Thank you for that information Peter. I'm wondering about a couple of points as a result:
With an oscillation frequency of about 150Hz, the wavelength in air will be about 2 metres so any vibration cancellation effects would not be due to air-wave interference at a distance from the source. (I'm not an acoustics expert by any means so I hope anyone with knowledge of this subject will join in....). Do the oscillating plates vibrate in the same direction (one goes into the 'fan' cavity as the other goes out) or do they vibrate in opposite directions (both go in/out at the same time) thus expanding the cavity and then compressing it? Given that a flat plate is vibrating at 150Hz and given the complexities of vibration and sound propagation inside a PC or laptop, I'm surprised that a nearby plate (on the other 'side') is able to cancel sound waves launched by the first plate.
Is the frequency of operation related to the mechanical resonance characteristics of the fan plate assembly, or is it related to requirements due to the characteristics of air flow through the fan?
It seems to be a fascinating and useful development and I look forward to large and silent PCs and laptops one day.