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Mingyu Kang Team Korea Hearing Light
Problem Statement Connected to AC Drilled hole Layer of soot
Soot absorbs light Absolutely opaque: ALL light is absorbed
Explanation #1: Thermal Vibration Allan Rosencwaig and Allen Gersho, Theory of the photoacoustic effect with solids, Journal of Applied Physics (Jan. 1976), vol. 47, No. 1
Explanation #2: Mechanical Vibration Soot itself expands and contracts! F. Alan McDonald, Photoacoustic effect and the physics of waves, American Journal of Physics (Jul. 1979), vol. 48
What 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- controllable Lightbulb Microphone Jar + Soot Empty Jar
Recorded Sound Sample rate: /s
Frequency-Domain Graph : Jar with soot : Empty jar (noise)
Frequency-Domain Graph 120hz 240hz 360hz Harmonics!
Light intensity – 120hz peak intensity Graph
Helmholtz Resonance Resonance frequency of AIR inside the jar
Parameter control for various jars Slide-glass covered with soot
Helmholtz Frequencies of jars RESONANCE!
Sound produced in various jars
Another method to change Helmholtz Frequency: Neck Length
Sound produced by jars of different neck length
1.Frequency Control 2.Extract only the sound produced by light New Experiment Setting!
Preliminary Experiment Setting
Stroboscope Experiment Setting Stroboscope
Flash frequency – Fundamental sound frequency graph
Limits of Stroboscope Setting Glass blocks ultraviolet rays Noise caused by jar itself
Revised Experiment Setting
Recorded Sound : Slide glass with soot : Empty slide glass (noise)
Zoom-in! silence IMPACT! stroboscope noise 5~7 small vibrations damping silence
Sound caused by only light
Speed Camera Resolution 32×32 Sample rate /s Duration of Stroboscope Flash
Flash at what point? stroboscope noise
Experiment on Flash Time Light sensor Sound sensor
Time gap between sound and light Sound sensor Light sensor
So the flash is at….. stroboscope noise s
Similar waveform! Sharp pencil broken Flash - soot
Samples of various powders SootActivated Carbon Graphite (Grained pencil lead) Charcoa l Iron
Sound from various powders Soot 3.8 Activated Carbon 0.90 Graphite 0.86 Charcoal 0.76 Iron 0.40
Sample of powder and chunk Charcoal powder Charcoal chunk
Powder VS Chunk Powder 0.76 Chunk 0.34
Sample of powder and lubricant Graphite powder Graphite lubricant
Powder VS Lubricant Graphite Powder 0.86 Graphite Lubricant ?
Samples of various surfaces PaperMarker Vinyl Plastic
Sound from various surfaces Paper 0.1 Marker 0.1 Vinyl 0.1 Plastic ?
Mechanism of heat conduction Something special about C
Hypothesis for Photoacoustic Mechanism Mechanical Vibration (sample) Thermal Vibration (air)
Thermal expansion coefficient
Porous Structure of Soot SEM
Porous Structure of Soot LARGE Sound!
Plane Structure of Graphite Lubricant
Conclusion Absorption Mechanical Vibration Thermal Vibration Helmholtz Frequency } Pores !
[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 Code FFT Number determined!
Heat vibration caused by lightbulb offon
Microphone inside the jar
Microphone position and Resonance effect
Stroboscope sound has not arrived Fast reaction!
FFT: Sound caused by only light
Depth of soot is not important Soot is opaque -> All light is absorbed!
Effect of heat from lightbulb (justification) Sound absorption due to thermal conduction (fundamentals of acoustics)
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