Characterizing powders using frequency-domain photon migration

• US 20030117622A1
• Filed: 10/21/2002
• Published: 06/26/2003
• Est. Priority Date: 10/22/2001
• Status: Active Grant

• Current Assignee: Texas A&M University System
• Original Assignee: Texas A&M University System
• Inventors: Pan, Tianshu, Sevick-Muraca, Eva M., Sun, Zhigang
• Granted Patent: US 6,771,370 B2
• Time in Patent Office: Days
• US Class Current: 356/338
• CPC Class Codes: G01J 3/4412 Scattering spectrometry particle sizing by light scattering G01N15/0205; optical velocimetry of particles G01P5/20, G01P5/26
• CPC Class Codes: G01N 15/0211 Investigating a scatter or diffraction pattern
• CPC Class Codes: G01N 2015/0096 Investigating consistence of powders, dustability, dustiness
• CPC Class Codes: G01N 2015/0216 from fluctuations of diffraction pattern
• CPC Class Codes: G01N 2015/0222 from dynamic light scattering, e.g. photon correlation spectroscopy
• CPC Class Codes: G01N 2021/4797 time resolved, e.g. analysis of ballistic photons
• CPC Class Codes: G01N 2021/8592 Grain or other flowing solid samples
• CPC Class Codes: G01N 21/51 inside a container, e.g. in an ampoule G01N21/53 takes precedence

Abstract

Characterizing a powder bed includes generating measurements by repeating the following. A location of the powder bed is illuminated with light having a time varying intensity with a resolution of less than one hundred nanoseconds. The particles scatter the light to alter the time varying intensity. The light propagates through a portion of the particles that defines a sampled volume. The light received from the powder bed is detected. The altered time-varying intensity of the light is measured to generate a time-dependent signal having a time-dependence that is less than or equal to a time-of-flight of a photon of the propagating light. An optical property is determined from the time-dependent signal, and a characteristic is determined from the optical property. The sampled volume is determined, and variance of the measurements is calculated. Uniformity of the powder bed is determined in accordance with the variance and the sampled volume.

Claims

1. A method for characterizing a powder bed, comprising:

generating a plurality of measurements of a powder bed comprising a plurality of particles by repeating the following for each location of a plurality of locations of the powder bed;

illuminating a location of the powder bed with a light, the light having a time varying intensity with a resolution of less than one hundred nanoseconds, the particles scattering the light to alter the time varying intensity of the light;

detecting the light received from the powder bed, the light having propagated through a portion of the particles, the portion of the particles defining a sampled volume interrogated by the propagating light;

measuring the altered time-varying intensity of the light to generate a time-dependent signal, the time-dependent signal having a time-dependence less than or equal to a time-of-flight of a photon of the propagating light;

determining a measurement of an optical property of the powder bed according to the time-dependent signal using a mathematical model describing light propagation; and

determining a measurement of a characteristic of the powder bed in accordance with the optical property;

determining the sampled volume interrogated by the propagating light;

calculating a variance associated with at least a subset of the measurements; and

determining a uniformity associated with the powder bed in accordance with the variance and the sampled volume.

2. The method of claim 1, wherein:

determining a measurement of an optical property of the powder bed comprises calculating an absorption coefficient according to a light propagation equation; and

determining a measurement of a characteristic of the powder bed in accordance with the optical property comprises determining a concentration of an ingredient of the powder bed in accordance with the absorption coefficient.

3. The method of claim 1, wherein:

determining a measurement of an optical property of the powder bed comprises calculating an isotropic scattering coefficient according to a light propagation equation; and

determining a measurement of a characteristic of the powder bed in accordance with the optical property comprises determining a particle size of a particle of the powder bed in accordance with the isotropic scattering coefficient.

4. The method of claim 1, wherein:

determining a measurement of an optical property of the powder bed comprises;

calculating an isotropic scattering coefficient according to a light propagation equation; and

calculating an absorption coefficient according to the light propagation equation; and

determining a measurement of a characteristic of the powder bed in accordance with the optical property comprises;

determining a particle size of a particle of the powder bed in accordance with the isotropic scattering coefficient; and

determining a concentration of an ingredient of the powder bed in accordance with the absorption coefficient.

5. The method of claim 1, wherein determining a measurement of a characteristic of the powder bed in accordance with the optical property comprises calculating an absorption coefficient in accordance with the selected member.

