2024-02-22 23:00:00
The development of electronic circuits processing low amplitude signals exposed to electromagnetic constraints, frequently requires the use of shielding. These include, shielded cablesof the connectorsof the filtersof the metal enclosuresbut also specific functions in relation to contacts with earth networks and the participation of additional protections. This enumeration also implies that theefficiency of shielding must harmonize with each component of an installation, to meet the standards of electromagnetic compatibilityas well as compromise linking the criteria of cost, reliability, electrical safety and operational safety.
This context therefore influenced the scientific analysis of the article, on the example of a generic electronic equipment, configured to collect, transmit and amplify analog signals. These functions and components will thus lend themselves more easily to exposure to various constraints, represented by electromagnetic fields, covering a wide range of frequencies, to which will also be added currents derived in the ground.
We will see that the use of generic equipment will lead directly to the concept of topological boundary, materialized by the sequence of various types of shielding, opposing the penetration of the constraints mentioned above. Knowing that this physical barrier is imperfect, we will be led to characterize it by parameters accessible to measurements, or to the calculation of the residual voltages arriving on a circuit or component considered vulnerable.
In the spirit of the preamble, we will proceed in the first chapter to the description of the generic equipment, completed with its topological boundary. We approach, in a second chapter, the study of the penetration of plane waves in plane shielding. This preliminary step will attempt to connect the attenuation of a shield to its internal structure, depending on whether it is composed of a highly conductive homogeneous metal, a metal grid, or a composite substitute. THE third chapter deals with the issue of shielded enclosures, we will analyze their behavior when exposed to electric and magnetic fields covering a wide range of frequencies, as well as to currents derived on their metallic structure. THE fourth chapter is interested in shielded cables, particular attention will be paid to the evaluation of the residual voltages generated by the transfer impedance. THE fifth chapter, devoted to connectors, emphasizes their link with the concept of electromagnetic immunity. THE sixth chapter presents some processes complementing the action of shielding, such as amplitude limiters, ferrite rings, as well as filtering or absorbing cables.
As a general rule, each chapter will be accompanied by examples, making it possible to identify the orders of magnitude of the physical data, affecting both the parameters qualifying the shielding and the electromagnetic constraints.
Let us add that the reader wishing to deepen the analysis of shielding or electromagnetic coupling phenomena can consult other articles appearing in the IT databases and recalled in the text and To find out more.
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