Loss Tangent Measurements Research Articles

Comments on "Measurement of Microwave Loss Tangent by Means of Microwave Resonator Bridge" [Letters

In the above paper, Kneppo and Weis claim that the microwave resonator bridge (MRB) is a new and highly sensitive method for measuring dielectric losses of materials. Contrary to their belief, the principles of measurement are not new but have already been reported in [1] and [2]. Especially, the system arrangement described in [2] is the same as that of MRB, except that the former uses a shutter in tandem with a matched termination as a reference load of the bridge, while the latter uses a reference resonator. Thus the point in question is whether or not this replacement of the reference load improves the sensitivity of the bridge.

Importance of the Massa correction for loss tangent measurements on the rheovibron

Importance of the Massa correction for loss tangent measurements on the rheovibron

Measurement of Microwave Loss Tangent by Means of Microwave Resonator Bridge (Short Papers)

A new cavity method of measurement of microwave loss tangent of a low-loss material is described. The method consists of the comparison of the reflection coefficient of the resonator filled with dielectric with the reflection coefficient of the reference resonator by means of microwave resonator bridge. Basic theoretical relations of a simplified resonator bridge are derived, a fundamental scheme of the measuring set is given, and some results of verified measurements presented. The obtained results confirm the suitability of the proposed method, especially for measuring low-loss dielectric materials, since the principle of comparison renders the method highly sensitive to small parameter differences of the resonator brought about by the measured sample.

Two‐component polymer systems: Physical properties as related to compatibility and interaction

AbstractThe physical properties of mechanical blends of poly (vinyl chloride) (PVC) with ethylene‐vinyl acetate copolymers (EVA) and with acrylonitrile‐butadiene copolymers (NBR) have been studied using light scattering. gas permeability, density, and dynamic‐mechanical (loss tangent) measurements for thin films. The data show that the PVC/EVA blends are not compatible at 45% VAc content in EVA. A “phase inversion” is indicated at 5‐7 wt‐% EVA. EVA containing 65% VAc interacts more with the PVC component and shows no indication of phase inversion. A mixed phase of PVC/EVA‐65 is formed with higher measured density than calculated, assuming additivity. NBR containing increasing amounts of AN (21.7, 29.6, and 41.6 wt‐%) shows increasing compatibility with PVC due to interaction. For 50:50 blends of PVC/NBR the measured densities are 0.033, 0.050, and 0.053 g/ml higher than the calculated values for the three NBR samples. There are some indications of a phase inversion at NBR contents of 5‐7 wt‐%.

The influence of crystallinity on the beta‐transition in poly(vinyl chloride)

AbstractThe effect of changes in crystallinity on the β‐transition in poly(vinyl chloride) was studied by dynamic mechanical measurements of loss tangent (tan δ) and storage modulus (E′) over the temperature range −160° to 85°C. Four frequencies were covered, 3.5, 11, 35, and 110 Hz. The data presented demonstrate that crystallinity has a significant influence on the relaxation processes involved in the β‐transition. The restrictions on segmental mobility imposed by crystallinity are most pronounced in the region between Tβ and Tg, with Tβ tending to shift to lower temperatures, Tg shifting to slightly higher temperatures, the magnitude of tan δ decreasing, and engineering tensile strength increasing. Our data also show that individual PVC resins have mechanical and physical properties which differ enough so that comparisons which are often made between them may be inconclusive. Moreover, the properties of one resin may be more sensitive to thermal treatment than those of another. We are continuing this study to establish correlations between the observed trends and other important mechanical properties such as impact strength, toughness, tensile, and compressive strength.

