Researchers in Sweden have demonstrated the first ever magnetic cellulose membrane applied as a loudspeaker device. The project aims to show the potential of natural and environmentally sustainable materials in an application that everybody should be familiar with, says Richard T. Olsson, assistant professor, KTH, Royal Institute of Technology.
Olsson explains that the biocomposite membrane is magnetic due to the presence of magnetic nanoparticles attached along native cellulose nanofibers. The fibers were obtained form commercial wood pulp. It operates as a freestanding membrane inside a coil. In this design, the membrane is permanently magnetized and the driving coil is stationary. This allows for the fabrication of extremely flat speakers without moving electrical parts, which is of great advantage.
The work was carried out under the Wallenberg Wood Science Center (WWSC) in Stockholm, Sweden, in collaboration with scientists at the Royal Institute of Technology, Sweden.
The prototype speaker and its biocomposite membrane are discussed in the technical article Cellulose Nanofibers Decorated with Magnetic Nanoparticles – Synthesis, Structure and Use in Magnetized High Toughness Membranes for a Prototype Loudspeaker by Sylvain Galland, Richard L Andersson, Michaela Salajkova, Valter Strom, Richard T Olsson and Lars A. Berglund (Journal of Materials Chemistry C, published by Royal Society of Chemistry, UK, London).
An article on the Royal Society of Chemistry web site says the biocomposite membrane eliminates the need for a bulky magnet and enhances sound quality because there is no coil in contact with the membrane.
The article further explains that the membrane is made by fastening magnetic nanoparticles along cellulose nanofibrils to make a magnetic gel. This gel can be sprayed from a spray gun nozzle to give a membrane with a uniform spread of particles.