A viable lightweight absorber is the current need for stealth technology as well as microwave absorption. Several microwave absorbers have been developed, but it is still a challenge to fabricate an absorber that facilitates microwave absorption in broad bandwidth or covers the maximum portion of the frequency range 2-18 GHz, the commonly used range for radar and other applications. Therefore, it is highly required to develop a wide bandwidth absorber that can provide microwave absorption in the most part of the frequency range 2-18 GHz while simultaneously being lightweight and can be fabricated in desired bulk quantities by the cost-effective synthesis methods. In this paper, an attempt has been made to design an ultra-wide bandwidth absorber with enhanced microwave absorption response by using nickel-phosphorus coated tetrapod-shaped ZnO (Ni-P coated T-ZnO). In the Ni-P coated T-ZnO absorber, ZnO acts as a good dielectric contributor, while Ni as a magnetic constituent to obtain a microwave absorbing composite material, which has favorable absorption properties. Ni-P coated ZnO nano-microstructures are synthesized by a simple and scalable two-step process. First, tetrapod-shaped ZnO (T-ZnO) structures have been grown by the flame transport synthesis (FTS) approach in a single step process and then they have been coated with Ni-P by an electroless coating technique. Their morphology, degree of crystallinity and existing phases were studied in detail by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD) techniques. The complex permittivity and permeability of the "as-fabricated" T-ZnO and Ni-P coated T-ZnO have been measured in the frequency range of 4-14 GHz and their microwave absorption properties are computed using the coaxial transmission-reflection method. The strongest reflection loss (RL) peak value of -36.41 dB has been obtained at a frequency of ∼8.99 GHz with coating thickness of 3.4 mm for the Ni-P coated T-ZnO sample with a broad bandwidth of 10.0 GHz (RL < -10 dB) in the frequency range of 4.0-14.0 GHz.
The development and adopting of advanced communication technologies provide mobile users more convenience to connect any wireless network anytime and anywhere. Therefore, a large number of base stations (BS) are demanded keeping users connectivity, enhancing network capacity, and guarantee a sustained users Quality of Experiences (QoS). However, increasing the number of BS leads to an increase in the ecological ad radiation hazards. In order to green communication, many factors should be taken into consideration, i.e., saving energy, guarantee QoS, and reducing pollution hazards. Therefore, we propose tethered balloon technology that can replace a large number of BS and reduce ecological and radiation hazards due to its high altitude and feasible green and healthy broadband communication. The main contribution of this paper is to deploy tethered balloon technology at different altitude and measure the power density. Furthermore, we evaluate the measurement of power density from different height of tethered balloon comparison with traditional wireless communication technologies. The simulation results showed that tethered balloon technology can deliver green communication effectively and efficiently without any hazardous impacts.
The present study focused on the formulation of suitable material combination for good microwave absorption with ultra-wide Bandwidth at minimum coating thickness. For this purpose, a unique materials combination of semiconductor, conductor and magnetic materials has been specifically designed through a simple fabrication method to meet the necessity of enhanced absorption characteristics in the frequency range of 4.0-12.0 GHz. The chosen bulk materials like zinc oxide (ZnO), iron (Fe), and graphite (C) have been subjected to high energy ball planetary mill for fabricating the nano-composites. The impact of milling time on microwave absorption behavior of zinc oxide-iron-graphite nano-composites has been studied. The maximum microwave absorption value of -17.40 dB has been obtained for 15 h milled sample with average grain size of *10.0 nm for single-layer absorber of coating thickness 3.0 mm with broad Bandwidth of 6.43 GHz (4.0-10.43 GHz). The double-layer absorber has been optimized by multi-layering technique to increase the microwave absorption for less coating thickness. This type of material may be quite useful for radar cross section reduction at C and X-band.
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