Figure 1
Encapsulated microbubble-doped gel and experimental setup. (a) Undoped gel image. (b) Image of the gel doped to an encapsulated microbubble (EMB) equilibrium volume fraction ϕ = 2.41% ± 0.05%, which was fabricated in the same manner as those gels for which data is presented. (c) EMB size distribution: EMB count (in percent) versus equilibrium diameter DO determined with optical microscopy as presented in Ref. 17, and presented here with additional DO and EMB resonance frequency fO information as well as a Gaussian fit to the distribution (solid red line). The y-axis percentage reflects the number of EMBs at each DO out of the total number of measured EMBs. Indicated is the DO range, and the corresponding fO range, targeted by the experiments. Note, the experimental frequency range is 50–800 kHz, which extends to frequencies well below the lowest fO in the distribution. (d) The Uralite polymer shell into which the gel is poured for the in-water measurements. The center ports are sealed input/output through which the gel is injected. The top corner tabs are suspended from 0.6 mm diameter monofilament nylon line and the bottom corner tabs are weighted with two 63 g lead sinkers with a maximum dimension of 25.5 mm. (e) Sample cross-sectional side view showing the material thicknesses: LG and LU for the gel and Uralite layers, respectively. (f) Experimental setup showing the relative source, sample, and hydrophone positions for the in-water transmission measurements.
