Preface to the Special Topic on Devices and Circuits for Wearable and IoT Systems

The concept of Internet of Things (IoT) was first proposed by MIT Prof.Kevin Ash-ton in 1999.The implementation of IoT was mainly through RFID in its early time.With advanced technology and manufacture,diverse implementation forms ofIoT are becoming possible.Wearable devices,as an essential branch of IoT,will have broad application prospects in health monitoring and intelligent healthcare.     

可穿戴设备安全威胁与防护措施

随着信息通信技术日新月异地发展,信息通信产品的设备形态和业务功能不断演进,可穿戴设备正在成为信息通信技术的发展热点。一方面,可穿戴设备极大地方便了人们的工作和生活;另一方面,伴随其El益开放的体系架构和不断壮大的业务功能,可穿戴设备同时给人们带来越来越多的安全威胁。本文首先介绍可穿戴设备发展现状,然后分析可穿戴设备面临的安全威胁,继而提出可穿戴设备需要的安全措施,最后展望了可穿戴设备安全的未来发展。     

Wearable Biosensors for Body Computing

The challenges of growing and aging populations combined with limited clinical resources have created huge demand for wearable and portable healthcare devices. Research advances in wearable biosensors have made it easier to achieve reliable noninvasive monitoring of health and body status. In this review, recent progress in the development of body computing systems for personalized healthcare is presented, with key considerations and case studies. Critical form factors for wearable sensors, their materials, structures, power sources, modes of data communication, and the types of information they can extract from the body are summarized. Statistically meaningful data analysis considerations, including using cohort and longitudinal correlation studies, are reviewed to understand how raw sensor signals can provide actionable information on the state of the body. This informs discussions on how collected sensor data can be used for personalized and even preventative care, such as by guiding closed-loop medical interventions. Finally, outstanding challenges for making wearable sensor systems reliable, practical, and ubiquitous are considered in order to disrupt traditional medical paradigms with personalized and precision care.     

基于激光距离传感器的路况识别系统的设计

针对动力型下肢设备存在的运动模式识别率低的问题,设计了一种可穿戴式路况识别系统。通过安装在腰部的便携式激光距离传感器和惯性测量传感器分别采集激光距离信息和地形高度信息,利用小波去噪算法对所采集的数据进行处理,提取特征值,最后选择训练简单、结构清晰的概率神经网络进行路况识别。实验结果表明,该便携式系统能有效识别平地、上楼、下楼、上坡和下坡五种路况并提高识别精度,证明了将可穿戴式路况识别系统应用于假肢或助行器等动力型下肢设备环境感知系统的有效性和可行性。     

User centric three‐factor authentication protocol for cloud‐assisted wearable devices

Wearable devices, which provide the services of collecting personal data, monitoring health conditions, and so on, are widely used in many fields, ranging from sports to healthcare. Although wearable devices bring convenience to people's lives, they bring about significant security concerns, such as personal privacy disclosure and unauthorized access to wearable devices. To ensure the privacy and security of the sensitive data, it is critical to design an efficient authentication protocol suitable for wearable devices. Recently, Das et al proposed a lightweight authentication protocol, which achieves secure communication between the wearable device and the mobile terminal. However, we find that their protocol is vulnerable to offline password guessing attack and desynchronization attack. Therefore, we put forward a user centric three‐factor authentication scheme for wearable devices assisted by cloud server. Informal security analysis and formal analysis using ProVerif is executed to demonstrate that our protocol not only remedies the flaws of the protocol of Das et al but also meets desired security properties. Comparison with related schemes shows that our protocol satisfies security and usability simultaneously.     

