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DISTANCE DETECTIONEE 594 - Consumer OptoelectronicsDave VuMarch 17, 1999MOTIVATION• My Motives– Concept is simple• Why others may be interested– Distance/Velocity measurement is an essentialtool in many commercial and militaryapplications– Endless possibilities for future developmentand researchOVERVIEW• Many ways to detect distances using wavepropagation properties– visible light ( 380 - 770 nm)– infrared ( > 800 nm)– microwaves ( > 4000nm)• Best Detection Method depends on Level ofDetection desired– Application Specific: Range of distancedesired? Error allowed? Coherent Signals?Pros/Cons?Laser SourcesBASIC CONCEPT• Emitter: Direct a beam at approaching orreceding object• Receiver: Portion of beam is reflected andreceived by Detection Unit• Translation of Signal– Point Light Source: Flux Dens ∝ 1/distance2– Lasers: Time dependent using ‘c’ as reference; Distance = RT / 2– Interferometry: Phase Difference ∝ Distance– Microwaves: ∆ Frequency ∝ velocityPOINT SOURCEFlux Density = I / d2POINT SOURCE ERRORINTERFEROMETRY•Used for very small distances•Phase Difference and Position•Coherency: same wavelength and phase•Other Applications:Stress/Stain AnalysisMOIRE EFFECT• Mechanical Interference of light bysuperimposed network of linesIncident LightMaster Grating (reference)Specimen Grating (object)Actual Transmitted LightX = N * p ; where N = Order p = pitch of masterN=0 N=1N=1/2SPEED DETECTION• Radar Microwaves– Supported by the Doppler Effect:• ∆ Frequency ∝ velocity• beam of microwave energy (~9000-28000nm) hits target and aportion of it is reflected• reflected beam is shifted in frequency proportional to velocityof target => Signal Processing– Scatterability• Lasers– Similar concept as radar except:• Coherent light source• sample of change in distance over a period of time– Accuracy of reading are affected by:• halogen lamps,weather,reflection and refraction of beamAPPLICATIONS• Commercial– Vehicles, Speed Regulation– Personal use: Room Dimensions– Maufacturing, Robotics• Military– Positioning / Locating applications• Education/Research– NASA/NSF: Shuttle missions, measurement ofdistance in other mediums (ie. atmospheres,space)SUMMARY• General concept with lots of potential• Many ways of interpreting andmanipulating signals• The method we use to analyze it reliesheavily on the requirements of theapplicationREFERENCES• General Laser Reference Sites– http://www.fastguy.com/– http://www.intl-light.com/handbook• Laser measurement– http://www.renishaw.com/laserscale/• Position Determination Using Lasers– http://on-trak.com/psd• Laser Range Finders (LIDAR)– http://www.meos.com/_Pages/EXP15-ENG-NAV.htm– http://ranier.oact.hq.nasa.gov/Sensors_page/Laser/LaserOV.html– http://www.ksc.nasa.gov/shuttle/missions/sts-64/mission-sts-64.html• Distance Detection Using Interferometric Techniques–


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UB EE 594 - DISTANCE DETECTION

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