John H. Grosvenor

Dielectric characterization of low-loss materials a comparison of techniques

Measurements on low-loss materials using closed and open cavity resonators, and dielectric resonator methods are presented. Results indicate that consistent measurement results can be obtained with a number of well-characterized fixtures. Uncertainties associated with each method are addressed. Measurements also were performed on materials used in previous intercomparisons.

Applicability of effective medium theory to ferroelectric/ferrimagnetic composites with composition and frequency‐dependent complex permittivities and permeabilities

High‐frequency (1 MHz–1 GHz) transmission line measurements were used to determine the composition and frequency‐dependent complex permittivities and complex permeabilities of ferroelectric/ferrimagnetic (barium titanate and a magnesium‐copper‐zinc ferrite) composites. The effective medium rules of Maxwell–Garnett give both lower and upper bounds for the effective permittivities and permeabilities and yield accurate estimates of the bulk electric and magnetic properties at low volume fill fraction of either component provided the proper host matrix is chosen. Bruggeman theory yielded the best predictive values for the permittivity and permeability over the entire composition range. In all cases these complex quantities were shown to be constrained by Bergman–Milton bounds.

Dielectric and Magnetic Measurements: A Survey of Nondestructive, Quasi-Nondestructive, and Process-Control Techniques" *

A review of the most common methods for nondestructive permittivity and permeability measurements is presented. Transmission-line techniques, coaxial apertures, open resonators, surface-waves, and dielectric resonator methods are examined. Measurements on bulk, thin materials, and thin films are addressed. Measurement fixtures that can be used as sensors are highlighted. The frequency range of applicability and typical uncertainties associated with each method are addressed.

On RF material characterization in the stripline cavity

We examine the accuracy of the air-filled stripline cavity in measuring the dielectric and magnetic properties of bulk materials in the frequency range of 150-2000 MHz. Measured data on complex permittivity and permeability for several different-sized specimens of dielectric and magnetic materials were compared with reference values obtained using other techniques of known uncertainties. Major differences were noted for both complex permittivity and permeability data, and we largely attribute these to less-than-optimal perturbation of the internal cavity fields by the material specimens under test. The technique is particularly unsuited to measuring the dielectric loss of the higher-permittivity low-loss materials due to energy scatter by the specimen under test. In order to improve measurement accuracy, we suggest guidelines on the range of specimen electric and magnetic volume needed for optimal cavity perturbation.

RF material characterization using a large-diameter (76.8 mm) coaxial air line

We report on the development of a 76.84 mm (3.025 in) diameter coaxial air line system whose purpose is to measure the dielectric and magnetic properties of bulk dielectric and ferrite materials over a frequency range of approximately 0.3 - 1500 MHz. We summarize the relative advantages and disadvantages of using large-diameter coaxial air lines for material characterization and we discuss the particular problems associated with calibrating vector network analyzers in this form of transmission line. We also present broadband measurement data on two lossy materials, including a ferrite-loaded polymer and carbon-loaded concrete.

Improved technique for measuring permittivity of thin dielectrics with a cylindrical resonant cavity

A technique for measuring the relative permittivity of thin, low-loss dielectric materials in a cylindrical resonant cavity has been developed. A thin dielectric sample, of unknown characteristics, is placed upon a thicker dielectric sample whose permittivity is well characterized. Both samples are then placed on the end plate in the cylindrical resonant cavity. In this way, the thin sample is placed in a region of the cavity where interaction with the electromagnetic fields is greater. From knowledge of the cavitys resonant frequency, dimensions of the cavity and both dielectric samples, and from the permittivity of the thicker sample, the authors are able to use iterative techniques to accurately determine the permittivity of the thin dielectric sample. A derivation and discussion of the theory used in this layered-dielectric permittivity measurement technique are provided. Measurement results at frequencies between 9 and 10 GHz confirm the accuracy of the technique. Preliminary error estimates are also given to show the worst-case uncertainties associated with this new method.<<ETX>>

Permittivity Measurements of Low-Loss Dielectric Materials at 60 GHz

The National Institute of Standards and Technology is developing a Fabry-Perot resonator to measure the permittivity at 60 GHz. The system is designed to operate in a semi-confocal configuration with the ability to adapt the system for high-temperature measurements. This talk will focus on design of the system, mode identification, and measurements of permittivity for three low-loss materials.