1. DIELECTRIC AND STRAIN EFFECTS OF CORE-SHELL / BARRIER LAYER STRUCTURES IN MODIFIED BaTiO 3 CERAMICS - PARK, EUISUK
Current advanced technologies which increasingly require high dielectric constant for miniaturization of electronics and strain properties for actuator applications has motivated many investigations of ferroelectric BaTiO 3 (BT) ceramics. A new type of BT ceramic with core-shell matrix microstructure and barrier layer structure, therefore, was recently developed with simple one-step processing of BT ceramics, modified by isovalent ZrO 2 and donor Nd 2 O 3 dopants. Isovalent ZrO 2 addition alone does not exhibit the barrier layer formation but improves the temperature stability of dielectric constants by forming core-shell grains. The barrier layer (BL) behavior, which consists of insulating oxide...

2. Micromachined Tunable Dielectric Resonators - Wanling Pan Paolo; Paolo Fiorini; Orsola Di Monaco; Kris Baert; Bart Nauwelaers
Micromachined dielectric resonators (DR) and cavity filters are used in microwave technology. For many applications the resonance frequency of the DR must have a small degree of tunablity, to cope with drifts of different origins.

3. High frequency dielectric relaxation in lanthanum modified PbTiO3 ferroelectric ceramics - Guerra,José de los Santos; Eiras,José Antonio
Dielectric measurements of lanthanum modified lead titanate ceramics were carried out in a frequency and temperature range of 70 ´ 10(6)Hz - 2 ´ 10(9)Hz and 300 K - 420 K, respectively. Dielectric relaxation appears around 7 ´ 10(8)Hz at room temperature, and the maximum of the dielectric relaxation was around 393 K, the transition temperature (Tc). The relaxation frequency passes through a minimum at Tc and the dielectric relaxation exists in both paraelectric and ferroelectric phases. A fitting of the experimental data with the Debye relations gives some keys for understanding the dielectric behavior of such materials.

4. Propagation of instability in dielectric elastomers - Jinxiong Zhou A; Wei Hong A; Xuanhe Zhao A; Zhiqian Zhang C; Zhigang Suo A
When an electric voltage is applied across the thickness of a thin layer of an dielectric elastomer, the layer reduces its thickness and expands its area. This electrically induced deformation can be rapid and large, and is potentially useful as soft actuators in diverse technologies. Recent experimental and theoretical studies have shown that, when the voltage exceeds some critical value, the homogenous deformation of the layer becomes unstable, and the layer deforms into a mixture of thin and thick regions. Subsequently, as more electric charge is applied, the thin regions enlarge at the expense of the thick regions. On the...

5. Dielectric characterization of materials at microwave frequency range - de los Santos,J.; Garcia,D.; Eiras,J.A.
In this study a coaxial line was used to connect a microwave-frequency Network Analyzer and a base moving sample holder for dielectric characterization of ferroelectric materials in the microwave range. The main innovation of the technique is the introduction of a special sample holder that eliminates the air gap effect by pressing sample using a fine pressure system control. The device was preliminary tested with alumina (Al2O3) ceramics and validated up to 2 GHz. Dielectric measurements of lanthanum and manganese modified lead titanate (PLTM) ceramics were carried out in order to evaluate the technique for a high permittivity material in...

6. Collision-Induced Effects on the Dielectric Properties of Liquid Dimethylsulfoxide - Vechi,Sérgio M.; Skaf,Munir S.
We present a molecular dynamics (MD) simulation study of the dielectric properties of liquid dimethyl sulfoxide that includes interaction-induced effects due to molecular polarizability using a perturbative scheme in which the induced dipoles are computed a posteriori from the MD trajectories generated without explicit inductive forces. Static and dynamical quantities of relevance to the dielectric characterization of the liquid are reported for both polarizable and nonpolarizable versions of the system's collective dipolar densities. Our analysis within this scheme indicates that the role of the interaction induced contributions is predominantly to renormalize the magnitude of the permanent dipole fluctuations, with marginal...

7. Analysis of shielded rectangular dielectric rod waveguide using mode matching - Wells, Colin G.
The limit of current technology for mobile base station filters is the multimode filter, in which each cavity supports two (or possibly three) independent degenerate resonances. Shielded dielectric resonators with a rectangular cross-section are useful in this application. In the design of these filters, manufacturers are using software packages employing finite element or finite difference time domain techniques. However, for sufficient accuracy these procedures require large numbers of points or elements and can be very time consuming. Over the last decade research using the mode matching technique has been used to solve this kind of difficulty for various types of...

