The Iphone biosensor

1. The Iphone biosensor Group 5 Da Wei, David Wickland, & Derek Graff ECE 445 Senior Design December 2, 2011

2. Introduction • Attachment and iPhone Application • Turns iPhone 4 into Spectrometer • Utilizes Photonic Crystal to Evaluate Biomaterial • Benefits: • Cheaper • Mobile

3. Presentation Outline • System Overview • Optical Design • Box Design • Programming • Tests Performed • Challenges • Future Development

4. System Overview • Hardware: • iPhone 4 • Plastic Attachment (Ford Lab) • Collimator • Transmission Grating • Photonic Crystal • Polarizer • Mirrors • Software: • iPhone Application

5. Optical Design

7. Components • iPhone 4 LED • Light Source of System • Emits Mostly Visible Light • Extremely Bright • Collimating Tube • Aligns The Propagation Direction Of Light • Needed For Clearest Diffraction Pattern • Polarizer • Aligns The Oscillations Of Light • Needed For Clear TE/TM Resonant Mode Of Crystal

8. Components • Photonic Crystal • Periodic Dielectric • Band Gap Forbids Propagation Of Certain Frequency Ranges (Resonant Modes) • Modes Can Be Altered With Surface Biochemicals • Diffraction Grating • Glass With Periodic Surface Etching • Diffracts Light Angled Proportionally To Wavelength • Grating Equation: d sinθ=mλ

9. Components • Beam Expander • Aptly Named • Increases Beam Diameter • 2 Focusing Optical Components Placed The Sum Of Their Focal Distances Apart • Magnifies By Focal Length Ratio • iPhone CCD Array • Charge-Coupled Devices • Array Of Small Capacitors • Detect Light Intensity

10. Initial Results • Original Setup Somewhat Disheartening • Difficult Alignment On Optical Table • Extremely Unstable • Spectrum Small • Blurred Results • Too Intense

11. Problems With Beam Expander • Expensive • Error Prone • Extra Alignment Parameters • Extremely Small Tolerances • Troublesome Part Size Variation • Larger Than Necessary • Limited Benefit

12. Other Changes • Measuring Crystal’s Transmission Easier Than Reflection • Transmission Gradient Instead Of Reflection • Can Be Closer To Actual Lens • Less Alignment Parameters • Mirrors To Correctly Angle Light Into Grating • Additional Slit To Filter Out Intensity And Ensure Collimated Light

13. Performance • Theoretical Resolution: 0.29 nm/pixel • Experimental Resolution: • True Resolution Slightly Worse • Chromatic Coma • Intensity Saturation • Grating Imperfections • Sources Of Error • Manual Alignment • System Prone To Slight Movement • Box Design Should Help

14. Performance • Results Comparable To General Commercial Slit Spectrometer • Still Suffered From Excess Intensity Spectrum Of Incandescent Light -Science Photo Library iPhone Results

15. Box Design

16. Ford Lab Production • Printer: Eden 350 (Objet Geometries, Ltd.) • Material: Vero Black • Software Used: Pro Engineer • File Format: .stl

17. Top View 64 mm 60.5 mm

18. Bottom View 60 mm 10.5 mm

19. Front and Side View Front Side 34 mm 34 mm 64 mm 60.5 mm

20. 3-D View

23. The Final Box

24. Problems • We couldn’t seal off the light from the LED. • The plastic “gunk” left in the collimator cavity.

25. Programming

26. Components 1. Camera control 2. Pixel data extraction 3. RGB to Intensity conversion 4. Valid area estimation 5. Median filter 6. Averaging filter 7. Peak area estimation 8. Raw data integration 9. Curve fitting 10. Pixel index to wavelength translation

27. RGB to Intensity conversion • Unbiased algorithm:Intensity = max(R, G, B);

28. Valid area estimation • Very narrow spectra is captured • Large invalid area • Thermal noise significantly reduced the contrast of the spectra

29. Valid area estimation • Observe a fact: the sum of rows with spectra data is greater than the sum of rows without spectra data

30. Valid area estimation • Result:

31. Median filter • Basic rectangle window based algorithm • Window size 3 X 3 pixels

32. Averaging filter • Take the average value of each column

33. Averaging filter • Reverse the intensity curve

34. Averaging filter • Calculate the slope of the curve

35. Averaging filter • Filter out the irrelative part

36. Peak area estimation & Raw data integration • Gauss-Newton method need a start point • Gauss-Newton method may produce diverge result for even symmetry function

37. Curve fitting • Fitting integration of Gaussian curve • Approximation model:logistic function • Trigger condition: error per pixel greater than 1

38. Curve fitting • Testing case

39. Pixel index to wavelength translation IPhone CCD IPhone lenses Grating From experiment (acetone, 567.8 nm): = 0.001103

40. Isopropanol Test- Spectrometer Reading iPhone Result- 561.34 nm

41. Challenges • Optical table limitations • Unstable iPhone holder • Lack of access to parts • Optical Simulation Software • Large size tolerances • Difficult to access lab • Ford Lab • Objective C limitations

42. Future Development • Try to implement improved beam expander. • Utilize one dimensional convex lens for wider spectrum • Light-proofing box • Create better user interface • Secure all data acquired • Utilize dynamic filtering • Develop software to analyze spectrometer readings