Miniaturized Laser-Based Detection of Particles in Air

1Introduction1
1.1Motivation1
1.2Requirements for a miniaturized particle sensor4
1.2.1Main criteria4
1.2.1.1Sensitivity of particle size4
1.2.1.2Size and components of the system5
1.2.2Additional criteria5
1.2.3Cumulative requirements6
1.3State of the art of particle sensors6
1.3.1Scientific developments6
1.3.2Current commercial sensor systems8
1.4Thesis outline9
2Fundamentals11
2.1Optics11
2.1.1Geometrical optics11
2.1.2Laser beam intensity profile13
2.1.3Light scattering by particles16
2.1.3.1Single spherical particle, MIE theory16
2.1.3.2RAYLEIGH regime18
2.1.4Particle size identification19
2.1.4.1Amplitude-based19
2.1.4.2Intensity ratio19
2.1.4.3Influence by index of refraction21
2.1.4.4Influence by non-sphericity21
2.1.4.5Particle size distributions22
2.1.5Effects on particles by laser beams23
2.2Measurement technique26
2.2.1Signal26
2.2.2Noise27
2.2.3Signal-to-noise ratio29
2.3Fluidic behavior of aerosols30
2.3.1Gas movement30
2.3.2Forces on particles31
2.3.3Relaxation time33
2.3.4Impactor filter34
3Detection of the particle size37
3.1Definition37
3.2Description of the sensor system37
3.2.1Fundamental description37
3.2.2Components37
3.2.3Optics39
3.2.4Fluidics40
3.3Signal processing42
3.3.1Basic characteristics of scattering signals42
3.3.2Fitting43
3.3.3Time-of-flight45
3.3.4Filtering46
3.3.5Linear diversity combining46
3.3.6Scattering signal identification47
3.4Increasing the scattering signal50
3.4.1Using spherical mirrors50
3.4.1.1Alignment and configuration50
3.4.1.2Measurements54
3.4.1.3Discussion and conclusion56
3.4.2Using FRESNEL lenses58
3.4.2.1Alignment and configuration59
3.4.2.2Systematic behavior62
3.4.2.3Measurements66
3.4.2.4Discussion and conclusion68
3.5Uncertainties and possible errors69
3.5.1Optical69
3.5.2Fluidic70
3.5.3Systematic71
3.5.4Conclusion71
3.6Particle size identification72
3.7Characterization75
3.7.1Limit of miniaturization75
3.7.2Sensor behavior75
3.7.2.1Temperature compensation75
3.7.2.2Evaporation76
3.7.2.3Compensation of the spatial scattering signals variation77
3.7.2.4Spatial particle sensing efficiency79
3.7.2.5Sensor recovery81
3.7.3Particle size determination82
3.7.3.1Limit82
3.7.3.2Accuracy85
3.7.4Measurements of polydisperse particle distributions91
3.7.5Discussion and conclusion95
4Detection of the particle mass97
4.1Requirements for particle mass measurements97
4.2Impactor filter based technique98
4.2.1Characterization98
4.2.2Measurements100
4.2.3Discussion102
4.3Inertia and laser-based technique103
4.3.1Description103
4.3.2Simulation and measurements105
4.3.3Discussion108
4.4Conclusion108
5Conclusion109
5.1Summary109
5.2Outlook112
ADescription of scattering theoriesxi
A.1MIExi
A.2RAYLEIGHxv
A.3Simulation program implementationxvi
BCharacteristics of particlesxix
CCharacteristics of sensor componentsxxi
Bibliographyxxiii
Abbreviations and symbolsxxxvii
Acknowledgmentxxxix