Showing papers on "Dielectric loss published in 1984"

Microwave Dielectric Properties of Plant Materials

Abstract: Three waveguide transmission systems covering the 1-2, 3.5-6.5, and 7.5-8.5 GHz bands were used to measure the dielectric properties of vegetation material as a function of moisture content and microwave frequency. The materials measured included, primarily, the leaves and stalks of corn and wheat. Dielectric measurements also were made of the liquid included in the vegetation material after it was extracted from the vegetation by mechanical means. The extracted liquids were found to have an equivalent NaCl salinity of about 10 per mil, which can have a significant effect on the dielectric loss at frequencies below 5 GHz. The results of attempts to model the dielectric constant of the vegetation-water mixture in terms of the dielectric constants and volume fractions of its constituent parts (i. e., bulk vegetation, air, bound water, and free water) are discussed. Additionally, measurements of the temporal variations in the total attenuation at 10.2 GHz are presented for a corn canopy and a soybean canopy.

Preparation of ferroelectric PZT films by thermal decomposition of organometallic compounds

Abstract: Transparent PZT thin films with perovskite structure were successfully obtained by thermal decomposition of organometallic compounds at the temperatures of 500 to 700° C. The films deposited on platinum substrates were smooth and uniform, but microcrackings were observed in the films deposited on fused silica substrates. The ratio of metal composition in the PZT film agreed with that in the mixture of starting materials. Films obtained at 700° C on platinum substrate showed a hysteresis loop. A spontaneous polarization was 35.65μC cm−2, a saturation remanent polarization was 30.56μC cm−2 and a coercive field was 45 kV cm−1. Dielectric constant and dielectric loss angle were about 300 and 0.05, respectively.

Dielectric Measurements of Millimeter-Wave Materials

Abstract: It is no longer necessary to use extrapolated microwave dielectric data when designing millimeter-wave components, devices, and systems. Precision measurements can now be made to generate highly accurate millimeter-wave (5 to 1/2 mm) continuous spectra on complex refractive index, complex dielectric permittivity, and loss tangent for a variety of materials such as common ceramics, semiconductors, crystalline, and glassy materials. The continuous spectra reveal an increase in dielectric loss with increase in frequency in this wavelength range for most materials. Reliable measurements also reveal that the method of preparation of nominally identical specimens can change the dielectric losses by many factors. These broad-band measurements were carried out employing dispersive Fourier transform spectroscopy applied to a modular two-beam polarization interferometer. Data obtained with Fabry-Perot open resonator methods at wavelengths of 5 mm and longer will also be compared.

Losses on Multiconductor Transmission Lines in Multilayered Dielectric Media

Abstract: For the transmission-line modes, a multiconductor transmission line in a multilayered dielectric medium can be characterized by four matrix parameters the capacitance matrices [C], the inductance matrix [L], the shunt conductance matrix [G], and the series resistance matrix [R]. The first two matrices [C] and [L] can be obtained from equivalent electrostatic and magnetostatic problems. The conductance matrix [G] can be obtained by changing all dielectric constants epsilon/sub i/ to complex dielectric constants /angle over epsilon/sub i/ in the equivalent electrostatic problem. The resistance matrix [R] can be obtained by applying a perturbation method to each mode of the transmission line. A computer program has been written for an arbitrary line, and sample computations are presented.

Electrical and Dielectric Properties of Wet Bone as a Function of Frequency

Abstract: The electrical and dielectric properties of wet, bovine, compact bone were determined in three orthogonal planes, using a differential technique, for a frequency range of 1 kHz-l MHz. For axial specimens, at 10 kHz, the specific resistance, specific capacitance, and specific impedance were 16.6 k?/cm, 60.9 pF. cm-1 and 16.59/?3.65°k?·cm, respectively. Similarly, the dielectric properties, namely the relative dielectric constant, relative dielectric loss factor and dielectric dissipation factor were 688, 10.8 ×103, and 15.7, respectively. The electrical properties were found to be highly dependent on the frequency and the moisture content of bone. The bone was also found to be highly anisotropic in its electrical behavior, the impedance being lowest in the axial direction. It is shown that the differential method provides an accurate means of measuring the electrical properties of bone, avoiding stray capacitance errors.

Electric Properties of Polymers

Abstract: Some of the more important dielectric properties are dielectric loss, loss factor, dielectric constant (or specific inductive capacity), dc conductivity, ac conductivity, and electric breakdown strength. The term dielectric behavior usually refers to the variation of these properties within materials as a function of frequency, composition, voltage, pressure, and temperature.

