Cake testing

Totally off the wall here; but I've been watching someone make cakes and the method they use to determine if they're cooked or not is to slip a knife through it and see if it comes out clean. But that means that a cooked cake has a uniform consistency and an under-cooked one doesn't. So wouldn't that show up on radar?

Take a small hand-held device send a pulse through the cake and report on the first point of change. If the cake is sitting on a tray and is 10cm high than any reading under 10cm would indicate it was undercooked.

In a similar fashion on The Great British Menu one chef was cooking salt-basted trout [?] the whole fish covered in a salt crust and cooked. She had  to rely on timings and temperatures to determine if it was cooked or not because the coating prevented testing.

I don't know. It may be that the change wouldn't show up, but it would be a neat non-invasive sure-fire method if it did.

[Or sonar something like ultrasound that's already used to check some solids for cracks etc. I'm guessing it's not too portable though]