BWO连续太赫兹波成像检测

返波管（BWO）连续太赫兹波成像方法是一种新的无损检测方法。实验过程中把样品放在X-Z二维电控平移台上进行扫描成像,透过样品的太赫兹波强度信息由热释电探测器接收,再经由电脑成像。该文给出了应用0.71 THz的连续太赫兹波对打孔铝板、公交卡、校园卡的内部结构和对隐藏在信封内硬币等物体和信封内纸片上的铅字迹的成像实验研究事例,并且测知该系统能够分辨出最小直径为1.5 mm的小孔。并且对成像图像进行了数字图像处理,结论表明,优化处理后的图像更加直观明显,提高了连续波成像的应用能力。揭示了BWO连续太赫兹波成像系统在无损检测和安检领域是实际有效的。     

太赫兹波谱与成像

主要介绍太赫兹技术的两大基本应用领域:波谱技术与成像技术。总结了太赫兹波谱学中的时域光谱技术、时间分辨光谱技术和发射光谱技术以及相关的参数提取原理。介绍了太赫兹成像原理及相关的时域扫描成像、实时成像、层析成像、连续波成像和近场成像等太赫兹成像技术。列举了太赫兹光谱和成像技术在国家安全、生物研究、材料研究、无损检测等方面的应用。     

超宽带太赫兹调频连续波成像技术

太赫兹调频连续波成像技术具有高功率、小型化、低成本、三维成像等特点,在太赫兹无损检测领域受到了广泛关注。然而由于微波及太赫兹器件限制,太赫兹信号带宽难以做大,从而制约了成像的距离向分辨力。虽然高载频可实现较大宽带,但伴随的低穿透性和低功率会限制太赫兹调频连续波成像系统的应用场景。因此,聚焦于太赫兹波无损检测领域,提出一种时分频分复用的114~500 GHz超宽带太赫兹信号的产生方式,基于多频段共孔径准光设计,实现超带宽信号的共孔径,频率可扩展至1.1 THz。提出一种频段融合算法,实现了超宽带信号的有效融合,距离分辨力提升至460 μm,通过人工设计的多层复合材料验证了系统及算法的有效性,并得到封装集成电路(IC)芯片的高分辨三维成像结果。     

太赫兹成像检测算法研究

由于太赫兹波所处波段位置特殊性以及现阶段太赫兹成像系统性能的限制等,太赫兹波成像质量低,无法满足可视化效果,限制了其发展和应用。结合太赫兹图像模糊特征和灰度信息提出利用灰度特征对太赫兹图像进行图像分割来提高太赫兹图像质量,抑制太赫兹图像背景噪声,保留太赫兹图像目标重要信息,实现太赫兹成像目标检测。实验结果与其他太赫兹图像处理方法结果对比表明,基于灰度特征的图像处理算法可以提高图像清晰度和对比度,实现精确分割,为太赫兹成像在安全检查和医学成像等应用中实现快速检测和提取目标奠定基础。     

采用CMOS太赫兹波探测器的成像系统

太赫兹波成像技术在生物医疗和安全检测等领域具有广阔的应用前景。针对新一代信息技术对便携式太赫兹波成像设备的需求，设计了基于CMOS太赫兹波探测器的成像系统。该系统包括一款CMOS太赫兹波探测器、片外模数转换器（ADC）、FPGA数字信号处理器、二位步进机、四个抛物面镜和太赫兹波辐射源等。CMOS太赫兹波探测器集成了片上贴片天线以及作为检波元件的NMOS晶体管，探测器由180 nm标准CMOS工艺制成。太赫兹波探测器的输出被片外模数转换器（ADC）采集并转换为数字信号，该数字信号被FPGA采集并传输到电脑上成像。所有上述元件均被装备在印刷线路板（PCB）上以减小系统体积。该系统实现了透射式太赫兹波扫描成像而无需斩波-锁相技术，并给出在860 GHz的太赫兹波照射下隐藏在信封内部金属的成像结果。     

太赫兹波谱与成像技术

太赫兹波谱与成像是太赫兹科学与技术的重要内容,在生物、物理、化学、安检、航空航天等领域有重要的应用前景,是近年来的研究热点。首先简单介绍了太赫兹时域光谱、时间分辨光谱和超连续谱等波谱技术,并列举了相关波谱技术对爆炸物识别和对半导体材料超快载流子动力学的研究结果。讨论了时域扫描成像、实时焦平面成像、连续波成像和被动成像等太赫兹成像技术。相应地分别给出了利用上述技术对葵花籽、玩具手枪、航天泡沫和人体的成像研究结果。     

