**4. Conclusion**

So far metamaterial has stimulated a lot of revolutionary work in the traditional microwave antenna technology. Some typical applications such as 5G MIMO antenna, metamaterial absorber, and polarization controllers are already been used for telecommunications and imaging radar. Worth to mention that, in the booming area of high frequency applications like terahertz and optical regime, metalens is definitely more attractive subject, since the stronger bandwidth capacity and high resolution at high frequency will pave the way for countless more opportunities in the field of the high-speed communications, secure imaging, bio-medical sensing and novel microscopy [21, 22]. In this chapter, we have reviewed the design principle as the general routine and elaborate the focalization and beamforming effect. The content covers the broad range of application cases from microwave front-end antenna to optical achromatic imaging lens. However, the metamaterial is still a fast-paced and highly interdisciplinary area. Some cutting-edge technologies like the inverse deep-learning method are used to design the metalens for large aperture, achromatic and efficient focusing. The liquid crystal metamaterials (LCM) have been created for large-angle beamforming of microwave, and potentially infrared Laser for solid-state LiDAR technology.
