Terahertz metamaterials interact at terahertz frequencies, usually defined as 0.1 to 10 THz. This changing electrical polarization emits terahertz radiation. Graphene geometric diodes have been reported to rectify terahertz radiation. This type of antenna became an important component in terahertz time-domain spectroscopy. Electron mobility can be calculated from time-resolved terahertz probe measurement. Another example is FT-IR-Spectrometer VERTEX with a terahertz source. Such an antenna could be used to emit radio waves in the terahertz frequency range. The source of the terahertz radiation remains unidentified. "Alternative materials become more suitable for the terahertz and optical regimes". To overcome low resolution of the terahertz systems near-field terahertz imaging systems are under development. Some models suggest that terahertz frequencies are achievable with this material. Researchers have overcome the problem of terahertz frequencies by following various approaches. But the inherent drawback is they are difficult to find above terahertz frequencies. Swept sources in the terahertz regime have been demonstrated.