000, a 3D, multi-offset GPR survey was acquired at OU1 with two objectives: (1) to image the aquifer/aquitard boundary at a depth of about 30 ft, and (2) to evaluate quantitative processing and interpretation methodologies for direct detection of NAPL. Using pre-stack depth migration, we map the aquitard boundary to about {+-} 1 ft throughout the survey area. An unusual reflection is identified within the vadose zone that does not correlate with known geology. The region below this reflection has anomalously high velocity, implying low electric permittivity, and the amplitude of the anomalous reflection deviates significantly from the background AVO trend. Fitting the Fresnel equation to the AVO data, we estimate the velocity contrast at the anomaly boundary and find that it is in good agreement with the migration velocity model. We interpret the anomaly as a previously unidentified NAPL rich zone. Subsequent coring and chemical analyses verify our interpretation. This exciting result implies that these methodologies may be useful for direct detection of NAPL at other HAFB locations and at sites with similar hydrogeology.
Date: June 1, 2002
Creator: Deeds, Jake & Bradford, John
Partner: UNT Libraries Government Documents Department

Fresnel Integral Equations: Numerical Properties

Description: A spatial-domain solution to the problem of electromagnetic scattering from a dielectric half-space is outlined. The resulting half-space operators are referred to as Fresnel surface integral operators. When used as preconditioners for nonplanar geometries, the Fresnel operators yield surface Fresnel integral equations (FIEs) which are stable with respect to dielectric constant, discretization, and frequency. Numerical properties of the formulations are discussed.
Date: July 22, 2003
Creator: Adams, R J; Champagne, N J II & Davis, B A
Partner: UNT Libraries Government Documents Department

EE FY00 report: nanostructure multilayer materials for capacitors

Description: Only two intrinsic approaches to increasing the density of energy stored in capacitors are known: (1) Increase the Dielectric Constant while maintaining the breakdown filed; and (2) Increase the breakdown field for a given dielectric constant material. The maximum energy density, E{sub 0} (Joules/cm{sup 3}) that can be stored in the dielectric of a capacitor is given by: E{sub 0} = 1/2 k {var_epsilon}{sub 0} V{sub b}{sup 2} (Joules/cm{sup 3} dielectric). Where k is the relative permittivity (dielectric constant), {var_epsilon}{sub 0} is the permittivity of free space (8.894 x 10{sup -14} F/cm) and V{sub b} the dielectric material breakdown field. In this project we have successfully developed capacitor structures using dielectric materials with 3 < k < 50 that exhibit high breakdown fields. The observed performance of these capacitors as characterized by the energy stored per unit volume of dielectric at V{sub b} are compared on the basis of the breakdown field in Figure 1.
Date: October 26, 2000
Creator: Barbee, T W Jr
Partner: UNT Libraries Government Documents Department

LPM Interference and Cherenkov-like Gluon Bremsstrahlung in DenseMatter

Description: Gluon bremsstrahlung induced by multiple parton scattering in a finite dense medium has a unique angular distribution with respect to the initial parton direction. A dead-cone structure with an opening angle; theta2{sub 0}; approx 2(1-z)/(zLE) for gluons with fractional energy z arises from the Landau-Pomeran chuck-Migdal (LPM) interference. In a medium where the gluon's dielectric constant is; epsilon>1, the LPM interference pattern is shown to become Cherenkov-like with an increased opening angle determined by the dielectric constant$/cos2/theta{sub c}=z+(1-z)//epsilon$. For a large dielectric constant/epsilon; gg 1+2/z2LE, the corresponding total radiative parton energy loss is about twice that from normal gluon bremsstrahlung. Implications of this Cherenkov-like gluon bremsstrahlung to the jet correlation pattern in high-energy heavy-ion collisions is discussed.
Date: July 26, 2005
Creator: Majumder, Abhijit & Wang, Xin-Nian
Partner: UNT Libraries Government Documents Department

