Microwave Absorption and EMI Shielding Behavior of Nanocomposites Based on Intrinsically Conducting Polymers, Graphene and Carbon NanotubesParveen Saini1 and Manju Arora1[1] National Physical Laboratory, New Delhi, , India1. Our paper reviews the use of conductive polymer composite materials in various applications for semi conductive, static-dissipative, anti-corrosive, electromagnetic interference (EMI) shielding and stealth composite coatings. Most plastics are insulators from which electromagnetic waves can pass freely and the conductive barriers must be applied as shields to block the waves. Frequency and dopant concentration dependence of total shielding effectiveness (SET) value of samples prepared by doping of emeraldine base (EB) with different concentrations of acrylic acid (AA) viz.
It is particularly needed for the buildings containing power transformers, mobile towers and other electronic facilities which will radiate electromagnetic wave to the surrounding.
This is a true test of the service performance of the designed shielding of the finished product. Different phases of applications of electromagnetic radiations include mobile communication, radio communication, RADAR, wireless communication, different scanning methods in medical field, security applications and cooking microwave ovens.
Polymer-based nano-composite EMI shielding materials that add EMI shielding efficacy can provide significant weight savings as well as resistance to corrosion and other environmental degradation. A lot of researches are in progress to find the possible health hazards associated with the electromagnetic radiation.
All electromagnetic waves consist of two essential components, a magnetic field (H) and an electric field (E).
Applications of these range from electronics to aerospace sectors, such as electrostatic dissipation, EMI shielding, multilayer printed circuits to transparent conductive coatings. The mutual interference among electronic gadgets, business machines, process equipments, measuring instruments and appliances lead to disturbance or complete breakdown of normal performance of appliances. Shielding is the process by which a certain level of attenuation is extended using a strategically designed EM shield.
Thermal effect: When the electromagnetic wave penetrates through human body the energy is absorbed and it produces a heating effect.

Metals are excellent conductors of electricity and can absorb, reflect or transmit electromagnetic interference. IntroductionElectromagnetic interference (EMI) is an undesirable and uncontrolled off-shoot of explosive growth of electronics and widespread use of transient power sources.
To provide shielding, the substrate is coated with a conductive layer or the substrate material which itself is conductive.
The general principle is the same as the shielded box method except that each of the components of the measuring system, signal generator, transmitting antenna, receiving antenna and recorder are isolated in separate rooms to eliminate the possibility of interference. The weight of the ‘heavy’ metal can be an issue in the case of full metal shielding and plastic matrices with high metal filler content, especially in applications where mass should be as low as possible. EMI shielding consists of two regions, the near field shielding region and far field shielding region. The first section of this chapter gives a brief overview of fundamentals of EMI shielding & microwave absorption, theoretical aspects of shielding, governing equations, various techniques for measurement of shielding effectiveness and different strategies for controlling EMI. There is evidence that at the frequencies used in mobile phone technology, children will absorbs more energy per Kg of body weight from an external electromagnetic field than adults. The conducting and ferromagnetic type of materials can effectively shield electromagnetic waves generated by an electric source, whereas electromagnetic waves generated from a magnetic source can be shielded effectively only by magnetic materials [12, 13]. Theoretical shielding effectivenessBefore starting the shielding analysis, it is necessary to understand the various electromagnetic terminologies (Ott, 2009).
Thickness dependence of total shielding efficiency (SET) of various ‘‘crosslinked’’ polyaniline (XPANI-ES) samples. EMI shielding is very much related to the protection against electrostatic discharge (ESD) or Surges in electric devices and connections.
The primary mechanism of EMI shielding is usually reflection of the radiation by the shield.
It is observed that the high conductivity and dielectric constant of the materials contribute to high EMI shielding efficiency (SE) [8,28].

A shielding effectiveness of 30 dB, correspondingto 99.9% attenuation of the EMI radiation, is considered an adequate level of shielding for many applications [3, 24, 25]. This property of the nanocomposite can be used an electromagnetic shielding material since the electromagnetic wave consist of an electric (E) and the magnetic field (H) right angle to each other. Therefore, some shielding mechanism must be provided to ensure undisturbed functioning of devices even in the presence of external electromagnetic (EM) noises. Shielding theory This section presents the shielding basics based on the transmission line theory (Schelkunoff, 1943) and the plane wave shielding theory (Schulz et al,1988).
The third mechanism of EMI shielding is multiple reflections within the interlayer of MWCNTs.
Due to high electrical conductivity of Iron group metal nanoparticles (in order of magnitude 106S cm-1); they are particularly suitable as shielding material against electromagnetic fields. EMI shielding has become a more significant issue due to the increased use of plastic housings for electronic equipment. Therefore, to touch the theoretically predicted shielding performance of a materials and to satisfy stringent design criteria, elementary knowledge of shielding theory, set of governing theoretical equations, important design parameters and relevant measurement technique becomes a prime prerequisite. Open Field or Free Space Method: It uses to evaluate the practical shielding effectiveness of a complete electronic assembly. Shielding definitions and phenomenonEMI shield is essentially a barrier to regulate the transmission of the electromagnetic EM wave across its bulk. Shielded Box Method: It widely used for comparative test of SE of different shielding materials. The designing a EMI shielding with a certain level of attenuation, meeting a set of physical criteria, maintaining economics and regulating the involved shielding mechanism is not a straight forward task and involves complex interplay of intrinsic properties (?, and ?) of shield material and logical selection of extrinsic parameters.

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