双通道太赫兹成像雷达研究

介绍了一种具有双接收通道的太赫兹成像雷达,雷达工作频率为216 GHz,系统设计中,采用直接数字式频率合成器以及频率综合等方式,产生具有800 MHz 带宽的Ku 波段线性调频连续波信号,功分后分别与两个点频信号进行混频,产生36 GHz依400 MHz 的射频信号以及35. 95 GHz依400 MHz 的本振信号,分别驱动太赫兹发射机和接收机。本振信号功分两路,送入两个接收机,接收采用去斜接收体制,从而降低数据率。该雷达采用了6 倍频太赫兹发射模块,最终产生系统带宽为4. 8 GHz,从而获得3 cm 的距离分辨率。文中还重点研究了宽带系统标校,并开展了高分辨逆合成孔径成像实验,为后续太赫兹干涉合成孔径成像雷达研究奠定基础。     

太赫兹成像技术在站开式安检中的应用

在日益严峻的公共安全形势下,太赫兹技术的飞速发展为反恐安检提供了一项新的有效手段。分析了太赫兹波的特点及其在成像安检中应用的潜在优势,探讨了太赫兹成像安检的主要技术手段,比较了主动式和被动式成像的优劣,并总结介绍了用于安检的太赫兹被动成像和主动成像技术的国内外发展现状,通过对国际主要太赫兹安检成像研究机构的研究历程和近期项目支撑情况的分析,对太赫兹成像安检技术阵列化、多频段、复合式的发展趋势进行了预测,并对太赫兹成像技术在安检和反恐中的应用前景进行了展望。     

太赫兹近场成像技术及进展

太赫兹(THz)波具有能量低、穿透性强、频带宽等特点,因而太赫兹成像技术在无损检测、生物医药、安全检测等众多领域得到了广泛应用,在实际应用中如何提高太赫兹成像的分辨力变得越来越重要。由于太赫兹近场成像技术可突破衍射极限,获得分辨力为亚微米甚至是纳米量级的高质量图像,基于近场技术的高分辨THz成像技术相继被提出,并得到了进一步的应用。本文首先阐述了太赫兹近场成像的基本原理;其次总结了近场成像进展及增强方法;最后对太赫兹近场成像的未来进行了展望。     

150 μW小型化超短脉冲太赫兹辐射源

超短脉冲太赫兹(THz)辐射源在太赫兹波技术领域一直占有重要地位.随着太赫兹波技术在物理、化学、生物医学、成像、传感以及毒品检测等众多科研和技术领域应用的深入,对高效、高功率、小型化超短脉冲太赫兹辐射源的研究已逐步成为研究热点.     

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.     

Terahertz Wide-Angle Imaging and Analysis on Plane-wave Criteria Based on Inverse Synthetic Aperture Techniques

This paper presents two parts of work around terahertz imaging applications. The first part aims at solving the problems occurred with the increasing of the rotation angle. To compensate for the nonlinearity of terahertz radar systems, a calibration signal acquired from a bright target is always used. Generally, this compensation inserts an extra linear phase term in the intermediate frequency (IF) echo signal which is not expected in large-rotation angle imaging applications. We carried out a detailed theoretical analysis on this problem, and a minimum entropy criterion was employed to estimate and compensate for the linear-phase errors. In the second part, the effects of spherical wave on terahertz inverse synthetic aperture imaging are analyzed. Analytic criteria of plane-wave approximation were derived in the cases of different rotation angles. Experimental results of corner reflectors and an aircraft model based on a 330-GHz linear frequency-modulated continuous wave (LFMCW) radar system validated the necessity and effectiveness of the proposed compensation. By comparing the experimental images obtained under plane-wave assumption and spherical-wave correction, it also showed to be highly consistent with the analytic criteria we derived.     

All-Optoelectronic Terahertz Imaging Systems and Examples of Their Application

We give an overview over several all-optoelectronic measurement systems which we have developed for transmittive and reflective imaging in the terahertz (THz) frequency range. The systems employ either pulsed or continuous-wave THz radiation. In both cases, they work on the basis of single-pixel scanning. Addressing the potential for imaging in the medical and dental field, and the application of THz radiation for industrial surface and interface characterization, we explore dark-field imaging where the imaging contrast originates from diffraction and scattering effects coming from topography or refractive-index variations.     

