Multi-layer planar near field holography using MEMS microphone arrays in a noisy environment

Near-field acoustic measurements in noisy environments suffer from interference generated by undesired sources, especially when they are located close to the measurement equipment. Planar Near-field Acoustic Holography (PNAH) using a single layer pressure sensor array, is a proven method for determining sound pressure fields in high detail at the source of vibrating objects, however, its accuracy is impacted when an undesired source is present closely behind the measurement array. This paper presents a method for performing PNAH using an arbitrary number of MEMS pressure sensor arrays using a Multi-Layer method not bound to one or two measurement planes. The results are demonstrated by measurements using two MEMS microphone arrays which show that Multi-Layer PNAH is a qualitative improvement over single layer PNAH in both noisy but also non-noisy environments and that it can be easily implemented and used in practice by utilizing MEMS technology.