Ultra-wide bandwidth with enhanced microwave absorption of electroless Ni-P coated tetrapod-shaped ZnO nano- and microstructures

• Published in: Physical chemistry chemical physics : PCCP 2015-09, Vol.17 (35), p.22923-22933
• Main Authors: Najim, Mohd, Modi, Gaurav, Mishra, Yogendra Kumar, Adelung, Rainer, Singh, Dharmendra, Agarwala, Vijaya
• Format: Article
• Language: English
• Subjects: Bandwidth; Electroless coatings; Frequency ranges; Lightweight; Microwave absorption; Nickel; Scanning electron microscopy; Zinc oxide
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/c5cp03488d

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. Tetrapod-shaped ZnO structures were synthesized by a simple FTS approach and have been coated with Ni-P using the electroless deposition process. Ni-P coated T-ZnO exhibits an ultra-wide bandwidth of 10.0 GHz (4.0-14.0 GHz) at RL < −10 dB for the coating thickness of 3.4 mm.