Electromagnetic super scattered and invisible doors

| Author: Chen Huanyang Qilin Wurui New Horse Red Him STYLE = \”COLOR: RGB (0, 0, 0); Font-Family: Microsoft Yahei; FONT-SIZE: 16px; Letter-Spacing: 1px; White-Space: Pre-Wrap; Widows: 1; Caret-Color: Red; \”/>

(1 Xiamen University School of Physics and Technology)

(2 School of Electronic Science and Engineering, Nanjing University)

(3 Yunnan University physics and Academy of Astronomy)

This article is selected from\” Physics \”, No. 12, 2022

\”Phantom optical devices for transforming optical can show the phenomenon of no existence in nature, such as stealth, over-scattered and invisible doors. Among them, electricityThe phenomenon of magnetic super scattering uses the fold geometric transformation in the transformation of optics, so that the scattering section of the object is much larger than its geometric section, which subverts people\’s perception of the geometric section of the scattered scattering in the traditional scattering scattered section. This phenomenon also provides possibilities for realizing \”wall -through techniques\” in reality. The article focuses on the development process of transform -based superflugs and the method of using ultra -scattering to achieve invisible doors. The realization of invisible doors in free space provides new ideas for the design of future illusion devices.

Keywords Super scattered, invisible doors, transform optical, super materials

1 Introduction

Many film and television works of \”invisible\” in film and television and literary works are fascinating. Among them, the most famous one is \” The stealth clothes in Harry Potter, when we put on the stealth clothes, are not seen outside. People can perceive that the object is due to the light that the object is received, so the key to stealth is the manipulation of light. In the mythology, the wall of the wall refers to the superpowers of wearing a physical wall as the main body. In reality, \”through the wall\” needs to be achieved by changing the special optical properties of the wall. For electromagnetic waves, wall -piercing is a special door that objects can pass, but this door is not seen by the observer, that is, the \”invisible door\”. Wall -piercing techniques implemented with invisible doors are closely related to the illusion of illusion. The illusion optical effect of objects refers to a different optical phenomenon that the observed objects and actual objects themselves. One of the typical examples is the super -scattering effect. The size becomes very large. In 2009, the research team of Ma Hongzhang/Luo Xudong, Shanghai Jiaotong University, first found super dispersion in the study. Theoretical research shows that ultra -dispenser can be implemented by combining compensation medium binding to transform optics. This method has been used to design many wonderful and interesting illusion optical devices, such as stealth channels or invisible doors based on super -scattered effects, super absorbers, non -package hidden clothes and endoscopes. IllusionOptical device. Through reasonable design of the dielectric constant and magnetic guidance rate (or refractive index), the researchers first realized the invisible door in 2009. However, this invisible door requires extremely harsh requirements for the refractive index distribution of the required materials, and it is difficult to achieve in the experiment. Later, people proposed a stealth door design solution based on simplified parameters, and verified the existence of the invisible door with an equivalent method. However, it was not until 2021 that the real invisible door was confirmed in the experiment. Wu Rui\’s new research team and Chen Huanyang, Nanjing University, verified the phenomenon of ultra -scattered scattering in the free space of microwave frequency, and realized the illusion optical device of electromagnetic invisible doors in the experiment.

The invisible door has gone from the first theory to the final experiment for more than ten years. This article will focus on the development process of stealth door, mainly from three aspects: first of all, the proposal of changing the strong theory of optics; secondly, the proposal from the quasi -static limit to the electromagnetic super scatter; Door theoretical design and experimental verification. The success of the invisible door in the experiment will provide new ideas for the application and development of new type of light field regulatory devices in the future.

2 Transform optical

> Light spreads along the straight line in a uniform medium, and a deflection occurs when the light passes through the interface of the two media. In life, the chopsticks placed in a water -wide transparent cup seem to be \”broken\” by this principle. When the refractive index appears gradient distribution, such as the density of the air on the desert due to the unevenness of the temperature, the density of the air on the desert is different, thereby generating a gradient refractive index distribution, and then a magical mirage phenomenon. This makes us think that as long as the medium with a certain refractive index distribution is designed, the light will spread in a specific direction.

