CHAPTER 4: EXPERIMENTS PERFORMED USING FAST TECHNIQUE
4.5: MEASUREMENTS OF THE FAST TECHNIQUE FOR ALUMINA IN
Measurements using the mobile FAST setup took place in the anechoic jet lab chamber located in the NCPA shown in Figure 19-20 below.
Figure 19. Mobile FAST setup in Jet Lab of NCPA view 2.
Figure 20. Mobile FAST setup in Jet Lab of NCPA view 3.
For each particle size tested, 5 measurements were made at a wheel rotation of 600 rpm. Once light intensities were recorded at each photodiode, the LabView program generated values for the experimental angular distribution function. Angular distribution values were averaged over the 5 measurements for each aperture. Plots of the averaged angular distribution function for each particle size are shown below in Table 5. Aperture number go in order from smallest to largest diameter aperture.
Table 5. Average angular distribution function for all alumina particle sizes subjected to air flow.
0 0.5 1 1.5 2
1 2 3 4 5 6 7 8
𝑞(𝜃)
Aperture
0.05 Micron
0 0.5 1 1.5 2
1 2 3 4 5 6 7 8
𝑞(𝜃)
Aperture
0.3 Micron
0 0.5 1 1.5 2
1 2 3 4 5 6 7 8
𝑞(𝜃)
Aperture
1 Micron
0 0.5 1 1.5 2
1 2 3 4 5 6 7 8
𝑞(𝜃)
Aperture
3 Micron
5.0 CONCLUSION
The LS spectrometer was able to validate manufacturer labeled 0.05 micron, 0.3 micron, 1 micron, and 3 micron alumina particle sizes while suspended in ethanol solution using a single angle measurement. Successful solution preparation required a very small particle mass ( < 0.01g ) of alumina in order to limit the effects of multiple scattering.
Experiments performed using the FAST technique were ultimately not successful in validating alumina particle size under both environmental conditions. The results obtained undertaking this effort underscore the complexity of attempting to control all the different variables in this experiment. However, the FAST technique should not be looked upon as a flawed method for obtaining particle size. Particular problems noted throughout this experimental process certainly contributed to invalid data acquisition.
These include:
• Use of linearly polarized laser light
• Photodetectors not sensitive enough
• Unalignment and warping of wood disk resulting from repeated high rpm measurements
• Epoxy adhesive effecting transparency of acrylic containment apparatus (for solution measurements)
• Inability to introduce a consistent, and appropriately dispersed amount of particle
• The 0.05 micron alumina particle size parameter being too small resulting in the Rayleigh scatter of light.
Solutions to these problems include the implementation of a laser depolarizer.
Since calculating the phase function for the theoretical angular distribution function requires the assumption of unpolarized light, it is important to implement a laser depolarizer into the experimental setup.
Also, adding more sensitive photodetectors into the setup would allow for better detection of scattered light from experimental measurements.
Additionally, removal of the rotating disk and instead applying a motorized iris shutter would negate previous issues of warping and unalignment due to high rpm measurements. Utilizing an iris shutter would also provide a smoother angular distribution function as forward scattered light could be collected through a more numerous spectrum of aperture diameters.
For solution measurements, constructing a solution containment apparatus using an adhesive alternative, such as 3M clear adhesive, should alleviate the negative effects epoxy had on transparency.
For air flow measurements, Nefedov offers a technique to introducing a steady concentration of particle mass into a sample space utilizing a laminar-diffusion-flame design (Nefedov, 1997). For this design, a flat flame burner is composed of multiple flames in a closely spaced array. These flames are fueled through the combustion of propane with air. Flow rates for both propane and air are controlled by calibrated flowmeters. A fluidized bed of particles is admixed with the air to inject the particles into the body of the flame generating a dispersed aerosol.
Successful application of the FAST technique depends on the Forward scattering of light. Therefore, implementing a laser with a lower wavelength would increase the size parameter for the 0.05 micron alumina particle size and promote the Mie (forward) scattering of light.
