Martellucci / Chester / Mignani Optical Sensors and Microsystems

New Concepts, Materials, Technologies
1. Auflage 2007
ISBN: 978-0-306-47099-8
Verlag: Springer US
Format: PDF
Kopierschutz: 1 - PDF Watermark

E-Book, Englisch, 312 Seiten

Proceedings of the 22nd Course of the International School of Quantum Electronics, held 27 November-2 December 1997, in Erice, Italy.

In recent years, fiber optical sensors and optical microsystems have assumed a significant role in sensing and measurement of many kinds. These optical techniques are utilised in a wide range of fields, including biomedicine, environmental sensing, mechanical and industrial measurement, and art preservation. This volume, an up-to-date survey of optical sensors and optical microsystems, aims at combining a tutorial foundation with analysis of current research in this area, and an extensive coverage of both technology and applications.

Autoren/Hrsg.

Martellucci, S.

Chester, Arthur N.

Mignani, Anna Grazia

Inhaltsverzeichnis

1;PREFACE;5
2;CONTENTS;7
3;TECHNOLOGY;10
3.1;ADVANCED OPTOELECTRONICS IN OPTICAL FIBRE SENSORS;11
3.1.1;1. INTRODUCTION;11
3.1.2;2. LASERS AND AMPLIFIERS;12
3.1.3;3. NON LINEAR OPTICS IN SENSOR SYSTEMS;14
3.1.4;4. STRANGE AND DIFFERENT PROPAGATION PHENOMENA;17
3.1.5;5. INTEGRATED OPTICS AND MICROMACHINING;20
3.1.6;6. OPTICAL SIGNAL DETECTION SYSTEMS;21
3.1.7;7. CONCLUSIONS;21
3.2;INTERFEROMETRIC DISTANCE SENSORS;23
3.2.1;1. INTRODUCTION;23
3.2.2;2. INTERFEROMETRIC DISTANCE MEASUREMENTS;23
3.2.2.1;2.1 Displacement measurements;24
3.2.3;3. DOUBLE WAVELENGTH INTERFEROMETRY;26
3.2.4;4. FREQUENCY-MODULATED INTERFEROMETRY;30
3.2.5;5. WHITE LIGHT INTERFEROMETRY;32
3.2.5.1;5.1 Optical sources for white light interferometry.;32
3.2.5.2;5.2 Mechanically scanned white light interferometer;33
3.2.5.3;5.3 Electronic-scanning white light interferometry;35
3.2.5.4;5.4 Dispersive white light interferometry;35
3.2.6;6. COMPARISON OF THE DIFFERENT TECHNIQUES;37
3.2.7;REFERENCES;38
3.3;OPTICAL TOMOGRAPHY: TECHNIQUES AND APPLICATIONS;40
3.3.1;1. INTRODUCTION;40
3.3.2;2. OPTICAL TOMOGRAPHY;42
3.3.3;3. TIME-RESOLVED IMAGING;42
3.3.4;4. FLUORESCENCE IMAGING;42
3.3.5;5. COHERENCE IMAGING;43
3.3.6;6. DIRECT TRANSILLUMINATION IMAGING;44
3.3.7;7. OPTICAL TOMOGRAPHY SCANNERS;44
3.3.8;8. CONCLUSIONS;45
3.3.9;REFERENCES;45
3.4;OPTICAL WAVEGUIDE REFRACTOMETERS;47
3.4.1;1. INTRODUCTION;47
3.4.2;2. REFRACTOMETERS FOR LIQUIDS: AN OVERVIEW ;48
3.4.2.1;2.1. Classical refractometers;48
3.4.2.2;2.2. Interferometric refractometers;49
3.4.2.3;2.3. Non conventional refractometers;49
3.4.2.4;2.4. Optical fiber refractometers;50
3.4.2.5;2.5. Waveguide refractometers;51