In 2006, Pendry et al., Leonhardt independently proposed the method of transforming optical design stealth clothes, respectively. As shown in Figure 1 (a), in the \”virtual space\”, that is, in the vacuum, the light spreads along the line, and through the coordinate transformation, a point expansion in the space to form a circle in a \”physical space\” )) The light will spread around the red circle, so the interior of the red circle is not visible to the outside, showingInvisible effect. The proposal of this theory has the possibility of realizing the magical stealth clothes in Harry Potter. Subsequently, Smith et al. Using the opening resonance ring as a structural unit of the super -structure material, the single -frequency two -dimensional stealth device was implemented in the microwave band experiment. Since then, the transformation optical has attracted widespread attention because of the ability to freely control the light field.

1 coordinate transformation (a) Before the transformation, the light spreads in a straight line before the transformation; (b) the point swells into a circular (red circle) by transforming, and the light bypass the circular area spread

The core of transforming optics is to establish a transformation relationship in two spaces (virtual space and physical space) through coordinates. Because the Maxwell equation group has formal invisible forms before and after coordinates, the electromagnetic parameters in the two spaces (dielectric constant and magnetic guidance) can establish the corresponding relationship with coordinate transformation:

Among them, is virtual The elegance of space and physical space can be comparable to the matrix, and \’,\’ from 1 to 3 value selection to indicate separately Three space coordinates. Using transformation optics can design many new features, such as stealth jackets, rotating clothes, vessels, and illusion devices.

Figure 2 part of the illusion optical device and Its corresponding coordinate transformation relationship (A) ideal stealth clothes; (b) weakening the design after design; (C) the stealth jacket based on Fabri -Pero resonance; —H) The transformation relationship between the corresponding device corresponds to the virtual space and the physical space, of which the transformation point of the yellow dot corresponds to the transformation, which represents the radius of the concentric ring before and after the transformation. Text-Align: Justify \”> Since the transformation of optics, the most watched is the design of the\” stealth jacket \”. As shown in Figure 2 (a), the stealth clothing can guide the light to spread around objects, so that the object\” invisible \”\” invisible \” Essence existUnder the column pole coordinates, the corresponding transformation relationship of the ideal two-dimensional stealth jacket is shown in Figure 2 (e), that is,:

However, such an ideal stealth clothing can only work at a single frequency point and cannot achieve perfect stealth effects in a wide range. In response to this issue, Chen Huanyang and others proposed color dispersion stealth clothes. This stealth jacket has widened the frequency of the ideal stealth jacket, but accompanied by the sacrifice of part of the performance. The core idea of the design of the color scattered stealth jacket is to use a more general transformation form, as shown in Figure 2 (f), compressing a common heart ring area area <≤ ′ into another common heart circular area ′ <≤ ′, When = 0, the change should return to the ideal stealth. Such a stealth jacket is a weakened design after designing, as shown in Figure 2 (b), the weakened stealth jacket is equivalent to a small scattering with a radius in a free space. Therefore, the change point of the coordinate transformation corresponding to Figure 2 (f), that is, in the virtual space, is raised compared to Figure 2 (e).

In 2015, Chen Huanyang/Houbo\’s research team introduced Fabri-Pero resonance into the design of transforming optical devices. Such devices can resonate in multiple resonances in multiple resonance Working at the frequency makes multi -frequency applications of transforming optical devices possible. As shown in Figure 2 (g), the core of its transformation is to map the ≤ <in the virtual space to the concentric cylindrical layer of the physical space. Stealing vessels. When it is approaching, the stealth polyets corresponding to the extreme version. Furthermore, when ′ ≤ <′, order = ∞, = (′) and = 1 (the magnetic mode corresponding to the magnetic field in the direction), where the dielectric constant components in the corresponding direction and direction, the magnetic guide in the corresponding direction in the direction of the direction Rate weight; and when 0 ≤ ′ <′, order = (′/′), = 1, then this device is the stealth vessel device of Fabri -Pero resonance, and the Fabri -Pero -Pero resonance conditions in the direction are Can be written as

