During the last two decades, PT-based relaxor ferroelectric crystals such as (1−x)Pb(Zn 1/3 Nb 2/3 )O 3 -xPbTiO 3 (PZN-PT), (1−x)Pb(Mg 1/3 Nb 2/3 )O 3 -xPbTiO 3 (PMN-PT), and (1−x−y)Pb(In 1/2 Nb 1/2 )O 3 -yPb(Mg 1/3 Nb 2/3 )O 3 -xPbTiO 3 (PIN-PMN-PT or PIMNT) crystals, are widely studied due to their huge piezoelectric properties and super-high electro-mechanical coupling factors. They have excellent properties with compositions around the morphotropic phase boundary (MPB). It is gratifying that the PT-based relaxor crystals are replacing traditional PZT piezo-ceramics in many application fields. Most ferroelectrics with oxygen-octahedral structure, which show outstanding electro-mechanical properties, also have excellent optical performances. Ferroelectric single crystals with large electro-optic (EO) modulation are widely applied in laser communication devices. For the practical applications, the knowledge of detailed optical parameters is desirable. This paper tries to show a global review on the optical properties of PT-based relaxor ferroelectric crystals. In the present review, optical properties of the crystals are systematically summarized, including refractive index dispersion, transmittance, band gap, EO, acousto-optic, and photorefractive properties. These properties change with the crystal composition, orientation, and poling condition. The purpose of the review is to provide a resource for the researchers who are concerned with basic physical investigation or optical device applications of the PT-based relaxor ferroelectric crystals.
Chromium-doped CaMgSi2O6 (Cr[Formula: see text]: CMS) fluorescent ceramics with various concentrations were fabricated using solid-state reaction technique. All the samples were sintered at 1250[Formula: see text]C for 3 h. Analysis of microstructure of the Cr[Formula: see text]: CMS ceramics shows homogeneous structure with grain size distributions between 0.86 nm and 2.26 nm. Luminescent spectra of the ceramics show two emission peaks, a strong peak at 872 nm and a weak peak at 960 nm because of [Formula: see text] transition of the Cr[Formula: see text] ions. Intensity of the emission peaks increases with Cr[Formula: see text] concentration, reaches maximum with 0.1 at.% Cr[Formula: see text], then decreases with higher Cr[Formula: see text] concentration. Owing to the differences in crystal field strength, the luminescent properties of the Cr[Formula: see text]: CMS fluorescent ceramics and powder are quite different.
For low probability of intercept (LPI) radar waveform identication accuracy (ACC) problem at low Signal-to-Noise Ratios (SNRs), an approach based on time-frequency analysis (TFA) and Asymmetric Dilated Convolution Coordinate Attention Residual networks (ACDCA-ResNeXt) is proposed to recognize twelve kinds of LPI radar signals automatically. First, we apply Choi-Williams distribution (CWD), which shows superior performance at low SNRs, to transforming radar signals into time-frequency images (TFI). Then, in order to obtain the high-quality TFIs, a series of image processing techniques, including 2D Wiener ltering, image cutting, and image resize, are used to remove the background noise and redundant frequency bands of the TFI and obtain a xed-size gray scale image containing main morphological features of the TFI. Finally, the TFIs are input into ACDCA-ResNeXt network that can extract and learn deep features to recognize radar waveforms. Furthermore, a fusion loss function, which is composed of a soft-label smoothed cross entropy loss function and a center loss function, improves the generalization capability performance of network and achieves a better clustering eect. Experimental results demonstrate that, for twelve kinds of LPI radar waveforms, the overall recognition ACC of the proposed approach achieves 97.94% when SNR is -8 dB. INDEX TERMS Radar waveform recognition, time-frequency analysis (TFA), asymmetric convolution (AC), dilated convolution, coordinate attention (CA) mechanism.
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