Flexible controls of broadband electromagnetic wavefronts with a mechanically programmable metamaterial

Coding and programmable metamaterials have experienced a rapid development since 2014, leading to many physical phenomena and engineering applications from microwave to terahertz frequencies, and even in the acoustic regime. The major challenge for current programmable metamaterials based on switching diodes is the experimental realization of a huge number of feeding lines for independent control of each digital unit. In this work, we provide an alternative approach for the experimental realization of the programmable metamaterial by developing a mechanical system, which consists of an array of metal blocks with adjustable height. The system supports the combination with conventional coding metamaterials to take full controls of both the phase and polarization of EM waves. As a theoretical byproduct of this work, we propose group delay code to achieve diffraction-limited achromatic redirection of linearly polarized broadband beam from 4 to 6 GHz by combining the group-delay code with the conventional phase code, a feat that traditionally requires complex structural design of unit cell. In view of the multifunctional performance afforded by the full-control of the phase, polarization and group delay, the mechanically controllable metamaterial in the microwave region may benefit different applications, such as imaging, communication, and radar detection.