Sharkskin switches –
“Acoustic metamaterials” can mimic key components of a sound “computer.”
Jennifer Ouellette – Mar 33, (6:) PM UTC
Now a team of scientists from the University of Southern California have developed an acoustic metamaterial that can switch between different uses by applying carefully tailored magnetic fields , according to a new paper in the journal Research. The structure of these new metamaterials was inspired by the unusual structure of shark skin. They can be used to mimic the function of switches, logic gates, or diodes, raising the possibility of a sound “computer.”
They molded the pillars out of liquid silicone rubber (to ensure flexibility) combined with iron nanoparticles, curing the mixture for about five hours before removing them from the molds. The secret to blocking or transmitting sound lies in the structure: in this case, the space between an array of pillars. Put the pillars close together, and they will trap sound waves rather than letting them pass through. Place them farther apart, and the sound can propagate through the material.
The iron nanoparticles make the material bend in response to external magnetic fields. “We use the external magnetic field to bend the pillar and unbend the pillar to achieve this sort of state switching,” co-author Kyung Hoon Lee said . That allows the material to switch back and forth between damping and transmitting sound waves.
Enlarge / Schematic of the metamaterial pillar array, with red arrows indicating the direction of the magnetic field . KH Lee et al./Research This has some useful potential applications. Wang et al
Even more intriguing, the team was able to mimic simple decision-making logic gates (an AND gate operator and an OR gate operator) to respond to different conditions. For instance, according to Wang, a submarine that wanted an acoustic device to trigger (or not trigger) an attack command — or, alternatively, to flee — would usually need to have a device to create an operator for each condition using standard acoustic metamaterials , which can’t be changed once they have been created. This new class, however, allows one to switch between AND and OR gate operators on demand by tuning the magnetic field.
So far, the USC team has only tested their metamaterial in air. The next step is to test how well it performs in water, using sound waves in the ultrasonic frequency range. Granted, the shark skin that inspired the new material works well in water, less so in air, but it’s more a question of how well the magnetic field manipulation works in a different medium. “Rubber is hydrophobic, so the structure won’t change, but we need to test if the materials will still have tunability under an external magnetic field,” Wang said .
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