Session Chair: Nicole R Demarquette, École de Technologie Supérieure / Université du Quebec Session Chair: Narayan Chandra Das, Indian Institute of Technology, Kharagpur
1:30pm - 2:00pm Invited
Additive Processing of Soft Magnetic Nanomaterials for EMI Applications
Raju V. RAMANUJAN1, Rajarshi BANERJEE2
1Nanyang Technological University, Singapore; 2University of North Texas, USA
Soft magnetic nanomaterials have an enormous range of applications, including electromagnetic shielding and absorption. Such nanomaterials have been intensively studied following the commercial success of Fe-Si-B-Cu-Nb (Finemet) nanocrystalline alloys, the microstructure consists of a high density of soft magnetic nanometre size precipitates in an amorphous matrix. While there has been a substantial amount of activity on additive manufacturing (AM) of structural alloys, there is only limited effort on AM of functional alloys, such as magnetic materials. We have carried out laser additive processing of magnetic alloys using the laser engineered shaping (LENS) process from a feedstock consisting of a blend of elemental powders. Soft magnetic alloys have been processed using the LENS process, which is a directed energy deposition technique. These include permalloy type Ni-Fe-V and Ni-Fe-Mo alloys as well as Fe73.5Si13.5B9Nb3Cu1 Finemet alloys. The microstructure in these AM alloys can be varied via the laser deposition parameters and this, in turn, influences coercivity (Hc) and saturation magnetization (Ms). These results will be elucidated in the presentation. Our study shows the feasibility of AM processing of magnetic materials. These results can be highly beneficial to the future development of novel EMI shielding/absorption magnetic components of complex geometry in near net shape.
2:00pm - 2:30pm Invited
Coexistence of the Low Frequency Plasmonic State and Magnetic Resonance in Metal/Ferromagnet Granular Composite Materials
1Graduate School of Education, Hiroshima University, Japan; 2National Institute of Technology, Tokuyama College, Japan; 3Graduate School of Engineering, University of Hyogo, Japan
The electromagnetic metamaterials (EMMs) with negative permittivity (ENG) and/or permeability (MNG) have been the subjects of considerable interest in the EMC and related technologies. The perfect EM absorbers or the frequency selective shielding devices etc. have been developed using the periodic structure of the unit cell resonators with the EMM concepts . On the other hand, the EMM properties have been studied in the material science as well; the double negative (DNG) characteristics have been observed in some granular composite materials [2, 3]. In the granular composite materials, the ENG property can be realized by the low frequency plasmonic state (LFPS) in the percolated metal granular composite structure. Meanwhile, the MNG state can be achieved by the magnetic resonance of ferromagnetic particles. These ENG and MNG characteristics can be coexisted in the RF to microwave range.
In this report, we will present the complex permittivity and permeability spectra as well as the electrical conductivity of Metal/Ferromagnet granular composite materials. The coagulated copper (Cu) particles with elaborated shape were used to create the network of metal particles; the LFPS were realized in the metallic state above the electrical percolation threshold. As the ferromagnetic particles, Fe-Ni or Fe-Co alloys as well as ferrites were employed and the MNG spectra have been produced by the gyromagnetic resonance in the RF to X-band range. In these Metal/Ferromagnet granular composite materials, the ENG and MNG frequency range can be controlled by the particle content ratio or external magnetic field; the DNG property can be achieved in some frequency bands.
 R.D. Ziolkowski and N. Ehgheta, Metamaterials: Physics and Engineering Explorations, (Wiley & Sons, Inc.), 2006.
 T. Tsutaoka et al., Appl. Phys. Lett., 103, (2013) 261906.
 Z.-C. Shi et al., J. Mater. Chem. C, 1 (2013) 1633-1637.
2:30pm - 2:45pm Oral
Low Temperature Co-fired Nano Magnetic and Dielectric Based Composites for EMI Filter Application
Recently, multilayer chip LC filters with high attenuation and wide bandwidth have been developed as a promising electromagnetic interference (EMI) device. They are made with a co-fired multilayer structure of ferrite, dielectric and internal conductors. One of the most important processes in manufacturing defect-free multilayer chip LC devices involves capacitor and inductor material co-firing. Mismatched densification kinetics, chemical reaction and thermal expansion between the layers could generate undesirable defects such as delamination, cracks and camber in the final products. To solve the mismatch problems, a composite ceramic material prepared by mixing dielectric and magnetic materials can be used to fabricate an EMI filter.
A new dielectric-ferrite composite ceramics were prepared by mixing auto combustion synthesized two different (Ni0.25Cu0.20Zn0.55)Fe2O4& (Ni0.50Mg0.50)Fe2O4ferrite powders with solid state synthesized Ba0.75Sr0.25TiO3dielectric powder in different weight fraction. Composites of ‘x’ ferrite-‘(1-x)’ dielectric with x= 0, 0.25, 0.50, 0.75 and 1 were prepared by mixing respective powders. Uniaxially pressed toroids and pellets were sintered at temperatures ≤950oC/2h.
The co-existence of ferrite and dieletric phases were confirmed by X-ray Diffraction analysis. These composites exhibit nearly no chemical reaction between the dielectric and magnetic materials during sintering. Surface morphology of the samples has been investigated using Scanning Electron Microscope. Dielectric measurements were carried out using Impedance Analyzer. Saturation magnetization and hysteresis parameters were measured at room temperature with a maximum magnetic ﬁeld of 10 kOe. The permittivity of composites continuously decreases with increasing ferrite content and the initial permeability decreases with increasing dielectric content. Dielectric and magnetic losses were increased upon composite formation due to the generation of interfacial charges in the ferrite-ferroelectric interface. The composites exhibits superior dielectric and magnetic properties over a wide frequency range.
2:45pm - 3:00pm Oral
Smart Conductive Cotton Fabric by Macro-Structured Carbon Clusters for Electromagnetic Interference Shielding
1Indian Institute of Technology, Kharagpur, India; 2Calcutta University, India
Exclusive macro-structured carbon clusters are used to develop conductive cotton fabric for electromagnetic interference shielding applications. Rubber grade carbon particles are stabilised into the clustered composite form by using natural rubber latex, polyvinyl alcohol and others additives. The knife-over-roll coating technique is used to apply conductive composite on the surface of the plain woven cotton fabric. The main ingredients are optimised for lowest surface resistivity and highest electromagnetic interference shielding effectiveness. The surface morphology of the coated fabric is characterised by FESEM, AFM & HRTEM. The tomography of the composite is studied by the micro-CT scan. The two-dimensional topography reveals that an individual, as well as aggregates of 2-9 carbon black particles, are bounded by the blended matrix to form the macro-structured carbon clusters. The electrical properties of the composites and their effectiveness as the electromagnetic interference shielding are studied in details in the present article.