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Ultrasonic Phased Array for Investigations of Concrete Components

In the past years, low-frequency ultrasonic probes with dry point contact have been successfully used for non-destructive testing in civil engineering. Probe arrays of any size and shape can be designed using shear wave probes in order to get a higher signal amplitude and a more directed sound beam.

Ultrasonic Phased Array using Dry Point Contact Probes

By setting different transmission pulse delay times for each emitter element of a linear array, the ultrasonic beam can be deflected and/or focused in the measurement object. The ultrasonic field can be controlled by generation of transmitted pulses with mutual delays which are based on the transit times to focus on a desired target in the measurement object.

Ultrasonic Phased Array
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Modelling and measurement results show wave field by using beam deflection of 45 degree and clearly demonstrate a more concentrated and deflected ultrasonic beam.

Visualization of wave field generated with a nine probe phased array operated in focusing-mode for beam deflection of 45 degree: Calculation.
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Visualization of wave field generated with a nine probe phased array operated in focusing-mode for beam deflection of 45 degree: Measurement.
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Coded Transmission in Ultrasonic Non-Destructive Testing

Figure 2: The examined slab of concrete with one cladding tube in each step
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Coded transmission is a process of pulse compression and was initially applied in radar. The commonly used short rectangular pulses with high amplitudes are replaced by time-wise stretched and modulated transmission signals, which leads to a reduction of power whereas the energy increases. The actual compression takes place on the receiving side using matched filters (correlators). Within ultrasonic testing of concrete this enables the suppression of unwanted sound-scattering in reception patterns resulting in higher signal-to-noise ratios. Figure 3 present the short rectangular pulse and the Golay measurement on the concrete test object in Figure 2.

Figure 3a: Short rectangular pulse measurement
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Figure 3b: Golay pulse measurement
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Separation of Multi-Channel Ultrasonic Measurements

Ultrasonic testing of concrete structures based on the independent component analysis has been already successfully applied in other areas of ultrasonic testing. The basis of the ICA method is the statistical independence of source signals. The result of the separation process is the separation matrix W=A-1 which can be used to estimate the statistical independent sources S^ from the observed mixtures X.

Figure 4: Schematic of the ICA model
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The great capability of this method is the possibility to separate overlapping reflections of ultrasonic signals by only few measurements in real time. It is assumed that the original source signal and noise are statistically independent. The same goes also for two or more source signals, which have different object boundaries in the specimen as a cause.

References

  • Feller, V.; Mielentz, F.; Klewe, T.; Orglmeister, R.: Codierte Sendesignale für die Ultraschallprüfung von Betonbauteilen. tm-Technisches Messen, 2017.
  • Feller, V.; Mielentz, F.; Orglmeister, R.: Entmischung von Quellsignalen aus mehrkanaligen Ultraschallmessungen an Beton. tm-Technisches Messen. Vol. 82, issue 9, p. 432–439, De Gruyter, 2015, ISSN 0171-8096, DOI: 10.1515/teme-2014-0045.
  • Mielentz, F.; Feller, V.; Krause, M.; Orglmeister, R.: Ultraschallprüfung von Beton-bauteilen - Laufzeitgesteuerte Gruppenstrahler mit Punktkontaktprüfköpfen. MP Materials Testing. Vol. 55, issue 11-12, p. 856-864, Hanser-Verlag München, 2015, DOI: 10.3139/120.110510.
  • Mielentz, F.; Feller, V.; Krause, M.; Orglmeister, R.; Mayer, K.: Schallfeldmodellierung von Ultraschall-Transversalwellen-Prüfköpfen - Modellierung von Prüfkopfarrays mit der Elastodynamischen Finiten Integrationstechnik und der Punktquellensynthese. MP Materials Testing, Hanser-Verlag München, 2013.

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