Double modulated differential THz-TDS for thin film dielectric characterization

Terahertz differential time-domain spectroscopy (DTDS) is a new technique that uses pulsed terahertz radiation to characterize the optical properties of thin dielectric films. Characterizing thin films in the GHz to THz range is critical for the development of new technologies in integrated circuitry, photonic systems and micro-electro-mechanical systems. There are potential applications for gene and protein chips. This paper shows how DTDS can be combined with double modulation in the pump-probe system to improve sensitivity by an order of magnitude. An iterative algorithm is presented to estimate the optical properties of a given thin film. The technique is experimentally verified using 1-μm-thick samples of silicon dioxide on silicon.     

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.     

医用棉纱布的太赫兹波段透射特性

生物医学诊断是太赫兹成像的重要应用领域。利用透射式太赫兹时域光谱(THz-TDS)在实验室温湿度条件下研究了用于伤口覆盖的医用棉纱布在0.1 THz～1.34 THz波段的透射特性。结果表明,在该波段,纱布对太赫兹辐射具有良好的透过性,且随频率增加,透射率迅速下降。利用最小二乘拟合得到太赫兹波透射率和纱布层数关系曲线,相关系数达0.996,并由此获得0.37 THz处0.34 mm厚单层纱布对太赫兹波的透射衰减系数约为0.159 7。本研究表明太赫兹光谱成像是包扎情况下烧伤评估、伤口恢复期监测的有效临床工具。     

0.67 THz ISAR成像雷达收发链路设计

介绍了一种工作频率为0.67 THz的逆合成孔径雷达(ISAR)成像系统,该系统作用距离为2 m~8 m,成像分辨力1 cm×1 cm,采用收发分开的天线,发射信号形式为宽带线性调频连续波信号,可应用于安检和无损检测等多个领域。给出了其收发链路的设计方案,对作用距离、发射功率、信号相噪、分辨率、接收灵敏度、接收增益等指标进行了具体论证,并对收发链路各功能模块的组成结构进行了详细描述,为后续开展成像雷达系统的整机研制工作提供理论基础和技术支持。     

0.67 THz高分辨力成像雷达

为达到厘米甚至亚厘米级的成像分辨力,从电子学角度出发,设计并构建了0.67 THz线性调频连续波(FMCW)成像实验平台。平台通过将Ka波段带宽1.2 GHz、功率2 W的线性调频信号24倍频,获得0.66 THz~0.688 8 THz的发射信号,功率约为1.2 mW,接收端的回波经过谐波混频完成去斜(Dechirp)形成2.4 GHz中频信号,二次变频后经高速采样送入信号处理机箱完成成像。雷达发射信号带宽为28.8 GHz,经系统非线性校正处理后,成像分辨力达到1.3 cm,验证了太赫兹雷达的高分辨成像能力。     

反射式THz‒TDS用于轨道交通典型液体安检的实验

太赫兹时域光谱(THz-TDS)技术用于轨道交通易燃易爆危险液体的安全检测,需要兼顾速度和准确率。一般在大流量人群中,因为检测速度限制,不适合直接采用实验室常用的测试指纹谱之后再与样品数据库的吸收峰位置比对的方法来精确确定样品成分信息。针对轨道交通中典型液体样品,在常温常压和正常大气湿度(25 ℃、60%空气湿度)条件下,测试反射式THz-TDS的脉冲回波数据。建立非易燃易爆危险品、易燃易爆类、强酸类等分类数据库,结合样品光谱数据库特征,归纳了4种典型的时域脉冲谱线,即含有显著次级反射峰、微小次级反射峰、无反射峰和向下反转的次反射峰。依据太赫兹时域谱线次级反射峰的特征,结合分类识别决策模型,快速实现了综合分类判别,准确率达80%以上。     

高辐射强度的带THz扼流圈的偶极天线阵列模拟分析

为了提高太赫兹辐射强度, 设计了带THz扼流圈的偶极天线阵列.模拟结果表明, 增加直线阵的阵元数对平均匹配效率影响很小, 却能线性增加相干辐射强度.加入THz扼流圈可减小进入到传输线的交流分量, 进而减小共振频率的偏移, 使平均匹配效率提升了两倍.相比于网格排列的平面阵, 交错排列的阵元在垂直方向上具有更小的耦合, THz发射谱更窄.通过使用聚酰亚胺透镜代替硅透镜, 可有效提高输入电阻, 并将总效率由25%提高到35%.     

基于太赫兹衰减全反射光谱的固体乳糖测试

利用衰减全反射式太赫兹时域光谱技术研究了固态α-乳糖的光谱特性,首先实验以传统透射式光谱技术为基准,获得了0.53 THz,1.36 THz 2个较强的吸收峰;其次,取剂量分别为1.8 mg+2.56 mg与1.8 mg的α-乳糖,利用衰减全反射式太赫兹时域光谱系统获得吸收谱线,在0.53 THz,1.36 THz均有较强吸收峰,增加样品剂量对0.53 THz,1.36 THz处吸收强度未产生影响;最后取相同剂量的2份α-乳糖,一份过筛至75μm,另一份未过筛,利用衰减全反射式太赫兹时域光谱系统获得吸收谱线,在0.53 THz,1.36 THz均有较强吸收峰;减小样品颗粒度,在0.53 THz,1.36 THz附近吸收强度增加。