3.4.3;3. CERENKOV REFRACTOMETRY;52
3.4.4;4. INVERSE USE OF CERENKOV REFRACTOMETRY;55
3.4.5;5. CONCLUSIONS;56
3.4.6;REFERENCES;57
3.5;CHARACTERIZATION OF AN OPTICAL FIBRE pH SENSOR WITH METHYL RED AS OPTICAL INDICATOR;58
3.5.1;1. INTRODUCTION;58
3.5.2;2. OPTICAL FIBRE PROBE;58
3.5.3;3. SPECTROPHOTOMETRIC ANALYSIS: PHOTODEGRADATION;59
3.5.4;4. OPTICAL FIBRE SENSOR;60
3.5.5;5. IONIC STRENGTH EFFECTS;62
3.5.6;CONCLUSIONS;64
3.5.7;REFERENCES;65
3.6;OPTICAL SENSORS AND MICROSYSTEMS USING LIQUID CRYSTALS;66
3.6.1;1. INTRODUCTION;66
3.6.2;2. LIQUID CRYSTALS OPTICAL AND ELECTRO-OPTICAL PROPERTIES;67
3.6.3;3. OPTICAL SENSORS UTILISING LIQUID CRYSTALS;73
3.6.4;4. OPTICAL MICROSYSTEMS UTILISING LIQUID CRYSTALS;76
3.6.5;5. OUR EXPERIMENTAL WORK;78
3.6.6;6. CONCLUSIONS;80
3.6.7;REFERENCES;81
3.7;INDIUM TIN OXIDE FILMS FOR OPTICAL SENSORS;83
3.7.1;1. INTRODUCTION;83
3.7.2;2. CHARACTERISTICS OF INDIUM TIN OXIDE;83
3.7.3;3. DEPOSITION PROCESS;84
3.7.4;4. PHOTOCONDUCTIVE EFFECT;84
3.7.5;5. PHYSICAL INTERPRETATION OF THE OBSERVED PHENOMENA;86
3.7.6;6. REVERSIBILITY OF THE VARIATIONS OF THE RESISTIVITY AND FACTORS THAT INFLUENCE THE SPEED OF RETURN TO THE INITIAL CONDITIONS;86
3.7.7;7. POSSIBLE APPLICATIONS OF THE PHOTOCONDUCTIVE EFFECT;88
3.7.8;8. CONCLUSIONS;89
3.7.9;REFERENCES;89
3.8;OPTOELECTRONIC NEURAL NETWORKS;90
3.8.1;1. INTRODUCTION;90
3.8.2;2. OPTOELECTRONIC NEURAL PROCESSING;90
3.8.3;3. OPTOELECTRONIC NEURAL NETWORKS;92
3.8.4;4. SPATIAL LIGHT MODULATORS AND VERTICAL CAVITY SURFACE EMITTING LASERS IN NEURAL SYSTEMS;94
3.8.5;5. OPTOELECTRONIC NEURAL SYSTEM FOR OPTICAL SENSOR SIGNAL PROCESSING;95
3.8.6;6. RESULTS OF EXPERIMENTS;97
3.8.7;7. CONCLUSIONS;99
3.8.8;REFERENCES;99
3.9;COMPLEX ABCB-MATRICES: A GENERAL TOOL FOR ANALYZING ARBITRARY OPTICAL SYSTEMS;100
3.9.1;1. INTRODUCTION;100
3.9.2;2. COMPLEX ABCD-MATRICES;101
3.9.3;3. SPACE-TIME LAGGED COVARIANCE FOR COMPLEX ABCD SYSTEMS;104
3.9.4;4. LASER DOPPLER AND LASER TIMEOF-FLIGHT VELOCIMETERS;108
3.9.5;5. OUT-OF-PLANE ANGULAR DISPLACEMENT;110
3.9.6;6. IN-PLANE ANGULAR DISPLACEMENTS;113
3.9.7;7. TORSION ANGLE SENSOR;114
3.9.8;8. ROTATIONAL SPEED AND TORSIONAL VIBRATIONS OF A ROTATING SHAFT;114
3.9.9;9. CONCLUSION;116
3.9.10;REFERENCES;117
3.10;MICROSYSTEMS AND RELATED TECHNOLOGIES;118
3.10.1;1. INTRODUCTION;118
3.10.2;2. OVERVIEW OF TECHNOLOGIES SUITABLE FOR MICROSYSTEMS. ;119
3.10.2.1;2.1 Bulk Micromachining;119
3.10.2.2;2.2 Surface Micromachining;121
3.10.2.3;2.3 Mold Micromachining;123
3.10.2.4;2.4 Porous silicon;124
3.10.2.5;2.5 Gallium arsenide: an interesting material for micromechanics;125
3.10.2.6;2.6 Thin film technology;126
