4. Conclusion and outlook

The potential applications of space transformation are extremely varied. The examples presented above bear witness to this, even if industrial applications are still a long way off. At first glance, these applications can be transposed to any frequency. But in most cases, these are metal-dielectric structures, and metals do not behave in the same way at microwave, infrared and optical frequencies. As a result, there are major differences between applications in the microwave range, on the one hand, and infrared and visible frequencies, on the other. For these fields, the difficulty lies mainly in the production of materials with metal patterns of sizes of the order of a tenth of the wavelength, and in controlling their geometries