When = 3, ′ = 2, ′ = 1, (′) = (3 -′), its electromagnetic wave distribution is shown in Figure 2 (c) as shown in Figure 2 (c) And this device is verified in the experiment. The three changes are different, as shown in Figure 2 (h), the folding transformation shown in Figure 2 (h) will introduce negative refractive index materials (<0, <0) in the natural world because the slope is negative. The artificial super -constructor is constructed and negatively negatively negatively deflected material. The spread of light provides more possibilities. For the folding and transformation of the space, the single point in the virtual space corresponds to the three points in the physical space. In the area composition, there is no phase accumulation after the light is compensated after compensating the medium, and it looks like this area does not exist. The refractive index material (′ <<<<<<<) and the air (′ <<<<<<<<), the air layer and the negative refractive index layer constitute the compensation medium, that is, the optical empty cave is formed between the region (′ <<<<<ut). The scattering characteristics of this system mainly depends on objects placed on the nuclear layer. Phantom optical device. Enter the inside of r = r ′, so Figure 2 (A)Observator inside the medium stealth device cannot see the external situation, not an observer inside the package stealth internal. By folding geometric transformation, you can also design anti -stealth devices to destroy the stealth effect of stealth device composed of positive refractive index materials. These magical illusion devices can\'t help but think about it, is it real?

3 electromagnetic The proposal and development of ultra-scattering

Electromagnetic waves are incident into objects to objects Scattering occurs on the surface, and electromagnetic scattering is a very common physical phenomenon. For example, the clear sky is blue from Ruili scattering: the molecular size in the air is far less than the wavelength of light. It can be seen that the blue light wavelength in the light is shorter, so it is more likely to scatter. This is the physical mystery contained in the blue sky. When there are more dust particles and droplets in the air in the air, Mi\’s scattering occurs, and the light of all wavelengths of the wavelength in the Mi\’s scattered scattering, so the sky is gray -white. Electromagnetic scattering also has many important applications. For example, in the field of communication, the scattering effect of the electromagnetic waves can be used to conduct over -the -Lial distance communication with the stream layer; in the military radar detection, the information of the scattering object can be obtained by analyzing the scattering characteristics.

You can see that in traditional scattering, the scattering characteristics are closely related to the size of the scattering body. The scattering section of the object is usually less than its geometric section. Ordinary materials have limited regulation of electromagnetic waves. Even compared with the large wavelength scattering, its scattering section only increases geometric sections. Some scattering sections exceeded by the resonance effect based on the resonance effect can also distinguish it from the non -resonant scatter -scattered radio by analyzing the loose scattering coefficients at all levels. The emergence of transforming optics and super materials has greatly enhanced people\’s ability to control the electromagnetic field. In addition to perfectly eliminating the stealth effect of scattering, it can also make the scattering characteristics of small objects and large objects unswerving, that is, the phenomenon of \”super scattering\”. This phenomenon subverts the maximum scattering section of large -scale objects in electric power is the traditional cognition of its geometric section.

Ultra-scattering makes an object look larger than its actual size by enhancing the scattering section. This phenomenon has extensive application prospects in terms of sensing, aggregating energy, fluorescent imaging, and power wireless transmission. Considering the scattering problem of the nuclear layer structure shown in Figure 3 (a), under the quasi -static limit (that is, the size of the object is far less than the wavelength), you can use the approximate Maxwell equation group to solve the problem, and you can ignore other items and only only items. Consider the response of the objects composed of the core layer (), shell (), and background materials () to the source of the core layer. When+= 0 and+= 0, the object has no effect on the external field; when only+= 0, the scattering of the core layer will exceed the scattering of the shell layer, as if the radius of the core layer is enlarged. Under the quasi -static limits, the core layer can be enlarged, and the transition from the quasi -static limit to the electromagnetic scattering (need to consider the scattering of other steps). At present, there are three main methods that can achieve super scattering: the first is to enlarge the object by changing the optical method and introducing the concept of compensation media to achieve super scattering; the second is to use multi -layer metal -medium sub -long nano -column surface, etc. The resonance of Liquida breaks the single -channel scattering limit to achieve the phenomenon of super scattered radiation. This method can only achieve a limited order amplification through the resonance, and the loss of material loss has a great effect on the effect of scattering enhancement; the third is to use nearly zero near zero The refractive index material is used to enhance the scattering of the object. This method requires a background environment with a near zero refractive index, which has further challenged the preparation and compatibility. This article focuses on the first method of achieving ultra -scattering, which will be further introduced below.

