High-Resolution Detection of Rock-Forming Minerals by Permittivity Measurements with a Near-Field Scanning Microwave Microscope

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.

Cutting Edge High‐Throughput Synthesis and Characterization Techniques in Combinatorial Materials Science

“…[93] Copyright 2003, Elsevier B.V. e) Dielectric constant response images of the gneiss specimen (L-labradorite plagioclase; Px-pyroxene; I-ilmenite). [133] Copyright 2022, MDPI. f) HT screening of dielectric constant and tangent loss of a gradient spreads.…”

“…[93,131,135] Gutiérrez-Cano et al used this technique for nondestructive mapping of permittivity of rock specimens at μm scale with a dielectric constant resolution of 3% (see Figure 19d). [133] It also can be used as an HT screening tool for advanced tunable materials development applied for microwave tunable filters (see Figure 19f).…”

“…The near-field scanning microwave microscope technique is used to investigate the dielectric/ferroelectric and strongly correlated electronic materials, [131][132][133][134][135] as well as the combinatorial materials libraries. [60,93,110] The scanning evanescent microwave probe (SEMP, Figure 19a) can be used for HT characterization of electrical properties of insulators, semiconductors, and metals in a spatial resolution of 2-3 μm.…”

“…Copyright 2005, Elsevier B.V. d) Local dielectric constants of different materials tested by SEMP [93]. Copyright 2003, Elsevier B.V. e) Dielectric constant response images of the gneiss specimen (L-labradorite plagioclase; Px-pyroxene; I-ilmenite) [133]. Copyright 2022, MDPI.…”

Feasibility of Using a 300 GHz Radar to Detect Fractures and Lithological Changes in Rocks

“…Nevertheless, in order to avoid lateral spatial limitations, a near-field scanning microwave microscope has recently been proposed that measures the dielectric permittivity of minerals with a spatial resolution of tens of microns [12,13]. This sub-wavelength resolution is achieved by working in the near field.…”