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INSTITUTE OF PHYSICS SERIES ON SENSORS THIN FILM MAGNETORESISTIVE SENSORS ISBN 0 7503 0702 1 IOP Publishing Ltd. 2001 Bristol and Philadelphia CONTENTS 1 AMR SENSORS 1.1 Anisotropic magnetoresistive effect in thin ferromagnetic films 1 1.1.1. Essential information about the magnetoresistive effects 1 1.1.2. The origin of anisotropic magnetoresistance in ferromagnetic metals 81.1.3. The theory of magnetoresistance in ferromagnetic metals 12 1.1.4. Thin ferromagnetic film as the magnetic field sensor 17
1.1.5.
Applying the Stoner-Wohlfarth model for analysis of 1.2. Biasing and stabilizing techniques 27
1.2.1.
The biasing and stabilizing fields in ferromagnetic 1.2.2. The real thin film – the multidomain structure and the dispersion of anisotropy 33 1.2.3. The sensors biased by the hard magnetic layer 45 1.2.4. The sensors biased by the current conducting layer 52 1.2.5. Biasing by exchange coupled antiferromagnetic layer 58 1.2.6. The soft adjacent layers (SAL) biasing technique 63 1.2.7. Dual element sensors 70 1.2.8. AC biasing techniques 76 1.2.9. The reverse mode of biasing 81 1.3. Design and performances of AMR sensors 83 1.3.1. The influence of the sample geometry on the MR effect 83 1.3.2. The influence of magnetization non-uniformity on the MR effect 89 1.3.3. Technological factors affecting the performances of AMR sensors 97 1.3.4. The design and construction of AMR sensors 115 1.3.5. The performances of AMR sensors 132 1.4. References 159
2. GMR SENSORS2.1. Giant magnetoresistive effects 165 2.1.1. An historical review and the main terms 165 2.1.2 Oscillatory exchange coupling in the magnetic multilayers 173 2.1.3. Other coupling effects in multilayer structures 185 2.1.4. Theoretical models of giant magnetoresistance 191 2.1.5. Ferromagnetic multialayers as magnetic field sensors 199 2.2. Various types of GMR structures 209 2.2.1. Structures with aniferromagnetic coupling 209 2.2.2. Granular GMR structures 217 2.2.3. Spin valve structures with asymmetric magnetic layers (uncoupled structures) 222 2.2.4. Spin valve structures with exchange biased layer 229 2.2.5. Current perpendicular to plane (CPP) structures 241 2.2.6. Magnetic tunnel junction (MTJ) structures 247 2.2.7. Colossal magnetoresistance (CMR) thin film structures 251 2.2.8. Giant magnetoimpedance (GMI) structures 256 2.3. Preparation, design and performances of GMR sensors 260 2.3.1. The deposition of thin film GMR structures 260 2.3.2. Technological factors affecting the performances of GMR sensors 266 2.3.3. The shape effects in thin film GMR devices 276 2.3.2. Design and construction of GMR sensors 286 2.4. References 299
3. APPLICATIONS OF THE MAGNETORESISTIVE SENSORS 3.1. Magnetic measurements 325 3.1.1. Magnetometers and compasses 325 3.1.2 Gradiometers, magnetic anomaly detection 336 3.2. Electrical measurements 341 3.3. Current transducers 341 3.4. Electrical transducers, switching and logic elements 347 3.3. Magnetoresistive elements in data storage applications 353 3.3.1. Magnetic Random Access Memory (MRAM) devices 353 3.3.2. Magnetic card readers 357 3.3.3. Magnetoresistive heads for tapes and discs applications 361 3.3.4. Unshielded magnetoresistive reading heads 372 3.3.5. Shielded magnetoresistive heads 376 3.3.6. Yoke-type magnetoresistive heads 382 3.4. Transducers of mechanical values 384 3.4.1. Transducers of linear displacement 384 3.4.2. Transducers of angular position 391 3.4.3. Measurements of rotational speed 396 3.5. Material testing and magnetic field imaging 400 3.5.1. Material testing by means of thin film magnetoresistors 400 3.5.2. Magnetic imaging systems 406 3.6. References 417 List of Symbols 431 List of Abbreviations 433 Index 435 |
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TAYLOR&FRANCIS SERIES ON SENSORS PRINCIPLES OF ELECTRICAL MEASUREMENTS ISBN 0 7503 1038 3 CRC Press 2006 New York, London CONTENTS 1. Introduction to Measurements 1
2. Fundamentals of Electrical Measurements 13 2.1. Main Terms and Definitions 13 2.1.1. Basic terms of measurement technique 13 2.1.2. The main methods of measurements 18 2.2. Uncertainty of Measurements 26 2.2.1. Errors, uncertainty, and reliability of signal processing 26 2.2.2. Basic statistical terms and concepts 34 2.2.3. Methods of evaluation and correction of the uncertainty related to limited accuracy of measuring devices 40 2.2.4. The estimation of uncertainty in measurements 52 2.3. Standards of Electrical Quantities 57 2.3.1. Standards, etalons, calibration and validation 57
2.3.2. The standards of electrical quantities referred to 2.3.3. Material standards of electrical quantities 63 2.3.4. The reference multimeters and calibrators 69 References 71
