Weak Signals Detection Based On The Graded Reflection Acoustic Grating Metamaterials

Weak signal detection counts for much research significance in the field of equipment condition monitoring and fault diagnosis technology.In practical engineering,the signal-to-noise ratio of characteristic signals in the initial stage of mechanical equipment failure is low,which is easy to be covered up by background noise or disturbed by other signals,resulting in the failure of equipment to find abnormalities in time.The traditional weak signal detection method mainly reduces the interference of noise to the characteristic signal by weakening or filtering noise,but it will affect the characteristic signal itself when processing noise.As an artificial composite material,acoustic metamaterial s has superior acoustic regulation performance,can realize acoustic enhancement,broadband filtering and other functions,and provides a new direction for weak signal detect ion.In this thesis,a graded reflection acoustic grating metamaterials(GRAGM)is designed.The acoustic enhancement effect and direction positioning function of the structure in a wide working frequency band on the deep sub wavelength scale are analyzed by basic theoretical and finite element method.According to its acoustic characteristics,a method of using gradient reflection acoustic grating structure for weak signal detection is proposed.The method is verified by numerical simulations and experiments.The main research work of this thesis is as follows:(1)Design and theoretical analysis of gradient reflection acoustic gratingAccording to the acoustic enhancement theory of acoustic grating metamaterials,a graded reflection acoustic grating structu re is designed.The arrangement period of acoustic grating is different from that of traditional acoustic grating structure.The equivalent model of the structure is analyzed,and the principle of its broadband and low-frequency sound enhancement performan ce is explained.(2)Finite element analysis of acoustic characteristics of the GRAGMBased on the acoustic basis and finite element theory,the sound pressure field of the graded reflection acoustic grating metamaterial is calculated by using COMSOL Multiphysics 5.5 software,and it is verified that it has goo d acoustic enhancement performance for low-frequency and broadband sound waves;The sound pressure field after the change of structural parameters is calculated,and the law of effect of structural parameters on acoustic enhancement performance is summarized;The directional response sensitivity of the GRAGM is analyzed.(3)Simulation analysis of weak signal detection based on the GRAGMA method of detecting weak signal by using graded reflection acou stic grating is proposed.COMSOL multiphysics 5.5 is used to analyze the sound field response of periodic impact signal and weak harmonic signal incident o n the graded reflection acoustic grating.It is verified that the structure can amplify the amplitude of different weak signals and is easy to detect signals.The directional response of the gradient reflection sound grid to weak signals with different incident angles is also analyzed;The simulation results show that the graded reflection acoustic grating metamaterials can effectively enhance the detection and orientation of weak signals.(4)Experimental verification of weak signal detection based on the GRAGMThe broadband,deep subwavelength and directional response characteristics of graded reflection acoustic grating metamaterials are verified by experiments;According to the simulation results,the weak signal detection experiment is designed,and the enhancement effect of graded reflection acoustic grating metamaterials on periodic impact signal and weak harmonic signal is tested.It is verified that graded reflection acoustic grating metamaterials can realize the direction positioning of weak signal.The simulation and experimental results show that the gradient reflection acoustic grating can reduce the working frequency by controlling the boundary reflection phase,so as to realize broadband acoustic enhancement on the deep sub wavelength scale.In addition,the gradient reflection grating also has sensitive directional response.These acoustic characteristics provide a new method for gradient reflection acoustic grating metamaterials in the fields of weak signal detection,sound source location and so on.