Analysis of propagation characteristics of Rayleigh surface acoustic waves on Yb0.33Al0.67N piezoelectric films/high-velocity substrates

Piezoelectricity of YbAlN films has recently been shown to be almost as high as that of ScAlN films. YbAlN film surface acoustic wave (SAW) resonators are expected to have a high coupling factor. We theoretically investigated the propagation characteristics of first-mode Rayleigh SAWs (RSAWs) on Yb0.33Al0.67N film/high-velocity Si, sapphire, AlN, SiC, BN, and diamond substrates. The first-mode RSAWs on the YbAlN layered structures had high coupling factors, higher than those on ScAlN layered structures. An enhancement of the effective coupling factor of the first mode RSAWs was observed in polarity inverted YbAlN film/BN or diamond substrate structures.

Improved Calculation Method of Coupling Factors for Low-Frequency Wireless Power Transfer Systems

The concept of a coupling factor was introduced in International Electrotechnical Commission (IEC) 62311 and 62233 to provide a product safety assessment that considers the localized exposure when an electromagnetic field (EMF) source is close to the human body. To calculate the coupling factors between the human body and EMF source, a numerical calculation should be carried out to calculate the internal quantities of the human body models. However, at frequencies below 10 MHz, the computed current density or internal electric field has computational artifacts from segmentation or discretization errors. Specifically, coupling factors are calculated based on the maximum values, which may include computational artifacts due to abnormal peaks. In this study, we propose an improved calculation method to remove computational artifacts by applying the 99.99th percentile in calculating the coupling factors without underestimation. The performance of the proposed method is verified through a comparison based on various human body models with wireless power transfer (WPT) systems and compliance with the reference levels and basic restrictions. The results indicate that the proposed method can provide uniform coupling factors by reducing the computational errors by up to 65.3% compared to a conventional method.

Nonlinear dynamic analysis of gear system in shearer cutting section under wear failure

Gear wear failure is one of the important failures of the gear system in the shearer cutting section. To reveal the influence mechanism of shearer cutting gear wear on the system dynamic characteristics, considering coupling factors such as time-varying meshing stiffness, dynamic gear clearance, internal error excitation, end load constraint and bearing radial clearance under wear failure, an improved dynamic model of shearer drive gear system is introduced to present an in-depth investigation of uniform wear of gear teeth effect. The dynamic meshing stiffness of gears under different degrees of wear is analysed. Furthermore, the bifurcation diagram is utilized to observe the motion state of the system experiencing different excitation frequencies, support damping as well as terminal loads. It is demonstrated that the gear surface wear could bring a change in gear dynamic transmission error, vibration impact state and amplitude, which is mainly manifested in increasing the unstable area and the vibration amplitude of the gear system, providing a method for monitoring and diagnosing of gear surface faults.

Recent progress on AC poling of relaxor-PbTiO3 ferroelectric single crystals (Review)

Compared with conventional DC poling (DCP) treatment, a novel technology, AC poling (ACP) treatment was proved in 2014 as a low-cost, time-saving, and smart-process method to significantly enhance properties of relaxor-PbTiO3 (PT) ferroelectric single crystal (SC) transducers. In total, over 35 papers have been reported since 2018 in which researchers achieved piezoelectric coefficient (d 33) > 4000 pC/N and electromechanical coupling factors (k 33) > 96% for the ACP SCs. In this review, we introduce history of the ACP study on relaxor-PT SCs and our research group's ACP study in the past three years. Particularly, we focus on ACP conditions and their mechanisms of binary (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT) and ternary (1-x-y)Pb(In1/2Nb1/2)O3-yPb(Mg1/3Nb2/3)O3-xPbTiO3 (PIN-PMN-PT) SCs near morphotropic phase boundary (MPB). Furthermore, we provide insights for further studies on optimal ACP conditions and the reduction of spurious-mode vibrations (SMV). This work can offer promising prospect and practical value in the high-end ultrasonic imaging probe transducers

Investigation of Electro-Elastic Properties for LN Single Crystals at Low Temperature

Lithium niobate crystals (LiNbO3, LN) are multifunctional crystal materials with many outstanding properties. In this work, the electro-elastic properties of LN single crystals were explored at temperatures from −150 °C to 150 °C. The temperature dependences of dielectric permittivities, elastic compliances, electromechanical coupling factors and piezoelectric coefficients were determined using the impedance method. The LN crystals possessed large dielectric permittivities, the ε11T/ε0 and ε33T/ε0 were 83.2 and 29.4 at room temperature, respectively. The elastic compliances s11, s13, s33 and s44 presented a positive increase as the temperature increased, and the variations were 5.0%, 8.2%, 4.6% and 5.4%, respectively, showing a good temperature stability. Moreover, the temperature dependence of the electromechanical coupling factors and piezoelectric coefficients for different vibration modes were studied with a temperature range from −150 °C to 150 °C, where the thickness shear vibration mode d15 presented a large piezoelectric response and minimal temperature variation.