8. Radiation Patterns of Shielded Dielectric Horns: Analytical Versus Simulation Approaches - Carlos Salema; Carlos Fern; Re Martins; João Costa
Abstract — The theory of the dielectric cone antenna has been known since the early seventies. On their own, this antenna has a reasonably circular symmetric radiation pattern but exhibits an undesirably high side-lobe level. A properly designed metallic shield, which does not interfere with the field structure of the dielectric cone, may be used to reduce the side-lobe level. Although in principle this antenna should be quite broadband, prototypes show that this is not the case. After proving that the metallic shield performs as expected, aperture phase error and wave impedance mismatch at the aperture were identified as the...

9. Dielectric relaxations in side-chain liquid crystalline polymers - Zhong, Zhengzhong
Side-chain liquid crystalline polymers represent a novel class of mesogenic materials which exhibit electro- and magneto-optical properties that are similar to those observed for the low-molecular-weight liquid crystals, whilst also having the good film-forming qualities that are characteristic of the high molar mass polymers. From the rotational dynamic theory, four relaxation modes which are dielectrically active arise from combinations of certain time-correlation functions for the angular motions of the dipolar groups in the local (nematic) potential. The practical dielectric relaxation spectroscopy over a wide frequency range shows two typical relaxation processes of the mesogenic side chain when the environmental temperature...

10. Spectral diffusion of single semiconductor nanocrystals: The influence of the dielectric environment - Gomez, Daniel E.; van Embden, Joel; Mulvaney, Paul
We have explored the influence of different matrices on the emission line shape of individual homogeneously coated CdSeCdSZnS nanocrystals. The results obtained corroborate previous observations of a correlation between blinking events and spectral diffusion, but in addition we have found that the extent of spectral diffusion is almost independent of the dielectric environment of the nanocrystal (NC). Additionally, we report the observation of a correlation between the linewidth and emission energy which is not expected to occur in the spherical-symmetric NCs employed in this work. The implications of these results are discussed.

11. Spectral diffusion of single semiconductor nanocrystals: The influence of the dielectric environment - Gomez, Daniel E.; van Embden, Joel; Mulvaney, Paul
We have explored the influence of different matrices on the emission line shape of individual homogeneously coated CdSeCdSZnS nanocrystals. The results obtained corroborate previous observations of a correlation between blinking events and spectral diffusion, but in addition we have found that the extent of spectral diffusion is almost independent of the dielectric environment of the nanocrystal (NC). Additionally, we report the observation of a correlation between the linewidth and emission energy which is not expected to occur in the spherical-symmetric NCs employed in this work. The implications of these results are discussed.

12. Dielectric And Canopies - Kyle Mcdonald
This paper presents a very brief synopsis that were performed at the BOREAS sites examine the dielectric and hydraulic properties of several tree within sites. We installed designed to allow characterization of the hydraulic response of the vegetation in five stands within the BOREAS Northern and Southern Study Areas (NSA and SSA, The five stands were: (1) NSA Old Spruce (2) SSA Old Spruce (3) SSA Aspen (4) SSA Jack Pine and (5) SSA Young Jack Pine Within each stand, water flux and bole were monit in several trees. Microclimate and transpiration were supplemented with mid-canopy air temperature and relative humidity observations to allow calculation of mid-canopy vapor pressure deficit. Also, soil temperature was monitored al various...

13. A wideband probe-fed stacked dielectric resonator antenna - Ge, Yuehe; Esselle, Karu P; Bird, Trevor S
A novel two-layer stacked wideband dielectric resonator antenna (DRA) of rectangular shape is proposed. The DRA is composed of a dielectric resonator (DR) and a thin dielectric segment, which reside above a ground plane, and is excited by a small metallic patch connected to a coaxial probe. Unlike its previous designs that have a DRA of a lower permittivity above one or more thin segments of higher permittivity, the top DR in this antenna has a higher permittivity than the lower segment. Theoretical and experimental results show that the proposed DRA can achieve a very wide bandwidth.

14. Modeling Dielectric Absorption in Capacitors
It is well known that dielectric absorption plays a critical role in determining the accuracy of analog sampled-data systems that are based on charge storage, such as sample-and-holds and switched-capacitor ADCs. Less appreciated, but no less important, is the role it plays in determining the quality factor, or Q, of the capacitor. Dielectric absorption has both storage and loss components that act, and are significant, over the entire usable frequency range of the capacitor. Along with background information on the origins of dielectric absorption, this paper presents two models for a capacitor that exhibits dielectric absorption. The first is the...

