Conformal and Disposable Antenna-Based Sensor for Non-Invasive Sweat Monitoring.

Angie Eldamak,Elise Fear

doi:10.3390/s18124088

Angie Eldamak, Elise Fear

Open Access

https://doi.org/10.3390/s18124088

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Abstract

This paper presents a feasibility study for a non-wearable, conformal, low cost, and disposable antenna-based sensor for non-invasive hydration monitoring using sweat. It is composed of a patch antenna implemented on a cellulose filter paper substrate and operating in the range 2–4 GHz. The paper substrate can absorb liquids, such as sweat on the skin, through two slots incorporated within the antenna structure. Thus, the substrate dielectric properties are altered according to the properties of the absorbed liquid. Changes in reflection-based measurements are used to analyze salt solutions and artificial sweat, specifically the amount of sampled solution and the sodium chloride (NaCl) concentration. Using the shift in resonant frequency and magnitude of the reflection coefficient, NaCl concentrations in the range of 8.5–200 mmol/L, representing different hydration states, are detected. The measurements demonstrate the feasibility of using microwave based measurements for hydration monitoring using sweat.

Highlights

Health monitoring technologies have drawn significant attention from consumers and the scientific community in recent years [1,2,3]
The performance of the antenna changes when liquids are absorbed by the substrate, and we demonstrate that these changes are linked to the sodium chloride concentrations and amount of solution absorbed
The paper substrate is a good alternative in terms of cost, losses and fabrication complexity compared to existing flexible substrates

Summary

Introduction

Health monitoring technologies have drawn significant attention from consumers and the scientific community in recent years [1,2,3]. These include heart rate, calorie count and daily exercise tracking, currently available in wearable fitness devices. Hypertonic describes states where tissue loses more water than sodium, resulting in higher salt concentration [9,10] This can be caused by inadequate fluid intake, sweating and vomiting [7]. If the body lacks both water and sodium, isotonic dehydration occurs [7,9] This loss is caused through perspiration, urine or diarrhea [7]. Dehydration can be monitored through weight changes [7], blood pressure [7], skin (stratum corneum) [9,13], saliva [14], urine and blood tests, as well as analysis of sweat [15]

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