Social-based smart objects discovery and composition in internet of things

Jung, Jooik Graduate School, Yonsei University 2018 국내박사

Recent advances in the Internet of Things (IoT) technology have led to the rise of a new paradigm: Social Internet of Things (SIoT). The emerging Social Internet of Things has undoubtedly opened up a myriad of new business, social, and research opportunities by allowing smart objects to autonomously establish social relationships with each other and exchange information. However, the new paradigm, as inspired by the idea that smart objects will soon have a certain degree of social consciousness, is still in its infant state for several reasons. One of the most fundamental research challenges posed by SIoT is the fact that there is yet to be a coherent social network structure for organizing and managing smart objects that elicit social-like features. In particular, a social network of smart objects must be built upon three design principles. First of all, the network structure must be designed such that it exhibits scalability in terms of embracing the explosive accumulation of smart objects and inter-object relations. Moreover, the network structure must be able to cope with the heterogeneity of smart objects as they are extremely diverse in terms of functionality and descriptions. Last but not least, the ability to efficiently adapt to the dynamicity of smart objects must be incorporated into the social network structure by reorganizing itself. To fully understand how and to what extent these objects may mimic the behaviors of humans, there is an urgent need for a method that quantitatively estimates the link strengths of inter-object relations within the social network. In human-centric social networks, people are connected by friendship relations, which indicate the degree of their closeness and how much they share similar interests. Furthermore, these relations are augmented with trust among people so that they can be utilized for various real-world applications such as service recommendations, viral marketing and so on. Similarly, the strengths of social relationships among smart objects must be properly quantified and integrated with trust in smart object discovery and composition, so as to proliferate the provisioning of SIoT composite services. In this thesis, we propose a hypergraph-based overlay network model for effectively organizing and managing smart objects and their social relations. This particular social network structure is a generically constructed model, which exposes various SIoT interactions at different granularity levels to ensure the flexibility and consistency of the model. We further design a smart objects discovery mechanism which utilizes the proposed SIoT network structure. Then, we introduce a model named social strength prediction model (SSPM), which infers social connections and quantitatively predicts the strengths of inter-object connections using the co-usage data of smart objects. Based on the social strength measures, we integrate the model with our trust computation algorithm, eventually yielding a trust-augmented social strength (TASS) management protocol that can support smart objects composition. Finally, we perform various experiments to test the feasibility of the proposed network model as well as the trust-augmented social strength computation method. We built a smart home automation demo box to evaluate the social network structure in terms of the three design principles, and conducted additional experiments using real-world datasets to demonstrate the resiliency along with the accuracy of the proposed TASS protocol. Overall, our work and findings provide valuable insights to the development of future SIoT systems.

