Ultrasonic Phased Array Sensors

Sprachauswahl/Language selection

Dieser Artikel ist auch auf Deutsch verfügbar

A service provided by

Polymer Service GmbH Merseburg
Tel.: +49 3461 30889-50 E-Mail: info@psm-merseburg.de Web: https://www.psm-merseburg.de
Our further education offers: https://www.psm-merseburg.de/weiterbildung
PSM on Wikipedia: https://de.wikipedia.org/wiki/Polymer Service Merseburg

Ultrasonic phased array sensors

General remarks

The so-called phased array technique has been used in medical ultrasound diagnostics since around 1970 and is successfully used to visualise internal organs in addition to radiographic diagnostics or MRT (magnetic resonance tomography), which is referred to in the technical field as NMR (nuclear magnetic resonance spectroscopy) [1–3]. The term phased array refers to the phase-selective control of the phased array (PA) individual elements of a sensor field (also called a sector sensor or group), e.g. with the aim of focusing and diffracting (swivelling) the resulting sound beam in the test object. In medicine, this ultrasound diagnostic method, which works with phase- and time-controlled sound beams and generates specific sound beams, is suitable for displaying cross-sectional images of human organs.

Phased array testing and evaluation technique

The practical use of phased array technology in non-destructive testing is still relatively new, which is due in particular to the greater impedance differences in technical materials (metals with inclusions and cavities, composite materials with filling and reinforcing materials) and the very different acoustic properties of these components. The differences in human tissue (bone, cartilage or connective tissue) are much smaller, so that the technical device parameters and conditions of image analysis have to meet comparatively lower requirements [4]. The introduction of this ultrasonic testing technology was greatly advanced from around 2000 onwards as a result of miniaturisation and the development of portable testing systems based on microprocessor technology (see also: testing microcomponents), and the further development of software solutions is constantly opening up new and more demanding fields of application. Regardless of this, this complex testing and evaluation technology also places ever higher demands on testers in terms of the application of PA systems and the assessment of data and image information from test objects.

Technically, phase array (PA) technology is based on composite or piezoelectric composite materials and the active application of wave physics and acoustics. The PA sensors required for this usually consist of 16 to 256 individual elements that can transmit and receive ultrasound in the range between approx. 2 and 10 MHz. If the dimensions of the vibrating elements are sufficiently small in relation to the wavelength λ, each element represents a single point sound source with spherical radiation characteristics. While simultaneous excitation of the individual elements creates a uniform sound field in the test medium, time-delayed or phase-controlled activation generates an interference field (constructive and destructive interference) in the test object, in which the maxima and minima of the sound pressure or energy are caused by cancellation or amplification. With the freely programmable time delay using software integrated in the testing device, runtime differences in the test medium can be compensated for and so-called synthetic sound fields with special acoustic properties can be actively generated and controlled [4, 5].

This makes it possible to influence the direction of ultrasound radiation with a suitable delay, i.e. by exciting the individual elements at different times with a shift in the nanosecond range (Fig. 1). This allows the ultrasonic beam to be swivelled (Fig. 1a), focused (Fig. 1b) or simultaneously swivelled and focused (Fig. 1c) in the test object, resulting in effects comparable to those recorded with a variable angle beam sensors or a transmitter (S)-receiver (E) sensor.

Fig. 1:

Influencing the radiation characteristics of ultrasound through targeted time delay (a) for swivelling, (b) for focusing, and (c) for both focusing and swivelling

Fig. 2:

Excitation of individual elements as a group (PA) for (a) focusing and (b) scanning

Ultrasonic sensors and application examples

In testing practice, the individual elements of the sensor are usually excited in groups of 4, 8, 16 or 32 elements in order to increase both sensitivity and the degree of focus (Fig. 2), whereby these measures are supported or reinforced by the application of geometrically varying delay lines (curvature and thickness). If, after the time-delayed initiation of the group, the scan is advanced by one field element, a focused scan (Fig. 2a) or a normal scan (Fig. 2b) is produced, even though the sensor has not moved on the surface of the test object. In a similar way, the properties of the moving angle sensor or a tandem of two angle sensors can be simulated. Since each element is capable of transmitting and receiving ultrasound, the wavefront reflected at the backwall, cracks or other discontinuities is also individually time-delayed by the individual elements and summed (Fig. 3). This allows the phase array system to assign the reflections temporally according to their arrival time and spatially according to their amplitude, whereby the reflections can be demodulated and visually processed with regard to the angle, a point or a defined focus depth. In the case of a line scanner, as shown in Fig. 3, the intensity of the reflection is recorded and this results in a B-scan of the test object at the scanned position.

