Magnetic Sensors for Biomedical Applications

Hadi Heidari, PhD, is an Assistant Professor (Lecturer) in the School of Engineering and lead of the Microelectronics Lab (meLAB) at the University of Glasgow, UK. He is a senior member of the IEEE, and is a Fellow of Higher Education Academy (FHEA). Dr Heidari has authored/co-authored over 100 peer-reviewed publications in top-tier journals or conference proceedings. He has been the recipient of a number of awards including the 2019 IEEE Sensors Council Young Professional Award. Vahid Nabaei, PhD, is a Postdoctoral Research Assistant in the Microelectronics Lab (meLAB) at the School of Engineering, University of Glasgow, UK. Before this he was an assistant professor at the Department of Electrical Engineering, Islamic Azad University, Hidaj Branch, Iran. He has worked as an author/co-author of top-tier journals in modeling and simulation of magnetic sensors for different applications.

• Preface xiii1 Introduction 11.1 Overview 11.2 History of Magnetism Studies and of Its Use in Magnetic Sensors 21.3 Natural and Technical Magnetic Fields and Their Order of Magnitude 31.3.1 Natural Magnetic Fields 31.3.1.1 The Earth’s Magnetic Field 31.3.1.2 Magnetic Fields in Outer Space 31.3.1.3 Biomagnetic Fields 31.3.2 Technical Magnetic Fields 51.3.2.1 Magnetic Fields in the Vicinity of Transformers and Electric Motors 51.3.2.2 Fields of Permanent Magnets 51.4 Magnetic Terms and Units 61.5 Magnetic (Micro) Sensors 71.5.1 Definition of Magnetic Sensors 71.5.2 Soft and Hard Magnetic Materials for Sensors 81.5.2.1 Shape of the Hysteresis Loop 81.5.2.2 Saturation Polarization Js and Coercivity Hc 101.5.2.3 Initial Permeability μi 101.5.2.4 Specific Electrical Resistivity ρ 111.5.3 Mechanical Properties of Magnetic Materials 121.5.4 Relations Between Sensing Techniques and Sensor Applications 121.5.5 Classification of Magnetic Sensors 141.6 Characteristics of Magnetic Sensors 151.6.1 Characteristics Related to OUT(B)C 151.6.1.1 Magnetosensitivity 151.6.1.2 Nonlinearity 161.6.1.3 Calibration 171.6.1.4 Sensor Excitation 171.6.1.5 Frequency Response 171.6.1.6 Resolution 171.6.1.7 Error 171.6.1.8 Accuracy 181.6.1.9 Hysteresis 181.6.1.10 Repeatability 181.6.2 Characteristics Related to OUT(C)B 181.6.2.1 Noise 181.6.2.2 Offset 181.6.2.3 Cross-Sensitivity and Temperature Error 191.6.2.4 Drift and Creep 191.6.2.5 Response Time 191.6.3 Characteristics Related to the System Description 191.6.3.1 Electrical Excitation 191.6.3.2 Input and Output Impedance 201.6.3.3 Environmental Conditions 201.7 Magnetic Noise 201.7.1 Noise Formalism 201.7.1.1 Fluctuations, Average and Distribution 201.7.1.2 Correlations 221.7.1.3 Frequency Space and Spectral Density 221.7.2 Sensitivity, Signal-to-Noise Ratio, and Detectivity 241.7.3 Different Sources of Noise 251.7.3.1 Separation of Magnetic and Nonmagnetic Noise 251.7.3.2 Frequency-Independent Noise (Thermal or Johnson–Nyquist Noise), Shot Noise 251.7.4 Low Frequency Noise 261.7.4.1 1/f Noise 261.7.4.2 Random Telegraph Noise 281.7.5 High Frequency Noise and Ferromagnetic Resonance 281.7.6 External Noise 291.7.7 Electronics and