太赫兹频段金属粗糙表面散射特性
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摘要
根据基尔霍夫近似理论分析了金属粗糙表面在太赫兹频段的散射规律及影响因素,通过加工不同粗糙度的金属铝板样品,基于远红外激光器搭建的单频点散射特性测量系统及远红外傅里叶光谱仪(FTIR)的宽带反射率测量系统,对粗糙铝板的散射规律进行了实验测量与验证,发现实验测量结果与基尔霍夫近似计算结果具有良好的一致性,证明了峰值散射系数与粗糙度和频率的负相关性,以及与入射角度的正相关性。分析了近似光滑和较大粗糙度两种极限情况下的散射特性,给出了基尔霍夫近似理论在太赫兹频段的适用条件。相关结论为复杂目标散射特性的理论计算奠定了基础,对太赫兹频段雷达相关理论和技术的发展具有重要意义。
The scattering characteristics and the affecting factors of rough metal surface were analyzed based on the Kirchhoff approximation theory. Rough aluminum(Al) plates with different roughness were manufactured and their scattering characteristics were measured by two systems: a single-frequency system built with a far-infrared(IR) laser and a wide-band Fourier Transform IR spectroscopy(FTIR)system. Good consistency was found from the comparison of theoretical and experimental results. It is proved that the peak scattering coefficient has negative correlation with roughness and frequency, and positive correlation with incident angle. Additionally, the applicability of Kirchhoff approximation theory in the terahertz range was given by analyzing two limiting cases for near-smooth and high-roughnesssamples. The conclusions lie the foundation for theoretical calculation of complicated targets and will promote the development of the theories and techniques of terahertz radar.
The scattering characteristics and the affecting factors of rough metal surface were analyzed based on the Kirchhoff approximation theory. Rough aluminum(Al) plates with different roughness were manufactured and their scattering characteristics were measured by two systems: a single-frequency system built with a far-infrared(IR) laser and a wide-band Fourier Transform IR spectroscopy(FTIR)system. Good consistency was found from the comparison of theoretical and experimental results. It is proved that the peak scattering coefficient has negative correlation with roughness and frequency, and positive correlation with incident angle. Additionally, the applicability of Kirchhoff approximation theory in the terahertz range was given by analyzing two limiting cases for near-smooth and high-roughnesssamples. The conclusions lie the foundation for theoretical calculation of complicated targets and will promote the development of the theories and techniques of terahertz radar.
引文
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[14] Gatesman A J, Giles R H, Waldman J. High-precision reflectometer for submillimeter wavelengths[J]. JOSA B,1995, 12(2):212-219.
[15] Guo S B, Zhong K, Wang M R, et al. Theoretical and experimental study on broadband terahertz atmospheric transmission characteristics[J]. Chinese Physics B, 2017, 26(1):019501.
[2] Wang Maorong, Zhong Kai, Liu Chu, et al. Radar cross section measurement at 3.11 THz based on terahertz gas lasers[J]. Infrared and Laser Engineering, 2018, 47(2):0225001.(in Chinese)王茂榕,钟凯,刘楚,等. 3.11 THz标准体雷达散射截面测量[J].红外与激光工程, 2018, 47(2):0225001.
[3] Dikmelik Y, Spicer J B, Fitch M J, et al. Effects of surface roughness on reflection spectra obtained by terahertz timedomain spectroscopy[J]. Optics Letters, 2006, 31(24):3653-3655.
[4] Ortolani M, Lee J S, Schade U. Surface roughness effects on the terahertz reflectance of pure explosive materials[J].Applied Physics Letters, 2008, 93(8):081906.
[5] Jagannathan A, Gatesman A J, Giles R H. Characterization of roughness parameters of metallic surfaces using terahertz reflection spectra[J]. Optics Letters, 2009, 34(13):1927-1929.
[6] Cacciari I, Siano S. THz characterization of corroded metals:The influence of surface roughness[C]//18th Italian National Conference on Photonic Technologies(Fotonica 2016), 2016:1-4.
[7] Yang Yang, Liu Bing, Zhang Jingshui, et al. Influence of rough metal surface on the scattering properties of terahertz frequency[J]. Laser&Infrared, 2014, 44(8):922-926.(in Chinese)
[8] Chen Gang, Dang Hongxing, Tan Xiaomin, et al. Scattering properties of electroma gnetic waves from randomly oriented rough metal plate in the lower terahertz region[J]. Journal of Radars, 2018, 7(1):75-82.(in Chinese)
[9] Ge Chengxian, Wu Zhensen, Bai Jing, et al. Difference field scattering properties between multiple inlaid redundant particles and slightly rough optical surface[J]. Optics&Precision Engineering, 2018, 26(2):268-275.(in Chinese)
[10] Davies H. The reflection of electromagnetic waves from a rough surface[J]. Proceedings of the IEE-Part IV:Institution Monographs, 1954, 101(7):209-214.
[11] Bennett H E, Porteus J O. Relation between surface roughness and specular reflectance at normal incidence[J].Journal of the Optical Society of America, 1961, 51(2):123-129.
[12] Huang Kuntao, Fang Fengzhou, Gong Hu. Study on the optical characteristics of the surface microscopic topology generated by ultra-precision turning[J]. Optics&Precision Engineering, 2013, 21(1):101-107.(in Chinese)
[13] Liu C, Zhong K, Shi J, et al. Accurate measurement of terahertz spectrum and target velocity based on Michelson interferometry[J]. Infrared and Laser Engineering, 2018, 47(11):1117006.(in Chinese)
[14] Gatesman A J, Giles R H, Waldman J. High-precision reflectometer for submillimeter wavelengths[J]. JOSA B,1995, 12(2):212-219.
[15] Guo S B, Zhong K, Wang M R, et al. Theoretical and experimental study on broadband terahertz atmospheric transmission characteristics[J]. Chinese Physics B, 2017, 26(1):019501.