Project M01 - THz Channel Measurements for Material Characterization and Localization

Principal Investigators: Prof. Dr. Thomas Kaiser, UDE / Prof. Dr. Clara Saraceno, RUB

Achieved Results in the 1st Phase

M01, WP5 The novel research about “Time variant THz channels”THz SAR Imaging of Indoor Objects. During the research on WP5, it turned out that the merged topic of “time variant THz channels” and the succeeding “material mapping” could be best and even jointly matched by the THz extension of conventional GHz SAR imaging methods since the time variant nature originates from the moving robot.

Fig. 1: (left) Optical image,(right) SAR image of an electrical wires mount.

Such extension broadens the SAR applications to sub-mm resolution imaging associated with sub-surface imaging and material characterization as many materials have THz fingerprints. For example, the left part of Fig. 1 shows an optical image of an electrical wire mount consist of three holes (a,b,c) for wires while the right part shows the corresponding SAR image at 275 GHz. The imaging is performed at a distance of1.1 m, the propagation direction is along the x-axis and the azimuth direction is along y-axis. In the resulted SAR image, all the three holes are observable and in addition, the SAR technique offers the geometric properties extraction of this object such as material thickness and dimensions in 3D space. The impact of small and large bandwidths of 20 GHz, 50 GHz and 110 GHz on the multi-object imaging has been analyzed in [5]. The corresponding range resolutions are 7.5 mm, 3 mm and 1.36 mm. The achieved results show the image with the highest resolution offering sharp visibility of the target edges and lowest pixel spread.

To investigate THz SAR techology, a simulation framework was designed based on signal modeling [12] and EM propagation. The model explains the signal processing, imaging geometry for 2D imaging in an in-room environment with a flying robot based THz SAR. The impact of the system parameters such as the robots velocity, azimuth step size, beam spot size, aperture length, frame size are evaluated. In complementarity with M02, a simulation system with EM propagation is designed to realize the THz SAR imaging in a virtual scenario in consideration with EM fields calculation, based on Maxwell equations and material properties.

For experimental analysis, a Vector-Network-Analyzer (VNA) based measurement testbed has been set up at DSV-UDE [13, 26, 30]. The theoretically achievable sub-mm resolution with conventional SISO SAR has been preliminary validated by simulations and measurements with a maximum range resolution of 1.3 mm and azimuth resolution of 3 mm at the 220 GHz to 330 GHz band, having 110 GHz bandwidth. The range plays a significant role in the quality of the image, and we presented it up to propagation distance of 1.35 m [6]. Additionally, beam based range imaging of different materials has been studied even up to 8 m [7]. In the context to MARIE, in-room objects of various materials such as ceramic, glass, plastic, wood have been considered for SAR analysis. The THz SAR results reveal the possibility of visually comparable image generation and these images can be further analyzed for shape-based object classification similar to optical technology domain. Moreover, the penetration property has also been investigated to explore the sensing and imaging of concealed and hidden objects [11]. Another important challenge for THz SAR imaging is MOCO because of robot vibrations possibly being larger than the wavelength and compact state-of-the-art inertial measurement units mounted on the robot do not provide the required sub-mm accuracy. MOCO for 2D THz imaging has been investigated based on the accurate S04 sub-mm localization system. Moreover, a collaborative simulation framework has been setup for in-room THz SLAM, which offers the localization of a flying robot based on S04 and mapping of remote objects with sub-mm resolution using THz SAR techniques. The impact of motion errors has also been demonstrated experimentally and the research findings reveal that the highest positioning accuracy is required along the propagation direction. Additionally, real-time THz SAR 2D imaging has been investigated using High Performance Computing (HPC) platform. The algorithms are optimized to be processed in a parallel environment to reduce the computational time.

Moreover, in collaboration with M05, a long range VNA based THz imaging with a method of inverse circular SAR is realized. The measurement is performed at 240 GHz with 40 GHz of bandwidth in bi-static configuration. The raw data is processed with Kirchhoff migration algorithm and the results are analysed for comparison purposes between a Time-Domain-Spectroscopy (TDS) and VNA based approach. Although much higher resolution can be achieved with the TDS system, yet VNA based imaging offers higher SNR and therefore long propagation range sensing and comparable high quality focused image [6].

Selected Project-related publications

For all project-related publications please click here and scroll to the M01 section.

[1] M. Alissa, B. Friederich, F. Sheikh, A. Czylwik, T. Kaiser, "Experimental Investigation of Terahertz Scattering: A Study of Non-Gaussianity and Lateral Roughness Influence", IEEE Access, September 2020. [DOI: 10.1109/ACCESS.2020.3025361]

[2] F. Sheikh, M. Hasan, T. Kaiser, book chapter 12 "Novel Aspects in Terahertz Wireless Communications," in Antennas and Propagation for 5G and Beyond, IET, UK, 2020 (accepted, published in Nov. 2020).

[3] F. Sheikh, Y. Zantah, I. Mabrouk, M. Alissa, J. Barowski, I. Rolfes, T. Kaiser, “Scattering and Roughness Analysis of Indoor Materials at Frequencies from 750 GHz to 1.1 THz,” in IEEE Transactions on Antennas and Propagation, (major revision submitted, on 02.08.2020).

[4] F. Sheikh, Y. Zantah, N. Zarifeh, M. Hassan, T. Kaiser, “Horn Antenna Misalignments at 100, 300, 400, and 500 GHz in Close Proximity Communications,” in IEEE Transactions on Antennas and Propagation, (submitted, on 16.07.2020).

[5] A. Batra, M. Wiemeler, D. Goehringer and T. Kaiser, "Comparison Analysis of Small and Large Bandwidth Indoor SAR Multi- Object Imaging at Low Terahertz Spectrum," 45th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz 2020), Buffalo, New York, USA, November 2020 [accepted].

[6] D. Damyanov, A. Batra, B. Friederich, K. Kolpatzeck, X. Liu, T. Kaiser, T. Schultze, J. C. Balzer, "High Resolution VNA THz Imaging for Large Distances," 45th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz 2020), Buffalo, New York, USA, November 2020 [accepted].

[7] F. Sheikh, Y. Zantah, A. Batra, I.B. Mabrouk, M.A. Hasan, T. Kaiser, "Far-Distance VNA-based Measurements of Indoor Materials at 300 GHz", ICEAA-IEEE APWC 2020, Honolulu, Hawaii, USA, August 2020 [accepted].

[8] F. Sheikh, Y. Zantah, T. Kaiser, "Novel Aspects of Horn-Antenna Beam Misalignment at THz Frequencies", ICEAA-IEEE APWC 2020, Honolulu, Hawaii, USA, August 2020. [accepted].

[9] J.u.R. Kazim, M. Ur-Rehman, A. Abohmra, F. Sheikh, T. Kaiser, M. Al-Hasan, I.B. Mabrouk, M.A. Imran, Q.H. Abbasi, “A 1-bit High-Gain Flexible Metasurface Reflectarray for Terahertz Application”, IEEE 3rd Int. Workshop on Mobile THz Systems (IWMTS), July 2020. [under press].

[10] D. Cahyono, F. Sheikh, T. Kaiser, “Deterministic Approach of Indoor Room THz Multipath Channel Model”, 8th International Conference on Information and Communication Technology (ICoICT 2020), Yogjakarta, Indonesia, June 2020. [under press].

[11] A. Batra, V. T. Vu, Y. Zantah, M. Wiemeler, M. I. Pettersson, D. Goehringer and T. Kaiser, "Sub-mm Resolution Indoor THz Range and SAR Imaging of Concealed Object ," ICMIM 2020, Linz, Austria, April 2020 [accepted].