Preparation of NiAl2O4-Based Flexible Substrates for Metamaterials with Negative Dielectric Properties

Abstract

Various techniques are commonly used to produce nano-crystalline NiAl2O4 materials; however, their practical applications in the microwave region remain very limited. In this work, flexible substrates for metamaterials containing two different concentrations of NiAl2O4 (labelled Ni36 and Ni42) have been synthesised using a sol-gel method. The formation of spinel structures in the synthesised materials is confirmed, and their crystalline sizes are determined using scanning electron microscopy, X-ray diffraction, and energy dispersive X-ray techniques. The dielectric properties, conductivities, loss tangents, and other parameters of the NiAl2O4-based substrates are analysed to evaluate their applicability as dielectric materials for the microwave frequency range. The obtained results show that the fabricated Ni36 and Ni42 nickel aluminates possess dielectric constants of 4.94 and 4.97 and loss tangents of 0.01 and 0.007, respectively; in addition, they exhibit high flexibility and light weight, which make them suitable for applications as metamaterial substrates. The synthesised structures are also validated experimentally using a commercially available electromagnetic simulator; as a result, double negative behaviour of the flexible metamaterials has been observed. Furthermore, it is found that the prepared NiAl2O4 substrates can be used in the S-, C-, and X-bands of the microwave frequency region.

Mechanochemical Activation and Spark Plasma Sintering of the Lead-Free Ba(Fe1/2Nb1/2)O3 Ceramics

“…The first reports of such rare dielectric behavior in the real material were presented Mao et al [ 36 , 37 ]. In recent years, more and more papers present the occurrence of this phenomenon in various ceramic materials [ 38 , 39 , 40 ], but so far, the mechanism of the appearance of a negative dielectric constant is not yet fully examined and explained. Mao et al [ 36 ] reported that the negative value of the dielectric constant is related to the change in the nature of the electrical conductivity from capacitive to inductive.…”

Flexible Antennas: A Review

“…Another challenge of designing flexible antennas is identifying suitable conducting materials that sustain different bending and twisting conditions and have reasonable resistance value as not to affect the antenna radiation efficiency. Various methods have been considered to find the conductive substrates, such as chemically modifying fabrics surface [ 252 ] or physical mixing of several conductive materials [ 253 , 254 , 255 ].…”

Nickel Particle-Based Compact Flexible Antenna for Modern Communication Systems

“…The sol-gel method is used to manufacture the final substrate [18]. Figure 3 presents a flow chart of the synthesis steps of nickel aluminate powder by the sol-gel method.…”

“…The sol-gel method is used to manufacture the final substrate [18]. Table 2 shows the relative molecular mass (JMR) and the volume of solvent and other materials used to produce solutions for calculation purposes.…”