Front Cover

Wearable Sensors

Copyright Page

Contents

List of Contributors

Introduction

1.1 Wearables: Fundamentals, Advancements, and a Roadmap for the Future

1 World of Wearables (WOW)

1.1 The Role of Wearables

1.2 Data-Information-Knowledge-Value Paradigm

1.2.1 The Emerging Concept of Big Data

1.2.2 Medical Loss Ratio and Wearables

1.3 The Ecosystem Enabling Digital Life

1.3.1 Smart Mobile Communication Devices

1.3.2 Social Media Tools

2 Attributes of Wearables

2.1 Taxonomy for Wearables

2.2 Advancements in Wearables

2.2.1 The Wearable Motherboard – a User-Centric Approach to the Design of Wearables

2.2.2 Research in Flexible Electronics

2.2.3 The Latest Trends in Commercial Wearables

3 Textiles and Clothing: The Meta-Wearable

3.1 Attributes of the Textile Meta-Wearable

3.2 Realization of the Meta-Wearable: The Wearable Motherboard

3.2.1 Wearable Motherboard Architecture

3.2.2 Convergence and Interactive Textiles

3.3 Applications of Wearables

4 Challenges and Opportunities

4.1 Technical Challenges

4.2 Making a Business Case

5 The Future of Wearables: Defining the Research Roadmap

5.1 Imagine the Future

5.2 The Research Roadmap: A Transdisciplinary Approach to Realizing the Future

References

1.2 Social Aspects of Wearability and Interaction

1 Introduction

2 Social Interpretation of Aesthetics

2.1 Visual Processing of Aesthetics

2.2 Visual Expression of Individual and Group Identity

3 Adoption of Innovation and Aesthetic Change

3.1 The Fashion Cycle: Aesthetic Change in Fashion

3.2 Social Leadership in Fashion

4 On-Body Interaction: Social Acceptance of Gesture

4.1 Conspicuity and Social Weight

4.2 Impact of Body Location and Handedness

4.3 Impact of Cultural Norms

4.4 The “Vocabulary” of Gesture

4.5 Differentiating Passive and Active Gestures

5 Case Study: Google Glass

6 Conclusion

References

1.3 Wearable Haptics

1 Introduction

2 The Need for Wearable Haptic Devices

3 Categories of Wearable Haptic and Tactile Display

3.1 Force Feedback Devices

3.2 Vibro-Tactile Feedback Devices

3.3 Electro-Tactile Feedback Devices

4 Display of Friction and Weight Illusions Based on Fingertip Manipulation

4.1 Creation of Haptic Sensation via Finger Pulp Manipulation

4.2 Deformation of the Contact Area

4.3 Weight and Friction Illusion Display

5 A Wearable Sensorimotor Enhancer

5.1 Improvement of Haptic Sensory Capability for Enhanced Motor Performance

5.2 A Wearable Sensorimotor Enhancer Based on the Stochastic Resonance Effect

5.2.1 Two-Point Discrimination Test

5.2.2 One-Point Touch Test

5.2.3 Active Sensory Test – Texture Discrimination

5.2.4 Motor Skill Test – Minimal-Force Grasping

6 Conclusions

References

2.1 Wearable Bio and Chemical Sensors

1 Introduction

1.1 Chemical and Biochemical Sensors

1.2 Parameters of Interest

2 System Design

2.1 Sample Handling

2.1.1 Transport of Fluids in a Textile

2.1.2 Microneedle Technology

2.1.3 Sampling Gases

2.2 Types of Sensors

2.2.1 Wearable Colorimetric Sensing Platforms

2.2.2 Electrochemical

3 Challenges in Chemical Biochemical Sensing

3.1 Sensor Stability

3.2 Interface with the Body

3.3 Textile Integration

3.4 Power Requirements

4 Application Areas

4.1 Personal Health

4.2 Sports Performance

4.3 Safety and Security

5 Conclusions

References

2.2 Wearable Inertial Sensors and Their Applications

1 Introduction

2 Wearable Inertial Sensors

2.1 Principles of Inertial Sensors

2.2 Accelerometers

2.3 Gyroscopic Sensors

2.4 Magnetic Sensors

2.4.1 The Hall Effect

2.4.2 Magnetoimpedance Sensors

2.4.3 Magnetoresistance Sensors

2.4.4 Giant Magnetoresistance Sensors

3 Obtained Parameters from Inertia Sensors

3.1 Mathematical Analyses

3.2 Comparison between Rehabilitation Score and Acceleration

4 Applications for Wearable Motion Sensors

4.1 Fall Risk Assessment with Rehabilitation Battery

4.2 Fall Detection

