Showing papers on "Dielectric loss published in 1981"

A new understanding of the dielectric relaxation of solids

Abstract: The frequency dependence of the dielectric response of solids shows an apparently bewildering variety of patterns, virtually none of which corresponds to the classical Debye behaviour. However, a wide ranging critical analysis of the existing wealth of data shows that the dielectric loss obeys power-law dependences on frequencies, both below and above any loss peaks that may be present. This corresponds to power-law dependences on time under step-function excitation and it applies completely generally regardless of the detailed physical and chemical nature of the materials in question and also applies equally to dipoles, ions and hopping electrons as the polarizing species. Moreover, the power-law responses persist down to the lowest temperatures in the milliKelvin range, thus proving the importance of non-thermal transitions. The power laws are characterized by exponents in the range ± 1 and they cover as special cases the complete range of the observed types of response, from virtually frequency-independent “flat” losses often seen in low-loss materials, through various forms of asymmetric loss peaks to strongly dispersive behaviour in which both the real and the imaginary components of the susceptibility vary almost inversely with frequency. The “universality” of the power law strongly suggests the dominance in all materials of a common mechanism of dielectric relaxation and this is found in many-body interactions which provide a model capable of explaining the totality of the observed responses of solids, including both the frequency- and the temperature-dependence. In this interpretation, the classical one-particle Debye law represents but a singularity in a more general behaviour and is usually overshadowed by the new many-body mechanisms.

Nonradiative Dielectric Waveguide for Millimeter-Wave Integrated Circuits

Abstract: A nonradiative dielectric waveguide is proposed in which dielectic strips are sandwiched between two parallel metal plates separated by a distance smaller than half a wavelength. Though the structure is substantially the same as that of the H-guide, it is based on a quite different principle of operation. This dielectric guide is particularly applicable in millimeter-wave integrated circuits, since it is not only small in size, but also allows bends and junctions to be incorporated into the circuits with very little radiation and interference. A design diagram is given. Losses and coupling coefficients of the strips are calculated, as well. Some basic circuit components, such as 90° and 180° bends and T-junctions, made of polystyrene strips, are measured to confirm their usefulness in millimeter-wave integrated circuits.

Application of Dielectric Resonators in Microwave Components

Abstract: Dielectric resonators are being used in microwave filters and oscillators now that high-dielectric-constant, high-Q, temperature-stable ceramics have been developed. This paper reviews dielectric resonators with emphasis on applications, contains tutorial material, deseribes new 2-, 4-, and 6GHz bandpass filters, and presents several examples of oscillator applications. A complete blbliography to English language publications on dielectric resonators is included.

Temperature dependence of dielectric losses in chalcogenide glasses

Abstract: The frequency (2 × 10 4 −2 × 10 7 Hz) and temperature (250–600 K) dependence of the imaginary part of the permittivity, ϵ′', of As 2 Se 3 and Tl 2 SnSe 8.61 is explained within a theoretical model. The dielectric premittivities of these compounds are correctly explained by means of a model of a hopping process over a potential barrier between localized sites. We have found that the glassy system of chalcogenide can exist in the form of dipoles. The theory shows, in agreement with the experimental results, that ϵ ′' = Aω m , where m is a function of temperature.

Precise Calculations and Measurements on the Complex Dielectric Constant of Lossy Materials Using TM/sub 010/ Cavity Perturbation Techniques

Abstract: An exact field theory solution for the cylindrical TM/sub 010/ cavity with a coaxial lossy dielectric cylinder is given. The error in the calculated field solutions is estimated to be less than 1 percent of the true values. Correction for the cavity holes used to introduce the sample is taken into account. The exact solution shows that the real part of the permittivity (epsilon') is a complex function of both the frequency shift and the change in the loaded Q-factor (Q/sub L/). On the other hand the imaginary part (epsilon") is nearly proportional to delta(1/Q/sub L/) and it has different slopes for varying frequencies. By means of active cavity techniques already reported, experimental measurements on epslion' and epsilon" taken at 2.2 GHz on a number of materials (water, teflon, n-proponal, methanol, etc.) agree with published data within 1 percent even when rising large samples.

Dielectric components of charge movements in skeletal muscle.

