Showing papers on "Dielectric loss published in 1968"

Losses in Microstrip

Abstract: Expressions are derived for the conductor loss in microstrip transmission lines. The formulas take into account the finite thickness of the strip conductor and apply to the mixed dielectric system. Good agreement with experimental data is obtained for rutile and alumina substrates.

Microwave Bandpass Filters Containing High-Q Dielectric Resonators

Abstract: This paper is concerned with dielectric disks used as resonators in microwave bandpass filters. For many years it has been known that modes of resonance occur in isolated dielectric bodies having air boundaries, and that very compact high-Q resonators can be achieved when /spl epsiv/ /sub r/, is high and tan /spl delta/ is low. High-purity TiO/sub 2/ ceramic material, for example, has an /spl epsiv/ /sub r/ about 100, tan /spl delta/ about 0.0001, and Q/sub u/ about 10 000. Practical applications of dielectric resonators have previously been limited by insufficient design information. Formulas are derived for the coupling coefficient between adjacent dielectric-disk resonators within a metal waveguide below cutoff. This metal enclosure is necessary for shielding and to prevent radiation loss. Comparisons between theoretical and experimental coupling coefficient values show very good agreement in each of the three bandpass configurations treated in this paper. Techniques of loop and probe coupling to the end resonators of a multiresonator bandpass filter are discussed and methods of supporting the resonators are suggested. The conclusion is made that microwave dielectric resonators offer important size reductions compared to conventional resonators of similar high Q, but that the center-frequency change of the dielectric resonators as a function of temperature is excessive for many applications. Temperature stabilization is one solution, but preferably a material should be developed having electrical characteristics similar to TiO/sub 2/ ceramic, but with at least an order of magnitude improvement in temperature sensitivity.

Piezoelectricity as a fundamental property of wood

Abstract: The piezoelectric effect in wood, i.e. the occurrence of electric polarization under mechanical stress and also of mechanical strain in an electric field, was accounted for by considering the uniaxial orientation of cellulose crystallites in fibers and their monoclinic symmetry. A shear stress in one plane, including the grain direction, produced electrical polarization perpendicular to it. The value of the piezoelectric modulus for wood was approximately one twentieth of that of a quartz crystal. The chemical treatments which transform the lattice structure from cellulose I to II or III, increased the piezoelectric modulus. However, gamma-ray irradiation up to a dose sufficiently high to decrease the molecular weight had only little influence on the piezoelectric modulus. The variation with temperature of the phase angle between sinusoidal stress and polarization showed a maximum of advanced phase around room temperature and a maximum of delayed phase at about-100°C. Dielectric and viscoelastic measurements indicated that the former was caused by the dielectric loss due to water at a temperature above freezing and the latter by the viscoelastic loss due to local vibrations of cellulose molecules. The piezoelectric polarization in wood can be utilized in technical problems such as the measurement of shock velocity in timber. The physiological meaning of the piezoelectrical effect in plants has not been investigated.

O−−-Lücken-Dipole in Alkalihalogenidkristallen

Abstract: Dielectric loss measurements are reported for KBr, KCl, and NaCl crystals containing O−− ions. The frequency and temperature dependences can be well represented by a Debye curve.

A general model for junction circulators; choice of magnetization and bias field

Abstract: The properties of nonreciprocal ferrite devices depend strongly on the ferrite properties. The dependence of several device specifications, such as insertion loss, power capability, etc., on, for instance, linewidth, dielectric loss tangent, critical field, etc., is similar for the three different groups of nonreciprocal devices. The dependence of bandwidth and insertion loss on ferrite magnetization and polarization field is specific for a special group. To investigate the latter dependence for junction circulators, a general model for that group of devices is introduced and discussed. Junction circulators consist of a number of identical resonators. These resonators, mutually coupled by means of the ferrite, are connected to the ports. The lumped element circulator is discussed qualitatively and the stripline circulator quantitatively. For the latter, ranges of magnetization and bias field are determined for operation both above and below resonance. Obtainable bandwidths are estimated.

Effect of a Metastable Precipitate on the Electrical Properties of an Li2,O-SiO2 Glass

Abstract: Glass structural differences in a 17.5 wt% (30 mole %) Li2O-SiO2 glass resulting from thermal treatments in the annealing-transformation range were studied using electron microscopy, X-ray analysis, and dc and ac electrical properties. Metastable, crystalline lithium metasilicate precipitates and subsequently redissolves prior to the appearance of the equilibrium lithium disilicate crystals. The lithium metasilicate gives rise to dielectric loss peaks in the 100 hz to 1 Mhz range which can be rationalized on the basis of the Maxwell-Wagner-Sillars heterogeneous dielectric model.

A Note on the Millimeter and Submillimeter Wave Dielectric Constant and Loss Tangent Value of Some Common Materials

Abstract: A tabulation of relative dielectric constant and loss tangent is presented for a number of common materials. Measurements were made by using an interference spectrometer to measure insertion loss and phase shift of dielectric samples.