At the Dawn of a New Era in Terahertz Technology

The National Institute of Information and Communications Technology (NICT, Japan) started the Terahertz Project in April 2006. Its fundamental purpose in the next five years is to enable a nationwide technical infrastructure to be created for diverse applications of terahertz technology. The technical infrastructure includes the development of semiconductor devices such as terahertz quantum cascade lasers, terahertz-range quantum well photodetectors, and high-precision tunable continuous wave sources. It also includes pulsed terahertz measurement systems, modeling and measurement of atmospheric propagation, and the establishment of a framework to construct a materials database in the terahertz range including standardization of the measurement protocol. These are common technical infrastructure even in any terahertz systems. In this article, we report the current status of developments in these fields such as terahertz quantum cascade lasers (THz-QCLs) (with peak power of 30 mW, 3.1 THz), terahertz-range quantum well photodetectors (THz-QWPs) (tuned at 3 THz) an ultrawideband terahertz time domain spectroscopy (THz-TDS) system (with measurement range of from 0.1 to 15 THz), an example of a database for materials of fine art, and results obtained from measuring atmospheric propagation.     

太赫兹光场成像的实验与处理研究

太赫兹波的频率介于红外线与微波之间,其独特优势使得太赫兹三维成像已成为国内外的研究热点。为了将光场成像技术拓展到太赫兹波段,介绍了太赫兹光场成像的实验与处理方法。采用太赫兹相机阵列采集到了一系列特定视角的太赫兹光场数据。针对由成像系统的器件限制导致图像存在较强噪点等问题,通过离散余弦变换（Discrete Cosine Transform, DCT）滤波达到了较好的去噪效果并有效保留了图像的细节信息。利用峰值信噪比（Peak Signal-to-NoiseRatio, PSNR）和结构相似性（Structural SIMilarity, SSIM）图像质量评价指标对比了多种滤波去噪方法,证明了DCT滤波方法对于太赫兹图像预处理的可行性。通过选取不同深度值得到了不同景深处的图像重构结果,初步实现了太赫兹光场成像的数字重聚焦。     

Terahertz Imaging System for Medical Applications and Related High Efficiency Terahertz Devices

A terahertz (THz) imaging system and high efficient terahertz sources and detectors for medical applications were developed. A fiber laser based compact time domain terahertz tomography system was developed with a high depth resolution of less than 20 μm. Three-dimensional images of porcine skin were obtained including some physical properties such as applied skin creams. The discrimination between healthy human tissue and tumor tissue has been achieved using reflection spectra. To improve the THz imaging system, a ridge waveguide LiNbO₃ based nonlinear terahertz generator was studied to achieve high output power. A ridge waveguide with 5-7 μm width was designed for high efficiency emission from the LiNbO₃ crystal by the electro-optic Cherenkov effect. Terahertz electronic sources and detectors were also realized for future imaging systems. As electronic source devices, resonant tunneling diode (RTD) oscillators with a patch antenna were fabricated using an InGaAs/InAlAs/AlAs triple barrier structure. On the other side, Schottky barrier diode (SBD) detectors with a log-periodic antenna were fabricated by thin-film technology on a Si substrate. Both devices operate above 1 THz at room temperature. This electronic THz device set could provide a future high performance imaging system.     

隔热板的太赫兹无损检测

为了研究太赫兹无损检测技术对复合材料与金属板黏合面粘接质量的检测能力,在隔热板上制造了不同特征的人工缺陷,并使用德国SynViewScan 300连续太赫兹波成像系统对样件进行了检测。结果表明,太赫兹波能够穿透复合材料,并获得复合材料与金属板的黏合面处的2维太赫兹图像,从图像中能够清晰地分辨出不同特征的缺陷。该研究结果为检测复合材料黏合质量及脱黏状况提供了有效的办法。     

太赫兹超分辨率成像评述I:非实时成像

作为太赫兹波最重要的应用之一,太赫兹成像技术在生物医疗、安防安检、无损检测和质量监控等方面都具有非常重要的应用前景。由于受衍射极限的限制,传统太赫兹成像技术的分辨率只能达到工作波长级别,还无法满足很多应用的需求。本文对几种非实时的太赫兹超分辨率成像手段进行了介绍,包括近场扫描显微成像、基于空间调制器的单探测器成像、基于时间反转的成像和基于空间频谱采样的成像,并对每一种成像手段的原理、发展过程及其优缺点进行了综述和讨论,最后对非实时太赫兹超分辨率成像的发展进行了展望。     

复合材料内隐藏分层的太赫兹检测和识别

因为太赫兹技术可以克服传统无损检测技术的局限性,具有穿透普通非金属材料等优点,可被用于分析层状材料的内部结构和内层厚度。本文首先介绍了太赫兹时域光谱系统(THz-TDS)在透射模式下的工作原理,然后使用Rouard等效界面理论来描述多层结构中波的传播,推导得到透射模式下太赫兹波在三层介质中的理论传输模型。通过太赫兹时域光谱系统对制备的样品进行了透射成像。结果证明样品内部聚氯乙烯(PVC)薄片的位置和形状等信息可以被探测到,从而为探测多层材料内部结构提供理论和实验依据。