Inspired by the human ear, they create a tissue that “hears”

Writing Science, 16 Mar A new fabric, inspired by the human ear, is able to function as a microphone and convert audible sounds into electrical signals, which allows, if applied to a shirt, to detect the features of the heartbeat, according to a study published today by Nature. Engineers at the Massachusetts Institute of Technology (MIT) have created this fabric, designed from a “piezoelectric” material that produces an electrical signal when it is mechanically bent or deformed, providing a means for tissue to convert sound vibrations into electrical signals. All tissues vibrate in response to audible sounds, although they are on the nanometer scale, too small to be perceived normally. To capture these imperceptible signals, the researchers created a flexible fiber that, when put into a fabric, bends with it like algae on the ocean surface, MIT explained. The canvas can capture sounds at different decibels, from a quiet library to heavy traffic, and determine the precise direction of sudden sounds, such as claps. In addition, when knitted into a shirt, it can detect the subtle features of the wearer's heartbeat. These fibers can also generate sounds, such as a recording of spoken words, that other tissue can detect. The lead author of the research Wei Yan considered that such a fabric can have many applications, because with an acoustic garment “you can talk through it to answer phone calls and communicate with others”. In addition, it can interact imperceptibly with human skin, allowing users to monitor their heart and respiratory status “comfortably, continuously, in real time and in the long term”. The fabric feels “almost like a thin jacket, lighter than denim, but heavier than a shirt,” explained another of the signers, Elizabeth Meiklejohn, from the Rhode Island School of Design (USA). Audible sound travels through the air as light pressure waves, and when they reach our ears, the eardrum uses a circular layer of fibers to translate them into mechanical vibrations. These vibrations travel through small bones to the inner ear, where the cochlea converts waves into electrical signals that are perceived and processed by the brain. Drawing inspiration from the human hearing system, the team sought to create a fabric “ear” that was soft, durable, comfortable and capable of detecting sound. The fabric had to incorporate rigid fibers to effectively convert sound waves into vibrations, but it must also be able to bend and produce an electrical output in the process.