3.10.3;3. AN EXAMPLE OF MICROSTRUCTURES : A MICROHEATER ARRAY FOR SELECTIVE GAS SENSING ;126
3.10.3.1;3.1 Design and simulation;126
3.10.3.2;3.2 Device fabrication and performance;129
3.10.4;4. CONCLUSIONS;130
3.10.5;REFERENCES;130
3.11;THE STRETCH-AND-WRITE TECHNIQUE FOR FABRICATION OF FIBER BRAGG- GRATING ARRAYS;132
3.11.1;1. INTRODUCTION;132
3.11.2;2. FBG-ARRAY FABRICATION AND CHARACTERIZATION;133
3.11.3;3. FBG SENSING APPLICATIONS;135
3.11.4;4. FBG-ARRAYS FOR TELECOMMUNICATION SYSTEMS;135
3.11.5;5. CONCLUSIONS;137
3.11.6;REFERENCES;138
4;APPLICATIONS;139
4.1;FLUORESCENCE LIFETIME-BASED SENSING FOR BIOPROCESS AND BIOMEDICAL APPLICATIONS;140
4.1.1;1. INTRODUCTION;140
4.1.2;2. pCO2 RESONANCE ENERGY TRANSFER SENSOR;141
4.1.3;3. pCO2 SENSOR FABRICATION;142
4.1.4;REFERENCES;143
4.2;A PIEZOELECTRIC BIOSENSOR AS A DIRECT AFFINITY SENSOR;144
4.2.1;1. INTRODUCTION;144
4.2.2;2. SENSOR PRINCIPLE;144
4.2.2.1;2.1. Measurement of the Resonant Frequency;145
4.2.2.2;2.2. Measurement Procedure;145
4.2.2.3;2.3. Chemicals;146
4.2.3;3. ADSORPTION EXPERIMENTS;146
4.2.4;4. AFFINITY SENSING EXPERIMENT;147
4.2.4.1;4.1. Covalent immobilization of the 2,4-D:;148
4.2.4.2;4.2. Modification of the 2,4-D for coupling;148
4.2.5;5. CONCLUSIONS;150
4.2.6;REFERENCES;150
4.3;THE COMPLEX PHASE TRACING BASED SHAPE EVALUATION SYSTEM FOR ORTHOPAEDIC APPLICATION;152
4.3.1;1. INTRODUCTION;152
4.3.2;2. PRINCIPLE OF THE MEASUREMENT;153
4.3.3;3. COMPLEX PATTERN RECONSTRUCTION AND CORRECTION OF THE PHASE ERROR;155
4.3.4;REFERENCES;158
4.4;OPTICAL FIBRE CHEMICAL SENSORS FOR ENVIRONMENTAL AND MEDICAL APPLICATIONS;159
4.4.1;1. INTRODUCTION;159
4.4.2;2. SENSING PRINCIPLES;160
4.4.2.1;2.1 Absorption;160
4.4.2.2;2.2 Fluorescence;161
4.4.2.3;2.3 Plasmon Resonance;163
4.4.2.4;2.4 Raman Scattering;163
4.4.2.5;2.5 Chemiluminescence;164
4.4.3;3. THE PROBE AND THE OPTICAL LINK;164
4.4.3.1;3.1 Sensing Mechanisms;164
4.4.3.2;3.2 The Probe;165
4.4.3.3;3.3 The Optical Link;166
4.4.4;4. OPTICAL FIBRE SENSORS FOR ENVIRONMENTAL APPLICATIONS;167
4.4.4.1;4.1 Pesticides;167
4.4.4.2;4.2 Hydrocarbons and Related Derivatives;170
4.4.4.3;4.3 Biological Oxygen Demand;172
4.4.5;5. OPTICAL FIBRE SENSORS FOR BIOMEDICAL APPLICATIONS;173
4.4.5.1;5.1 Bile;173
4.4.5.2;5.2 pH;174
4.4.5.3;5.3 Oxygen;178
4.4.5.4;5.4 Carbon Dioxide;179
4.4.6;6. CONCLUSIONS;180
4.4.7;REFERENCES;180
4.5;INTRODUCTION TO THE MULTICOMPONENT ANALYSIS WITH ARRAYS OF NON- SELECTIVE CHEMICAL SENSORS;183
4.5.1;1. INTRODUCTION;183
4.5.2;2. QUANTITATIVE ANALYSIS;185
4.5.2.1;2.1 Chemometrics;186
4.5.2.1.1;2.1.1 Multiple Linear Regression:;188
4.5.2.1.2;2.1.2 Principal Component Regression:;188
4.5.3;3. QUALITATIVE ANALYSIS (ELECTRONIC NOSE);188
