Foreign object debris discrimination with modulated laser light
A method of foreign object debris discrimination includes illuminating a particle located within a sensing volume with a modulated electromagnetic radiation pulse emitted from a source; receiving one or more electromagnetic radiation return signals that have been scattered by the particle illuminated by the modulated electromagnetic radiation pulse at a detector; mixing, using a controller, the electromagnetic radiation return signal of amplitude I RS and frequency f RS with a reference signal of amplitude I LS and frequency f RS ; analyzing, using the controller, an amplitude of the mixed signal √{square root over (I LS I RS )}, and frequency of the mixed signal, f RS −f LS ; and classifying, using the controller, a particle position, a velocity, and electromagnetic characteristic of the particle based on the amplitude, √{square root over (I LS I RS )}, and frequency, f RS −f LS , of the mixed signal.
1. A system for particulate discrimination, comprising:
a continuous wave (CW) laser;
a modulator downstream of the continuous wave (CW) laser;
a circulator downstream of the modulator;
a detector in communication with the circulator;
a controller; and
a tangible, non-transitory memory configured to communicate with the controller, the tangible, non-transitory memory having instructions stored thereon that, in response to execution by the controller, perform operations comprising:
analyzing a frequency beats of a particle at different points in a modulated electromagnetic radiation pulse from the continuous wave (CW) laser to provide a particle velocity and a relative position of the particle; and
determining the particle velocity and a relative distance with respect to the source with a triangular modulation depending on a modulation rate B/I measuring two beats (Δf up and Δf down ) where the source emits at a frequency within a modulation bandwidth (B=f max −f 0 ).
2. The system as recited in claim 1 , wherein the modulated electromagnetic radiation pulse is a visual signal.
3. The system as recited in claim 1 , wherein the modulated electromagnetic radiation pulse is an infrared signal.
4. The system as recited in claim 1 , wherein the modulated electromagnetic radiation pulse is a terahertz signal.
5. The system as recited in claim 1 , further comprising a sensor interface optic system downstream of the circulator.
6. The system as recited in claim 5 , wherein the sensor interface optic system comprises a coupling optic in a surface of a gas turbine engine.
7. The system as recited in claim 6 , further comprising a fiber optic in optical communication with the sensor interface optic system.
8. The system as recited in claim 7 , wherein the fiber optic comprises a single core.
9. The system as recited in claim 7 , wherein the fiber optic comprises a multiple of cores for coupling scattered light back to the circulator to mix the transmitted modulated electromagnetic radiation pulse with a return signal for processing.