A Comprehensive Review and Analysis of Nanosensors for Structural Health Monitoring in Bridge Maintenance: Innovations, Challenges, and Future Perspectives

This paper presents a thorough review and detailed analysis of nanosensors for structural health monitoring (SHM) in the context of bridge maintenance. With rapid advancements in nanotechnology, nanosensors have emerged as promising tools for detecting and assessing the structural integrity of bridges. The objective of this review is to provide a comprehensive understanding of the various types of nanosensors utilized in bridge maintenance, their operating principles, fabrication techniques, and integration strategies. Furthermore, this paper explores the challenges associated with nanosensor deployment, such as signal processing, power supply, and data interpretation. Finally, the review concludes with an outlook on future developments in the field of nanosensors for SHM in bridge maintenance.publishedVersio

Using a Second Order Sigma-Delta Control to Improve the Performance of Metal-Oxide Gas Sensors

Controls of surface potential have been proposed to accelerate the time response of MOX gas sensors. These controls use temperature modulations and a feedback loop based on first-order sigma-delta modulators to keep constant the surface potential. Changes in the surrounding gases, therefore, must be compensated by average temperature produced by the control loop, which is the new output signal. The purpose of this paper is to present a second order sigma-delta control of the surface potential for gas sensors. With this new control strategy, it is possible to obtain a second order zero of the quantization noise in the output signal. This provides a less noisy control of the surface potential, while at the same time some undesired effects of first order modulators, such as the presence of plateaus, are avoided. Experiments proving these performance improvements are presented using a gas sensor made of tungsten oxide nanowires. Plateau avoidance and second order noise shaping is shown with ethanol measurements.Postprint (author's final draft

Room Temperature Gas Sensing Using Pure and Modified Metal Oxide Nanowires

Recently, various quasi 1D metal oxide semiconductor nanostructures (nanorods, nanowires, nanotubes, nanobelts) of various binary oxides have been found to be excellent materials for gas sensing. However, some of the sensitive gas sensors can work only at elevated temperatures. The sensing performance can be further improved when these oxides are doped with noble metal nanoparticles and form hetero-junction with other oxides, especially different types of metal oxide. These modifications can substantially change the surface properties as well as electronic properties due to their enhancement of the depletion layer at the metal nanoparticle-metal oxide nanowire and homo/hetero-interfaces. The objective of this dissertation study is to investigate the sensing performance of WO3, ZnO, NiO and TiO2 nanowires towards various air pollutant gases such as NH3, NO2, H2S and CO at room temperature. The sensing performance of pure metal oxide nanowires are further improved by doping these nanowires with noble metal nanoparticles and through the formation of n-p hetero-junction of two dissimilar oxides. Based on this study, it was found that pure ZnO and NiO nanowires show a high sensitivity and the best selectivity performance towards the ppm level NO2 (1 ppm) with respect to other interfering gases. On the other hand, both WO3/Ag and WO3-NiO gas sensors show enhanced sensing and highly selective performance towards H2S (~10ppm) at room temperature. Additionally, sensor response and recovery become faster with WO3/Ag than pure WO3 nanowires. The plausible reasons for such improvements with these surface modifications are discussed. This study provides a scientific foundation to engineer practical room-temperature gas sensors with enhanced performance

