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

^{Source: left -- right}

• 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?