COMSOL finite element simulation of acoustic emission spectra in water. Blue curve – an all fluid-like layers model; green curve – a solid-like layers model (PZT and barrier) with external vibration source; orange curve – a realistic model of solid layers where the PZT is excited by electrical oscillaltions. (a) and (b) Perfect matching layer. (c) and (d) Titanium layer. Color bar – the acoustic level at 500 kHz in a naive fluid-like layer model.