Showing papers on "Dielectric loss published in 1994"

Light propagation in a cylindrical waveguide with a complex, metallic, dielectric function.

Abstract: Motivated by problems in scanning near-field optical microscopy, we discuss light propagation in circular dielectric waveguides with finite aluminum cladding. In order to understand the origin of the different solutions, optical modes are first investigated for the dielectric waveguide with infinite aluminum cladding and for the aluminum cylinder. For aluminum a plasma dispersion law is assumed, leading to complex dielectric constants with negative real parts and to generally complex propagation constants. The dependence of the dispersion on the geometry and on the frequency is discussed for the various kinds of modes. We find that the existence of most of the modes is limited to certain frequencies and geometries, i.e., the solutions have a cutoff in the complex propagation constant plane. Contrary to dielectric waveguide theory, where cutoff describes the abrupt transition from propagating to evanescent modes, no other solution is generated when cutoff of a mode is reached. Surface modes and other kinds of modes, such as guided or bulk modes, can either couple between each other or transform into each other.

Dielectric properties of single crystals of Al/sub 2/O/sub 3/, LaAlO/sub 3/, NdGaO/sub 3/, SrTiO/sub 3/, and MgO at cryogenic temperatures

Abstract: A dielectric resonator technique has been used for measurements of the permittivity and dielectric loss tangent of single-crystal dielectric substrates in the temperature range 20-300 K at microwave frequencies. Application of superconducting films made it possible to determine dielectric loss tangents of about 5/spl times/10/sup -7/ at 20 K. Two permittivity tensor components for uniaxially anisotropic samples were measured. Generally, single-crystal samples made of the same material by different manufacturers or by different processes save significantly different losses, although they have essentially the same permittivities. The permittivity of one crystalline ferroelectric substrate, SrTiO/sub 3/, strongly depends on temperature. This temperature dependence can affect the performance of ferroelectric thin-film microwave devices, such as electronically tunable phase shifters, mixers, delay lines and filters. >

Measurement of radiation efficiency of dielectric resonator antennas

Abstract: Radiation efficiency (due to conduction and dielectric losses) of dielectric resonator antennas has been measured. Results show that for dielectric resonators placed directly on a metallic plane, the conduction losses are quite small. A radiation efficiency of >98% has been measured for dielectric resonator antennas operated in the dominant hybrid (HE/sub 11/spl delta//) mode. Theoretical considerations show scope of further improvement in the radiation efficiency by choosing optimum resonator parameters. >

Substrates for high-Tc superconductor microwave integrated circuits

Abstract: This review paper presents a discussion on dielectric substrate materials suitable for the preparation of YBa2Cu3O7-x thin-film based microwave integrated circuits. The requirements on the properties of the substrate materials are specified. They cover the properties crucial both for the preparation of high-quality YBa2Cu3O7-x films and for the design of microwave elements. The former includes mainly the lattice match, the match of thermal expansivities, chemical stability, and absence of twinning. The latter includes the relative dielectric permittivity ( epsilon ) and the related tolerances, the microwave loss tangent, and the substrate area required for the accommodation of a microwave circuit. The properties of the currently available substrates suitable for YBCO film epitaxy are discussed in view of these requirements. The main attention is paid to the microwave properties. Current achievements and potential difficulties of the crystal growth technology in the preparation of the substrates are taken into account as well.

Estimation of materials characteristics from power measurements at 60 GHz

Abstract: The RACE-MBS (Mobile Broadband System) project deals with the development of a mobile communications system at the 60 GHz band, which means that its propagation models, both for indoor and outdoor environments, have to be developed for that specific frequency band. The article presents estimated values, at 60 GHz, for the electrical characteristics of several building materials (only for flat surfaces), namely the relative dielectric constant, the loss tangent, and the attenuation coefficient. The estimations are based on power reflection and transmission measurements of the material samples, and the multiple internal reflections in a dielectric slab are used as a model. A least-square approach is used to obtain the numerical values of the parameters from the measurements. The attenuation coefficient ranges from 1 dB/cm to 8 dB/cm.

