Electronics shields

The design of electronic circuits, processing low-amplitude voltages, exposed to electromagnetic interferences, frequently requires the use of shielding. These include shielded cables, connectors, filters and shielded enclosures, as well as the configurations of ground contacts and the involvement of additional protection devices. This thing, also suppose that the shielding effectiveness concerns each component of an electronic equipment, in order to agree with electromagnetic compatibility standards, as well as satisfy compromises according to the criteria of cost, reliability, electrical and operating safety.

The scientific analysis as suggested here, is therefore based on the example of simple electronic equipment, configured to collect, transmit and amplify voltage signals. These functions and components will thus lend themselves more readily to exposure to various interferences, given by electromagnetic fields, covering a large frequency range, to which will also be added currents diverted in the ground wiring or directly in earth.

We shall see that the use of simple equipment leads to the concept of a topological diagram, involved by the combination of various types of shielding, which attenuate strongly the effects of interferences as mentioned above. Since this physical barrier is imperfect, we’ll need to characterize it by means of the parameters that can be measured or computed to determine the reduced amplitude voltage reaching the circuit or any electronic component assumed to be vulnerable.

According to this foreword, chapter one describes the simple equipment and its topological diagram. Chapter two, will be focused to the coupling of EM plane waves through a conductive plane. This preliminary step will attempt to relate the attenuation of a shield to its internal structure, depending on whether it is made of a highly conductive homogeneous metal, a metal grid, or a composite substitute. Chapter three deals with shielded enclosures, in order to analyze their behavior under the coupling of electromagnetic fields within a wide frequencies range, as well as to the currents flowing on their walls. Chapter four deals with shielded cables, especially with the evaluation of the voltages related to the concept of transfer impedance. Chapter five, will be devoted to connectors, in focusing their relationship with the concept of electromagnetic immunity. Chapter six considers the contribution of additional components which improve the shield efficiency, like the arrestors, ferrite rings, and absorbing cables.

As a general rule, each chapter will be helped by examples to evaluate more easily the orders of magnitude of the physical data, about the shielding parameters or electromagnetic interferences.