15. Synthesis of self-assembled island-structured complex oxide dielectric films - Sriram, Sharath; Bhaskaran, Madhu; Kostovski, Gorgi; Mitchell, David R. G.; Stoddart, Paul R.; Austin, Michael W.; Mitchell, Arnan
A self-assembly driven process to synthesize island-structured dielectric films is presented. An intermetallic reaction in platinized silicon substrates provides preferential growth sites for the complex oxide dielectric layer. Microscopy and spectroscopy analyses have been used to propose a mechanism for this structuring process. This provides a simple and scalable process to synthesize films with increased surface area for sensors, especially those materials with a complex chemistry. The ability of these island-structured dielectric films to improve sensitivity by a factor of 100 compared to continuous films in applications as substrates for surfaceenhanced Raman scattering (SERS) is demonstrated.

16. Dielectric Titanate Ceramics : Contributions From Uncommon Substituents And Microstructural Modifications - Jayanthi, S
This thesis deals with the investigations on the dielectric properties of polycrystalline ceramics having uncommon substitutions in barium titanate and other related phases of BaTiO3-CaTiO3, MgTiO3-CaTiO3 and MgTiO3-BaTiO3 systems. After presenting a brief introduction on the ceramic materials studied in terms of their crystal structures, electrical properties, nonstoichiometry and microstructural characteristics. The thesis describes the synthesis of the ceramics and the methodology of different techniques utilized in characterizing the samples. Barium calcium titanate was synthesized through novel wet chemical techniques and the dielectric properties of calcium substituted barium titanate do not reveal multi-site occupancy whereas they are predominantly influenced by...

17. Inhomogenous Dielectric Media: Wave Propagation and Dielectric Permittivity Reconstruction - Permittivity Reconstruction
In this paper we study the propagation of electromagnetic waves in a waveguide completely filled with a inhomogeneous dielectric material. The material is inhomogeneous in the longitudinal direc- tion, i.e. the dielectric permittivity is described by a function a a0a (z). We first solve the direct problem; then we develop a computational procedure for solving the inverse problem and apply the procedure to the estimation of an unknown dielectric permittivity profile. An important feature of our approach is the expansion of the unknown a (z) into a power series. The dielectric permittivity profile estimation consists in determining the unknown coefficients through error function minimiza- tion. We test...

18. Temperature-dependent dielectric response of BaTiO
. Monte Carlo simulations with an effective Hamiltonian parametrized from first principles are performed to study the dielectric response of BaTiO 3 as a function of temperature, with particular emphasis on the behavior of the dielectric constant near the transition from the ferroelectric tetragonal phase to the paraelectric cubic phase. The peculiar dielectric properties of ferroelectric materials stem from the coupling of the electric field to polar distortions of the crystal lattice. In one common scenario, the progressive softening of a lattice vibrational mode in the neighborhood of a phase transition brings about a dramatic rise in the value of the dielectric constant. The resulting very large relative permitivities...

19. Compact wideband dielectric-resonator-on-patch antenna - Janapsatya, J; Esselle, K.P; Bird, T.S
A method to reduce the size of the dielectric-resonator-on-patch (DRoP) antenna, using a shorting metal wall, is presented. An experimental antenna demonstrates several advantages including better bandwidth, less weight, less volume and a lower profile when compared to the original DRoP antenna without shorting walls. The predicted return loss and radiation patterns of the antenna are compared with measured data.

20. Optical/Dielectric Properties of Materials: - James L. Lamb
A new method, based on Effective Mean Field Theory, is proposed for the evaluation of the optical/dielectric properties of inhomogeneous materials, in which the real and imaginary parts of the dielectric function are determined by solving a simultaneous non-linear equation. It is seen that the method yields precise and unambiguous results and can be applied to any type of inhomogeneous material. Key words: optical, Dielectric, Effective Mean Field Theory, Composite Films. * Indian Center, Space Research Organization ISRO Satellite Airport Road, Vimanapura, Banpalore-560017, India 1. Introduction: The optical/dielectric properties of materials can be modified by mixing two or more materials in different proportions.' -3 The constituent materials can be metals, semiconductors and insulators which may be either in or...

Página de resultados:
1  2  3  4  5  6  7  8  9  10  Siguiente