Browsing by Author "Wang, K."

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Open Access
Thermal tuning of infrared resonant absorbers based on hybrid gold-VO2 nanostructures
(American Institute of Physics Inc., 2015) Kocer H.; Butun, S.; Banar, B.; Wang, K.; Tongay, S.; Wu J.; Aydin, K.
Resonant absorbers based on plasmonic materials, metamaterials, and thin films enable spectrally selective absorption filters, where absorption is maximized at the resonance wavelength. By controlling the geometrical parameters of nano/microstructures and materials' refractive indices, resonant absorbers are designed to operate at wide range of wavelengths for applications including absorption filters, thermal emitters, thermophotovoltaic devices, and sensors. However, once resonant absorbers are fabricated, it is rather challenging to control and tune the spectral absorption response. Here, we propose and demonstrate thermally tunable infrared resonant absorbers using hybrid gold-vanadium dioxide (VO2) nanostructure arrays. Absorption intensity is tuned from 90% to 20% and 96% to 32% using hybrid gold-VO2 nanowire and nanodisc arrays, respectively, by heating up the absorbers above the phase transition temperature of VO2 (68°C). Phase change materials such as VO2 deliver useful means of altering optical properties as a function of temperature. Absorbers with tunable spectral response can find applications in sensor and detector applications, in which external stimulus such as heat, electrical signal, or light results in a change in the absorption spectrum and intensity. © 2015 AIP Publishing LLC.
Open Access
Unmanned aerial vehicle assisted communications and networking
(Elsevier, 2020) Duman, Tolga M.; Zhao, N.; Chen, Y.; Li, C.; Wang, K.; Yu, F. R.; Fan, L.; Alouini, M.-S.
In 5G and beyond networks, the explosive data and the massive connections are some of the key challenges. To alleviate the pressure on the ground networks and reduce the cost of densely deployed small cells, unmanned aerial vehicle (UAV) can be exploited as a promising technology in future communications networks. The UAV technology is becoming more and more mature, which owns advantages on high reliability, flexible deployment, cooperative operation and low cost. In particular, the air-to-air and air-to-ground channels are much better than the ground-to-ground channels. In many cases, they have line-of-sight (LoS) links. For these channels, mmWave transmission becomes practicable for UAV communications, which provides much higher data rate. Furthermore, UAVs can be combined with massive MIMO technology to meet ever-increasing data demand. Considering the device miniaturization and cost reduction of UAVs, it is more feasible than ever before to deploy UAV as relay to realize range extension in wireless communication systems. Meanwhile, in order to reduce the transmission latency as well as the load of backhaul links, UAVs are equipped with the ability of caching popular contents. In addition, UAVs can also be utilized in other important applications, such as emergency networks, traffic monitoring and military attacks, etc. However, there still exist many challenges in this emerging technology of UAV communications and networking, such as interference management, security and safety, beam tracking and alignment, trajectory and placement optimization, and so on. Furthermore, UAV enabled networking also requires great effort to reshape the current ground systems for satisfactory performances. Therefore, it is imperative to conduct thorough investigation and research on the UAV enabled communications and networking. Motivated by this, a collection of papers are included in this special issue, which mainly focus on the analysis and optimization of UAV-enabled networks and cache-aided UAV relay networks. Moreover, the analysis of energy efficiency, the design of secure transmission, and the optimization of outage probability and UAV-aided localization are investigated as well.