Flexible MXene-Based Composites for Wearable Devices

In recent decades, flexible and wearable devices have been extensively investigated due to their promising applications in portable mobile electronics and human motion monitoring. MXene, a novel growing family of 2D nanomaterials, demonstrates superiorities such as outstanding electrical conductivity, abundant terminal groups, unique layered-structure, large surface area, and hydrophilicity, making it to be a potential candidate material for flexible and wearable devices. Numerous pioneering works are devoted to develop flexible MXene-based composites with various functions and designed structures. Therefore, the latest progress of the flexible MXene-based composites for wearable devices is summarized in this review, focusing on the preparation strategies, working mechanisms, performances, and applications in sensors, supercapacitors, and electromagnetic interference shielding materials. Moreover, the current challenges and future outlooks are also discussed.     

Wearable Self-Powered Electrochemical Devices for Continuous Health Management

The wearable revolution is already present in society through numerous gadgets. However, the contest remains in fully deployable wearable (bio)chemical sensing. Its use is constrained by the energy consumption which is provided by miniaturized batteries, limiting the autonomy of the device. Hence, the combination of materials and engineering efforts to develop sustainable energy management is paramount in the next generation of wearable self-powered electrochemical devices (WeSPEDs). In this direction, this review highlights for the first time the incorporation of innovative energy harvesting technologies with top-notch wearable self-powered sensors and low-powered electrochemical sensors toward battery-free and self-sustainable devices for health and wellbeing management. First, current elements such as wearable designs, electrochemical sensors, energy harvesters and storage, and user interfaces that conform WeSPEDs are depicted. Importantly, the bottlenecks in the development of WeSPEDs from an analytical perspective, product side, and power needs are carefully addressed. Subsequently, energy harvesting opportunities to power wearable electrochemical sensors are discussed. Finally, key findings that will enable the next generation of wearable devices are proposed. Overall, this review aims to bring new strategies for an energy-balanced deployment of WeSPEDs for successful monitoring of (bio)chemical parameters of the body toward personalized, predictive, and importantly, preventive healthcare.     

Smart Clothing: Connecting Human with Clouds and Big Data for Sustainable Health Monitoring

Traditional wearable devices have various shortcomings, such as uncomfortableness for long-term wearing, and insufficient accuracy, etc. Thus, health monitoring through traditional wearable devices is hard to be sustainable. In order to obtain healthcare big data by sustainable health monitoring, we design “Smart Clothing”, facilitating unobtrusive collection of various physiological indicators of human body. To provide pervasive intelligence for smart clothing system, mobile healthcare cloud platform is constructed by the use of mobile internet, cloud computing and big data analytics. This paper introduces design details, key technologies and practical implementation methods of smart clothing system. Typical applications powered by smart clothing and big data clouds are presented, such as medical emergency response, emotion care, disease diagnosis, and real-time tactile interaction. Especially, electrocardiograph signals collected by smart clothing are used for mood monitoring and emotion detection. Finally, we highlight some of the design challenges and open issues that still need to be addressed to make smart clothing ubiquitous for a wide range of applications.     

Multifunctional and Wearable Patches Based on Flexible Piezoelectric Acoustics for Integrated Sensing,Localization, and Underwater Communication

Flexible and wearable sensors are highly desired for health monitoring, agriculture, sport, and indoor positioning systems applications. However, the currently developed wireless wearable sensors, which are communicated through radio signals, can only provide limited positioning accuracy and are often ineffective in underwater conditions. In this paper, a wireless platform based on flexible piezoelectric acoustics is developed with multiple functions of sensing, communication, and positioning. Under a high frequency (≈13 MHz) stimulation, Lamb waves are generated for respiratory monitoring. Whereas under low-frequency stimulation (≈20 kHz), this device is agitated as a vibrating membrane, which can be implemented for communication and positioning applications. Indoor communication is demonstrated within 2.8 m at 200 bps or 4.2 m at 25 bps. In combination with the sensing function, real-time respiratory monitoring and wireless communication are achieved simultaneously. The distance measurement is achieved based on the phase differences of transmitted and received acoustic signals within a range of 100 cm, with a maximum error of 3 cm. This study offers new insights into the communication and positioning applications using flexible acoustic wave devices, which are promising for wireless and wearable sensor networks.     