Abstract: 1. Voltage clamp experiments measured transients from 10 mV steps applied about different membrane potentials, VT. Their analysis employed the Fourier transform relationship between dielectric spectra of permittivity as a function of frequency, and the step transient admittance, as well as established methods. 2. The membrane capacitance measured between -85 mV and about -50 mV rose monotonically and was associated with simple decaying transients in both ‘on’ and ‘off’ steps. At more depolarized potentials the capacitance increased sharply and was associated with a charging current of complex form, before falling again beyond the transition potential. 3. Step-transient responses for dielectric analysis were sampled in the above voltage range. Dielectric spectra of the non-linear transients were obtained by subtracting Fourier transforms of transients at VC = -85 mV from test transforms at VT. 4. The imaginary transform coefficients represent a spectrum of dielectric loss against frequency. These showed two non-linear components. The q beta component formed a broad peak, when charge movements were simple monotonic decays. A sharp low-frequency q gamma peak became superimposed at particular voltages when charge-movement kinetics became complex. 5. In contrast, ‘off’ transients were simple monotonic relaxations. Their transforms showed only one dielectric loss peak, whose frequency was relatively voltage-independent when q gamma occurred in ‘on’ transforms. 6. Both altering holding potential from VH = -85 to -50 mV and adding 1 mM-tetracaine to the bathing solution reduced the dependence of capacitance on voltage. The non-linear polarization currents became simple monotonic relaxations at both the beginning and end of the voltage step. 7. It is concluded that charge movements are composed of at least two components: q beta, and the tetracaine and voltage-inactivated q gamma. Any causal relationship between q beta and q gamma and the membrane processes they might underlie would be expected to be complex.

Maximum Q-Factor of Microstrip Resonators

Abstract: The quality factors of microstrip half-wavelength resonators have been calculated as a function of substrate thickness for frequencies in the range 8-96 GHz, for different epsilon/sub r/. Conductor, dielectric, and radiation losses have been included. The optimum substrate thickness for the maximum Q-factor for 50-omega microstrip resonators has been derived as a function of frequency for different dielectric constants.

Characterization of dielectric materials

Abstract: Recent examination of the form of the dielectric susceptibility as a function of frequency has shown the presence of power law behaviour at both low and high frequencies, with respect to the frequency of maximum loss. The magnitudes for the power law exponents of one hundred dielectric loss peaks are reported together with relevant experimental information. It is observed that very few materials show the characteristics of the standard susceptibility functions.

SAW propagation loss mechanism in piezoelectric ceramics

Abstract: The surface acoustic wave (SAW) propagation loss mechanism of piezoelectric ceramics is examined using lead titanate (PbTiO3) ceramics modified with additives of Nd2O3, MnO2, and In2O3, which have zero temperature coefficients of SAW delay time. The propagation loss L in the frequency range 30 to 300 MHz consists of two parts. One is the Rayleigh scattering loss LS caused by grain, and the other is the true dissipative loss LF caused by internal friction. Thus, total loss results in L(dB/cm) = LS+LF = 3.2×103D3f4+6.8×10−4f2 (where D and f denote average grain size in cm and frequency in MHz, respectively). It is also revealed experimentally that the internal friction causing the latter loss has a close correlation with the dielectric loss through piezoelectric combination. Therefore, materials with fine grain (<0.5 μm) and low dielectric loss (<10−3) must be developed to reduce SAW propagation losses which prevent the piezoelectric ceramics from being used in higher frequency (≳100 MHz) SAW applications. Based on these requirements, fine grained (∼0.5 μm) specimens are fabricated. The propagation losses obtained from these specimens, 9 dB/cm at 100 MHz, are the lowest values ever reported for piezoelectric ceramics. This result suggests that the present ceramics have high potential as materials for high‐frequency SAW devices.