Effect of Sn Substitution on Cation Ordering in (Zr1–xSnx)TiO4 Microwave Dielectric Ceramics

Abstract: The crystal structure and microwave dielectric properties of (Zr1–xSnx)TiO4 ceramics with x ranging from 0.0 to 0.15 have been investigated to characterize the effect of Sn substitution on cation ordering and the effect of ordering on dielectric loss. The crystal structure of the samples was investigated using high-resolution transmission electron microscopy and electron diffraction. Although Sn substitution inhibits ordering, the effect is progressive and ordering still proceeds to an observable degree in samples with x= 0.15. The ordered structure of all samples is of the incommensurate modular type previously observed for Sn-free zirconium titanate compositions. In this structure individual (100) cation layers are observed to switch abruptly from Zr-rich to Ti-rich occupancy, indicating that ordering proceeds by the segregation of Zr and Ti into elongate two-dimensional domains on (100). The domains get smaller as the Sn content of the samples increases and in Zr0.5Sn0.15TiO4 the length scale of the cation correlations is approximately 25–50 A. We propose that the decrease in the driving energy for the coarsening of the domains during the ordering transformation is due to the preferential segregation of Sn to the Zr-Ti domain boundaries. Whereas the long-range cation ordering increases the dielectric loss of Sn-free ceramics by 30%, it results in a negligible change in the loss properties of Zr0.91Sn0.09TiO4. It is possible that the hypothesized effect of Sn in stabilizing the Zr-Ti boundaries may also affect the contribution of these sites to the dielectric loss of the ordered structures.

Study of whispering gallery modes in anisotropic single-crystal dielectric resonators

Abstract: The Rayleigh-Ritz method and the finite element method nongenerating spurious solutions are employed for analysis of whispering gallery modes (WGMs) in cylindrical single-crystal anisotropic dielectric resonators. These methods allow accurate computation of the resonant frequencies, the Q-factors (depending on the dielectric and on the conductor losses), and the electromagnetic field distributions for all WGMs in the presence of additional elements like metal shields, MIC substrate, or supports. Different families of modes are studied both theoretically and experimentally. The mode coupling phenomenon is investigated. A WGM single-crystal quartz resonator is presented having an unloaded Q-factor greater than 30000 at about 100 GHz, including radiation and dielectric losses. >

Structure of Ba(Y+31/2Ta+51/2)O3 and its dielectric properties in the range 102–1014 Hz, 20–600 K

Abstract: The goal of this work was to understand the correlation between microscopic material parameters and the dielectric function of candidate materials for applications in the microwave frequency range. The structure and dielectric properties of Ba2+(Y3+ 1/2Ta5+ 1/2)O3 (BYT), a typical representative of the Ba(B3+ 1/2B5+ 1/2)O3 complex perovskite family, has been investigated from 102 to 1014 Hz and from 20 to 600 K. At T c =253±1 K, BYT undergoes an equitranslational improper ferroelastic, second‐order phase transition, characterized by the tilting of the oxygen octahedra. The space group symmetry changes from Fm3m, in the high temperature phase, to I4/m below T c . The existence of an intermediate temperature region (T c −40

Effects of La2O3/ZnO Additives on Microstructure And Microwave Dielectric Properties of Zr0.8Sn0.2TiO4 Ceramics

Abstract: Dielectric ceramics of Zr[sub 0.8]Sn[sub 0.2]TiO[sub 4] containing La[sub 2]O[sub 3] and ZnO as sintering aids were prepared and investigating for microstructure and microwave dielectric properties. Low-level doping with La[sub 2]O[sub 3] and ZnO (up to 0.30 wt%) is good for densification and dielectric properties. These additives do not affect the dielectric constant and the temperature coefficient. Dielectric losses increase significantly at additive levels higher than 0.15 wt%. The combined additives La[sub 2]O[sub 3] and ZnO act as grain growth enhancers. With 0.15 wt% additives, a ceramic having a dielectric constant, a quality factor, and a temperature coefficient of frequency at 4.2 GHz of 37.6, 12,800 and [minus]2.9 ppm/C, respectively, was obtained. The quality factor was considerably improved by prolonged sintering.

Dielectric materials for gyrotron output windows

Abstract: The dielectric parameters of materials for gyrotron output windows measured in the range 65–300 GHz are given The special attention is paid to the spread of values of the refractive index and loss tangent of dielectrics produced by different firms The refractive index and loss tangent are measured for sapphire at the cryogenic temperatures and for boron nitride and silica glass at the temperatures 300–1000K

Far‐Infrared Reflection Spectra of Dielectric Ceramics for Microwave Applications