Body Heat Powered Wirelessly Wearable System for Real-time Physiological and Biochemical Monitoring

Through harvesting energy from the environment or human body, self-power wearable electronics have an opportunity to break through the limitations of battery supply and achieving long-term continuous operation. Here, a wireless wearable monitoring system driven entirely by body heat is implemented. Based on the principle of maximizing heat utilization, while optimizing internal resistance and heat dissipation, the stretchable TEG improves the power density of previous similar devices from only a few microwatts per square centimeter to tens and makes it possible to continuously drive wireless wearable electronic systems. Furthermore, ceaseless self-power energy gives wearable electronics unparalleled continuous working ability, which can realize the tracking and monitoring of biochemical and physiological indicators at different time scale. A practical system demonstrates the ability to real-time monitor heart rate, sweat ingredient and body motion at a high sampling rate. This study marks an important advance of self-powered wearable electronics for wirelessly real-time healthy monitoring.     

Flexible and Waterproof Resistive Random‐Access Memory Based on Nitrocellulose for Skin‐Attachable Wearable Devices

Memory for skin‐attachable wearable devices for healthcare monitoring must meet a number of requirements, including flexibility and stability in external environments. Among various memory technologies, organic‐based resistive random‐access memory (RRAM) devices are an attractive candidate for skin‐attachable wearable devices due to the high flexibility of organic materials. However, organic‐based RRAMs are particularly vulnerable to external moisture, making them difficult to apply as skin‐attachable wearable devices. In this research, RRAMs are fabricated that meet the requirements for skin‐attachable wearable devices using a novel organic material, nitrocellulose (NC), which is biocompatible with high water‐resistance and high flexibility. The fabricated NC‐based RRAMs show a stable bipolar resistive switching characteristic. In addition, the formation of a native Al oxide between Al and NC is verified, which is the source of the bipolar switching characteristic of NC‐based RRAMs. Furthermore, electrical and chemical analysis is conducted after dipping and submersion into various solutions as well as deionized water to confirm the water‐resistance of the NC‐based RRAMs. Finally, it is also confirmed that NC‐based RRAMs are suitable for use in skin‐attachable wearable devices through a flexibility test. In conclusion, this study suggests that NC‐based RRAMs can be applied in skin‐attachable wearable devices, simplifying healthcare in the future.     

基于智能感知的物联网云平台探究

近年来,智能设备获得了迅猛的发展,且广泛出现在人们的日常生活中,小到音影娱乐、智能家居以及穿戴设备,大到警务应用、建筑监测、交通监管控制以及农业生产等。首先介绍了系统的核心特征,然后探究了智能感知下的物联网云平台设计策略,最后提出了系统应用场景。     

Self-Healing Photochromic Elastomer Composites for Wearable UV-Sensors (Adv. Funct. Mater. 20/2023)

Photochromic materials have recently received strong interest for the development of wearable ultraviolet (UV) detection technologies because they do not require electronic components, resulting in systems and devices that change color upon irradiation. However, their implementation in wearable technology has lightweight, compliance, and durability (especially under mechanical stress) requirements that are limited by the materials’ properties. Here, a self-healing photochromic elastomer composite (photoPUSH) consisting of phosphomolybdic acid (PMA) in a self-healing polyurethane dynamic network with reversible disulfide bonds (PUSH) is presented. The unique properties of the dynamic polymer matrix enable multiple complementary functions in the UV-sensing composite: i) photochromism via electron donor groups without requiring additional dopants, ii) stretchability and durability via elastomeric properties, iii) healing of extreme mechanical damage via dynamic bonds, and iv) multimaterial integration via adhesive properties. PhotoPUSH composites exhibit excellent durability, tunable sensing range, and no loss of performance under mechanical stress and severe damage, as well as in underwater environments (waterproof). Leveraging these properties, soft, portable, multimaterial photoPUSH-based UV-sensing devices are developed for applications in environmental monitoring, packaging, and healthcare wearable technology (including skin-mounted, textile-mounted, and wristband devices) in challenging environments and tunable to different skin types.     