Fabrication of morphing structure using woven type smart soft composite

한민우 서울대학교 대학원 2013 국내석사

소프트 모핑(soft morphing)은 주위의 환경 혹은 특정 기능에 맞추어 유연하게 모양을 변화시킬 수 있는 생물체의 행동 변화를 모방한 유연 구조체의 변형을 의미한다. 이를 구현하기 위하여 복합 재료와 지능 재료(형상기억합금, 압전소자, 이온 폴리머 금속 복합체(IPMC) 등)를 활용하는 지능형 구동기에 대한 연구들이 다양하게 진행되고 있다. 하지만 이들 구동기의 대부분은 복합재의 높은 강성으로 인한 작은 변위, 지지체(scaffold) 구조의 복잡성으로 인한 대면적 제작에 한계를 지니고 있다. 이에 본 연구에서는 딱딱한 재료가 아닌 유연 물질을 기반으로 하며, 스스로 큰 변형(large deformation)을 일으킨 후, 원래의 상태로 복원(reversible)이 가능하고 대면적(large area)으로의 제작이 용이한 모핑 구동기(morphing actuator)를 제작하고자 한다. 이를 위해 형상기억합금 와이어와 유리 섬유가 직조된 직조물을 유연한 성질의 폴리머인 Polydimethylsiloxane(PDMS)에 함침시켜 직조 형태의 지능형 연성 복합 구조물(Woven type Smart Soft Composite)을 제작하였다. 제작된 복합 구조물을 한 층씩 적층하여 최종 구동기가 완성이 되며 이러한 적층 기반 공정을 통해 제작 절차를 단순화 시키고자 하였다. 모핑 구동기의 구동 특성 파악을 위해 유리 섬유 직물이 적층된 레이어(layer)의 수, 형상기억합금 와이어의 두께를 바꾸어 가며 변형량과 구동힘을 측정하였다. 또한 개발된 모핑 구동기는 대면적으로의 제작 및 대변형이 용이한 쉘(shell) 형태로써 응용이 되었으며 변형 모드를 다양하게 만들기 위해 구조체 내에 삽입된 형상기억합금 와이어를 전류 채널로 활용하여 비틀림과 굽힘 운동을 발생시켰다. 완성된 쉘 구동기를 응용하여 모형 자동차(1/8 scale)의 후방 스포일러(spoiler)를 제작하였으며, 제작된 스포일러의 성능 검증을 위한 풍동 실험(wind tunnel test)을 수행하였다. 풍동 실험은 스포일러 단일 모델과 모형 자동차에 장착된 스포일러, 각 두 차례에 걸쳐 진행되었으며 각각에서 발생하는 다운 포스(down force) 및 항력(drag force)을 측정하여 차량으로 적용 시, 일어날 수 있는 힘의 변화에 대해서도 관찰 하였다. In the field of engineering, the word ‘soft morphing’ is used when referring to continuous shape change by mimicking the ability of natural organisms to adapt environments based on flexible materials. To realize the soft morphing, new kinds of actuator combining composites with smart materials such as Shape Memory Alloy (SMA), piezoelectric materials, Ionic Polymer Metal Composite (IPMC) have been developed. However, these actuators have several restrictions, e.g., the limited deformation, operational voltage and difficulties to fabricate in large scale caused by complicated scaffold structures. In this study, a morphing structure was fabricated using woven type Smart Soft Composite (SSC) which can recover its original shape after undergoing large deformation. The woven type SSC consists of a polydimethylsiloxane (PDMS) matrix and a woven structure combining SMA wires and glass fibers. The fabricated composite structure was layered on top of the other before finally getting the desired actuator in terms of stiffness, actuating motion and shape. In order to investigate the performances of the actuator, the deformation and actuating force were measured depending on certain fabrication parameters, such as the number of the lamina and diameter of SMA wires. To enhance the deformation capacity and manufacturability in large-area applications, the woven type SSC was made in the form of a shell. By controlling the actuation of the SMA wires which are embedded in the shell actuator, the actuator can generate a bend-twist deformation without requiring any additional parts. As an application of the shell actuator using woven type SSC, a morphing car-spoiler was developed. The performance of the spoiler by itself and mounted on a small-scale vehicle (1/8 scale) were tested through wind tunnel testing and the dynamic characteristics related to the generated down force and drag force were observed.

Development of 2D Functionalized Nanomaterials-Based Wearable Sensing Devices for Electronic Skin and Human-Machine Interaction Applications

