Abstract According to the foreign science and technology media ScienceDaily, the French National Scientific Research Center (CNRS) and the French School of Advanced Chemical Physics (Boris University/National Bordeaux Institute of Technology/French National Engineering and Technology University)...
According to the foreign science and technology media ScienceDaily, the French National Scientific Research Center (CNRS) and the French School of Advanced Chemical Physics of Bordeaux (CNRS/Bordeaux University/National Bordeaux Institute of Technology/French National Engineering and Technology University) have combined physical and chemical composition. And microfluidic technology, developed the first three-dimensional metamaterial. Metamaterials are new materials with extraordinary properties, in which the microstructure is smaller than the wavelength at which it acts, and can affect waves, especially sound waves and light waves. Metamaterials can make objects invisible or increase the resolution of the lens.
The metamaterials in this study are a new generation of soft metamaterials that are more easily shaped. In the experiment, the researchers realized that the ultrasonic oscillation moved backward, and the energy carried by the wave moved forward. This research opens up new prospects, especially for high-resolution imaging. The study was published in the December 15th issue of Nature Materials.
Since the 21st century, the international academic community has shown increasing interest in metamaterials and their unparalleled characteristics. In metamaterial media, the phase velocity of an acoustic wave or light wave can be negative (ie, the material has a negative refractive index), and the phase of the wave (continuous oscillation) and the direction of movement of the energy carried by the wave are opposite. It has never been found that any naturally occurring substance has this property.
In order to obtain metamaterials, scientists must make a homogeneous medium containing a large amount of inclusions (ie, microresonators). Micro-mechanical methods (such as etching, deposition, etc.) are typically used to machine one- or two-dimensional carriers having metamaterial properties. However, this method cannot be applied to micron-sized soft materials required for ultrasonic applications, and the currently obtained metamaterials are limited to one-dimensional or two-dimensional.
In this study, scientists invented a new metamaterial, a fluid phase formed in porous silicon particles embedded in a water-based gel. This "superfluid" is the first three-dimensional metamaterial that can operate at ultrasonic frequencies. In addition, due to its fluid properties, it can also be fabricated using physicochemical processes and microfluidic processes, which is easier to implement than micromechanical methods.
One of the characteristics of porous media is that sound waves can pass through them at very slow speeds (tens of meters per second), while the speed of sound waves in water is 1,500 meters per second. Due to this strong contrast, the entire suspension has metamaterial properties as long as the suspension concentration is sufficiently large. When researchers studied the propagation properties of ultrasound in such media, they measured the negative refractive index directly. In such a superfluid, the energy carried by the wave is transmitted from the transmitting end to the receiving end as expected, but the oscillation seems to move backwards in the opposite direction, just like a dancer dancing a moonwalk.
These experimental results have opened up a number of potential applications for metamaterials such as high-resolution ultrasound imaging, acoustic insulation, and underwater auditory invisibility. In addition, the soft-physical-chemical techniques used to make such metamaterials make it possible to produce fluids and flexible materials with characteristic shapes on an industrial scale.
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