Dielectric behaviour of cobalt-zinc ferrites

Abstract: Variation de la constante dielectrique et de tgδ avec la composition de Co x Zn 1−x Fe 2 O 4 (avec x=0 a 1)

Dynamics of helical worm‐like chains. IV. Dielectric relaxation

Abstract: Dielectric relaxation of both flexible and stiff chain polymers in dilute solution is studied on the basis of the discrete helical worm‐like chain such that an electric dipole moment is attached rigidly or with a rotational degree of freedom to each of the subbodies composing the chain. The complex dielectric constant is formulated with the dipole correlation function, which may be expressed in terms of the L=1 time‐correlation functions derived previously. Then, dielectrically active branches of the eigenvalue spectrum are identified for a given type of dipoles, and a mode analysis of them is made in order to inquire into the interaction between global and local modes. The decay behavior of the dipole correlation function is also examined numerically for various chains. A comparison of theory with experiment is made with respect to the dispersion and loss, and also the dielectric correlation time τD as determined from the loss peak. The theory cannot always well explain the asymmetry of the loss curve, e...

Dielectric properties due to crystallographic shear planes in chromia-doped rutile (TiO2)

Abstract: Dielectric properties of rutile (TiO2) doped with chromia (Cr2O3) have been measured as a function of frequency between 30 Hz and 60 kHz at temperatures between 77 and 350 K. Two types of specimen were produced. One sort was prepared by heating (001) sections of rutile in Cr2O3 pellets at 1173–1137 K for various times and then annealing them in air at 1373 K for 1 week (‘oxidized’ specimens). The other sort was prepared simply by just heating (001) sections in Cr2O3 pellets (‘as-doped’ specimens). The dielectric properties depend on the frequency of measurement. The static dielectric constant of ‘oxidized’ specimens, which was measured at 293 K, increases with sample preparation time, while that of as-doped specimens increases when the heating time is short, but it decreases and increases again at prolonged heating times. In every specimen, a relaxation peak is distinguished by an activation energy of 0–2 eV in the temperature dependence of the dielectric loss tangent or loss factor. This relaxat...

Loss Measurements of Nonradiative Dielectric Waveguide (Special Papers)

Abstract: A technique has been developed for precisely measuring the attenuation constant of the nonradiative dielectric waveguide (NRD-guide) at 50 GHz. The novelty of the present technique lies in incorporating the NRD-guide directional coupler into the measurement system and taking advantage of the total reflection of waves at the truncated end of the dielectric strip to facilitate the construction of the setup and to attain a high degree of accuracy in measurements. Measured attenuation constants were found to be about 13 dB/m for a polystyrene NRD-guide and 4 dB/m for a Teflon NRD-guide. These values indicate that the NRD-guide can be of practical use as a waveguide for millimeter-wave integrated circuits because of its low-loss nature as well as its radiation suppression capability. Calculation is also carried out in order to support measurements.

Polar glass ceramics for sonar transducers

Abstract: Glass ceramics are shown in this study to be a new class of transduction materials for application in sonar transducers. It is found that glass ceramics of Ba2TiSi2O8 have high hydrostatic voltage sensitivity, low dielectric loss, and low dielectric constant. These properties are also shown to be practically independent of pressure up to 35 MPa. The free‐field voltage sensitivity of a glass‐ceramic prototype hydrophone is higher than that based on a commonly used lead zirconate titanate ceramic element.

Low temperature study of w/o microemulsions by differential scanning calorimetry and dielectric measurements

Abstract: The temperature dependence of the dielectric constant and loss tangent in parallel with differential scanning calorimetry (DSC) were used to study the low-temperature properties of a w/o microemulsion in the concentration interval (C, mass fraction) 0024 ≤ C < 04, within the temperature range (20°C ÷ -150°C) For 0222 < C < 04 the dielectric constant exhibits, with decreasing temperature, a sharp peak centred around - 35 °C It is shown that the latter cannot be justified exclusively in terms of a Maxwell-Wagner interfacial polarization By means of DSC analysis the temperatures of the different thermal transitions occurring in the w/o microemulsion were obtained; a differentiation between samples that possess a « free water » fraction (0222 < C < 04) and those that do not (0024 ≤ C ≤ 0222) was made; the enthalpic change associated with the melting of the dodecane-oil (ΔHd) and the water (ΔHw), contained in the samples was determined against increasing concentration An enthalpic contribution around - 10 °C due to water adsorbed at the interphase region was detected superimposed on that of the dodecane (- 96 °C) Polydispersed samples were identified by means of the analysis of the frequency dependence of the dielectric loss of «liquid» microemulsions at T = 20 °C Samples exhibiting a time dependent behaviour were found in which, upon ageing, the free water Δ Hw tends to zero accompanied by the increase of the dodecane Δ Hd contribution The phenomenon was interpreted in terms of the formation of 4 H2O-molecule hydration structures on the hydrophilic groups of the surface active molecules The hydration process develops at constant surface tension at the expenses of the free water fraction of the dispersed phase The energy balance of the latter process was investigated and the « surface increment » enthalpy associated with the formation of the 4 H2O-molecule hydrated structures was estimated

