Accuracy gets better as the frequency gets higher. But range gets shorter as frequency gets higher. So really high accuracy only works are really REALLY close range. So a transducer with 0.05mm accuracy probably won't work at distances farther than 5mm.
For reference, there is a 2MHz transducer out there that claims 25 micron resolution (not accuracy) in air, but does not say in what conditions.
Also, at longer range there's much higher chance for worse conditions which makes readings much less accurate since there is more distance for noise and disturbance to get into the signal.
Needless to say, transducers that can do this are very expensive.