4.3 Quantitative Evaluation of Hemiplegic Patients

4.4 Clinical Assessment for Parkinson’s Disease

4.5 Energy Expenditure

5 Practical Considerations for Wearable Inertial Sensor Applications in Clinical Practice and Future Research Directions

References

2.3 Application of Optical Heart Rate Monitoring

1 Introduction

2 Photoplethysmography Basics

2.1 History

2.2 Measurement Principles

2.3 Measurement Sites

2.4 Factors Affecting the Quality of Signal

2.5 Motion Artifact Minimization and Removal

2.5.1 Tissue Modifications Due to Movements

2.5.2 Relative Motion of the Sensor-Skin Interface

2.5.3 Changes in the Pressure between the Optical Probe and the Skin

2.6 Optomechanical Design

2.7 Dedicated Signal Processing

3 Applications

3.1 Sport and Fitness

3.2 Daily Life

3.3 HRV Applications

4 Conclusion and Outlook

Nomenclature

References

2.4 Measurement of Energy Expenditure by Body-worn Heat-flow Sensors

1 Introduction

2 Energy Expenditure Background

3 Examples of Body-Worn Devices

3.1 Motion-Based Estimation of Energy Expenditure

3.2 Indirect Calorimeters

3.2.1 Cosmed K4b2

3.2.2 MicroLife Bodygem

3.3 Direct Calorimeters

3.3.1 Historical Water-Cooled Suits

3.3.2 Historical Heat-Flow Gauges

3.4 Body Media

3.5 MetaLogics Personal Calorie Monitor

4 Design considerations

5 Performance

6 Validations

6.1 Comparison to Metabolic Cart

6.2 Comparison to Room Calorimeter

7 Conclusion

Glossary

References

3.1 Knitted Electronic Textiles

1 From Fibers to Textile Sensors

2 The Interlaced Network

3 Textile Sensors for Physiological State Monitoring

4 Biomechanical Sensing

5 Non-Invasive Sweat Monitoring by Textile Sensors

6 Smart Fabrics and Interactive Textile Platforms for Remote Monitoring

7 System for Remote Rehabilitation

8 Systems for Emotional State Assessment

9 Conclusions

Glossary

References

3.2 Woven Electronic Textiles

1 Introduction

2 Textiles

2.1 Yarn

2.2 Textile Weaves

2.3 Looms

3 Applications

3.1 Touchpad

3.2 Textile Switch

3.3 Textile Electrodes

3.4 RFID Textiles

4 Summary

Glossary

References

3.3 Flexible Electronics from Foils to Textiles: Materials, Devices, and Assembly

1 Introduction

2 Thin-Film Transistors: Materials and Technologies

3 Review of Semiconductors Employed in Flexible Electronics

4 Thin-Film Transistors Based on a-IGZO

4.1 Thin-Film Transistor Fabrication and Characterization

4.2 Influence of Mechanical Strain

4.3 Analog and Digital Circuits Based on a-IGZO

4.3.1 Digital Circuits

4.3.2 Analog Circuits

5 Further Improvements and Limitations

5.1 Thin-Film Transistors by Self-Aligned Lithography

5.2 Flexible Double-Gate TFTs

5.3 Flexible a-IGZO TFTs with Vertical Channel

6 Plastic Electronics for Smart Textiles

6.1 Textile E-nose

6.2 Textile Integrated Near-Infrared Spectroscopy System

7 Outlook and Conclusions

References

4.1 Energy Harvesting at the Human Body

1 Introduction to Energy Harvesting Systems

2 Energy Harvesting from Temperature Gradient at the Human Body

2.1 Thermoelectric Generators

2.2 DC-DC Converter Topologies

2.3 DC-DC Converter Design for Ultra-low Input Voltages

2.3.1 Maximum Power Point Tracking for Impedance Matching

3 Energy Harvesting from Foot Motion

3.1 Physical Principles

3.2 AC-DC Converters

4 Wireless Energy Transmission

4.1 Inductive Wireless Energy Transfer in the Near Field

4.2 Capacitive Wireless Energy Transfer in the Near Field

4.3 Electromagnetic Wireless Energy Transmission in the Far Field

4.4 RFID Technology as an Example Application

4.5 Wireless Power Transmission Regulations

4.6 Influence of the Body on the Wireless System

5 Energy Harvesting from Light

5.1 Physical Principles

5.2 DC-DC Converter

6 Energy and Power Consumption Issues

7 Conclusions and Future Considerations

References

S.1 Energy Harvesting from Temperature Gradient at the Human Body: DC-DC Converter Design for Ultra-low Input Voltages