Abstract: Far-infrared reflection spectra of dielectric ceramics, BaSm2Ti5O14, BaTi4O9, and some pcrovskites such as Ba(Zn1/3Nb2/3)O3, have been measured at room temperature using a Fourier transform infrared spectrometer in order to investigate the effect of the crystal structure on the dielectric properties. As for perovskites, Sr(Zn1/3Nb2/3)O3 and Sr(Mg1/3Nb2/3)O3, in which B site ions are ordered, were also measured. Reflectance data were analyzed by means of a factorized form of dielectric functions instead of the classical dispersion theory, and all of the spectra were well fitted. The values of dielectric constants and tan δ calculated from the reflectance data were in good agreement with resonant cavity measurements at 5 GHz. Furthermore, results of this study have shown that the main contribution to the microwave dielectric properties is caused by low-frequency optically active modes located at 50 to about 300 cm−1, and for perovskite structures it is suggested that the ordering of B site ions is significant in obtaining low dielectric losses.

Preparation of (Ba, Sr)TiO3 Thin Films by Chemical Vapor Deposition Using Liquid Sources

Abstract: Thin films of (Ba, Sr)TiO3 with high dielectric constant were prepared on Pt/SiO2/Si substrates of 6-inch-diameter by chemical vapor deposition using liquid sources. Ba(DPM)2 and Sr(DPM)2 dissolved into tetrahydrofuran were vaporized in a vaporizer at 523 K, and Ti(O-i-C3H7)4 was bubbled at 313 K. The mixture of the source vapors with O2 and N2O was supplied to the reactor (10 Torr) at uniform velocities through a shower-type nozzle, which realized uniform profiles in the deposited film thickness and composition. The electrical properties are significantly influenced by the film composition, and the typical properties obtained for a 800-A-thick film prepared at the substrate temperature of 823 K are an equivalent SiO2 thickness t eq of 5.2 A, a leakage current J L of 2.4× 10-6 A/cm2 (at 1.65 V), and a dielectric loss tan δ of 0.07.

The dynamics of poly(n-butyl acrylate) above the glass transition

Abstract: Measurements of the dielectric constant of poly(n-butyl acrylate) have been taken in the frequency range 100 Hz-3 GHz, for temperatures between 254 and 359 K. Analysis of dielectric data and their comparison with results recently obtained on the same system by Brillouin light scattering have evidenced a two-step relaxation process. Dielectric spectra account for the behaviour of the slower process, i.e. the structural relaxation, while Brillouin spectra are particularly sensitive to the faster process, i.e. the secondary relaxation. The temperature behaviour of these processes is not in accordance with the predictions of the mode-coupling theory, while it can be suitably interpreted by a model that relates the high-frequency dependence of the dielectric loss curve to the local chain dynamics and the low-frequency dependence to the intermolecular correlation.

High-Q LaAlO/sub 3/ dielectric resonator shielded by YBCO-films

Abstract: We have investigated a dielectric resonator consisting of a single crystalline LaAlO/sub 3/-cylinder shielded by a cylindrically shaped copper cavity with endplates made from epitaxial films of YBa/sub 2/Cu/sub 3/O/sub 7/ or niobium. For YBa/sub 2/Cu/sub 3/O/sub 7/ films unloaded quality factors Q/sub 0/ of 4.5/spl middot/10/sup 5/ at 10 K and 1.3/spl middot/10/sup 5/ at 77 K were achieved at 11.6 GHz using a compact shielding cavity with a diameter of 15 mm and a height of 3.8 mm. The loss contributions of the dielectric resonator, the normal conducting cylinder wall, and the superconducting endplates, with one of them being separated by a small distance h from the dielectric cylinder, were calculated by modeling the electromagnetic fields of the TE/sub 0/spl nu//spl mu//-modes. The dielectric loss tangent of the LaAlO/sub 3/-cylinders was found to be 10/sup -6/ at 4.3 K and f=11.6 GHz and to increase slightly with temperature. Moreover, the calculations indicate the tunability of the resonance frequency by changing h over a range of 1 GHz without significant degradation of Q/sub 0/. These resonators are considered to be useful devices for stable oscillators and narrowband filters. >

Dielectric Dispersion in Ferrielectric Phase of Antiferroelectric Liquid Crystal

Abstract: We studied the dielectric behavior in the ferroelectric SmC* and ferrielectric SmCγ* phases of the antiferroelectric liquid crystal (R)-1-methylheptyl-4-( 4''-n-dodecyloxybiphenyl- 4' carbonoyloxy)-3-fluoro-benzoate. In the SmCγ* phase, 3 dielectric relaxations were recognized in the frequency range under consideration. The 2 relaxation processes at low frequency with high dielectric loss were attributed to azimuthal fluctuation of the molecules around the cone angle . Those relaxations are investigated as functions of temperature and applied bias electric field. Besides the 2 low-frequency loss processes, one additional loss process with weak intensity was observed.

