太赫兹二维成像技术研究进展

太赫兹成像技术在人体安检、无损探伤、质量监控、生物医学、半导体特性表征等许多领域展现出广泛的应用前景。本文综述了各类太赫兹二维成像技术,包括太赫兹扫描成像、太赫兹单像素成像、电光调制太赫兹成像、太赫兹相机直接成像等技术,综述各类成像技术的研究背景,分析了具体的成像方法和成像结果,总结了不同太赫兹成像技术的优缺点并对今后太赫兹成像技术的发展趋势做出展望。     

Contactless Transient THz Temperature Imaging by Thermo-transmittance Technique on Semi-transparent Materials

THz waves have shown to be effective for several applications, such as security, non-destructive testing, and water content monitoring for porous materials and food products. This study aims to highlight the use of THz radiation to measure temperature variations of thin insulating materials opaque in the visible or IR range (PVC, PTFE, PMMA, and wood) by using a spectral thermo-transmittance technique. THz wave optical transmittance in materials show high sensitivity to temperature variations. The goal of this paper is to demonstrate the transient temperature gradient dependence of THz transmitted signals inside materials to develop a new contactless method for measuring temperature of thin materials semi-transparent to THz radiation. The principle is based on synchronous detection, using an infrared camera coupled with a THz to infrared thermal converter (TTC) with modulated millimeter-scale waves (2.7 mm). The results show a correlation between the transient temperature and the optical transmittance coefficient. Several types of samples semi-transparent to THz radiation are tested, and the corresponding thermo-transmittance coefficients as reported for PVC, PTFE, PMMA, and wood are respectively 0.805, 0.395, 0.640, and 1.177 K^?1 m^?1.     

Camera for High-Speed THz Imaging

Journal of Infrared, Millimeter, and Terahertz Waves - We present a 24 × 24 pixel camera capable of high-speed THz imaging in power-detection mode. Each pixel of the sensor array consists of a...     

磺苄西林、舒他西林、美洛西林、替卡西林的太赫兹指纹谱

以一类常用的抗生素-青霉素类抗生素作为研究对象,选取4 种具有代表性的药品磺苄西林、舒他西林、美洛西林、替卡西林,基于太赫兹时域光谱（THz-TDS）技术,进行实验研究。通过光谱实验及理论分析,获取药品的太赫兹时域光谱,结合傅里叶变换,获得频域光谱及太赫兹吸收系数曲线。结果表明,4 种药品在0.40~1.60 THz 波段存在明显不同的吸收特征。因此,太赫兹光谱技术十分适合检测抗生素这种化学结构有微小不同的药品,并且可以清晰通过吸收峰的位置分辨出抗生素药类的种类。为国家食品药品监督管理提供一种新的可靠的检测技术,且可以以数据库的形式为药品的鉴定提供标准。     

Terahertz Transmission Imaging with 2.52 THz Continuous Wave

In this article, two terahertz transmission imaging systems are built with a 2.52 THz continuous wave laser and two types of sensors. One is array scanning system using a 124×124 pyro-electric array camera as the detector; the other is a point-wise scanning system utilizing a Golay cell as the detector. The imaging speed and quality is briefly analyzed. Terahertz （THz） imaging results demonstrate that the array scanning system has higher imaging speed with lower resolution. The point-wise scanning system has higher imaging quality with lower speed.     

Dynamically inserting, operating, and eliminating thermal sensors of FPGA-based systems

In this paper, a new thermal monitoring strategy suitable for field programmable logic array (FPGA)-based systems is developed. The main idea is that a fully digital temperature transducer can be dynamically inserted, operated, and eliminated from the circuit under test using run-time reconfiguration. A ring-oscillator together with its auxiliary blocks (basically counting and control stages) is first placed in the design. After the actual temperature of the die is captured, the value is read back via the FPGA configuration port. Then, the sensor is eliminated from the chip in order to release programmable resources and avoid self-heating. All the hardware of the sensor is written in Java, using the JBits API provided by the chip manufacturer. The main advantage of the technique is that the sensor is completely stand-alone, no I/O pads are required, and no permanent use of any FPGA element is done. Additionally, the sensor is small enough to arrange an array of them along the chip. Thus, FPGAs became a new tool for researchers interested in the thermal aspects of integrated circuits.     

