Nano-membrane transparent loudspeaker attaches to skin

August 13, 2018 //By Rich Pell
Nano-membrane transparent loudspeaker attaches to skin
Researchers at the Ulsan National Institute of Science and Technology (Ulsan, South Korea) have developed a flexible nano-membrane loudspeaker that attaches to skin.

Comprising a polymer matrix with orthogonally positioned silver nanowire arrays, the transparent and stretchable hybrid nano-membrane emits sounds when fed with audio frequency electric currents. It can also function as a microphone.

Silver nanowires were chosen for the nano-membrane over materials like graphene and carbon because of the structural advantages associated with the material at nanometer scales, say the researchers. Silver nanowires also have excellent electrical properties, are capable of withstanding greater force and pressure compared to other materials, and are relatively easy to hybridize into a polymer membrane, making it possible to develop nano-membranes with good optical transparency.

The principle behind the production of sound in the device - called Joule heating - results when an electric current causes a temperature oscillation that triggers a thermoacoustic sound.

For use in microphone mode, the nano-membrane is placed between micro-patterned elastic films - an arrangement that allows the nano-membrane to detect the sound and vibration of vocal cords based on triboelectric voltage, which is generated through the contact with the elastic films.

"The biggest breakthrough of our research is the development of ultrathin, transparent, and conductive hybrid nano-membranes with nanoscale thickness, less than 100 nanometers," says Hyunhyub Ko, an associate professor at UNIST and coauthor of the research. "These outstanding optical, electrical, and mechanical properties of nano-membranes enable the demonstration of skin-attachable and imperceptible loudspeaker and microphone."

The researchers see many possible applications for their technology, including conformal wearable sensors and health care devices. For one such example, they say, the membrane might be used as a personal security interface that can send signals based on a user's voice commands in microphone mode and subsequently receive notification in the speaker mode.

Looking ahead, the researchers hope to add further reinforcement to their nano-membrane to ensure it can successfully withstand the pressure, and to make it commercially viable. For more, see " Transparent and conductive nanomembranes with orthogonal silver nanowire arrays for

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