Under the quasi-static conditions, the low-order scattering coefficient plays a decisive role. When the size and wavelength of the object are comparable, the high-level scattering cannot be ignored. The means can realize the super scattering of objects with wavelengths that can be compared with size. Starting from the negative folding rate tablet in Figure 3 (b), the point sources are placed in the position of the thickness of the thickness of the negative folding meter (yellow area), and the point source can be seen in harmony through geometric optical. When setting the perfect electrical conductive boundary (PEC), the light will be rebounded back, and the area <<<<<cting the region to form a pair of compensation medium, the perfect electrical conductor boundary of the place seems to be moved to the place. Then roll the tablet into a cylinder, as shown in Figure 3 (c), using the coordinate transformation of Figure 2 (h). Similarly, the area <<<<<<ct, your region <<<<<<ct constitutes compensation medium, the perfect electrical conductive boundary boundary inside = the boundaries of the electrical conductive border boundary Visually moved to =, the geometric size of the object was equatedly put into the extensive exposure effect. Figure 3 (d) and 3 (e) are the calculation results of the COMSOL simulation. Among them, the black solid line represents the cylindrical boundary, and the black dotted line represents the equivalent area after the scattering enhancement.

3 (a) the electromagnetic scattering diagram of the nuclear layer structure; the transmission of light in the negative refractive index material (C) in the negative refractive index material (B) in the flat plate, the green solid line is perfect Directors; (D) The inner and outer radius is the total electric field distribution of = 0.1 m and = 0.2 m over -scattered cylinder; (E) Total electric field distribution of perfect electrical conductors with radius = 0.3 m, (D), (E), (E), (E) All are graphic wave incidents

When the frequency is 3 GHz (the electric field is along the direction) of the plane wave, Figure 3 (d), (. (D) e) The distribution of electric fields is the same, which proves that the physical mechanism behind it is the enlarged of the negative refractive index shell layer. Other shapes. STYLE: SOLID; Text-DECORATION-COLOR: RGB (59, 26, 19); \”> The implementation of the electromagnetic invisible door

In the movie\” In Harry Potter, Platform is the invisible channel (or invisible door) of the Hogwarts Express train, as shown in Figure 4 (a), which is both magic and an illusion optical effect, that is, this channel is in The space is actually existing, but the observer outside the channel cannot be seen from the visual level. /p>

In 2009, Ma Hongzhang/Luo Xudong\’s research team of Shanghai Jiaotong University further developed the super-loose ejaculation proposed in Figure 3 (d), which promoted it as a square supermodel The scattering is placed between two properly distance metal walls. When super -loose ejaculation, this channel area (|| ≤ +) obviously can obviously be detected by analyzing the scattered electromagnetic waves, and when the designed square superprooper is placed in the channel area The surrounding area), because the overlap scattering section is larger than its geometric section, the electromagnetic wave cannot be passed, so a \”invisible\” channel is constructed. When the sides of the invisible channel, you will see the \”scene\” that is completely different, as shown in Figure 4 (d), (e). The refractive index distribution of materials is demanding, which limits the development of invisible channel devices. CN-I-QVJ2LQ49K0/E28C429969484EEABA16ACE10CAA2F87 ~ TPLV-Orig in-Web: GIF.JPEG? _IZ = 58558 & FROM = Article.pc_detail & LK3S = 953192F4 & X-EXPIRES = 1738813625 & X-Signature = S%2BRUBWUGSDFTYLQGRQgtyz76hji%3d \”/>

Figure 4 The theoretical prototype design of the invisible door (A) The platform in\” Harry Potter \”; (b) a package type The invisible door is the perfect electrical conductor area. It is a negative refractive index package area, which is an area where the electromagnetic wave cannot pass through; The effects of the observer are demonstrators on both sides through simulation; (f) corresponding to the invisible door effect in (c)

In the same year, Chen Huanyang and others proposed A simplified invisible door prototype design is shown in Figure 4 (C). A certain working bandwrker is in the light source, and due to the existence of the negative folding rate material (the red area in Figure 4 (c)), the surface wave will be stimulated in the air and material interface, and the phenomenon Equivalent to the mirror part of the device itself filled with the refractive index area area. In the case of considering the cross -electric mode, the perfect conductivity is placed at both ends of the overlap, which naturally forms an invisible channel. ) It is shown that the electromagnetic wave on one side is perfectly \”blocked\” when passing through the air channel of the device, but it can allow the object to pass through the perfect invisible door. The solution has been simulated to verify. In the year, Li Chao and Chen Huanyang, Institute of Electronics, Institute of Electronics of the Chinese Academy of Sciences, used the transmission line model to simulate the invisible door device in the experiment for the first time. , Use series capacitors and parallel inductors to simulate negative refractive index materials, and optimize the boundaries of the two. Finally, the invisible door device is constructed on the circuit board. It can be seen from the experimental measurement results of Figure 5 (b). Progressive communication signal.

