Sebastian Kümmritz

Improvement of the resolution limit caused by the width of the sound beam

Determining of size and shape of reflector with ultrasound imaging is subjected to several limitations. Beside the wavelength, the sound beam width is a second known constraint. However, the resolution can also be restricted by the analysed reflector itself by its shape, alignment, surface roughness and material. Furthermore, different reflectors can be displayed identically with a simple c-scan, so that no differentiation is possible. In this work two different basic reflectors, balls and circular disks, were analysed. An easy method to distinguish between them will be introduced. In addition, several approaches for estimating the size of balls with ultrasound will be presented.

Simultane Bestimmung von Dicken und Schallgeschwindigkeiten geschichteter Strukturen

Zusammenfassung In diesem Beitrag wird ein Verfahren zur simultanen Bestimmung von Schichtdicken und Schallgeschwindigkeiten von zweischichtigen Strukturen vorgestellt. Um zusätzliche Information zu gewinnen, wird neben der Laufzeit die Amplitude ausgewertet. Die Amplitude einer reflektierten Schallwelle hängt von der Position der Grenzfläche im Schallfeld des Schallwandlers ab und ist maximal, wenn sich die Grenzfläche im Fokus befindet. Mit Hilfe eines Annular-Arrays wird die Fokusposition variiert und die Amplitude als Funktion der eingestellten Fokussierung ausgewertet. Auf diese Weise werden Schallgeschwindigkeiten und Dicken von Stahl- und Aluminiumplatten nach einem Wasservorlauf bestimmt.

Simultaneous measurement of thickness and sound velocities of each layer in multi-layered structures

In this contribution, a novel method for determining the thickness of one layer and its sound velocity simultaneously with only one probe will be presented. Furthermore, an approach for the determination of thickness and sound velocities for two or more layers is discussed.

Determination of size and shape of small inclusions from sound-field information

The resolution of scanning ultrasonic systems is limited to the wavelength used and the focus size. Common methods for determination of object sizes close to or even smaller than wavelength require knowledge of the object geometry and use absolute amplitude information only. We present new approaches for determining shape and size of small objects by additional evaluation of sound field effects like the directivity of reflected waves. First measurements show that determining size and shape of objects smaller than the size of the sound field is possible with geometric considerations on maximum amplitude positions of different reflection modes. Practical usable relative evaluation criteria for time changes in dependence of displacement can be found for ball sizes down to 1/5 wavelength.

Approach for Simultaneous Determination of Thickness and Sound Velocity in Layered Structures Based on Sound Field Simulations

This paper describes a non-invasive, nondestructive method for the simultaneous determination of sound velocity and thickness of the different layers of a layered structure by means of ultrasound. It will be demonstrated how further information about the reflected sound field, in addition to the time of flight, is acquired by using annular arrays. Because of this supplementary information, reflectors or other probes at known distances are not necessary and the specimen does not have to be placed in a medium with known sound velocity. Two different evaluation methods combined with a geometric model are explained. To improve the accuracy, measured signals are also evaluated by a wave propagation model.

Investigation of Embedded Structures in Media with Unknown Acoustic Properties

For the nondestructive evaluation of components with ultrasound a priori information about the specimen is necessary. So the time of flight to a defect is measured and, with known sound velocity, it is possible to determine the correct location of the defect. In general, the sound velocity is assumed as known. If it is not known, the sound velocity has to be determined additionally. This can be done, for example, by measuring the time of flight to the backwall with ultrasound and the thickness of the specimen with a caliper gauge. However, this is impossible to realize with single-sided access to the specimen. For determining the size of inclusions, several techniques like the half-value method or the DGS-method (Distance Gain Size) are established. These methods are based on the assumption of (circular) plane reflectors. Therefore, they cannot be applied on the size determination of inclusions with curved surfaces.

Determination of the size of spherical inclusions smaller than the width of the sound beam

The current presentation introduces a new method for the determination of the size of balls with a diameter from nearly a wavelength up to the width of the sound beam (and higher). The basic approach is to analyse the directional pattern of the reectors, which