Tag Archives: Chinese Academy of Sciences (CAS)

3-D underwater acoustic carpet cloak

Who can resist a ‘Black Panther’ reference (Wikipedia Black Panther film entry)? Certainly not me. Scientists from the Chinese Academy of Sciences made this June 4, 2018 announcement (also on EurekAlert),

Cloaking is one of the most eye-catching technologies in sci-fi movies. In two 2018 Marvel films, Black Panther and Avengers: Infinity War, Black Panther conceals his country Wakanda, a technologically advanced African nation, from the outside world using the metal vibranium.

However, in the real world, if you want to hide something, you need to deceive not only the eyes, but also the ears, especially in the underwater environment.

Recently, a research team led by Prof. 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.

The research was published online in Applied Physics Letters on June 1 [2018].

Like a shield, the carpet cloak is a material shell that can reflect waves as if the waves were reflecting off a planar surface. Hence, the cloaked target becomes undetectable to underwater detection instruments like sonar.

Using transformation acoustics, the research team first finished the 2D underwater acoustic carpet cloak with metamaterial last year (Scientific Reports, April 6, 2017). However, this structure works only in two dimensions, and becomes immediately detectable when a third dimension is introduced.

To solve this problem, YANG Jun and his IOA team combined transformation acoustics with a reasonable scaling factor, worked out the parameters, and redesigned the unit cell of the 2D cloak. They designed the 3D underwater acoustic carpet cloak and then proposed a fabrication and assembly method to manufacture it. The 3D cloak can hide an object from top to bottom and deal with complex situations, such as acoustic detection in all directions.

The 3D underwater acoustic carpet cloak is a pyramid comprising eight triangular pyramids; each triangular pyramid is composed of 92 steel strips using a rectangle lattice, similar to a wafer biscuit. More vividly, if we remove the core from a big solid pyramid, we can hide something safely in the hollow space left.

“To make a 3D underwater acoustic carpet cloak, researchers needed to construct the structure with 2D period, survey the influence of the unit cell’s resonance, examine the camouflage effect at the ridge of the sample, and other problems. In addition, the fabrication and assembly of the 3D device required more elaborate design. The extension of the UACC from 2D to 3D represents important progress in applied physics,” said YANG.

In experimental tests, a short Gaussian pulse propagated towards the target covered with the carpet cloak, and the waves backscattered toward their origin. The cloaked object successfully mimicked the reflecting surface and was undetectable by sound detection. Meanwhile, the measured acoustic pressure fields from the vertical view demonstrated the effectiveness of the designed 3D structure in every direction.

“As the next step, we will try to make the 3D underwater acoustic carpet cloak smaller and lighter,” said YANG.

Funding for this research came from the National Natural Science Foundation of China (Grant No.11304351, 1177021304), the Youth Innovation Promotion Association of CAS (Grant No. 2017029), and the IACAS Young Elite Researcher Project (Grant No. QNYC201719).

Prof. YANG Jun and Dr. JIA Han led the research team from the Institute of Acoustics (IOA) of the Chinese Academy of Sciences. Prof. YANG Jun engages in research on sound, vibration and signal processing, and especially sound field control and array signal processing. They also work on other devices based on metamaterial in order to manipulate the propagation of sound waves.

A model of the device,

Caption: This is a model and photograph of the 3D underwater acoustic carpet cloak composed of over 700 steel strips. Credit: IOA

Here’s a link to and a citation for the paper,

Experimental demonstration of three-dimensional broadband underwater acoustic carpet cloak by Yafeng Bi, Han Jia, Zhaoyong Sun, Yuzhen Yang, Han Zhao, and Jun Yang.
Appl. Phys. Lett. 112, 223502 (2018); https://doi.org/10.1063/1.5026199 Published Online: June 2018

This paper is open access.

Ice-free materials courtesy of penguins

The Humboldt penguin’s feathers don’t allow ice to form and a team of scientists have figured out why according to a Feb. 24, 2016 news item on Nanotechnology Now,

Humboldt penguins live in places that dip below freezing in the winter, and despite getting wet, their feathers stay sleek and free of ice. Scientists have now figured out what could make that possible. They report in ACS’ Journal of Physical Chemistry C that the key is in the microstructure of penguins’ feathers. Based on their findings, the scientists replicated the architecture in a nanofiber membrane that could be developed into an ice-proof material.

A Feb. 24, 2016 American Chemical Society (ACS) news release on EurekAlert, which originated the news item, provides a bit more detail,

The range of Humboldt penguins extends from coastal Peru to the tip of southern Chile. Some of these areas can get frigid, and the water the birds swim in is part of a cold ocean current that sweeps up the coast from the Antarctic. Their feathers keep them both warm and ice-free. Scientists had suspected that penguin feathers’ ability to easily repel water explained why ice doesn’t accumulate on them: Water would slide off before freezing. But research has found that under high humidity or ultra-low temperatures, ice can stick to even superhydrophobic surfaces. So Jingming Wang and colleagues sought another explanation.

The researchers closely examined Humboldt penguin feathers using a scanning electron microscope. They found that the feathers were comprised of a network of barbs, wrinkled barbules and tiny interlocking hooks. In addition to being hydrophobic, this hierarchical architecture with grooved structures is anti-adhesive. Testing showed ice wouldn’t stick to it. Mimicking the feathers’ microstructure, the researchers developed an icephobic polyimide fiber membrane. They say it could potentially be used in applications such as electrical insulation.

The researchers have provided an image illustrating their work,

[downloaded from http://pubs.acs.org/doi/abs/10.1021/acs.jpcc.5b12298]

[downloaded from http://pubs.acs.org/doi/abs/10.1021/acs.jpcc.5b12298]

Here’s a link to and a citation for the paper,

Icephobicity of Penguins Spheniscus Humboldti and an Artificial Replica of Penguin Feather with Air-Infused Hierarchical Rough Structures by Shuying Wang, Zhongjia Yang, Guangming Gong, Jingming Wang, Juntao Wu, Shunkun Yang, and Lei Jiang. J. Phys. Chem. C, Article ASAP DOI: 10.1021/acs.jpcc.5b12298 Publication Date (Web): February 3, 2016

Copyright © 2016 American Chemical Society

This paper is behind a paywall.