Some references have introduced the positive refractive index and isotropic material to induce РІР‚СљinvisibilityРІР‚Сњ in the Rayleigh limit for two-dimensional objects 16, 67, 70, 71. If the isotropic positive refractive index materials can also be used to design the metamaterials, we think the cloaking will become more useful. At present, material doping has been used to fabricate some new materials with specific properties 68, 69. Generally speaking, existing designs are based either on anisotropic negative refraction index materials or on the geometric dimensions of the cloak structure 65, 66, 67. Therefore, it is an interesting and meaningful research topic to design a device that does not notably perturb the applied electric field, but it still keeps the original information of the incident field, or it can adjust the localized field exactly according to our will. In contrast, the precise control of the electric field in the target test area helps improve the experimental accuracy. In these applications, the placed sensor will undoubtedly cause electric field perturbations, which may affect the experimental results.

Some conditions we need effectively manipulate the electric field, for example, the measurement of electrostatic phenomena in sandstorms and other aerosol weather 59, 60, neuro-medicine 61, the shielding of an static electromagnetic field for some special devices or sensors 62, the enhancement of localized electric field 63, polymer self-assembly properties induced by strong electric field 64, etc. Can we find alternatives to negative index materials?Р”В«esides, the electric field commonly exists in the nature, and it may change the objectРІР‚в„ўs physical characteristic 56, 57, 58. It is well known that the negative refractive index materials or metamaterials are hard to be produced, and usually, its sizes are much larger than the targets 55.

Some papers also discuss the tunable electromagnetically induced transparency metamaterial based on solid-state plasma 49 and the broadband perfect absorption based on plasmonic nanoparticles 54. However, the materials used in these devices are anisotropic, negative refractive index medium, chiral materials, even double-negative materials or field gain materials 50, 52, 53. Based on the metamaterial, people can also design an electrostatic field concentrator 3, magnetic field concentrator 40, asymmetric universal and invisible gateway 41, the perfect lens 42, 43, perfect transmission channel 44, general illusion device 21, transparency coating 45, dc electric concentrator 46, tunable invisibility cloaking 47, special imaging probe 48 and so on 48, 49, 50, 51. As some of the literatures suggests that each cloaking technique has its own advantages and disadvantages 7, 19, exploring the new methods, for example, the illusion optics, or the common materials that can also make targets invisible from different ways, will significantly promote the practical application of relevant research results 20, 21, 22.Р”Р„t presents some researchers have reported that the invisibility cloak can be widely used in electromagnetic waves 23, 24, 25, 26, mechanical waves 27, elastic waves 28, 29, matter waves 30, water waves 31, magnetic fields 32, DC magnetic or electric fields 33, 34, 35, current 36, and thermal fields 37, 38, 39. Scattering cancellation-based cloaking mainly using metamaterial, meta-surfaces, graphene and/or plasmonic materials to eliminate the scattering field of target object, and it can also be used in some physical fields 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18. The basic idea of transformation optics is to manipulate electromagnetic waves by precisely designing the refractive index and permeability of every point and every direction in space. The transformation optics and scattering cancellation-based cloaking should be two powerful tools 4, 5, 6. Several studies have confirmed that using metamaterials or designing special structures can make the target cloaking or hiding in the environment 2, 3.

In military and some scientific experiments, hiding one object from the environmental is a fundamental requirement 1.

Equivalent particle illusion