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Abstract. Acoustic streaming combined with cavitation bubble has a potential application in pore-based gel preparation, where the pore-based gel may be used as biosensor related to bio-chemical industry. In this study, particle image velocimetry (PIV) measurements of the acoustic streaming induced by ultrasound radiation at excitation frequency of 20 kHz are presented. Particular focus is placed on the influence of a bounding wall placed normal to the axis of the ultrasound beam on local flow structures, including the on-axis streaming velocity and the axial location of the peak streaming velocity. The PIV data reveal that the on-axis streaming velocity shows a monotonic and drastic increase from the radiating surface of the beam till the focal region where the velocity peaks. This is confirmed by cavitation bubble images captured with high-speed camera. An existing analytical model is modified to take into account of the influence of the cavitation bubbles on the speed of sound, viscosity, and sound absorption coefficient of the fluid-gas mixture, with good overall agreement between analytical predictions and experimental measurements achieved. The formation of air bubbles in distilled water is found to elevate the streaming velocity dramatically in the entire axial range except for a region near the bounding wall due to stagnation. The peak streaming velocity and its axial location are reduced significantly as the bounding wall is brought closer to the beam.