Measurement Of Field Inside Phononic Crystals Based On Surface Acoustic Waves And Related Physical Effects

Phononic crystals are artificial bandgap materials consisting of periodically distributed elastic parameters(mass densities and/or elastic moduli)in space.Since its abilities for controlling acoustic waves are significantly different from traditional materials and structures,phononic crystals have attracted considerable attention of many experts and scholars in various fields such as materials science,condensed matter physics,acoustics.From the perspective of fundamental research,the band structure of phononic crystals with different symmetries are totally different,resulting in variety of exotic physical effects such as negative refraction,negative birefraction,self-collimation,unidirectional propagation.It also can mimic some phenomena such as quantum Hall effect,quantum spin Hall effect and valley states in electronic systems.From the view of application,the bandgap properties of phononic crystals can be used for shock insulation,noise reduction,earthquake protection and defective waveguide.Surface acoustic waves(SAW)technology based on interdigital electrode has penetrated into people’s daily life for long.SAW filters,duplexers,resonators and delay lines are applied to many fields such as mobile communication,automobile,television,broadcast and so on.SAW sensors and microfluidics can monitor environment and manipulate particles precisely.This thesis focuses on combing phononic crystals and SAW featured in practicability,aiming to utilize phononic crystals for controlling the propagation of SAW.The finite element(FEM)simulation,fabrication of samples,measurement of SAW phononic crystals are all included.The details are listed as follows:1.The calculation method of SAW phononic crystals’ band being able to solve the existence of piezoelectric coupling has been proposed based on commercial FEM software COMSOL.The band characteristics and lattice with Dirac dispersion of SAW phononic crystals are analyzed.2.The processing technology of integrating SAW phononic crystals and interdigital transducer on one chip are described clearly.A set of laser interference scanning system is established,which can measure SAW vibration and image in a plane.With this system,we obtain the field of Bloch waves inside the SAW phononic crystals.3.Combining the self-collimation effect and defect layer,a kind of SAW beam splitter based on phononic crystals has been realized by simulation.The energy ratio between transmitted beam and reflected beam can be adjusted by varying the geometric parameters of defect layer.4.The valley state in SAW phononic crystals has been realized by breaking the inversion symmetry of honeycomb lattice.Chiral valley state can be excited selectively by applying a chiral source.Valley-dependent edge state exists on the interface of two topologically distinct valley SAW phononic crystals.Above all,we make a comprehensive discussion of the basic band calculation,mode analysis,sample processing and Bloch wave imaging of SAW phononic crystals.Some physical effects are also studied in this thesis.