Fig. 3

Characterization of the acoustic system. (a) Schematic characterization of the full width at half maximum (FWHM). The acoustic pressure was driven from the linear amplifier connected with a function generator, and then the pressure was measured by hydrophone to convert the mechanical output into electrical signals. (b-c) FWHM of UT and FT, showing that a larger FWHM was detected in the UT than in the FT. (d) Schematic procedure of spatial characterization (Investigated size: 10 \(\times\) 10 mm\(^2\) for UT; 4 \(\times\) 4 mm\(^2\) for FT). (e) Evaluation of the focal diameter at -6 dB, indicating that 8.57 and 1.91 mm were measured in UT and FT, respectively