Even though ghost imaging (GI), an unconventional imaging method, has received increased attention by researchers during the last decades, imaging speed is still not satisfactory. Once the data-acquisition method and the system parameters are determined, only the processing method has the potential to accelerate image-processing significantly. However, both the basic correlation method and the compressed sensing algorithm, which are often used for ghost imaging, have their own problems. To overcome these challenges, a novel deep learning ghost imaging method is proposed in this paper. We modified the convolutional neural network that is commonly used in deep learning to fit the characteristics of ghost imaging. This modified network can be referred to as ghost imaging convolutional neural network. Our simulations and experiments confirm that, using this new method, a target image can be obtained faster and more accurate at low sampling rate compared with conventional GI method.

Relaxor-PbTiO₃ crystals possess ultrahigh piezoelectricity when compared with state-of-the-art Pb(Zr,Ti)O₃ ceramics. Recently, even higher piezoelectricity is observed in alternating current electric-field-poled (AC-poled) crystals. This poling technique may benefit many piezoelectric materials and corresponding applications. The scaling effect is quite important for piezoelectric applications, since the operational frequency of devices is associated with the dimension of piezoelectric elements. Here, we investigated the thickness dependence of dielectric and piezoelectric properties for AC-poled relaxor-PbTiO₃ crystals. Compared with the traditional poling method, the piezoelectric coefficient (d₃₃) and dielectric permittivity (ɛ^T₃₃/ɛ₀) were found to be increased by 20%-30% via alternating current electric field poling (AC-poling). A weak scaling effect was observed for the samples with thickness above 200 μm. While, for 100-μm samples, the dielectric permittivity was only enhanced by 6%, and a clear degradation of properties was observed when the cycle of alternating current electric field is beyond three. These features are thought to be associated with the impacts of surface damages for thin samples. Of particular interest is that the coercive field was found to decrease during AC-poling, which should be considered for the design of piezoelectric devices. This work provides important information for AC-poled relaxor-PbTiO₃ crystals and will benefit the piezoelectric applications using these crystals.

The low uniformity in properties of relaxor ferroelectric crystals is a long‐standing issue in the ferroelectric community, which limits the available volume of the entire crystal boule. The aim of this study is to develop a relaxor ferroelectric crystal with improved property uniformity and excellent piezoelectricity. To this end, Pb(In_1/2Nb_1/2)O₃–Pb(Mg_1/3Nb_2/3)O₃–PbTiO₃ is doped with Nd₂O₃ (Nd–PIN–PMN–PT) to improve the crystal performance. Along the crystal boule, the piezoelectric coefficient d₃₃ varies from 2800 to 3500 pC N⁻¹, and the dielectric constant ranges from 8400 to 9800, with variations of 25% and 16%, respectively. Such high property uniformity results in over 75% available volume of the crystal boule, compared to 30–50% for undoped crystals grown by Bridgman method. At the electric field of 1 kV cm⁻¹, the converse piezoelectric response is up to 4780 pm V⁻¹. In addition, its Curie temperature (T_C) and coercive field (E_C) are above 150 °C and 3 kV cm⁻¹, respectively. Compared with Pb(Mg_1/3Nb_2/3)O₃–PbTiO₃ crystal (d₃₃: 1500 pC N⁻¹, T_C: 135 °C, E_C: 2.3 kV cm⁻¹), the larger piezoelectricity, the higher T_C and E_C, and improved uniformity make Nd–PIN–PMN–PT crystals promising candidates for advanced piezoelectric applications.

Simultaneously generating various motion modes with high strains in piezoelectric devices is highly desired for high-technology fields to achieve multi-functionalities. However, traditional approach for designing multi-degrees-of-freedom systems is to bond together several multilayer piezoelectric stacks, which generally leads to cumbersome and complicated structures. Here, we proposed a transparent piezo metasurface to achieve various types of strains in a wide frequency range. As an example, we designed a ten-unit piezo metasurface, which can produce high strains (ε₃ = 0.76%), and generate linear motions along X-, Y- and Z-axis, rotary motions around X-, Y- and Z-axis as well as coupled modes. An adaptive lens based on the proposed piezo metasurface was demonstrated. It can realize a wide range of focal length (35.82 cm ~ ∞) and effective image stabilization with relatively large displacements (5.05 μm along Y-axis) and tilt angles (44.02′ around Y-axis). This research may benefit the miniaturization and integration of multi-degrees-of-freedom systems.