So either you did not read that paper, or you do not understand it (sorry I don't intend that to come across harshly). If you read it again, and you will see that it is exactly as I stated above and will go over again here.
You will also see that this is not about an product fitted to a Hull somewhere and how well it works. This was nothing more than a lab test carried out by some Uni guys. Also they were using a range of frequencies and a very small test area. Basically no more than the surface of the transducer. I would expect that surface of the transducer.likely coupled to a plate, woul