Low-temperature dielectric relaxation in polyethylene

The technique due to Vincett has been developed to extend previous measurements of the dielectric loss tangent of polyethylene at cryogenic temperatures upwards in frequency to 100 MHz. A second relaxation peak, centred at 4 MHz, found in oxidized polyethylene is both broader and larger than the well-documented peak at 3 kHz. The dielectric loss is changed by steaming in D 2 O and H 2 O vapour at elevated tempera­tures. In all cases the 3 kHz relaxation is removed. Steaming in D 2 O moves the 4 MHz peak to 30 kHz and subsequent steaming in H 2 O restores it, indicating that there is an interchange of labile hydrogen and deuterium atoms at the site of the dipoles. Subsequent drying in vacuo of polyethylene treated in D 2 O also partially restores the 4 MHz peak, suggesting a further secondary diffusion process. The magnitude of the loss in Rigidex 50 (high-density polyethylene) shows little temperature variation between 1.5 and 4.2 K, while the frequency of maximum loss varies linearly with temperature for the 30 kHz peak; there is, however, a small deviation from linearity at 1.5 K for the 4 MHz peak. The results are analysed in terms of phonon-assisted tunnelling of a particle between two nearly-equivalent potential wells, using exact solutions of Pauling’s cosine model. Tentative estimates of the parameters of the model indicate that the results can be explained by 180° rotation of the proton in a dipolar group of bond length 0.11 nm.

Analysis and Evaluation of a Method of Measuring the Complex Permittivity and Permeability Microwave Insulators

Theory and experimental results are presented to show the possibility of using a resonant post technique for characterizing dielectric and magnetic materials at microwave frequencies. Results of the temperature dependence of the relative dielectric constant of nonmagnetic materials with /spl epsilon//sub r/, varying from 4 to 60 are presented and also loss tangent measurements at room temperature. The complex permittivity and permeability of a number of garnet materials has also been measured with 4/spl pi//spl gamma/M/sub s/ / /spl omega/ varying from 0.25 to 0.8. The measured real part of the permeability is in good agreement with the theoretical predictions of Schlomann and the imaginary part of the permeability agrees with measurements by Green et al. on similar materials.

Dielectric properties of polymethylsorbate

Measurements of dielectric constant and loss tangent were performed on the tritactic highly crystalline polymer, polymethylsorbate. In the frequency range 33 Hz-100kHz and temperature (100-460 K) explored, two distinct relaxation processes were observed. The high temperature process is ascribed to segmental motions of the molecular backbone of the polymeric chain, whilst the low temperature process is associated with relaxation of the orientational polarization of the side groups. The experimental data can be fitted with the Fuoss-Kirkwood equation.

Measurement of Dielectric Constant and Loss Tangent in Materials Having Large Dielectric Constants (Correspondence)

Measurement of Dielectric Constant and Loss Tangent in Materials Having Large Dielectric Constants (Correspondence)

Technique for Measuring Dielectric Loss Tangent

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Low frequency dielectric losses in thin films of NaCl and NaBr

Abstract Measurements of permittivity and loss tangent in the frequency range 0.01 to 1000 c/s have been made on thin polycrystalline films of sodium chloride and sodium bromide. Two regions of dielectric dispersion have been found to exist, having loss tangent maxima typically near 1 c/s and 0.003 c/s at room temperature. The activation energies associated with these peaks are respectively 0.9±0.2, 0.95±0.1 for NaCl, and 0.7±0.1, 1.0±0.1 for NaBr. Permittivity values exceed 104 at high temperatures and low frequencies. It is proposed that the results may be interpreted in terms of two interfacial polarization mechanisms, which involve the blocking of cation vacancies, firstly at intercrystalline boundaries, and secondly at the electrodes, the latter process predominating at sufficiently low frequencies.

Permittivity and loss tangent of pyrolised polyacrylonitrile fibre

Microwave absorbers are used to reduce the power scattered in free-space determinations to a negligible level. In this letter the results of permittivity and loss-tangent measurements on absorbing materials of pyrolised polyacrylonitrile fibres are reported.

Microwave measurement of permittivity and tan δ

A method of measuring the permittivity and loss tangent of dielectric specimens at 9375 Mc/s over a temperature range 20–700°C is described. Circular specimens 0.900in in diameter and λ/4 or 3λ/4 thick are measured in a 0.900in-diameter silver specimen chamber, using a slotted line, and in circular waveguide. The method is based on the short-circuited-line method and allows for the gaps produced by the differential expansion of the chamber and specimen and the variation in wavelength along the waveguide due to expansion.The effect of errors in the measurements is given. Typical measurements of permittivity and loss tangent of alumina and beryllium oxide specimens are given.

