LAUSR

The Poynting vector (PV) has been widely used to calculate propagation vectors of a pressure field (PF) in acoustic media. The most widely-used acoustic PV formula is the negative of a product of time and space derivatives. These two derivatives result in a phase-shift between the PF and its PV; particularly, for a PF at a local magnitude peak, the PV modulus is zero and thus the propagation direction there is undefined. This “zero-modulus’ issue is not consistent with the physical definition of the PV, which is the directional energy flux density of a PF, because this definition indicates that the variation of the PV modulus should be consistent with the PF magnitude. This PV is only considered as kinematically-correct and defined as K-PV. We derive the dynamically-correct PV (D-PV) formula for acoustic media, which is the negative of the product of the reciprocal of the density, the PF itself, and a factor that is obtained by applying both a time integration and a space derivative to the PF. There are t...