The fundamental shear horizontal (SH0) wave in plate-like structures is of great importance in non-destructive testing (NDT) and structural health monitoring (SHM) as it is non-dispersive, while excitation or reception of SH0 waves using piezoelectrics is always a challenge. In this work, we firstly demonstrate via finite element simulations that face-shear piezoelectrics is superior to thickness-shear piezoelectrics in driving SH waves. Next, by using a newly defined face-shear d ₂₄ PZT wafer as an actuator and face-shear d ₃₆ PMN-PT wafers as sensors, pure SH0 wave was successfully excited in an aluminum plate from 130 to 180 kHz. Then, it was shown that the face-shear d ₂₄ PZT wafer could receive the SH0 wave only and filter the Lamb waves over a wide frequency range (120–230 kHz). The directionality of the excited SH0 wave was also investigated using face-shear d ₂₄ PZT wafers as both actuators and sensors. Results show that pure SH0 wave can be excited symmetrically along two orthogonal directions (0° and 90°) and the amplitude of the excited SH0 wave can keep over 90% of the maximum amplitude when the deviate angle is within 30°. This work could greatly promote the applications of SH0 wave in NDT and SHM.

The fundamental shear horizontal (SH0) wave in plate-like structures is extremely useful for non-destructive testing (NDT) and structural health monitoring (SHM) as it is non-dispersive. However, currently, the SH0 wave is usually excited by electromagnetic acoustic transducers (EMAT) whose energy conversion efficiency is fairly low. The face-shear (${\mathrm{d}}_{36}$ ) mode piezoelectrics is more promising for SH0 wave excitation, but this mode cannot appear in conventional piezoelectric ceramics. Recently, by modifying the symmetry of poled PbZr_1−xTi_xO₃ (PZT) ceramics via ferroelastic domain engineering, we realized the face-shear ${\mathrm{d}}_{36}$ mode in both soft and hard PZT ceramics. In this work, we further improved the face-shear properties of PZT-4 and PZT-5H ceramics via lateral compression under elevated temperature. It was found that when bonded on a 1 mm-thick aluminum plate, the ${\mathrm{d}}_{36}$ type PZT-4 exhibited better face-shear performance than PZT-5H. We then successfully excite SH0 wave in the aluminum plate using a face-shear PZT-4 square patch and receive the wave using a face-shear 0.72[Pb(Mg_1/3Nb_2/3)O₃]-0.28[PbTiO₃] (PMN-PT) patch. The frequency response and directionality of the excited SH0 wave were also investigated. The SH0 wave can be dominated over the Lamb waves (S0 and A0 waves) from 160 kHz to 280 kHz. The wave amplitude reaches its maxima along the two main directions (0° and 90°). The amplitude can keep over 80% of the maxima when the deviate angle is less than 30°, while it vanishes quickly at the 45° direction. The excited SH0 wave using piezoelectric ceramics could be very promising in the fields of NDT and SHM.

Excitation of single fundamental torsional wave T (0, 1) mode is of practical importance in inspecting or monitoring the structural integrity of pipelines, as T (0, 1) wave is the only non-dispersive mode in pipe-like structures. This work presents a piezoelectric ring array to excite and receive single T (0, 1) mode which is made up of a series of equally-spaced face-shear d24 PZT elements around the pipe. Firstly, we proposed that single T (0, 1) mode can be excited by the piezoelectric ring, when the number of d24 PZT elements is slightly greater than n , where F ( n , 2) is the highest circumferential order flexural torsional mode within the frequency bandwidth of the drive signal. Then this proposed principle was confirmed by finite element simulations. Later, experimental testing was conducted on a 100 mm outer diameter, 3 mm thick aluminum pipe. Results show that the ring of 24 face-shear d24 PZT elements can suppress all the non-axisymmetric flexural modes at the excitation frequency of 150 kHz so that single T (0, 1) mode is generated. Moreover, such a piezoelectric ring transducer can also filter flexural modes and receive the T (0, 1) mode only at 150 kHz. Note that here the highest circumferential order flexural torsional mode within the frequency bandwidth is F (20, 2), so the experimental results are in good agreement with the proposed principle. The presented ring of face-shear d24 PZT elements is very suitable for severing as the T (0, 1) wave transducer in structural health monitoring system, as it is cost-effective and no external load is required for operation.

The fundamental shear horizontal (SH ₀ ) wave in plates is of great importance in the field of nondestructive testing (NDT) and structural health monitoring (SHM) since it is the unique non-dispersive guided wave mode. For practical applications, a phased array system based on omnidirectional SH ₀ wave transducers is most useful as it can cover a wide range of a plate. However, so far very few omnidirectional SH wave transducers have been developed. In this work, we proposed an omnidirectional SH wave piezoelectric transducer (OSH-PT) based on a thickness poled piezoelectric ring. The ring is equally divided into twelve sectors and the electric field is circumferentially applied, resulting in a new thickness-shear (d ₁₅ ) mode. Finite element analysis shows that the proposed OSH-PT can excite single-mode SH ₀ wave and receive the SH ₀ wave only. Experiments were then conducted to examine the performance of the proposed OSH-PT. Results indicated that it can generate and receive single-mode SH ₀ wave in a wide frequency range with nearly uniform sensitivities along all directions. Considering its quite simple configuration, compact size and low cost, the proposed OSH-PT is expected to greatly promote the applications of SH waves in the field of NDT and SHM.