Nanotechnology has contributed to all sorts of important medical and scientific breakthroughs, but when is it going to make speakers sound better? It’s a question we all ask ourselves every hour of every day, of course, but your nanotech speakers are almost ready. A team of researchers from Sweden’s KTH Royal Institute of Technology have created a new kind of loudspeaker that relies on nanoparticle-infused membranes to generate sound without need of a permanent magnet.
The main constituent of the membrane is cellulose fiber — the polysaccharide component of plant cell walls. Researchers mixed the cellulose fibers in solution with ferromagnetic salts at 90 degree Celsius, then left the mixture to bond over the course of two months. The remaining water was drained at the end of this period to reveal a hydrogel (a hydrophilic collection of polymers) composed of magnetic cellulose fibers.
The researchers found that the magnetic particles had bound extremely strongly to the cellulose fibers with a roughly even distribution. The hydrogel was further dried and used to fashion a speaker membrane about 20cm in diameter. When comparing the hybrid cellulose material to an analog created simply by mixing magnetic nanoparticles with cellulose, there was no comparison — the original preparation had much more even distribution of nanoparticles.
A traditional speaker has a voice coil wrapped around a magnet. The induced magnetic field of the coil interacts with the permanent magnet whenever a current is applied. This results in the generation of mechanical force, which is what moves the speaker cone to produce sound waves. The speaker made out of the nanotech material from the Royal Institute of Technology can interact with the voice coil on its own because it is the magnet. The voice coil isn’t even attached to the cone — it’s all driven by air.
The team behind this work measured the sound quality of their prototype speaker and declared it to be at least as good as a standard speaker, and perhaps better if overall volume isn’t taken into account. The membrane has the potential to create very smooth, even sound thanks to the distribution of magnetic material throughout its volume.
Producing this material doesn’t require any hugely complicated facilities or machinery — just a little patience. If the time to make the magnetic cellulose (or something like it) could be shortened, this could be a viable technology for consumer audio products. It has the potential to produce better quality sound in a much smaller package. Smartphones and tablets in particular could see a great benefit from slimmer speakers. We might finally see phones with speakers that are neither tinny, nor huge.
Research paper: DOI: 10.1039/C3TC31748J – ”Cellulose nanoﬁbers decorated with magnetic nanoparticles – synthesis, structure and use in magnetized high toughness membranes for a prototype loudspeaker” (Open-access PDF)