Rational Design of Flexible and Stretchable Electronics based on 3D Printing

Flexible and stretchable electronics have been considered as the key component for the next generation of flexible devices. There are many approaches to prepare the devices, such as dip coating, spin coating, Mayer bar coating, filtration and transfer, and printing, etc. The effectiveness of these methods has been proven, but some drawbacks cannot be ignored, such as lacking pattern control, labor consuming, requiring complex pretreatment, wasting conductive materials, etc. In this investigation, we propose to adopt 3D printing technology to design flexible and stretchable electronics. The objective is to rationally design flexible and stretchable sensors, simplify the preparation process, form the sample with the complex desirable patterns, and promote the performance of the samples. The dissertation comprises of three major parts: water-induced polymer swelling and its application in soft electronics, utilizing 3D printing to transfer conductive layer into elastomer for building soft electronics, and 3D printing of functional devices. In the first part, we developed the soft electronics with wrinkled structure via 3D printing and water-induced polymer swelling, which can avoid some disadvantages in conventional method, e.g., pre-stretching and organic solvent-induced polymer swelling, including mechanical loss, negative effect to human health, and unidirectionally response to external deformation. Water-induced polymer swelling was achieved by introducing soluble particles into silicone matrixes and soaking the polymer composites in aqueous solution. We have investigated the characteristics and mechanisms of water-induced polymer swelling. Then, the conductive materials were deposited on the swollen sample to form the desired wrinkled structures for stretchable sensors. Furthermore, a dopamine layer was adopted to enhance the adhesion of matrix and conductive layer. The improvement was a key enabler to achieve superior electrical properties of 3D printed stretchable sensors for long-term cyclic stretching. We have demonstrated a series of human motion detection by using these stretchable strain sensors. Another part is designing flexible electrodes with desirable complex pattern by transferring a conductive layer into soft substrates during a 3D printing process. Taking advantage of extrusion pressure and polymer adhesion, the thin conductive layers were embedded into the printed polymer patterns, which can achieve conductive flexible electronics with desirable complex patterns. High-quality transfer has been achieved through adjusting conductive layer thickness, nozzle-to-substrate distance, and printing parameters, etc. Moreover, various printing patterns were created, and their properties were exhibited. The stretchable sensors showed an outstanding stress-strain relationship and electrical response to external deformations. The third part is about 3D printing of functional devices. In the collaborated study, the drug particles were introduced into silicone matrix to prepare the drug-eluting devices. When water molecules transported into the silicone matrix, the loaded drug particles decomposed and released nitric oxide (NO) enabling antibacterial properties. It is noted that 3D printing is creatively employed to form the desirable patterns. We also observed a self-wiring effect in the printing process, i.e., the printed device is covered by a drug-free layer due to the diffusion of a low viscosity silicone component during printing, which can be utilized to prevent drug release bursts and to form a gradient drug-loaded device. The printed samples showed a sustainable NO release and good antibacterial property. Furthermore, the water-induced polymer swelling was possible to be used as actuator in humidity environment. There are some highlights deserving emphasis in the dissertation. Firstly, the water-induced polymer swelling is proposed to develop the flexible and stretchable electronics. The findings have a wide potential application. Additionally, a drug-eluting polymer device with a drug-loaded bulk and a drug-free coating is prepared via leveraging self-wiring effect in 3D printing. The structure can regulate the drug release rate. On the other hand, the additive manufacturing platform offers unique opportunities to produce drug-eluting silicone devices in a customized manner. Finally, 3D printing is employed to encapsulate the conductive layers to achieve the flexible electronics with patterned structure and high performances. The facile and effective approach provides a distinctive view in advancing the development of stretchable electronics

Roadmap on semiconductor-cell biointerfaces.

This roadmap outlines the role semiconductor-based materials play in understanding the complex biophysical dynamics at multiple length scales, as well as the design and implementation of next-generation electronic, optoelectronic, and mechanical devices for biointerfaces. The roadmap emphasizes the advantages of semiconductor building blocks in interfacing, monitoring, and manipulating the activity of biological components, and discusses the possibility of using active semiconductor-cell interfaces for discovering new signaling processes in the biological world

Metal oxide semiconductor nanomembrane-based soft unnoticeable multifunctional electronics for wearable human-machine interfaces

Wearable human-machine interfaces (HMIs) are an important class of devices that enable human and machine interaction and teaming. Recent advances in electronics, materials, and mechanical designs have offered avenues toward wearable HMI devices. However, existing wearable HMI devices are uncomfortable to use and restrict the human body's motion, show slow response times, or are challenging to realize with multiple functions. Here, we report sol-gel-on-polymer-processed indium zinc oxide semiconductor nanomembrane-based ultrathin stretchable electronics with advantages of multifunctionality, simple manufacturing, imperceptible wearing, and robust interfacing. Multifunctional wearable HMI devices range from resistive random-access memory for data storage to field-effect transistors for interfacing and switching circuits, to various sensors for health and body motion sensing, and to microheaters for temperature delivery. The HMI devices can be not only seamlessly worn by humans but also implemented as prosthetic skin for robotics, which offer intelligent feedback, resulting in a closed-loop HMI system

