Scholte R., Roozen B., Lopez I.

Planar Near-field Acoustic Holography (PNAH) is nowadays practically implemented at various companies and institutes. At all times, seemingly correct acoustic images are created that are treated accordingly. Caution has to be taken while interpreting these results, since incompetent windowing and filter implementation leads to results that are far from the exact solution. In order to avoid certain cases and probable misinterpretations, a number of recent developments were made. A significant part of the most recent developments are discussed shortly, followed by an in-depth comparison and verification of results, based on both sound pressure and particle velocity measurements. Various anti-leakage windowing techniques will be discussed and compared. Border-padding is compared to classical windowing on larger grid sizes. Sound pressure and particle velocity measurements on a stationary spinning hard disk are used to obtain inverse solutions on various distances. Also, multiple distances are measured and compared to the obtained inverse solutions. The flat top cover of the hard disk is scanned by a traversed laser vibration system. These velocities of the cover are compared to inverse solutions of the particle velocity at the source plane, where both sound pressure and particle velocity are used to obtain these results. This makes it possible to quantitatively compare pressure to velocity and velocity to velocity PNAH.