Ventilated acoustic metasurface with low-frequency sound insulation.

A ventilated acoustic metasurface consisting of a membrane covered with a combination of different depth sub-chambers is proposed. It can achieve at least a 5 dB sound insulation acoustic performance in the wide frequency range from 100 to 1700 Hz, in particular a 10 dB noise reduction in the range from 100 to 200 Hz and from 437.4 to 1700 Hz, which can therefore cover the low-frequency range of the environmental noise.

Efficient flapping wing drone arrests high-speed flight using post-stall soaring.

The aerobatic maneuvers of swifts could be very useful for micro aerial vehicle missions. Rapid arrests and turns would allow flight in cluttered and unstructured spaces. However, these decelerating aerobatic maneuvers have been difficult to demonstrate in flapping wing craft to date because of limited thrust and control authority.