چكيده به لاتين
Invisibility has long been a human desire. The astonishing invisibility of objects, the design of invisible electromagnetic and optical coatings has been considered in later years. More research has been done on this idea, which has even been refined in other areas, including acoustics and thermodynamics. Practical examples in the field of electromagnetism from DC to X-ray are now available and in development. Ideally, the object can be completely hidden from the outside observer within a certain frequency range so that it cannot be detected by any powerful radar. In fact, moderation is a deceptive cover. The main feature of these coatings is the change of the scattering pattern of the object, both in the near-field and in the far-field. The purpose of this dissertation is to design and create a metamaterial coating for an object with the desired geometry so that it can choose its scattering pattern as desired.
In the first chapter, a summary of the approvals of the proposal and the work done is provided. In the second chapter, we have reviewed the researches conducted on the subject of illusionary and concealing coverings in recent years. In other chapters, we have done various activities in order to achieve an illusionary coating layer to control the scattering pattern of the object with the desired shape. In the third chapter, we designed a cover that is placed around a cylindrical object with a desired cross-section and material. Regardless of the propagation direction, before the wave reaches the inner core, it absorbs the EM fields, and as a result, it greatly reduces the radar cross section. In the fourth chapter, with the help of a material with extreme characteristics, we designed a concealment for surface waves, which keeps an object with a desired geometry hidden from the view of the propagating wave. In the fifth chapter, we presented a method to arbitrarily control the scattering pattern of a surface. In fact, according to the direction of wave radiation, it is possible to control the number of scattering beams, their direction and the level of each beam relative to the others. As a result, it can be used as an illusionary cover. In all the works done in order to control the scattering pattern, it was necessary to completely surround the object by the cover. Although efforts have been made to design external cloaking devices, their material depends on the desired object, and by changing the geometry or material of the object, the cloaking cover must be designed from scratch. In the sixth chapter, we presented a structure that, if placed in the vicinity of any object (with specific dimensions), keeps it hidden from the view of the third observer. As we explained in detail in this chapter, although efforts have been made in the field of electromagnetics, the presented structures have problems that cannot be used in practice. As a result, in this treatise, we have presented the general idea and realized it in acoustic physics. In the seventh chapter, with the help of materials with extreme characteristics, we have presented a carpet cloak for objects placed on the ground. The main features of this cloak, compared to the work done, are the lack of dependence on the angle, and extremely low thickness. In this research, we presented the most general possible case and as we have shown, we can use this cover for any desired geometry. In the eighth chapter, for cylindrical structures with an arbitrary cross-section, we designed a cover of electromagnetic metasurfaces based on GSTC, which keeps it hidden from the view of electromagnetic waves, regardless of the geometry of the shape. In the same chapter, using materials with extreme characteristics, we designed a cover for cylindrical structures whose far field and near field scattering patterns can be transformed into any other desired object. After we found out that these materials with extreme characteristics have very interesting properties, we didn't stop with this thesis and started to design other devices that, besides being hidden from the view of the external wave, also have other functions at the same time. In the ninth chapter, we verified the idea of concentrator of electromagnetic waves using these extreme materials. As we will see, we have shown that by using materials with extreme characteristics, in addition to the fact that the device itself cannot be seen, it is possible to concentrate electromagnetic energy in an area with an arbitrary geometry. In the tenth, eleventh and twelfth chapters, we implemented this idea for other physics of acoustics, static electric fields and thermodynamics. In the twelfth chapter, using extreme materials, in addition to the concentrator design, we also implemented other structures such as thermal cloak. In fact, we were able to provide omnidirectional concealment using only two anisotropic materials, which is made of simple and realizable materials, unlike previous works. In the 13th chapter, using the aforementioned extreme materials, we designed a lens that can be used to image in the acoustic field, below the diffraction limit, and to identify details that are less than the wavelength.
As a result, in this treatise, in addition to obtaining different coatings to hide objects with desired geometry, we were able to design and implement various other tools in different physics.
