1. Measurements in Fluid Mechanics 058:180 (ME:5180) Time & Location: 2:30P - 3:20P MWF 3315 SC Office Hours: 4:00P – 5:00P MWF 223B-5 HL Instructor: Lichuan Gui lichuan-gui@uiowa.edu Phone: 319-384-0594 (Lab), 319-400-5985 (Cell) http://lcgui.net

2. 2 Lecture 9. Optical experimentation: Recording

3. 3 Light transmission, sensing, and recording Fiber optics Core - Thin glass center of the fiber where the light travels Cladding - Outer optical material surrounding the core that reflects the light back into the core Buffer coating - Plastic coating that protects the fiber from damage and moisture Fiber optic cables n 1 – refractive index in core n 2 – refractive index in cladding n 0 – refractive index of surrounding medium n 2 < n 1 n 0 < n 1 Total internal reflection required at interface between core and cladding Numerical aperture of the fiber

4. 4 Light transmission, sensing, and recording Conventional photography & cinematography Still camera - lens - aperture - shutter - photographic film (sensor) f – focus length D f-number (f/#): Camera for motion pictures

5. 5 Light transmission, sensing, and recording Photodetectors Photomultiplier tubes (PMTs) Photodiodes (PDs) - gas-filled or vacuum tube that is extremely sensitive to light in the ultraviolet, visible, and near-infrared ranges of the electromagnetic spectrum. - photoeletric effect: incoming photons strike a photocathode, generating electrons, which are attracted to an anode. Photoelectric effect photons electrons - semiconductor diodes - capable of converting light into either current or voltage Quantum efficiency: N p – number of absorbed photons N e – number of emitted electrons - internal amplification - external amplification required - smaller size, less expensive but lower signal-to-noise ratio (vs. PMTs)

6. 6 Light transmission, sensing, and recording Video standard camera - Low cost; - Low digital resolution: 640  480 ~ 768  576 pixels; - Frame rate: 25 Hz (PAL) or 30 Hz (NTSC); - 2 interlaced fields per frame with time interval 1/50s or 1/60s; - Frame separation necessary before evaluation

7. 7 - High resolution (up to 5000×7000 pixels or more) - Low pixel read out rate - Very low frame rate (e.g. <1 Hz) Light transmission, sensing, and recording Full-frame CCD (charge coupled device) camera

8. 8 - Mega pixel full frame CCD - Two halves of CCD array for imaging and storage, respectively - Rows shifted down at high rates (e.g. 1  s per row) - Time gap between frames within 0.5  1 ms - Low frame rate Light transmission, sensing, and recording Frame transfer CCD

9. 9 - Mega pixel full frame CCD - One masked storage area for each pixel - Charge shift from light sensitive area to storage area at high very high rates - Time gap between frames as low as 200 ns - Low frame rate (e.g. 15 & 30 fps) Light transmission, sensing, and recording Interline transfer CCD

10. 10 Color CCD - Color filter on top of each pixels - Reduced digital resolution CMOS (Complementary metal–oxide–semiconductor) sensors - higher image capture speed - lower pricevs. CCD - lower image quality ultima APX CMOS camera 1024 × 1024-pixel resolution Pixel size 17 × 17 µm² 10 bit dynamic range 8 GB image memory in camera 2000 fps at full resolution (up to 120,000fps) Minimal inter-framing time 8333 ns PCD2000 CCD camera 2048 × 2048-pixel resolution Pixel size 7.4 × 7.4 µm² 14 bit dynamic range 4 GB image memory in camera frame rate of 14.7 fps at full resolution Inter-framing time for PIV 180 ns Light transmission, sensing, and recording

11. 11 Full-frame CCD - Double/multi exposures - Low and high velocity Frame transfer CCD - Single exposures - Low to medium velocity Interline transfer CCD - Single exposures -  t down to 75 ns - High velocity TimeExposureRead-out Camera frame rate Laser light pulses Camera frame rate Laser light pulses Charge transfer period (>1  s) Camera frame rate Laser light pulses Charge transfer period (<1  s) Light transmission, sensing, and recording Timing diagrams for PIV recording based on CCDs