4.5.4;4. SELF ORGANIZING MAP (SOM);190
4.5.4.1;4.1 Tools for Sensor Array Modeling and Data Analysis;191
4.5.4.1.1;4.1.1 Data classification:;191
4.5.4.1.2;4.1.2 Evaluation of single sensors contribution:;191
4.5.4.1.3;4.1.3 Sensor drift effects:;191
4.5.5;REFERENCES;192
4.6;HIGH SENSITIVITY TRACE GAS MONITORING USING SEMICONDUCTOR DIODE LASERS;193
4.6.1;1. INTRODUCTION;193
4.6.1.1;1.1 Detector noise;194
4.6.1.2;1.2 Laser Excess Noise;195
4.6.1.3;1.3 Residual Amplitude Modulation;196
4.6.1.4;1.4 Interference Fringes;196
4.6.1.5;1.5 Detection Techniques;197
4.6.1.6;1.6 Bandwidth reduction;198
4.6.2;2. EXPERIMENTAL SET-UP;199
4.6.3;3. RESULTSANDDISCUSSION;201
4.6.3.1;3.1 Ammonia NH3;201
4.6.3.2;3.2 Carbon Monoxide CO, Carbon DioxideCO2 and Hydrogen SulphideH2S;201
4.6.3.3;3.3 Molecular Oxygen O2;201
4.6.3.4;3.4 Hydrogen Chloride HCl;202
4.6.4;4. CONCLUSION;202
4.6.5;REFERENCES;203
4.7;OPTICAL FIBER SENSORS FOR THE NUCLEAR ENVIRONMENT;204
4.7.1;1. INTRODUCTION;204
4.7.2;2. POTENTIAL NEEDS FOR OFS(N) IN NUCLEAR POWER PLANTS ;204
4.7.2.1;2.1 The Nuclear Fuel Cycle : From Mining to Waste Conditioning;204
4.7.2.2;2.2 Nuclear Power Plant instrumentation improvement;204
4.7.3;3. ANALYSIS & EXPERIMENTS OF SOME OFS & OFSN FOR NPP;205
4.7.3.1;3.1 Nuclear shield monitoring ;206
4.7.3.1.1;3.1.1 Bragg gratings for structure monitoring.;206
4.7.3.1.2;3.1.2 Sensitivity of Bragg gratings to main physical parameters.;207
4.7.3.1.3;3.1.3 Bragg grating behaviour under .-ray irradiation.;207
4.7.3.1.4;3.1.4 Bragg grating extensometer' experiments with concrete.;208
4.7.3.2;3.2 Hydrogen risk ;214
4.7.3.2.1;3.2.1 Motivations for safety.;214
4.7.3.2.2;3.2.2 "H2 risk" monitoring system specifications.;214
4.7.3.2.3;3.2.3 System development and experiments.;214
4.7.3.2.4;3.2.4 Experimental.;215
4.7.3.2.5;3.2.5 Conclusion.;216
4.7.3.3;3.3 Steam pipe monitoring;218
4.7.3.3.1;3.3.1 OTDR Method.;219
4.7.3.3.2;3.3.2 In-Fiber Bragg Grating technology.;219
4.7.3.4;3.4 Nuclear radiation detection;220
4.7.3.5;3.5 Waste conditioning and disposal monitoring;221
4.7.4;4. CONCLUSION;223
4.7.5;REFERENCES;223
4.8;CRLORINATED HYDROCARBONS TRACE DETECTION IN WATER BY SPARGING AND LASER IR GAS PHASE DETECTION;226
4.8.1;1. INTRODUCTION;226
4.8.2;2. GENERAL ABOUT THE SPARGING TECHNIQUE;226
4.8.3;3. PROJECT DEVELOPMENTS AT TRI LAB;227
4.8.4;4. CONCLUSIONS;231
4.8.5;LEGENDA OF SYMBOLS;232
4.8.6;REFERENCES;232
4.9;HOLLOW CORE FIBER GUIDES AS GAS ANALYSIS CELLS FOR LASER SPECTROSCOPY;234
4.9.1;1. INTRODUCTION;234
4.9.2;2. TDLAS EXPERIMENTS WITH HOLLOW WAVEGUIDES GAS CELLS ( IRGAS PROJECT, TRI LAB);235
4.9.3;3. CONCLUSIONS;238
