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Recently, engineers at the Massachusetts Institute of Technology (MIT) and the Rhode Island School of Design have developed a new "acoustic fabric" that can not only "hear" sound like a microphone, but also "emit" sound like a speaker.
From quiet libraries to busy traffic noises, this acoustic fabric captures sounds within these decibel ranges and is able to determine the precise direction of sounds such as clapping hands. When this material is woven into the lining of a shirt, subtle heartbeat characteristics of the wearer can also be detected.
A detailed description of the results, published in the latest issue of the journal Nature.
Lead author Wei Yan, a postdoctoral fellow at MIT (now an assistant professor at Nanyang Technological University in Singapore), said the results of this study provide a whole new way to listen to our bodies and our surroundings, which will lead to many unimaginable applications.
"Wearing a sound costume, you can use it to answer calls and communicate with others. In addition, the fabric can also be in contact with human skin, enabling the wearer to monitor their heart and breathing conditions in a comfortable, continuous, real-time and long-term manner. Fink said.
Sound-sensitive material inspired by the human ear
Traditional fabrics are often used to suppress or block sound. For example, the sound insulation layer of the concert hall, and the carpet in our lives. But MIT's research team has been working for years to reinvent fabrics' traditional roles. They focus on extending the properties of materials, such as making fabrics more functional.
This time, when looking for a way to sense fabrics, the "listening principle" of the human ear gave researchers a lot of inspiration.
Sound is actually a kind of pressure wave that travels through the air. When these sound waves reach our ears, the extremely sensitive and complex three-dimensional organ, the eardrum, converts pressure waves into mechanical vibrations, which then enter the inner ear through the ossicles, which in turn convert these vibrational waves into electrical signals that can be sensed and processed by the brain.
Although some sounds are so small that we can't perceive them normally, they all cause corresponding vibrations, but sometimes this vibration is nanoscale. To capture these imperceptible vibrational signals, inspired by the human hearing system, the team attempted to create a fabric "ear" that is soft, durable, comfortable and capable of detecting sound.
(Source: Nature)
To achieve this, they found that the fabric must be fed hard or "high modulus" fibers to effectively convert sound waves into vibrations, and secondly, a special fiber that can bend with the fabric and produce electrical output in the process.
With these prerequisites in mind, the team developed a layered block of material called a preform, made from piezoelectric layers and reinforcing material components that respond to the vibrations of sound waves. The resulting block of prefabricated material is about the size of a marker pen, then heated and pulled into 40 meters of fine fibers like gummies.
In fact, this fiber is designed by a "piezoelectric" material that generates an electrical signal when bent or mechanically deformed, thus providing fabrics with a way to convert acoustic vibrations into electrical signals. When this flexible fiber is woven into a fabric, it can also be bent arbitrarily with the fabric like seaweed in the ocean.
Not only can I hear, but I can also make sounds
To test the sensitivity of the acoustic fibers, the researchers attached the acoustic fibers to a piece of suspended polyester film and then used a laser to measure the vibration of the flakes — and in turn the vibrations of the fibers — in response to sounds played through nearby speakers.
Although the decibels of sound vary between quiet libraries and busy road traffic, the sound fibers are able to vibrate accordingly and produce an electric current proportional to the sound played.
"This shows that the performance of the acoustic fibers on the film is comparable to that of handheld microphones." One of the authors of the research paper, Grace Noel of MIT's Department of Chemical Engineering, said.
Next, the research team woven special sound-sensitive fibers with traditional yarns to produce drapable, machine-washable fabrics. The researchers say the synthetic fabric feels like a lightweight jacket, lighter than denim but heavier than a formal shirt.
The researchers then sewed a piece of fabric inside the shirt and tested the fabric's sensitivity to directional sound perception by clapping their hands while standing at a different angle from the shirt. The results show that the fabric is able to detect sound angles within 1 degree at a distance of 3 meters.
The researchers believe that this sensing fabric, which can direct the perception of sound, can help people with hearing loss listen to outside sounds in noisy environments.
(Source: MIT)
In addition, the research team also stitched a fiber on the inner lining of the shirt, about above the chest area, and found that the sound-sensing material could accurately detect the heartbeat of healthy volunteers, as well as subtle changes in heart beating characteristics.
In addition to monitoring the heartbeat, the researchers believe that incorporating the acoustic fabric into maternity clothing could also help monitor the fetal heartbeat.
What's even more interesting is that the researchers have come up with a new idea, if the function of the sound fiber is reversed, no longer used as a sound detector, but as a speaker, what will happen?
To this end, the researchers first recorded a string of spoken language, and in the form of applying a voltage to feed the recording to the sound fiber, found that the sound fiber can convert the electrical signal into audible vibration, and then used another sound fiber as the "ear" to successfully detect the sound vibration emitted by the sound fiber.
In addition to wearable hearing aids, clothing for voice communication, and clothing that tracks vital signs, the team sees more application possibilities.
"It can be integrated with spacecraft clothing to monitor space dust, or embedded in buildings to detect cracks or strains," Yan suggested. "It could even be woven into a smart web to monitor fish in the ocean." It can be seen that sound fibers are opening up a great opportunity. ”
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