Bragg And Non-Bragg Resonances Of Metal Surface Waves

Laser ultrasonic technology is an effective way to stimulate surface acoustic waves and is widely used in various fields;Laser ultrasound combined with fiber optic sensors enables accurate detection of surface acoustic waves.The propagation of surface acoustic waves in the periodic structure has always been a research hotspot.The study of the Bragg bandgap in the periodic structure in photonic crystals and some phononic crystals has made significant progress.Due to the complex mode,the elastic wave becomes a difficult point in the study of phonon bandgap.Based on the theory of the surface acoustic wave propagating in the metal surface calculation,the dispersion relation of the surface acoustic wave propagation time,so as to find a Bragg resonance and non-Bragg resonance of the frequency range.The built-in laser ultrasonic detection system is used to detect the aluminum plates with different periodic structures.The Bragg and non-Bragg resonances of the metal surface waves in the periodic structure are discussed.The main contents of this paper include the following aspects:First,the theoretical study on the propagation of metal surface waves in periodic structural media.Firstly,the laser ultrasonic excitation mode of metal surface waves is discussed.Since the laser ultrasound has many advantages,so the research of laser ultrasonic excitation mechanism,and using the theory of elastic wave analysis and multi-mode laser ultrasonic excitation is derived.Secondly,the metal surface of aluminum plate using a laser excitation of a surface wave propagation mode detailed study,and its propagation velocity is detected;Propagating velocity of the surface of the aluminum plate obtained metal periodic wave having a symmetrical structure in the boundary,the conclusion is not less than the propagation velocity of the surface of the aluminum plate structure;A phonon effective impedance similar to the effective refractive index in the photonic crystal is inferred.Finally,the dispersion curve of the metal surface wave propagation in periodic structures was calculated to obtain three different structures of the dispersion curve corresponding to the aluminum plate,and calculate the position of a band gap corresponding to the Bragg and non-Bragg resonance generated.Second,build and improve laser ultrasonic detection system based on fiber Fizeau interferometric sensors designed to detect the Bragg and non-Bragg resonance phenomenon of aluminum plate experimental methods and procedures.Firstly,a laser ultrasonic testing system is built to detect metal surface waves propagating on the surface of the aluminum plate;Because sound waves when passing periodic structure interaction will occur and produce a variety of complex patterns,it requires careful debug the system set up after the system is completed.The next test(point light source and line light source),the waveform and amplitude change of the metal surface wave excited by a laser in various laser energy source or different.Secondly,the research and discussion on the fiber surface acoustic wave detector device fiber Fizeau interferometer sensor;Analyze the detection principle of detecting metal surface waves and the adjustment of the detecting device.Finally,the experimental design method for detecting the surface wave propagating in the metal surface of the aluminum plate periodic structureIn the end,the experimental results of the propagation of metal surface waves in periodic structural aluminum plates were analyzed and summarized.When we study the Bragg and non-Bragg resonance of metal surface waves,we design three kinds of aluminum plates,which are symmetrical structure,antisymmetric structure and periodic staggered ?/2 phase structure.The research results show that in the symmetrical structure,the metal surface when the wave propagates,it will generate Bragg resonance with a Bragg band gap.In the antisymmetric structure,the metal surface wave will generate non-Bragg resonance when it propagates,with a non-Bragg band gap;and the period between the two is in the structure.In the staggered ?/2 phase structure,the surface wave propagation of the metal will have both Bragg and non-Bragg resonances,corresponding to two band gaps,the Bragg band gap and the non-Bragg band gap Further research has found that the Bragg band gap and the non-Bragg band gap can be regulated by adjusting the phase of the periodic structure.For the forbidden band coupling structure combined with two cycles,two Bragg band gaps are generated;By adjusting the period parameters,the two Bragg band gaps can be deeply controlled,which has great research significance for surface wave devices such as sensors fabricated by surface acoustic wavesThe laser ultrasonic detection system combined with laser ultrasonic and fiber Fizeau interferometer has important scientific significance for the detection of metal surface waves in the periodic structure.It provides reference for the design and manufacture of optical detection or surface acoustic wave functional devices,and can also provide reference for the field of phononic crystal research.