In reference to the patent: US20150308983
It is questionable whether is patent may be patent-able.
Apart from the Cointrust app that does an acoustic test for the authenticity of coins, precious metal dealers have known for centuries that you can differentiate between authentic and fake coins by their "ring".
I would advance that the proposed invention fails the obviousness test.
As an application, it may very well be that the independent claims are not patentable as they are currently written. That is almost always the case with patent applications as they don't get a "First action allowance", meaning the patent office just said "Yup, here's your patent." without any rejections. The final state of the claims may be very different. If you look at the dependent claims, they can give you a hint of where the applicant may look for narrowing material if the independent claims are rejected. In this case, adding the limitation of using Finite Element Analysis as in claim 10 may be a way of overcoming a rejection.
The question of the existing art of listening to a metal's ring would invalidate the claims of the referenced application, I would guess probably not. The claims recited structures that aren't in the prior art, such as a transducer to incite the "ringing" rather than a whacking. The meaning of Obvious for patentability and the plain english meaning of the word are not all that related, because there have been decades upon decades of case law describing what obvious means in the patent context that has given the word a very paricular meaning. I most commonly explain this meaning as "Obvious means described in two or more publications which provide an intrinsic motivation to combine the references into the claimed invention." Not a fully accurate definition, but it serves the purpose of explaining obvious doesn't mean what it (obviously) means.
