In a paper recently published in the journal Advanced Material Technologies, researchers prepared a complete textile woven capacitive sensor to present the viability of interdigitated sensors integrated into fabrics. The sensor was further tested for moisture detection.
Study: A Full Textile Capacitive Woven Sensor. Image Credit: Jesus Sanz/Shutterstock.com
Background
Researchers have frequently been working to replace traditional electronic components with wearable electronics and smart textiles. Integrated textile sensors have benefits such as the capacity to detect physical or chemical stimulation without dramatically changing the fabric's structure, the ability to survey longer regions as compared to traditional sensors at a lower cost, and lesser requirements than electronic components.
Large-scale production of woven fabrics is believed to be more affordable than that of embroidery. Additionally, woven technology could result in fully integrated, non-touchable textile sensors. The incorporation of the textile sensor performs better when performed using the weaving technique, which also preserves the substrate's textile qualities.
About the Study
In the present study, the team used an interdigitated structure as the foundation of the suggested woven sensor. The Dornier LWV8/J weaving machine was used to weave the sensor. The warp yarns were guided up or down using a Jacquard system in accordance with the position necessary for the weave for the configuration of the structure of the finished fabric.
Two different conductive threads were employed to weave the sensor. Shieldex conductive yarns were used to replace 12 separate warp yarns during the manufacturing procedure of the sensors. Shieldex warp and Bekaert weft yarn sensors were categorized as USTS, while Bekaert weft and warp yarn sensors were classified as UBTB.
The team examined the designed woven textile sensor in the role of a presence sensor and comparative relative humidity characteristics. In order to characterize the humidity, the sensor was placed within a climatic chamber in order to study how it responded to a range of relative humidity between 30% and 90% while maintaining a constant temperature of 20 °C. It was placed over a chair to test the sensor's functionality as a presence sensor. The capacitance data were recaptured from a 70-kilogram individual sitting on a chair.
Observations
According to the sensor capacitance versus humidity responses for the UBTB and USTS, the capacitance for the two sensors increased as the relative humidity increased. With respect to relative humidity, the Bekaert yarns had good stability.
In terms of the average value, USTS showed the highest dispersion, ranging between 75% and 85%, with the values of standard deviation ranging between 4.3% and 5.5%. The standard deviation figures for UBTB, however, were more consistent. Not as many variances existed as noted for the USTS values. Meanwhile, the USTS's range of values was broader because of the conductivity of silver. Furthermore, USTS had a higher standard deviation than UBTB.
On average, embroidery had a 2.1% standard deviation, while the average standard deviation for woven sensors was 1.34%. Thus, it was determined that this method creates sensors that have less dispersion and higher repeatability. Between embroidery and weaving, the team also noted differences in sensitivity. For woven sensors, the sensitivity increased by 0.0168 log(C)(RH)-1.
After an individual sat on the sensor, USTS responded by significantly increasing the capacitance, which was kept at a higher level until the person got up. Furthermore, the sensor showed a modest rise in void condition after someone moved in and got up. When presence was detected, the UBTB sensor responded well. Subsequently, the sensor's results increased by 120–170%.
When a heavy object like a shopping bag, was placed on the sensor, the capacitance stayed steady in the range of 15% to 20% for all the varied load instances. This indicated that the bag's textile, which had variable permittivity, was the cause of the sensor variation. The sensor's ability to distinguish between a person and a bag was thus proven. When the space was occupied, both sensors were present and exhibited an increase in their capacitance. A person-occupied state was easily distinguished from object occupation and a void state.
Conclusions
To summarize, the researchers demonstrated a woven sensor and showed how effectively it could measure relative humidity and detect the presence of persons or objects. When compared to the embroidery technique, capacitive values exhibited a linear dependency with a smaller standard deviation which increased immediately with humidity.
The utility of presence detection was demonstrated by the test results, which provided clear values for void and occupied conditions and should allow easy applications. According to the authors, the cloth capacitive sensor can be used in more applications where the touch feel or other characteristics were previously a deterrent.
Source
Martínez-Estrada, M., Ventura, H., Gil, I., Fernández-García, R., A Full Textile Capacitive Woven Sensor, Adv. Mater. Technol. 2022, 2200284, DOI: https://doi.org/10.1002/admt.202200284
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