summary: A new textile sensor accurately measures body movements without the need for electronic components. Sensors that can be added to your workout clothes can predict in real time how tired you will be during exercise.
sauce: ETH Zurich
Fatigue makes you more prone to injury while exercising or performing physical work.
A group of researchers at ETH Zurich, led by Professor Carlo Menon, head of the Biomedical and Mobile Health Technology Lab, has developed a textile sensor that measures in real time how tired a person is during exercise.
To test the new sensor, they built it into their athletic leggings. With just a quick glance at the phone, our testers could see when they were hitting their limits and if they needed a break.
The invention, patented by ETH Zurich, could pave the way for a new generation of smart clothing. Many of the products on the market today are retrofitted with electronic components such as sensors, batteries and chips. In addition to driving up prices, this makes these products difficult to manufacture and maintain.
In contrast, the ETH researchers’ stretch sensors can be incorporated directly into the material fibers of stretchy, form-fitting sportswear and workwear. This makes large-scale production easier and cheaper.
Menon highlights another advantage. “Because the sensors are placed so close to the body, it is possible to capture body movements with great precision without the wearer noticing.”
extraordinary thread
People move differently when they are tired. Running is no exception. Your stride becomes shorter and irregular. Using a new sensor made from a special type of thread, ETH researchers can measure this effect.
It’s all due to the structure of the thread. The internal fibers are made of conductive elastic rubber. The researchers wrapped a stiff wire covered with a thin layer of plastic in a spiral around this inner fiber.
“These two fibers act as electrodes, creating an electric field. Together they form a capacitor that can hold an electric charge,” said a postdoc in Menon’s group, who was involved in the research and development that led to the invention. Tyler Cuthbert says:
smart running leggings
This thread is sewn into the thigh area of elastic running leggings and stretches and relaxes in a particular rhythm as the wearer runs. With each movement he changes the gap between the two fibers, as well as the electric field and the charge on the capacitor.
Under normal circumstances, these charge fluctuations are too small to measure body motion. However, the characteristics of this thread are not normal.
“Unlike most other materials, our material actually thickens when stretched,” says Cuthbert.
As a result, the thread is more sensitive to minimal movement. Any stretching will cause a clearly measurable variation in the charge on the sensor. This makes it possible to measure and analyze subtle changes in running form.
But how can this be used to determine a person’s fatigue level? Observed. They recorded how the electrical signal changed as the runner became more and more tired.
Their next step was to translate this pattern into a model that could predict runner fatigue. You can now use this for your new textile sensor. However, many additional tests and large amounts of gait pattern data are required before the model can make accurate predictions outside the lab.
Textile antenna for wireless data transfer
To enable the textile sensor to transmit electrical signals wirelessly to the smartphone, the researchers equipped it with a loop antenna made of conductive thread, which was also sewn directly onto the leggings.
“Together, the sensors and antennas form an electrical circuit that is fully integrated into the garment,” says Valeria Galli, a doctoral student in Menon’s group.
An electrical signal travels from a stretchable sensor to an antenna and is transmitted at a specific frequency that can be read by a smartphone. As the wearer runs, the sensor moves, generating a signal pattern with continuously varying frequencies. A smartphone app records and evaluates this in real time. However, researchers still have considerable development work to make this happen.
Applications include sports and workplace
At the moment, researchers are working on turning the prototype into a marketable product. To this end they have applied for one of the Pioneer Fellowships he is seeking at ETH Zurich.
“Our goal is to make smart clothing manufacturing cost-effective and accessible to more people,” says Menon.
Beyond sports, he sees potential applications in the workplace to prevent fatigue-related injuries and in rehabilitative medicine.
About this Neurotech Research News
author: Christoph Erhardt
sauce: ETH Zurich
contact:Christoph Erhardt – ETH Zurich
image: Image credit to Valeria Galli/ETH Zurich
Original research: open access.
“A helical auxetic yarn capacitive strain sensor with sensitivity exceeding the theoretical limit” By Cuthbert T et al. advanced materials
overview
A helical auxetic yarn capacitive strain sensor with sensitivity exceeding the theoretical limit
The development of flexible strain sensors over the past decade has focused on access to high strain rates and high sensitivities (gauge factors). Strain sensors that use capacitance as the electrical signal correlated to strain typically have limited sensitivity due to the Poisson effect.
By adopting an auxetic structure, we have surpassed the sensitivity limits of capacitive sensors and improved the competitiveness of this sensing modality.
In this work, the first adoption of helical auxetic yarns as capacitive sensors is presented. It can be seen that the response of the helical auxetic yarn capacitive sensor (referred to as HACS) depends on two key manufacturing variables: diameter ratio and helical wrapping length.
Depending on these variables, we can obtain sensors that respond to strain with increasing or decreasing capacitance values.
The greater the auxetic properties, the greater the sensitivity that can be accessed at small strains. This is a property not commonly seen when accessing high gauge factors. Moreover, it yields the highest sensitivity of any auxetic capacitive sensor ever reported.
We propose a mechanism of sensor response that explains both the variable capacitance response and the experimentally obtained high gauge factor.
