Acoustic Enhancement And Weak Signals Detection Based On The Space-coiling Gradient Acoustic Grating

Weak signals detection is widely used in military and industry,which has great significance for research.In practical engineering applications,the useful information in the acoustic signals we get is always weak,and it is vulnerable to be interfered by other signals and polluted by complex background noise,which make the accurate measurement of the signals very difficult.The traditional weak signals detection methods aim to suppress or filter the noise,but they always weaken the useful signals at the same time,which may greatly influence the effect of weak signals detection.The space-coiling metamaterials a kind of acoustic metamaterial which can realize low sound velocity and high refractive index by spatial folding.The special structure features make the metamaterial have excellent filtering characteristic and the acoustic enhancement characteristic,which can realize filtering and sound energy enhancement of specific frequency or frequency band.Many studies have shown that the application of space-coiling acoustic metamaterials with excellent acoustic properties can provide a new solution for weak signals detection.In order to achieve filtering and acoustic enhancement in the wide frequency band,the space-coiling gradient acoustic grating based on the action mechanism of space-coiling metamaterials is designed in this thesis.In order to enrich the theoretical methods of weak signal detection,we propose a weak signals detection method based on the space-coiling gradient acoustic grating,and verify the effectiveness of the detection method by finite element simulation.The main research work of this thesis is as follows:(1)Design and analysis of the space-coiling gradient acoustic gratingReferring to the design principle of space-coiling acoustic metamaterial,the space-coiling gradient acoustic grating is constructed,and the finite element model is established in the finite element simulation software.Moreover,we calculate the sound pressure field of the space-coiling gradient acoustic grating,and verify the excellent separation of frequency in space domain characteristics and acoustic enhancement performance.(2)Optimization of the space-coiling gradient acoustic gratingThe sound pressure fields with different structure parameters are calculated.Through the analysis of the maximum sound pressure gain and the maximum sound pressure gain frequency with different structure parameters,the effects of the five parameters(including the size of air gap,the thickness of gratings and the size of space-coiling structure)and the mechanical deformation coefficient on the acoustic enhancement characteristic are obtained.According to the results of the parameter analysis,we determine the optimal structure of the space-coiling gradient acoustic grating.(3)Analysis of weak signals detection method based on space-coiling gradient acoustic gratingTo solve the problem of weak signals extraction and detection,we propose a weak signals detection method based on space-coiling gradient acoustic grating.Then we calculate the sound pressure fields of the space-coiling gradient acoustic grating under the weak harmonic signals and periodic impact signals respectively.Through the comparative analysis,the effectiveness of detection for weak harmonic signals and periodic impulse signals is verified,which further enriches the theoretical method of weak signal detection.(4)Experiment of weak signals detection based on space-coiling gradient acoustic gratingAccording to the simulation results,the weak signals detection experiment based on the space-coiling gradient acoustic grating is carried out.The amplification effect of the space-coiling gradient acoustic grating on the weak harmonic signals and periodic impulse signals is tested under different signal-to-noise ratio.We calculate the sound pressure gain and the signal-to-noise ratio gain.And the experimental results verify the effectiveness of the space-coiling gradient acoustic grating on the weak harmonic signals and periodic impact signals detection.The numerical and experimental results show that the space-coiling gradient acoustic grating has excellent filtering characteristics and acoustic enhancement effect,which can effectively realize the sound enhancement detection of weak acoustic signals.These researches enrich the weak signals detection methods and provide an effective way for the application of space-coiling acoustic metamaterials.