Not only invisible, but also inaudible

December 20, 2011

Progress of metamaterials in nanotechnologies has made the invisibility cloak, a subject of mythology and science fiction, become reality: Light waves can be guided around an object to be hidden, in such a way that this object appears to be non-existent. This concept applied to electromagnetic light waves may also be transferred to other types of waves, such as sound waves. Researchers from Karlsruhe Institute of Technology (KIT) have now succeeded in demonstrating for the first time an invisibility cloak for elastic waves. Such waves also occur in strings of a guitar or drum membranes.

It is as if Harry Potter had a cloak that also makes him unhearable. "Maybe a place of peace and quiet in the Christmas season," say the KIT researchers, who succeeded in transferring the concepts underlying the optical invisibility cloak to acoustic waves in a plate.

"The key to controlling waves is to specifically influence their local speed as a function of the 'running direction' of the wave," says Dr. Nicolas Stenger from the Institute of Applied Physics (AP). In his experiment, he used a smartly microstructured material composed of two polymers: A soft and a hard plastic in a thin plate. The vibrations of this plate are in the range of acoustic frequencies, that is some 100 Hz, and can be observed directly from above. The scientists found that the sound waves are guided around a circular area in the millimeter-thin plate in such a way that vibrations can neither enter nor leave this area. "Contrary to other known noise protection measures, the sound waves are neither absorbed nor reflected," says Professor Martin Wegener from the Institute of Applied Physics and coordinator of the DFG Center for Functional Nanostructures (CFN) at KIT. "It is as if nothing was there." Both physicists and Professor Martin Wilhelm from the KIT Institute for Chemical Technology and Polymer Chemistry have now published their results in the journal "Physical Review Letters."

The scientists explain their idea by the following story: A city, in the shape of a circle, suffers from noisy car traffic through its center. Finally, the mayor has the idea to introduce a speed limit for cars that drive directly towards the city: The closer the cars come to the city area, the slower they have to drive. At the same time, the mayor orders to build circular roads around the city, on which the cars are allowed to drive at higher speeds. The cars can approach the city, drive around it, and leave it in the same direction in the end. The time required corresponds to the time needed without the city. From outside, it appears as if the city was not there.
-end-


Helmholtz Association

Related Invisibility Cloak Articles from Brightsurf:

Topology-optimized thermal cloak-concentrator
Cloaking a concentrator in thermal conduction via topology optimization. A simultaneous cloaking and concentrating of heat flux is achieved through topology optimization, a computational structural design methodology.

New invisibility concept and miniaturization of photonic circuits using ultrafast laser
Thanks to its unique three-dimensional manufacturing capacity, ultrafast laser writing is a prime candidate to meet the growing demand for the miniaturization of photonic circuitry, e.g., for scaling up optical quantum computers capacity.

The invisibility cloak of a fungus
The human immune system can easily recognize fungi because their cells are surrounded by a solid cell wall of chitin and other complex sugars.

Artificial intelligence (AI) designs metamaterials used in the invisibility cloak
The research group of Prof. Junsuk Rho, Sunae So and Jungho Mun of Department of Mechanical Engineering and Department of Chemical Engineering at POSTECH developed a design with a higher degree of freedom which allows to choose materials and to design photonic structures arbitrarily by using Deep Learning.

Dashing the dream of ideal 'invisibility' cloaks for stress waves
Some have dreamt of the perfect cloak to make buildings impervious to stress waves caused by bombs, earthquakes or other calamities.

New technique to make objects invisible proposed
Researchers at the University of Extremadura have demonstrated the electromagnetic invisibility of objects using an alternative technique, based on filler cloaking.

Extremely small magnetic nanostructures with invisibility cloak imaged
In novel concepts of magnetic data storage, it is intended to send small magnetic bits back and forth in a chip structure, store them densely packed and read them out later.

Chinese researchers achieve 3D underwater acoustic carpet cloak first with 'Black Panther'-like features
A research team led by professor YANG Jun from the Institute of Acoustics (IOA) of the Chinese Academy of Sciences designed and fabricated a 3D underwater acoustic carpet cloak (UACC) using transformation acoustics.

Scientists discover the secrets behind the cuttlefish's 3-D 'invisibility cloak'
An international team of scientists has identified the neural circuits that enable cuttlefish to change their appearance in just the blink to eye -- and discovered that this is similar to the neural circuit that controls iridescence in squids.

Electromagnetic water cloak eliminates drag and wake
Engineers at Duke University develop a realistic proposition for creating a water cloak that moves water around an object by applying forces on dissolved ions through a carefully designed electromagnetic field.

Read More: Invisibility Cloak News and Invisibility Cloak Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.