A novel matching technique and the field enhancement at the terminals of a bowtie nanoantenna are utilized to develop compact, highly efficient, and flexible thermophotovoltaic (TPV) cells. The bowtie antenna is designed for maximum power transfer to a near infrared band (1 μm to 2.2 μm) of a TPV cell using Indium Gallium Arsenide Antimonide (InGaAsSb). A nano-meter size block of InGaAsSb with a low bandgap energy of 0.52 eV is mounted at the terminals of the antenna. Such a load presents a frequency dependent impedance with a high resistance and capacitance at the desired frequency (180 THz). For maximum power transfer, a high impedance bowtie antenna operating at the anti-resonance mode in conjunction with an inductive stub is realized. The plasmonic behavior of the metal that tends to reduce the antenna size is partially compensated by the extra length needed to achieve the anti-resonance condition. At the desired band, the proposed nanoantenna loaded with InGaAsSb block shows an electric field intensity at the antenna terminals, which is approximately 23.5 times higher than the incident electric field intensity. This feature allows for development of efficient TPV cell and sensitive IR detectors. The infinite array of the bowtie antennas backed by a metallic reflector located at a quarter-wave behind the array is shown to absorb ∼95% of the incident power, which is more than 50% higher than the bulk InGaAsSb TPV cell. A novel configuration of the bowtie nanoantenna array is also presented that allows for collection of DC currents through an almost arbitrary parallel or series configuration of TPV cells without adversely affecting the IR performance of the individual antennas. In this scheme, elements can be arranged to be polarization dependent or independent.
In this letter, radio-frequency characterization of fully transparent thin-film transistors (TFTs) based on chemically synthesized nanowires (NWs) has been carried out. The NW TFTs show current-gain cutoff frequency f T of 109 MHz and powergain cutoff frequency f max of 286 MHz. The TFTs were fabricated on glass substrates using aligned SnO 2 NWs as the transistor channel and sputtered indium-tin-oxide films as the source-drain and gate electrodes. Besides exhibiting > 100-MHz operation frequencies, the transparent NW TFTs show a narrow distribution of performance metrics among different devices. These results suggest the NW-TFT approach may be promising for high-speed transparent and flexible integrated circuits fabricated on diverse substrates.
High transmission efficiency metasurface unit cells have been designed based on surface electric and magnetic impedances derived from Huygens’ principle. However, unit cells for low transmission loss (<1 dB) over a wide transmission phase range require at least three metallic layers, which complicates the unit cell design process. In this paper, we introduce high-efficiency Huygens’ metasurface unit cell topologies in double-layer FR4 printed circuit board (PCB) by implementing surface electric and magnetic current using the top and bottom metallic patterns and via drills. Eleven unit cells were optimized for wide phase coverage (−150° to 150°) with a low average transmission loss of −0.82 dB at 10 GHz. To demonstrate the high-efficiency of the designed unit cells, we designed and fabricated two focusing lenses with dimensions of near 150 × 150 mm (5λ × 5λ) to focus a spherical beam radiated from short focal distances (f = 100 and 60 mm). The fabricated focusing lens showed 12.87 and 13.58 dB focusing gain for f = 100 and 60 mm at 10 GHz, respectively, with a 1 dB fractional gain bandwidth of near 10%. We expect that the proposed focusing lens based on high-efficiency double-layer metasurface unit cells can help realize compact and high-gain focusing lens-integrated antenna systems.
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