S.1.1 Bipolar DC-DC Converter Design

S.1.2 ASIC Design and Demonstrator

S.1.3 Maximum-Power Point Tracking for Impedance Matching

S.2 Energy harvesting from Foot Motion: AC-DC Converter

S.2.1 AC-DC Linear Rectifiers

S.2.2 AC-DC Nonlinear Rectifiers

S.3 Energy harvesting from Light: MPPT Algorithms

References for the Supplemental Material

4.2 Introduction to RF Energy Harvesting

1 RF Energy Harvesting Fundamentals and Practical Limitations

1.1 Wave Propagation, Antenna Effective Area, and Available Power

1.2 Antenna-Rectifier Interface Voltage

1.3 Practical Limitations

2 Impedance Mismatch, Losses, and Efficiency

2.1 Available Components and Technology

2.2 Regulations and Maximum Achievable Distance

3 Distribution of Harvested Power in a Realistic Environment

3.1 Ambient RF Power

4 Charge Pump Rectifier Topologies

5 Effect of Load and Source Variations

5.1 Optimum Power Transfer Techniques

6 Antenna-Rectifier Co-Design

6.1 Measurements and Verification

7 Conclusion

Acknowledgement

References

4.3 Low-Power Integrated Circuit Design for Wearable Biopotential Sensing

1 Introduction

2 Biopotential Signals and Their Characteristics

3 Electrode-Body Interface and Electrode Noise

3.1 Electrode-Body Interface

3.2 Electrode Noise

4 Low-Power Analog Circuit Design Techniques for Biopotential Sensors

4.1 Subthreshold Weak Inversion Operation of MOS Transistors

4.2 Requirements for Instrumentation Amplifiers

4.3 Basic Instrumentation Amplifier

4.4 Amplifier Design Techniques and Considerations

4.4.1 Noise and Power Perspective

The gm/ID Design Methodology

4.4.2 Stability Perspective

4.5 Noise Across Sampling Capacitor

4.6 Chopper Stabilization Techniques

4.7 Pseudoresistors for Sub-Hz High-Pass Cut-Off

4.8 CMRR Enhancement Techniques

4.8.1 DRL Technique

4.8.2 Input Impedance-Boosting Techniques

5 Low-Power Design for ADCs

6 Low-Power Digital Circuit Design Techniques

6.1 Minimum Energy Design Methodology

7 Architectural Design for Low-Power Biopotential Acquisition

7.1 Architectural Design Strategies

7.2 Power Domain Design

8 Practical Considerations

9 Conclusion

Glossary

References

5.1 Wearable Algorithms: An Overview of a Truly Multi-Disciplinary Problem

1 Introduction

2 Why Do Wearable Sensors Need Algorithms?

2.1 Battery Selection

2.1.1 Supplied Voltage

2.1.2 Maximum Continuous Current

2.1.3 Maximum Pulse Current Capability

2.1.4 Effective Capacity and Lifetime

2.2 Hardware Platform

2.2.1 Data Acquisition

2.2.2 Wireless Transmission Controller

2.3 Wireless Transmitter

2.3.1 Quality of the Packet Transmission

2.3.2 Hardware Overhead

2.3.3 Air Data Rate vs. Effective Data Rate

2.4 Practical Example and the Impact of Data Compression

2.4.1 Node Design

2.4.2 Optional Data Compression

2.4.3 Power Performance Results

2.5 Summary

3 What are Wearable Algorithms?

3.1 Power–Lifetime Trade-Off

3.2 Big Data Performance Testing

3.3 Performance–Power Trade-Off

3.4 Summary

4 Wearable Algorithms: State-of-the-Art and Emerging Techniques

4.1 Making the Signal Processing Algorithm

4.1.1 Procedure

4.1.2 Feature Extraction

4.1.3 Classification Engines

4.2 The Hardware Platform: Analog Vs. Digital; Generic Vs. Custom

4.2.1 Analog Signal Processing

4.2.2 Fully Custom Hardware

4.3 Towards Wearable Algorithms: Examples from the Literature

4.3.1 Generic Processors

4.3.2 Generic Processors with Accelerators

4.3.3 Fully Hardware Electronics and Design Trends

5 Conclusions

References

5.2 Mining Techniques for Body Sensor Network Data Repository

1 Introduction

2 Machine Learning Approaches to Data Mining

2.1 Mining Techniques

2.2 Structural Recognition in BSN

3 Mining BSN Data

3.1 BSN System

3.2 Wearable Sensor Hardware

3.3 Pilot Application

3.4 Desirable Solution Properties

4 Data Representation

4.1 Primitive Construction

4.1.1 Data Clustering

4.2 Motion Transcripts

5 Comparison Metric

5.1 N-gram Selection

6 Classifier

7 Data-Mining Model

7.1 Training

7.2 Query Processing

8 Experimental Results

8.1 k-Means or GMM?