Development of NOx Sensors for Heavy Vehicle Applications

Description: A DOE CRADA was initiated in February 2000 between Ford Motor Company and the US Department of Energy's Oak Ridge National Laboratory (ORNL). The overall objective of the research agreement was to characterize the performance of emission sensors and identify potential areas of improvement and to develop improved insulating materials with a lower capacitance to minimize radio frequency (RF) interference. A bench-scale device was developed at ORNL to evaluate sensor performance. The test stand was designed to enable control of the gas composition, flow rate, and temperature. An air-actuated three-way valve was used to control the injection of the test gas in order to elucidate the transient behavior of the sensor. The major finding from the studies was that transient test results showed that response time of the sensor to NO was highly dependent on the temperature. The time constant decreased with increasing gas temperature and achieved a constant valve of 610 ms for temperatures greater than or equal to 350 C. The steady-state valves O{sub 2} and NO{sub x} pumping currents were measured under steady-state conditions using a picoammeter. The measured pumping currents were extremely low and required an electrically quiet environment for accurate readings. ORNL developed also modified the existing insulator material to decrease its dielectric constant in order to reduce radio frequency interference from the internal heater. This was accomplished by adding low dielectric constant sintering aids to alumina.
Date: January 18, 2002
Creator: Armstrong, T.R. & Soltis, R.E.
Partner: UNT Libraries Government Documents Department

The equivalent electrical permittivity of gas-solid mixtures at intermediate solid volume fractions.

Description: Several mixture models are evaluated for their suitability in predicting the equivalent permittivity of dielectric particles in a dielectric medium for intermediate solid volume fractions (0.4 to 0.6). Predictions of the Maxwell, Rayleigh, Bottcher and Bruggeman models are compared to computational simulations of several arrangements of solid particles in a gas and to the experimentally determined permittivity of a static particle bed. The experiment uses spherical glass beads in air, so air and glass permittivity values (1 and 7, respectively) are used with all of the models and simulations. The experimental system used to measure the permittivity of the static particle bed and its calibration are described. The Rayleigh model is found to be suitable for predicting permittivity over the entire range of solid volume fractions (0-0.6).
Date: July 1, 2005
Creator: Torczynski, John Robert; Ceccio, Steven Louis & Tortora, Paul Richard
Partner: UNT Libraries Government Documents Department

The performance of measurement-based simple models for the x-band complex permittivity of 370 ohms/sq. Kapton XC

Description: The X-band complex permittivity of a commercially-available, carbon loaded, polyamide film is measured. Simple though approximate models are obtained which are shown to be necessary and suitable for analytic or computational modeling of thin absorbing structures realized with the thin lossy film. The utility of each model is tested against experimental results for thin high-impedance surface (HIS) enhanced Salisbury absorbers, enhanced in the sense that the HIS augmented absorber is much thinner than a conventional Salisbury absorber. Kapton XC(reg.) is a commercially-available, carbon-loaded polyamide film manufactured by Dupont(reg.). Though these films are exceptionally durable and available in a range of surface resistivities, their effective permittivity is complex valued and, therefore, their sheet impedance is frequency dependent as is typical of carbon-loaded dielectrics. We have measured the X-band complex permittivity of Kapton XC(reg.) with a manufacture's quoted direct current (DC) sheet resistivity of approximately 370 {Omega}/sq. and thicknesses of 40.0 {mu}m. This study showed the need for relatively precise knowledge of the real part of a carbon particulate loaded, lossy thin film's permittivity in order to accurately engineer the reflection coefficient of high-impedance surface enhanced electromagnetic absorbers. Specifically, simple, approximate models can be obtained for the X-band complex pennittivity of commercially available, carbon loaded, 370 {Omega}/sq., Kapton XC(reg.) thin film. These simple, approximate models can be used in the analytic modeling of high-impedance surface enhanced X-band absorbers or computational modeling of other possibly more complicated absorbing structures which are composed, in part, of 370 {Omega}/sq. Kapton XC(reg.) and designed to operate within the X-band. Finally, the results of this study illustrate the need for simgle models for calculating the complex permittivity spectra of 370 {Omega}/sq. Kapton XC(reg.) over a relatively broad bandwidth (1-20 GHz) to facilitate accurate analytical and computational modeling.
Date: January 1, 2009
Creator: Glover, Brian B; Whites, Kieth W & Amert, Tony
Partner: UNT Libraries Government Documents Department