A team of researchers created a durable ultra-thin film made from natural wood, which was then used as a diaphragm for an audio speaker.
Thin films made from plastic, metal, ceramic and carbon are widely used in applications ranging from food packaging and water purification to electronics and solar cells. However, membranes, used in acoustic systems must not only be thin, but also have high mechanical strength in order to provide the necessary sensitivity and vibration amplitude.
Films made of metal, ceramic and carbon are very resilient, but difficult and expensive to manufacture, while plastic films are less efficient and pollute the environment. Therefore, a team of materials scientists and engineers at the University of Maryland at College Park decided to use natural cellulose-based materials as a base..
To create ultra-thin films less than 8.5 micrometers thick, they partially removed lignin (delignification) and hemicellulose from longitudinally cut balsa wood to preserve the canal structure. Further, to increase the density of the obtained porous material, it was subjected to hot pressing, which also reduced its thickness by 97%. Cellulosic nanofibers in ultra-thin film remained highly oriented, but more densely laminated compared to natural wood.
Mechanical tests have shown that the material has a tensile strength of up to 342 MPa and a Young’s modulus of 43.65 GPa. This is 20 and 35 times better than natural wood, respectively.
These characteristics of the film allowed the team to bend and fold it without any problems, as well as use it as an acoustic transducer for assembling a miniature speaker with a wide bandwidth, high sensitivity and high sound pressure levels. The prototype contained a wooden diaphragm and a board with a miniature speaker made of copper coil and permanent magnet.
In the future, the group plans to improve the design of the membrane and develop technology for industrial use in the production of microphones, hearing aids and acoustic sensors..
We also previously reported on the invention of transparent wood and wood-based thermoelectric generator..
text: Ilya Bauer, photo and video: University of Maryland
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