Multi-Layer Planar Near Field Holography using MEMS microphone arrays in a noisy environment
Regular paper
University of Technology Eindhoven
Wednesday 3 june, 2015, 09:00 - 09:20
0.8 Rome (118)
Abstract:
Near-field acoustic measurements in noisy environments suffer from
interference generated by undesired sources, especially when these 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 at the source of vibrating objects in high
detail, however, its accuracy is impacted when an undesired source is present
closely behind the measurement array. A few examples are performing acoustic
measurements of vehicle interiors or inside of devices such as power
generators or computers. This paper presents a method for performing PNAH
using multiple pressure sensor arrays. The advantages of this method are
twofold. Firstly, it has the ability to measure in environments where
undesired sources are present behind the measurement plane, especially when
these sources are in close proximity to the array. Secondly, assuming only
pressure measurements, a measurement array for the method can be easily
constructed using MEMS microphone technology. This paper will first describe
the Multi-Layer method, then cover some of the difficulties when implementing
and using it such as the half wavelength condition needed for non-aliased
measurements and the signal processing techniques used to improve quality of
the results and finally show the advantages of this method in noisy
environments. 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.