基于红外阵列传感器的人体行为识别系统研究

随着人口老龄化的到来,为了避免发生意外事故,对老人日常活动行为进行识别和监测的安全监护系统的需求不断增长。传统的基于摄像头拍摄或者穿戴式传感器的活动状态监测系统存在着隐私保护和使用不方便等不足。为此,本文设计一种基于红外阵列传感器的人体行为识别系统。该系统通过检测环境中的温度分布和变化情况识别人体行为,不需要在老人身上佩戴任何设备,尺寸小易于安装,在黑暗环境中可正常工作,且由于采集到的是低分辨率信息,不会造成隐私泄露,对比传统方案具有明显优势。从采集到的温度分布信息中提取特征并采用K最近邻(K-Nearest Neighbor,KNN)算法实现了“走”、“坐”和“跌倒”3种状态的识别。实验结果表明平均准确率可达到95%,其中跌倒准确率为97.5%,行走准确率高达100%,坐下准确率为92.5%。     

微带线馈电的宽带单层贴片天线

微带贴片天线已广泛应用于雷达系统,文中介绍了一种新型背腔式单层微带贴片天线,辐射贴片采用微带线馈电,为增加工作带宽,提供了两种不同的贴片形状,第一种是E形贴片,仿真及测试结果表明,此种单元在驻波比优于2的条件下可实现45%的阻抗带宽,但该单元的波瓣带宽较窄。为抑制交叉极化,通过在E形贴片上开四个槽,得到了第二种改进的E形贴片。该单元可实现14%的频带内驻波比优于1.5,同时交叉极化优于-15dB。对C波段8×16单元实验小阵的测试结果表明,该天线在17.9%的频段内具有良好的交叉极化性能及较高的工作效率。     

太赫兹量子级联激光器及其光束表征技术

简要介绍太赫兹量子级联激光器(THz QCL)的工作原理及其进展。研究多个器件输出激光的光束质量,分别采用热探测器阵列和THz量子阱探测器(THz QWP)表征连续激射和脉冲激射THz QCL激光的光束图形,对比分析不同热探测器阵列对THz激光的表征能力,比较热探测器阵列和THz照相机对平行THz激光表征的差异。分析光束改善后THz激光光斑的尺寸、二维强度分布等特点,根据对THz QCL输出激光的改善效果,给出采用外部手段改善THz QCL激光光束的几种方法。研究表明,除了采用精细的波导工艺之外,锗(Ge)透镜、超半球高阻硅透镜和聚乙烯透镜都是外部改善技术中很好的手段。     

使用梯度折射率液晶微透镜阵列的光场成像

光场成像可以获取场景的三维信息。通过在主透镜和图像传感器之间插入一个微透镜阵列,不仅可以记录光线的辐射度,还记录了光线入射的方向。提出了使用梯度折射率液晶微透镜阵列进行光场成像的方法。该阵列基于向列相液晶材料,利用其各向异性和双折射的特点,通过紫外光刻技术和湿法刻蚀技术制作,具有圆孔阵列图案。在该阵列的上下电极之间加载一个交流电压信号后,每个微透镜可以有效会聚入射光,搭建了测试系统来测试该阵列的聚焦特性和焦距。将该阵列与一个主透镜和一片图像传感器耦合得到一个光场成像相机,并使用该相机采集了图像。     

