Electromagnetic and absorption properties of some TPNR/Fe3 O4/YIG microwave absorbers as revealed by a microwave vector network analyser and specular absorber method

Ahmad Nazlim Yusoff, Junaidah Mat Sani, Mustaffa Hj Abdullah, Sahrim Ahmad, Nazree Ahmad

Research output: Contribution to journalArticle

7 Citations (Scopus)

Abstract

The complex scattering parameters (S11* and S21*), relative dielectric permittivity (εr* = εr'- jεr″), relative magnetic permeability (μr* = μr' - jμr″) and absorption characteristics of some thermoplastic natural rubber (TPNR) - Fe3O/(YIG composites were investigated by means of a microwave vector network analyser and specular absorber method. The measurements were performed in the frequency range of 1 - 13 GHz with and without the presence of a transverse external magnetic field with magnitude of 1 T. The specular absorber method is used in determining the reflection loss (RI) of the composites and its dependence on material properties, thickness and the external magnetic field. In toroidal form, the composites under study seem to transmit more (Pt > 60%) but absorb and reflect less (Pa + Pr < 30%) microwave power in the frequency range used in this study and in both unmagnetised and magnetised states. The external magnetic field is seen to have the effects of reducing S11*, S21*, εr', εr″, μr' and μr″. The suppression of the relaxation and resonance behaviours on the μr' and μr″ plots for all samples are observed for measurements performed in the presence of the external field. The composites, as revealed by the specular absorber method, show conditions of minimal reflection on RL versus frequency plot for all sample thickness where more than 95% of the microwave power is not reflected back. The location of the dips of minimal reflection on the frequency domain depend on the thickness, the dielectric and magnetic properties of the materials. The conditions of minimal reflection was found to occur when the thickness (t) of the sample equals the odd number multiple of a quarter wavelength in the material (λm), t = nλm/4 (n = 1, 3, 5, 7...), where a geometrical cancellation took place at the surface of the absorber between the reflected waves, resembling a thin filem inteference phenomenon. The dips are suppressed and shifted to a higher frequency in the presence of the external magnetic field. With the knowledge of the dielectric permeability and magnetic permeability of a material, the specular absorber method may provides a simple theoretical graphic aids in determining the absorption characteristics and location of the matching condition in the frequency domain.

Original languageEnglish
Pages (from-to)65-75
Number of pages11
JournalSains Malaysiana
Volume36
Issue number1
Publication statusPublished - Jul 2007

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electromagnetic properties
yttrium-iron garnet
electromagnetic absorption
rubber
absorbers
microwaves
composite materials
magnetic fields
plots
frequency ranges
dielectric permeability
magnetic permeability
reflected waves
cancellation
dielectric properties
permeability
retarding
permittivity
magnetic properties
scattering

Keywords

  • Quarter wavelength thickness
  • Reflection loss
  • Specular absorber method
  • Thermoplastic natural rubber
  • Yttrium iron garnet

ASJC Scopus subject areas

  • General

Cite this

Electromagnetic and absorption properties of some TPNR/Fe3 O4/YIG microwave absorbers as revealed by a microwave vector network analyser and specular absorber method. / Yusoff, Ahmad Nazlim; Sani, Junaidah Mat; Abdullah, Mustaffa Hj; Ahmad, Sahrim; Ahmad, Nazree.

In: Sains Malaysiana, Vol. 36, No. 1, 07.2007, p. 65-75.

Research output: Contribution to journalArticle

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abstract = "The complex scattering parameters (S11* and S21*), relative dielectric permittivity (εr* = εr'- jεr″), relative magnetic permeability (μr* = μr' - jμr″) and absorption characteristics of some thermoplastic natural rubber (TPNR) - Fe3O/(YIG composites were investigated by means of a microwave vector network analyser and specular absorber method. The measurements were performed in the frequency range of 1 - 13 GHz with and without the presence of a transverse external magnetic field with magnitude of 1 T. The specular absorber method is used in determining the reflection loss (RI) of the composites and its dependence on material properties, thickness and the external magnetic field. In toroidal form, the composites under study seem to transmit more (Pt > 60{\%}) but absorb and reflect less (Pa + Pr < 30{\%}) microwave power in the frequency range used in this study and in both unmagnetised and magnetised states. The external magnetic field is seen to have the effects of reducing S11*, S21*, εr', εr″, μr' and μr″. The suppression of the relaxation and resonance behaviours on the μr' and μr″ plots for all samples are observed for measurements performed in the presence of the external field. The composites, as revealed by the specular absorber method, show conditions of minimal reflection on RL versus frequency plot for all sample thickness where more than 95{\%} of the microwave power is not reflected back. The location of the dips of minimal reflection on the frequency domain depend on the thickness, the dielectric and magnetic properties of the materials. The conditions of minimal reflection was found to occur when the thickness (t) of the sample equals the odd number multiple of a quarter wavelength in the material (λm), t = nλm/4 (n = 1, 3, 5, 7...), where a geometrical cancellation took place at the surface of the absorber between the reflected waves, resembling a thin filem inteference phenomenon. The dips are suppressed and shifted to a higher frequency in the presence of the external magnetic field. With the knowledge of the dielectric permeability and magnetic permeability of a material, the specular absorber method may provides a simple theoretical graphic aids in determining the absorption characteristics and location of the matching condition in the frequency domain.",
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AU - Yusoff, Ahmad Nazlim

AU - Sani, Junaidah Mat

AU - Abdullah, Mustaffa Hj

AU - Ahmad, Sahrim

AU - Ahmad, Nazree

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