Dielectric Constant Ferrites and Loss Tangent of Microwave at Elevated Temperatures

Experimental data are given on the effect of elevated temperature on the dielectric properties of ferrites intended for microwave applications. Measurements were made at X band. The real part of the dielectric constant generally increases slowly with temperature, the maximum temperature coefficient observed being 300 parts per million per degree C. The dielectric loss tangent also generally increases with temperature. Measurements were made in a rectangular waveguide cavity, using a modified perturbation technique. It is shown that the simple perturbation technique may cause an appreciable error in the measurement of the real part of the dielectric constant. The effect of the finite resistivity of the cavity walls and the effect of the cavity irises on the measurement of the dielectric loss tangent, are also considered.

A Microwave Technique for the Measurement of the Dielectric Properties of Soils (Correspondence)

During a recent investigation of antennas mounted flush with the earth, it was necessary to measure the dielectric properties of soil. Many different techniques for the measurement of dielectric constants and loss tangent have been developed. These techniques generally fall into two categories: those which utilize transmission through a sample and those which use the reflection from the sample. The particular technique employed is modified to suit the range of parameters being measured and the physical characteristics of the sample. In general, a measurement that provides an accurate determination of dielectric constant is relatively insensitive to variations in loss tangent and vice versa. The technique described here utilizes both types of measurements to find in a practical manner the dielectric constant and loss tangent of relatively moist loamy soil at microwave frequencies.

Recent developments in 50 c/s bridge networks with inductively coupled ratio arms for capacitance and loss-tangent measurements

It is shown that considerable advantage may be obtained from the use of bridge networks, for dielectric measurements, which are based on ampere-turn ratio arms. Portable bridges for use at voltages up to 30kV are described, together with a general-purpose 50c/s bridge.

Properties of Polyvinylidene Fluoride. I. Dielectric Measurements

Dielectric constant (K) and loss tangent (tan δ, the dissipation factor) measurements on the plastic polyvinylidene fluoride have been made over the frequency range 50 cycles to 9800 Mc at room temperature. Pronounced anomalous dispersion in K and a peak in tan δ near 10 Mc were observed. Theoretical and practical applications of the data are briefly mentioned. This material has an unusually high dielectric constant and is quite lossy, especially when compared to the chemically and structurally related plastics polyethylene and polytetrafluoroethylene.

Research and Test Apparatus

The Boeing Aero‐Space Research Division, Seattle, 24, Washington, U.S.A., has recently developed an extremely accurate resonant cavity X‐band dielectrometer for measuring the electrical behaviour of radomes and antennae covering materials at temperatures up to 2,700 deg. F. This new device, a third‐generation version of two earlier similar instruments, measures dielectric constant to within 1 per cent, and can also measure loss tangent. Temperature limits for continuous exposure of most current refractory dielectrics without serious electrical degradation are generally in the neighbourhood of 1,500 deg. F.

Rapid Measurement of Dielectric Constant and Loss Tangent

The problem of evaluating dielectric constant and loss tangent by the short-circuited-waveguide technique has been encountered continually in recent years in the study of artificial dielectric media and radome materials. In general, practical measurements have involved materials with low loss and dielectric constants less than 10. The analytical method normally applied to data on such materials requires laborious computation. The available graphical methods have not completely eliminated computation and have provided answers of unsatisfactory accuracy. The present paper describes rapid graphical techniques for evaluating dielectric constant and loss tangent from the quantities normally measured with the slotted line, using samples of arbitrarily chosen length. It begins with equations previously derived for the case of low-loss media. By use of a new parameter, the relationship between dielectric constant and the measured shift in standing-wave minimum is plotted in such a way that all possible values of dielectric constant within any predetermined range are read directly from the graph with no computation whatsoever. A graph can be readily prepared to apply over a full range of frequency to all sizes of rectangular waveguide.