Hi, I'm trying to understand what makes materials lossy and how to measure that lossiness - this is for either/or electromagnetics or acoustics. So far, I haven't really found good explanations/resources other than that a complex permittivity can cause loss. However, how do viscosity or antennas cause loss, for instance? And moreover, how can these values be measured? Sorry for the vague question, I'm not too sure on the subject itself. Thanks!