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

Linear phased arrays consist of several single transducers. By excitat ing e ch single transducer at its particular time wave fronts can be tilted, focused or both combined. The required set o f delays is called „focal law“. Hence, the shape of the resulting wave front depends significantly on focal law calc ulation. The typical single transducer in linear phased array probes has a rectangle shap e wit a width-to-length-ratio of approximately 0.01. The width of the short side is called „active aper ture size“, the larger one is called „passive aperture size“. In state of the art calculations of the focal laws onl y the pitch between the single elements is considered. The elements were approximated with a point source in the center o f its aperture and the real size of active and passive aperture has no further leverage. The EFIT (elasto dynamic finite integration technique) in combination wit h PSS (point source synthesis) enables the flexible and fast simulation of four -dimensional sound fields in homogeneous and layered half spaces, respectively. Thereby all wave physical effects like scattering and mode con v rsion will be considered. The calculations with different geometrical parameters for the probes show that bo t he active as well as the passive aperture size impact the time and frequency characteristic of the signal in the fo cus point. Based on the focal laws calculated with and without re spect to the aperture size, sound fields were simulated for selected focus points. The results were qualitatively and quantitatively co mpared whereby the difference between both methods will be distinguishable. The feasibility of corrections for the focal laws with respect to time and f requency characteristics in the focus point as well as the improvement of resolution will be discussed. The re sults allow an estimation about the optimal width-to-length-ratio for the single transducers of linear phased array s.