Fixes
There is a simple fix, but it costs a few pennies and takes up a little space: filter out the ultrasonics before digitising. An analog filter can take the form of a physical muffler or, depending on your mic technology, a low-pass filter circuit.
There is another, more complex fix: use multiple digital mics, clock each at a slightly different sample rate and compare their audio outputs. Any significant difference can be reverse-processed back out to recover the true audio common to all the mics. The main engineering annoyances are the multiple sample clocks and the processing overhead in recovering the true signal.
Biting the hand that feeds IT
