A new technique known as beamforming has been used for determining noise location ofpassing vehicles. Traditional pass-by noise tests are uscful for detecting the sound level ofnoise seurces on a vchicle duxing operation. __35__Pass-by noise source identification takesthis onc step further by identifying the source of the noisc as well, so engineers can fine-tunevehicle design to miinimize noisc. __36__ NAH operates in a sound's so-called "near Gield," within one or two wavelengthsof the source, where sound waves act as circular waves cmanating 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 emanating from the source is likethe waves that come from where the pebble hil.__37__  If you are standing far away on theshore, however, the waves no longer look like circles but just a straight line coming towardyou. Sound waves behave in the same way. Bccause measurement sensors can often not beclose 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 beanformingon passing objects so that the end result is an accurate analysis of noise on vehicles.

(A) When you arc closc to where the pebble fell, the waves ans clcarly in a circle, centeredon where the pcbble fell.
(B) These are measured to ensure compliance with laws that govern acceptable soundemitted from a vehicle.
(C) Engineers can use scveral analysis tochriqucs to identify noise sources includingnear-lield acoustic holography (NAH) and beamforming.
(D) Beamforming presents several challenges including simultaneously measuring a largcnumber of microphone sensors, transmitting and saving this large amount of acquiredwaveform data, and being able to quickly process large data sets.
【題組】35.