Dielectric studies of poly(vinyl chloride)

Abstract: Measurements of the dielectric constant and loss factor of polyvinyl chloride (PVC) have been made over a wide range of temperature and frequency. Maxima in dielectric loss were observed at a temperature corresponding to the α or glass transition temperature and secondary β transition temperature. The sensitivity of these maxima to both frequency and thermal pretreatment was investigated. It was found that the position of the β peak on the temperature axis changed markedly with frequency, while the glass transition or α peak showed only small variations. Neither the α nor the β peak were very sensitive to thermal pretreatment, but interesting changes in the minimum between these peaks were observed. In quenched samples a distinct shoulder peak at Tβ < Ts < Tα was observed; it was possible to eliminate it by a slow cooling of the samples. The effect of plasticizer content was also studied.

Dielectric relaxation studies of some linear crosslinked and branched polymers

Abstract: Dielectric loss measurements are reported for polystyrene, crosslinked polystyrene, polyacrylamide, branched polyacrylamide, and poly(methyl methacrylate) at 1 and 10 kHz f over the temperature range −85 to +100°C. Crosslinking and branching have a pronounced effect on the dielectric relaxation spectra of polymers. The methods of preparation of these polymers and their viscosity molecular weight data are also reported.

A broad-band measuring equipment for determining the complex permittivity of liquid dielectric materials within the frequency range of 1 MHz to 1 GHz

Abstract: A technique is presented to determine the complex permittivity epsilon = epsilon '-j epsilon " by means of a coaxial line set-up for transmission coefficient measurement within the frequency range of 1 to 1000 MHz A highly sensitive broad-band vectorvoltmeter and dielectric sample cells of the cut-off variety enable precise measurements in a comparatively short time and ease of handling The cells are designed for the investigation of weakly as well as highly polar liquid dielectrics The relative error of the real part epsilon ' of the complex permittivity typically amounts to 1-2% and the absolute error of the dielectric loss angle up to 03 degrees

Application of a Dielectric Resonator on Microstrip Line for a Measurement of Complex Permittivity

Abstract: A cylindrical dielectric resonator placed on microstrip line is used for measuring the complex permittivity of microwave low-loss high epsilon/sub r/ dielectric materials. The method is based on the accurate solution of this resonator with TE/sub 01delta/ mode and is compared to the method of dielectric rod resonator with TE/sub 11/ mode. The accuracy of the both method is similar - the measurement accuraoy of relative dielectric constant is better than 0.2 percent and measurement accuracy of loss tangent is about 1·10/sup -4/.

Piezoelectric properties and dielectric losses in PVDF-PMMA blends

Abstract: Piezoelectric properties and dielectric losses have been measured in polyvinylidene fluoride (PVDF)/polymethyl methacrylate (PMMA) blends to assess the value of this class of polymers as ultrasonic transducer materials. The electromechanical coupling factor kt has been found to become vanishingly small in blends having a PMMA content of about 20% by weight. For the same blend composition, the peak of dielectric losses, which at room temperature is located in the low megahertz range, decreases only by 20%. For low PMMA content blends at room temperature, the slow decrease of dielectric losses and the slight frequency shift of the loss peak in the megahertz region are ascribed to the presence of two conjugate amorphous phases. This structure prevents much stronger effects on dielectric losses which could be expected from blending PVDF with a polymer having a high glass transition temperature, such as PMMA. PVDF–PMMA blends, therefore do not represent an attractive class of ultrasonic transducer mat...

