Textination Newsline

A new study from NC State University combines three-dimensional embroidery techniques with machine learning to create a fabric-based sensor that can control electronic devices through touch.

As the field of wearable electronics gains more interest and new functions are added to clothing, an embroidery-based sensor or “button” capable of controlling those functions becomes increasingly important. Integrated into the fabric of a piece of clothing, the sensor can activate and control electronic devices like mobile apps entirely by touch.  

The device is made up of two parts; the embroidered pressure sensor itself and a microchip which processes and distributes the data collected by that sensor. The sensor is triboelectric, which means that it powers itself using the electric charge generated from the friction between its multiple layers. It is made from yarns consisting of two triboelectric materials, one with a positive electric charge and the other with a negative charge, which were integrated into conventional textile fabrics using embroidery machines.

Rong Yin, corresponding author of the study, said that the three-dimensional structure of the sensor was important to get right.

“Because the pressure sensor is triboelectric, it needed to have two layers with a gap in between them. That gap was one of the difficult parts in the process, because we are using embroidery which is usually two-dimensional. It’s a technique for decorating fabric,” he said. “It’s challenging to make a three-dimensional structure that way. By using a spacer, we were able to control the gap between the two layers which lets us control the sensor’s output.”

Data from the pressure sensor is then sent to the microchip, which is responsible for turning that raw input into specific instructions for any connected devices. Machine learning algorithms are key to making sure this runs smoothly, Yin said. The device needs to be able to tell the difference between gestures assigned to different functions, as well to disregard any unintentional inputs that might come from the cloth’s normal movement.

“Sometimes the data that the sensor acquires is not very accurate, and this can happen for all kinds of reasons,” Yin said. “Sometimes the data will be affected by environmental factors like temperature or humidity, or the sensor touches something by mistake. By using machine learning, we can train the device to recognize those kinds of things.

“Machine learning also allows this very small device to achieve many different tasks, because it can recognize different kinds of inputs.”

The researchers demonstrated this input recognition by developing a simple music playing mobile app which connected to the sensor via Bluetooth. They designed six functions for the app: play/pause, next song, last song, volume up, volume down and mute, each controlled by a different gesture on the sensor. Researchers were able to use the device for several other functions, including setting and inputting passwords and controlling video games.

The idea is still in its early stages, Yin said, as existing embroidery technology is not capable of easily handling the types of materials used in the creation of the sensor. Still, the new sensor represents another piece of the developing wearable electronics puzzle, which is sure to continue picking up interest in the near future.

The paper, “A clickable embroidered triboelectric sensor for smart fabric,” is published in Device.

Researchers at ETH Zurich have developed an electronic yarn capable of precisely measuring how a person’s body moves. Integrated directly into sportswear or work clothing, the textile sensor predicts the wearer’s exhaustion level during physical exertion.

Exhaustion makes us more prone to injury when we’re exercising or performing physical tasks. A group of ETH Zurich researchers led by Professor Carlo Menon, Head of the Biomedical and Mobile Health Technology Lab, have now developed a textile sensor that produces real-time measurements of how exhausted a person gets during physical exertion. To test their new sensor, they integrated it into a pair of athletic leggings. Simply by glancing at their smartphone, testers were able to see when they were reaching their limit and if they ought to take a break.

This invention, for which ETH Zurich has filed a patent, could pave the way for a new generation of smart clothing: many of the products currently on the market have electronic components such as sensors, batteries or chips retrofitted to them. In addition to pushing up prices, this makes these articles difficult to manufacture and maintain.

By way of contrast, the ETH researchers’ stretchable sensor can be integrated directly into the material fibres of stretchy, close-fitting sportswear or work clothing. This makes large-scale production both easier and cheaper. Menon highlights another benefit: “Since the sensor is located so close to the body, we can capture body movements very precisely without the wearer even noticing.”

An extraordinary yarn
When people get tired, they move differently – and running is no exception: strides shorten and become less regular. Using their new sensor, which is made of a special type of yarn, the ETH researchers can measure this effect. It’s all thanks to the yarn’s structure: the inner fibre is made of a conductive, elastic rubber. The researchers wrapped a rigid wire, which is clad in a thin layer of plastic, into a spiral around this inner fibre. “These two fibres act as electrodes and create an electric field. Together, they form a capacitor that can hold an electric charge,” says Tyler Cuthbert, a postdoc in Menon’s group, who was instrumental in the research and development that led to the invention.

Smart running leggings
Stitching this yarn into the thigh section of a pair of stretchy running leggings means that it will stretch and slacken at a certain rhythm as the wearer runs. Each movement alters the gap between the two fibres, and thus also the electric field and the capacitor’s charge.

Under normal circumstances, these charge fluctuations would be much too small to help measure the body’s movements. However, the properties of this yarn are anything but normal: “Unlike most other materials, ours actually becomes thicker when stretched,” Cuthbert says. As a result, the yarn is considerably more sensitive to minimal movements. Stretching it even a little produces distinctly measurable fluctuations in the sensor’s charge. This makes it possible to measure and analyse even subtle changes in running form.