Dielectric dispersion and its temperature variation in calcite single crystals

Abstract: The variation of dielectric constant and loss of calcite single crystals with frequency and temperature over wide ranges (102 to 2.4×1010c/s and −193 to 450 °C) in two orientations of the crystal, namely, the electric field (i) parallel to the optic axis and (ii) perpendicular to the optic axis, has been studied and the results reported. The dielectric constant at 25 °C in both orientations (E‖, 7.8 andE⊥, 8.2) is frequency-independent. The dielectric loss shows a minimum in the 105 to 108 c/s region. Dielectric constant as a function of temperature exhibits two distinct regions: frequency-independent (−193 to 50 °C) and frequency-dependent (50 to 450 °C). The temperature variation of specific conductivity can be represented by a sum of two exponentials, e.g.,\(\sigma = Ae^{ - E_1 /kT} + Be^{ - E_2 /kT}\) with the usual notation; the constants have different values in the two orientations. The intrinsic conductivity with larger activation energy (E‖ 0.91 eV andE⊥ 1.05 eV) is attributed to the movement of lattice vacancies in the crystal. The 15% larger value for the intrinsic activation energy alongE⊥ optic axis over the other orientation may be due to a probably large electrostatic interaction between the charge carriers and the lattice ions in this orientation.

The effect of hydrogen on the electrical properties of rutile

Abstract: Hydrogen in rutile has two influences on the electrical properties: Verneuil crystals contain hydrogen compensating the trivalent impurities. Excess hydrogen acts as an electron donor, thereby increasing the conductivity. Removal of hydrogen above 650°C in vacuum causes structural changes accompanied by enhanced conductivity and dielectric loss. There is also a change in the activation energy for diffusion at this temperature. Values of the coefficient of diffusion of protons in the temperature range 450-800°C in crystals of differing impurity content are presented. The position of the hydrogen, in the basal plane of the rutile lattice, is confirmed by the dichroism of the absorption. Weight-loss experiments suggest that hydrogen leaves the crystal in combination with oxygen in the proportions required to form water.

Dielectric Properties of Potatoes and Potato Chips

Abstract: SUMMARY— Dielectric properties (dielectric constant, ɛ′r; loss tangent, tans; and dielectric loss factor, ɛ″r) were determined for raw potatoes and for potato chips, using the precision slotted line technique. Measurements on raw potatoes were made at 77°F (25°C) and at frequencies of 300, 1,000, and 3,000 MHz (megahertz). Measurements on potato chips were made at three moisture levels; at 77°F (25°C), 125°F (51.6°C), and 180°F (82.2°0; and at frequencies of 300, 1,000, and 3,000 MHz. Moisture, total lipids, and nitrogen contents are reported for both the raw potatoes and the potato chips. As would be expected from their high moisture content and the presence of various dissolved salts, the raw potatoes possess extremely high dielectric values. Potato chips show a rapidly decreasing dielectric loss as moisture content is reduced; the loss values of the chips approach those of the oil used for frying them after moisture has been reduced to approximately 3% and the oil content has been increased accordingly. For finish drying of potato chips, a frequency of 3,000 MHz will result in 3–4.5 times greater power production in the chips than will the use of a frequency of 1,000 MHz (in the moisture and temperature range at which the data were obtained). However, this difference in power production is due almost entirely to the difference in frequency since the difference in dielectric loss values at the two frequencies is quite small.

Dielectric properties of polytetrafluoroethylene and tetrafluoroethylene-hexafluoropropylene copolymer

Abstract: Precision measurements of dielectric properties of polytetrafluoroethylene and copolymers of tetrafluoroethylene and hexafluoropropylene were made over a temperature range of –40 to +180°C. at frequencies of 10 Hz to 300 kHz. Polytetrafluoroethylene exhibited the typical dielectric behavior of a nonpolar substance: no dielectric loss peak was found over the experimental range of temperature and frequency. The dissipation factor remained constant, being about 2 × 10−5. Copolymers of tetrafluoroethylene and hexafluoropropylene showed two dielectric loss peaks: one occurred at about 100°C. and the other at about −20°C. There was a break point, or an abrupt bend, near 60°C. in the curve of dielectric constant versus temperature, indicating the existence of a transition point. The high- and low-temperature loss peaks correspond to the α and γ relaxations, respectively, which have been found for the mechanical behavior of this copolymer. The dielectric relaxation in the copolymer was attributed to the slightly polar nature of the perfluoromethyl side groups. The activation enthalpy and entropy are 80 kcal./mole and 180 eu for the α relaxation and 12 kcal./mole and 15 eu for the γ relaxation, respectively. The σ and γ relaxations are discussed in connection with the molecular motion of the copolymer chain.