Electrical and dielectric behavior of a zinc oxide composite

Abstract: Room‐temperature studies of I‐V characteristics and variation of both the dielectric constant and dielectric loss with frequency are presented for ZnO‐Bi2O3 samples having different compositions and prepared by sintering at different temperatures The nonlinearity parameter, dc resistivity, dielectric constant, and dielectric loss depend on the composition and sintering temperature These parameters have been optimized for obtaining maximum nonlinearity and dielectric constant The occurrence of a loss peak is, however, seen to be independent of the composition and sintering temperature The present study, supported by a scanning electron microscope analysis, confirms the necessity of a two‐phase structure in the composite for its nonlinearity and high dielectric constant The variation in the dielectric constant and nonlinearity parameter with sintering temperature for samples of different compositions has been explained on the basis of change in barrier height of Schottky barriers; the presence of these barriers has been inferred by the observed behavior of capacitance variation with bias

OH in vitreous silica

Abstract: The low-temperature experiments relating to the properties of the hydroxyl group OH in vitreous silica are analysed and correlated in terms of a model involving rotation of the OH group about an SiO bond. At low temperatures this is an atomic tunnelling model, but one in which the parameters are known, and for which the distribution functions for the local potentials can be deduced from dielectric measurements above 50 K. These distribution functions are used to calculate the effect of OH on the low-temperature dielectric loss, the temperature variation of the real part of the dielectric constant at low and high frequencies, the heat capacity, the acoustic attenuation and the thermal conductivity. For all these experiments the agreement between calculation and experiment is within 50%, indicating that the tunnelling model can provide a consistent and plausible explanation in this particular case. The dielectric echo experiments are also analysed in detail, and it is shown that the tunnelling mode...

(1-x)BaO.xTiO2 System dielectric material for use in a microwave device

Abstract: The present invention provides a dielectric material adapted for microwave integrated circuits (MIC) and an electric circuit making use of said dielectric material. More particularly, an oxide dielectric material principally consisting of (1-x)BaO.xTiO2 (0.7≦x≦0.95) and containing both 0.007 to 0.7 weight % of manganese and 0.037 to 3.7 weight % of zirconium, has a large dielectric constant, a small dielectric loss and a small temperature coefficient of dielectric constant and is uniform over a broad range, and especially it is possible to easily manufacture a substrate having a uniform dielectric constant and a uniform dielectric loss. Transistors and MIC's employing such substrates can attain uniform and excellent high-frequency characteristics.

Dielectric Relaxation Strength of a Low‐Alkali Glass

Abstract: The low-frequency dielectric loss maxima for glasses with low alkali concentrations are often obscured by a much larger dc conductivity contribution to the dielectric loss. Therefore, quantitative determination of the dielectric relaxation strengths for these glasses is difficult. An approximate relation between the impedance, electric modulus, and dielectric constant relaxation maxima is developed for glasses exhibiting small dielectric relaxation strengths. Using the obtained relations, the dielectric relaxation strength, Δe, for a GeO2 glass containing 47 wt ppm Na2O is estimated to be ≅0.3.

Dielectric behavior of copolymers of vinylidene fluoride and tetrafluoroethylene

Abstract: Dielectric behavior and related bulk properties have been studied on copolymers of vinylidene fluoride (VDF) and tetra-fluoroethylene (TFE) with TFE contents of 10 to 30 mol-%, Dielectric properties of copolymers did not vary much with TFE contents. Copolymers exhibited the dielectric relaxation similar to that as found for poly(vinylidene fluoride) (PVDF) at low temperature which was connected with micro-Brownian motions of the molecular chain backbone in amorphous regions. Variation of the relaxation frequency with temperature in the vicinity of the glass transition was fitted by the modified WLF equation. No noticeable dielectric loss peak associated with the relaxation in crystalline regions in form I1 of PVDF was found at high temperature. This may be understood because the VDF-TFE copolymer has the same structure as form I of PVDF. The dielectric constant and loss increased with increasing temperature and/or decreasing frequency above room temperature owing to the space charge polarization ...

Dielectric Properties of Lossy KH2PO4Crystals

Abstract: Single crystals of KH2PO4 have been prepared from aqueous solutions which contain a large amount of KOH. These crystals have high dielectric constants and dielectric losses at room temperature and show dielectric dispersion below about 105 Hz. The dispersion frequency increases with the increase of the amount of KOH in the aqueous solution. In the ferroelectric phase, these crystals exhibit low dielectric constants and show anomalous frequency dependence of the coercive field.

