基于超材料的太赫兹角度滤波器研究

提出了一种基于超材料的太赫兹低通角度滤波器,该角度滤波器是一种仅允许法向入射太赫兹波透过而将其他方向传播太赫兹波滤除的器件,其结构为螺旋的左右对称开口的金属双环。仿真结果表明,在0.94 THz频率处,该器件的透射效果随着入射角的增大明显降低,且对法向入射的透射率达到94.4%,3 dB角域带宽达到25.0°。所提出的太赫兹角度滤波器在角度波谱分析、雷达数据处理、隐私保护、高信噪比检测器等领域具有重要的应用前景。

纳米金属薄膜同时实现多通道频率和角度滤波

为了研究纳米金属银薄膜和空气构成的周期结构的光学传输特性,采用周期结构的Bloch原理和传输矩阵法研究了光波在其中的传输特性。由分析可知,对特定的入射角度,有多个分离的频道可以让光波传播;对特定的光波频率,有多个入射方向让光透射。通过改变空气层的厚度,频道位置和角谱位置可以根据需要进行调节。银层在研究的光谱范围内的损耗对传输的透射率产生影响,但不改变滤波通道的位置。通过设计合适的厚度,这种影响可以得到有效的降低。结果表明,可以将该结构设计成多通道频率滤波器和多通道角度滤波器。

相干频率分集阵雷达匹配滤波器设计

相干波形频率分集阵(frequency diverse array,FDA)雷达通过引入阵元间的频率差异,在观测空间中形成距离-角度-时间依赖的发射方向图。针对相干FDA雷达体制回波接收处理的问题,提出了角度-时间二维匹配滤波器,同时实现了快时间波形匹配和等效发射波束形成,不同于传统匹配滤波器。并进一步考虑某些应用情况下,通过设计匹配时间窗,提出了分段匹配的二维匹配滤波接收处理方法。将雷达脉冲时间划分为多个子脉冲接收时间窗,并采用发射方向图调制的角度-时间二维匹配滤波函数对回波信号进行相干积累。仿真实验给出了所提接收处理方法的性能验证。

Visual navigation in orchard based on multiple images at different shooting angles

The orchards usually have rough terrain,dense tree canopy and weeds.It is hard to use GNSS for autonomous navigation in orchard due to signal occlusion,multipath effect,and radio frequency interference.To achieve autonomous navigation in orchard,a visual navigation method based on multiple images at different shooting angles is proposed in this paper.A dynamic image capturing device is designed for camera installation and multiple images can be shot at different angles.Firstly,the obtained orchard images are classified into sky and soil detection stage.Each image is transformed to HSV space and initially segmented into sky,canopy and soil regions by median filtering and morphological processing.Secondly,the sky and soil regions are extracted by the maximum connected region algorithm,and the region edges are detected and filtered by the Canny operator.Thirdly,the navigation line in the current frame is extracted by fitting the region coordinate points.Then the dynamic weighted filtering algorithm is used to extract the navigation line for the soil and sky detection stage,respectively,and the navigation line for the sky detection stage is mirrored to the soil region.Finally,the Kalman filter algorithm is used to fuse and extract the final navigation path.The test results on 200 images show that the accuracy of visual navigation path fitting is 95.5%,and single frame image processing costs 60 ms,which meets the real-time and robustness requirements of navigation.The visual navigation experiments in Camellia oleifera orchard show that when the driving speed is 0.6 m/s,the maximum tracking offset of visual navigation in weed-free and weedy environments is 0.14 m and 0.24 m,respectively,and the RMSE is 30 mm and 55 mm,respectively.

Cross-sensitivity of Fiber Grating Solved by FFP Triangle Notch Filter

Employing a fiber Fabry-Perot (FFP) interferometer has been considered as a triangle notch filter to demodulate the wavelength of fiber Bragg grating (FBG) sensor.The single parameter of strain has been demodulated,and the cross-sensitivity influence of temperature has been eliminated.The principle of this method is simple and easy to be implemented,and has been used to design a 30 t fiber grating weightbridge successfully.The maximal temperature drift error of the weightbridge is 4 με,which means that the full scale error is 8‰. The result reveals that the accuracy is high enough to be used in measurement.

A novel estimation algorithm for torpedo tracking in undersea environment

A novel estimation algorithm is introduced to handle the popular undersea problem called torpedo tracking with angle-only measurements with a better approach compared to the existing filters. The new algorithm produces a better estimate from the outputs produced by the traditional nonlinear approaches with the assistance of simple noise minimizers like maximum likelihood filter or any other algorithm which belongs to their family. The introduced method is extended to the higher version in two ways. The first approach extracts a better estimate and covariance by enhancing the count of the intermediate filters, while the second approach accepts more inputs so as to attain improved performance without enhancement of the intermediate filter count. The ideal choice of the placement of towed array sensors to improve the performance of the proposed method further is suggested as the one where the line of sight and the towed array are perpendicular. The results could get even better by moving the ownship in the direction of reducing range. All the results are verified in the MATLAB environment.

Simple Adaptive Filtering Scheme to Improve Measurement Accuracy of Gyroscope on Angular Motion Base

The objective of this work is to improve the measurement accuracy of a gyroscope on a angular motion base with a simple adaptive filter scheme.Two main topics are highlighted in this work.The first topic is to show building a dual-process model employed for the conventional Kalman filter.The second topic is to show developing a modified noise adaptive algorithm when measurement noise and process noise are unknown.The experimental results are presented to show that the simple adaptive filtering scheme outperforms the other conventional scheme in this paper in terms of noise reduction.