8.2 Classification Accuracy

8.3 Parameter Trade-offs

8.4 Movement Template Evaluation

9 Conclusion and Recommendations

Acknowledgment

References

5.3 Modeling Physical Activity Behavior Change

1 Introduction – Physical Activity Monitoring Capabilities

1.1 Sensors can Inform Personalized Behavior-Change Interventions

2 Physical Activity Body Sensor Technology

3 Modeling Physical Activity

3.1 Critical Power (CP) Model

3.2 Banister Impulse Response (IR) Model

4 Behavior-Change Theories Relevant to Physical Activity Interventions

4.1 A Framework for Quantitative Modeling of Physical Activity Behavior-Change Interventions

4.2 Assessing Stages of Change

4.3 Opportunities to Use Behavior-Change Models to Guide Intervention Programs

5 Conclusion

References

6.1 Human Body Communication for a High Data Rate Sensor Network

1 Capacitive-Coupling Communication Through Human Body

2 Channel Properties of Human Body

3 Effects of Electrode’s Structure

3.1 Effects of the Electromagnetic Environment Outside the Human Body

3.2 Channel Model for Human Body Communication

4 Transmission Scheme of Human Body Communication

4.1 Walsh Code

4.2 Frequency-Selective Digital Transmission

5 Analog Front-End for Human Body Communication

5.1 Received Signal

5.2 Design of an Analog Front-End

5.3 Operation of CDR

6 Performance of the Analog Front-End

7 Commercialization of Human Body Communication and its Challenges

References

6.2 Channel Models for On-Body Communications

1 Introduction

2 IEEE 802.15.6 TG6 Standard Models

2.1 Aoyagi et al. Model

2.2 Dolmans and Fort Model

2.3 Miniutti et al. Model

2.4 Astrin Model

2.5 Aoyagi et al., Power Delay Profile Model

2.6 Dolmans and Fort Wideband Model

2.7 Kang et al. Model

2.8 Kim et al. Model

3 Independent Studies

3.1 CWC Oulu University Model

3.2 Wang et al. Model

3.3 Reusens et al. Model

3.4 Queen’s University of Belfast Models

3.5 University of Birmingham and Queen Mary University Models

4 Conclusions

Acknowledgements

References

6.3 Trust Establishment in Wireless Body Area Networks

1 Introduction

2 WBAN Device Authentication Techniques

2.1 Cryptographic Authentication Mechanisms in WBAN

2.1.1 Symmetric Key-Based Authentication

2.1.2 Public Key-Based Authentication

2.2 Non-Cryptographic Authentication Mechanisms in WBAN

2.2.1 Biometric-Based Authentication

2.2.2 Channel-Based Authentication

2.2.3 Proximity-Based Authentication

2.2.4 Other Authentication Schemes

2.3 Summary of Authentication Methods

3 Secret Key Establishment in WBAN

3.1 Secret Key Establishment Based on Biometrics or Motion