Energy challenges for ICT

The energy consumption from the expanding use of information and communications technology (ICT) is unsustainable with present drivers, and it will impact heavily on the future climate change. However, ICT devices have the potential to contribute signi - cantly to the reduction of CO2 emission and enhance resource e ciency in other sectors, e.g., transportation (through intelligent transportation and advanced driver assistance systems and self-driving vehicles), heating (through smart building control), and manu- facturing (through digital automation based on smart autonomous sensors). To address the energy sustainability of ICT and capture the full potential of ICT in resource e - ciency, a multidisciplinary ICT-energy community needs to be brought together cover- ing devices, microarchitectures, ultra large-scale integration (ULSI), high-performance computing (HPC), energy harvesting, energy storage, system design, embedded sys- tems, e cient electronics, static analysis, and computation. In this chapter, we introduce challenges and opportunities in this emerging eld and a common framework to strive towards energy-sustainable ICT

웨어러블 센서 및 에너지 소자의 공간 신호 및 열 전달 증진을 위한 나노복합체를 이용한 기계적 순응성 향상

학위논문 (박사) -- 서울대학교 대학원 : 공과대학 전기·정보공학부, 2020. 8. 홍용택.Electronic skin (e-skin) that mimics mechanical and functional properties of human skin has a strong impact on the field of wearable electronics. Beyond being just wearable, e-skin seamlessly interfaces human, machine, and environment by perfectly adhering to soft and time-dynamic three-dimensional (3D) geometries of human skin and organs. Real-time and intimate access to the sources of physical and biological signals can be achieved by adopting soft or flexible electronic sensors that can detect pressure, strain, temperature, and chemical substances. Such extensions in accessible signals drastically accelerate the growth of the Internet of Things (IoT) and expand its application to health monitoring, medical implants, and novel human-machine interfaces. In wearable sensors and energy devices, which are essential building blocks for skin-like functionalities and self-power generation in e-skin, spatial signals and heat are transferred from time-dynamic 3D environments through numerous geometries and electrical devices. Therefore, the transfer of high-fidelity signals or a large amount of heat is of great importance in these devices. The mechanical conformability potentially enhances the signal/heat transfer by providing conformal geometries with the 3D sources. However, while the relation between system conformability and electrical signals has been widely investigated, studies on its effect on the transfer of other mechanical signals and heat remain in their early stages. Furthermore, because active materials and their designs for sensors and energy devices have been optimized to maximize their performances, it is challenging to develop ultrathin or soft forms of active layers without compromising their performances. Therefore, many devices in these fields suffer from poor spatial signal/heat transfer due to limited conformability. In this dissertation, to ultimately augment the functionalities of wearable sensors and energy devices, comprehensive studies on conformability enhancement via composite materials and its effect on signal/heat transfer, especially in pressure sensors and thermoelectric generators (TEGs), are conducted. A solution for each device is carefully optimized to reinforce its conformability, taking account of the structure, characteristics, and potential advantages of the device. As a result, the mechanical conformability of each device is significantly enhanced, improving signal/heat transfer and consequently augmenting its functionalities, which have been considered as tough challenges in each area. The effect of the superior conformability on signal/heat transfer is systematically