Near-field scanning based shielding effectiveness extraction for board level shielding cans

The conventional definition of shielding effectiveness is well suited for calculating electromagnetic shielding in the far-field. However, in the near field, shielding effectiveness calculation is not so straight forward. In radio frequency interference problems, most of the field coupling occurs in near field. Having a well-defined method to calculate near-field shielding effectiveness is important for estimating the suppression of radio frequency interference using the shield cans. In this research, a method to extract the shielding effectiveness of board level shielding cans using near field scanning is developed. Shielding effectiveness is defined by modelling the shielded noise source as equivalent dipole moments. Accuracy of the equivalent source is analyzed by using least square error and correlation coefficient as confidence check parameters. Applying reciprocity theorem, the voltage coupled on a PIFA antenna from an unshielded and a shielded source is calculated. Coupled voltage from a shielded noise source serves as the reference and is used to validate the effectiveness of the developed method. Practical shield cans were used to study and develop the shielding effectiveness extraction method using full wave 3D simulations --Abstract, page iv