Arrays of gold, pillar-supported bowtie nanoantennas (bottom left) can be used to record distinct musical notes, as shown in the experimentally obtained dark-field microscopy images (bottom right). These particular notes were used to compose "Twinkle, Twinkle, Little Star."Engineers have built a ‘nano-piano’ to demonstrate a high-tech new recording medium.

A team from the US has used an array of gold bowtie nanoantennas (pBNAs) to store sound and audio files.

The Univeristy of Illinois team used it to make the first-ever recording of optically encoded audio onto a non-magnetic plasmonic nanostructure.

“The chip's dimensions are roughly equivalent to the thickness of human hair,” explained professor of mechanical science and engineering Kimani Toussaint.

The storage capacity of the pBNA array is around 5,600 times larger than conventional magnetic film.

To demonstrate the chip’s ability to store sound and audio files, the researchers created a musical keyboard or ‘nano piano’, to play ‘Twinkle, Twinkle, Little Star’ on a near molecular level.

Eight basic musical notes, including middle C, D, and E, were stored on a pBNA chip and then retrieved and played back in a desired order to make a tune.

This demonstrated that the pBNAs could be used to store sound information either as a temporally varying intensity waveform or a frequency varying intensity waveform.

“A characteristic property of plasmonics is the spectrum,” said Hao Chen, first author of the new paper, ‘Plasmon-Assisted Audio Recording’, which will appear in the Nature journal Scientific Reports.

“Originating from a plasmon-induced thermal effect, well-controlled nanoscale morphological changes allow as much as a 100-nm spectral shift from the nanoantennas.

“By employing this spectral degree-of-freedom as an amplitude coordinate, the storage capacity can be improved.

“Moreover, although our audio recording focused on analog data storage, in principle it is still possible to transform to digital data storage by having each bowtie serve as a unit bit 1 or 0. By modifying the size of the bowtie, it's feasible to further improve the storage capacity,” he said.

“Our approach is analogous to the method of ‘optical sound’, which was developed circa 1920s as part of the effort to make 'talking' motion pictures,” the team said in its paper.

“Although there were variations of this process, they all shared the same basic principle. An audio pickup, e.g., a microphone, electrically modulates a lamp source. Variations in the intensity of the light source is encoded on semi-transparent photographic film (e.g., as variation in area) as the film is spatially translated.

“Decoding this information is achieved by illuminating the film with the same light source and picking up the changes in the light transmission on an optical detector, which in turn may be connected to speakers,” the paper states.

“In the work that we present here, the pBNAs serve the role of the photographic film which we can encode with audio information via direct laser writing in an optical microscope.”

The researchers recorded audio signals by using a microscope to scan a sound-modulated laser beam directly on their nanostructures.

Retrieval and playback was achieved by using the same microscope to visualise the recorded waveform onto a digital camera, whereby simple signal processing can be performed.