EXTENDING THE USABILITY OF NEAR-FIELD ACOUSTIC HOLOGRAPHY AND BEAMFORMING BY USING FOCALIZATION
Filip Deblauwe, Karl Jansen, Maxime Robin · 2007
In view of source localization techniques, two methods, Near-Field Acoustic Holography (NAH) and Beamforming, are widely used and well-known techniques. Both techniques have their advantages and disadvantages. Near-field Acoustic holography, the oldest commercially available method, 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 analyse higher frequencies, the method becomes very tedious from a measurement standpoint. Beamforming, a far-field technique, has as major advantage that with a limited amount of measurement channels a relative large frequency range can be analysed, making the measurement sequence very simple. On the other hand, Beamforming has as disadvantage that its spatial resolution is proportional to the wavelength making the method not really useful for frequencies under 2000 Hz. In this paper, a technique called focalisation is discussed which can ameliorate the shortcomings from NAH and Beamforming. Focalisation is a near-field beamforming technique that can be used on data taken for NAH to extend the frequency range and double the usable frequency range for the same microphone spacing. In case of beamforming the same array can be used to take data in the near-field. When using focalisation in this near-field data, the spatial resolution is improved by a factor of 2. In addition, the focalisation allows calculating the sound power which is not possible with beamforming.