A Dual‐Functional Graphene‐Based Self‐Alarm Health‐Monitoring E‐Skin

Diseases such as cardiovascular problems and sleep apnea cause mass deaths annually due to a lack of timely and portable monitoring and alarm measures. Various wearable devices for health monitoring have been intensely researched to reduce mortality. However, these devices themselves can only detect physiological signals; they cannot sound an alarm. Therefore, they must rely on mobile phones or other peripheral devices such as speakers or vibration motors to sound an alarm, which may result in a patient missing the optimal treatment. It is valuable to develop a self‐alarm health monitoring device with the dual functions of physiological signal detection and sound alarm simultaneously. A one‐step laser‐induced graphene (LIG)‐based electronic skin (E‐skin) is fabricated to perform health monitoring and alarm at the same time, which benefit from its both excellent mechanical and acoustical performance. These customized shutter‐patterned E‐skins have an ultrahigh sensitivity of 316.3 and can detect various biosignals such as wrist pulse, respiratory, etc. They also have a self‐alarm function and can sound an alarm when detecting abnormal situations. This study addresses the multifunctional integration required for multisensors, which will open further applications in wearable sensors and health‐care devices.     

A Survey on Wearable Sensor-Based Systems for Health Monitoring and Prognosis

The design and development of wearable biosensor systems for health monitoring has garnered lots of attention in the scientific community and the industry during the last years. Mainly motivated by increasing healthcare costs and propelled by recent technological advances in miniature biosensing devices, smart textiles, microelectronics, and wireless communications, the continuous advance of wearable sensor-based systems will potentially transform the future of healthcare by enabling proactive personal health management and ubiquitous monitoring of a patient's health condition. These systems can comprise various types of small physiological sensors, transmission modules and processing capabilities, and can thus facilitate low-cost wearable unobtrusive solutions for continuous all-day and any-place health, mental and activity status monitoring. This paper attempts to comprehensively review the current research and development on wearable biosensor systems for health monitoring. A variety of system implementations are compared in an approach to identify the technological shortcomings of the current state-of-the-art in wearable biosensor solutions. An emphasis is given to multiparameter physiological sensing system designs, providing reliable vital signs measurements and incorporating real-time decision support for early detection of symptoms or context awareness. In order to evaluate the maturity level of the top current achievements in wearable health-monitoring systems, a set of significant features, that best describe the functionality and the characteristics of the systems, has been selected to derive a thorough study. The aim of this survey is not to criticize, but to serve as a reference for researchers and developers in this scientific area and to provide direction for future research improvements.      

Wearable Organic Electrochemical Transistor Array for Skin-Surface Electrocardiogram Mapping Above a Human Heart

Electrocardiogram (ECG) mapping can provide vital information in sports training and cardiac disease diagnosis. However, most electronic devices for monitoring ECG signals need to use multiple long wires, which limit their wearability and conformability in practical applications, while wearable ECG mapping based on integrated sensor arrays has been rarely reported. Herein, ultra-flexible organic electrochemical transistor (OECT) arrays used for wearable ECG mapping on the skin surface above a human heart are presented. QRS complexes of ECG signals at different recording distances and directions relative to the heart are obtained. Furthermore, the ECG signals are successfully analyzed by the devices before and after exercise, indicating potential applications in some sports training and fitness scenarios. The OECT arrays that can conveniently monitor spacial ECG signals in the heart region may find niche applications in wearable electronics and healthcare products in the future.     

