On MiG 29 series aircraft, and have been for some years now. they are deployed during taxi and takeoff regimes of flight, and retracted during normal flight. I've tried to find photos on the web, but these search engines are no help. But trust me, i've seen them in action. they look like plates with small slots that come from the top of the intakes down to match its profile. maybe you all will have better luck locating an image. Helicopters uese defector plates to siphon sand and debris as well, consisting of a plate that causes a sharp bend in airflow into the engine. this sharp turn causes heavier particles to be thrown clear of the intake (because their mass causes their angular momentum to throw them clear) and the lighter less dense fluids (air) is ingested. not practical at high speeds or altitudes though.
The last of the famous international playboys