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

Abstract

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.