Dielectric properties of quenched and laser-excited or field-treated LiF single crystals irradiated with X-rays

Abstract: Frequency and temperature dependences of dielectric constant, K, and loss, tan δ, and hence a.c. conductivity, σ, have been studied for LiF single crystals under a combination of treatments such as quenching, laser excitation, a.c. field treatment and X-ray irradiation. The measurements were made in the frequency range 102–107 Hz and in the temperature range 30–400 °C. The dielectric constant, K, of LiF at 30 °C was found to be 8.4 and to be independent of frequency, while the dielectric loss, tan δ, was below 10−3 at 102 Hz. The results indicate that the different treatments on LiF single crystals increase the room-temperature and also high-temperature K and tan δ values appreciably in the low-frequency region. Log σ versus 1/T plots at frequency 102 Hz give the activation energy for conduction in the intrinsic region as 0.97 eV for as-cleaved LiF; this value was found to decrease in variously treated LiF samples. The different treatments on LiF help to increase the concentration of charged lattice defects which, in turn, increases the K and tan δ values.

Effective Dielectric Permittivity of r-Cut Sapphire Microstrip

Abstract: The effective dielectric constant of a microstrip is given as a function of the strip geometry and its orientation on the surface of the substrate. An "isotropized" dielectric constant is inroduced which can be used in commercial microwave software for simulation of r-cut sapphire substrate based micrstrip devices. Experimental velification of the analysis is also given.

Growth Conditions, Optical and Dielectric Properties of Yttrium Oxide Thin Films

Abstract: Thin Y2O3 films are grown by reactive synthesis, their optical and dielectric properties (electric resistivity, dielectric losses and permittivity, electric strength, and refractive index) are measured. Their dependence upon deposition parameters (deposition rate and reactive gas pressure) is investigated. Comparison of experimental data with those obtained by film growth modelling by the Monte-Carlo method suggests an insignificant influence of diffusion jumps and long-range order on the formation of Y2O3 films at low deposition temperature (300 to 400 K). The perspectives of Y2O3 films as dielectric layers in integrated circuits and high refractive layers for laser mirrors are shown.

Measurement of dielectric loss tangent of alumina at microwave frequencies and room temperature

Abstract: The use of whispering gallery modes allows the dielectric loss tangent of polycrystalline Al/sub 2/O/sub 3/ (alumina) to be accurately determined at microwave frequencies without the use of a cavity. The dielectric loss tangent of alumina is shown to be strongly variable from sample to sample with a lowest measured value of 4.3*10/sup -5/ observed at 9.0 GHz in a 99.5% alumina sample.

Inclusion of scattering losses in the models of the effective permittivity of dielectric mixtures and applications to wet snow

Abstract: Several dielectric models have been previously proposed to explain the permittivity of mixtures from the known dielectric constant and volume fractions of the constituents. The materials may be lossy and this leads to a complex effective permittivity for the mixture where the imaginary part stands for the absorption losses of the mixture. However, the scattering losses are not incorporated in the effective permittivity. The result is therefore confined to a low-frequency limit. In this paper an attempt is made to incorporate the scattering losses in the effective permittivity of the medium consisting of the discrete scatterers immersed in a host material. The inclusions are assumed to be spherical. The results are applicable to general multiphase mixtures, and the scattering spheres of the different phases may have size distribution. The results are applied to calculating the complex effective permittivity of wet snow. The prediction of the model seems to agree with the experimental data if the scattering...

Ferroelectric switching and fatigue behavior for PZT/YBCO thin film heterostructures

Abstract: The dielectric and ferroelectric properties for Au/Pb(Zr,Ti)O3/YBa2Cu3O7−x heterostructures at low temperatures are reported. The fatigue behavior and the ferroelectric switching effect for the structures are also investigated. The PZT/YBCO thin film heterostructures were deposited on MgO(100) substrates by laser ablation. The ferroelectric and dielectric properties and optical response of the oriented PZT films with different thicknesses have been studied over the temperature range from 20 K to 300 K. The dielectric loss of the structure was found to decrease by an order of magnitude when the YBCO bottom electrode became superconducting. A very low fatigue rate of the structure has also been obtained below T c of YBCO layer.