Terahertz Quality Inspection for Automotive and Aviation Industries

Abstract

Nondestructive quality inspection with terahertz waves has become an emerging technology, especially in the automotive and aviation industries. Depending on the specific application, different terahertz systems-either fully electronic or based on optical laser pulses-cover the terahertz frequency region from 0.1 THz up to nearly 10 THz and provide high-speed volume inspections on the one hand and high-resolution thickness determination on the other hand. In this paper, we present different industrial applications, which we have addressed with our terahertz systems within the last couple of years. First, we show three-dimensional imaging of glass fiber-reinforced composites and foam structures, and demonstrate thickness determination of multilayer plastic tube walls. Then, we present the characterization of known and unknown multilayer systems down to some microns and the possibility of measuring the thickness of wet paints. The challenges of system reliability in industrial environments, e.g., under the impact of vibrations, and effective solutions are discussed. This paper gives an overview of state-of-the-art terahertz technology for industrial quality inspection. The presented principles are not limited to the automotive and aviation industries but can also be adapted to many other industrial fields.

Fully Superconducting Josephson Bolometers for Gigahertz Astronomy

“…Notably, the current bias modulates the device sensitivity over about 6 orders of magnitude. Furthermore, the extracted data indicate that the JES [34] reaches best sensitivities several orders of magnitude better than nano-TES bolometers [33] and all other sensors proposed and realized [16][17][18][19][20][21][22][26][27][28][29][30][31][32][35][36][37]48] so far. Specifically, the JES showed unprecedented values of NEP TFN,JES as low as ∼1 × 10 −25 W/ √ Hz for the highest bias current I = 370 nA (I C,0 /I 1.5) corresponding to a working temperature of about 18 mK.…”

“…As a consequence, these sensors could be the basis of detectors pointing towards unprecedented sensitivities in the GHz and THz bands. In addition to gigahertz astronomy, these sensors could be employed in medical imaging [35], industrial quality controls [36] and security applications [37].…”

Glass–Adhesive–Steel Joint Inspection Using Mechanic and High Frequency Electromagnetic Waves

“…There are several techniques in application, including continuous wave (CW) imaging (single frequency or swept frequency excitation and single point or matrix detection) or time-domain spectroscopy (TDS) with femtosecond order pulsed excitation and detection using photoconductive antennas. The first setup enables higher power (and in consequence testing of thicker and more lossy structures) and faster inspection, while TDS enables spectroscopic information about an examined structure (dispersion curves and absorption peaks for specified frequencies correlated with specific molecules) [ 7 , 8 , 9 ] and relatively intuitive information about cross-section (in depth profile) because of operating principle similar to radar [ 10 , 11 , 12 , 25 ]. The excitation pulse is directed into the examined material and after interaction (reflection of interfaces having various dielectric properties) is picked up by a receiving antenna.…”

“…Both techniques are not as standardized as ultrasonic or X-ray testing; however, their potential is being developed by many laboratories and applied in industrial inspections. Microwave and terahertz non-destructive evaluation (NDE) techniques were widely utilized for dielectric structure production stage evaluation (including polymerization process monitoring) [ 5 , 6 ], as well as in exploitation stage examination, including aviation, automotive and rail industry structures [ 7 ], wind turbine blades [ 8 , 9 ], moisture detection and monitoring [ 10 ] and new types of materials examination [ 1 , 11 , 12 ]. The application of high frequency electromagnetic waves also includes dielectric material based joint inspection—thermal fusion joints (e.g., in the case of HDPE pipes) [ 13 ] or adhesive bonds [ 14 ].…”

High-Resolution Long-Range THz Imaging for Tunable Continuous-Wave Systems

“…Other areas of interest are non-destructive testing [6], hydration monitoring [7] and spatially resolved thickness measurements, e.g. of tablet coatings [8] - [9], paint layer thickness [10] and in the field of art and heritage conservation [11] - [12]. For these applications, the object under test (OUT) is typically located at the focus of a THz time-domain spectroscopy (TDS) system either in reflection [13] or in transmission [14] mode.…”