基于几何相位超表面的高效独立双频点圆偏振太赫兹波束调控

为了克服超表面普遍具有的波长依赖性,提出了一种基于几何相位的多功能超薄超表面,在双频点处对透射圆偏振太赫兹波实现独立波前调控。该超表面单元由表层金属层和中间介质层组成,其中表层金属图案相同,均是由双C型开口环谐振器、中间金属圆环和长方形金属片谐振器构成。通过分别旋转表层金属谐振器,可以控制交叉偏振透射光具有相同的振幅和不同的相位。将单元结构按照特定的规律排列,可对入射波的波前实现任意调控,例如,在低频f₁=0.701 THz,分别实现了携带拓扑电荷数+1、+2、+3、+4的涡旋波束,其纯度均在60%以上;在高频f₂=1.663 THz,实现了对入射圆偏振波的汇聚,且焦距误差仅为0.04。仿真结果表明,设计的超表面在双频点处对电磁波具有良好的调控。     

A new photonic crystal fiber gas sensor based on evanescent wave in terahertz wave band: design and simulation

In this paper, we present the design of a new photonic crystal fiber （PCF） gas sensor for evanescent-field sensing in terahertz （THz） wave band. This sensor can be used to identify the gas, and its size is very large, so that it is beneficial to fill it with the test substance. Based on simulation, we demonstrate that the gas sensor using PCFs with four noncir- cular large holes in the cladding has high sensitivity and low loss, the confinement loss is less than 0.007 dB/m, and the bending loss is very small. The new PCF gas sensor can detect kinds of gases, for example, if test gas is water va- por, it has obvious absorption peaks in THz band, and the sensitivities of gas sensor are 64% and 73% at 1.097 THz and 0.752 THz, respectively. Due to the ultra-low loss and high sensitivity of the model, the novel steering-wheel structured fiber is very suitable for evanescent-field sensing and the detection of chemical and biological products.     

基于FPGA的大面阵CMOS相机高速率电子学系统设计

目前深空遥感探测多采用CCD作为高分辨率相机的传感器,相较于CCD,面阵CMOS驱动更简单、功耗更低、抗辐射能力更强,是深空遥感探测目前的发展趋势。为此,本文基于CMOSIS公司生产的型号为CMV20000,图像分辨率为5 120×3 840的CMOS探测器,设计完成了一个大面阵CMOS高分辨率相机,图像分辨率为5 120×3 840。详细阐述了以FPGA为核心的电子学系统的整体结构,结合CMV20000的工作模式和时序电路,实现了高分辨图像的高速传输以及数据校正。试验结果表明,设计的相机系统方案合理,解决了CMV20000数据无法对齐的数据校正问题,系统运行稳定可靠,安装光学系统后能够获取高质量图像。     

Is there a Biological Basis for Therapeutic Applications of Millimetre Waves and THz Waves?

Millimetre wave (MMW) and THz wave (THz) applications are already employed in certain industrial and medical environments for non-destructive quality control, and medical imaging, diagnosis, and therapy, respectively. The aim of the present study is to investigate if published experimental studies (in vivo and in vitro) provide evidence for “non-thermal” biological effects of MMW and THz. Such effects would occur in absence of tissue heating and associated damage and are the ones that can be exploited for therapeutic medical use. The investigated studies provide some evidence for both MMW and THz that can influence biological systems in a manner that is not obviously driven by tissue heating. However, the number of relevant studies is very limited which severely limits the drawing of any far-reaching conclusions. Furthermore, the studies have not addressed specific interaction mechanisms and do not provide hints for future mechanistic studies. Also, the studies do not indicate any specific importance regarding power density levels, frequencies, or exposure duration. It is also unclear if any specific biological endpoints are especially sensitive. Any therapeutic potential of MMW or THz has to be evaluated based on future high-quality studies dealing with physical, bio-physical, and biological aspects that have specific health-related perspectives in mind.     

太赫兹波段可调窄带滤波器

提出了一种基于FDTD模拟的亚波长阵列结构的太赫兹波段可调窄带滤波器,其结构尺寸由16μm至160μm可调,因此可以实现滤波频率在2.5THz～20THz大范围内的调节,最小带宽达到0.04THz,实现了非常好的窄带滤波效应.此外,这种人工复合结构还可以通过改变其与太赫兹偏振夹角的方式改变太赫兹波偏振态,同时实现窄带滤...     