4.9.4;REFERENCES;238
4.10;CHEMILUMINESCENCE IMAGING OF PLANT ORIGIN MATERIALS;240
4.10.1;1. INTRODUCTION;240
4.10.2;2. MATERIALS AND METHODS ;241
4.10.2.1;2.1 Instrumentation;241
4.10.2.1.1;2.1.1 Single photon counting imaging.;241
4.10.2.1.2;2.1.2 Spectral analysis.;242
4.10.2.2;2.2 Methods;244
4.10.3;3. RESULTS AND DISCUSSION ;245
4.10.3.1;3.1 CL of cereal food products;245
4.10.3.2;3.2 Photoinduced Chemiluminescence of wood;247
4.10.4;4. CONCLUSIONS;250
4.10.5;REFERENCES;250
4.11;OPTICAL FIBER SENSORS FOR THE CULTURAL HERITAGE;251
4.11.1;1. INTRODUCTION;251
4.11.2;2. OPTICAL FIBERS FOR MONITORING THE EFFECTS OF TEMPERATURE ON PICTURE VARNISHES;251
4.11.3;3. THE MONITORING OF LIGHTING IN MUSEUM ENVIRONMENTS BY MEANS OF OPTICAL FIBERS;254
4.11.4;4. CONCLUSIONS;255
4.11.5;REFERENCES;256
4.12;FIBER OPTICS REFLECTANCE SPECTROSCOPY: A NON- DESTRUCTIVE TECHNIQUE FOR THE ANALYSIS OF WORKS OF ART;257
4.12.1;1. INTRODUCTION;257
4.12.2;2. EXPERIMENTAL;258
4.12.3;3. PIGMENT IDENTIFICATION;259
4.12.4;4. CONCLUSION;261
4.12.5;REFERENCES;263
4.13;OPTICAL DIAGNOSTIC SYSTEMS AND SENSORS TO CONTROL LASER CLEANING OF ARTWORKS;264
4.13.1;1. INTRODUCTION;264
4.13.2;2. THE CLEANING PROCESS;264
4.13.3;3. IMAGE DIAGNOSTICS;266
4.13.3.1;3.1. Analysis ;267
4.13.3.1.1;3.1.1. QS pulses.;267
4.13.3.1.2;3.1.2. SFR pulses.;269
4.13.4;4. OPTICAL SENSOR;271
4.13.5;REFERENCES;271
4.14;ELECTRO-OPTICAL SENSORS FOR MECHANICAL APPLICATIONS;272
4.14.1;1. INTRODUCTION;272
4.14.2;2. E-O SENSORS IN MECHANICAL INDUSTRY: RATIONALE;273
4.14.3;3. EXAMPLES OF APPLICATIONS OF ELECTROOPTIC SENSORS TO MECHANICAL MEASUREMENTS ;274
4.14.3.1;3.1 Dimensional control;274
4.14.3.2;3.2 Tests of surface properties of industrial manufacts;276
4.14.3.3;3.3. 3-D Macro- and Microprofilometry;276
4.14.3.4;3.4. Color measurements;278
4.14.4;4. PERSPECTIVES;278
4.14.5;REFERENCES;286
4.15;OPTICAL FIBRES AND THEIR ROLE IN SMART STRUCTURES;287
4.15.1;1. INTRODUCTION;287
4.15.2;2. THE MEASUREMENT REQUIREMENTS - SENSING ON A LARGE SCALE;290
4.15.3;3. THE MEASUREMENT PROCESS - POINT DISTRIBUTED AND QUASI DISTRIBUTED SENSING;291
4.15.4;4. WHY USE FIBRE OPTICS;292
4.15.5;5. PHYSICAL MEASUREMENTS - STRAIN AND TEMPERATURE FIELDS;292
4.15.6;6. CHEMICAL MEASUREMENTS IN STRUCTURAL MONITORING – SAFETY AND CORROSION;296
4.15.7;7. CONCLUSIONS;299
4.15.8;REFERENCES;300
4.16;ALL OPTICAL FIBER ULTRASONIC SOURCES FOR NON DESTRUCTIVE TESTING AND CLINICAL DIAGNOSIS;302
4.16.1;1. INTRODUCTION;302
4.16.2;2. THEORETICALBACKGROUND;303
4.16.3;3. FIBER OPTIC ULTRASONIC SOURCE DESIGN;305
4.16.4;4. EXPERIMENTAL SETUP AND RESULTS;306
4.16.5;5. CONCLUSION;310
4.16.6;REFERENCES;310
5;INDEX;311

