Terahertz Radome Inspection

Abstract

Radomes protecting sensitive radar, navigational, and communications equipment of, e.g., aircraft, are strongly exposed to the environment and have to withstand harsh weather conditions and potential impacts. Besides their significance to the structural integrity of the radomes, it is often crucial to optimize the composite structures for best possible radio performance. Hence, there exists a significant interest in non-destructive testing techniques, which can be used for defect inspection of radomes in field use as well as for quality inspection during the manufacturing process. Contactless millimeter-wave and terahertz imaging techniques provide millimeter resolution and have the potential to address both application scenarios. We report on our development of a three-dimensional (3D) terahertz imaging system for radome inspection during industrial manufacturing processes. The system was designed for operation within a machining center for radome manufacturing. It simultaneously gathers terahertz depth information in adjacent frequency ranges, from 70 to 110 GHz and from 110 to 170 GHz by combining two frequency modulated continuous-wave terahertz sensing units into a single measurement device. Results from spiraliform image acquisition of a radome test sample demonstrate the successful integration of the measurement system.

Terahertz Quality Inspection for Automotive and Aviation Industries

“…The reflected signals are each shifted in time with respect to the generated frequency ramps serving as a local oscillator reference. Heterodyne mixing of the reference with the received reflection signals leads to a beat frequency signal f b , which can be sampled directly by a data acquisition unit (DAQ) and which, via Fourier transform, relates the detected beat frequency to a time-of-flight τ directly correlated with a range distance d of the reflecting interface [15]…”

“…2c, the most established method for regular inspection is tap tests [17], which must be performed manually and provide only limited information. Furthermore, radomes are built layer by layer and an inline production quality control can be realized to detect possible structural imperfections, delaminations, and other defects already during the manufacturing process [15]. Figure 3 depicts a dual-frequency FMCW imaging system, which we integrated into a production environment of aircraft radomes.…”

Terahertz Frequency-Scaled Differential Imaging for Sub-6 GHz Vehicular Antenna Signature Analysis

“…In [ 3 ], the ultrawide-band (UWB) imaging radar system used in this paper is tested at mmWave and terahertz bands, validating the spatial resolution on the order of millimeters and its imaging capabilities. The work presented in [ 4 ] is an imaging system that inspects a polymer radome in the frequency range of 70–170 GHz, reporting good performance in resolution and proposing to increase the frequency up to 300 GHz for improved resolution. Continuing with frequencies around 300 GHz, the three-dimensional (3D) imaging system presented in [ 5 ] is a synthetic aperture radar (SAR) operating at 340 GHz, utilizing the Fourier transform in two dimensions for the reconstruction process.…”

Linear and Circular UWB Millimeter-Wave and Terahertz Monostatic Near-Field Synthetic Aperture Imaging

“…In Reference [3], a synthetic aperture radar (SAR) was used for an imaging system using a specific algorithm, demonstrating the capability of recovering scattering information from a system operating at 36.5 GHz. In Reference [4], a terahertz inspection system for radome polymer object inspection operating from 70 to 110 GHz and from 110 to 170 GHz was presented with very good resolution results, proposing the use of higher frequencies around 300 GHz for better resolution. In Reference [5], a terahertz three-dimensional (3D) linear frequency modulated (LFM) SAR imaging system for security detection at the 340 GHz band was tested using a two-dimensional (2D) Fourier transform.…”