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A fabric that can "hear" sounds

Time : 2022-06-27 Hits : 36

The continuous development of fiber technology has made it possible to explore a wider range of uses for traditional fabrics. In nature, fibers often play a role in transmitting sound. In the human auditory system, for example, the eardrum, which is responsible for resolving the acoustic impedance mismatch between the air in the ear canal and the fluid in the inner ear, happens to be made of high-modulus fibers. The eardrum converts sound pressure into mechanical vibrations in the bones of the middle ear, which are then transmitted to the cochlea in the inner ear. In the cochlea, fiber-like hair bundles deflect, ultimately converting mechanical vibrations into electrical signals that are received by the nervous system.

Inspired by the conduction mechanism by which the auditory system converts sound pressure into mechanical vibrations, and then mechanical vibrations into electrical signals, and the importance of fibers in the auditory system, the team of Professor Yoel Fink at MIT designed an acoustic fabric . Unlike the complex three-dimensional structure of the auditory system, the fabric is flat, consisting of a fabric matrix with fiber sensors woven into it. The fabric matrix can efficiently convert sound pressure into mechanical vibrations like the eardrum, and the fiber sensor can convert mechanical vibrations into electrical signals like the cochlea.

It is found that the deformation energy generated by mechanical vibration can be concentrated and distributed in the fiber core efficiently. The asymmetric structure of the fiber allows the fiber to produce greater strain during deformation. Therefore, the research team used thermal drawing technology based on fiber production to fabricate a large number of fibers composed of six materials for the sensor, including a core composed of P(VDF-TrFe) and barium piezoelectric titanate (BaTiO3) ceramic particles, an electrode composed of nano carbon powder and polyethylene, a copper wire electrode, and a SEBS elastomer.

To prepare highly sensitive acoustic fabrics, we designed a woven fabric consisting of cotton yarn (warp) and high modulus Twaron filament (weft), and then directly woven heat-drawn fibers into the fabric substrate, as a control of pure cotton fabric of the same size. Finally, it was found that the acoustic response of Twaron/ cotton fabric was much higher than that of pure cotton fabric. At the same sound frequency, Twaron/ cotton fabric had a low order mechanical vibration mode, which induced the fiber to produce a higher vibration amplitude and bending deformation in only one direction. Moreover, after 10 machine washing cycles, the electrical and acoustic properties can still be maintained.

Woven a Twaron/cotton acoustic fabric into a garment that accurately detects the direction of a sound source. Directional monitoring of sound sources can be very helpful for people wearing hearing aids, promising to eliminate background noise while allowing them to hear only sounds in a specific direction, as well as law enforcement seeking to detect the source of gunfire. In addition, in the field of biomedicine, the garment can function as a stethoscope, providing a new solution for comfortable, continuous, real-time and long-term monitoring of human heart and respiratory health.

In addition to sensing sound, the fabric can also play audible sounds. The two shirts enable bidirectional acoustic communication, with matched time domain waveform and frequency spectrum between transmitted and received speech. This is conducive to the realization of person-to-person acoustic communication, and has a good application prospect for deaf or hard of hearing people, concealed communication, and even underwater communication.

(Source: Official Account of China Textile Leader)

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