Abstract
The identification of the minerals composing rocks and their dielectric characterization is essential for the utilization of microwave energy in the rock industry. This paper describes the use of a near-field scanning microwave microscope with enhanced sensitivity for non-invasive measurements of permittivity maps of rock specimens at the micrometer scale in non-contact mode. The microwave system comprises a near-field probe, an in-house single-port vectorial reflectometer, and all circuitry and software needed to make a stand-alone, portable instrument. The relationship between the resonance parameters of the near-field probe and the dielectric properties of materials was determined by a combination of classical cavity perturbation theory and an image charge model. The accuracy of this approach was validated by a comparison study with reference materials. The device was employed to determine the permittivity maps of a couple of igneous rock specimens with low-loss and high-loss minerals. The dielectric results were correlated with the minerals comprising the samples and compared with the dielectric results reported in the literature, with excellent agreements.
Highlights
Identifying the minerals that constitute rocks is a fundamental task in earth sciences, as well as in other engineering and industrial applications
This paper describes the use of a near-field scanning microwave microscope with enhanced sensitivity for non-invasive measurements of permittivity maps of rock specimens at the micrometer scale in non-contact mode
The scientific literature reveals a large number of alternative techniques for this identification process, such as laser-induced breakdown spectroscopy (LIBS), scanning electron microscope supported with energy dispersed spectroscopy (SEM/EDS), or an electron probe microanalyzer (EPMA) [4,5,6,7]
Summary
Identifying the minerals that constitute rocks is a fundamental task in earth sciences, as well as in other engineering and industrial applications. The development of an NSMM device able to determine permittivity maps at the submicrometric scale without contact between the sample and the probe would improve the applicability of this technology in the rock industry for predicting the heating patterns of samples to be processed under microwave irradiation. This device would be interesting to use as an automated system to reduce times in other industrial applications, such as drill core logging, widely used for geological exploration in mining or geotechnics, for lithology, mineral identification, or structures identification [59,60,61]. The NSMM sensor was employed to determine the permittivity maps of some representative specimens of ornamental rocks and compare the permittivity results with those reported in previous works
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