Electromagnetic and microwave properties of single-layer thermoplastic natural rubber (TPNR)/yttrium iron garnet (Y₃Fe₅O₁₂)/magnetite (Fe₃O₄) composites backed by a perfect conductor

Abstract

The use of a single-layer material for microwave applications continues to attract many researchers due to materials’ homogeneity in an acceptable range of thickness. This study outlines the microwave electromagnetic characteristics and interpretation of results based on a single-layer material backed by a perfect conductor. Data from three different laboratory prepared thermoplastic natural rubber (TPNR)/yttrium iron garnet (Y₃Fe₅O₁₂)/magnetite (Fe₃O₄) composites were presented. The microwave relative complex dielectric permittivity (ε_r*) and magnetic permeability (µ_r*) were measured using a microwave vector network analyser (MVNA) in the frequency range of 0.1846–10.0104 GHz. The specular material model backed by a perfect conductor was used to obtain the frequency-dependent reflection loss (R_L) assuming a normal incident of electromagnetic (EM) wave. The real and imaginary components of ε_r* (ε_r′ and ε_r″) and µ_r* (µ_r′ and µ_r″) for the three samples show a similar trend of frequency dependent. TPNR/Y₃Fe₅O₁₂ reflected the EM wave less when its thickness (t) equals a quarter of the propagating wavelength (λ_m/4) inside the material. Interestingly, in the presence of Fe₃O₄, multiple minimal reflections occur at smaller thicknesses (e.g. t = λ_m/32). For both cases, this is the condition where the reflected wave at the surface of the material is in a 180°-phase difference from the wave reflected earlier at the material-conductor interface. Destructive interference occurs when these two waves meet and is visualized as the dip on the reflection loss (R_L) vs. frequency plot. The number of dips increases with thickness. The lowest frequency dip occurs at a lower frequency for a thicker material. For TPNR/Y₃Fe₅O₁₂/Fe₃O₄ and TPNR/Fe₃O₄, as the material gets thicker, the high-frequency dips on the R_L plot become smaller and the use of the material in microwave application is no longer practical due to the increase in its weight and a smaller reflection loss.

Keywords:

• Reflection loss
• permeability
• permittivity
• impedance
• perfect conductor

Acknowledgement

The authors would like to thank the Faculty of Health Science and the Faculty of Science and Technology of Universiti Kebangsaan Malaysia and the Department of Physics, Universiti Technology MARA, Jengka, Pahang Darul Makmur for the supports in the analysis of the data and in the writing of the manuscript. This study was funded by the Universiti Kebangsaan Malaysia under the Faculty of Health Science research code of NN-2019-056.

Disclosure statement

No potential conflict of interest was reported by the authors.