The investigation on the physical acoustics problems of the NAH technique and its application

The NAH technique may be useful for detection of vibration of underwater structures and calibration of parameters of sonar projector array.When this technique is brought into practice,a facility must be developed,which include hydrophone array,amplifier,A/D adapter and computer with controlling and calculating software.It is expressed that,some parameters used for design of facility and requirements of their application will be related to some physical sound problems.These physics parameters and requirements used for NAH technique are analyzed,based on investigation and calculation of the sound wave number spectrum of source signal and the sound pressure distribution in near-field of source.Such parameters and requirements as partial waves with higher wave number of need,choice of the dimension of the hologram with different form,the distance from hologram to the sound source,and the distance between measuring points on hologram etc.,are relative to the form of source and the ratio of its dimension to wavelength.All these relations used for NAH are given out.