Phase transitions and ferroelectric behavior in the Pb3(MF6)2 family (M=Ti, V, Cr, Fe, Ga)

Abstract: The atomic arrangement in Sr3(FeF6)2 determined by von der Muhll [C. R. Acad. Sci. Paris 278, 713 (1974)] differs from a structure of opposite polarity by atomic displacements of 1.3 A or less for F and 0.4 A or less for Sr and Fe. The structure is hence potentially ferroelectric, with an estimated transition temperature TC to the paraelectric state of about 1160 K: experimentally, TC=922 K. The Pb3(MF6)2 family is isomorphous with Sr3(FeF6)2 and the corresponding TC(M) has been measured as 695 (Ti), 635 (V), 550 (Cr), 740 (Fe), and 645 (Ga) K. The respective nonlinear dielectric susceptibilities are 0.010, 0.010, 0.005, 0.045, and 0.010×10−12 V−1 m. A dielectric anomaly is observed close to TC in each material at 1 kHz with a maximum permittivity e′r of 2740 (Ti), 300 (V), 2015 (Cr), 4000 (Fe), and 7800 (Ga). Dielectric losses in each material reach a minimum at the phase transition temperature.

Silicon nitride substrate

Abstract: A densified silicon nitride/magnesium oxide article which can be used as a substrate for a silicon device such as an integrated circuit chip is made by a unique process which imparts to the densified article of the combined properties of high relative density, low relative dielectric constant, low dielectric loss tangent, high thermal conductivity, thermal expansion coefficient matched to that of silicon, and a high modulus of rupture without hot pressing.

Fundamental Superstrate Effects on Printed Circuit Antenna Efficiency

Abstract: Printed circuit antennas integrated on typically used substrates such as quartz, GaAs or Si exhibit low radiation efficiency due to surface wave effects in the substrate (e.g., a GaAs substrate yields on optimum radiation efficiency of e/sub s/ /spl sime/ 28%). It is demonstrated in this paper that e/sub s/ = 100% is feasible with practical materials either by using a magnetic superstrata layer or by integrating the antennas on the lower side of a dielectric superstrata (such as GaAs), while in this case, the substrate is merely a supporting layer with lower dielectric constant. The effect of the composite layer is to eliminate surface waves, provided the layer thicknesses are chosen properly.

Correlation of Dielectric and Mechanical Damping at Low Temperatures

Abstract: When an alternating mechanical or electric load is applied, loss factors are necessary for estimating the energy dissipation or heat generation. For AC-superconducting magnets or rotating machinery with LHe-cooling this might become a non-neglegible factor of cooling costs.

The permittivity and dielectric loss of reaction-bonded silicon nitride

Abstract: Using recently developed coaxial line methods values of permittivity and dielectric loss have been determined over the frequency range 0.5 to 7 GHz for a series of reaction-bonded silicon nitride specimens in which the degree of nitridation has been varied. For fully nitrided material (having a weight gain of 62% and a volume porosity of 19%) the measured permittivity was 4.60 and was almost independent of frequency; fitting both the permittivity and loss data to the Universal Law of dielectric response confirmed that the limiting condition of lattice loss applied withn=0.98±0.02. Reduction of the degree of nitridation caused progressive increases in permittivity and loss, both of which closely approached the quoted values for pure silicon at weight gains below about 40%.

Dielectric Properties of Millimeter Wave Materials

Abstract: It is no longer necessary to use extrapolated microwave dielectric values when designing millimeter wave components, devices and systems. We are now furnishing highly accurate millimeter wave (5 mm to 1/2 mm) data on complex dielectric permittivity and loss tangent to engineers for a variety of materials such as common ceramics, semiconductors, crystalline and glass materials. For most materials the dielectric loss increases with frequency in the millimeter, unlike the microwave, is an important feature of our new data. Reliable measurements also reveal that the method of Preparation of nominally identical specimens can change the dielectric losses by many factors.

Reduction of Propagation Losses in Coplanar Waveguide

Abstract: Coplanar Waveguide (CPW) is finding increasing use in microwave and millimeter wave integrated circuits. CPW has several advantages over microstrip, but its ohmic loss tends to be larger because of the concentration of its currents near the metal edges. Two methods for reducing ohmic loss in CPW are proposed and studied using a numerical technique. It is shown that the propagation loss can be reduced by approximately a factor of four.

Deuterium effect in the dielectric losses of wheat seeds

Abstract: A detailed dielectric/gravimetric study within a frequency range from 10 kHz to 10MHz of intact H2O- or D2O-hydrated wheat seeds detects a clear isotopic effect in the dielectric dissipation. Using a Maxwell-Wagner analysis of these data, this dissipation peak can be attributed to protonic currents which are greatly enhanced by the absorbed water, in the hydration range where wheat germination occurs.