Due to time constraint, solutions to the noted problems above were not able to be applied into the experimental setup. However, if implemented for future measurements, these discussed solutions should improve acquiring valid data using the FAST technique.
BIBLIOGRAPHY
[1] Bohren, C. F. and Huffman, D. R., Absorption and scattering of light by small particles, Wiley-Interscience, New York, 1998.
[2] Frisvad, Jeppe Revall. “Phase Function of a Spherical Particle When Scattering an Inhomogeneous Electromagnetic Plane Wave.” Journal of the Optical Society of America A, vol. 35, no. 4, 2018, p. 669., doi:10.1364/josaa.35.000669.
[3] Hovenier, J. W. Scattering Matrix Elements. Jan. 2004, www.astro.uva.nl/scatter or www.iaa.es/scattering.
[4] Kerker, M., The scattering of light and other electromagnetic radiation, Academic Press, 1969
[5] Kocifaj, Miroslav. “Approximate Analytical Scattering Phase Function Dependent on Microphysical Characteristics of Dust Particles.” Applied Optics, vol. 50, no. 17, 2011, p. 2493., doi:10.1364/ao.50.002493.
[6] Lee, S.-C., Dependent scattering of an obliquely incident plane wave by a collection of parallel cylinders. J. Appl. Phys. 68(10), 1990.
[7] Lisitsyn, Aleksey V., et al. “Near-Infrared Optical Properties of a Porous Alumina Ceramics Produced by Hydrothermal Oxidation of Aluminum.” Infrared Physics &
Technology, vol. 77, 2016, pp. 162–170., doi:10.1016/j.infrared.2016.05.028.
[8] LS Spectrometer. (n.d.). Retrieved March 27, 2019, from https://lsinstruments.ch/en/products/3d-ls-spectrometer
[9] LS Instruments AG. (2014). LS Spectrometer User’s Manual. Retrieved from https://lsinstruments.ch/download/145/Specifications_LS_Spectrometer_v1.04.pdf.
[10] Malvern Instruments Ltd. Dynamic Light Scattering: An Introduction in 30 Minutes.
warwick.ac.uk/fac/cross_fac/sciencecity/programmes/internal/themes/am2/booking/
particlesize/intro_to_dls.pdf.
[11] Matzler, C. (n.d.). MATLAB Functions for Mie Scattering and Absorption (Tech.).
doi:https://omlc.org/software/mie/maetzlermie/Maetzler2002.pdf [12] McLinden , Chris. “Mie Scattering.” Mie Scattering, 22 July 1999, www.ess.uci.edu/~cmclinden/link/xx/node19.html#eq:escat.
[13] Nefedov, A. P., Petrov, O. F., & Vaulina, O. S. (1997). Analysis of particle sizes, concentration, and refractive index in measurement of light transmittance in the forward-scattering-angle range. Applied Optics, 36(6), 1357.
doi:10.1364/ao.36.001357
[14] Nefedov, A. P., Petrov, O. F., Vaulina, O. S., & Lipaev, A. M. (1998). Application of forward-angle-scattering-transmissometer for simultaneous measurements of particle size and number density in an optically dense medium. APPLIED OPTICS, 37, 20th ser., 1682-1689.
[15] Scattering. (n.d.). Lecture. Retrieved March 27, 2019, from
http://pages.mtu.edu/~scarn/teaching/GE4250/scattering_lecture_slides.pdf [16] Schäfer, J.-P.,Implementierung und Anwendung analytischer und numerischer Verfahren zur Lösung der Maxwellgleichungen für die Untersuchung der Lichtausbreitung in biologischem Gewebe, PhD thesis, Univerität Ulm, 2011, http://vts.uni-ulm.de/doc.asp?id=7663
[17] Schäfer, J. and Lee, S.-C. and Kienle, A,, Calculation of the near fields for the scattering of electromagnetic waves by multiple infinite