1. Photoelastic Experiments Andrew Pskowski Arif Patel Alex Sheppard Andrew Christie

2. Elliptical Polarization  E-electric vector however can also be regarded as light vector  =phase increase  =variable part of phase factor  Curve which is described by end point of light vector where and are coordinates

3. Elliptical Polarization Want to eliminate After some algebra

4. Elliptical Polarization Squaring and adding a 1 and a 2 are half the sides of a rectangle which the ellipse is circumscribes in

5. Circular Polarization  a 1 =a 2 =a (rectangle now square) ,  Quarter plate causes this change

6. Right Handed  Right Handed-viewing from source light waves travel clockwise

7. Left Handed  Left Handed-viewing from source light waves travel counter-clockwise

8. Photoelasticity  It an experimental method used to study the stress distribution in a model.  It involves inducing birefringence on the material being studied.  Our experiment uses 2D photoelasticity.  It an experimental method used to study the stress distribution in a model.  It involves inducing birefringence on the material being studied.  Our experiment uses 2D photoelasticity.

9. Birefringence  It is the splitting of a ray of light into two rays when it passes through a material.  It is a property of certain transparent materials.  It occurs when the material is stressed.  It creates fringes or stress patterns.  It is the splitting of a ray of light into two rays when it passes through a material.  It is a property of certain transparent materials.  It occurs when the material is stressed.  It creates fringes or stress patterns.

10. Birefringence 1 st principal stress direction 2nd principal stress direction Each point of interest has a principal stress direction. This is where the only stresses present are normal stresses. Polarized light transmitted through a birefringent material splits into two light rays, each traveling at different velocities parallel to one of the two principal stress directions. 1 st principal stress direction

11. Polariscope Light Source First Polarizer Second Polarizer Specimen observer

12. Picture of our setup Front view Top view

13. No Polarized FilterPolarized Filter Experimental Pictures

14. Image Processing  Can be low or high level  Our task is fairly low level because it requires very rigidly defined input  Low level processing typically uses filtering or morphological operations  Filtering can be in spatial or frequency domain  Can be low or high level  Our task is fairly low level because it requires very rigidly defined input  Low level processing typically uses filtering or morphological operations  Filtering can be in spatial or frequency domain

15. Filtering  Edge detection is a common filtering task  Sobel operator is commonly used here  Based on central difference approximation  Template matching is also based on filters  Edge detection is a common filtering task  Sobel operator is commonly used here  Based on central difference approximation  Template matching is also based on filters

16. No Polarized FilterPolarized Filter Processing Images Determine Centers, Diameters Extract Forces

17. Method Used  Create an Ideal Particle Image D = 12; w = 1.05

18. Finding Position and Diameter  Search for minimum difference between ideal particle and real particle  Use least squares fitting and convolution  Search for minimum difference between ideal particle and real particle  Use least squares fitting and convolution

19. Coloring Particles Based on Force  Use the location of particles from the non-polarized images  Average the ‘intensity’ inside of each particle from the polarized image  Create a new image with  Color the each particle with the average intensity  Use the location of particles from the non-polarized images  Average the ‘intensity’ inside of each particle from the polarized image  Create a new image with  Color the each particle with the average intensity

20. Processed Image

21. References  Born,Max and Emil Wolf. Principles of Optics. Cambridge: Cambridge University Press, 1999.  http://www.doitpoms.ac.uk/tlplib/photoelastic ity/history.php http://www.doitpoms.ac.uk/tlplib/photoelastic ity/history.php  http://en.wikipedia.org/wiki/Photoelasticity http://en.wikipedia.org/wiki/Photoelasticity  http://gibbs.engr.ccny.cuny.edu/technical/Tra cking/ChiTrack.php http://gibbs.engr.ccny.cuny.edu/technical/Tra cking/ChiTrack.php  Born,Max and Emil Wolf. Principles of Optics. Cambridge: Cambridge University Press, 1999.  http://www.doitpoms.ac.uk/tlplib/photoelastic ity/history.php http://www.doitpoms.ac.uk/tlplib/photoelastic ity/history.php  http://en.wikipedia.org/wiki/Photoelasticity http://en.wikipedia.org/wiki/Photoelasticity  http://gibbs.engr.ccny.cuny.edu/technical/Tra cking/ChiTrack.php http://gibbs.engr.ccny.cuny.edu/technical/Tra cking/ChiTrack.php