Identification of biological tissue using chirped probe THz imaging

We consider the application of pulsed THz imaging systems in biomedical diagnostics and mail/packaging inspection. The sub-millimetre spectroscopic measurements obtained from T-ray systems contain a wealth of information about the sample under test. We demonstrate that different types of tissue can be classified based on their terahertz response measured with the chirped probe pulse technique. We demonstrate the performance of a quadratic classifier using linear filter models for feature extraction in the discrimination between different tissues.

Modern THz systems are hindered by the slow acquisition speed. The chirped probe pulse technique offers a significant improvement in this context. We present the terahertz responses of biological samples measured using a chirped probe pulse, and discuss the problem of data processing and extracting sample characteristics.     

小波阈值去噪的改进方法

利用小波方法去噪,是小波应用于工程实践一个重要的方面;本文指出了采用常见的阈值确定方法对含有较强高频分量的信号进行小波阈值去噪时,去噪效果与实时性存在着矛盾,不利于信号特征的提取。提出了一种新型的阈值确定方法,进一步提出了以小波去噪后特征频率分量的功率谱密度值的下降程度为依据的待定因子确定方法。以Mallat算法为例,对新型阈值确定方法进行了分析和比较,指出运用该方法进行小波去噪处理,增强了算法的实时性,同时信号拟关注的信息损失较小,去噪效果比较理想。交-交变频器输出电流的小波去噪实验结果表明,该方法行之有效。     

基于小波去噪的T-ray图像复原

针对实时THz脉冲（T-ray）成像系统所成图像分辨率低、受l/f相关噪声干扰严重的特点,提出一种新的基于小波去噪的T—ray图像复原算法。对T-ray图像进行离散小波变换后,先利用广义交叉确认估计出各个分辨率层的噪声闽值,然后对每个分辨率层的高频子带进行迭代去噪,最后对去噪后的T-ray图像采用Jasson-Van-Cittert算法进行复原处理以提高分辨率。实验结果表明,该方法在提高T-ray图像分辨率的同时,能显著地抑制THz成像系统的l/f相关噪声。创新之处在于以广义交叉确认作为T-ray图像中l/f噪声的估计方法,大幅度提高了图像信噪比（-5dB）,避免了噪声带来的复原算法中的不适定问题,达到较好的图像复原效果。     

太赫兹(THz)成像的进展概况

评述了太赫兹射线成像的进展情况.太赫兹(THz)辐射介于微波和红外之间.与微波、X射线、核磁共振(NMR)成像相比,太赫兹成像不仅能给出物体的密度信息,而且能给出频率域的信息,以及在光频、微波和X射线范围内所不能给出的材料的转动、振动信息.太赫兹射线与其他频段的电磁波相比,它能量低,不会造成对生物样品的电离损伤,而且太赫兹射线很容易穿过介电材料,因而可以用于产品的安全监测.因此太赫兹成像技术在生物学、工业安全监测等方面有可能带来新的关键性的突破.     

Material and process considerations for terahertz planar nanodevices

Using a two-dimensional ensemble Monte Carlo method, we have studied the capacitances in a planar nano-diode, called the self-switching device (SSD) that is based on an asymmetric nanochannel. We show that the terahertz (THz) response of the SSD can be affected by the dielectric constant and width of the insulating trenches that confine the nanochannel of the diode. The simulations reveal that the capacitive coupling over the insulating trenches has little influence on the device RF properties below 100 GHz, but significantly affects the device performance around and beyond 1 THz. We show that the capacitance is more sensitive to the dielectric constant of the substrate but is relatively less sensitive to the width of the insulating trench or the dielectric constant of the infill material in the insulating trenches. This differs significantly from a conventional capacitor with two parallel plates. The findings in this work provide useful implications in optimizing the material and lithography parameters of such and similar nanodevices for THz applications.     

