Acoustic fibres can hear and sing
Researchers at the Massachusetts Institute of Technology (MIT) have announced that they’ve achieved a significant milestone on their quest to produce sophisticated fibres that interact with their surroundings.
In the August issue of Nature Materials, a research team has revealed that it has produced fibres that can both detect and produce sounds.
Applications could include clothes that are themselves sensitive microphones, for capturing speech or monitoring bodily functions, and tiny filaments that could measure blood flow in capillaries or pressure in the brain.
For the past decade, Yoel Fink, an associate professor of materials science and principal investigator at MIT’s Research Lab of Electronics, has been working to develop fibres with ever more sophisticated properties, enabling fabrics to interact with their environment.
The heart of the new acoustic fibres is a plastic commonly used in microphones. By playing with the plastic’s Fluorine content, they researchers were able to ensure that its molecules remain correctly aligned even during the heating and drawing processes associated with fibre manufacture.
This is important as the fibres derive their functionality from the elaborate geometrical alignment of several different materials. It is this that grants the plastic its piezo-electric properties.
Despite the delicate balance required by the manufacturing process, the researchers were able to build functioning fibres in the lab. "You can actually hear them, these fibres," says Chocat, a graduate student in the materials science department. "If you connected them to a power supply and applied a sinusoidal current" — an alternating current whose period is very regular — "then it would vibrate. And if you make it vibrate at audible frequencies and put it close to your ear, you could actually hear different notes or sounds coming out of it." For their Nature Materials paper, however, the researchers measured the fibre's acoustic properties more rigorously. Since water conducts sound better than air, they placed it in a water tank opposite a standard acoustic transducer, a device that could alternately emit sound waves detected by the fibre and detect sound waves emitted by the fibre.
In addition to wearable microphones and biological sensors, applications of the fibres could include loose nets that monitor the flow of water in the ocean and large-area sonar imaging systems with much higher resolutions: A fabric woven from acoustic fibres would provide the equivalent of millions of tiny acoustic sensors.
Zheng, a research scientist in Fink's lab, also points out that the same mechanism that allows piezoelectric devices to translate electricity into motion can work in reverse. "Imagine a thread that can generate electricity when stretched," he says.
Ultimately, however, the researchers hope to combine the properties of their experimental fibres in a single fibre. Strong vibrations, for instance, could vary the optical properties of a reflecting fibre, enabling fabrics to communicate optically.