The purpose of an EM shield is to prevent undesired electromagnetic coupling between an EM source and a susceptible EM device. The mechanism of electromagnetic coupling is by radiation, inductive and capacitive coupling. The radiation of energy by electromagnetic waves characterizes the EM coupling in the far field region, while inductive (or lowimpedance) and capacitive (or high-impedance) couplings are the driving mechanism of coupling in the near field region. In all the cases, a complete analysis of the shielding performances of an EM shield should require a full-wave solution of the electromagnetic problem. This means to solve a classical eddy current problem and in presence of magnetically permeable materials the analysis shall combine the Maxwell’s equations with the magnetic properties of the shield. Numerous studies of shielding problems can be found in the literature showing how this topic has been the subject of great interest to the scientific community for many years (Moser; 1988; Schelkunoff; 1943; Schulz et al.; 1988). Several analytical and numerical techniques have been developed during the years especially with the advent and proliferation of the electronic devices. Different materials with a wide range of electrical and magnetic properties are used for shielding applications. As a matter of fact, an accurate knowledge of the electromagnetic properties of the material is an important task for a correct modeling and design phase. Further, shields have different shapes and contain apertures and all these parameters influence the shielding effectiveness, thus the electromagnetic susceptibility of the combined shieldelectronic equipment system. In a first part, this chapter reports on basic aspects of the shielding theory and standard measurement methods of shielding effectiveness in the frequency and time domain. Concepts and measurement techniques are discussed with reference to basic shield configurations and following the relevant standards (IEEE Std 299; 2006). A basic configuration of the experimental setup and instrumentation chain for shielding effectiveness measurements is reported. In the second part, we focus on the magnetic shields that received most of the attention for shielding low-frequency magnetic fields (Celozzi & D’Amore; 1996; Hoburg; 1995; Sergeant et al.; 2006). The case of a circular loop magnetically coupled to an indefinite conducting plate and that of a hollow ring shield placed coaxially around a circular loop are treated to support our discussion (Di Fraia et al.; 2009). Then, we conclude with a discussion on the characterization of magnetic materials. As better discussed in the chapter, an accurate knowledge of the magnetic characteristics of a magnetic material is at the basis for an accurate study and measurement of the shielding effectiveness of a magnetic shield. Experimental setups and instrumentation chain commonly adopted for magnetic materials characterization are shown.
Data Acquisition Systems for Magnetic Shield Characterization
MARRACCI, MIRKO;TELLINI, BERNARDO;
2010-01-01
Abstract
The purpose of an EM shield is to prevent undesired electromagnetic coupling between an EM source and a susceptible EM device. The mechanism of electromagnetic coupling is by radiation, inductive and capacitive coupling. The radiation of energy by electromagnetic waves characterizes the EM coupling in the far field region, while inductive (or lowimpedance) and capacitive (or high-impedance) couplings are the driving mechanism of coupling in the near field region. In all the cases, a complete analysis of the shielding performances of an EM shield should require a full-wave solution of the electromagnetic problem. This means to solve a classical eddy current problem and in presence of magnetically permeable materials the analysis shall combine the Maxwell’s equations with the magnetic properties of the shield. Numerous studies of shielding problems can be found in the literature showing how this topic has been the subject of great interest to the scientific community for many years (Moser; 1988; Schelkunoff; 1943; Schulz et al.; 1988). Several analytical and numerical techniques have been developed during the years especially with the advent and proliferation of the electronic devices. Different materials with a wide range of electrical and magnetic properties are used for shielding applications. As a matter of fact, an accurate knowledge of the electromagnetic properties of the material is an important task for a correct modeling and design phase. Further, shields have different shapes and contain apertures and all these parameters influence the shielding effectiveness, thus the electromagnetic susceptibility of the combined shieldelectronic equipment system. In a first part, this chapter reports on basic aspects of the shielding theory and standard measurement methods of shielding effectiveness in the frequency and time domain. Concepts and measurement techniques are discussed with reference to basic shield configurations and following the relevant standards (IEEE Std 299; 2006). A basic configuration of the experimental setup and instrumentation chain for shielding effectiveness measurements is reported. In the second part, we focus on the magnetic shields that received most of the attention for shielding low-frequency magnetic fields (Celozzi & D’Amore; 1996; Hoburg; 1995; Sergeant et al.; 2006). The case of a circular loop magnetically coupled to an indefinite conducting plate and that of a hollow ring shield placed coaxially around a circular loop are treated to support our discussion (Di Fraia et al.; 2009). Then, we conclude with a discussion on the characterization of magnetic materials. As better discussed in the chapter, an accurate knowledge of the magnetic characteristics of a magnetic material is at the basis for an accurate study and measurement of the shielding effectiveness of a magnetic shield. Experimental setups and instrumentation chain commonly adopted for magnetic materials characterization are shown.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
