The two-phonon scheme of generation of terahertz (THz) photons by gold nanobars (GNBs) is considered. It is shown that in GNBs, by choosing their sizes, it is possible to provide conditions for converting the energy of longitudinal phonons with THz frequencies into the energy of THz photons. The prospects of designing GNBs-based soft THz radiation sources (frequencies: 0.14; 0.24; 0.41 and 0.70 THz) with a large flow cross-section (diameter ~40 cm) intended for detection of hidden objects under clothing to ensure security in public places (airports, railway stations, stadiums, etc.) are assessed. The choice of the above frequencies is a compromise between the requirements of low absorption of THz radiation by water vapor in air, good penetration through the fabric of clothing, favoring a sufficient resolution of the imaging system, and an abundance of corresponding longitudinal phonons, capable of exciting Fermi electrons in GNBs. Estimates of the characteristics of the terahertz-to-infrared converter based on gold nanospheres (GNSs), which could work in tandem with these sources of THz radiation -- as a means of visualization of hidden objects -- are also given.
Xiang Shi, Jian Chen,
https://onlinelibrary.wiley.com/doi/abs/10.1002/mop.31688
In this article, terahertz imaging system based on a single‐channel 360 GHz transceiver front‐end and optical‐machine scanning platform, is studied. The transmitting antenna is irradiated by a wide beam of a small aperture antenna to reduce the “angular glint” effect caused by high frequency electromagnetic radiation. The receiving antenna is of a large aperture to ensure high resolution. Beam scanning is achieved through a fast conical scanning method using a total reflector to achieve fast real‐time imaging.
Ibrahim, A.A. ; Sarabandi, K.
; Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, MI, USA
http://ieeexplore.ieee.org/xpl/articleDetails.jsp?reload=true&arnumber=7073667&filter%3DAND%28p_IS_Number%3A5741778%29
This paper reports on complex permittivity values of different natural and synthetic materials at ${mmb J}$-band (220– 325 GHz ). The materials considered in this study include different types of fabrics (wool, polyester, acrylic, jeans, vinyl, and cow leather), in addition to human skin. For the wool and jeans materials, we consider both dry and wet conditions. The knowledge of dielectric constant of these materials is needed for evaluation of radar based concealed object detection methods. The measurement setup used consists mainly of a vector network analyzer (VNA) combined with two${mmb J}$-band frequency extenders. A free space transmission only measurement technique is used to obtain both the complex dielectric constant and the effective thickness of all the fabric materials. Such approach is adequate for fabric materials as they do not have a well-defined thickness. The major factors affecting the uncertainty in the measurements are shown to be related to the sample thickness inhomogeneity, and to the unrepeatability of the network analyzer measurement itself. For the human skin case, a reflection measurement method from a terminated waveguide is adapted.
