Howard E. Bussey

Dielectric Measurements in a Shielded Open Circuit Coaxial Line

A coaxial transmission line terminated by a shielded open circuit is convenient for dielectric measurements over a frequency range from quasi-static to microwave in a single sample holder. The transmission line analysis including the open circuit termination covered by lossy dielectric is outlined. Examples of measurements of known liquids are given. Errors may arise because the support bead of a coaxial connector may excite various-higher modes depending on the perfection of the symmetry and on the product frequency times refractive index of the sample. Criteria are given for the onset of higher modes.

Method for measuring complex permeability at radio frequencies

An established method for measuring complex rf magnetic permeability is based on the change in inductance and resistance of a coaxial transmission line upon insertion of a sample toroid. It is not necessary to wind coils on the toroid or correct for geometric demagnetization factors. The use of modern commercial impedance analyzers, as described in this paper, makes measurements from 1 kHz to 1 GHz particularly easy, fast, and accurate.

Measurement and Standardization of Dielectric Samples

The selection of a material suitable for use as a standard of dielectric properties at microwave frequencies is discussed, and tests are described which indicate that a glass and a glass ceramic are satisfactory for such standards. The probable accuracy of measurement of the real part of the dielectric constant is estimated at ± 0.3 per cent. Loss measurements are discussed. A correction is developed for the error resulting from the small airgap often present around the sample in transmission-line measurements. The effects of humidity and temperature variations are examined, and preliminary results of measurements to 800°C are given.

Cavity Resonators for Dielectric Spectroscopy of Compressed Gases

Convenient, tunable, sealed‐off cavity resonators are described at frequencies of 1, 2, 9, and 24 kMc, for use with internal pressures up to 1000 psi. The modes of oscillation employed were TE01n, TE11n, and TM01 hybrid, all in a circular cylinder. A convenient method for sealing an iris, applicable over a wide‐frequency range, is to insert a tapered Teflon plug. A Kovar‐glass seal for coaxial lines is described that provides a good impedance match in a 50‐ohm line. The measuring procedure is described. Accuracy of dielectric loss measurements was increased by calibrating the loss changes of the cavity arising from reresonating it upon admission of lossless gas.

Ferromagnetic Resonance Relaxation, Wide Spin‐Wave Coverage by Ellipsoids

The role of degenerate spin‐wave coupling in ferromagnetic resonance (FMR) losses has been studied as a function of sample shape. Measurements of linewidth ΔH and peak absorption intensity s″ both show that FMR loss above the 90°, k→0 limit of the spin‐wave spectrum is much less than within the spectrum. An investigation of unsymmetrically magnetized spheroids, i.e., with the external field H0 not along the symmetry axis revealed that there are regions of the spin‐wave spectrum which can be reached by more than one sample shape and that in these regions of overlap the different shapes yield different values of ΔH and s″. A similar result can be calculated from the usual equation of motion using either Landau‐Lifshitz or Bloch‐Bloembergen damping. (The asymmetric case has not yet been treated by the spin‐wave model.) Despite the strong variations of ΔH and s″, the gyromagnetic ratio changed less than 1% under all variations of shape and orientation. The variable shape technique gives greater coverage of th...

Polycrystalline Spin Wave Theory of Ferromagnetic Resonance Compared with the Tilting Experiment

Schlomanns spin wave theory of polycrystalline ferromagnetic resonance has been tested in detail using the tilting method reported earlier. Among the quantities measured were the linewidth ΔH, and the maximum value of the imaginary part of the effective susceptibility (χm″)eff. The measurement method is equivalent to measuring asymmetric (Nx≠Ny) ellipsoids and thus, introduces another shape dependence in addition to that due to spin waves. Direct comparison with the symmetric (Nx=Ny) form of the theory is inaccurate. A proper comparison can be made in two ways: (1) generalizing the theory to include the Nx≠Ny case and then using the data directly, (2) transforming the data and then comparing with the Nx=Ny theory. Both comparisons are reported and their equivalence is demonstrated.It is concluded that Schlomanns theory does not fit the data within the spin wave (SW) manifold. It is suggested that the theory of Sparks may provide a better fit. The difference between coupling models seems to be the basic ...

Cavity resonator dielectric measurements on rod samples

The aim of our research is to make a convenient and accurate resonant cavity dielectric measuring system for samples in the shape of a small rod or filament. The use of a circular TM OlO mode for rod samples is well known (1) but is not always so convenient because the sample changes the cavity frequency, which may necessitate re-matching of several parts of the system. This mode is, however, very useful at frequencies of the order of 1000 Mc, or when the rod is very small. We have increased the utility of this mode by giving a hole correction for the hole through which the sample is inserted (2).

Amplitude, Scale, and Spectrum of Refractive Index Inhomogeneities in the First 125 Meters of the Atmosphere

An extensive series of observations was obtained with two refractometers and meteorological equipment installed on various levels of a 128-meter tower at the Brookhaven National Laboratory, Long Island, New York. One of the refractometers was equipped with a multiple cavity unit for the study of correlation between two positions in the horizontal direction. The errors arising from the exposure of the cavity to the atmosphere and its ventilation were investigated. The amplitude of the refractive index variations could be correlated with various meteorological conditions. From the experimentally determined cross-correlation coefficient, and assuming that its variation with distance is given by the exponential (Taylor) form, scales in the neighborhood of 60 meters were obtained. A crude analysis of the data indicated that the intensity of the refractive index inhomogeneities varied, on the average, as the 1.6 power of their size.

Accurate Microwave Wavemeters with Convenient Calibration Tables

Accurate and convenient microwave cavity wavemeters are described that are suitable for many precise physical measurements. High Qs were attained by refined construction techniques. At 9000 Mc a precision of 0.02 Mc was obtained. The absolute accuracy also may be very high after strains in the metal have stabilized. A calibration table containing 104 entries, easily formed by means of a high speed computer, makes the wavemeters convenient to use. The curve fitting method, accurate to one in 106, is described.

Correction to “dielectric measurements in a shielded open circuit coaxial line”

A coaxial transmission line terminated by a shielded open circuit is convenient for dielectric measurements over a frequency range from quasi-static to microwave in a single sample holder. The transmission line analysis including the open circuit termination covered by lossy dielectric is outlined. Examples of measurements of known liquids are given. Errors may arise because the support bead of a coaxial connector may excite various-higher modes depending on the perfection of the symmetry and on the product frequency times refractive index of the sample. Criteria are given for the onset of higher modes.