In view of source localization, Near-Field Acoustic Holography (NAH) and beamforming are well-known and widely-used techniques. NAH has as major advantage its spatial resolution being equal to the microphone spacing and independent of frequency. This makes it a very powerful technique for low-frequency problems. However when trying to analyze higher frequencies, the method becomes very tedious from a measurement point of view.
Beamforming, a far-field technique, has as main advantage that with a rather limited amount of measurement channels a relative large frequency range can be analyzed. The disadvantage is its spatial resolution which is proportional to the wavelength, making the method hardly useful for frequencies lower than 2000 Hz. In this paper, a focalization method is discussed that can improve the shortcomings of both NAH and beamforming.
Focalization is a near-field beamforming technique that can be used on measurement data taken for NAH to extend the frequency range for the same microphone spacing. In case of beamforming the same array can be used to measure data in the near-field. When using focalization on this near-field data, the spatial resolution is improved by a factor 2. In addition, the focalization allows to calculate the sound power which is not possible with beamforming.