6. The method of claim 1, wherein:

illuminating a location of the powder bed with a light comprises illuminating the location of the powder bed with a periodic, time-varying modulated light;

measuring the altered time-varying intensity of the light to generate a time-dependent signal comprises determining a member selected from a group consisting of a phase shift, an average of the time varying intensity, and an amplitude associated with the altered time-varying intensity; and

determining a measurement of a characteristic of the powder bed in accordance with the optical property comprises calculating an absorption coefficient in accordance with the selected member.

7. The method of claim 1, wherein determining a measurement of a characteristic of the powder bed in accordance with the optical property comprises calculating an isotropic scattering coefficient in accordance with the selected member.

8. The method of claim 1, wherein:

illuminating a location of the powder bed with a light comprises illuminating the location of the powder bed with a periodic, time-varying modulated light;

measuring the altered time-varying intensity of the light to generate a time-dependent signal comprises determining a member selected from a group consisting of a phase shift, an average of the time varying intensity, and an amplitude associated with the altered time-varying intensity; and

determining a measurement of a characteristic of the powder bed in accordance with the optical property comprises calculating an isotropic scattering coefficient in accordance with the selected member.

9. The method of claim 1, wherein determining a uniformity associated with the powder bed in accordance with the variance and the sampled volume comprises:

determining a variance threshold for a perfectly mixed powder bed according to the sampled volume and a target concentration;

evaluating whether the variance satisfies the variance threshold for the perfectly mixed powder bed; and

determining the uniformity associated with the powder bed in accordance with the evaluation.

10. The method of claim 1, wherein:

illuminating a location of the powder bed with a light comprises using a plurality of wavelength sources, each wavelength source modulated with an identifiable intensity modulation;

detecting the light received from the powder bed comprises detecting the light having a plurality of modulation frequencies at a detector;

measuring the altered time-varying intensity of the light to generate a time-dependent signal comprises separating the modulation frequencies and generating a time dependant signal for each modulation frequency and each wavelength; and

determining a measurement of a characteristic of the powder bed in accordance with the optical property comprises determining a characteristic.

11. The method of claim 1, wherein:

illuminating a location of the powder bed with a light comprises illumination the location with a light having a plurality of modulation frequencies; and

detecting the light received from the powder bed comprises detecting the light having the plurality of modulation frequencies, the light at each modulation frequency describing a measurement of the characteristic.

12. The method of claim 1, wherein:

illuminating a location of the powder bed with a light comprises using a plurality of sources, each source operable to generate light at a different modulation frequency, the sources generating light having a plurality of modulation frequencies; and

detecting the light received from the powder bed comprises detecting the light having the plurality of modulation frequencies using a detector, each source associated with a different source-detector distance, the light at each frequency describing a measurement of the characteristic associated with a source-detector distance.

13. The method of claim 1, wherein:

illuminating a location of the powder bed with a light comprises interfacing a probe with the powder bed, the probe comprising a source operable to generate the light; and

detecting the light received from the powder bed comprises detecting the light using the probe comprising a detector operable to detect the light.

14. The method of claim 10, wherein the probe comprises a disposable probe.

15. The method of claim 1, wherein:

illuminating a location of the powder bed with a light comprises directing the light towards a location of the powder bed using a source operable to generate the light, the source moving with respect to the location of the powder bed, the source coupled to a receptacle, the powder bed disposed within the receptacle; and

detecting the light received from the powder bed comprises detecting the light using a detector operable to generate the light, the detector coupled to the receptacle.

16. The method of claim 1, wherein the characteristic of the powder bed comprises an element selected from a group consisting of particle packing density and particle shape.

17. A system for characterizing a powder bed, comprising:

a source operable to illuminate a location of the powder bed with a light, the light having a time varying intensity with a resolution of less than one hundred nanoseconds, the particles scattering the light to alter the time varying intensity of the light;

a detector operable to detect the light received from the powder bed, the light having propagated through a portion of the particles, the portion of the particles defining a sampled volume interrogated by the propagating light; and

a processor coupled to the source and the detector and operable to;

generate a plurality of measurements of a powder bed comprising a plurality of particles by repeating the following for each location of a plurality of locations of the powder bed;

measure the altered time-varying intensity of the light to generate a time-dependent signal, the time-dependent signal having a time-dependence less than or equal to a time-of-flight of a photon of the propagating light;

determine a measurement of an optical property of the powder bed according to the time-dependent signal using a mathematical model describing light propagation; and

determine a measurement of a characteristic of the powder bed in accordance with the optical property;

determine the sampled volume interrogated by the propagating light;

calculate a variance associated with at least a subset of the measurements; and

determine a uniformity associated with the powder bed in accordance with the variance and the sampled volume.

