Design and Performance of Extraordinary Low-Cost Compact Terahertz Imaging System Based on Electronic Components and Paraffin Wax Optics

Abstract

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.

Narrowband Thermal Terahertz Emission from Homoepitaxial GaAs Structures Coupled with Ti/Au Metasurface

“…In general, the cost of a THz imaging system will depend on the type of setup and specific components. For example, pre-made components such as commercially available 200 nm gate-length GaAs high-electron-mobility transistors (HEMTs) as a cheap THz solution for 94 GHz detection were presented recently [ 7 ]. Moreover, diffraction gives the opportunity to manipulate a phase shift of radiation that passes through specific designed optical elements [ 8 ] or a variety of diffractive optics [ 9 ].…”

Study of the low-cost HIPS and paraffin-based terahertz optical components

“…As a result, the development of old-style refractive lenses is still considered reasonable. Such lenses were successfully applied along with low-cost THz detector solutions, significantly decreasing the price of the total imaging system [13]. Still, the proper optimization of materials and shapes can further substantially increase the imaging quality and efficiency.…”