Measurement of the Dielectric Constant and Loss Tangent of Thallium Mixed Halide Crystals KRS-5 and KRS-6 at 95 GHz

Abstract: The dielectric constants and loss tangents of KRS-5 and KRS-6 thallium halide mixed crystals have been measured at 95 GHz using both the shorted waveguide (SWG) reflection method and the Fabry-Perot (F-P) transmission method on samples filling standard WR-10 waveguide The results--KRS-5: epsilon'/sub r/ = 31; tan delta = 18 x 10/sup -2/; KRS-6: epsilon'/sub r/ = 29, tan delta = 2 x 10/sup-2/-- agree reasonably well with a simple theoretical fit to the far-infrared Iattice absorption of TIBr and TICI centered at about 1400 GHz The dielectric samples were hot-pressed into copper wafers with dimensions matching WR-10 waveguide, and then machined and polished to obtain flat, parallel air-dielectric interfaces

Determination of moisture level in materials

Abstract: A method for determining the moisture content of dielectric materials is described wherein a sample of the material is placed between two electrodes and an electric field is applied An alternating frequency in the range of radio waves and lower is applied to the electrodes and the dielectric loss properties of the material are determined The dielectric loss properties are then used to determine moisture content In an alternate embodiment, a step voltage is applied to the electrodes and the direct current is monitored The decrease in value of direct current during a time interval following the application of the step voltage is used to determine the moisture content

Helical Resonators for Measuring Dielectric Properties of Materials

Abstract: A theoretical and practical investigation is given of superconducting helical resonators with quality factors greater than 10/sup 8/ which allow the determination of dielectric loss tangents in the frequency range of 0.1 to 5 GHz and below 15 K with high accuracy. The underlying measurement theory is an extension of perturbation theory. They are evaluated for the fields in a shielded multiple quarter-wave helical resonator with a cylindrical dielectric specimen inside the helix. Measurement results on optimized resonators made from superconducting Nb and Nb/sub 3/Sn are reported as well as further applications.

A simple experimental method for separating loss parameters of a microstrip antenna

Abstract: A simple method is presented for the computation of both the dielectric loss tangent and the conductivity of the metal cladding of printed circuit boards at microwave frequencies. Since the treatment of the cladding in the lamination process affects its conductivity, losses in the dielectric and the metal cannot be measured separately. Thus an analytical means for separating these losses must be employed. The method described accomplishes this by utilizing the different dependence of the two losses on dielectric thickness in thin cavities.

Frequency Dependence of the Dielectric Properties of Coai — Part II1

Abstract: The dielectric properties of 18 pulverized coal samples, including run-of-mine and light and dense fractions, were measured over the frequency range from 1 MHz to 12 GHz at 22°C and are presented graphically. For Iowa coal, the dielectric loss factors of dense fractions containing most of the pyrite tended to increase noticeably as frequency increased. The loss factors of dense fractions of eastern coal (Kentucky and Ohio) tended to decrease with increasing frequency and then rose somewhat as frequency approached the microwave range. Data are also presented on the dielectric constant as a function of bulk density. Plots of the square root of the dielectric constant vs. bulk density resulted in straight lines that can be extrapolated with confidence to the coal particle density, thus providing estimates for the dielectric constant of the solid coal from measurements on pulverized samples.

AC loss and DC conduction mechanisms in polyethylene under high electric fields

Abstract: The paper describes extensive experimental investigations concerning AC loss and DC conduction in polyethylene (PE) subjected to strong electric fields up to about l00kV/mm. Based on an electronic charge carrier hopping transport model including trap-like and donor-like states it is shown that the current is bulk-limited under both AC and DC conditions. However, the sources of the electronic charge carriers taking part in the AC loss and DC conduction processes, respectively, are different from each other: At direct voltage the electrons are injected from the cathode whereas at alternating voltage they are predominantly activated from donor-like states in the bulk of the dielectric by a Poole-Frenkel-mechanism.

Slots in Dielectric Image Line As Mode Launchers and Circuit Elements

Abstract: Slots in the ground plane of dielectric image lines are investigated using a planar resonator model. An equivalent circuit representation of the slot discontinuity is derived and the launching efficiency of the slot as a mode launcher is discussed. Slots are also demonstrated to be useful in the realization of dielectric image line array antennas.

