“…The rotatable disc inside of the enclosure, the grooves along the circumference, and three spare shopping-cart tokens can clearly be resolved, allowing for non-destructive testing and end-of-line tests. This imaging technique can also be used to extract spatial material parameters as shown in [30], [31].…”
In this paper a D-band frequency modulated continuous wave (FMCW) radar for industrial and scientific applications is presented. It covers an ultra-wide 56 GHz sweep bandwidth (126 GHz-182 GHz, 36.4%) and is based on a custom 1 TRX + 2 RX SiGe transceiver MMIC manufactured in Infineon's B11HFC 130 nm BiCMOS process with an T of 250 GHz and max of 370 GHz. An innovative versatile multichannel edge-launch waveguide frontend-module architecture allows covering applications requiring dual polarization sensing or azimuth & elevation angle-of-arrival estimation based on the same mm-wave circuit board. The FMCW sweeper is based on measurement equipment grade commercial fractional-N PLL synthesizers in an offset dual-loop configuration for highly linear wideband FMCW sweep generation with a phase noise of better than -80 dBc/Hz ( off > 10 kHz) and superior performance even for ultra-fast ramp slopes of more than 56 GHz / 1 ms. Intermediate frequency (IF) signals of a single target measurement are presented to demonstrate the dynamic range capabilities of the FMCW radar. An SNR of 81 dB is achieved using a metal plate reflector target in free space. Due to the ultra-wide bandwidth and the resulting calibrated range resolution of 2.7 mm (-3 dB width, Tukey window), target separation is even possible in dense multi-target environments. Additionally, synthetic aperture radar (SAR) images are presented as an example application utilizing the high range resolution capabilities.
“…The rotatable disc inside of the enclosure, the grooves along the circumference, and three spare shopping-cart tokens can clearly be resolved, allowing for non-destructive testing and end-of-line tests. This imaging technique can also be used to extract spatial material parameters as shown in [30], [31].…”
In this paper a D-band frequency modulated continuous wave (FMCW) radar for industrial and scientific applications is presented. It covers an ultra-wide 56 GHz sweep bandwidth (126 GHz-182 GHz, 36.4%) and is based on a custom 1 TRX + 2 RX SiGe transceiver MMIC manufactured in Infineon's B11HFC 130 nm BiCMOS process with an T of 250 GHz and max of 370 GHz. An innovative versatile multichannel edge-launch waveguide frontend-module architecture allows covering applications requiring dual polarization sensing or azimuth & elevation angle-of-arrival estimation based on the same mm-wave circuit board. The FMCW sweeper is based on measurement equipment grade commercial fractional-N PLL synthesizers in an offset dual-loop configuration for highly linear wideband FMCW sweep generation with a phase noise of better than -80 dBc/Hz ( off > 10 kHz) and superior performance even for ultra-fast ramp slopes of more than 56 GHz / 1 ms. Intermediate frequency (IF) signals of a single target measurement are presented to demonstrate the dynamic range capabilities of the FMCW radar. An SNR of 81 dB is achieved using a metal plate reflector target in free space. Due to the ultra-wide bandwidth and the resulting calibrated range resolution of 2.7 mm (-3 dB width, Tukey window), target separation is even possible in dense multi-target environments. Additionally, synthetic aperture radar (SAR) images are presented as an example application utilizing the high range resolution capabilities.
Microwave and millimetre-wave non-destructive testing and evaluation (NDT&E) has a long history dating back to the late 1950s (Bahr 1982
Microwave non-destructive testing methods
; Zoughi 2000
Microwave Non-destructive testing and evaluation principles
; Feinstein 1967
Surface crack detection by microwave methods
; Ash 1973 In
3rd European Microwave Conference
; Auld 1981
Phys. Technol.
12
, 149–154; Case 2017
Mater. Eval.
75
). However, sustained activities in this field date back to the early 1980s (Zoughi 1995
Res. Nondestr. Eval.
7
, 71–74; Zoughi 2018
Mater. Eval.
76
, 1051–1057; Kharkovsky 2007
IEEE Instrumentation & Measurement Magazine
10
, 26–38). Owing to various limitations associated with using microwaves and millimetre waves for NDT&E, these techniques did not see much utility in the early days. However, with the advent and prevalence of composite materials and structures, in a wide range of applications, and technological advances in high-frequency component design and availability, these techniques are no longer considered as ‘emerging techniques’ (Zoughi 2018
Mater. Eval.
76
, 1051–1057; Schull 2002
Nondestructive evaluation: theory, techniques, and applications
). Currently, microwave and millimetre-wave NDT&E is a rapidly growing field and has been more widely acknowledged and accepted by practitioners over the last 25+ years (Case 2017
Mater. Eval.
75
; Bakhtiari 1994
IEEE Trans. Microwave Theory Tech
.
42
, 389–395; Bakhtiari 1993
Mater. Eval.
51
, 740–743; Bakhtiari 1993
IEEE Trans. Instrum. Meas.
42
, 19–24; Ganchev 1995
IEEE Trans. Instrum. Meas.
44
, 326–328; Bois 1999
IEEE Trans. Instrum. Meas.
48
, 1131–1140; Ghasr 2009
IEEE Trans. Instrum. Meas.
58
, 1505–1513). Microwave non-destructive testing was recently recognized and designated by the American Society for Nondestructive Testing (ASNT) as a ‘Method’ on its own (Case 2017
Mater. Eval.
75
). These techniques are well suited for materials characterization; layered composite inspection for thickness, disbond, delamination and corrosion under coatings; surface-breaking crack detection and evaluation; and cure-state monitoring in concrete and resin-rich composites, to name a few. This work reviews recent advances in four major areas of microwave and millimetre-wave NDT&E, namely materials characterization, surface crack detection, imaging and sensors. The techniques, principles and some of the applications in each of these areas are discussed.
This article is part of the theme issue ‘Advanced electromagnetic non-destructive evaluation and smart monitoring’.
“…In these applications, radar systems are a robust measurement tool and also are able to provide additional information about the material parameters of the target. Therefore, radar imaging is not just used for simple surface imaging but also for tasks in the field of material characterization like it is shown in [4] and [5]. Another relevant application is the imaging of hidden objects, for instance in the field of GPR [6], through the wall imaging [7] or security screening [8].…”
Radar imaging using the synthetic aperture radar (SAR) principle is a common method to obtain information about e.g., the surface of a target. However, most image formation algorithms for such systems assume (quasi-)static measurements. This may lead to errors in the processed images if the sensor is moving during the measurement process. This is especially the case for frequency-modulated continuous-wave (FMCW)based sensors since the signal duration is longer than in a pulsed system and the achievable bandwidth is much larger and introduces additional challenges. Motion compensation in the context of radar imaging is usually related to the correction of deviations from an ideal trajectory. In contrast, this article presents a method to take the sensor movement during a single FMCW ramp into account and therefore addresses the effects caused by a continuous path during the transmit/receive process. Hence, faster movement can be achieved during the scanning of the synthetic aperture without being bound by stop-and-go approximations. In addition, it will be shown that the algorithm is suitable to reduce systematic errors due to aliasing caused by spatial sampling below the Nyquist rate. For this purpose, this article presents simulations and measurement results, obtained by an ultrawideband D-band FMCW radar operating between 122 and 170 GHz.
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