analyzed via a series of experiments and finite element analyses. Demonstrations of practical wearable electronics show the feasibility of the proposed strategies. For wearable pressure sensors, ultrathin piezoresistive layers are developed using cellulose/nanowire nanocomposites (CNNs). The unique nanostructured surface enables unprecedentedly high sensor performances such as ultrahigh sensitivity, wide working range, and fast response time without microstructures in sensing layers. Because the ultrathin pressure sensor perfectly conforms to 3D contact objects, it transfers pressure distribution into conductivity distribution with high spatial fidelity. When integrated with a quantum dot-based electroluminescent film, the transferred high-resolution pressure distribution is directly visualized without the need for pixel structures. The electroluminescent skin enables real-time smart touch interfaces that can identify the user as well as touch force and location. For high-performance wearable TEGs, an intrinsically soft heat transfer and electrical interconnection platform (SHEP) is developed. The SHEP comprises AgNW random networks for intrinsically stretchable electrodes and magnetically self-assembled metal particles for soft thermal conductors (STCs). The stretchable electrodes lower the flexural rigidity, and the STCs enhance the heat exchange capability of the soft platform, maintaining its softness. As a result, a compliant TEG with SHEPs forms unprecedentedly conformal contact with 3D heat sources, thereby enhancing the heat transfer to the TE legs. This results in significant improvement in thermal energy harvesting on 3D surfaces. Self-powered wearable warning systems indicating an abrupt temperature increase with light-emitting alarms are demonstrated to show the feasibility of this strategy. This study provides a systematic and comprehensive framework for enhancing mechanical conformability of e-skin and consequently improving the transfer of spatial signals and energy from time-dynamic and complex 3D surfaces. The framework can be universally applied to other fields in wearable electronics that require improvement in signal/energy transfer through conformal contact with 3D surfaces. The materials, manufacturing methods, and devices introduced in this dissertation will be actively exploited in practical and futuristic applications of wearable electronics such as skin-attachable advanced user interfaces, implantable bio-imaging systems, nervous systems in soft robotics, and self-powered artificial tactile systems.인간 피부의 기계적 특성 및 기능을 모방하는 전자피부(electronic skin, e-skin)는 웨어러블 전자기기 분야의 트렌드를 바꾸고 있다. 기존의 웨어러블 전자기기가 단지 착용하는데 그쳤다면, 전자피부는 인간의 피부와 장기 표면에 완벽하게 붙어 동작함으로써 기존에는 접근 불가능 했던 다양한 생체 신호를 높은 신뢰도로 감지하고 처리할 수 있다. 실시간으로 감지 가능한 생체 신호의 확장은 사물인터넷(Internet of Things, IoT)의 성장을 획기적으로 가속화하고 헬스케어, 의료용 임플란트, 소프트 로봇 및 새로운 휴먼 머신 인터페이스로의 응용을 가능하게 한다. 전자피부의 필수요소인 센서와 에너지 소자에서는 삼차원 표면의 공간신호와 열에너지를 손실 없이 전달하는 것이 매우 중요하다. 이러한 공간 신호와 열에너지는 다양한 기하 구조와 전자소자를 거쳐 처리 가능한 신호로 전달된다. 이 과정에서 3차원 표면에 빈틈없이 붙는 기계적 순응성(mechanical conformability)은 공간신호와 열에너지를 왜곡 없이 전달하는 것을 가능하게 한다. 전자피부의 기계적 순응성을 증가시키는 방법은 크게 다음과 같이 두 가지로 나눌 수 있다. (1) 전자피부를 두께를 낮추는 전략과 (2) 전자피부의 영률(Youngs modulus)을 낮추어 고무와 같이 부드럽게 만드는 전략이다. 하지만, 기존 센서 및 에너지 소자를 위한 재료와 디자인이 각 장치의 성능을 향상시키는 것에 초점이 맞추어져 있기 때문에, 고성능을 유지하면서 매우 얇거나 연질 형태의 소자를 개발하는 것은 매우 도전적이었다. 따라서 고유연성을 확보하지 못한 기존 센서와 에너지 소자는 공간 신호 및 열 전달이 심각하게 저해되고, 이로 인해 공간 압력의 왜곡, 열전 효율의 저하와 같은 한계를 보여준다. 이 논문에서는 웨어러블 센서와 에너지 소자의 비약적인 기능 향상을 궁극적인 목표로, 각 소자에 최적화된 재료와 제작방식, 구조를 이용해 이들의 기계적 순응성을 획기적으로 높이고, 이를 통한 공간 신호 및 열 전달의 향상을 심도 있게 분석한다. 특히, 두께를 낮추거나 영률을 낮추는 두 가지 전략 중 각 소자에 가장 적합한 전략을 선택하고, 체계적인 방법론을 적용하여 이들의 기계적 순응성과 공간 신호 및 열 전달을 증진시킨다. 이 과정에서 나노융복합재료가 각 전략을 구현하는 핵심 요소로 작용한다. 각 소자에 따른 구체적인 연구 내용은 다음과 같다. 첫째, 압력 센서의 경우 초박막 셀룰로오스/나노와이어 복합체를 이용하여 고성능의 저항방식 압력 센서를 개발한다. 이러한 복합체는 표면에 형성된 고유한 나노구조 덕분에 마이크로구조체를 이용한 기존 압력 센서보다 월등한 성능을 보여준다. 