Noise Measurements 291.7.7.1 Electronics Design 291.7.7.2 Connections Noise 301.7.7.3 Correlation for Preamplification Noise Suppression 30References 302 Magnetic Sensors Based on Hall Effect 332.1 Overview 332.2 Devices Based on Hall Effect 342.2.1 Geometry 342.2.2 Material 352.3 Horizontal Versus Vertical CMOS Hall Devices 362.4 Current-Mode Versus Voltage-Mode Technique 372.5 Magnetic Sensor Characteristics 392.5.1 Sensitivity 392.5.2 Offset 432.5.2.1 Current Spinning Technique 442.5.3 Noise 462.5.4 Nonlinearity 462.6 State-of-the-art in CMOS Hall Magnetic Sensors 472.6.1 Sensitivity Improvement 472.6.2 Offset Reduction 482.7 Applications of Hall Magnetic Sensors 492.7.1 Biosensors 492.7.2 Contactless Current Sensors 502.7.3 Contactless Angular, Linear, and Joystick Position Sensors 502.7.4 Electronic Compass 512.7.5 Speed and Timing Sensors 522.7.6 Specific Sensors 52References 533 Magnetoresistive Sensors 573.1 Introduction 573.2 Materials and Principles of AMR, GMR, and TMR 583.2.1 Anisotropic Magnetoresistance 583.2.1.1 Anisotropic Magnetoresistance Effect and Principles 583.2.1.2 AMR Device Material 613.2.2 Giant Magnetoresistance 623.2.2.1 Giant Magnetoresistance Effect and Principles 623.2.2.2 Mechanism of GMR Effect 643.2.2.3 GMR Effect in Multilayers 663.2.3 Magnetic Tunnel Junctions 673.2.3.1 TMR Structures 693.3 Classes of Magnetoresistive Sensors 713.3.1 General Purpose Magnetometers 713.3.2 MR Sensors in Harsh Environments 733.3.3 Electrical Current Sensing 743.3.3.1 Industrial Electronics Applications (Large to Medium Currents) 753.3.3.2 Differential Currents 763.3.3.3 Switching Regulators 763.3.3.4 Wattmeter 773.3.3.5 IC Current Monitoring 783.3.4 Automotive Applications 783.3.4.1 BLDC Rotor Position Measurement 783.3.4.2 Steering Angle Application 793.3.4.3 Crankshaft Speed and Position Measurement 793.3.4.4 Wheel Speed Measurement for ABS and ESC Systems 803.3.5 Magnetoresistive Elements in Data Storage Applications 803.3.6 Space 813.4 Modeling and Simulations 813.4.1 Finite Element Modeling and Methodology 813.4.2 Finite Element Method 823.4.3 Finite Difference Method 823.4.4 The Boundary Element Method 823.4.5 MR Sensors Simulation and Modeling 833.5 Design and Fabrication Technologies 873.5.1 GMR Devices 873.5.1.1 Deposition Techniques 873.5.1.2 Patterning 903.6 Biomedical Magnetoresistive Sensing Applications 943.6.1 Detection of Bioanalytes 953.6.2 Monitoring of Magnetic Fluids 953.6.3 Biomolecular Recognition Experiments 953.6.4 Ultrasensitive Magnetic Array for Recording of Neuronal Activity (UMANA) 98References 1004 Resonance Magnetometers 1134.1 Introduction 1134.2 Nuclear Magnetic Resonance 1154.2.1 Classical Model 1164.2.1.1 Rotating Frame of Reference 1174.2.1.2 Strength of RF Pulses 1174.2.2 Basic Design of a NMR Spectrometer 1184.2.3 Nuclear Magnetic Resonance in Molecular and Atomic Beams 1204.2.4 The Sources of Magnetic Fields 1234.2.5 NMR Spins Used in Life Science 1244.2.6 NMR Relaxation 1254.2.6.1 Relaxation Rates 1254.2.6.2 Molecular Mechanisms Leading to Relaxation 1264.2.7 NMR and Biological Structures 1274.2.8 Difficulties in Studying