PowerPoint

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)