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.
The ability of the shielding to block or absorb the RF signals is determined by several factors – the conductivity of the material, the permeability of the material, and the material thickness. However, regardless of the gasket type, key factors to consider when choosing a gasket are RF impedance (R + jX, where R = resistance, jX = inductive reactance), shielding effectiveness, compressibility, compression forces, compression range, compression set, and environmental sealing.
Differential-mode currents, flowing synchronously through both signal and power distribution loops, produce time-variant electromagnetic fields and, on simple one- or two-layer PCBs, loops are formed by the digital signals being transferred from one device to another that return by means of the power distribution traces. The resonant frequency is the frequency where integer half-wavelengths correspond to the dimension of the shielding enclosure. However, shielding gaskets typically fall into four principle categories: beryllium copper and other metal spring fingers, knitted wire mesh, conductive particle filled elastomers, and conductive fabric-over-foam. This article will examine some of the approaches and off-the-shelf products that can be used to minimize RF interference through the use of shielding and ground planes to prevent spurious signals from interfering with wireless system operation.
In addition to the many off-the-shelf solutions, designers can work with the shielding vendors to create a custom shape to meet their specific system needs. Each of these materials has distinct advantages and disadvantages, depending upon the application. 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.


Therefore, some shielding mechanism must be provided to ensure undisturbed functioning of devices even in the presence of external electromagnetic (EM) noises. 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. Shielding is the process by which a certain level of attenuation is extended using a strategically designed EM shield. 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). EMI is basically disruptive electromagnetic energy that is emitted by one portion of the circuit and reaches other portions of the circuit or the external world via conducted or radiated paths. This overview of shielding approaches shows that basic shielding theory is really not so basic. In addition to metal shields that surround key circuits, additional shielding in the form of gaskets and other materials are often used to effectively shield as much of the entire enclosure as possible. These loops also act as antennas and pick up the time-variant electromagnetic fields, which create noise in the loops.
Part of the design challenge for shielding must take into account such issues as airflow, mechanical strength, and still other factors. In the next section, a comprehensive account of potential materials for handling of EMI are described with special reference to nanocomposites based on intrinsically conducting polymer matrix filled with conducting [e.g.


Shielding definitions and phenomenonEMI shield is essentially a barrier to regulate the transmission of the electromagnetic EM wave across its bulk. Theoretical shielding effectivenessBefore starting the shielding analysis, it is necessary to understand the various electromagnetic terminologies (Ott, 2009).
Shielding can be a stand-alone solution, but it is more cost-effective when used in conjunction with other suppression techniques such as grounding, filtering, and, as mentioned earlier, proper circuit-board design to minimize the loop area. 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. Unfortunately, designers often leave shielding as a last option since the shields can be installed once the design is completed. However, by incorporating shielding considerations from the beginning of the design process, designers can deliver a more cost-effective and generally more efficient system design. Additionally, the ability of the material to reflect the signals is controlled by both the permeability and conductivity.



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