Leseproben

COMPLEX ABCB-MATRICES: A GENERAL TOOL FOR ANALYZING ARBITRARY OPTICAL SYSTEMS (p. 97-98)


1. INTRODUCTION

In this paper, we describe a novel formulation of light beam propagation through any complex optical system that can be described by an ABCD ray-transfer matrix.1,2 Within the framework of complex ABCD-optical systems, we then present novel speckle methods for analyzing linear and angular velocities and displacements. All methods rely on the dynamics of speckle patterns, produced by scattering of coherent light off solid surfaces undergoing angular and/or translational displacements.

Coherent light scattered off a rough surface produces a granular diffraction pattern some distance away from the object. This pattern is referred to as speckles,3 and originates from elementary interference of the waves emanating from many microscopic areas on the surface within the illuminated region. If the illuminated object is in motion, the resulting speckle pattern also evolves with time, i.e., a dynamical speckle pattern results. The target motion or displacement is usually determined by calculating the space- or time-lagged covariance of the detector currents before and after object displacement: and then determine the position where the peak of the covariance attains its maximum.

We first present the basic properties of the ABCD ray-matrix method,1,2 and summarize raymatrices for Simple optical elements,5 e.g., thin lenses, mirrors, and free-space propagation. Additionally, we present the ray-transfer matrix for a Gaussian shaped aperture.1,2 Thus, armed with matrix elements describing the most common elements in an optical system, the resulting ray-transfer matrix can be obtained for most systems encountered in practice. The resulting raytransfer matrix connects the input ray position and slope with the corresponding output parameters. Rather than dealing with rays, a Gaussian Green’s function has been developed,1,2 valid for arbitrary ABCD systems, to reveal the transition of the field in the input plane, through the ABCD-optical system, to the output plane.

Armed with the Green’s function that reveals the field in the output plane of an arbitrary ABCD-system, provided the field in the input plane is known, we then present a general equation, valid for arbitrary ABCD-optical systems, for the space-time lagged covariance of photocurrent: The position where the Gaussian-shaped covariance attains its maximum reveals information about target velocity or displacement. We discuss, how, in practice, the target velocity/ displacement is assessed. The theoretical results alluded to above are then applied to a series of novel optical sensor applications, all described by the ABCD kernel.

Two systems for measuring hear velocities, viz. the laser Doppler velocimeter6 and the laser time-of-flight velocimeter,7,8 are presented. A compact system for measuring linear surface velocities is presented, where all passive optical components are replaced with a single holographic optical element.9 Additionally, other novel schemes for further system miniaturization are presented.

We then present a new method for measurement of out-of-plane angular displacement in one or two dimensions.12,13 It is demonstrated that the angular displacement sensor is insensitive to both object shape and target distance, and any transverse or longitudinal movements of the target. It is further shown that the method has a resolution of 0.3 mdeg (5 µrad). A new method for measuring in-plane angular velocities or displacements are then presented.14 Here, we consider off-axis illumination, and it is shown that, for Fourier transform optical systems, in-plane rotation causes the speckles to translate in a direction perpendicular to the direction of surface motion, whereas for an imaging system, the translation is parallel to the direction of surface motion. Based on this, we discuss a novel method, which is independent of both the optical wavelength and the position of the laser spot on the object, for determining either the angular velocity or the corresponding in-plane displacement of the target object. The out-of-plane angular displacement sensor can be modified to measure the distribution of static torsion angles of targets undergoing twisting motion.15 Because the torsion angle sensor is independent of object shape, we measure the distribution of torsion angles in both uniform and non-uniform deformation zones.

Finally, we present a novel method for measuring out-of-plane angular velocities. Besides measuring angular velocities, the sensor can measure, simultaneously, torsional vibrations of the rotating shaft.