12. 12 - Mega pixel full frame possible at >2000 fps - 10,000 fps available at standard video resolution (i.e. 640  480 pixels) - High intensity light source required - Commercially available high-speed imaging systems: Light transmission, sensing, and recording Digital High speed digital imaging system

13. 13 Light transmission, sensing, and recording Small particle imaging Circular aperture diffraction - Airy pattern of a point light source - Image of sub-micron particle - Depth of field - Airy disk diameter f # – f-number M – magnification factor – wave length - Particle image diameter d p – particle diameter

14. 14 Homework - Questions and Problems: 13 on page 143 - Read textbook 5.5-5.6 on page 128-141 - Due on 09/14

15. Determine positions (x,y) and values G(x,y) of the 9 pixels in the 3x3 neighborhood of the maximal gray value with a linear coordinate trans formation Start to write a Matlab program x y 0 i j 0 15 60 49 45 51 44 49 37 45 50 35 54 47 57 41 39 40 44 52 38 52 50 22 23 48 48 43 49 50 42 40 33 47 36 29 40 50 47 26 26 54 56 38 45 42 32 46 40 38 62 48 38 40 51 36 48 58 47 40 48 48 43 43 51 43 30 35 39 34 34 50 36 51 49 38 44 50 52 59 56 46 51 32 43 43 43 45 21 33 35 41 45 33 43 41 52 49 46 37 37 37 49 36 39 50 42 42 44 26 12 25 26 30 47 41 33 53 53 40 50 59 40 33 41 45 39 37 36 29 28 35 44 32 26 44 34 38 35 24 67 53 50 46 49 23 33 46 47 39 36 63 36 33 25 34 55 44 38 28 28 28 30 43 39 27 39 44 39 39 58 37 34 34 48 37 15 38 36 35 36 51 36 60 38 35 40 47 35 53 53 27 30 48 33 47 34 38 35 37 30 40 41 36 50 34 33 53 39 30 34 46 53 52 41 43 41 44 54 41 53 44 34 39 16 24 32 53 50 30 29 57 33 36 56 48 44 56 33 34 37 46 45 54 41 30 24 14 29 39 40 39 46 51 36 39 35 31 51 47 56 57 54 43 50 32 54 46 27 32 28 34 27 34 42 40 39 47 44 36 33 61 30 47 48 59 45 46 38 53 52 28 32 41 52 29 36 36 35 45 36 39 35 22 36 21 24 50 46 54 41 37 27 27 31 23 33 31 33 21 26 34 28 43 40 32 42 50 27 32 44 54 51 60 58 43 31 43 48 40 61 39 36 32 41 35 44 33 50 44 29 37 35 33 55 56 75 85 60 39 40 52 33 50 39 36 23 37 12 21 22 23 55 41 26 27 26 49 68 103 255 167 73 36 12 12 30 28 46 37 19 29 28 30 27 48 43 43 29 40 51 57 84 184 149 63 29 20 5 28 31 47 46 28 35 26 37 35 46 26 37 35 32 39 41 47 59 50 54 48 31 22 21 30 38 37 37 48 20 38 35 33 37 23 27 44 48 59 37 44 42 47 50 36 41 24 37 28 48 35 41 22 50 47 51 32 38 28 41 45 48 55 42 34 38 27 42 22 31 19 24 46 38 44 39 55 44 56 38 40 40 31 33 34 36 32 25 39 19 19 25 27 14 10 54 34 22 43 50 54 52 36 38 21 34 18 46 46 44 52 38 24 30 23 32 45 15 26 48 38 44 32 49 46 47 37 29 47 40 21 47 36 40 38 26 27 31 34 37 35 24 36 31 43 42 31 38 47 40 28 21 30 36 54 47 32 31 41 27 30 36 25 31 25 28 44 A(i,j) for i=1,2,3 , M; j=i=1,2,3 , N x = j - N/2 y = M/2 - i G(x,y)