Temporary changes in electrical properties of polymer dielectrics due to ionizing radiation

Abstract: Measurements of conductivity, permittivity, and dissipation factor on polystyrene, low-density polyethylene, poly(ethylene terephthalate), and polytetrafluoroethylene under irradiation with x-rays at exposure rates from 0004 to 400 r/sec are presented The radiation-induced anomalous conductivity as well as the induced dielectric loss are interpreted by Maxwell-Wagner polarization due to radiation imbalance in surface layers of the specimen The nature of radiation-induced steady-state conductivity is also discussed

A Quasi-Optic Technique for Measuring Dielectric Loss Tangents

Abstract: A method for measuring dielectric loss tangents is described that combines coherent optical resonator techniques with conventional microwave techniques to yield very high measurement accuracies. A very important feature of the technique is that the equation relating tan ? to the experimentally measurable quantities is an algebraic expression instead of a transcendental equation. The method basically consists of perturbing a microwave confocal resonator with a dielectric sheet placed normal to the axis of the resonator. The change in Q and the change in cavitylength necessary to restore resonance can then be related to the loss tangent of the dielectric. For the general case, where the dielectric is placed at any location along the axis of the resonator, the working mathematical equation is a complex transcendental expression. However, if the dielectric sheet is constrained to be at the center of the resonator and each reflector is moved inward an equal amount to restore resonance, then the equation simplifies and is no longer transcendental. These constraints are easily satisfied experimentally. The technique has been used to measure the loss tangents of several common dielectrics at 35 GHz and the results are presented.

Effects of Ultraviolet Irradiation on the Properties of Evaporated Silicon Oxide Films

Abstract: The optical and dielectric properties of silicon oxide films formed by reactive evaporation of silicon monoxide are investigated. The films are prepared at a deposition rate of 4 A/sec in 1×10−4 Torr oxygen. The optical absorption of the films is found to increase with increasing substrate and source temperatures; these variations are consistent with previously reported chemisorbed oxygen and gas‐phase oxidation film‐growth mechanisms. Post‐deposition exposure to uv radiation affects both the optical and dielectric properties of these films. Optical absorption in the 200 to 400‐mμ wavelength region is essentially eliminated by 1 h irradiation for films deposited at 145°C or less; a residual absorption is evident for films prepared at a higher substrate temperature. The magnitude of the dielectric loss and relative dielectric constant, the variation of the dielectric loss and dielectric constant with frequency, and instabilities of the dielectric properties are decreased by the uv treatment. For example, a...

Dielectric losses in solids at cryogenic temperatures

Abstract: Measurements were made of the permittivity and loss tangent of polyethylene, poly(4-methyl pentene-1), polyethylene terephthalate, polyvinyl chloride (containing 33% tritolyl phosphate), poly-ω-undecanolactum, cellulose triacetate and insulating paper for temperatures between 4.2 and 295°K over a frequency range from 47Hz to 89.5kHz. In polyethylene and poly(4-methyl pentene-1), a single small absorption region (maximum value, 1-2 × 10 -4 was observed in the temperature range 150-200°K. The loss tangent of polyethylene decreased to a constant value (~2 × 10 -5 ) near absolute-zero temperature, whereas, in the case of poly(4-methyl pentene-1), below 70°K it increased with increasing frequency and decreasing temperature. With the exception of polyvinyl chloride, which did not exhibit any distinct absorption regions, the remaining materials investigated possessed one or more loss regions with a maximum loss tangent between 4 × 10 -3 and 3 × 10 -2 . The peaks occurred in the temperature range 150-300°K. The loss tangent of these materials decreased to 1-3 × 10 -4 as the temperature was reduced to 4.2°K, with the exception of poly-ω-undecanolactum, for which it was 3 × 10 -5

The Design of a Dielectric Spectrograph

Abstract: The design and principle of operation of a transistorized dielectric spectrograph operating at a frequency of 1650 ±1 MHz are presented. The apparatus has high sensitivity and can measure the dielectric constant to a relative uncertainty of 1×10-7 and the loss tangent to about 2×10-7. It can be used up to pressure ranges of 100 atm or better. The apparatus is particularly useful for the quick measurement of very small dipole moments (less than 1 Debye) to an accuracy better than 1 percent. The results for mixtures of helium with 1) carbonylsulfide, a linear molecule, 2) carbontetrafluoride, a spherical top, and for 3) pure nitric oxide, a diatomic molecule, are briefly presented.

Dielectric loss of poly(4-methyl pentene-1) at cryogenic temperatures

Abstract: The loss-tangent of aged samples of poly(4-methyl pentene-1) have been measured within the temperature range 2.5?295° K and frequency range 229Hz?21.5kHz. These results have been compared with published results made on a new sample of the polymer. The nature of the loss tangent and the number of absorption regions depended on the age of the polymer. The aged samples exhibited absorption regions at temperatures of about 250, 150 and 4°K; the maximum loss tangent in each region was about 1?5 × 10?4. The highest temperature region was not observed in the new sample and appeared to be due to oxidation. The other regions were exhibited by the new sample, and both appeared to be due to the side group of the polymer. The loss tangent in these regions decreased with increasing age; an effect which seemed to be due to increased crystallinity. During 18 months aging, the increased crystallinity increased the activation energy of the lowest-temperature loss region from 2.2 to 10.3cal/mol, increased the most probable relaxation time from 9 ?s to 27 ?s but did not affect the distribution of relaxation times.

The reflection coefficient of a TEM mode symmetric parallel-plate waveguide illuminating a dielectric layer

Abstract: Reflection coefficient of symmetric parallel plate waveguide operating in TEM mode illuminating lossless dielectric layer, using wedge diffraction and geometrical optics methods