A simple water-based broadband metamaterial absorber has been proposed for the terahertz region. The absorption bandwidth is extended based on large frequency dispersive permittivity and high relative dielectric loss of water. The simulated result indicates that the absorption of the proposed structure achieves over 90% in the frequency range from 0.6 to 10 THz at a normal incident angle. Moreover, the performance maintains high over 80% with a wide incident angle up to 60o for transverse electronic (TE) mode and over 90% up to 700 transverse magnetic (TM) mode in the entire operating frequency range. Therefore, the designed absorber has a potential candidate for broadband THz applications.

The integration of multiple varied functionalities into a single and compact EM-based device is greatly demanded in EM integration due to their miniaturized configurations. In this paper, a broadband and high-efficiency bifunctional metasurface employing vanadium dioxide (VO2) is proposed for the terahertz (THz) frequencies. Due to the dielectric-to-metal transition of VO2, the metasurface can be dynamically tuned from a reflecting surface to a broadband absorber under low-temperature conditions. When VO2 is in the dielectric phase, the designed metasurface shows excellent reflection (> 96 %) in a broad frequency range from 0.5 THz to 4.5 THz. Once VO2 is heated up and transited to its metal phase, the proposed metasurface structure efficiently absorbs normally incident EM waves in the frequency range of 1.29 THz to 3.26 THz with an average absorption of 94.3 %. Moreover, the high absorption characterization of the proposed metasurface is maintained with a wide incident angle and is polarization-insensitive due to its symmetric structure, which makes it suitable for THz applications.