Kuzhichalil Peethambharan Surendran

Tailoring the microwave dielectric properties of GdTiNb1−xTaxO6 and Sm1−x YxTiTaO6 ceramics

Abstract Microwave dielectric ceramics based on GdTiNb 1− x Ta x O 6 and Sm 1− x Y x TiTaO 6 have been prepared by conventional solid state method. The GdTiTaO 6 and SmTiTaO 6 have aeschenite structure with positive τ f and GdTiNbO 6 and YTiTaO 6 have euxenite structure with negative τ f . The τ f of the ceramics has been tuned by preparing solid solution phases between the aeschynites and euxenites for a possible zero τ f material. It is observed that GdTiNb 1− x Ta x O 6 undergoes a phase transition from aeschynite to euxenite when x =0.75 and in Sm 1− x Y x TiTaO 6 for x =0.73. The microwave dielectric properties change abruptly near the transition region. The τ f value approaches zero near the phase transition region while the samples have poor sinterability and poor quality factor. The unloaded quality factor, dielectric constant and the sign of τ f of the solid solution phases are found to depend on the average ionic radius of the rare earth ion in RE 1− x RE′ x TiTaO 6 . The boundary of the euxenite-aeschynite phase transition occurs at an average (RE) ionic radius of 0.915 A in Sm 1− x Y x TiTaO 6 solid solution phases.

Polyol derived Ni and NiFe alloys for effective shielding of electromagnetic interference

Ni and NiFe alloys with different compositions have been successfully synthesized using a simple, surfactant-free polyol method. The morphological analysis demonstrated a uniform spherical nature of the alloys, with size range ∼10–30 nm. A very thin oxide layer was found to form over the alloy nanoparticles (NPs) which is weakly visible in TEM and later confirmed by XPS analysis. The magnetic properties of the Ni and NiFe NPs were measured using a vibrating sample magnetometer (VSM) at room temperature. The saturation magnetization value was found to be lowest in Ni and keeps on increasing with increasing Fe content in the composition. The resistivity, as revealed from I–V characteristics, was shown to be lowest for the permalloy (Ni80Fe20) phase, while the values increase with further increment in the Fe content. The microwave shielding properties of the Ni and its Fe alloy NPs were investigated in the Ku band range. The lower EM wave transmittance with good reflection and absorption coefficients is responsible for the high shielding values. All of the alloys tested in this investigation showed excellent microwave shielding properties ranging from −21 to −41 dB in the entire Ku band, for ∼1 mm thick samples. The lowest EMI shielding range (−21 to −29 dB) was noted for Ni NPs while the highest was observed in the case of permalloy (−30 to −41 dB). The rest of the NiFe combinations show intermediate shielding effectiveness as compared to Ni and permalloy. Certainly, all of the NiFe alloy combinations we tested showed excellent EMI shielding above −30 dB, with significant enhancements in the absorption shielding efficiency. These alloys are good candidates for EMI shielding having the ability to attenuate 99.9% of electromagnetic radiation.

Printable Hierarchical Nickel Nanowires for Soft Magnetic Applications

Hierarchical nickel nanowires (h-NiNWs) were synthesized by a simple reduction method and their electrical, magnetic, and electromagnetic characteristics were investigated. These nanowires possess a high magnetic saturation (Ms) of 51 emu/g and also a coercivity (Hc) of 34.5 Oe, which makes them suitable for soft magnetic sensor applications. Hall transport is being reported for the first time for h-NiNWs, and electrical conductivity at room temperature was studied to assess their applicability as a Hall sensor wherein the Hall coefficient RH was found to be −1.39 × 10–12 Ω cm/Oe. Electromagnetic characterization of synthesized h-NiNWs shows excellent microwave shielding effectiveness of above 24 dB for the Ku band (12.4–18 GHz) and a maximum value of 32 dB at 14 GHz for a sample with a thickness of about 1 mm. A room-temperature-curable screen-printable ink was formulated using the synthesized magnetic nanostructures and printed on different flexible substrates. Printed patterns show promising ferromagnetic properties, and they could be potential candidates for soft magnetic sensor applications.

Screen printable MWCNT inks for printed electronics

Development of oxidation resistant conductive inks with low curing temperatures is a challenging problem in printed electronics. The present work introduces a newly formulated room temperature curable conducting ink using multiwalled carbon nanotubes (MWCNTs) for printable electronic application. The organic vehicle composition of the ink is meticulously controlled based on their rheological characteristics. The ink was screen printed on different flexible substrates like paper, Mylar®, photopaper, cellulose acetate sheets and silicone rubber. A morphological study of the printed pattern was also performed using SEM and AFM. The electrical characterization of the ink printed on flexible substrates was studied and a sheet resistance of 0.5–13 Ω sq−1 for three strokes was reported.