Pidilite Industries Ltd., Andheri (E.), Mumbai-400059. We presents the ... Traditionally, metals, alloys and carbon-black particles have been used as electrically.
Conductive Nano-Composites for Radiation Shielding Vishal Udmale, Deepak Mishra, Ravindra Gadhave Pidilite Industries Ltd., Andheri (E.), Mumbai-400059 We presents the use of conductive polymer composite materials in various applications for static-dissipative, semi conductive, electromagnetic interference (EMI) shielding, anticorrosive and stealth composites. A composite consisting of conductive fillers and an insulating polymer becomes electrically conductive as the filler content exceeds a certain critical value, generally termed as Percolation Threshold Value (PTV). Traditionally, metals, alloys and carbon-black particles have been used as electrically conductive filler materials, however, too high a level of these fillers can be detrimental for the processability, density, surface quality of the material, cost and the mechanical properties of the composite. By using nano conductive fillers, conductivity will be achieved while retaining the original plastic processing properties of the composite. Recently, one and two dimensional nano-structures based on carbon such as carbon nanotubes (CNTs) and graphene have received significant attention owing to their outstanding electronic, thermal and mechanical properties. The proliferation of electronic devices and mobile towers in the world results in harmful EMI and radio frequency interference (RFI) ultimately causing operational malfunction to electronic instruments and also harmful to human health, signifies the importance of this detailed review for EMI/RFI shielding applications.
EM - RADIATIONS
HARMFUL EFFECTS
Cause operational malfunction to electronic instruments. Unwanted interference to the Electronic devices. Damage to electronic data. Suspected group 2b carcinogen (by WHO) Non- Thermal effects: Damage to gene, affect the synthesis of radical scavenging hormone ‘Melatonin’, which ultimately cause leukemia, breast cancer, miscarriages, infertility, etc. Thermal effects: Heating of material or tissue.
SOLUTIONS
The effect of EMI can be reduced or diminished by positioning a shielding material between the source of EM field and sensitive component. Electrical conductivity is important for EMI shielding and EMD. For electromagnetic shielding applications, the electrical conductivity range should be higher than 1 S m −1 when the conductivity is >10-3S m −1 Highly electrically conductive metals (106 S cm-1) are used to shield EM radiations. But it also adds weight, cost & space. Thus light weight as well as effective material is required. Polymer composite based on nanoconductive fillers are thus preferred. DEVELOPMENT TREND Metal coating Eg. Ag, Cu has conductivity in range of 106 S/cm
Core shell metal /polymer nanocomposites
Conductive polymers Eg. Polyaniline, poly acetylene (14 S/cm)
Metal fielded polymer nanocomposites
Eg. C coated Ni, Fe; SiO2 coated FeOx
Eg. Ferromag. Metals/ intrinsically conductive polymer
CNT/Polymer nanocomposites
Graphene/polymer nanocomposites
Eg. Chiral SWCNTs/ MWCNTs in polymer matrix
Eg. Mono/ Multi – layered Graphene in polymer matrix
SYNTHESIS/ PROCESSING REQUIREMENTS
The traditional routes to prepare nanocomposites of layered or tubular compounds as reinforcement material especially clays, CNTs & graphene can be summarized as follows:In situ intercalative polymerization Melt intercalation Intercalation of pre-polymer from solution Exfoliation/adsorption
OTHER APPLICATIONS MECHANISM OF EMI/RFI SHIELDING & SHIELDING EFFECTIVENESS (SE) Automotive part with EMI shielding
‘SE’ is normally expressed in decibels (dB) as a function of the logarithm of the ratio of the incident and exit electric (E), magnetic (H), or planewave field intensities (F): SE (dB) = 20 log (Ei/Et), SE (dB) = 20 log (Hi/Ht), SE (dB) = 20 log (Fi/Ft) Where, Ei, Hi and Fi are the electric, magnetic and plane wave field intensity incident on the shield; Et, Ht and Ft are the counterparts transmitted through the shield The total SE is the sum of the absorption factor (SEA), the reflection factor (SER) and the correction factor to account for multiple reflections (SEM)
SE = SEA + SER + SEM
Measurement of SE: Open field method Shielded box method Shielded room method Coaxial transmission line method Factors affecting SE: Conductivity Permittivity Surface Morphology of coating Coating thickness EMI/RFI SHIELDING OPTIONS BY TYPE, 2006-2012 ($ MILLIONS)
properties Stealth fighter Jets, choppers & missiles Military radio with high level EMI shielding; Grounding plug earth pin Telecommunication and Others NanoElectronic Security systems Nanodimensional electronics: transistors, sensors and actuators, detectors, diagnostic, processors, memories etc. Nano-conductive Adhesives for Nanoelectronics Interconnection Antistatic coating in aerospace Electrostatic charge dissipation in space
CONCLUSION:
The expanding use of wireless electronics leads to severe EMI/RFI problems, not only to the electronic equipment but also to the ecosystem. This review highlights the importance and necessity of use, particularly of conducting nanocomposites for the shielding of EMI/RFI. REFERENCES:
Hussain et. al., Polymer-matrix Nanocomposites (2006), 40, 17 William Gacitua E., Aldo Ballerini A.,Jinwen Zhang; Ciencia y tecnología (2005); 7(3): 159-178. S. Geetha, K. K. Satheesh Kumar, Chepuri R. K. Rao, M. Vijayan, D. C. Trivedi; Journal of Applied Polymer Science (2009); 112, 4, 2073-2086 Press release - N 208; International agency for research on Cancer, WHO; 31st May, 2011 Harland J D, Liburdy RP; Bioelectromagnetics (1997); 18 (8): 555–562 Recent advances in research on Radio frequency Fields and Health: 20012003, The Royal Society of Canada
ACKNOWLEDGEMENT:
Source: BCC Research
We acknowledge the support of Pidilite Industries Limited (Andheri, Mumbai) and our superiors in the department of R&D for allowing and helping us to present this review at ICT (Matunga, Mumbai).
