Recently, Aoyama University, Japan, in a study, realized the movement of magnetic suspension graphene with laser for the first time. By changing the temperature of graphene, it can change its suspension height, control the direction of movement and make it rotate, and demonstrated that sunlight Let graphene rotate. This achievement is of great significance for the study of light-driven human transportation vehicles, and is expected to bring a new type of light energy conversion system. Related papers were published in the recently published "Journal of the American Chemical Society".
Magnetic levitation has proved effective for various objects from trains to frogs, but so far there is no magnetic levitation brake that converts external energy into kinetic energy. The researchers explained that the magnetic levitation is due to the object's diamagnetic properties, which will repel the magnetic field. All substances have different degrees of diamagnetism. Usually, diamagnetism is very weak and cannot make objects float. Only when the diamagnetic strength of an object exceeds its paramagnetism (attracted by a magnetic field), the combined magnetic force is a repulsive force and the repulsive force is greater than gravity, it may float. Graphene is one of the most diamagnetic materials.
The levitation height of diamagnetic objects depends on the applied magnetic field and the diamagnetism of the material itself. The levitation position can be controlled in advance by changing the applied magnetic field. To date, no one has been able to use external stimuli such as temperature, light, sound, etc. to change the material's diamagnetism to control the motion of magnetically suspended objects.
"The most important point of this research is the realization of real-time motion control technology, which for the first time promotes a suspended diamagnetic object without contact." The paper co-author and professor of Aoyama University University Abejiro said, "Because the technology is simple And basically, it is expected to be used in many areas of daily life, such as transportation systems, entertainment activities, light brakes, and light energy conversion systems. "
In the experiment, the researchers demonstrated that using a laser to control the temperature, a small piece of disk-shaped graphene was suspended above a piece of NdFeB permanent magnet. The flying height of graphene will decrease as the temperature increases, and vice versa. The researchers explained that changing the temperature will change the magnetic susceptibility of graphene, or the degree to which it is magnetized by an external magnetic field. At the atomic scale, the photothermal effect of laser light increases the number of thermally excited electrons in graphene. The more thermally excited electrons, the weaker the diamagnetism of graphene, and the lower the suspension height.
Aiming the laser at the center of the graphene disc can control the height, and aiming at the edge allows it to move and rotate. Because changing the temperature distribution will change the magnetic susceptibility distribution, so that the repulsive force of graphene in the magnetic field is uneven, so that it moves in the same direction as the beam movement. The rotating device they designed will also rotate in the sun, with a speed of more than 200 rpm. This is very useful for developing optically driven turbines.
Researchers predict that amplifying the ability of this laser to control the magnetic levitation movement is expected to promote the development of magnetic levitation brakes, solar thermal conversion systems, and can also be used in low-cost environmentally friendly power generation systems and new optical drive transportation systems.
Abe said: "At present, we are planning to develop a magnetic levitation turbine blade suitable for the system. There may be frictional force to destroy the rotation, so we want to use a technology related to MEMS (micro-electromechanical system) to develop an efficient Light energy conversion system. In terms of brakes, magnetic suspension graphene can transport any object that weighs nearly its own weight. If this system can be successfully amplified, it is not a dream to develop personal transportation.
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