Study of the Dielectric Properties of Artificial Sweat Mixtures at Microwave Frequencies

Abstract

Analysis of sweat is of interest for a variety of diagnosis and monitoring applications in healthcare. In this work, detailed measurements of the dielectric properties of solutions representing the major components of sweat are presented. The measurements include aqueous solutions of sodium chloride (NaCl), potassium chloride (KCl), urea, and lactic acid, as well as their mixtures. Moreover, mixtures of NaCl, KCl, urea, and lactic acid, mimicking artificial sweat at different hydration states, are characterized, and the data are fitted to a Cole–Cole model. The complex dielectric permittivity for all prepared solutions and mixtures is studied in the range of 1–20 GHz, at temperature of 23 °C, with ionic concentrations in the range of 0.01–1.7 mol/L.

Coplanar Waveguide Based Sensor Using Paper Superstrate for Non-Invasive Sweat Monitoring

“…CPW lines have demonstrated higher sensitivity in dielectric properties extraction and material characterization compared to microstrip and slot lines [12,18,22,24,[29][30][31][32]. Normally, microstrip-based structures are used in resonance-based sensors due to the sensitivity of the microstrip gap.…”

“…This could help in diagnosis of dehydration and CF through sweat. Among major sweat electrolytes [14,23,24], NaCl has been proved to have the dominant effect in changing electrical properties of sweat over the other components [23,24].…”

“…These values match concentration of the samples prepared for measurements and representing different hydration states. Usually, the concentrations of NaCl in sweat for normal and dehydration states are 0.01 and 0.1 mol/L respectively [23,24]. Moreover, a concentration higher than 0.06 mol/L is an indication that cystic fibrosis is a likely diagnosis [3].…”

“…Recently microwave-based sensors offer a non-invasive solution to characterize biofluids [14][15][16][17][18][19][20][21][22][23][24]. Body fluids with different electrolytic concentrations can result in different losses and hence attenuation of electromagnetic waves.…”

“…This includes tracking concentrations of NaCl [14,15,[21][22][23], glucose [16][17][18][19][20][21], KCl and CaCl [22]. The distinctive dielectric properties of biofluids could help in monitoring kidneys status through urine [22], diabetes through glucose levels [17][18][19][20]25,26], dehydration through sweat [23,24,27] and blood [28]. Among different sensors reported for tracking electrolytes [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27], sodium chloride (NaCl) results in the largest recorded variations with changing hydration states [23,24].…”