A New Stand-Alone Microwave Instrument for Measuring the Complex Permittivity of Materials at Microwave Frequencies

Abstract

This paper reports the development of a stand-alone and portable instrument designed to measure the complex permittivity of dielectric materials at microwave frequencies. The equipment consists of an in-house singleport vectorial reflectometer and a resonant coaxial bi-reentrant microwave cavity where the material under test is placed inside a Pyrex vial, making the device appropriate for measuring liquids, semi-solids, powders and granular materials. The relation between the dielectric properties of the involved materials and the cavity resonance has been solved by numerical methods based on mode-matching and circuit analysis. In order to increase the measurement range, so that low to high loss materials can be characterized in the same cavity, the effect of the coupling network is de-embedded from the resonance measurements. The performance of the newly devised instrument is evaluated by error/uncertainty analysis and comparative studies with other wellestablished instruments and methods. Errors lower than 2% in the dielectric constant, and 5% in the loss factor, are found. This simple, portable, affordable and robust device could help non-specialized personnel to accurately measure dielectric properties of materials used in a wide range of microwave applications.

Permittivity Measurements for Cypress and Rockrose Biomass Versus Temperature, Density, and Moisture Content

“…This standalone equipment implements a resonant coaxial bi-reentrant microwave cavity, where the material under test is placed inside a vial and the complex permittivity is obtained by using numerical methods based on mode-matching and circuit analysis. Although resonant techniques are usually preferred for low-loss materials, the technique employed by DKV includes the de-embedding of the feeding network to be suitable for high-loss materials [ 22 ].…”

“…Additionally, there is a wide extension of literature containing data with the electrical properties of materials at different frequencies. Available techniques can be divided into resonant and non-resonant [22]. Resonant methods can also be subdivided into resonant cavities, open resonators, and dielectric resonators [23].…”

High Temperature Dielectric Properties of Iron- and Zinc-Bearing Products during Carbothermic Reduction by Microwave Heating

“…These measurements were carried out with microwave equipment specifically designed for very accurate determination of dielectric properties of particulate materials at room temperature. The samples were placed inside a standard 1 mL pyrex tube and the equipment reported in [22] was used. It provides an accuracy of approx.…”

Evidence of a new phase in gypsum–anhydrite transformations under microwave heating byin situdielectric analysis and Raman spectroscopy

“…1% for the dielectric constant and 2-5% for the loss factor). 64 Dielectric measurements were based on the resonance frequency shift and the quality factor of the microwave cavity with the sample inside. The complex permittivity of the sample was calculated based upon the structure's electromagnetic model and a numerical procedure controlled by Labview software.…”

“…The complex permittivity of the sample was calculated based upon the structure's electromagnetic model and a numerical procedure controlled by Labview software. 64 For the experiments, milled gypsum (o50 mm grain size) was prepared, and subsamples were heated in a conventional electric furnace at selected temperatures, as follows: 140 1C (30 min) to obtain bassanite, 250 1C (30 min) for g-anhydride, 550 1C (30 min) for b-anhydride, and 1200 1C (30 min) to obtain a-anhydride. Cooled samples were stored in a closed dry environment until they were placed in a standard 1 mL glass vial for the dielectric measurements.…”