장세붕 광운대학교 일반대학원 2023 국내박사

2D materials-based wearable devices have emerged as a promising technology for human-machine interaction and biomedical health applications. The unique properties of 2D materials, such as their high surface-to-volume ratio, excellent mechanical flexibility, and electrical conductivity, make them ideal for developing highly sensitive and responsive sensors for various physiological signals. These wearable devices can be used to monitor vital signs such as heart rate, blood pressure, and body temperature, and transmit the data in real-time to healthcare professionals or family members. In addition, they can also be used to track physical activity, and sleep patterns, and detect abnormalities in movement, enabling early detection and prevention of diseases. Moreover, 2D materials-based wearable devices can also be applied in human-machine interaction, such as in the field of virtual and augmented reality. These devices can provide accurate tracking and detection of human movement and gestures, enabling a more intuitive and natural user interface for immersive experiences. Firstly, an ultra-high sensitive, flexible, wireless, battery-free, and fully integrated (no external analysis equipment) electrochemical sensing patch system, including a microfluidic-sweat collecting unit, was newly developed for the on-site monitoring of the [K+] concentration in human sweat. Multiwalled carbon nanotube (MWCNT) and MXene-Ti3C2TX-based hybrid multi-dimensional networks were applied to obtain a high surface activation area and faster charge transfer rate, strongly adsorbing the valinomycin membrane to protect the ionophore for effective transhipment and immobilization of the [K+]. Secondly, MXene-Ti3C2Tx and 3, 4-ethylene dioxythiophene (EDOT) deposited on laser-induced graphene (LIG/MXene-Ti3C2Tx@EDOT) composite-based flexible and stretchable multifunctional sensors were proposed and developed for strain, temperature, and electrocardiogram (ECG) monitoring. In-situ electrophoretic deposition (EPD) of MXene-Ti3C2Tx@EDOT composite into LIG outperforms high strain sensitivity of 2,075, temperature coefficient of resistance (TCR) of 0.86%, and low skin-contact impedance. The sensor platform is integrated into an ultrathin and highly resilient polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (SEBS). Finally, we demonstrate on-site detection of human body-induced deformations and physiological health indicators, such as temperature and ECG. Thirdly, a simple and robust low-conductivity loss transfer technique was proposed and developed. Successfully embedded LIG onto SEBS to obtain high stretchability, high flexibility, and low conductivity losses. Electrophoretic deposition (EPD) of poly(3,4-ethylenedioxythiophene):polystyrenesulfonic acid (PEDOT:PSS) on LIG forms an ultrathin polymer conductive coating. The deposition thickness of the conductive polymer is adjusted by controlling the EPD deposition time to achieve optimal conductivity and chemical stability. SEBS/LIG/PEDOT:PSS (SLPP) dry electrodes have high conductivity (114 Ω/Sq), stretchability (300%) and reliability (30% stretch, 15,000 cycles), and low electrode-skin impedance (14.39 kΩ, 10 Hz). The detected biopotential signal has a high signal-to-noise ratio (SNR) of 35.78 dB. Finally, the feasibility of SLPP dry electrodes for long-term biopotential monitoring and biopotential-based human-machine interface control of household appliances was verified. Finally, a wearable self-powered toroidal triboelectric sensor (STTS) with a pyramidal structure was proposed and developed for self-powered human-machine interactions based on an extremely simplified design strategy. 3D printing technology is employed to fabricate pyramidal arrays on MXene/Ecoflex nanocomposites, thus providing a comfortable space between the finger skin and the negatively charged layer to overcome the space requirements in traditional triboelectric-based sensors. Furthermore, the developed pyramidal structure of the nanocomposite and flexible conductive fabric electrodes assembled with 3D-printed gloves based on the flexible TPU material maintained the wearability of the sensing system. The flexible and simplified single-electrode design strategy of the STTS can be easily worn on the human hand for comfortable and natural interaction with machines and devices. The STTS enable the generation of high-quality output signals for the accurate detection of various finger movements exhibiting great potential for use in human-machine interaction applications. In conclusion, 2D materials-based wearable devices have great potential for revolutionizing the field of human-machine interaction and biomedical health. With further development and refinement, they could become a ubiquitous and invaluable tool for enhancing human health and performance.

