Application research on diseases stressed plant based on near-field acoustic holography

In this paper, the basic principle of planar near field acoustic holography is expatiated and the reconstruction formula of sound source localization is given. We take theoretical results of sound pressure radiating from a point source to the holographic plane as the experimental data, and then substitute it in the reconstruction formula to reconstruct the sound source information. By changing holographic plane size, spacing and holographic measurement distance, we compared the sound source reconstruction results with the known sound source to see how these measured conditions parameters affect the reconstruction accuracy. Test results show that precise result can be got when the sound bandwidth exceed 5Khz, the hologram plane size is 6 times greater than the sound wavelength, the spacing of measurement point on holographic plane is less than 1/3 of the wavelength and the holographic measurement distance is less than 1/34 of the wavelength. We applied the planar near field acoustical holography in plant disease stress monitoring, and choose the signal with frequency of 2KHz to carry out the reconstruction experiment. The holographic plane was 0.6m side length square, measuring point spacing was 0.06m and the distance between hologram plane and reconstruction plane was 0.015m. Three sound sources were finally identified. By modifying the parameter setting and comparative analysis, we seek the best selection for simulation and use it as a reference in the ultrasonic signal tests of the diseases stressed plant. Having collected acoustic emission signals, we identified the sound source by near field acoustic holography and located plant diseases stress. Consequently, we can conduct a new crop disease forecast and precision spraying of pesticides.