Pan Pacific Symposium Conference Proceedings


DESIGN AND OPTIMIZATION OF A MULTILAYER SHIELD OF DIELECTRIC

Authors: D. Monopoli, M. Mussetta, A. Gandelli and R. Zich
Company: Politecnico di Milano, Dipartimento di Elettrotecnica
Date Published: 1/24/2008   Conference: Pan Pacific Symposium


Abstract: The problem of electromagnetic compatibility (EMC) is relevant for the design of modern devices. In every electronics device are always present some parts that can not function for electromagnetic field effects. This phenomenon is called Ellectromagnetic Interference. EMI is the unwanted phenomenon that occurs when extra voltages or currents are present to affect device’s performance due to these fields which represent the electromagnetic environment. Generally, it is possible to classify EMI in terms of its causes and sources. The cause of interference and noise may be within the system (intrasystem) or from the outside (intersystem), and all the two problems are equally dangerous. The EMC is based on three solution approach: geometrical, topological and shielding. The first consists ion the design of the shape of the radiating elements, in order to produce electromagnetic field only in particularly zones. The second increases the distance from the source of the disturb and the critical device, in order to reduce the order of magnitude of electromagnetic field. The last one has the same approach of the previous, but it has some advantages. In fact, it can reduce the space between source and receiver. Also, it is possible to use a partial shield for a particular frequency, therefore are used also with radiating elements.

The our work studies the planar shield made by a suitable superimposition of dielectrics layers of different thickness. In order to do that it is necessary to model a transfer function of the shield. During this step we assume a planar and infinite shield. These hypothesis are useful for vertically multilayer device. However, it do not take into account the diffracted effect of the wedges of the device.

Under these assumptions every dielectric layer can be considered as an equivalent impedance. Consequently the shield is described by a transmission line. It yields to a transfer function H in function of the frequency, the dielectrics parameters and the thickness of the layers. The following step consist in the design of the shield. In order to do that it must be chose an ideal transfer function of frequency. This will be the goal to optimize by an evolutionary code. It take as fitness function a combination of H, numbers of dielectrics layers and thickness of shield. Moreover, it can be easily design partial shield.

Finally we design a shield of wireless sensor as example.



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