18. The system of claim 17, wherein the processor is operable to:

determine a measurement of an optical property of the powder bed by calculating an absorption coefficient according to a light propagation equation; and

determine a measurement of a characteristic of the powder bed in accordance with the optical property by determining a concentration of an ingredient of the powder bed in accordance with the absorption coefficient.

19. The system of claim 17, wherein the processor is operable to:

determine a measurement of an optical property of the powder bed by calculating an isotropic scattering coefficient according to a light propagation equation; and

determine a measurement of a characteristic of the powder bed in accordance with the optical property by determining a particle size of a particle of the powder bed in accordance with the isotropic scattering coefficient.

20. The system of claim 17, wherein the processor is operable to:

determine a measurement of an optical property of the powder bed by;

calculating an isotropic scattering coefficient according to a light propagation equation; and

calculating an absorption coefficient according to the light propagation equation; and

determine a measurement of a characteristic of the powder bed in accordance with the optical property by;

determining a particle size of a particle of the powder bed in accordance with the isotropic scattering coefficient; and

determining a concentration of an ingredient of the powder bed in accordance with the absorption coefficient.

21. The system of claim 17, wherein the processor is operable to determine a measurement of a characteristic of the powder bed in accordance with the optical property by calculating an absorption coefficient in accordance with the selected member.

22. The system of claim 17, wherein:

the source is operable to illuminate a location of the powder bed with a light by illuminating the location of the powder bed with a periodic, time-varying modulated light; and

the processor is operable to;

measure the altered time-varying intensity of the light to generate a time-dependent signal by determining a member selected from a group consisting of a phase shift, an average of the time varying intensity, and an amplitude associated with the altered time-varying intensity; and

determine a measurement of a characteristic of the powder bed in accordance with the optical property by calculating an absorption coefficient in accordance with the selected member.

23. The system of claim 17, wherein the processor is operable to determine a measurement of a characteristic of the powder bed in accordance with the optical property by calculating an isotropic scattering coefficient in accordance with the selected member.

24. The system of claim 17, wherein:

the source is operable to illuminate a location of the powder bed with a light by illuminating the location of the powder bed with a periodic, time-varying modulated light; and

the processor is operable to;

measure the altered time-varying intensity of the light to generate a time-dependent signal by determining a member selected from a group consisting of a phase shift, an average of the time varying intensity, and an amplitude associated with the altered time-varying intensity; and

determine a measurement of a characteristic of the powder bed in accordance with the optical property by calculating an isotropic scattering coefficient in accordance with the selected member.

25. The system of claim 17, wherein the processor is operable to determine a uniformity associated with the powder bed in accordance with the variance and the sampled volume by:

determining a variance threshold for a perfectly mixed powder bed according to the sampled volume and a target concentration;

evaluating whether the variance satisfies the variance threshold for the perfectly mixed powder bed; and

determining the uniformity associated with the powder bed in accordance with the evaluation.

26. The system of claim 17, wherein:

the source is operable to illuminate a location of the powder bed with a light by using a plurality of wavelength sources, each wavelength source modulated with an identifiable intensity modulation;

the detector is operable to detect the light received from the powder bed by detecting the light having a plurality of modulation frequencies at a detector; and

the processor is operable to;

measure the altered time-varying intensity of the light to generate a time-dependent signal by separating the modulation frequencies and generating a time dependant signal for each modulation frequency and each wavelength; and

determine a measurement of a characteristic of the powder bed in accordance with the optical property by determining a characteristic.

27. The system of claim 17, wherein:

the source is operable to illuminate a location of the powder bed with a light by illuminating the location with a light having a plurality of modulation frequencies; and

the detector is operable to detect the light received from the powder bed by detecting the light having the plurality of modulation frequencies, the light at each modulation frequency describing a measurement of the characteristic.

28. The system of claim 17, further comprising a plurality of sources comprising the source, each source operable to generate light at a different modulation frequency, each source associated with a different source-detector distance, the sources generating light having a plurality of modulation frequencies, wherein the detector is operable to detect the light having the plurality of modulation frequencies using a detector, the light at each frequency describing a measurement of the characteristic associated with a source-detector distance.

29. The system of claim 17, further comprising a probe comprising the source and the detector, the probe operable to interface with the powder.

30. The system of claim 29, wherein the probe comprises a disposable probe.

31. The system of claim 17, further comprising a receptacle coupled to the source and the detector, the powder bed disposed within the receptacle, wherein:

the receptacle is operable to move the powder bed with respect to a location of the powder bed; and

the source is operable to illuminate the location of the powder bed.

32. The system of claim 17, wherein the characteristic of the powder bed comprises an element selected from a group consisting of particle packing density and particle shape.