스마트복합재의 손상 분류 및 예측을 위한 기계학습기법 연구

Khan, Asif 동국대학교 대학원 2018 국내박사

스마트 적층 복합재는 뛰어난 특성을 가지고 있으며, 산업 및 공학 분야에서 다양한 응용 재료로 선호되고 있다. 하지만 복합 재료의 이방성 및 비등방성으로 인해 스마트 적층 복합재는 아주 복잡한 파괴 모드를 가지며, 이로 인해 비파괴 검사나 실시간 구조 건전성 평가에 많은 어려움을 야기한다. 본 논문에서는 스마트 적층 복합재의 저주파 구조 진동 응답으로부터 주구조물의 층간 분리, 센서 및 액추에이터의 부분 분리 등과 같은 다중 손상의 분류 및 예측을 위한 시스템 식별과 기계 학습의 효과적인 결합에 대한 연구를 수행하였다. 스마트 적층 복합재의 층간 분리 및 트랜스듀서 부분 분리에 대한 효과적인 모델링과 전기-기계 연성효과를 모사하기 위해 향상된 층간 변위장 및 고차전기포텐셜을 도입하였다. 유한요소법과 확장된 해밀턴의 원리를 적용하여 운동방정식을 유도하였다. 개발된 모델을 적용하여, 센서의 부분 분리가 있는 스마트 적층 복합재의 동적 응답에 대해 먼저 해석하였다. 다음으로 구조적인 층간 분리와 트랜스듀서의 부분 분리가 같이 나타나는 경우에 대해 연구하였다. 액추에이터를 이용하여 랜덤조화가진을 손상이 있는 경우와 없는 경우의 구조물에 대하여 가하였으며, 시간영역에서 운동방정식을 풀어 표면에 부착된 센서의 과도응답을 구하였다. 압전소자의 입력-출력 정보와 시스템 식별 알고리즘을 통해 식별 특징공간을 구성하였다. 스마트 적층 복합재의 다중 손상이 있는 경우의 손상 분류 및 예측을 위한 식별 특징 공간을 조사하기 위해 지도학습, 비지도학습 등 다양한 기계학습 기술들을 적용하였으며, 최적의 지도학습 분류법을 확인하였다. 결과들은 물리적으로 합리적이며, 제안한 기법은 사전 정의된 손상 임계치를 적용하면 스마트 적층 복합재의 자율적 구조 건전성 평가를 위해 사용할 수 있다. Smart Composite laminates have remarkable properties and are becoming preferred materials in a wide variety of industrial and engineering applications. However, due to anisotropic and heterogeneous nature of composite materials, the complex failure modes of smart composite laminates pose challenges in nondestructive evaluation and structural health monitoring of these materials. This thesis investigates the synergetic integration of system identification and machine learning for the classification and prediction of multi-damages (delaminations in the host structure, debonding of transducers) in smart composite laminates from their low frequency structural vibration response. Improved layerwise theory and higher order electric potential field are incorporated to develop the electromechanically coupled displacement field of the smart laminated composite with structural delaminations and transducers (piezoelectric sensor & actuator) partial debonding. Finite element method and extended Hamilton’s principle are employed to obtain the governing equation of motion. At first, the developed model is employed to study the effect of sensor partial debonding on dynamic response of smart composite laminates. At the next stage, the combined problem of structural delaminations and transducers partial debonding is considered. A set of random harmonic excitations is applied to the healthy and damaged structures through the actuator and the corresponding transient responses are obtained through a surface bonded sensor by solving the governing equation in the time domain. The discriminative feature space is constructed by processing the input-output information of piezoelectric transducers via a system identification algorithm. Various machine learning techniques (both supervised & unsupervised) are employed to investigate the discriminative feature space for the classification and predictions of multi-damages in smart composite laminates and optimum supervised learning classifiers are identified. Results of the proposed technique are consistent with physics of the problem and could be used for autonomous structural health monitoring of smart composite laminates with a predefined damage threshold.

A Comprehensive Coupled Theory for Smart Composite Structures Including Delaminations

김흥수 Arizona State University 2003 해외박사

A general framework is developed for the analysis of smart composite structures with delamination and embedded/surface bonded sensors/actuators. To maintain local accuracy of stress distributions, the trial displacement field is modeled using the superposition of overall first order shear deformation and layerwise functions, accommodating zigzag in-plane warping and interlaminar shear stress continuity. The temperature and electrical fields are modeled using higher order descriptions, which can satisfy surface flux boundary conditions at structural surfaces and equilpotential conditions at electrode surfaces. A variational principle, addressing the two-way interaction between thermal, piezoelectric and mechanical fields, is used to derive the equations of motion. A Linear Quadratic Gaussian control system of composite laminates with surface bonded/segmented piezoelectric actuators is designed to improve the damping characteristics. The presence of multiple discrete delaminations in composite plate of arbitrary thickness is modeled using Heaviside unit step functions, which are introduced in the layerwise zigzag displacement field. This allows modeling of the separation and slipping effects at the delaminated interface by introducing independent displacement field above and below the delamination. The accuracy of developed theory is validated by comparison with published experimental results as well as results obtained using laser scanning vibrometer. Next, linear and nonlinear transient implicit algorithms are developed to study the transient response of laminated composite plates with embedded discrete and continuous sensors in the presence of multiple discrete delaminations. The presence of delamination causes changes in tip displacement and sensor voltage output (magnitude and phase). Embedded sensors provide good information about the presence of delamination. Both multiple discrete and continuous sensors provide comparable information regarding existence of delamination. The contact problem at delaminated interfacial surfaces is modeled in terms of fictitious linear springs to provide an accurate description of the delaminated upper and lower laminates during plate vibration. Geometric nonlinearity due to large deformation and the coupled effect of the large deformation and bimodular behavior of the contact impact of the delaminated interfaces during breathing phenomena are modeled. A potential application of the developed procedure is in structural health monitoring where accurate predictions of dynamic response in the presence of delamination are important issues.

