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Scientists in Germany have created a way to cloak objects acoustically, according to research published in Physical Review Letters and reported on in The Engineer. It seems that lately, invisibility of one kind or another seems to be among the hottest scientific pursuits. Recently we wrote about a new technology that shows possibilities for cloaking objects from radar and in the dark of night. (See previous article here.)
The new acoustically cloaking material, developed at the Karlsruhe institute of Technology (KIT), neither absorbs nor reflects sound. Rather, it bends sound waves, guiding them around the cloaked object in much the same way lightwaves can be bent. To quote Prof Martin Wegener from the Institute of Applied Physics (AP) at KIT in his interview with the The Engineer, this bending of soundwaves creates a situation where, "It is as if nothing was there."
The material is made from a micro-structured material composed of two polymers, one hard and one soft. These are contained in a millimeter-thin plate that vibrates at frequencies around 100Hz within the audible acoustic range. The material's deception comes from speeding up sound waves as they travel around the outside of the circle. The result is that, despite traveling further than if they had passed straight through the object, they arrive at the other side at the same time. In other words, the secret behind the invention is controlling soundwaves to "specifically influence their local speed as a function of the 'running direction' of the wave,' according to KIT's Dr Nicolas Stenger.
If you're interested in acoustic cloaking, check out this technology reported earlier this year.