Harry Potter's invisibility cloak comes closer to reality

Scientists have pointed out that with the emergence of metamaterials and transformation optics, invisibility has become a scientific possibility.

Recently, a review paper reviewed pointed out that the combination of "forward designs" and "inverse designs" rather than using a single cloaking strategy is very likely to make invisibility cloaks far more realistic.

There are three popular design methodologies: the use of transformation optics, conformal mapping, and scattering cancellation. The key point of cloaking techniques is to use materials with specific constitutive parameters and refractive index.

A competent candidate is a metamaterial, which can be realized with a collection of artificial "atoms" with subwavelength size and spacing.

The three invisibility strategies can be categorized as "forward designs", where the properties of the cloak can be worked out only after completing the design process.

The paper focused on the review of an alternative target-oriented invisibility strategy, which is referred to as an "inverse design" and profoundly different from the forward design.

From a practical point of view and with reverse thinking, the inverse design allows the possibility of integrating the technical advantages of forward strategies; e.g., (i) the central concept of invisibility is to minimize the total scattering cross section, (ii) anisotropic materials ensure invisibility without violating the uniqueness theorem of the inverse problem, and (iii) non-superluminal propagation provides cloaking performance with a relatively broad bandwidth.

The study has been published in SCIENCE CHINA Information Sciences.