MIT researchers have produced acoustically active piezoelectric polymer fibres.
"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," claimed the university.
The work has been lead by Dr Yoel Fink at MIT's Research Lab of Electronics.
These are not the first piezoelectric fibres, but previous types have largely been made by coating existing fibres, rather than 'drawing' - the process by which a fat 'pre-form' containing all necessary features is heated and stretched to form the final fibre. Optical fibres are made by drawing.
"The fibres developed in Fink's lab derive their functionality from the elaborate geometrical arrangement of several different materials, which must survive the heating and drawing process intact," said MIT. "The heart of the fibres is a plastic commonly used in microphones. By playing with the plastic's fluorine content, the researchers were able to ensure that its molecules remain with fluorine atoms on one side and hydrogen atoms on the other even during heating and drawing."
The ferroelectric polymer's piezoelectric action comes from this molecular asymmetry.
A post-drawing electric field polarises the 30µm piezo layer to activate it.
Deformable electrode layers in the structure are made from a graphite-loaded conductive plastic, and a plastic outer cladding protects the active structure.
"You can actually hear them, these fibres," said researcher Noémie Chocat.
Future work includes an attempt to combine acoustic and optical properties in a singe 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," said MIT.
The research covered by a Nature Materials paper, which reports piezoelectric response and acoustic transduction from kHz to MHz.