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On the influence of active and passive aperture size of the focused wave field sent from lineare phased array probes

: Gommlich, A.; Schubert, F.

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Fraunhofer-Institut für Zerstörungsfreie Prüfverfahren -IZFP-, Institutsteil Dresden:
7th International Workshop NDT in Progress. Online Proceedings : NDT of Lightweight Materials. Dresden, Germany, November 7 - 8, 2013
Online im WWW, 2013
2 S.
International Workshop "NDT in Progress" <7, 2013, Dresden>
Konferenzbeitrag, Elektronische Publikation
Fraunhofer IZFP, Institutsteil Dresden ( IKTS-MD) ()

Linear phased arrays consist of several single transducers. By excitating each single transducer at its particular time wave fronts can be tilted, focused or both combined. The required set of delays is called "focal law". Hence, the shape of the resulting wave front depends significantly on focal law calculation. The typical single transducer in linear phased array probes has a rectangle shape with a width-to-length-ratio of approximately 0.01. The width of the short side is called "active aperture size", the larger one is called "passive aperture size". In state of the art calculations of the focal laws only the pitch between the single elements is considered. The elements were approximated with a point source in the center of its aperture and the real size of active and passive aperture has no further leverage. The EFIT (elasto dynamic finite integration technique) in combination with PSS (point source synthesis) enables the flexible and fast simulation of four-dimen sional sound fields in homogeneous and layered half spaces, respectively. Thereby all wave physical effects like scattering and mode conversion will be considered. The calculations with different geometrical parameters for the probes show that both the active as well as the passive aperture size impact the time and frequency characteristic of the signal in the focus point. Based on the focal laws calculated with and without respect to the aperture size, sound fields were simulated for selected focus points. The results were qualitatively and quantitatively compared whereby the difference between both methods will be distinguishable. The feasibility of corrections for the focal laws with respect to time and frequency characteristics in the focus point as well as the improvement of resolution will bediscussed. The results allow an estimation about the optimal width-to-length-ratio for the single transducers of linear phased arrays.