Figure 2

The ultrasound beam plots. (A, B) 3D beam plots for the fundamental andthe third harmonic frequency, respectively. At the third harmonic frequency,the focal area is more compact with higher intensity. (C-E) Intensityprofiles in three directions (x, y, z) for the twofrequencies. The peak amplitude could reach 0.25 V at the fundamentalfrequency (red curve) while 0.38 V at the third harmonicfrequency (blue curve).