My name is Simone Brocco, I'm an Italian student in his final year in Biomedical Engineering- "La Sapienza" University in Rome (Italy). I'm working on my thesis concerning Ultrasonic Transducers for Noninvasive Medical Application: probe (backing load,bonding layer,PZT,matching layers and acoustical lens). For my thesis I'm now verifying the correspondence between the texts on the argument and the effective realization by constructors. Now I'm studing the function of matching layer. I read that it modify the band pass characteristic of system. My question is: what is the best bandpass characteristic for a short impulse and why? There are other? Why?