특히, 1 마이크로 미터 수준의 매우 얇은 두께로 인해 접촉 물체의 복잡한 형상에 완벽하게 순응할 수 있고, 이로 인해 고해상도 압력 분포를 왜곡 없이 저항 분포로 전달할 수 있다. 이러한 압력 센서를 양자 점 발광소자와 결합하여 고해상도의 압력분포를 높은 정밀도로 이미징 가능한 발광 소자를 보고한다. 둘째, 열전 소자의 경우 기존의 금속 전극으로 인한 낮은 유연성과 탄성중합체의 낮은 열 전도도를 극복하기 위해 열 전달 능력이 획기적으로 향상된 낮은 영률의 소프트 전극 플랫폼을 개발한다. 소프트 플랫폼은 내부에 은 나노와이어 기반의 신축성 전극을 갖고 있으며, 자기장을 통해 자가 정렬된 금속 입자들이 효과적으로 외부 열을 열전 재료에 전달한다. 이를 기반으로 제작된 고유연성 열전 소자는 삼차원 열원에 빈틈없이 붙어 열 손실을 최소화 하며, 이로 인해 높은 열전 효율을 달성한다. 이 논문은 다양한 전자소자의 유연성을 증진시키고 이를 통한 공간 신호 및 열 전달의 향상을 도모하고 분석하는 체계적이고 종합적인 방법론을 제시했다는 데 큰 의의가 있다. 제안된 방법론은 분야에 국한되지 않고 다양한 소자의 개발에 적용할 수 있어 웨어러블 기기와 전자피부 분야의 기계적, 기능적 발전에 크게 기여할 것으로 기대된다. 뿐만 아니라 이 연구에서 최초로 개발한 소재 및 소자들은 다양한 웨어러블 어플리케이션과 산업에 곧바로 융합되고 응용될 수 있다. 이를 통해 신체 부착 및 삽입 가능한 생체 이미징 시스템, 소프트 로봇을 위한 신경 체계, 자가 발전이 가능한 인공 감각 기관, 가상 및 증강 현실을 위한 새로운 유저 인터페이스와 같은 미래 지향적 융합 어플리케이션의 실현을 앞당길 것으로 기대된다.Chapter 1. Introduction 1 1.1 Wearable Electronics and Electronic Skin 1 1.2 Mechanical Conformability of Electronic Skin 6 1.2.1 Definition and Advantages 6 1.2.2 Thickness-Based Conformability 11 1.2.3 Softness-Based Conformability 15 1.3 Conformability for Enhanced Signal/Heat Transfer in Wearable Sensors and Energy Devices 19 1.3.1 Conformability for Spatial Signal Transfer in Pressure Sensors 20 1.3.2 Conformability for Heat Transfer in Thermoelectric Generators 22 1.4 Motivation and Organization of This Dissertation 24 Chapter 2. Ultrathin Cellulose Nanocomposites for High-Performance Piezoresistive Pressure Sensors 28 2.1 Introduction 28 2.2 Experimental Section 31 2.2.1 Fabrication of the CNNs and Pressure Sensors 31 2.2.2 Measurements 34 2.3 Results and Discussion 38 2.3.1 Morphology of CNNs 38 2.3.2 Piezoresistive Characteristics of CNNs 41 2.3.3 Mechanism of High Sensitivity and Great Linearity 45 2.3.4 Fast Response Time of CNN-Based Pressure Sensors 49 2.3.5 Cyclic Reliability of CNN-Based Pressure Sensors 53 2.3.6 Mechanical Reliability and Conformability 57 2.3.7 Temperature and Humidity Tolerance 63 2.4 Conclusion 66 Chapter 3. Ultraflexible Electroluminescent Skin for High-Resolution Imaging of Pressure Distribution 67 3.1 Introduction 67 3.2 Main Concept 70 3.3 Experimental Section 72 3.3.1 Fabrication of Pressure-Sensitive Photonic Skin 72 3.3.2 Characterization of Photonic Skin 74 3.4 Results and Discussion 76 3.4.1 Structure and Morphology of Photonic Skin 76 3.4.2 Pressure Response of Photonic Skin 79 3.4.3 Effect of Conformability on Spatial Resolution 85 3.4.4 Demonstration of High-Resolution Pressure Imaging 99 3.4.5 Pressure Data Acquisition 104 3.4.6 Application to Smart Touch Interfaces 106 3.5 Conclusion 109 Chapter 4. Intrinsically Soft Heat Transfer and Electrical Interconnection Platforms Using Magnetic Nanocomposites 110 4.1 Introduction 110 4.2 Experimental Section 115 4.2.1 Fabrication of SHEPs 115 4.2.2 Measurements 117 4.3 Results and Discussion 119 4.3.1 Fabrication Scheme and Morphology of SHEPs 119 4.3.2 Calculation of Particle Concentration in STCs 124 4.3.3 Enhancement of Heat Transfer Ability via Magnetic Self-Assembly 127 4.3.4 Softness of STCs 131 4.3.5 Mechanical Reliability of Stretchable Electrodes 133 4.3.6 Optimization of Magnetic Self-Assembly Process 135 4.4 Conclusion 139 Chapter 5. Highly Conformable Thermoelectric Generators with Enhanced Heat Transfer Ability 140 5.1 Introduction 140 5.2 Experimental Section 142 5.2.1 Fabrication of Compliant TEGs 142 5.2.2 Measurements 144 5.2.3 Finite Element Analysis 147 5.3 Results and Discussion 149 5.3.1 Enhancement of TE Performance via STCs 149 5.3.2 Mechanical Reliability of Compliant TEGs 157 5.3.3 Enhanced TE Performance on 3D Surfaces via Conformability 162 5.3.4 Self-Powered Wearable Applications 167 5.4 Conclusion 171 Chapter 6. Summary, Limitations, and Recommendations for Future Researches 172 6.1 Summary and Conclusion 172 6.2 Limitations and Recommendations 176 6.2.1 Pressure Sensors and Photonic Skin 176 6.2.2 Compliant TEGs 177 Bibliography 178 Publication List 186 Abstract in Korean 192Docto

