Most people all over the world can remember Harry Potter’s transparent cloak. In the Harry Potter series, Harry gets information using the cloak. People are excited about the possibility of such a cloak and transparent technology has received a lot of attention. Many methods have been developed to create transparent covers and objects.
 At first, what does transparency mean? It means that something cannot be seen. Light goes straight through it and the light is refracted with an intrinsic index of refraction when meeting an object. If light is reflected and it comes into the eyes, people can see an object. If light is not reflected despite its contact with the object, light will keep going straight and people can not detect the existence of the object. So the task of transparency technology is to make material that prevents light from reflecting into people’s eyes or prevents reflection completely. Another option is to create an image of what is behind the object and make it appear in front of the object.
Strong candidates are carpet cloak and the use of Meta material.
The carpet cloak prevents reflected light from entering eyes. The cloak consists of SiN and SiO2 and the surface has 7,000 holes filled with SiN. When light comes to it, the holes change the speed and the direction of the refracted light. So it looks invisible from any angle, and, most importantly, it can work in the full visible spectrum, unlike other technologies. At first, it could only be created about the size of a red blood cell, but can now be produced in sheets over 10 cm2. 
Meta material is a case that prevents light reflection completely. Meta material does not exist in nature and it is made artificially in laboratories. Its important character is that its index of refraction has a negative value and it makes light bend. The light repeatedly bends along the surface of the object and keeps going straight beyond it. So the light cannot come into the eyes and people think that there is nothing. It hadn’t worked when folded, but Korea researchers recently created a bendable transparent cloak. Prof. Kyoungsik Kim (Yonsei University) and Dongheok Shin (Ph.D. candidiate, Yonsei University) developed smart Meta material. If normal material is pressed up or down, the sides of the material are stretched. But if smart Meta material is pressed up or down, the sides are also diminished. It changes the shape of all sides at the same time. So it does not lose the effect in spite of bending and folding. But it is only effective in radio wave region, not in the visible spectrum. As technologies of 3D printing and nano printing have developed rapidly, the size is expected to sharply increase.
The technology is applied to various fields in various ways. For example, stealth technology relates to national defense technology. Additionally, because this technology reduces reflection, it could increase the efficiency of solar cells and LED. In addition, as the size is decreased through nano technology, monitors in the air may also become possible.