Fig. 3:

Detection of discontinuities in a test piece using a phased array

Phased array sensors are manufactured in a wide variety of designs as line arrays (1D PA), 2D matrix, ring or S/E fields for a wide range of applications, whereby in many cases there is the advantage of a fixed test position (Fig. 4). Like angle or standard sensors, these sensors can be equipped with delay or focusing sections, designed for direct coupling or immersion bad technology, and used for dynamic focusing. Examples of such phased array sensors are shown in Fig. 5.

Fig. 4:

Types of phased array sensors: (a) 1D sensor, (b) 2D matrix, (c) convex sensor, (d) ring sensor, (e) angle beam sensor and (f) linear S/E sensor

550px

Fig. 5:

Phased array sensor for various applications: (a) from R/D-Tech, Quebec, Canada, and (b) from Olympus Deutschland GmbH, Hamburg

Powerful testing systems are required to generate and process the complex fault representations (e.g. C-scans). These systems must also be able to withstand the harsh conditions on-site, be equipped with a high-resolution monitor and be portable (Fig. 6). The many advantages of phased array technology, which opens up completely new fields of application for non-destructive testing, are already evident in the current state of development.

Fig. 6:

Phased array technique: (a) Phasor XS from GE Inspections Technologies GmbH, Hürth, and (b) Omniscan from OLYMPUS EUROPA SE & CO. KG, Hamburg

Test fields in the area of pipe characterisation, welded pipe joints [6, 7] or defectoscopy on metallic and polymeric materials [5, 8], such as rotor blades of wind turbines [9], demonstrate the successful application of this modern testing method (see: ultrasound testing), in particular through the excellent visual evaluation and documentation of the test results. The potential of phased array testing technology will open up further fields of application for the testing methodology [10, 11], the scope of which cannot be realistically estimated at this stage. Regardless of this, a significantly higher level of qualification of the testing personnel is required to solve these testing tasks.

References

[1]	Dössel, O.: Bildgebende Verfahren in der Medizin – Von der Technik zur medizinischen Anwendung. Springer Verlag, Berlin (2016), 2nd Edition, (ISBN 978-3-642-54406-4)
[2]	Jenderka, K.-V.: Ausbreitung von Ultraschall im Gewebe und Verfahren der Ultraschallbildgebung. Der Radiologe 53 (2013) 12, pp. 1137–1150, DOI: https://link.springer.com/article/10.1007/s00117-013-2567-5#citeas
[3]	Sohn, C., Holzgreve, W.: Ultraschall in Gynäkologie und Geburtshilfe. Georg Thieme Verlag, Stuttgart (2012), 3rd Edition, (ISBN 978-3-131-58633-9)
[4]	Kass, D., Moles, M., Nelligan,T.: Olympus – Phased-Array-Prüfung – Grundlagen für industrielle Anwendungen. Olympus DMTA-20003-01DE (2014)
[5]	Deutsch, V., Platte, M., Vogt, M.: Ultraschallprüfung – Grundlagen und industrielle Anwendungen. Springer, Berlin (2012), (ISBN 978-3-642-63864-0)
[6]	Deutsch, W., Joswig, M., Maxam, K., Nitsche, S., Vahe, M., Noël, A., Pichard, P., Deutsch, S.: Phased Array Ultrasonic Testing of Heavy-Wall Seamless Tubes by Means of a Testing Portal. WCNDT World Conference for Nondestructive Testing, Moscow, Russia (2010)
[7]	Bulavinov, A., Schenkel, J., Pinchuk, R., Schröder, H. C.: Von der Phased Array zur Sampling Phased Array – Prüftechnik von Rohrnähten. 27. FDBR-Fachtagung Rohrleitungstechnik, Magdeburg (2012)
[8]	Splitt, G., Kauth, G.: Phased Array – eine zeitgemäße Lösung von Prüfaufgaben in der ZfP. DGZfP-Jahrestagung 2001, Berlin, Proceedings 75-CD, DOI: https://www.ndt.net/article/dgzfp01/papers/p13/p13.htm
[9]	Bruch, T., Oberdörfer, Y.: Prüfung von GFK Windkraft Rotorblättern mittels 500 kHz Phased-Array Technologie. DGZfP-Jahrestagung 2015, Salzburg, Proceedings B.3, DOI: https://www.ndt.net/search/docs.php3?id=19064
[10]	Deutsch, W. A., Kierspel, G.: Manuelle Schweißnahtprüfung mit Ultraschall – Konventionell oder mit Phased Array ?. DGZfP-Jahrestagung 2011, Bremen, Proceedings A.1 Download as pdf
[11]	Ernst, H., Algernon, D., Dressler, K.: Charakterisierung und Größenbestimmung sicherheitstechnisch relevanter Fehler mit Ultraschall, Einsatz von Phased Array Technik und Rekonstruktionsalgorithmen. Seminar FA Ultraschallprüfung (2016) Download as pdf

General remarks

Phased array testing and evaluation technique

Ultrasonic sensors and application examples

See also

References