小波阈值法在图像去噪中的应用

介绍了小波去噪的基本理论以及小波阈值法去噪的原理。小波阈值法去噪的关键是阈值的设置和阈值函数的选择。本文归纳了阈值的设置方法和阈值函数的选择方法,并针对图像去噪进行了仿真实验,将一幅混有不同水平高斯白噪声的图像分别进行软、硬阈值函数去噪。实验得出软阈值函数的去噪效果比硬阈值函数的去噪效果好这个结论。     

小波神经网络用于双模噪声的消噪

小波神经网络利用了小波变换的良好的时域和频域的分析能力以及神经网络的自学习能力,具有良好的容错能力和逼近能力。针对双模斯噪声,提出基于小波神经网络的双模噪声背景下信号的消噪算法,介绍了双模噪声的3种简化模型,阐述了小波神经网络的基本概念以及基于此方法的消噪算法。将小波神经网络用于此3种双模噪声背景下信号的消噪。实验结果表明,该方法能有效地消除已知信号中的双模噪声。     

Complex permittivity characterization of benzocyclobutene for terahertz applications

High-quality polymers such as the benzocyclobutene polymer (BCB) provide interesting dielectric feature for terahertz applications. Already used in silicon integrated circuit technologies, this material could become one of the most promising candidates for the realization of future THz waveguides and interconnections on a silicon substrate but also after active devices process on the top of any other technology (GaAs, InP, GaN…). A frequency-dependent complex permittivity of spin-coated thick layers of this low-k dielectric is obtained from transmittance spectra measured with Fourier transform spectroscopy in the frequency range of 0.5-5.4 THz. The dielectric constant and the loss tangent are discussed according to curing conditions of the photosensitive resin used. A low loss tangent value of 7 − 9 × 10^-3 at 1 THz is obtained with polymerisation in oxygen-free atmosphere. An incomplete curing and a high dose UV exposure have a weak impact on losses. These results associated with the high compatibility of this polymer with silicon and metals make BCB layers well suited for the design of microelectronic THz devices and circuits.     

双线圈感应测井信号反褶积处理方法

在对于双线圈感应测井信号处理的研究中,提出两种对于几何因子信号反褶积处理的方法。包括了最佳维纳滤波反褶积与窗函数滤波反褶积对于背景电导率信号还原的处理方法。其特点在通过仿真,比较两种处理方法的有效性和各自的优势,有利于对于测量信号还原真电导率的实际应用,提高测量分辨率,使测量数据处理结果比传统处理更有利于薄层解析。     

Image denoising and quality measurements by using filtering and wavelet based techniques

An image is often corrupted by noise in its acquisition and transmission by various kinds of noises. Image denoising using thresholding methods find appropriate values (threshold) which separates noise values to actual image values without affecting the significant features of the image. Wavelet transform represents image energy in compact form and representation helps in determining threshold between noisy features and important image feature. In this paper we have worked with denoising of salt–pepper and Gaussian noise. The work is organized in four steps as follows: (1) image is denoised by filtering method, (2) image is denoised by wavelet based techniques using thresholding, (3) hard thresholding and filtering method applied simultaneously on noisy image, (4) results of PSNR (peak signal to noise ratio) and MSE (mean square error) are calculated by comparing all cases.     

干涉型光纤传感信号去噪方法的研究

针对干涉型光纤传感信号的特点,采用数字滤波和小波去噪两种方法对干涉信号进行了消噪处理,并对去噪效果进行了比较和分析。结果表明,截止频率为4 kHz,阶次为3的Butterworth低通滤波器和Birge-Massart阈值小波去噪算法在干涉型光纤传感系统中有较好的使用价值。     

基于DSP和小波变换电能质量检测的研究

本文简要介绍了小波变换和多分辨率分析及其非线性信号消噪原理,并将该项技术应用于交交变频调速系统电能质量信号的消噪处理中,本文采用了一种在以数字信号处理器(DSP)为核心所构成的交交变频调速电能质量检测系统中对信号进行消噪的新设计方案.采用这种消噪方法,不但可以保留信号的突变特性,还可以大大降低对信号调理电路的设计要求,简化电路结构,严格保证原始信号之间的相位关系,适用于对实时性要求不高的信号检测系统.     

