Analysis of signal oscillation patterns
View Patent ↗A method for identifying and determining the frequency of scattered radiation fringe patterns for applications such as particle or droplet sizing and laser Doppler velocimetery. The method utilizes a series of windowed Fourier transforms performed on an intensity profile of the scattered radiation to locate a segment where a fringe pattern is located on the intensity profile. A standard Fourier transform is then performed on the segment to determine a dominant frequency of the fringe pattern, from which a physical quantity such as diameter or velocity of the particle or droplet may be derived. The method may be utilized with a line or an array sensor to measure the fringe patterns in a spatial domain, or with a point detector to measure the fringe patterns in the time domain.
1. A method for analyzing a fringe or oscillation pattern comprising: performing a plurality of windowed Fourier transform analyses on a plurality of unique subsets of a one-dimensional intensity profile, each of said plurality of windowed Fourier transform analyses being performed on one of said plurality of unique subsets; generating an abscissa-frequency profile; identifying an abscissa parameter segment of said abscissa-frequency profile having a substantially constant frequency greater than zero; performing a standard Fourier transform analysis on said one-dimensional profile across said abscissa parameter segment; identifying a peak frequency from said standard Fourier transform analysis; and deriving a physical quantity from said peak frequency.
2. The method of claim 1 , wherein generating an abscissa-frequency profile comprises:
identifying a set of dominant frequencies, one within each of said unique subsets; and
generating said abscissa-frequency profile from said set of dominant frequencies.
3. The method of claim 1 wherein said subsets overlap each other in the domain of said abscissa parameter of said abscissa-frequency profile.
4. The method of claim 1 wherein each of said subsets comprises a continuous portion of said one-dimensional intensity profile.
5. The method of claim 1 wherein said abscissa parameter is a time parameter.
6. The method of claim 5 wherein said physical quantity is a velocity.
7. The method of claim 1 wherein said abscissa parameter is a spatial parameter.
8. The method of claim 7 wherein said physical quantity is a particle size or a droplet size.
9. The method of claim 8 wherein a fringe spacing is determined from said peak frequency and said droplet size or particle size is derived from said fringe spacing.
10. The method of claim 7 further comprising:
providing an electromagnetic radiation measuring device that measures a plurality of radiation intensities with a matrix of sensors on a sensing plane, said sensing plane being defined by a first axis and a second axis; and
scanning said array of sensors in a direction defined by said second axis to obtain said one-dimensional intensity profile.
11. A method of analyzing overlapping fringe or oscillation patterns, comprising:
(a) performing a windowed Fourier transform analysis on a subset of a one-dimensional intensity profile to determine a power-frequency spectrum of said subset;
(b) identifying a dominant frequency within said power-frequency spectrum of said subset;
(c) repeating steps (a) and (b) for a plurality of unique subsets across said one-dimensional intensity profile to obtain an abscissa-frequency profile;
(d) identifying a plurality of abscissa parameter segments of said abscissa-frequency profile having substantially constant dominant frequencies greater than zero;
(e) identifying a plurality of peak frequencies, one for each of said abscissa parameter segments; and
(f) determining a physical quantity from each of said peak frequencies.
12. The method of claim 11 wherein said dominant frequency is selected from a predetermined range of frequencies.
13. The method of claim 11 wherein the abscissa parameter of said abscissa parameter segment is a time parameter.
14. The method of claim 13 wherein said physical quantity is a velocity.
15. The method of claim 11 wherein the abscissa parameter of said abscissa parameter segment is a spatial parameter.
16. The method of claim 15 wherein said physical quantity is a particle size or a droplet size.