While looking at the Boeing Chinook CH-47 for [this question][1], I noticed the screens in front of the engines, and found similar devices in other photos:

[![enter image description here][2]][2]  
<sup>Source: [left][3] -- [right][4]</sup>

 - What are these devices used for?

A recurrent question here is about protecting turbine engines against bird/FOD ingestion. It seems that a screen can be used, at least at low speed. 

 - It is the case? Is it used for this purpose?


  [1]: https://aviation.stackexchange.com/q/44918/3201
  [2]: https://i.sstatic.net/QlbTi.png
  [3]: http://www.airliners.net/photo/USA-Army/Boeing-MH-47G-Chinook-414/2281241
  [4]: http://www.worldwide-military.com/Military%20Heli's/US-transport/CH-47_English.htm