0.2THz连续波近场扫描成像方法及实验研究

太赫兹(Terahertz-THz)电磁波是指频率在0.1THz～10THz(波长在30μm～3mm)之问的电磁波,它的独特性质使得它在许多领域具有重要的应用前景.本文简要地综合了THz信号的产生与检测方法以及THz成像技术的发展概况,基于固态电子学和准光学技术研究了一种0.2THz连续波成像方法,利用搭建的成像系统开展了典型目标的成像实验及其图像处理方法的研究.成像结果表明, 0.2THz电磁波对泡沫塑料、纸盒、皮革等非极性材料具有较好的穿透能力,系统的成像分辨率优于3mm.本文的研究成果在安检、生物医学成像、无损检测等方面具有广阔的应用前景,也为便携式THz成像系统的实现提供了可能.     

0.33 THz雷达三维近场成像系统设计及成像试验

提出了采用步进频率结合平面扫描的THz雷达近场成像系统设计方案,基于宽带全息成像原理,可以实现三维高分辨率近场成像。采用多通道收发探头阵列缩短机械扫描行程,提高成像速度。给出了基于快速傅里叶变换（Fast Fourier Transform,FFT）和Stolt插值的三维图像重建算法,成像理论分辨率与波长相当。利用THz矢量网络分析仪和辅助设备,搭建了0.215~0.33 THz成像试验装置,完成了对多层金属-泡沫目标三维成像,成像分辨率达到预期水平,验证了系统设计和三维图像重建算法的正确性。     

基于石墨烯的波束可重构太赫兹天线

设计了一种工作在太赫兹(THz)频率下的微带八木(QYU)天线.该天线由金属微带传输线、金属反射器、金属半圆形辐射贴片和三组单分子层-石墨烯-贴片导向器组成.由于石墨烯的电导率可电调谐特性,可以通过调整施加在石墨烯导向器上的偏置电压来动态调控天线的辐射方向.通过对天线的基本性能和可调特性系统地模拟和优化,数值结果表明,通过改变加在石墨烯导向器的偏压,天线的主辐射波瓣角φ(方位角)可以在30°-150°的范围内进行扫描,并且具有非常快的调制速度和非常低的回波损耗.该天线非常适合于相控阵雷达等THz波束可重构应用。     

Joint demosaicing and denoising.

The output image of a digital camera is subject to a severe degradation due to noise in the image sensor. This paper proposes a novel technique to combine demosaicing and denoising procedures systematically into a single operation by exploiting their obvious similarities. We first design a filter as if we are optimally estimating a pixel value from a noisy single-color (sensor) image. With additional constraints, we show that the same filter coefficients are appropriate for color filter array interpolation (demosaicing) given noisy sensor data. The proposed technique can combine many existing denoising algorithms with the demosaicing operation. In this paper, a total least squares denoising method is used to demonstrate the concept. The algorithm is tested on color images with pseudorandom noise and on raw sensor data from a real CMOS digital camera that we calibrated. The experimental results confirm that the proposed method suppresses noise (CMOS/CCD image sensor noise model) while effectively interpolating the missing pixel components, demonstrating a significant improvement in image quality when compared to treating demosaicing and denoising problems independently.     

中波红外固体激光器的指向监视系统

高重频3~5 m中波红外固体激光器由于其多方面的潜在应用而受到了广泛的重视,但由于其本身固体激光的特性,在传输过程中难免受到本身腔体温度梯度及外界环境振动的影响,而产生指向上较大的抖动和漂移,难以用于对指向精度要求较高的场合,需要在激光器出口处加入监视对准系统来抑制激光指向的抖动和漂移。因此,拟采用两种不同的探测器（四象限探测器和热释电探测器）作为此种激光器的监视对准元器件,对其在监视对准系统中的性能进行了对比试验分析。结果表明:两种监视系统得到的激光指向抖动的P-V值都在9左右,热释电探测器的指向监视误差为5.39。四象限探测器相比于热释电探测器具有更高的响应带宽,而热释电探测器由于基于图像的方法更加直观,因此,对于中波红外激光器而言,可以根据实际使用需要来选择相应的探测器以搭建指向监视系统。