Flexible manipulation of electromagnetic waves has always been fascinating and created interest among people. Proficient control over these waves has been gradually improved with better understanding of the wave theories and properties. But the emergence of metamaterials and metasurfaces in the last decade was the most significant in tailoring wavefront. In our first work in this dissertation, we presented a reflective metasurface to send back an incident wave into anomalous reflection angle by suppressing undesired harmonics. Generally, a dense unit cell array used in a metasurface for a high reflection angle (θr > 50°) leads to high coupling among the unit cells; thus, parasitic reflections are unavoidable. The up-do-date patch-based metasurfaces for high reflection angles were electrically large (> 80 λ²), but for a practical point of view, a more compact metasurface design is needed. As a solution for these issues, we use the folded dipole-based unit cells with closed-loop currents for low near-field coupling and design compact metasurfaces (~ 40 λ²) for high reflection angles (θr = 56° and 70°) at 10 GHz. The folded dipole unit cells are arranged according to the recently developed non-linear phase boundary condition for low harmonic reflections. As a counterpart, we also designed a metasurface using conventional patch-shaped unit cells with the same reflection phases (θr = 70°). In experiments, the folded dipole metasurface shows lower harmonic levels (θr = 0° and -70°) and a comparable anomalous reflection (θr = 70°) versus the patch-shaped metasurface. The time-domain analysis demonstrates that the low harmonic levels from the folded dipole metasurface are due to low scattering from the guided waves and the edge scattering. The proposed compact folded dipole-based metasurface with low undesired harmonics can be used as a practical reflect-array for millimeter-wave communication links.
In our second work, we tried to investigate about the the energy harvesting possibility from waste heat sources. Low-temperature waste heat in the infrared (IR) wavelength region offers an opportunity to harvest power from waste energy and requires further investigation to find efficient conversion techniques. Although grating-coupled metal-oxide-semiconductor (MOS) diode devices offer efficient conversion from low and moderate-temperature thermal sources, the integration of such diodes with a nanoantenna structure has yet to be explored. We propose a bowtie nanoantenna coupled MOS diode for IR to direct current (DC) conversion without any bias voltage at 28.3 THz. Two different types of diode configuration has been presented. One with only p-doped silicon layer and another one with p and n-doped silicon layer. The nanoantenna was designed and optimized to provide maximum field enhancement in a 4 nm-thick oxide layer at the resonant frequency. The devices were fabricated following the complementary MOS (CMOS) fabrication process and measured in a custom DC and optical characterization setup using a 10.6 μm wavelength CO₂ laser. The results reveal two different types of device performances with linear and nonlinear I-V curves having kΩ and MΩ zero-bias resistance, respectively. The linear device generates a micron-level open-circuit voltage (Voc) with clear polarization dependence from the laser input, but the nonlinear case suffers from a weak noise-like signal. Finally, we analyze two types of devices using thermoelectric and tunneling effects and discuss the future direction of nanoantenna-integrated MOS devices for efficient IR harvesters.