Recently, "Physical Review Letter" published the research results of the research group titled "Experiments on active cloaking and illusion for Laplace equation" by Associate Professor Mei Zhonglei's research group of Lanzhou University School of Information and Professor Cui Tiejun's research group of Southeast University Millimeter Wave State Key Laboratory. The paper reported the first active stealth and deformation experiment for Laplace equation, and the first active stealth and deformation experiment for all bands. This is the second report of the joint research group's work on freely regulating the electrostatic field since the paper titled "dc electric invisibility cloak" was published as a cover paper in the Physics Review Letters in August 2012.
Research on electromagnetic stealth devices has always been a hot issue in the scientific field. In 2006, the British physicist Sir JB Pendry published a paper in Science, proposed the theory of transforming optics to control electromagnetic waves, and designed an extremely elegant and perfect stealth device based on it, which aroused people's attention to stealth devices. In the same year, the research team of Professor DR Smith of Duke University in the United States verified the simplified electromagnetic stealth device for the first time in experiments. This research was rated by Science Magazine as one of the top ten scientific breakthroughs in 2006. In 2009, the joint research group of Professor Smith of Duke University and Professor Cui Tiejun of Southeast University realized the first two-dimensional experiment of the broadband broadband stealth device (ie, stealth carpet), which was published in Science. Since then, research on electromagnetic stealth has been in full swing around the world. However, the experimental design of these stealth devices has some similarities, and there is still a lack of experimental verification of perfect stealth devices.
As a special case of time-varying electromagnetic fields, the study of electrostatic and magnetostatic stealth devices also has important theoretical and practical significance. In early 2012, Science and Advanced Material reported independently on the research results of DC and magnetic superconducting stealth devices from the research groups of Harvard University in Spain and the United States. Later, Associate Professor Mei Zhonglei of Lanzhou University and Professor Cui Tiejun of Southeast University proposed and experimentally verified DC stealth devices on Physical Review Letters, which just complemented the above research and constituted a set of static and magnetostatic stealth fields. Complete theory. The joint research group proposed a new idea of ​​using a resistance network to construct a non-uniform, anisotropic equivalent conductivity medium, which can achieve any conductivity distribution (including singularity), thus verifying perfect stealth under DC conditions. On the basis of the above work, based on the theory of transformation electrostatics, the research group conducted a systematic and in-depth study on the regulation of the DC field, and achieved a series of results. Including: designing and verifying an external stealth device for the first time, it does not need to cover the target to be hidden, just placed next to the target to achieve the stealth effect; successively designed and implemented: DC illusion equipment, which can change the object in EIT Bioimpedance imaging) detects the "fingerprint" information under the device to achieve passive "deformation"; DC stealth carpet can hide objects placed on flat ground; DC field concentrator to complete the enhancement of current density; a super Thin stealth devices, using a single layer structure can achieve the ideal stealth effect. In principle, this idea can realize all possible conversion electrostatic devices.
Unlike the method of transforming electrostatics, the recent Physical Review Letters paper achieves electromagnetic stealth from a new perspective. Instead of wrapping the target to be detected with stealth devices, some controlled sources are placed around the target, and the fields generated by these controlled sources just offset the scattered fields generated by the target. According to the uniqueness theorem and superposition principle, these controlled sources protect the target from being detected like an invisibility cloak, so it is called active stealth. Similarly, this method can also achieve active deformation. Its advantage is that it does not require the use of complex new artificial electromagnetic media, flexible, and online controllable; the disadvantage is that it is currently only applicable to DC or low frequency conditions (such as sound waves). After the work was published, BBC Website Future conducted a follow-up report entitled "Shape-shifting: how to build an 'illusion cloak'" on the Under the Radar Column column on November 5, 2013.
It should be noted that the use of a resistor network is of universal significance to other regulation problems based on the Laplace equation field. For example, because resistance generates heat when current flows, it is also possible to use this type of network for arbitrary control of heat transfer (based on the Laplace equation).
This research was supported by major projects of the National Natural Science Foundation of China.
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