Cloak for sounds

The idea of cloaks that make objects disappear is really capturing. It has been realized at least in the lab by a theory called "transformation optics", which relates to the transformation properties of Maxwell's equations. However, this idea not only blossoms in optics but also in acoustics, where similar equations exist in 2D. A new paper in PRL designs a cloak for ultrasonic waves[Phys. Rev. Lett. 106, 024301 (2011) – Published January 10, 2011]. The difficulty lies in varying the density of materials in a desired way[Physics 4, 2 (2011)].

Invisibility devices based on coordinate transformation have opened up a new field of considerable interest. We present here the first practical realization of a low-loss and broadband acoustic cloak for underwater ultrasound. This metamaterial cloak is constructed with a network of acoustic circuit elements, namely, serial inductors and shunt capacitors. Our experiment clearly shows that the acoustic cloak can effectively bend the ultrasound waves around the hidden object, with reduced scattering and
shadow. Because of the nonresonant nature of the building elements, this low-loss ( 6 dB=m) cylindrical cloak exhibits invisibility over a broad frequency range from 52 to 64 kHz. Furthermore, our experimental study indicates that this design approach should be scalable to different acoustic frequencies and offers the possibility for a variety of devices based on coordinate transformation.

Neutrino helps shielding seismic waves

This experiment is said to be a significant step toward a better understanding of the chemical makeup inside the earth. Glad to know that, knowledge of neutrino can be useful even in predicting seismic events, which recently happened frequently.

shielding earthquakes

Earthquakes tend to cause disasters to humans. It is desirable to screen them. Seismic waves are generally composed of two components, the transverse one (i.e., the S waves, which represents the up-down vibrations of crust) and the longitudinal one (P waves, left-right vibrations). The latter travels faster and can reach more distant places, while the former is more fierce. Here is a piece of work coming up with a design, which assumes a concentric structure, to shield P waves. Their numeric simulations show that, this design is efficient with a broad frequency band.
(1)Ultrabroadband Elastic Cloaking in Thin Plates
(2)brief introduction to seismic waves