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.