High-resolution FMCW millimeter-wave and terahertz thickness measurements

Schreiner, Nina S.; Baccouche, B.; Sauer-Greff, W.; Urbansky, R.; Friederich, Fabian

doi:10.23919/eurad.2017.8249216

Cited by 3 publications

(4 citation statements)

References 5 publications

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“…For the next device generation, we will modify the diode laser architecture to suppress multimode emission and mode hopping, and to achieve higher difference frequencies. Thus, the device will enable continuous tuning of the THz frequency and enable frequency modulated continuous wave (FMCW) approaches [19] for thickness and depth measurements without mechanically scanning a delay line. Such a laser will be highly attractive as a single light source for multi-purpose systems, including simultaneous Raman and THz sensing.…”

Section: Resultsmentioning

confidence: 99%

Continuous Wave THz System Based on an Electrically Tunable Monolithic Dual Wavelength Y-Branch DBR Diode Laser

Gwaro

Brenner

Theurer

et al. 2020

J Infrared Milli Terahz Waves

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We analyse the use of a tunable dual wavelength Y-branch DBR laser diode for THz applications. The laser generates electrically tunable THz difference frequencies in the range between 100 and 300 GHz. The optical beats are tuned via current injection into a micro-resistor heater integrated on top of one of the distributed Bragg reflector (DBR) section of the diode. The laser is integrated in a homodyne THz system employing fiber coupled ion-implanted LT-GaAs log spiral antennas. The applicability of the developed system in THz spectroscopy is demonstrated by evaluating the spectral resonances of a THz filter as well as in THz metrology in thickness determination of a polyethylene sample.

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Section: Resultsmentioning

confidence: 99%

Continuous Wave THz System Based on an Electrically Tunable Monolithic Dual Wavelength Y-Branch DBR Diode Laser

Gwaro

Brenner

Theurer

et al. 2020

J Infrared Milli Terahz Waves

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“…To resolve thicknesses close to the Rayleigh resolution limit and even below, a promising method is the correlation coefficient-based comparison of measurement signals and signal models, which represent the material structure of the SUT [18]. The highest correlation indicates the best approximation of the real positions and hence the evaluated thicknesses.…”

Section: Model-based Signal Processing Approachmentioning

confidence: 99%

“…Within this contribution, we focused on the industrial application of the FMCW technique for layer thickness determinations of multilayer systems. We used a model-based signal processing technique to overcome the inherent lower resolution limit [18] with a priori information such as the number of individual layers and a reference measurement for evaluating the material parameters. Similar to the approaches in [3,14,15], we fitted the calculated signals resulting from propagation models of the sample under test to the measured ones.…”

Section: Introductionmentioning

confidence: 99%

Multilayer Thickness Measurements below the Rayleigh Limit Using FMCW Millimeter and Terahertz Waves

Schreiner

Sauer-Greff

Urbansky

et al. 2019

Sensors

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We present thickness measurements with millimeter and terahertz waves using frequency-modulated continuous-wave (FMCW) sensors. In contrast to terahertz time-domain spectroscopy (TDS), our FMCW systems provide a higher penetration depth and measurement rates of several kilohertz at frequency modulation bandwidths of up to 175 GHz. In order to resolve thicknesses below the Rayleigh resolution limit given by the modulation bandwidth, we employed a model-based signal processing technique. Within this contribution, we analyzed the influence of multiple reflections adapting a modified transfer matrix method. Based on a brute force optimization, we processed the models and compared them with the measured signal in parallel on a graphics processing unit, which allows fast calculations in less than 1 s. TDS measurements were used for the validation of our results on industrial samples. Finally, we present results obtained with reduced frequency modulation bandwidths, opening the window to future miniaturization based on monolithic microwave integrated circuit (MMIC) radar units.

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“…Furthermore, FMCW has been demonstrated to apply to thickness measurements, such as industrial films and coatings [20,21], and ice and snow thickness measurements [22,23]. Since the frequency bandwidth directly affects the measurement accuracy, in order to obtain higher measurement accuracy, ultra-wideband millimeter-wave and terahertz radars have been studied.…”

Section: Introductionmentioning

confidence: 99%

Improving FMCW GPR Precision through the CZT Algorithm for Pavement Thickness Measurements

Huang

Zhang

et al. 2022

Electronics

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Ground Penetrating Radar (GPR) application in road surface detection has been greatly developed in the past few decades, which enables rapid and economical estimation of pavement thickness and other physical properties in non-destructive testing (NDT) and non-contact testing (NCT). In recent years, with the rapid development of microwave and millimeter-wave solid-state devices and digital signal processors, the cost of Frequency-Modulated Continuous-Wave (FMCW) radar has dropped significantly, with smaller size and lighter weight. Thereafter, FMCW GPR is considered to be applied during pavement inspection. To improve the precision of FMCW GPR for NDT and NCT of pavement thickness, a Chirp Z-transform (CZT) algorithm is introduced to FMCW GPR and investigated in this paper. A FMCW + CZT GPR at 2.5 GHz with a bandwidth of 1 GHz was built, and laboratory and field experiments were carried out. The experimental results demonstrate that the FMCW + CZT GPR radar can obtain the sample thickness with low error and recognize subtle thickness variations. This method realizes the high precision thickness measurement of shallow asphalt pavement by FMCW radar with a narrow bandwidth pulse signal and would provide a promising low-cost measurement solution for GPR.

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High-resolution FMCW millimeter-wave and terahertz thickness measurements

Cited by 3 publications

References 5 publications

Continuous Wave THz System Based on an Electrically Tunable Monolithic Dual Wavelength Y-Branch DBR Diode Laser

Continuous Wave THz System Based on an Electrically Tunable Monolithic Dual Wavelength Y-Branch DBR Diode Laser

Multilayer Thickness Measurements below the Rayleigh Limit Using FMCW Millimeter and Terahertz Waves

Improving FMCW GPR Precision through the CZT Algorithm for Pavement Thickness Measurements

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