Dielectric characterization and modelling of aqueous solutions involving sodium chloride and sucrose and application to the design of a bi-parameter RF-sensor

Abstract

This paper reports on dielectric properties of ternary mixtures involving sodium chloride (NaCl) and sucrose (C12H22O11) dissolved into water (H2O). Broadband electromagnetic characterizations of such mixtures at various concentrations were performed, evidencing a dual behavior made of conductive effects at low frequencies and dipolar relaxation at microwave frequencies. Conductive and dielectric properties resulting from these both effects were integrated into predictive models for variations of Cole–Cole model parameters. Based upon this modelling, an innovative microwave-based sensor able to retrieve concentrations of both sodium chloride and sucrose in ternary aqueous solutions was introduced, designed, realized and assessed. The proposed sensor shows an error lower than 5.5% for concentration ranges of 0 to 154 mmol/L for sodium chloride and 0 to 877 mmol/L for sucrose.

Noninvasive Glucose Sensing in Dielectrically Equivalent Multilayer Skin Phantoms

“…First, the presence of a lot of electrolytes increased the relative permittivity and dielectric loss below 1 GHz due to the resonance motion of ions which strongly absorb radio waves. 27 Second, a lot of glucose tended to slightly decrease the permittivity and increase the dielectric loss below 1 GHz. Finally, covering the hydrogel with paraffin paper, hydrogel + paper (w/NaCl and glu), significantly decreased the dielectric constant and dielectric loss and induced dielectric constant inflection points near 0.5 and 5 GHz, as observed in real skin.…”

“…Here, 20% gelatin gels composed of water or interstitial fluid (glucose 0 or 100 mM) are expressed as hydrogel (w/o NaCl), hydrogel (w/NaCl), and hydrogel (w/NaCl and glu). First, the presence of a lot of electrolytes increased the relative permittivity and dielectric loss below 1 GHz due to the resonance motion of ions which strongly absorb radio waves . Second, a lot of glucose tended to slightly decrease the permittivity and increase the dielectric loss below 1 GHz.…”

“…Minimally invasive measurements can be made with microneedle patches − or implantable sensors , consisting of glucose-responsive materials such as glucose oxidase ,, or phenylboronic acid gel. − Although securing enough glucose selectivity is a challenging issue, noninvasive measurements using electromagnetic waves, − ultrasonic waves, and magnetic resonance have great potential to liberate patients of the above-mentioned burden. In particular, gigahertz-band electromagnetic waves (microwaves) that penetrate the skin can be used to measure glucose in aqueous solutions, − saline solutions, − and hydrogels, − as well as in animals and humans. , In addition, there are various means of radiating radio waves, for example, open-ended coaxial probes, split-ring resonators, , microstripe antennas, patch antennas, cavity sensors, coplanar sensors, and multimodality analysis . Biomimetic homogeneous hydrogel phantoms − made of, for instance, gelatin, agarose, poly­(methyl methacrylate), and flour can be used in combination with computer simulations , for validation before the experiments are conducted on actual organisms.…”

“…Here, the skin is not a uniform tissue but rather is multilayered consisting of the stratum corneum, epidermis, and dermis with sweat glands or moles. Its appearance differs, depending on its location on the body. − Thus, making complex and well-reproduced skin phantoms, such as parafilm-attached gels, have a role in the analysis of skin responses to physical stimuli by perforation and neutron beams and in the analysis of chemical compositions such as glucose by microneedles. , In addition, simulations of complex structures with cancer embedded in the skin enable tumor exploration. − However, the microwave-based glucose sensing methods developed so far have been mostly for uniform materials rather than for multilayer structures, − and some phantoms suffer dielectric loss differences below 1 GHz, making perfect dielectric matching difficult; the parafilm-gel phantom also needs further adjustments for radio waves. Therefore, noninvasive glucose sensing requires a multilayer skin phantom for microwaves and an analysis method for detecting slight amounts of glucose in a complex skin environment.…”

Sensor de glucosa biocompatible basado en Qu con resonador de microondas en microstrip invertida

“…En efecto, este parámetro es habitualmente empleado en otros escenarios de medida, como por ejemplo la caracterización dieléctrica [18]. Recientes estudios han demostrado sus potencialidades incluso para la medida multiparámetro [19], cosa que permite desarrollar estrategias híbridas de medida multicomponente en el entorno biológico [20].…”