LMS与RLS算法仿真消噪对比研究

讨论了RLS（递归最小二乘）和LMS（最小均方）自适应滤波算法及原理,对两种算法进行了系统全面的分析,对比研究了各自的优势及不足,提出了两种算法在语音消噪仿真中的算法实现,对实际语音信号进行了仿真消噪,研究表明选用算法对语音消噪是明显有效的,RLS自适应消噪算法及LMS自适应噪声抵消算法具有很强的实际应用价值。     

小波变换在舰船辐射噪声消噪处理中的应用

针对舰船辐射噪声信号的特点，根据小波消噪的原理设计了一种消噪的方案，利用MATLAB在计算机上用不同的小波基函数对实船信号进行了消噪处理试验，井对结果进行了简要的比较说明。试验结果表明，在选择了适当的小波基函数和阚值的情况下，采用小波变换的消噪方法对舰船辐射噪声信号进行消噪处理。可以取得良好的效果。     

基于小波变换的图像阈值去噪分析

小波阈值去噪是小波域去噪的主要方法之一,该方法通过对合适阈值的选取,采用阈值函数对小波系数进行相应的非线性处理,获得基于均方差的最佳去噪效果。针对图像去噪,将图像分别进行软阈值、硬阈值、软硬折中法和模幂次法去噪,对各个阈值去噪效果进行了比较分析,得到相对有效的处理方法,为小波去噪方法的选择提供了参考。     

利用小波变换对表面肌电信号的消噪处理研究

上技做屈伸运动时,采集肱二头肌群的表面肌电信号,然后采用小波变换的方法,应用Matlab软件,对表面肌电信号进行去噪处理.对去噪结果的分析表明,对于小波分解后获得的不同频段的信号才用不同的阈值所获得的去噪效果更为理想,为后续的研究工作奠定了良好的基础.     

基于小波变换的磁定向信号去噪

磁定向信号中畸变噪声的存在严重地影响了磁定向系统的性能。在介绍了磁定向系统工作原理,分析磁定向系统中噪声的产生和特性的基础上,将小波变换的方法应用于磁定向系统去噪,提出用小波软阈值函数对磁定向信号进行去噪处理。首先分析了信号和噪声在小波变换下统计特性的不同点,基于统计特性上的差异,对小波变换后的小波系数进行软阈值函数处理,提取那些模极大值随尺度增大而减小的系数,并保留这些系数,同时滤除模极大值与尺度无关的系数,达到滤除信号中噪声的目的。仿真结果表明：该算法能很好滤除磁定向信号中存在的畸变噪声,使得磁定向信号稳定性得到增强,最终提高了磁定向系统的性能。     

Performance analysis of an open-loop resonator loaded terahertz microstrip antenna

In this paper, an enhanced electrical performance of the open-loop loaded microstrip patch antenna at terahertz frequency has been investigated. The proposed antenna is designed to radiate at frequencies in the range of 0.5-0.7 THz with high gain and radiation efficiency. The effect of various substrate parameters on the electrical performance of the proposed antenna has been analyzed and simulated. The simulation has been performed using the CST Microwave studio, a commercial simulator based on finite integral technique. The directivity and radiation efficiency of the proposed antenna is 22.58 dBi and 94.50%, respectively, at 600 GHz. Further, the simulated results have been compared with Ansoft HFSS, a commercially available simulator based on the finite element method. We have also compared this proposed analytical result with reported literature with scale down approach.     

基于B样条小波的偏微分方程图像去噪方法

提出一种基于B样条小波的偏微分方程图像去噪方法.先对图像进行B样条小波变换,将得到的高频系数采用偏微分方程方法去噪,迭代次数采用去相关最优停止准则进行控制;将得到的低频系数进行阈值处理,阈值选取采用基于信息熵的阈值选择策略,然后对处理后的小波系数进行B样条小波逆变换,得到去噪后的图像.数值实验表明,改进算法能克服B样条小波变换与偏微分方程去噪的不足,增强去噪能力,同时有效保护图像边缘和细节信息.     

基于平移不变的小波变换去噪快速算法

在介绍小波变换去噪理论的基础上,针对传统的小波变换去噪算法的缺陷,提出了一种基于平移不变的小波去噪快速算法.着重探讨平移不变小波去噪方法中平移量的选取对去噪效果以及计算复杂度的影响.仿真实验证明该算法能够在不影响去噪效果的前提下,较大程度降低计算复杂度.