基于声学脉冲响应的室内建图算法研究

由于室内环境下噪声及混响干扰造成声学脉冲响应(Acoustic Impulse Response,AIR)的波达时间(Time of Arrival,TOA)模糊,导致现有室内空间几何建图技术存在计算复杂等缺点,提出一种基于AIR可信度判断与霍夫变换结合的定位和建图一步完成的方法。该方法基于到达时间差(Time Difference of Arrival,TDOA)迭代估计声源位置并计算准确的TOA,随后基于声收发设备与一阶反射TOA关于反射面的椭圆约束关系,结合可信度判断与霍夫变换,筛选可信低阶TOA以实现室内反射面的二维位置估计。蒙特卡洛仿真结果表明,在混响时间T60为0.1347 s、AIR误差标准差为22.7×10^-3 ms、大小为10 m×8 m×4 m复杂室内环境下,墙面定位平均距离误差为10.1 cm,平均角度误差为2.7958°。在大小为5.26 m×3.5 m×3.35 m的真实房间中,该方法可以实现声源与墙体位置的同时定位,完成规则盒型房间的二维地图重构,且墙面定位平均距离误差为2.6 cm,平均角度误差为2.17°。     

Microwave dielectric properties of a low firing and temperature stable lithium magnesium tungstate (Li4MgWO6) ceramic with a rock-salt variant structure

The Li₄MgWO₆ ceramic was synthesized by the conventional solid-state reaction method, and its sintering behavior and microwave dielectric properties were studied for the first time. The XRD patterns and structural refinements indicated that Li₄MgWO₆ formed an orthorhombic phase at temperatures above 900 °C, and TEM analyses confirmed the ordered and layered rock-salt superstructures for the orthorhombic Li₄MgWO₆. The SEM photographs and relative density curve showed that the sample sintered at 950 °C had the highest densification. When sintered at 950 °C in a WO₃-rich atmosphere for 4 h, Li₄MgWO₆ had the following optimum properties: ε_r = 15.06±0.33, Q×f = 28,300±600 GHz (f = 10.1 GHz), and τ_f = 0.9±3.4 ppm/°C. Compared with other reported low permittivity compounds, Li₄MgWO₆ shows more potential for the Low-Temperature Cofired Ceramics (LTCC) substrate materials due to its intrinsic low sintering temperature, novel temperature stability, and relatively low dielectric loss.     

Plasma-assisted rapid sintering of nanotitania powders

In this work, Plasma-Assisted Rapid Sintering (PARS), a pulsed DC plasma system in a hollow cathode regime, is presented as a novel technology to sinter nanoceramics. Nano-TiO₂ powders are used as proof of concept and submitted to thermal treatment using several PARS conditions and sintering schedules. PARS heating process induced solely by the hollow cathode effect is consistent and affordable, providing a homogeneous temperature distribution to the compact. Furthermore, the heating rate and the maximum temperature are easily tunable by the discharge current applied in the plasma source and can go safely from room to maximum temperature in a matter of seconds with heating speed comparable with other reported rapid sintering techniques. Using 1-min of non-isothermal PARS cycles up to 1000 °C, porous nanostructured samples were obtained; reaching 80 % relative density while the grains remained at the nanoscale. Adding dwell times, the relative density was increased up to 96 % using a temperature plateau for up to 10 min, but the TiO₂ grains grow intensively when temperatures exceeded 1000 °C. The results indicate that the developed process is a promising new alternative technology for sintering nanoceramics.     

Modeling,analysis and suppression of current harmonics of Langevin-type ultrasonic motors under high voltage

For achieving high speed and large thrust, Langevin-type ultrasonic motors (LTUM) are generally operated under high voltage. However, high voltage causes the current harmonics of piezoelectric material nonlinear phenomena, which will decrease the efficiency, the output force, and the accuracy of LTUMs. In this study, the nonlinearity of current harmonics of LTUM are described and analyzed by a novel nonlinear equivalent circuit model using Lagrange equations. Thereafter, based on a nonlinear tuning method, a specific driver circuit is suggested to suppress the current harmonics. Experimental results validate that the time response of the current is consistent with that of the model and furtherly demonstrate that the total harmonic current distortion decreases by 68% utilizing the proposed nonlinear tuning method under 500 Vpp.     