Nonlinear Analysis of Smart Composite Plate and Shell Structures

이승준 Texas A & M University 2004 해외박사

Theoretical formulations, analytical solutions, and finite element solutions for laminated composite plate and shell structures with smart material laminae are presented in the study. A unified third-order shear deformation theory is formulated and used to study vibration/deflection suppression characteristics of plate and shell structures. The von Ka´rma´n type geometric nonlinearity is included in the formulation. Third-order shear deformation theory based on Donnell and Sanders nonlinear shell theories is chosen for the shell formulation. The smart material used in this study to achieve damping of transverse deflection is the Terfenol-D magnetostrictive material. A negative velocity feedback control is used to control the structural system with the constant control gain. The Navier solutions of laminated composite plates and shells of rectangular planeform are obtained for the simply supported boundary conditions using the linear theories. Displacement finite element models that account for the geometric nonlinearity and dynamic response are developed. The conforming element which has eight degrees of freedom per node is used to develop the finite element model. Newmark's time integration scheme is used to reduce the ordinary differential equations in time to algebraic equations. Newton-Raphson iteration scheme is used to solve the resulting nonlinear finite element equations. A number of parametric studies are carried out to understand the damping characteristics of laminated composites with embedded smart material layers.

ASSESSING THE STATUS OF CLIMATE-SMART AGRICULTURAL PRACTICES BY SMALLHOLDER FARMERS IN EAST GONJA MUNICIPAL, GHANA

David Adugbire Akuribire 강원대학교 대학원 2024 국내석사

The study examined the status of Climate Smart Agricultural (CSA) practices in the East Gonja Municipal in Ghana. Climate Change is having a growing effect on the Agricultural sector, hitting the already vulnerable farmers the hardest, exposing them to yield losses and food insecurity. Climate Smart Agriculture is advocated as an alternative agricultural approach aimed at enhancing food security and alleviating poverty, particularly in developing nations. Although there have been several programs by successive Governments in Ghana to acquaint farmers with the concept and improve their production, the adoption status of Climate Smart Agricultural practices by smallholder farmers in The East Gonja Municipal is unknown as farmers continue to record low yield. Hence, the study's particular objectives focused on; assessing the awareness of farmers on CSA practice, the frequency of use, the status of Adoption, and the factors influencing the status of adoption of CSA practices. The study used Descriptive statistics to assess the awareness and the frequency of use of CSA. A Composite Score Index, and Ordered Logit Models were used to categorize farmers into Low, Moderate, and High users, and examine the factors affecting the status of use of CSA practices respectively. The parallel assumption test was conducted which proved that the parallel odds assumption was not violated leading to the use of the ordered logit Model for the study. The results showed that 90.5% of the sampled farmers are aware of CSA practices while 9.5% are naïve of the concept. Also, the most frequently used CSA practices were soil conservation, cover crops, Mulching, crop rotation, conservative agriculture, and agroforestry in descending order. In contrast, organic manure, wetland, as well as crop diversification were the least used CSA practices among