The non-dispersive fundamental shear horizontal (SH) wave in plate-like structures is of practical importance in non-destructive testing (NDT) and structural health monitoring (SHM). Theoretically, an omnidirectional SH transducer phased array system can be used to inspect defects in a large plate in the similar manner to the phased array transducers used in medical B-scan ultrasonics. However, very few omnidirectional SH transducers have been proposed so far. In this work, an omnidirectional SH wave piezoelectric transducer (OSH-PT) was proposed, which consists of a ring array of twelve face-shear (d) trapezoidal PZT elements. Each PZT element can produce face-shear deformation under applied voltage, resulting in circumferential shear deformation in the OSH-PT and omnidirectional SH waves in the hosting plate. Both finite element simulations and experiments were conducted to examine the performance of the proposed OSH-PT. Experimental testing shows that the OSH-PT exhibits good omnidirectional properties, no matter it is used as a SH wave transmitter or a SH wave receiver. This work may greatly promote the applications of SH waves in NDT and SHM.

The widely used ferroelectric ceramics based actuators always suffer from small output strains (typically ~0.1-0.15%). Non-180° domain switching can generate large strain in ferroelectrics but it is usually irreversible. In this work, we tailored the domain structures in a soft lead titanate zirconate (PZT) ceramic by periodically orthogonal poling. The non-180° switching in this domain-engineered PZT ceramics turns to be reversible, resulting in giant electrostrains up to 0.57% under a field of 2kV/mm (dynamic d33 * (=S/E) of 2850pm/V). The large electrostrain keeps quite stable and even slightly increases after 10 4 cycles of loading, which is very promising for next-generation large-strain actuators.

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.

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The morphotropic phase boundary (MPB) plays an important role in ferroelectric materials. Typically, two phases coexist in materials near the MPB. Such materials usually exhibit large piezoelectricities, dielectricities, and actuation strains. In this work, we produce an MPB-like effect in hybrid electrically poled, mechanically depolarized (HEPMD) BaTiO3 and lead zirconate titanate ceramics where depolarized region A and vertical electrically poled region C intersect each other with a period of 400 μm in both in-plane directions. The polarization and strain of both HEPMD samples are over 3 times those of conventionally poled samples under unipolar electric loading. The large polarization and strain decrease steadily as the frequency increases and stabilize at approximately twice the values from the conventionally poled samples. Furthermore, the large polarizations and actuation strains of the HEPMD samples are fairly stable and change little after 30 000 cycles of operation. Under bipolar electric loading, the tendencies are similar and the coercive fields of the HEPMD samples are considerably smaller, which is similar to the MPB effect in traditional ferroelectric ceramics. Enhanced polarization and strain occur in HEPMD samples due to reversible ferroelectric domain switching during loading and unloading under large electric fields. In comparison, the small-signal properties, i.e., the d33 and dielectric properties, are slightly larger in HEPMD samples than in conventionally poled ones. The HEPMD method may be applied to all types of multiaxial ferroelectric ceramics to enhance actuation strain and polarization.

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In order to develop novel fast charge/discharge carbon anode materials, an organic hard carbon material (PTCDA-1100) is obtained by calcination of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) at high temperature of 1100 oC....

Lead titanate zirconate (PZT) ceramics based piezoelectric actuators always suffer from small output strains (typically 0.1%–0.15%) and have recently been criticized for the toxicity problem of the high-concentration lead. In our recent work (Li et al 2017 J. Appl. Phys. 122 074103), we realized large local actuation strain nearly 0.6% in a periodically orthogonal poled (POP) PZT ceramics via reversible domain switching. In this work, we applied the POP method to barium titanate (BT) ceramics and proposed a specially designed multilayer actuator which can output large uniform strain. The simple tetragonal structure of BT ceramics makes it easier to understand the mechanism of reversible domain switching in POP ceramics and its lead-free characteristic is more promising. Firstly, a POP BT ceramic piece was fabricated and the actuation testing results show that local large actuation strain of 0.36% can be obtained under a field of 2 kV mm−1 at 0.1 Hz. However, the actuation strain is non-uniform along the period direction, varying from 0.22% to 0.36%. Then, to output uniform large strain, a four-layer actuator based on the POP BT ceramics was designed and fabricated in which only the in-plane poled regions of the adjacent layers were bonded. Results show that the output strain turns to be uniform in this way, which is 0.34% under 2 kV mm−1, resulting in a very high large-signal (=Smax/Emax) of 1700 pm V−1. The large actuation strain is very stable and keeps unchanged after 20k cycles of operation. It drops quickly with the increasing frequency and is stabilized at 0.18% above 1.0 Hz. Finally, bipolar field testing was conducted on the POP BT based actuator. Results show that the actuator shows electrostriction-like symmetric bipolar actuation behavior with the repeatable actuation strain of 0.3% under 2 kV mm−1. This work may provide a feasible solution to low frequency, large-strain lead-free piezoelectric actuation.