Ultrathin metasurfaces with local phase compensation deliver new schemes to cloaking devices. We demonstrate a remarkable large size carpet cloak realized by an ultrathin metasurface at terahertz frequencies. The metasurface cloak is constructed by periodically arranging 12 different elements. The reflected wave front is perfectly reconstructed by an ultrathin metasurface cloak, which perform well under both intensity-sensitive and phase-sensitive detectors. The invisibility is verified when the cloak is placed on a reflecting triangular surface (bump). The multi-step discrete phase design method would greatly simplify the design process and is probable to achieve large-dimension cloaks, for applications in radar and antenna systems as a thin and easy-to-fabricate solution for radio and terahertz frequencies.
At present, the mechanism and devices of terahertz radar detection and imaging has attracted a lot of interest. Based on 4-f terahertz time-domain spectroscopy (THz-TDS) technology, a broad-band time domain terahertz radar system (0.1- 1.3 THz) was built for scattering and imaging characteristics of objects. Far-field radar cross-section measurements of different metal scaled models at terahertz frequencies were performed. The novel broadband radar can provide RCS distributions at arbitrary frequency and frequency-averaged RCS. Moreover, based on improved filtered back projection algorithm, imaging of the scaled models has also been retrieved, which can be helpful for scattering points searching and military shape optimization.