A new technique known as beamforming has been used for determining noise location ofpassing vehicles. Traditional pass-by noise tests are useful for detecting the sound level ofnoise sources on a vehicle duning operation. __35__ Pass-by noise source identification takesthis one step further by identifying the source of the noise as well, so engineers can fine-tunevehicle design to minimize noise. __36__ NAH operates in a sound's so-called 'near field," within one or two wavelengthsof the source, where sound waves act as circular waves emanating from the source.Beamforming, on the other hand, is more suited to the far field, located at roughly sevenwavelengths from the noise source, where sound waves act as planar waves. If you can thinkof a sound source like a pebble falling in water, then sound cmanating from the source is likcthe waves that come from where the pebblc hit. __37__  If you are standing far away on thoshore, however, the waves no longer look like circles but just a straight line coming towardyou. Sound waves behave in the same way. Because measurement sensors can often not beclosc enough to passing vehicles to be in the near field and perform NAH, beamforming is thepreferred technique for noise location in such applications. __38__  This application note strives to offer best techniques for performing beamformingon passing objects so that the end result is an accurate analysis of noise on vehicles. 
(A) When you are close to where the pebble fell, the waves ars clcarly in a circlc, centeredon where the pebble fell. 
(B) These are measured to ensure compliance with laws that govern acceptable soundemitted from a vehicle. 
(C) Engincers can use several analysis techniques to identify aoise sources includingnear-ficld acoustic holography (NAH) and beamforming. 
(D) Beamforming prcscnts several challenges including simultaneousty measuring a largenumber of microphone serisors, transmitting and saving this large amount of acquiredwavcform data, and being able to quickly process large data sets.
【題組】35.