Low-pass filter without the end effect for estimating transmission characteristics—Simultaneous attaining of the end effect problem and guarantee of the transmission characteristics

A Gaussian filter (GF) is the most commonly used low-pass filter of measuring surface roughness. However, undesirable distortions, called “end effects," occur near the end points of the data ends in GF. The transmission characteristics are one of the most important indicators that show the quality of a filter. Previously, it was only possible to obtain theoretical values for the transmission characteristics of filters whose weights were given by an explicit function. In recent years, it has also become possible to obtain the transmission characteristics of a filter whose weights are given by an implicit function. However, this method has a problem in that the values near the end points of the measurement data become significantly different from each other. The consequence is that end effects may occur in the filter outputs due to side effects of the periodic extension. In the case of a spline filter (SF) applied to open profiles, the transmission characteristics of a periodic SF with an end effect can be obtained uniquely. However, the transmission characteristics of a nonperiodic SF, which has no end effect, cannot be uniquely obtained. This results in a trade-off between the two states: end effects exist in a filter whose transmission characteristics can be obtained, and the transmission characteristics of a filter without end effects cannot be uniquely obtained. To address this problem, we propose a method for the GF processing that uses shearing, point symmetric extension, and periodic extension, and produces no end effect but allows the transmission characteristics to be obtained. Previously, there was a problem with the proposed method in that the rationale was unclear regarding how to determine the reference points for point symmetric extension. We resolved this and optimized the reference points. As a result, the proposed method was shown to be successful in not only resolving the end effects in the GF, but also obtaining the transmission characteristics.     

低通型阻抗匹配网络的计算机辅助设计

本文在推导阻抗匹配网络输入端反射系数极点解析式和分子多项式的基础上，编写了设计任意偶数阶具有Ｂｕｔｔｅｒｗｏｒｔｈ响应和Ｃｈｅｂｙｓｈｅｖ响应阻抗匹配网络的计算机程序，程序用Ｆｏｒｒａｎ语言编写，当输入匹配网络的阶数ｎ＝２ｍ和阻抗变换比ｒ＝Ｒ２／Ｒ１对Ｃｈｅｂｙｓｈｅｖ响应，通带容许的最大波纹αｄＢ，计算机程序输出匹配带宽和匹配网络归一化元件值。     

夏玉米可见/近红外光小波主成分提取与氮素含量神经网络检测

使用高光谱仪ASD Field Spec于吐丝期采集不同氮素处理的夏玉米叶片光谱,并进行对数变换处理;通过对"绿峰"(450～680nm)和"近红外反射平台"(760～1000nm)谱段光谱数据进行多尺度小波分解,获取第二层离散近似小波系数向量;采用主成分分析,从第二层离散近似小波系数向量中提取特征作为输入参数,建立对...     

颜色保真的遥感图像融合方法的研究

针对遥感图像融合Brovey变换法存在颜色失真的现象,提出了一种低通比值融合法,该融合法首先对高几何分辨率的全色波段进行低能滤波,尔后将低分辨率多光谱图像与全色波段图像相乘,再除以滤波后的全色波段图像,便得到融合图像。从辐照的角度证明了该低通比值融合法具备理论基础,并从目视评价、定量分析、分类精度证实了该低通比值融合法优于Brovey变换法,该低通比值融合法是一种能较好地保全低分辨率多光谱图像颜色的融合方法。     

无参考模糊图像质量评价改进算法

针对传统无参考模糊图像质量评价算法存在高计算复杂度的问题,通过改进经典的二次模糊处理算法,提出一种快速有效的无参考模糊图像质量评价方法。该算法基于人眼视觉系统(HVS)特性,利用局部方差选取人眼感兴趣图像块代替整体图像,并将感兴趣图像块通过低通滤波处理,构造模糊图像块,通过计算滤波前后图像块相邻像素差值变化大小获取原始整体图像的客观质量评价参数。仿真测试结果表明,该算法与传统整体图像二次模糊算法相比,皮尔逊相关系数提高0.01,与主观评价结果更为一致;运算速度提高一倍,降低了运算复杂度。     

利用Z_i及Z~'_i综合非等波纹低通滤波器

非等波纹低通滤波器具有较好的过渡带特性。它的衰减零极点很容易确定。本文提出利用输入阻抗及其导数进行综合的方法。这一方法不必运用零点移位技术,因而综合过程比较简单。     

一种新颖的自动频率控制系统

提出了一种新颖的基于低通滤波控制特性的AFC系统。用低通滤波器的过渡带代替传统的中频鉴频器的鉴频特性曲线,把由各种因素造成的发射机频率不稳的频率偏差转化为符号函数,结合DDS技术,形成一种新颖的具有宽频率跟踪范围的AFC系统。     

基于霍尔传感器的高压电流测量方法与实现

提出了一种利用霍尔传感器对电网电流进行非接触测量的方法 ,推导出了用霍尔传感器测量高压大电流的数学模型 ,在三相并行输电下 ,理论上推导出总磁场公式 ,并确定出检测方案。对传感器部分的电路结构进行了论证 ,利用单片机进行标度变换和数字显示。     

基于瞬时无功功率理论的改进型有源电力滤波器的数字化研究

介绍了一种基于瞬时无功功率理论的改进型谐波电流检测方法和电压补偿控制方法,设计了数字低通滤波器,并将此方法运用到有源电力滤波器数字化设计中,实现对电网谐波电流的检测和补偿。通过PowerSim软件对三相电源有源电力滤波器进行仿真,证明该设计具有良好的检测和补偿控制效果。     

任意阶无漂移全极点有源低通滤波器的原理与实现

本文提出了一种有源低通滤波器的无漂移基本节电路,并将它推广到任意阶无漂移全极点有源低通滤波器的实现,给出了一般的电路结构,系统的设计方法和工程实验结果。这种滤波器具有良好的低漂移,低元件灵敏度特性,具有实际的工程应用价值。