Phased array probes for non-contact ultrasonic testing

Mück, Andreas; SONOTEC Ultraschallsensorik Halle GmbH; Germany

Mück, A.; SONOTEC Ultraschallsensorik Halle GmbH; Germany

ID: ECNDT-0348-2018
Download: PDF
Session: Ultrasonic Inspection, Transducers
Room: G2
Date: 2018-06-12
Time: 16:00 - 16:20

Andreas Mück1
Tobias Gautzsch1

1 SONOTEC Ultraschallsensorik Halle GmbH

Non-contact air-coupled ultrasonic testing has grown in importance during the last years especially due to the application of new composite materials. The main advantage of waiving couplants like water is set against the disadvantage of high coupling losses, which make the interpretation of testing results more complicated. Therefore improvements in the testing system and its components are necessary.
A promising approach is the application of the phased array technique to the contact-free ultrasonic testing. By using probes with multiple elements and a multi-channel instrument it is possible to adapt the ultrasonic sound field to the application as well as improving testing processes. This technique is introduced and has proved its performance in industry and medicine since decades. However, only a few systems are available for the use of non-contact testing. One reason is, that the design of non-contact probes differs from conventional probes. An adaption of the concepts of phased array probes to the design of such probes is necessary.
The novel SONOSCAN CF400 series includes a piezocomposite transducer of Ø20 mm. The mean frequency is 400 kHz. In the standard type the transducer is curved, leading to a focal distance of 50 mm. Typically these transducers are used in transmission technique, which gives an optimum distance of transmitter and receiver of 100 mm. A shorter focal distance cannot be achieved by a stronger bending of the transducer due to material limits.
Based on this probe the SONOSCAN CF400 3E type with the same transducer dimension has been developed. The electrode was constructed as an annular array with 3 equal-sized elements. By applying an appropriate delay law the focal distance has been adjusted to 10 mm. The focal width has been measured with 4 mm. The corresponding sound field is shown in Figure 1.
The advantage of electronic focussing phased array probes against conventional probes can be found in applications, where the distance between transmitter and receiver is limited by external restrictions. Because of interference in the near field of the probe, the presentation of scans using conventional probes will include artefacts. Phased array probes will avoid these.