Powered by “Soft Transmission Lines,” a New E-Textile May Give Rise to Smart Hospital Bedsheets

June 11, 2020 by Vanessa Samuel

Swiss researchers have employing liquid metal conductors and electrical reflectometry to create one giant sensor.

In a recent article on a washable smart garment, which employs conductive ink and waterproof circuitry, we pointed out the trend toward electronic textiles or "e-textiles."

Researchers at the Swiss Federal Institute of Technology in Lausanne (EPFL) are continuing that trend with a new smart textile that can sense and measure deformations in the fabric.


Professor Fabien Sorin and doctoral assistant Andreas Leber

Professor Fabien Sorin and doctoral assistant Andreas Leber from EPFL helped developed the e-textile. Image used courtesy of EPFL


This textile technology may be of use in medical and automotive industries since the fabric offers more flexibility and safer interactions with the human body.

“Imagine clothing or hospital bedsheets capable of monitoring your breathing and other vital movements, or AI-powered textiles that allow robots to interact more safely and intuitively with humans,” said doctoral assistant Andreas Leber.

The EPFL sensor is founded on the transmission line theory, which AAC contributor Arthur Anderson discusses in further detail in his introduction to the transmission line.

This article will cover the functionality of EPFL’s soft textiles and a few other wearable technologies. 


The Challenges of Mechanical Sensing

When it comes to soft technologies, one must consider mechanical sensing. This is the process by which sensors are used to determine deformation within the fabric. The deformation is then turned into an electrical signal.

Mechanical sensing can be difficult to implement because typically, each sensor is only capable of measuring a single parameter. Another challenge is that sensors can easily break under too much pressure. For a sensor-embedded fabric to be effective, you need many of them, too, which often detracts from the comfort level of such wearables.


A "Soft Transmission Line"

The EPFL fiber sensor is extremely small (500 µm) and simultaneously measures the stretch, pressure, and torque on multiple parts of the fabric. Within the fibers are liquid metal conductors applying electrical reflectometry all throughout the fabric. These sensors are essentially the “soft transmission lines.”


Researchers describe the sensors as soft transmission lines

Researchers describe the sensors as soft transmission lines. Image used courtesy of EPFL

The EPFL sensor works similarly to that of radar, except the EPFL sensor sends out electrical pulses as opposed to electromagnetic waves. Time is measured from when the signal was sent to when the signal was received, and this time-domain tells the location, intensity, and type of the deformation in the fabric. 


How The EPFL Sensor Is Distinct from Other E-Textiles

This sensor differs from other wearable technologies using e-textiles because typically other sensors use intentional touch to complete a circuit. In the case of the EPFL sensor, the sensor automatically detects movement and acts accordingly. 


Measuring the resistance of the e-textile when stretched

Measuring the resistance of the e-textile when stretched. Image used courtesy of EPFL


Creating the fabric for final EPFL sensor was no small task. Researchers used an optical fiber fabrication process including elastomers and conductive liquid metals. The resulting fabric is essentially a large sensor. 

The researchers' next step is to reduce the size of the peripheral electronics for a more portable footprint.


Wearables Make a Splash in Medical and Automotive Industries

Wearable and e-textile technologies are continuously emerging in more practical applications. In the medical field, a sensor like the one by EPFL could be used to monitor vital signals such as breathing and heart rate. One company, Siren, has even created sensor-embedded "smart socks" to help patients with diabetic neuropathy. E-textiles have also been developed to assist patients who are prone to falling and imbalance

The automotive industry can use sensors like these for heating and cooling seats or steering wheels. Exercise attire can also implement smart textiles to detect body movements and send information on athletic performance. It's likely that as smart textiles continue to progress, they will make wearable electronics safer and more comfortable.