3.2 Secret Key Establishment Based on Wireless Channel Characteristics

3.3 Authenticated Secret Key Establishment in WBAN

3.3.1 Challenges

3.3.2 ASK-BAN: Authenticated Secret Key Establishment Utilizing Channel Characteristics for Wireless BAN

3.4 Wireless In-Band Trust Establishment in WBAN

3.4.1 Related Work

3.4.2 “Chorus”: Authenticated Message Comparison over Wireless Channel

4 Summary

References

6.4 Wireless Body Area Networks

1 Introduction

2 Evaluation Metrics

3 Technologies

3.1 Wearable Active Transducers

3.1.1 Ultrasound Systems

3.1.2 RFID Tags

3.1.3 Ultra-Wide Band Systems

3.2 Packet Radio Systems (Active and Passive)

3.3 Wearable Passive Systems

3.4 Device-Free Localization

3.5 Hybrid Techniques

3.5.1 Data Fusion

3.5.2 SLAM (Simultaneous Location and Mapping)

4 Wearable Radios

4.1 Range-Free

4.1.1 Centroid

4.1.2 APIT

4.1.3 SeRLoc

4.2 Range-Based

4.2.1 Fingerprinting

4.2.1.1 Radio Map

4.2.1.2 Location Estimation

4.2.1.2.1 Deterministic Approaches

4.2.1.2.2 Probabilistic Approaches

4.2.2 Propagation Model

4.2.2.1 Indoor Signal Propagation Model

4.2.2.2 Multi-Lateration Algorithm

4.2.2.3 Maximum-Likelihood Distance Estimator and Cramér-Rao Bounds

4.2.2.3.1 RSS Information: Single Sample Case

4.2.2.3.2 RSS Information: Multiple Samples Case

5 Conclusions

References

7.1 Fundamentals of Wearable Sensors for the Monitoring of Physical and Physiological Changes in Daily Life

1 Introduction

2 Wearable Sensors for Physiological Signal Measurement

2.1 Fundamentals of the Three Types of Electrodes and ECG Monitoring by Non-Contact Electrodes

2.2 Biosignal Sensors for Cardiovascular System Monitoring

2.2.1 Measurement of Blood Pressure

2.2.2 Plethysmogram and Oximeter

2.2.3 Respirometry

2.2.4 Measurement of Body Temperature

2.3 Biosignal Sensors for Sleep Monitoring

2.3.1 Ballistic Cardiogram

2.3.2 Non-Restrictive Heart-Rate Measurement

2.3.3 Sheet Type Respiratory and Body Motion Sensor

2.3.4 Video Camera

2.4 Wearable Sensors for Physical Activity Measurement

2.4.1 Flexible Goniometer for Articular Motion

2.4.2 Joint Motion Measurement Using Two Accelerometers Set Near Both Sides of the Joint

2.4.3 Force Monitoring During Walking

3 Summary

7.2 Wearing Sensors Inside and Outside of the Human Body for the Early Detection of Diseases

1 Introduction

2 Cardiovascular Diseases

2.1 Monitoring Risk Factors of Cardiovascular Diseases

2.2 Diagnosis of Cardiovascular Diseases

2.3 Summary and Future Development

3 Neurological Diseases

3.1 Motor Activity Monitoring and Intervention for Neurological Rehabilitation

3.2 Seizure Activity Monitoring for Epilepsy Patients