Design Criteria for Horseshoe and Spiral-Based Interconnects for Highly Stretchable Electronic Devices

Stretchable electronics can be used for numerous advanced applications such as soft and wearable actuators, sensors, bio-implantable devices, and surgical tools because of their ability to conform to curvilinear surfaces, including human skin. The efficacy of these devices depends on the development of stretchable geometries such as interconnection-based configurations and the associated mechanics that helps to achieve optimum configurations. This work presents the essential mechanics of silicon (Si) island-interconnection structures, which include horseshoe and spiral interconnections, without reducing the areal efficiency. In particular, this study demonstrates the range of the geometrical parameters where they have a high stretchability and cyclic life. The numerical results predict the areas that are prone to breaking followed by experimental validation. The figure-of-merit for these configurations is achieved by mapping the fracture-free zones for in-plane and out-of-plane stretching with essential implications in stretchable and wearable system design. Furthermore, this work demonstrates the mechanical response for a range of materials (i.e., copper, gold, aluminum, silver, and graphene) that experience the plastic deformations in contrast to conventionally used Si-based devices that represent the extended usage for advanced stretchable electronic devices. The detailed mechanics of these configurations provides comprehensive guidelines to manufacture wearable and stretchable electronic devices.     

Wearable Thermoelectric Generators for Body-Powered Devices

This paper presents a discussion on energy scavenging for wearable devices in conjunction with human body properties. Motivation, analysis of the relevant properties of the human body, and results of optimization of a thermopile and a thermoelectric generator for wearable and portable devices are presented. The theoretical limit for power generation on human beings is evaluated and confirmed by experimental results. The requirements for wearable thermopiles are summarized. The results allow certain conclusions to be drawn concerning directions for future development of body-powered devices.     

The Era of Digital Health: A Review of Portable and Wearable Affinity Biosensors

Digital health facilitated by wearable/portable electronics and big data analytics holds great potential in empowering patients with real‐time diagnostics tools and information. The detection of a majority of biomarkers at trace levels in body fluids using mobile health (mHealth) devices requires bioaffinity sensors that rely on “bioreceptors” for specific recognition. Portable point‐of‐care testing (POCT) bioaffinity sensors have demonstrated their broad utility for diverse applications ranging from health monitoring to disease diagnosis and management. In addition, flexible and stretchable electronics‐enabled wearable platforms have emerged in the past decade as an interesting approach in the ambulatory collection of real‐time data. Herein, the technological advancements of mHealth bioaffinity sensors evolved from laboratory assays to portable POCT devices, and to wearable electronics, are synthesized. The involved recognition events in the mHealth affinity biosensors enabled by bioreceptors (e.g., antibodies, DNAs, aptamers, and molecularly imprinted polymers) are discussed along with their transduction mechanisms (e.g., electrochemical and optical) and system‐level integration technologies. Finally, an outlook of the field is provided and key technological bottlenecks to overcome identified, in order to achieve a new sensing paradigm in wearable bioaffinity platforms.     

Textile‐Based Triboelectric Nanogenerators for Self‐Powered Wearable Electronics

Wearable smart electronic devices based on wireless systems use batteries as a power source. However, recent miniaturization and various functions have increased energy consumption, resulting in problems such as reduction of use time and frequent charging. These factors hinder the development of wearable electronic devices. In order to solve this energy problem, research studies on triboelectric nanogenerators (TENGs) are conducted based on the coupling of contact‐electrification and electrostatic induction effects for harvesting the vast amounts of biomechanical energy generated from wearer movement. The development of TENGs that use a variety of structures and materials based on the textile platform is reviewed, including the basic components of fibers, yarns, and fabrics made using various weaving and knitting techniques. These textile‐based TENGs are lightweight, flexible, highly stretchable, and wearable, so that they can effectively harvest biomechanical energy without interference with human motion, and can be used as activity sensors to monitor human motion. Also, the main application of wearable self‐powered systems is demonstrated and the directions of future development of textile‐based TENG for harvesting biomechanical energy presented.