Researchers Develop Transparent Loudspeakers

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Researchers at Ulsan National Institute of Science and Technology (UNIST) developed an innovative wearable technology that turns skin into a loudspeaker

A research led by Professor Hyunhyub Ko at the School of Energy and Chemical Engineering of UNIST created a novel wearable technology that can help hearing and speech impaired people along with various potential applications. The team developed ultrathin, transparent, and conductive hybrid nanomembranes (NMs) with nanoscale thickness. The membrane consists of an orthogonal silver nanowire array that is embedded in a polymer matrix. The nanomembrane was later developed into a loudspeaker that can be attached to any surface to produce sounds. Moreover, a similar device that acts as a microphone was introduced. The microphone can be connected to smartphones and computers to unlock voice-activated security systems.

NMs are molecularly thin separation layers with nanoscale thickness and are extreme flexible, ultralight in weight, and have excellent adhesibility. However, theses NMs tear easily and exhibit no electrical conductivity. To overcome the drawback, the team embedded a silver nanowire network within a polymer-based nanomembrane. These hybrid NMs were used to fabricate skin-attachable NM loudspeakers and microphones. Moreover, these devices are unobtrusive in appearance owing to their excellent transparency and conformal contact capability. These wearable speakers and microphones are paper-thin and are capable of conducting sound signals efficiently. The NM loudspeakers emit thermoacoustic sound through temperature-induced oscillation of the surrounding air. The temperature oscillations are a result of periodic Joule heating, which occurs when an electric current passes through a conductor and produces heat.

Wearable microphones are sensors that when attached to a speaker’s neck are capable of sensing the vibration of the vocal folds. The sensor convert the frictional force produced from oscillation of the transparent conductive nanofiber into electric energy. The hybrid nanomembrane, for the operation of the microphone, is inserted between elastic films with tiny patterns. This enables precise detection of sound and the vibration of the vocal cords based on a triboelectric voltage generated from the contact with the elastic films. The research was published in the journal Science Advances on August 03, 2018.

 

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