An international collaboration of researchers has developed new wearable technology that can turn the human skin into a loudspeaker, an advancement that could help the hearing and speech impaired.

The researchers, affiliated with the Ulsan National Institute of Science and Technology (UNIST), developed ultrathin, transparent and conductive hybrid nanomembranes with nanoscale-thickness that comprises an orthogonal silver nanowire array embedded in a polymer matrix.

The team then demonstrated the nanomembrane by converting it into a loudspeaker that can be attached to virtually any surface to produce sound.

The researchers also created a similar device that acts as a microphone and can be connected to smartphones and computers to unlock voice-activated security systems.

In recent years, scientists have used polymer nanomembranes for emerging technologies because they are extremely flexible, ultra lightweight and adhesive. However, they also tear easily and do not exhibit electrical conductivity.

To bypass those limitations, the UNIST researchers embedded a silver nanowire network within the polymer-based nanomembrane that allowed the demonstration of the skin-attachable and imperceptible loudspeaker and microphone.

“Our ultrathin, transparent and conductive hybrid NMs facilitate conformal contact with curvilinear and dynamic surfaces without any cracking or rupture,” Saewon Kang, a student in the doctoral program of Energy and Chemical Engineering at UNIST and the first author of the study, said in a statement. “These layers are capable of detecting sounds and vocal vibrations produced by the triboelectric voltage signals corresponding to sounds, which could be further explored for various potential applications, such as sound input/output devices.”

The team was able to fabricate the skin-attachable nanomembrane loudspeakers and microphones using hybrid nanomembranes so that they are unobtrusive in appearance because of their transparency and conformal contact capability.

“The biggest breakthrough of our research is the development of ultrathin, transparent, and conductive hybrid nanomembranes with nanoscale thickness, less than 100 nanometers,” professor Hyunhyub Ko, of the School of Energy and Chemical Engineering at UNIST, said in a statement. “These outstanding optical, electrical, and mechanical properties of nanomembranes enable the demonstration of skin-attachable and imperceptible loudspeaker and microphone.”

The loudspeakers emit thermoacoustic sound by temperature-induced oscillation of the surrounding air. The periodic Joule heating that occurs when an electric current passes through a conductor and produces heat leads to the temperature oscillations.

For the microphone, the hybrid nanomembrane could be inserted between elastic films with tiny patterns to detect the sound and vibration of the vocal cords based on a triboelectric voltage that results from the contact with the elastic films.

The new technology could eventually be fitted for wearable Internet of Things sensors, as well as conformal health care devices. The sensors could be attached to a speaker’s neck to sense the vibration of the vocal folds and convert the frictional force generated by the oscillation of the transparent conductive nanofiber into electric energy.

The study was published in Applied Sciences and Engineering.