Miniaturized laser-based detection of particles in air

1 Introduction 1 1.1 Motivation 1 1.2 Requirements for a miniaturized particle sensor 4 1.2.1 Main criteria 4 1.2.1.1 Sensitivity of particle size 4 1.2.1.2 Size and components of the system 5 1.2.2 Additional criteria 5 1.2.3 Cumulative requirements 6 1.3 State of the art of particle sensors 6 1.3.1 Scientific developments 6 1.3.2 Current commercial sensor systems 8 1.4 Thesis outline 9 2 Fundamentals 11 2.1 Optics 11 2.1.1 Geometrical optics 11 2.1.2 Laser beam intensity profile 13 2.1.3 Light scattering by particles 16 2.1.3.1 Single spherical particle, MIE theory 16 2.1.3.2 RAYLEIGH regime 18 2.1.4 Particle size identification 19 2.1.4.1 Amplitude-based 19 2.1.4.2 Intensity ratio 19 2.1.4.3 Influence by index of refraction 21 2.1.4.4 Influence by non-sphericity 21 2.1.4.5 Particle size distributions 22 2.1.5 Effects on particles by laser beams 23 2.2 Measurement technique 26 2.2.1 Signal 26 2.2.2 Noise 27 2.2.3 Signal-to-noise ratio 29 2.3 Fluidic behavior of aerosols 30 2.3.1 Gas movement 30 2.3.2 Forces on particles 31 2.3.3 Relaxation time 33 2.3.4 Impactor filter 34 3 Detection of the particle size 37 3.1 Definition 37 3.2 Description of the sensor system 37 3.2.1 Fundamental description 37 3.2.2 Components 37 3.2.3 Optics 39 3.2.4 Fluidics 40 3.3 Signal processing 42 3.3.1 Basic characteristics of scattering signals 42 3.3.2 Fitting 43 3.3.3 Time-of-flight 45 3.3.4 Filtering 46 3.3.5 Linear diversity combining 46 3.3.6 Scattering signal identification 47 3.4 Increasing the scattering signal 50 3.4.1 Using spherical mirrors 50 3.4.1.1 Alignment and configuration 50 3.4.1.2 Measurements 54 3.4.1.3 Discussion and conclusion 56 3.4.2 Using FRESNEL lenses 58 3.4.2.1 Alignment and configuration 59 3.4.2.2 Systematic behavior 62 3.4.2.3 Measurements 66 3.4.2.4 Discussion and conclusion 68 3.5 Uncertainties and possible errors 69 3.5.1 Optical 69 3.5.2 Fluidic 70 3.5.3 Systematic 71 3.5.4 Conclusion 71 3.6 Particle size identification 72 3.7 Characterization 75 3.7.1 Limit of miniaturization 75 3.7.2 Sensor behavior 75 3.7.2.1 Temperature compensation 75 3.7.2.2 Evaporation 76 3.7.2.3 Compensation of the spatial scattering signals variation 77 3.7.2.4 Spatial particle sensing efficiency 79 3.7.2.5 Sensor recovery 81 3.7.3 Particle size determination 82 3.7.3.1 Limit 82 3.7.3.2 Accuracy 85 3.7.4 Measurements of polydisperse particle distributions 91 3.7.5 Discussion and conclusion 95 4 Detection of the particle mass 97 4.1 Requirements for particle mass measurements 97 4.2 Impactor filter based technique 98 4.2.1 Characterization 98 4.2.2 Measurements 100 4.2.3 Discussion 102 4.3 Inertia and laser-based technique 103 4.3.1 Description 103 4.3.2 Simulation and measurements 105 4.3.3 Discussion 108 4.4 Conclusion 108 5 Conclusion 109 5.1 Summary 109 5.2 Outlook 112 A Description of scattering theories xi A.1 MIE xi A.2 RAYLEIGH xv A.3 Simulation program implementation xvi B Characteristics of particles xix C Characteristics of sensor components xxi Bibliography xxiii Abbreviations and symbols xxxvii Acknowledgment xxxix