This nano-membrane turns your skin into a loudspeaker

We all are familiar with loudspeakers; the critical element found in almost every household in one form or the other – whether they’re in smartphones, TV’s or stashed in a cupboard somewhere.... And we all know that a typical loudspeaker has standard parts like a cone, voice coil, and a magnet that can be found in both the cheapest, and the most expensive speakers on the alike that convert amplified electrical signals into sound that we can hear.

Now though a group of researchers from Ulsan National Institute of Science and Technology in South Korea have tipped that concept on its head and come up up with an innovative solution that might revolutionise loudspeaker technology as we know it. The team has developed a Hybrid Nano-Membrane, that looks like any ordinary plaster, that emits sounds waves when fed with an electric current.

Listen to it in action

It can also act in reverse, making it function like a microphone. The membrane developed by the researchers consists of a polymer matrix that carries orthogonally positioned silver nanowire arrays.

The result is a thin, transparent and stretchable membrane that can act as a microphone or a loudspeaker. The membrane can be easily attached to the human skin and the flexibility guarantees that it does not tear when it’s under tension.

The researchers opted for silver nanowires over the popular materials like graphene and carbon because of the structural advantages associated with the material at nanometer-scales. Silver nanowires also have excellent electrical properties and are capable of withstanding greater force and pressure compared to others.

Also, silver is fairly easy to hybridize into a polymer membrane, making it possible to develop nano-membranes with good optical transparency.

When the electric signals are fed into the membrane it acts as a loudspeaker. The same nanotubes convert the vibrations resulting from the voice into electrical signals and turn the device into a microphone.

The researchers even demonstrated its versatility by sticking a thin Hybrid Nano-membrane to a human hand and played the final movement of a violin concerto of La Campanella by Niccolo Paganini.

The principle behind the production of sound in this hybrid nano-membrane is called Joule heating. The electric current causes a temperature oscillation that triggers a thermo-acoustic sound. This, in turn, moves the air around that we humans perceive as sound waves.

For the microphone, the nano-membrane is placed between micro-patterned elastic films. This arrangement allows the nano-membrane to detect the sound and vibration of the vocal cords based on tribo-electric 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 nanomembranes with nanoscale thickness, less than 100 nanometers. These outstanding optical, electrical, and mechanical properties of nanomembranes enable the demonstration of skin-attachable and imperceptible loudspeaker and microphone”, said Hyunhyub Ko, an associate professor at UNIST and coauthor of the research.

The researchers are hoping to see wide adoption of this new technology because of its multiple use cases with one proposed use case being to use it as a personal security interface that can send signals based on user’s voice commands in microphone mode and subsequently receive notification in the speaker mode. Although while that might be one of their main use cases I’m not too sure about that one myself…

That said though the team believes their innovation still needs further reinforcement to successfully withstand the pressures that it’d be exposed to when playing a wider range of sounds in order to make it commercially viable. The thin transparent film, however, is already stronger than polymers of the same dimensions because of the fillers used in the nanocomposites so it’ll be interesting to see how it all pans out, and who knows, as I discussed in my Future of Smartphones 2020 to 2070 report, when we finally move beyond the smartphone we’ll have a host of new opportunities in front of us and perhaps it can find a place in one of those.

Source: Science Advances.