Dielectric loss of poly(vinylidene fluoride) at low temperatures and effect of poling on the low temperature loss

Abstract: Dielectric constant and loss of poly(vinylidene fluoride) (PVDF) were measured at 20 Hz. 110 Hz and 1 kHz in the temperatures ranging from 4.2 K to 300 K. Dielectric loss peaks (1 kHz) were observed respectively at 75 K (δ peak) for melt-crystallized PVDF with form I1 crystals and at 18 K (e peak) for rolled PVDF with oriented form 1 crystals. Activation energies were evaluated to be 12.6 and 1.9 kJ/mol for δ and e respectively. The height of e loss peak is suppressed by poling the sample at a rather low poling field. suggesting that the dipolar orientation in the form I crystal accompanying reduction of crystal detects occurs at the early stage of poling process.

Grain boundary layer dielectric ceramic compositions

Abstract: Grain boundary layer dielectric ceramic compositions comprising semiconductive ceramic grains having a composition of 50.23 to 49.47 mol% of SrO and CaO, 49.72 to 50.23 mol% of TiO 2 , 0.05 to 0.3 mol% of Nb 2 O 5 , substantially each of said grains being surrounded by grain boundary layer dielectric materials which is formed by grain boundary diffusion of a mixture having a composition of 93.5 to 8.5 mol% of Bi 2 O 3 , 4.5 to 45 mol% of Cu 2 O, 0.5 to 4 mol% of MnO 2 , 1 to 8.5 mol% of B 2 O 3 , 0.5 to 17 mol% of La 2 O 3 , and below 17 mol% of TiO 2 . These ceramic compositions provide capacitors having the temperature coefficient of capacitance less than ± 15%, the apparent dielectric constant higher than 35,000, the dielectric loss less than 0.01 and the breakdown voltage higher than 500 V/mm or capacitors having the temperature coefficient of capacitance less than ± 10%, the apparent dielectric constant higher than 20,000, the dielectric loss less than 0.01 and the breakdown voltage higher than 700 V/mm or capacitors having the temperature coefficient of capacitance less than ± 5%, the apparent dielectric constant higher than 5,000, the dielectric loss less than 0.01 and the breakdown voltage higher than 700 V/mm.

A Variational Theory for Wave Propagation in Inhomogeneous Dielectric Slab Loaded Waveguides

Abstract: A novel numerical technique based on the variational formulation defined only in the slab is developed to study the loaded rectangular waveguide with an inhomogeneous dielectric slab. The variational equation for the boundary value problem is formulated and solved numerically, using the finite element method with piecewise quadratic trial functions. A comparison of this new technique with the conventional variational ones is presented. Various propagation characteristics, such as the phase constant, useful bandwidth, power handling capacity, and attenuation constants due to conductor and dielectric losses, are investigated for the waveguide centrally loaded with a slab of parabolic dielectric profile. The effects of changes in dielectric profiles are discussed by examining the results for the slabs with constant and parabolic profiles.

Glass ceramic materials having controllable temperature coefficients of dielectric constant

Abstract: Glass ceramic materials having controllable temperature coefficients of dielectric constant or capacitance (TCC) are provided. The ceramic component of the composition possesses paraelectric properties at least over the temperature range of -55° C. to 125° C. and can be controllably crystallized from the glassy matrix initially formed. Heat treatment of the glass produces crystallization of the ceramic component and results in glass ceramic materials with controlled TCC values which are useful as capacitors, resonators, microwave substrates, and the like because of their low dielectric loss characteristics and temperature stability.

Improvement of Dielectric Properties of Plasma Polymerized Styrene with Hydrogen Plasma Treatment

Abstract: Capacitance and dielectric loss tangent of plasma polymerized styrene films are obtained as a function of temperature. The stability of these films is investigated with heating in a vacuum and in air. It was found that the hydrogen plasma treatment is effective in improving and stabilizing the dielectric properties of the plasma polymerized styrene films.

Low-temperature radiation damage studies in silicon by hopping conductance

Abstract: Radiation damage studies at low temperatures are described, based on measurements of capacitance and dielectric loss on thin specimens with gold electrodes. Results on electron irradiated n- and p-type silicon are discussed in the light of known defect and impurity behaviour, and damage rates are evaluated for specimens of different impurity content.