Biological System by NMR 1284.2.8.1 Sensitivity 1284.2.8.2 Resolution 1294.2.8.3 Water Signal 1294.2.8.4 Line Widths 1304.2.8.5 Quantification 1304.3 Magnetic Resonance Imaging 1304.3.1 Introduction 1304.3.2 The Obtaining of Spin Images from NMR Induction Signals in Inhomogeneous Field 1314.3.3 MRI Instrumentation 1324.3.3.1 Magnets and Designs 1354.3.3.2 Resistive Electromagnets 1354.3.3.3 Permanent Magnets 1364.3.3.4 Superconducting 1364.3.3.5 Stability, Homogeneity, and Fringe Field 1374.3.3.6 Gradient Coils 1374.3.3.7 RF Coils 1384.3.3.8 RF Decoupling 1384.3.4 MRI of Flow 1394.3.4.1 Time-of-Flight Techniques 1394.4 Electron Spin Resonance 1434.4.1 The ESR Experiment 1454.4.1.1 Sensitivity 1464.4.1.2 Saturation 1474.4.2 Operation of an ESR Spectrometer 1474.4.3 Optimization of Operating Parameters 1504.4.3.1 Microwave Frequency 1504.4.3.2 Center Field, Sweep Width, and Field Offset 1514.4.3.3 Sweep Time 1514.4.3.4 Modulation Frequency 1514.4.3.5 Second Harmonic Detection 1514.4.3.6 Modulation Amplitude 1524.4.3.7 Modulation Phase 1524.4.3.8 Signal Gain 1524.4.4 Biological Application of the ESR 1524.4.4.1 ESR Oximetry 1534.4.4.2 Direct Detection of Paramagnetic Species 1544.4.4.3 EPR Revealed the Nitrite Reductase Activity of Myoglobin 1554.4.4.4 Mitochondrial Dysfunction in Severe Sepsis 1554.4.4.5 Spin Trapping ESR 155References 1575 SQUID Sensors 1635.1 Introduction 1635.1.1 History 1635.2 SQUID Fundamentals 1645.2.1 Josephson Junctions 1645.2.2 DC SQUIDs 1665.2.2.1 Practical Devices 1715.2.3 rf SQUID 1745.2.4 Cryogenics and Systems 1775.2.5 SQUID Electronics 1785.2.5.1 Flux Locked Loop 1785.3 SQUID Fabrication 1805.4 Lithography and Thin-Film Techniques 1805.4.1 Junction Fabrication 1825.5 SQUID Applications in Biomagnetism 1835.5.1 Biomagnetism 1835.5.2 History of SQUID Applications in Biomagnetism 1845.5.3 Biomagnetic Fields 1855.5.3.1 Gradiometers 1865.5.4 Magnetoencephalography 1885.5.4.1 MEG Signals 1895.5.4.2 Sensor Types for MEG 1915.5.5 Magnetocardiography 1955.5.5.1 Cardiomagnetic Instrumentation 1965.5.6 Magnetoneurography 1975.5.6.1 History of Measuring Signal Propagation in Nerves 1975.5.6.2 Measurement Technique and Signal Processing 1995.5.6.3 Source Modeling for Magnetoneurography 2005.5.6.4 Clinical Perspective 200References 2016 Conclusion 2136.1 Outlook 2136.2 A Conclusion on Galvanomagnetic Sensors 2146.2.1 Hall Elements: Hall Voltage Mode Versus Hall Current Mode and Magnetoresistance Mode of Operation 2156.2.2 Hall Sensors Versus Ferromagnetic Magnetoresistors 2156.2.3 Performance of Integrated Hall Magnetic Sensors 2166.2.4 Performance of Ferromagnetic Magnetoresistors 2166.2.5 Integrated Hall Sensors Versus AMRs and GMRs 2186.3 A Conclusion on NMR and ESR Spectroscopy 2186.3.1 Differences Between NMR and ESR 2196.3.1.1 Resonant Frequency 2196.3.1.2 Relaxation Times 2196.3.1.3 Differences Between ESR and NMR Imaging 2206.3.1.4 ESR Applications 2206.4 Superconductive Quantum Interference Devices 2216.4.1 SQUID Fabrication Trend 2216.4.2 Trends in SQUID Electronics 2226.4.3 Trends in SQUIDs for Nondestructive Evaluation of Materials 222References 223Index 225