Nanosized barium ferrite (BaFe12O19) powders are synthesized using co-precipitation technique at three different annealing temperatures. The X-Ray Diffraction pattern indicates the presence of hexagonal structure for all the three samples. Transmission electron microscopy (TEM) shows the particles are hexagonal in shape. The synthesized BaFe12O19 powder samples are mechanically mixed with Novolac phenolic resin (NPR) with filler to polymer weight ratio of 30:60 to prepare pellets of BaFe12O19/NPR composites of dimensions, 10.38 mm x 22.94 mm x 4 mm. The complex permittivity, εr and complex permeability, μr of the developed samples are measured at X-band by Nicolson-Ross method using Agilent E8362C vector network analyzer. The effect of the annealing temperature on the complex permittivity and permeability in the X-band is studied. The maximum dielectric constant and permeability is obtained of the BaFe12O19/NPR composite with BaFe12O19 annealed at 9000C as 6 and 2 respectively. The composite is a good candidate for microwave absorption study.
In the present investigation, microwave absorption properties of a conductor back single layer designed on graphite
flakes (GF)-novolac phenolic resin (NPR) composites is studied. The complex permittivity of the developed composite
enhance for higher GF percentages. The reflection loss(RL) measured using E8362C VNA shows a maximum RL values
-25 dB at 9.8 GHz for 7 wt. % composition with -10 dB bandwidth of 0.3 GHz. The developed composites are being
light weight and cost effective shows potential to be used as dielectric absorber.
Microstrip patch antenna is fabricated on a magnetodielectric substrate synthesized using 5% volume fraction of
nano-sized cobalt ferrite and nickel ferrite inclusions. The permittivity, Εr and permeability μr, of the tailored substrate is determined by in touch superstrate method and cavity perturbation respectively. The S11 parameters are measured in the frequency range from 8 to 11.5 GHz with varying external magnetic field. Unlike antennas made on bulk ferrites, the antennas on these substrates show very low resonant frequency tenability. An
enhancement of return loss from -26dB to-31 dB for CoFe2O4/LDPE antenna at 9 GHz and -25dB to -32.5 dB for NiFe2O4/LDPE antenna at 10GHz is observed.
Expanded graphite/novolac phenolic resin (EG/NPR) composites are developed as dielectric absorbers with 4mm
thickness and its microwave absorption ability studied in the frequency range 8.4 to 12.4 GHz. A high reflection loss
~ -43 dB is observed at 12.4 GHz for 5 wt. % EG/NPR composites. With the increase in EG concentration in the
composite the reflection loss decreases and the absorption peak shifts towards lower frequency. 7 wt. %, 8 wt. % and 10 wt. % composites shows a 10dB absorption bandwidth of order of 1GHz. Light weight EG/NPR composite shows
potential to be used as cost-effective broadband microwave absorber over the X-band.
Low density polyethylene (LDPE)/Alumina (Al2O3) composite systems have been studied as an alternate substrate for microstrip patch antennas (MPA). Morphological, thermal and microwave characterizations of the composites are carried out for different volume fractions of Al2O3 in the LDPE matrix. The size and the distribution of alumina particles are quite uniform in the composite. Enhancement of thermal and microwave properties of the composite over the parent polymer is observed. Simple rectangular MPA in X-band is fabricated on the composite material to verify its applicability as substrates for MPA. A return loss of ~ -26dB is observed at the design frequency.
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