U.S. develops fiber that emits and detects sound waves

For centuries, man-made fibers refer to the raw materials of clothes and ropes. In the information age, the significance of fibers has become the glass filaments carrying data in communication networks. However, for Yule Fink, an associate professor at MIT's Electronic Research Laboratory, these fibers used in textiles or fiber are too passive. Over the past decade, his laboratory has been working on the development of fibers with more advanced properties to enable fiber fabrics to interact with their surroundings.

In a recent issue of Nature Materials, Fink and its collaborators announced a landmark new type of functional fiber: a fiber that can detect and produce sound. Applications for such fibers include: clothes that can be used as microphones to capture speech or monitor bodily functions; or microscopic monofilaments that measure blood flow or brain pressure in capillaries.

New fiber containing asymmetric molecular plastic

Conventional optical fibers are made from "preforms," ​​which are large cylindrical single materials that can be heated, drawn, and cooled. In contrast, fibers developed by Fink Laboratories are carefully geometries of several different materials, allowing them to remain intact during heating and stretching processes.

The core of the new acoustic fiber is a plastic that is commonly used in microphones. The fluorine content of this plastic allows researchers to ensure that their molecules are in an unbalanced state, that is, one side of the fluorine atom and one hydrogen atom, even during heating and stretching. This molecular asymmetry gives the plastic a "piezoelectricity," meaning that when an electric field is applied to it, it changes shape.

In a conventional piezoelectric microphone, an electric field is generated by a metal electrode. However, in a fiber microphone, the stretching process causes the metal electrodes to lose their shape. Therefore, the researchers replaced it with a conductive plastic containing graphite. Conductive plastics produce a dense liquid when heated, maintaining a higher viscosity than metal electrodes. This not only prevents the mixing of the material, but, more critically, it also gives the fiber a normal thickness.

After the fiber is stretched, the researchers need to arrange all the piezoelectric molecules in the same direction. At this point, you need a powerful electric field (more than 20 times stronger than the electric field that triggers lightning in a thunderstorm). Because the fiber is very narrow everywhere, it will produce a tiny ball of lightning that can destroy the surrounding material.

Sound fiber is widely used

Although the manufacturing process requires this delicate balance, researchers can still produce this functional fiber in the lab. If they are connected to a power supply and a sinusoidal current is applied (a very stable period of alternating current), these fibers vibrate. If you make it vibrate at the audio frequency and bring it near your ear, you can hear different notes or sounds from it. In the "Natural Materials" paper, researchers have more rigorously measured the acoustic properties of fibers. Since water conducts sound better than air, they place the fiber in a water tank opposite the standard acoustic energy converter. The acoustic energy converter can alternately emit sound waves that the fiber can detect. It can also detect the sound emitted by the fiber. Sound waves.

Researchers hope to eventually combine the performance of these experimental fibers in a single fiber. For example, strong vibration can change the optical properties of the reflective fiber so that the fiber fabric can communicate optically. In addition to wearable microphones and biosensors, applications for this fiber include webs that monitor the flow of water in the ocean, as well as high-resolution large-area sonar imaging systems. Fabrics made from such acoustic fibers equate to millions of tiny Acoustic sensor. Researchers say that using the same mechanism, piezoelectric elements can, in turn, convert electricity into motion.