Fig. 3.

Experimental demonstration of coherent averaging and adaptive backpropagation. (a) An ‘AOL’ shape structure was made with a black PET fiber of 200 μm diameter (top), which was embedded within an optically opaque PDMS made by mixing with 0.3 % weight TiO₂ particles (bottom). (b) The 2D displacement maps captured at the PDMS surface for different time delays. (c) The map coherently averaged with 20 displacement maps, after compensating for the overall phase drift. (d) The 3D image reconstructed by using the acoustic velocity of 1076 m/s, a literature value for the 10:1 ratio PDMS. (e) The image reconstructed by applying adaptive backpropagation algorithm for finding the proper acoustic velocity. At the velocity of 1045 m/s, we could reconstruct the image with optimal contrast and resolution. Scale bars in (b)-(e): 2 mm.