Polymer-Thread-Based Fully Textile Capacitive Sensor Embroidered on a Protective Face Mask for Humidity Detection

Abstract

The COVID-19 pandemic has created a situation where wearing personal protective masks is a must for every human being and introduced them as a part of everyday life. This work demonstrates a new functionality embedded in single-use face masks through an embroidered humidity sensor. The design of the face mask humidity sensor is comprised of interdigitated electrodes made of polyamide-based conductive threads and common polyester threads which act as a dielectric sensing layer embroidered between them. Therefore, the embroidered sensor acts as a capacitor, the performance of which was studied in increasing humidity conditions in the frequency range from 1 Hz to 100 kHz. The moisture adsorbed by sensitive hygroscopic polyester threads altered their dielectric and permittivity properties which were detected by the change in capacitance values of the face mask sensors at different relative humidity (RH) levels. The calculated limit of detection (LOD) values for the two proposed sensors at different frequencies (1, 10, and 100 kHz) were found in the range from 11.46% RH−27.41% RH and 29.79% RH−38.65% RH. The tested sensors showed good repeatability and stability under different humidity conditions over a period of 80 min. By employing direct embroidery of silver-coated polyamide conductive threads and moisture-sensitive polyester threads onto the face mask, the present work exploits the application of polymer-based textile materials in developing novel stretchable sensing devices toward e-textile applications.

Wearable humidity sensor embroidered on a commercial face mask and its electrical properties

“…Unlike capacitive sensors where a sensing material with very low conductivity is required for effective use as a dielectric material [ 18 ], resistive sensors rely upon the flow of current through the sensing layer [ 16 , 23 ]. Therefore, as the sensing layer (in this work polyester threads) react to the presence of water, the conductivity of the hygroscopic thread changes.…”

“…In the present case, the resistive IDEs represent a chain of individual resistors arranged in parallel. The polyester core-based moisture-sensitive threads embroidered between the fingers of IDE served as water adsorption centers to create the Van der Waals interactions between the carbonyl group (C=O) of the polymer [ 18 ] and water molecules [ 22 ]. The hydrogen bonds that formed as shown in Scheme 1 b play a dominant role in eliciting the sensor response [ 24 ].…”

“…2 c) while the presence of carbon (C) and oxygen (O) justifies the water absorbing group (C=O) of polyester threads (Fig. 2 d) [ 18 ]. Moreover, elemental mapping of conductive silver thread and polyester thread is shown in Figure S1 and Figure S2 of Supplementary Information (SI).…”

“…Most frequently used RH sensors fall under mainly two categories capacitive and resistive. In capacitive sensors, the sensing layer acts as the dielectric between two parallel interdigitated electrodes [ 18 ] while in resistive sensors, the sensing layer acts as a resistor between two electrodes in an interdigitated pattern [ 16 ]. As a result, the reaction of a capacitive sensor to humidity change is measured by a change in the capacitance of the sensor while by a change in resistance of the sensor for a resistive sensor.…”

Development of Embroidery-Type Sensor Capable of Detecting Respiration Using the Capacitive Method

“…In recent years, monitoring physiological data using wearable health sensors has become a fundamental feature of health and well-being applications. Some recent studies have used humidity and temperature created from breathing as a signal to recognize human breathing rate [ 1 , 2 , 3 ]. These studies take the initiative to utilize nonwoven face masks using relative humidity changes to measure human respiration.…”