S. Bringhurst

Open-ended metallized ceramic coaxial probe for high-temperature dielectric properties measurements

A metallized ceramic coaxial probe has been developed for high temperature complex permittivity measurements. The probe is made of alumina and metallized with a 3.0-mil-thick layer of moly-manganese, and a 0.5-mil-thick protective coating of nickel plating. It is shown that based on carrying out the network analysis calibration procedure up to 1000/spl deg/C, and on actual dielectric properties measurements, the probe provides accurate dielectric measurements over a broad frequency range (500 MHz to 3 GHz) and for temperatures up to 1000/spl deg/C. An uncertainty analysis based on two different calibration techniques was also given to help quantify possible measurement errors.

High Temperature Broadband Dielectric Properties Measurement Techniques

This paper discusses theoretical and practical aspects of the development and implementation of various measurement techniques for high-temperature broadband microwave characterization of materials at the University of Utah. Objectives include materials measurements in the frequency range from 45 MHz to 12 GHz and for temperatures as high as 1000°C.

High-Temperature Dielectric Properties Measurements of Ceramics

This paper dicusses experimental arrangements, describes measurement techniques and presents experimental results for hightemperature broadband dielectric properties measurements of ceramics. The cavity perturbation technique and the open-ended coaxial line method are used in these experimental measurements. The design and construction details of cavities and probes are described and representative results of measurements on zirconia and alumina samples (green and sintered) are presented. Results of measurements made on insulating materials are shown. In general measurements are made in the frequency band 1 to 10 GHz and temperatures up to 1000°C.

Numerical simulation and experimental validation of RF drying

The Finite-Difference Time-Domain (FDTD) method has been used by the group to simulate a wide variety of Radio Frequency (RF) and induction-drying processes and realistic, microwave-sintering experiments. Many results were presented and some guidelines towards the effective use of the microwave and RF heating technologies of ceramic ware were developed. In this paper the authors describe an experimental effort which was used to validate the FDTD simulation results. Specifically an experimental RF dryer, Thermax Model No. T3GB operating at 25 MHz, was used to dry ceramic ware of various materials, sizes, and shapes and the temperature distribution pattern was monitored using six fiber-optic temperature probes. The measured heating patterns were then compared with the FDTD simulation results. Many of the guidelines developed using the numerical simulations were confirmed experimentally. Results from various comparisons between simulation and experimental data will be presented. Additional results from the simulation efforts illustrating possible procedures for improving the efficiency and the uniformity of RF drying will also be described.

FDTD simulations and analysis of thin sample dielectric properties measurements using coaxial probes

A metallized ceramic probe has been designed for high temperature broadband dielectric properties measurements. The probe was fabricated out of an alumina tube and rod as the outer and inner conductors respectively. The alumina was metallized with a 3 mil layer of moly-manganese and then covered with a 0.5 mil protective layer of nickel plating. The probe has been used to make complex dielectric properties measurements over the complete frequency band from 500 MHz to 3 GHz, and for temperatures as high as 1,000 C. A 3D Finite-Difference Time-Domain (FDTD) code was used to help investigate the feasibility of this probe to measure the complex permittivity of thin samples. It is shown that by backing the material under test with a standard material of known dielectric constant, the complex permittivity of thin samples can be measured accurately using the developed FDTD algorithm. This FDTD procedure for making thin sample dielectric properties measurements will be described.

Broadband, high-temperature dielectric properties measurements of thin substrates using open-ended probes

A metallized-ceramic probe has been designed for high-temperature broadband dielectric properties measurements. The probe has been used to make complex dielectric properties measurements over the frequency band from 500 MHz to 3 GHz, and up to temperatures as high as 1000/spl deg/C. We present results illustrating the use of this probe for broadband, high-temperature, dielectric properties measurements of thin samples and substrates. It is shown that by backing the material under test with a standard material of known dielectric constant such as air or metal, the complex permittivity of thin samples can be accurately measured. A 2D cylindrical FDTD code utilizing the symmetry of the probe was used for these thin-sample measurements. Results for thin (0.6 mm) alumina and sapphire samples for temperatures up to 800/spl deg/C are presented. This measurement method has important applications in the on-line characterization of semiconductor wafers.

Design and FDTD analysis of open-ended coaxial probes for broadband high-temperature dielectric properties measurements

In conjunction with ongoing research in the area of microwave processing of materials and, in particular, in the microwave sintering of ceramics, the authors found it necessary to make dielectric properties measurements at temperatures as high as 1000/spl deg/C. The authors have developed a new metallized ceramic coaxial probe for broadband, high-temperature dielectric properties measurements. Initial experience with the probe showed good experimental results in the frequency range from 500 MHz to 3 GHz, and for temperatures up to 1000/spl deg/C. To help further optimize the design of the probe, its performance was numerically simulated using FDTD. A TEM mode is excited in the coaxial feed, and the propagation, fields penetration in the sample, and the reflection coefficients were calculated using FDTD. Several probe designs were examined and the ability to make accurate and broadband measurements were examined, based on the obtained numerical results. Numerical and and graphical results illustrating some the basic guidelines of probe design, and its effective and accurate use in making dielectric measurements are presented. Parameters such as bandwidth, sample thickness, probe length, probe sensitivity to various properties of materials, and methods to increase the penetration of fields into the sample under test are discussed.<<ETX>>

Microwave dielectric measurements of ceramic composites at high temperatures

Summary form only given. The authors describe ongoing efforts at broadband, high-temperature characterization of materials at the University of Utah. For narrowband measurements at S and X bands, the cavity perturbation method is used, and the rectangular cavity designs and high-temperature measurement techniques using a fused silica sample holder and a modern network analyzer are explained. Experimental results of zirconia and alumina have been obtained for temperatures up to 1200 degrees C. Broadband measurements at high temperatures were obtained using the open-ended coaxial line technique. For these measurements, a novel probe using metallized, low-thermal expansion ceramics was designed and constructed. A simple and accurate analytical procedure to calculate the complex permittivity of the sample from the measurement of the probe admittance has been developed. Experimental results have been obtained for some ceramic samples for temperatures up to 1200 degrees C.<<ETX>>