  There exists serious miscomprehension in the open literature about the
electromagnetic interference shielding effectiveness (EMI SE) as a critical
index to evaluate the shielding performance, which is misleading to the
graduates and newcomers embarking on the field of electromagnetic shielding
materials. EMI SE is defined as the sum of three terms including reflection
loss, absorption loss and multiple reflection loss in the classical Schelkunoff
theory, while it is decomposed into two terms named reflection loss and
absorption loss in practice, which is called Calculation theory here. In this
paper, we elucidate the widely-seen misconceptions connected with EMI SE via
theoretical derivation and instance analysis. Firstly, the terms in Calculation
theory are often mistakenly regarded as the approximation of the terms with the
same names in Schelkunoff theory when multiple reflection loss is negligible.
Secondly, it is insufficient and unreasonable to determine the
absorption-dominant shielding performance in the case that absorption loss is
higher than reflection loss since reflection loss and absorption loss cannot
represent the actual levels of reflected and absorbed power. Power coefficients
are recommended to compare the contribution of reflection and absorption to
shielding performance. Thirdly, multiple reflection effect is included in the
definitions of reflection loss and absorption loss in Calculation theory, and
the effect of multiple reflections on shielding property is clarified as
against the commonly wrong understandings. These clarifications offer correct
comprehension about the shielding mechanism and assessment of reflection and
absorption contribution to the total shielding.