Wireless Remote Monitoring of Glucose Using a Functionalized ZnO Nanowire Arrays Based Sensor

This paper presents a prototype wireless remote glucose monitoring system interfaced with a ZnO nanowire arrays-based glucose sensor, glucose oxidase enzyme immobilized onto ZnO nanowires in conjunction with a Nafion® membrane coating, which can be effectively applied for the monitoring of glucose levels in diabetics. Global System for Mobile Communications (GSM) services like General Packet Radio Service (GPRS) and Short Message Service (SMS) have been proven to be logical and cost effective methods for gathering data from remote locations. A communication protocol that facilitates remote data collection using SMS has been utilized for monitoring a patient’s sugar levels. In this study, we demonstrate the remote monitoring of the glucose levels with existing GPRS/GSM network infra-structures using our proposed functionalized ZnO nanowire arrays sensors integrated with standard readily available mobile phones. The data can be used for centralized monitoring and other purposes. Such applications can reduce health care costs and allow caregivers to monitor and support to their patients remotely, especially those located in rural areas

Research progress of flexible wearable stress sensor

Flexible wearable pressure sensors are widely used in health diagnosis, sports monitoring, rehabilitation medicine, entertainment, and other fields due to some factors such as the stretch ability, bendability, light weight, portability, and excellent electrical properties. In recent years, significant progress has been made in flexible pressure sensors, and a variety of flexible pressure sensors that able to measure health status have been applied to the pulse wave, movement, respiration, and electrocardiogram (ECG) detection. However, there are still many problems to be solved in the development of flexible pressure sensors. This article summarizes the development of flexible pressure sensors in recent years, from the working principle to the structural design of the flexible pressure sensors; designs to build a high-performance flexible pressure sensors; discusses the problems existing in current flexible pressure sensors and envisions the development trend of flexible pressure sensors in the future. Flexible pressure sensors with excellent flexibility, good biocompatibility, rapid response, high sensitivity, and multifunctional integration have shown a broad application prospects