3. Classic Electrical Measurements 73 3.1. Indicating Measuring Instruments 73 3.1.1 Electromechanical instruments versus digital measuring systems 73 3.1.2. The moving coil meters 74 3.1.3. The moving iron meters 81 3.1.4. Electrodynamic meters – wattmeters 82 3.1.5. Induction type watt-hour meters 86 3.2. Recording and Displaying Measuring Instruments 88 3.2.1. Fundamentals of oscilloscopes 88 3.2.2. Recorders and data storage devices 93 3.3. Bridge Circuits 94 3.3.1. Balanced and unbalanced bridge circuits 94 3.3.2. Null-type DC bridge circuits 96 3.3.3. The AC bridge circuits 99 3.3.4. The transformer bridge circuits 104 3.3.5. The unbalanced bridge circuits 107 3.3.6. The alternatives for bridge circuits – Anderson Loop 112 3.4. Potentiometers and Comparators 114 References 118
4. Processing of the Analogue Measurement Signals 121 4.1. Signal Conditioning 121 4.1.1. Analogue measurement signals 121 4.1.2. Conditioning of resistance, capacitance and inductance 126 4.1.3. AC/DC conversion 131 4.1.4. Voltage to frequency conversion 141 4.2. Amplification of the Signals 143 4.2.1. Differential, operational and instrumentation amplifiers 143 4.2.2. Isolation amplifiers 147 4.2.3. Amplifiers of very small DC signals 150 4.2.4. Amplifiers of very small AC signals 154 4.2.5. Amplifiers of very large input resistance (electrometers) 159 4.2.6. The function amplifiers 161 4.3. Negative Feedback in the Measuring Technique 169 4.4. The Improvement of the Quality of the Analogue Signals 179 4.4.1. The noises and interferences of the analogue signals 179 4.4.2. The connection of the measuring signal to the amplifier 184 4.4.3. The analogue filtering of the signals 191 References 201
5. Digital Processing of the Measurement Signals 205 5.1. Analogue-to-Digital Converters 205 5.1.1. Sampling, quantization and coding of signals 205 5.1.2. Analogue-to-digital converters ADC 218 5.1.3. The main specifications of analogue-to-digital converters 234 5.2. Digital-to-Analogue Converters 238 5.2.1. The reconstruction of the analogue signal 238 5.2.2. The digital-to-analogue converters DAC 242 5.2.3. The main specifications of digital-to-analogue converters 247 5.3. Methods and Tools of Digital Signal Processing 249 5.3.1. The main terms of digital signal processing 249 5.3.2. The Discrete Fourier Transform DFT and Fast Fourier Transform FFT 259 5.3.3. Short-time Fourier Transform and Wavelet transform 268 5.3.4. Digital filters 275 5.4. Examples of Application of Digital Signal Processing in Measurements 287 5.4.1. The spectral analysis 287 5.4.2. Digital signal synthesis 297 5.4.3. Improvement of the signal quality and the signal recovery 303 5.5. Digital Measuring Instruments 312 5.5.1. Digital multimeters and frequency meters 312 5.5.2. Digital oscilloscopes 318 5.5.3. Digital measurement of power and energy 323 5.6. Intelligent Data Analysis 326 5.6.1 The artificial intelligence in measurements 326 5.6.2. The adaptive filters 327 5.6.3. Artificial neural networks 331 5.6.4. Fuzzy Logic 340 References 344
6. Computer Measuring Systems 349 6.1 Introduction 349 6.2. Input Circuits of the Measuring Systems 353 6.2.1. Circuits for data conditioning and acquisition 353 6.2.2. The sensors with built-in interface – intelligent sensors 354 6.2.3. Analogue and digital transmitters 356 6.2.4. Data loggers 357 6.2.5. IEEE P1451 standard – smart sensors 359 6.3. Data Acquisition Circuits – DAQ 362 6.3.1. Plug-in data acquisition board 362 6.3.2. External data acquisition board 365 6.4. Data Communication in Computer Measuring Systems 367 6.4.1. Interfaces, buses and connectors 367 6.4.2. Serial interfaces: RS-232C and RS-485 368 6.4.3. Serial interfaces: USB and FireWire 373 6.4.4. Parallel GPIB interface (IEEE-488/IEC-625) 377 6.4.5. Wireless interfaces: IrDA, Bluetooth and WUSB 382
6.4.6. Mobile telephony systems GSM and UMTS as a tool 6.4.7. Radio data acquisition and transfer 389 6.4.8. Computer systems using Ethernet and Internet 392 6.4.9. Dedicated interfaces: CAN, I2C, MicroLAN, SDI-12 396 6.4.10. HART interface and the 4 – 20 mA standard 400 6.4.11. Industrial communication standards – Fieldbus, Profibus, SCADA 401 6.4.12. Modular systems – VXI, PXI 406 6.4.13. Standard command for measuring devices – SCPI 408 6.5. Measuring Systems Basing on the Signal Processors 410
6.5.1. Microcontrollers and signal processors 6.5.2. Microinterfaces – SPI and UART 418 6.6. Virtual Measuring Systems 421 6.6.1. What is the virtual measuring device? 421 6.6.2. TestPoint 424 6.6.3. Agilent VEE Pro 428 6.6.4. LabVIEW of National Instruments 431 6.7. The Examples of Computer Measuring Systems 438 6.7.1. The measuring system for testing of magnetic materials 438 6.7.2. The arbitrary wave excitation systems 442 6.7.3. The scanning device for magnetic field imaging 449 References 452
Symbols used in the Book 455 Abbreviations used in the Book 457 Index 461
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