Three-Dimensional Scattering of an Incident Plane Shear Horizontal Guided Wave by a Partly through-Thickness Hole in a Plate

We investigate the three-dimensional （3D） scattering problem of an incident plane shear horizontal wave by a partly through-thickness hole in an isotropic plate, in which the Lamb wave modes are also included due to the mode conversions by the scattering obstacle in the 3D problem. An analytical model is presented such that the wave fields are expanded in all of propagating and evanescent SH modes and Lamb modes, and the scattered far-fields of three fundamental guided wave modes are analyzed numerically for different sizes of the holes and frequencies. The numerical results are verified by comparing with those obtained by using the approximate Poisson/Mindlin plate model for small hole radius and low frequency. It is also found that the scattering patterns are different from those of the SO wave incidence. Our work is useful for quantitative evaluation of the plate-like structure by ultrasonic guided waves.

The Frequency Selection of SH0 Waves for Total Transmission and Its Application in the Damage Detection of Aircrafts

Based on wave interference,a methodology to realize the total transmission phenomenon of SH0 waves is proposed in this paper.After a systematical theoretical investigation,an exact frequency of a flat plate consisting of another medium with finite length,is obtained,which is furthermore exemplified by the finite element method.This frequency is the same as the classical Fabry-Perot condition and dependent on the thickness of the material.It has been revealed that an SH0 wave,with its wavelength equal to twice of the length of another medium,can totally transmit across the medium without reflection.Especially when the impedance changes in a specific range,the energy of transmitted waves can keep in a high level,which is frequency-independent.Not limited by a flat plate,the Fabry-Perot condition is also suitable for a scraggy plate when the thickness variation is relatively small.Finally,using the transfer matrix method,the wave propagation in a plate with multiple layers is quantitatively investigated,and the frequency analysis for total transmission is carried out.The methodology,as well as the design scheme proposed,is achievable and artificially controllable,which opens a new prospect for the wave control and final applications in aeronautics and astronautics.

A unidirectional SH wave transducer based on phase-controlled antiparallel thickness-shear(d15)piezoelectric strips

In recent years,shear horizontal(SH)waves are being paid more and more attention to in structural health monitoring as it has only one displacement component.In this paper,a unidirectional SH wave transducer based on phase-controlled antiparallel thickness-shear(d15)piezoelectric strips(APS)is proposed.Here two pairs of identical APS were used each of which is a bidirectional SH wave transducer.By setting the interval between the two pairs of APS as 1/4 wavelength and the excitation delay between them as 1/4 period of the central operating frequency,unidirectional SH waves can be excited.Both finite element simulations and experiments were performed to validate the proposed design.Results show that SH0 waves were successfully excited only along one direction and those along the unwanted directions were suppressed very well.The proposed unidirectional SH wave transducer is very helpful to study the fundamentals and applications of SH waves.

Propagation behavior of SH waves in a piezomagnetic substrate with an orthorhombic piezoelectric layer

The dispersion behavior of the shear horizontal （SH） waves in the coupled structure consisting of a piezomagnetic substrate and an orthorhombic piezoelectric layer is investigated with different cut orientations. The surface of the piezoelectric layer is mechanically free, electrically shorted, or open, while the surface of the piezomagnetic substrate is mechanically free, magnetically open, or shorted. The dispersion relations are derived for four electromagnetic boundary conditions. The dispersion characteristics are graphically illustrated for the layered structure with the PMN-PT layer perfectly bonded on the CoFe2O4 substrate. The effects of the PMN-PT cut orientations, the electromagnetic boundary conditions, and the thickness ratio of the layer to the substrate on the dispersion behavior are analyzed and discussed in detail. The results show that, （i） the effect of the cut orientation on the dispersion curves is very obvious, （ii） the electrical boundary conditions of the PMN-PT layer dominate the propagation feature of the SH waves, and （iii） the thickness ratio has a significant effect on the phase velocity when the wave number is small. The results of the present paper can provide valuable theoretical references to the applications of piezoelectric/piezomagnectic structure in acoustic wave devices.

Surface wave transference in a piezoelectric cylinder coated with reinforced material

The present study deals with the propagation of a polarized shear horizontal(SH)wave in a pre-stressed piezoelectric cylinder circumscribed by a self-reinforced cylinder.The interface of the two media is assumed mechanically imperfect.For obtaining the dispersion relation,the mathematical formulation has been developed and solved by an analytical treatment.The effects of various parameters,i.e.,the thickness ratio,the imperfect interface,the initial stress,the reinforcement,and the piezoelectric and dielectric constants,on the dispersion curve are observed prominently.The dispersion curves for different modes have been also plotted.The consequences of the study may be used for achieving optimum efficiency of acoustic wave devices.

Beam-focused SH wave transducer based on YSr_(3)(PO_(4))_(3)piezoelectric crystal for high temperature structural health monitoring

Guided-wave-based structural health monitoring(SHM)technology is of great importance for real-time inspection of high-temperature structures.The fundamental shear horizontal(SH_(0))wave is believed to be an ideal wave mode for developing SHM systems due to its nondispersive characteristics.However,currently very limited SH_(0)wave transducers can be used for SHM of high-temperature structures due to the limitation of materials.Herein,a novel YSr_(3)(PO_(4))_(3)(YSP)piezoelectric crystal in the space group I43d was grown.Experiments show that the face-shear piezoelectric coefficient d_(14)(d_(14)=d_(25)=d_(36))is 9.7 pC/N and varies little from 25 to 800℃.Then a beam-focused SH_(0)wave piezoelectric transducer is developed based on face-shear-mode YSP wafers.Both finite element simulations and experimental results indicate that the YSP-based transducer can excite pure SH_(0)wave and focus the wave energy along two opposite main directions.Especially,the obtained SH_(0)wave beam is highly concentrated with a small divergence angle of less than 30°,originating from the high working frequency range from 300 to 400 kHz.The excellent temperature stability of the as-grown YSP crystal makes the proposed SH_(0)wave piezoelectric transducer very suitable for SHM of high-temperature structures.