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Problem # 7. Hearing Light. Mingyu Kang. Team Korea. Problem Statement. Drilled hole. Connected to AC. Layer of soot. DISTINCT SOUND?. W HY does the sound occur?. Soot absorbs light. Absorption coefficient ( : depth through sample). Absolutely opaque: ALL light is absorbed. - PowerPoint PPT Presentation
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Mingyu KangTeam Korea
Hearing LightProblem #7
Problem Statement
DISTINCT SOUND?Connected to ACDrilled holeLayer of soot
WHY does thesound occur?Soot absorbs lightAbsolutely opaque: ALL light is absorbed ! !4Explanation #1: Thermal VibrationConductionAllan Rosencwaig and Allen Gersho, Theory of the photoacoustic effect with solids, Journal of Applied Physics (Jan. 1976), vol. 47, No. 1
SOUNDCONDUCTIONRadiation radiation radiation !
: excitation (of molecules) : NONRADIATIVE DEEXCITATION5Explanation #2: Mechanical Vibration
Soot itselfexpands and contracts!F. Alan McDonald, Photoacoustic effect and the physics of waves, American Journal of Physics (Jul. 1979), vol. 48SOUNDWhat is the frequency?Manfred Euler, Hands-On Resonance-Enhanced Photoacoustic Detection, Physics Teacher (Oct. 2011), vol. 39
Blink twice at each AC wave!AC Bulb Experiment Setting
Power-controllableLightbulbMicrophoneJar + SootEmpty Jar
Recorded SoundFast Fourier TransformSample rate: 192000 /sLightbulb power: 500W9
Frequency-Domain Graph: Jar with soot: Empty jar (noise) y amplitude (!20hz peak ) y noise .( noise 120hz )Sensitivity is different according to frequencyFFT: UNIT!!!!!!! Fft .
10
Frequency-Domain Graph120hz240hz360hzHarmonics! peak ?Harmonics: mode of Helmholtz resonance(240Hz dies away quickly why jar does not resonate in 240hz)11Light intensity 120hz peak intensity GraphWhat is therole of the JAR?Helmholtz ResonanceResonance frequency ofAIR inside the jarLeff = L + 1.45r14
Various jars
Parameter control for various jarsSlide-glass coveredwith soot
Helmholtz Frequencies of jarsRESONANCE!Sound produced in various jars
Another method to change Helmholtz Frequency: Neck Length
Sound produced by jars of different neck lengthFrequency ControlExtract only the sound produced by light
New Experiment Setting!
Preliminary Experiment Setting
Stroboscope Experiment SettingStroboscopeFlash frequency Fundamental sound frequency graphLimits of Stroboscope Setting
Glass blocksultraviolet raysNoise causedby jar itself
Revised Experiment Setting
Fundamental Approach
WaveformMaterial strobo !27
Recorded Sound: Slide glass with soot: Empty slide glass (noise)
50Hz chopping frequencyDoes silence always happen?
plot28
Zoom-in!silenceIMPACT!stroboscope noise5~7 small vibrationsdampingsilenceEmpty slideglassAlways the same waveform prove (in one sound, and even in different mateirals)Strobo electrical signalMic response time20000Hz damping?!Sound sensor photodetector time gap (triggering)Dephase decay Decay lorenz curve fit or gaussian curve fit dephase frequency (47Hz)
Small vibration
stroboscope noise 29
Sound caused by only lightSpeed Camera Resolution 3232 Sample rate 83333 /s
Duration of Stroboscope Flash
frequency 31
Flash at what point?stroboscope noiseAMPLITUDEShockwave!!!!1!!!!!! 32
Experiment on Flash Time
Light sensorSoundsensor
Time gap between sound and lightSound sensor0.00124s
Light sensor sound sensor soot.wav stroboscope noise ? , amplitude flash 0.00005 light sensor ? 5V maximum 34
So the flash is at..stroboscope noise0.00124s
Shockwave?Shock waves are characterized by an abrupt, nearly discontinuous change in the characteristics of the medium.Across a shock there is always an extremely rapid rise inpressure,temperatureanddensityof the flow.36
Similar waveform!
Sharp pencil brokenFlash - soot
?Samples of various powdersSootActivatedCarbonGraphite(Grained pencil lead)CharcoalIron
Sound from various powders
Soot3.8ActivatedCarbon0.90Graphite0.86Charcoal0.76Iron0.40Sample of powder and chunk CharcoalpowderCharcoalchunk
Powder VS Chunk
Powder0.76Chunk0.34
Sample of powder and lubricantGraphite powder Graphite lubricantPowder VS Lubricant
GraphitePowder0.86
GraphiteLubricant?
Samples of various surfacesPaperMarkerVinylPlastic
Sound from various surfaces
Paper0.1Marker0.1Vinyl0.1Plastic? !46Mechanism of heat conductionSomething special about
C
Hypothesis for Photoacoustic MechanismMechanical Vibration(sample)ThermalVibration(air)POP!Thermal conductivitySpecific heat
49Thermal expansion coefficient
Porous Structure of SootSEM
Porous Structure of Soot
LARGESound!Plane Structure of Graphite Lubricant
Plane Structure of Graphite Lubricant
NOSound!ConclusionAbsorptionMechanicalVibrationThermalVibrationHelmholtzFrequency120Hz}RESONANCE!Pores!
Thank You
[nSamples, nChannels]=size(data);data=data*20;waveFileLength=nSamples/fs;N=2^(nextpow2(nSamples));Y=fft(data(:,1),N);NumbUniquePts=ceil((N+1)/2);Y=Y(1:NumbUniquePts);P=abs(Y)/waveFileLength;f=(0:NumbUniquePts-1)*fs/N;plot (f,P)xlabel('Frequency (Hz)')ylabel('Sound Intensity (Arbitrary Unit)')axis([0, 400, 0, 10000])MATLAB FFT CodeFFT Number determined!
Heat vibration caused by lightbulb30313233offon
Microphone inside the jar!59Microphone position and Resonance effectRESONANCE!
Stroboscope sound has not arrivedFast reaction!
FFT: Sound caused by only lightDepth of soot is not importantSoot is opaque -> All light is absorbed!Effect of heat from lightbulb (justification)Sound absorption due to thermal conduction (fundamentals of acoustics)