3.3 Summary and Future Development

4 Gastrointestinal Diseases

4.1 On-Body Wearable Sensor Design Based on Flexible Electronics

4.2 In-Body Chemical and Biological Flexible Sensors and Systems

4.2.1 Technical Challenges for Fabricating Flexible Sensory Systems

4.3 Design of High-Performance Flexible Sensory Systems

4.4 Transfer and Adherence of the Flexible System to Irregular Body Surface Seamlessly and Firmly

5 Conclusion

Acknowledgment

References

7.3 Wearable and Non-Invasive Assistive Technologies

1 Assistive Devices for Individuals with Severe Paralysis

1.1 Sip-n-Puff

1.2 Head Controllers

1.3 Eye-Tracking Systems

1.4 Electromyography-Based Controllers

1.5 Voice Controllers

1.6 Brain-Computer Interfaces

1.7 Tongue-Operated Devices

2 Why USE THE Tongue for Wearable Technology?

3 Wireless Tracking of Tongue Motion

4 Wearable Tongue Drive System

4.1 Permanent Magnetic Tracer

4.2 Wireless Headset

4.3 Wireless USB Receiver

4.4 Graphical User Interface

5 Sensor Signal-Processing Algorithm

5.1 External Magnetic Interference Attenuation

5.2 Feature Extraction

5.3 Command Classification

6 Dual-Mode Tongue Drive System

6.1 The Advantages of Multi-Modal System

6.2 The Concept of Dual-Mode Tongue Drive System

6.2.1 Wearable dTDS Prototype

6.2.1.1 Wireless Headset

6.2.1.2 Wireless USB Transceiver

7 Clinical Assessment

7.1 Subjects

7.2 Magnet Attachment

7.3 Command Definition

7.4 Training Session

7.5 Response Time Measurement

7.5.1 Powered Wheelchair Navigation

7.5.2 Results

8 Future Directions

8.1 Intraoral TDS

8.2 Multi-Modal TDS

8.3 Data Compression and Sensor Fusion

8.4 SSP Algorithm Improvement

8.5 Environmental Control

References

7.4 Detection and Characterization of Food Intake by Wearable Sensors

1 Introduction

2 Wearable Sensors

2.1 Handheld Devices

2.2 Body-Attached Sensors

2.2.1 Monitoring of Hand Gestures

2.2.2 Monitoring of Chewing

2.2.3 Monitoring of Swallowing

3 Signal Processing and Pattern-Recognition Methods for Automatic Detection of Food Intake

3.1 Food-Intake Detection from Imagery

3.2 Detection of Hand Gestures

3.3 Food-Intake Detection from Chewing

3.4 Food Intake Detection from Swallowing

4 Methods for Characterization of Food Intake

4.1 Recognition of Number of Foods in a Meal

4.2 Estimation of Ingested Mass and Energy Intake from Imagery

4.3 Estimation of Ingested Mass and Energy Intake from Counts of Chews, Swallows, and Hand Gestures

5 Applications

5.1 Laboratory Vs. Free-Living Monitoring

5.2 Wearable Devices for Free-Living Monitoring

6 Summary and Conclusions

References

Index