Tamošiūnas Vincas, Minkevičius Linas, Bučius Ignotas, Jokubauskis Domas, Redeckas Karolis, Valušis Gintaras
Institute of Photonics and Nanotechnology, Vilnius University, Saulėtekio Ave. 3, LT-10257 Vilnius, Lithuania.
Department of Optoelectronics, Center for Physical Sciences and Technology (FTMC), Saulėtekio Ave. 3, LT-10257 Vilnius, Lithuania.
Sensors (Basel). 2022 Nov 4;22(21):8485. doi: 10.3390/s22218485.
Terahertz (THz) imaging is a powerful technique allowing us to explore non-conducting materials or their arrangements such as envelopes, packaging substances, and clothing materials in a nondestructive way. The direct implementation of THz imaging systems relies, on the one hand, on their convenience of use and compactness, minimized optical alignment, and low power consumption; on the other hand, an important issue remains the system cost and its figure of merit with respect to the image quality and recording parameters. In this paper, we report on the design and performance of an extraordinary low-cost THz imaging system relying on a InP Gunn diode emitter, paraffin wax optics, and commercially available GaAs high-electron-mobility transistors (HEMTs) with a gate length of 200 nm as the sensing elements in a room temperature environment. The design and imaging performance of the system at 94 GHz is presented, and the spatial resolution in the range of the illumination wavelength (∼3 mm) and contrast of nearly two orders of magnitude is determined. The operation of two models of the HEMTs of the same nominal 20 GHz cut-off frequency, but placed in different packages and printed circuit board layouts was evaluated at 94 GHz and 0.307 THz. The presence of two competing contributions-self-resistive mixing and radiation coupling through the antenna effects of the printed circuit boards-to the detected signal is revealed by the signal dependence on the gate-to-source voltage, resulting in a cross-sectional responsivity of 27 V/W and noise-equivalent power of 510 pW/Hz at 94 GHz. Further routes in the development of low-cost THz imaging systems in the range of EUR 100 are considered.
太赫兹（THz）成像是一种强大的技术，使我们能够以无损方式探测非导电材料或其排列，如信封、包装材料和服装材料。太赫兹成像系统的直接应用一方面依赖于其使用的便利性、紧凑性、最小化的光学对准和低功耗；另一方面，一个重要问题仍然是系统成本及其在图像质量和记录参数方面的品质因数。在本文中，我们报告了一种超低成本太赫兹成像系统的设计和性能，该系统在室温环境下，以磷化铟耿氏二极管发射器、石蜡光学元件和栅长为200 nm的市售砷化镓高电子迁移率晶体管（HEMT）作为传感元件。介绍了该系统在94 GHz时的设计和成像性能，并确定了在照明波长范围内（约3 mm）的空间分辨率和近两个数量级的对比度。评估了两种标称截止频率为20 GHz但封装和印刷电路板布局不同的HEMT模型在94 GHz和0.307 THz下的运行情况。通过检测信号对栅极-源极电压的依赖性，揭示了对检测信号有两种相互竞争的贡献——自电阻混频和通过印刷电路板的天线效应产生的辐射耦合，从而在94 GHz时产生了27 V/W的横截面响应率和510 pW/Hz的噪声等效功率。还考虑了开发成本在100欧元范围内的低成本太赫兹成像系统的进一步途径。