改进ORB特征的机器人RGB-D SLAM算法

基于特征的视觉同时定位与地图构建（Simultaneous Localization and Mapping，SLAM）存在实时性和鲁棒性差等问题，提出一种改进的基于四叉树的ORB特征提取方法，设计包含前后端及地图构建的机器人RGB-D SLAM算法。在前端使用四叉树方法完成ORB特征的均匀提取，计算描述子间汉明距离实现特征匹配。根据随机采样一致性算法思想，结合EPNP（Efficient Perspective-N-Point）和迭代最近点法求解位姿，获取多次迭代后的准确位姿。采用关键帧进行回环检测，并且基于光速法平差优化位姿图，从而构建全局一致的3D地图，达到减少累积误差的目的。通过TUM数据集和多履带式全向移动机器人进行对比验证，实验结果满足实时性和稳定性要求，证明了算法的可行性和有效性。     

Thermally stable inverted organic light-emitting diodes using Ag-doped 4,7-diphenyl-1,10-phenanthroline as an electron injection layer

The thermal stability of organic functional materials affects the performance and lifetime of organic light-emitting diodes (OLEDs). We have developed a thermally stable inverted OLEDs (IOLEDs) by employing silver (Ag) doped into 4,7-diphenyl-1,10-phenanthroline (Bphen) as an n-type doped electron injection layer (EIL). We found that the formation of Ag complexes by coordination reaction could enhance the thermal stability and produce an asymmetric diffraction pattern based on an analysis of grazing incidence small angle X-ray scattering. Interestingly, with the annealing temperature increasing to 100 °C, the electrical properties of electron-only cells show differentiated phenomenon that the current density based on Ag dopant remains basically unchanged, which is opposite to Cs₂CO₃ dopant. In addition, at the high temperature of 100 °C, the IOLEDs with Cs₂CO₃ doped Bphen as an EIL was damaged completely, while the Ag dopant-based devices still maintained good photoelectrical characteristics. Finally, we have demonstrated that the optimized IOLEDs achieved a 40.3% enhancement in current efficiency compared to the conventional device. This work provides a new strategy to increase the thermal stability and performance for the application of IOLEDs operated under high temperature.     

Flexible and high-sensitivity piezoresistive sensor based on MXene composite with wrinkle structure

Due to the portability, good flexibility and excellent sensing performance, flexible piezoresistive sensors have received great attention in the field of transient electronic skin, intelligent robots and human-machine interaction. However, achieving both high sensitivity and wide sensing range by low-cost and large-scale method still remains a key challenge for developing high performance piezoresistive sensors. Here, a flexible and highly sensitive piezoresistive sensor was designed and realized by combining the 2D MXene material with wrinkle structure. The MXene composite based sensor with wrinkle structure was fabricated by spraying the active material onto the surface of a pre-stretched polyacrylate tape, which is facile, efficient and low-cost. The MXene composite based sensor demonstrates high sensitivity (148.26 kPa⁻¹), wide pressure range (up to 16 kPa), short response time (120 ms) and excellent durability (>13000 cycles). Moreover, benefiting from the extraordinary sensing performance and flexibility, the sensor can detect human physiological signals, monitor intelligent robot postures and map spatial pressure distributions, thus exhibiting great potential in physiological analysis systems, humanoid robotics and biomedical prostheses.     

Microwave dielectric properties of Li3A3Te2O12 (A = Y,Yb) garnets for low temperature cofired ceramic technologies

Te⁶⁺-containing microwave dielectric ceramics Li₃A₃Te₂O₁₂ (A = Y, Yb) with low firing temperatures were prepared using the solid-state reaction method. Li₃Y₃Te₂O₁₂ and Li₃Yb₃Te₂O₁₂ can be obtained as garnet single-phase ceramics with low sintering temperatures of 940 ℃ and 950 ℃, respectively. The cations, such as Li⁺, Te⁶⁺, and Y³⁺/Yb³⁺, fully occupied the tetrahedral, octahedral, and dodecahedral sites of garnet structure, respectively. Li₃A₃Te₂O₁₂ (A = Y, Yb) ceramics exhibit ε_r ～ 7.83 ± 0.2 and 5.94 ± 0.2, Q × f ～ 47,800 ± 500 GHz and 41,800 ± 500 GHz, and τ_f ～ –47 ± 3.0 ppm/°C and –76 ± 3.0 ppm/°C, respectively. The full width at half-maximum (FWHM) values of the A_1g Raman mode correlate negatively with the Q × f values. Moreover, Li₃A₃Te₂O₁₂(A = Y, Yb) ceramics possess good chemical compatibility with the Ag electrode, making them promising candidates for low-temperature cofired ceramics (LTCC) technologies.