Figure 5 The circuit experiment of the invisible door realization (A) uses the stealth door device simulated by the circuit model; \”> The verification method of circuit simulation provides a feasible solution for the realization of the implementation of illusion optical devices. However, this is still very different from the real scene. People are looking forward to realizing the real invisible door in the real environment. The research team cooperated with Chen Huanyang to use the simplified stealth door design scheme, using the self -biased 锶 magnet oxygen array to build an ultra -scattering body, and the invisible door was built in the free space, as shown in Figure 6 (a). For the first time, the air passage has a significant blocking effect on the electromagnetic field. As shown in Figure 6 (b), the incident electromagnetic waves are rapidly attenuated along the channel, and the electric field at the end of the air channel almost disappears, which realizes the real invisibility in the free space. The door. As shown in Figure 6 (C), the air channels with the same width between two perfection electrical conductors and Figure 6 (C) cannot block the transmission of electromagnetic waves. Evaphostic waves can penetrate the air channel without it. Attenuation is attenuated. Among them, the energy density of the electric field is rapidly attenuated, and 90%of the energy from the point to the ′ point is blocked, while the attenuation of the energy density of the electric field in the metal waveguide is only 15%. The relationship between the energy density ratio and frequency of the energy density ratio and frequency of the two port ports of the metal wave guide can see that the ratio of the ratio in the green shadow range is gradually decreasing and the ratio of the corresponding metal wave guide is relatively stable. Ability. The realization of the invisible door of the hyper structure has further promoted the development of illusion optical devices, making the application of invisible doors in real scenes possible. : // p3-sign.toutiaoimg.com/tos-cn- I-QVJ2LQ49K0/9C49FC614475EB0D1B87834B2A0A2~TPLV- origin-web:gif.jpeg? 58558&From=article.pc _Detail & lk3s = 953192F4 & X-EXPIRES = 1738813625 & X-Signature = T8RGCZOS8LDR1QMQEYG9AMig6a%3D \”/ >

Figure 6 Experiments of the free space of the invisible door in the microwave frequency band (A) The electromagnetic invisible door device built by the iron oxygen array (white trapezoidal array) , Metal aluminum combined with iron oxygen array as a perfect conductor; (b) the measurement results of the experimental measurement of electromagnetic invisible doors; Among the white dots marked with white spots, aluminum is represented by gray; (D) The return of the invisible door (corresponding (b)) and the air channel of metal waveguide (corresponding (c) figure) in the experiment and simulation Energy density of the electric field; (G) The relationship between the energy density ratio and frequency of the electric field energy density and frequency of the invisible door and the metal wave guide at the output port and the input port

5 Summary

People are tirelessly pursued. Not only have broad application prospects in the fields of sensing, energy collection, but also to construct optical illusion devices such as invisible doors. It is a big step forward in the field of illusion optical. , The size of the longitudinal electrical electricity is usually greater than 2), and it can be widenedTo other optical bands, such as visible light and infrared bands. However, the current implementation of the invisible door mainly relies on negative refractive index materials (refractive index = -1). Therefore, there are certain restrictions on the width of the working bandwidth and cannot be promoted to the geometric optical field. With the proposal of the negative refractive index material of acoustic science, the hidden door is expected to be promoted to the three -dimensional acoustics field for sound waves.

thanks There are many The collaborators have made great contributions and influence on this series of work, and cannot be listed one by one. For example, Professor Chen Ziting of the Hong Kong University of Science and Technology, Professor Zhang Zhaoqing and Professor Shen Ping, Professor Luo Xudong of Shanghai Jiaotong University and Professor Yang Tao of Ningxia University, Professor Lai Yun of Nanjing University, Professor Hou Bo and Professor Xu Yadong of Suzhou University, Southern University of Science and Technology Professor Wu Zihui, Professor Lin Zhifang of Fudan University, and Liu Shiyang of Zhejiang Normal University, etc., discuss with them, are extremely pleasant memories and luck of life! Thanks to the hard work and correction of Xiamen University\’s doctoral students, Yin Yuhang, Zhao Pengfei, and Zhu Shan.

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