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Although the superconductor can also shield the external magnetic field, the superconductor itself can still interfere with the external magnetic field and can be detected.
As shown in the figure, the line of magnetic induction does not enter this new type of invisibility cloak and looks as if it goes straight through.
According to the report of the British "Nature" magazine, physicists have revealed many types of invisibility cloaks, including invisibility cloaks that can make objects invisible to light, sound waves, seismic waves, or even waves. Now they have reported on a new type of cloak that is invisible to static magnetic fields, and the materials used to make this type of cloak are easily available in physical laboratories around the world. This means that in principle, this is the first Invisible cloak that can be actually produced. This cloak can be of great use in the medical field, but it may also subvert airport security facilities.
The team of theoretical physicists led by Alvaro Sanchez from the Autonomous University of Barcelona and experimental physicists of the Slovak Academy of Sciences showed us how the invisibility cloak works.
The inner surface of the cloak is formed by "high-temperature superconducting strips". Since superconductors can repel magnetic fields, anything with a magnetic field surrounded by superconductors cannot be detected from the outside, but the superconductor itself can still Interfering with the external magnetic field can be detected, so scientists have wrapped a common layer of ferromagnetic material on its outer surface (the magnet on the refrigerator door is made of this material). The superconductor tries to repel the external magnetic field outwards, while the ferromagnetic substance tries to attract the external magnetic field inwards, so that in general the response of the two material layers to the magnetic field exactly cancel each other out.
To test its performance, Slovakia's experimental physics team used liquid nitrogen to cool the cloak material to activate its superconductivity, and then put it into a static, uniform magnetic field with a magnetic induction of 40 microtesla. Afterwards, using the Hall probe to detect the magnetic field, the scientists discovered that the lines of magnetic induction did not enter the cloak and they seemed to go straight through from the outside. They claimed that their cloak was in the “real†sense. Invisibility cloak (because this is the perfect cape that can be made from existing materials)
In 2008, the physicist John Pendry and others showed for the first time the ability to hide stealth cloaks against static magnetic fields. The simplicity of this cloak compared to other types of invisibility cloaks is: Only the permeability of the material is required to change, and there is no requirement for the dielectric constant.
However, there is still a complicated aspect of this design: it is required that the magnetic permeability must be anisotropic (different values ​​in different directions). Alvaro Sanchez and his colleagues designed the invisibility cloak to be much simpler. Its permeability is isotropic (the same value in different directions).
John Penderru said that this new work is groundbreaking in the research of the invisibility cloak. He said: "Although the final measurement results show that this is not yet a perfect cloak, but it convincingly shows that the basic concept is feasible! And will undoubtedly improve its performance after an improved production process ."
Alvaro Sanchez pointed out that this kind of magnetic invisibility cloak is very easy to manufacture: it only needs ready-made materials and costs about 1000 euros (about 1300 US dollars), which is a very small expenditure in the research project. He believes that this type of cloak can be used first in medicine and can be used to protect delicate pacemakers from the strong magnetic fields in magnetic resonance imaging machines. At the same time, he also admitted that there will be bad applications. He said: "This technology can be used to hide metal texture weapons at security checkpoints, but I prefer the other side of the question - our ideas can also help The department designed a more secure inspection program."
Richard Tomsett, a border security adviser who works for a London-based consulting firm (Dextera Globa), pointed out that there are other inspection methods at airport security, such as X-ray machines and sniffing. Dogs and other dogs cannot be swept away. However, he believes that relevant departments still need to keep pace with the development of science and technology. He said: "The invisibility cloak poses an operational challenge to security agencies, which requires them to respond positively to scientists and technology manufacturers to deal with this potential threat." (Compiled: Double Helix)
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