| Acoustic wave has a wide application in engineering,such as acoustic resonators,filters,sensors,guided waves in non-destructive evaluation.In many cases,accurate calculation of dispersion curves is essential and imperative.However,the multi-physics coupling in acoustic devices and high anisotropy and viscoelasticity in non-destructive evaluation of composite structure result in that many dispersion equation calculating methods are not applicable,and missing mode even calculating completely failure are serious troubles.Motivated by this point,this paper presents a new numerical algorithm to solve multivariate transcendental equation sets in complex domain,which is used to calculate dispersion equation in wave motion.This algorithm has two steps including searching for local minimum function modulus and distinguishing the null points from nonzero minimum function modulus.Although some existing methods also used these two steps,the algorithm here has a special way to search local minimum function modulus along with a special null point judging criterion,which makes the calculation robust and avoids mode missing.This algorithm is further used to investigate wave in various materials and structures.The wave motion in the thin film bulk acoustic resonator(FBAR)is first discussed,including dispersion curves comparison between open and short circuit,and between inertial and elastic electrodes.The cutoff frequency and wave mode shapes of each branch are obtained,and the influence of mass ratio on frequency is discussed.These results are fundamental for device design.Some piezoelectric materials,such as zinc oxide,are semiconductors simultaneously.The coupling of piezoelectric and semiconductive effects may have an interference on piezoelectric acoustic device.Also this coupling effect can be used in energy harvest.Thus,the influence of semiconductive effect on waves propagating in piezoelectric plate is investigated,including size dependent dispersion curves,wave attenuation,wave mode shapes,distributions of carriers and potential,and two methods to improve potential.Based on these results,it is found energy can be harvested not only when the deformations are generated but also when the deformations are recovering.Another application of guided waves is in non-destructive evaluation.Therefore,the wave propagating in generally anisotropic viscoelastic/elastic plates is investigated,including comparison between elastic case and different viscoelastic cases,and the relation among wave mode shape conversion,dispersion branch veering,jumps of group velocity and energy velocity,jumps of attenuation,and branch exchange.The interfacial damage/failure is a great concern in composite structure,thus the wave propagating in a bilayer with imperfect interface is further discussed,including perfect interface,complete delamination,and the evaluation progress of dispersion curves and wave mode shapes from perfect to complete delamination.These results are obtained in generally anisotropic viscoelastic cases and therefore can be simplified and applicable in various situations.An exception is wave motion in small scale with size effect.Therefore,based on surface/ interface effect theory,the influence of size effect on wave motion is finally investigated,including size dependent dispersion curves,wave mode shapes and energy. |