But how can this be used to determine a person’s exhaustion level? In previous research, Cuthbert and Menon observed a series of testers, who ran while wearing athletic leggings equipped with a similar sensor. They recorded how the electric signals changed as the runners got more and more tired. Their next step was to turn this pattern into a model capable of predicting runners’ exhaustion which can now be used for their novel textile sensor.  But ensuring that the model can make accurate predictions outside the lab will require a lot of additional tests and masses of gait pattern data.

Textile antenna for wireless data transfer  
To enable the textile sensor to send electrical signals wirelessly to a smartphone, the researchers equipped it with a loop antenna made of conducting yarn, which was also sewn directly onto the leggings. “Together, the sensor and antenna form an electrical circuit that is fully integrated into the item of clothing,” says Valeria Galli, a doctoral student in Menon’s group.

The electrical signal travels from the stretchable sensor to the antenna, which transmits it at a certain frequency capable of being read by a smartphone. The wearer runs and the sensor moves, creating a signal pattern with a continuously fluctuating frequency, which a smartphone app then records and evaluates in real time. But the researchers still have quite a bit of development work to do to make this happen.

Applications include sport and workplace
At the moment, the researchers are working on turning their prototype into a market-ready product. To this end, they are applying for one of ETH Zurich’s sought-after Pioneer Fellowships. “Our goal is to make the manufacture of smart clothing cost-effective and thus make it available to a broader public,” Menon says. He sees the potential applications stretching beyond sport to the workplace – to prevent exhaustion-related injuries – as well as to rehabilitation medicine.

Stylish sensors to wear 
With sensors that measure health parameters and can be worn on the body, we do let technology get very close to us. A collaboration between Empa and designer Laura Deschl, sponsored by the Textile and Design Alliance (TaDA) of Eastern Switzerland, shows that medical monitoring of respiratory activity, for example, can also be very stylish – as a shirt.
 
With sensors that measure health parameters and can be worn on the body, we do let technology get very close to us. A collaboration between Empa and designer Laura Deschl, sponsored by the Textile and Design Alliance (TaDA) of Eastern Switzerland, shows that medical monitoring of respiratory activity, for example, can also be very stylish – as a shirt.

The desire for a healthy lifestyle has triggered a trend towards self-tracking. Vital signs should be available at all times, for example to consistently measure training effects. At the same time, among the continuously growing group of people over 65, the desire to maintain performance into old age is stronger than ever. Preventive, health-maintaining measures must be monitored if they are to achieve the desired results. The search for measurement systems that reliably determine the corresponding health parameters is in full swing. In addition to the leisure sector, medicine needs suitable and reliable measurement systems that enable efficient and effective care for an increasing number of people in hospital and at home. After all, the increase in lifestyle diseases such as diabetes, cardiovascular problems or respiratory diseases is putting a strain on the healthcare system.

Researchers led by Simon Annaheim from Empa's Biomimetic Membranes and Textiles laboratory in St. Gallen are therefore developing sensors for monitoring health status, for example for a diagnostic belt based on flexible sensors with electrically conductive or light-conducting fibers. However, other, less technical properties can be decisive for the acceptance of continuous medical monitoring by patients. For example, the sensors must be comfortable to wear and easy to handle – and ideally also look good.

This aspect is addressed by a cooperation between the Textile and Design Alliance, or TaDA for short, in eastern Switzerland and Empa. The project showed how textile sensors can be integrated into garments. In addition to technical reliability and a high level of comfort, another focus was on the design of the garments. The interdisciplinary TaDA designer Laura Deschl worked electrically conductive fibers into a shirt that change their resistance depending on how much they are stretched. This allows the shirt to monitor how much the subjects' chest and abdomen rise and fall while they breathe, allowing conclusions to be drawn about breathing activity. Continuous monitoring of respiratory activity is of particular interest for patients during the recovery phase after surgery and for patients who are being treated with painkillers. Such a shirt could also be helpful for patients with breathing problems such as sleep apnea or asthma. Moreover, Deschl embroidered electrically conductive fibers from Empa into the shirt, which are needed to connect to the measuring device and were visually integrated into the shirt's design pattern.

The Textile and Design Alliance is a pilot program of the cultural promotion of the cantons of Appenzell Ausserrhoden, St.Gallen and Thurgau to promote cooperation between creative artists from all over the world and the textile industry. Through international calls for proposals, cultural workers from all disciplines are invited to spend three months working in the textile industry in eastern Switzerland. The TaDA network comprises 13 cooperation partners – textile companies, cultural, research and educational institutions – and thus offers the creative artists direct access to highly specialized know-how and technical means of production in order to work, research and experiment on their textile projects on site. This artistic creativity is in turn made available to the partners as innovative potential.