|
Post by moabiter on Jan 6, 2011 7:38:18 GMT -8
January 05, 2011 Two dimensional acoustic cloak The cloak is made of metamaterial, a class of artificial materials that have enhanced properties as a result of their carefully engineered structure. Fang’s team designed a two-dimensional cylindrical cloak made of 16 concentric rings of acoustic circuits structured to guide sound waves. Each ring has a different index of refraction, meaning that sound waves vary their speed from the outer rings to the inner ones. “Basically what you are looking at is an array of cavities that are connected by channels. The sound is going to propagate inside those channels, and the cavities are designed to slow the waves down,” Fang said. “As you go further inside the rings, sound waves gain faster and faster speed.” Since speeding up requires energy, the sound waves instead propagate around the cloak’s outer rings, guided by the channels in the circuits. The specially structured acoustic circuits actually bend the sound waves to wrap them around the outer layers of the cloak. The researchers tested their cloak’s ability to hide a steel cylinder. They submerged the cylinder in a tank with an ultrasound source on one side and a sensor array on the other, then placed the cylinder inside the cloak and watched it disappear from their sonar. nextbigfuture.com/2011/01/two-dimensional-acoustic-cloak.html
|
|
|
Post by clone on Jun 28, 2011 9:05:50 GMT -8
June 15, 2011 A Carpet Cloak for Visible Light We report an invisibility carpet cloak device, which is capable of making an object undetectable by visible light. The cloak is designed using quasi conformal mapping and is fabricated in a silicon nitride waveguide on a specially developed nanoporous silicon oxide substrate with a very low refractive index (n less than 1.25). The spatial index variation is realized by etching holes of various sizes in the nitride layer at deep subwavelength scale creating a local effective medium index. The fabricated device demonstrates wideband invisibility throughout the visible spectrum with low loss. This silicon nitride on low index substrate can also be a general scheme for implementation of transformation optical devices at visible frequencies. nextbigfuture.com/2011/06/carpet-cloak-for-visible-light.htmlA Carpet Cloak for Visible Light (4pp) xlab.me.berkeley.edu/publications/pdfs/161.NL2011_Majid.pdf
|
|
|
Post by moabiter on Jul 23, 2011 23:19:08 GMT -8
should actually go in Time thread, but oh well, it's more about invisibility. [Time may vanish - pyrelog.proboards.com/index.cgi?board=astronomy&action=display&thread=34 ] First Demonstration of Time CloakingPhysicists have created a "hole in time" using the temporal equivalent of an invisibility cloak. kfc 07/14/2011 Invisibility cloaks are the result of physicists' newfound ability to distort electromagnetic fields in extreme ways. The idea is steer light around a volume of space so that anything inside this region is essentially invisible. The effect has generated huge interest. The first invisibility cloaks worked only at microwave frequencies but in only a few years, physicists have found ways to create cloaks that work for visible light, for sound and for ocean waves. They've even designed illusion cloaks that can make one object look like another. www.technologyreview.com/blog/arxiv/26992/
|
|
|
Post by clone on Aug 14, 2011 10:56:51 GMT -8
3D cloak is first to work in free space Aug 8, 2011 Physicists in the US claim to have created the first 3D invisibility cloak that can operate alone in free space. The cloak, based on a "plasmonic" shell, can hide a cigar-sized cylinder from microwaves – although it currently only operates for one microwave polarization. Invisibility cloaks have been around since 2006, when a team led by David Smith at Duke University in North Carolina, US, produced a device that could guide microwaves of a very narrow frequency around an area a few centimetres in diameter. The device was based on a "metamaterial" comprising an array of resonators that altered the electrical permittivity and magnetic permeability throughout the cloak. Variations in these properties resulted in the microwaves bending round the hidden space like water around a stone, albeit only in 2D. physicsworld.com/cws/article/news/46805
|
|
|
Post by clone on Jan 4, 2012 16:23:49 GMT -8
Pentagon Scientists Use ‘Time Hole’ to Make Events Disappear January 4, 2012 | 4:58 pm This is the first time that scientists have succeeded in masking an event, though research teams have in recent years made remarkable strides in cloaking objects. Researchers at the University of Texas, Dallas, last year harnessed the mirage effect to make objects vanish. And in 2010, physicists at the University of St. Andrews made leaps towards using metamaterials to trick human eyes into not seeing what was right in front of them. www.wired.com/dangerroom/2012/01/time-hole/
|
|
|
Post by clone on Jan 19, 2013 7:10:50 GMT -8
|
|
|
Post by clone on Mar 30, 2015 23:49:37 GMT -8
Landmark study proves that magnets can control heat and sound Mar 23, 2015 Researchers at The Ohio State University have discovered how to control heat with a magnetic field. In the March 23 issue of the journal Nature Materials, they describe how a magnetic field roughly the size of a medical MRI reduced the amount of heat flowing through a semiconductor by 12 percent. The study is the first ever to prove that acoustic phonons—the elemental particles that transmit both heat and sound—have magnetic properties. more: phys.org/news/2015-03-landmark-magnets.html
|
|