Fig. 9.

(a) Face-on pressure map at 8 mm distance from the front face of the transmitter, showing the symmetry of the field. (b) On-axis axial scan of peak-to-peak pressure (blue circles) and fitted function $\propto$$r^{-1}$. (c) Pressure map in the horizontal plane containing the acoustic axis and (d) row-by-row normalised version of the same, including dashed lines indicating the acoustic axis and e⁻¹ cut-off, encompassing the far-field opening angle of 45.8${}^{\circ }$.