Broad-band microwave absorption of Sr0.85La0.15(MnZr)xFe12-2xO19 hexagonal ferrite in 18-40 GHz frequency range

In this research, electro-magnetic (EM) absorption was investigated for M-type strontium hexaferrite with chemical composition, Sr0.85La0.15(MnZr)xFe12-2xO19 (x = 0, 0.25, 0.50, 0.75, 1.0) at microwave frequencies. Complex permittivity (ɛ′-jɛ′′) and complex permeability (µ′ - jµ′′) was measured using transmission and reflection (T/R) based waveguide method in the K-band (18-26.5 GHz) and Ka-band (26.5-40 GHz) frequency range. The variation of reflection loss (RL) with sample thickness, frequency and substitution has been analyzed. The matching thickness of the synthesized ferrite was successfully predicted from quarter-wavelength (λ/4) mechanism which helps to optimize the minimum reflection loss (RL) in the material. In K-band, the minimum reflection loss (RL) of −47.8 dB was obtained for composition x = 1.0 with −10 dB (90%) bandwidth of 7.97 GHz and −20 dB (99%) bandwidth of 5.6 GHz at sample thickness 1.1 mm. In Ka-band, the maximum absorption with minimum RL of −29.9 dB with −10 dB bandwidth of 8.72 GHz was obtained for composition x = 0.50 at 0.85 mm sample thickness. These synthesized ferrites find application as thin sheet of microwave absorber with broad bandwidth for EMI (electromagnetic interference) shielding and radar camouflaging.