12 Data Acquisition Systems for Magnetic Shield Characterization Leopoldo Angrisani 1 , Mirko Marracci 2 , Bernardo Tellini 2 and Nicola Pasquino 3 1 University of Naples “Federico II”, Department of Computer Science and Control Systems 2 University of Pisa, Department of Electrical Systems and Automation 3 University of Naples “Federico II”, Department of Electrical Engineering Italy 1. Introduction 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 low- impedance) 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 shield- electronic 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.