respondents. Furthermore, 76% making a majority of the farmers were moderate users, 15% were High users, while 9% were in the Low User category. The factors that influence the status of use of Climate Smart Agriculture in the study area were; Age, Alternative income, Perception of the effect of Climate Smart Agriculture, and Being part of a farming or agriculture group.. There is therefore the need for Government Through the Local Government Agencies to; increase sensitization of CSA among farmers. encourage the formation of social groups in rural areas, and train farmers on some alternative ventures to complement their farming activities. 이 연구는 가나의 동 곤자 시를 대상으로 기후 스마트 농업(CSA) 실행 현황을 분석하였다. 기후 변화는 농업 부문에 점점 더 큰 영향을 미치고 있으며, 이미 취약한 농업인들에게 가장 큰 타격을 주고 있으며, 이들은 수확량 감소와 식량 불안정에 노출되어 있다. 기후 스마트 농업은 식량 안보를 강화하고 빈곤을 완화하기 위한 대안적인 농업 방식으로, 특히 개발도상국에서 추진되고 있다. 가나의 역대 정부들이 농민들에게 그 개념을 이해시키고 생산량을 향상시키기 위한 여러 프로그램들이 있었지만, 동 곤자 시의 소규모 농민들에 의한 기후 스마트 농업 관행의 채택 현황은 농민들이 낮은 수확량을 계속 기록하고 있기 때문에 알려지지 않았다. 따라서 본 연구의 구체적인 목적은 CSA 관행에 대한 농민들의 인식, 사용 빈도, 채택 현황 및 CSA 관행의 채택 현황에 영향을 미치는 요인을 평가하는 것에 초점을 두었다. 본 연구는 CSA에 대한 인지도와 사용빈도를 평가하기 위해 기술통계를 활용하였다. 농업인을 저이용자, 중이용자, 고이용자로 구분하고 이용실태에 영향을 미치는 요인을 분석하기 위해 종합점수지수와 순서로짓모형을활용하였다CSA는 각각 실행하고 있다. 평행 오즈 가정이 위반되지 않았음을 증명하는 평행 가정 검정을 실시하여 순서 로짓 모형을 연구에사용하였다. 그 결과 표본 추출된 농업인의 90.5%가 CSA 관행에 대해 알고 있는 반면, 9.5%는 그 개념에 대해 순진한 것으로 나타났다. 또한 가장 많이 사용된 CSA 관행은 토양 보존, 덮개작물, 멀칭, 작물 윤작, 보수 농업, 혼농임업 순이었다. 이에 반해 유기분뇨, 습지 및 작물 다양화는 응답자 중 CSA 관행이 가장 적게 사용되었다. 또한 76%의 농업인은 중간 사용자였으며 15%는 높은 사용자였으며 9%는 낮은 사용자 범주에 속했다. 연구 지역에서 기후 스마트 농업의 사용 상태에 영향을 미치는 요인은 연령, 대체 소득, 기후 스마트 농업의 효과에 대한 인식 및 농업 또는 농업 그룹의 일원으로 나타났다. 따라서 지방 정부 기관을 통한 정부가 농업인들 사이에서 CSA에 대한 민감도를 높일 필요가 있다. 농촌 지역에 사회적 그룹을 형성하도록 장려하고 농업인들이 농업 활동을 보완할 수 있도록 일부 대체 벤처에 대해 교육한다.

Multi-mode high-speed actuator using smart soft composite

송성혁 Seoul National University 2016 국내박사

Soft morphing is an emerging technology for applications in various industrial fields, such as wearable devices and biomimetic soft robots, because of its advantages in adaptability to various environmental conditions by mimicking the ‘soft’ motions of nature. Various smart materials-based actuators have been developed to generate active soft morphing in structures, but their limited performance in terms of actuated morphing shapes and actuating speeds have prevented them from being used more widely. This work presents a soft composite actuator capable of achieving flexible and complex motions, using a shape-memory alloy (SMA). The anisotropic material properties of the composite, considered a major defect in composite structures, were accentuated using a scaffold structure, so that the actuator could generate more diverse motions, even in a simple, lightweight structure. The composite characteristics depend on the scaffold structure embedded in the actuator, so actuator motion could be designed according to the scaffold structure. The scaffold structure was easy to fabricate using a three-dimensional (3D) printer. SMA wires were also included to generate a force for actuation; these components were combined as a composite using a soft polymer. The actuating characteristics of the actuator depended on the type of scaffold: symmetric, anti-symmetric, and asymmetric scaffolds were evaluated, and four different modes of actuation were realized. A design methodology was proposed to permit more diverse and complex motions than the four basic modes of actuation, and was implemented in a turtle mimetic robot as an example application. The motion of a marine turtle flipper was analyzed and simplified into three sections. The required motion for each was matched with an appropriate scaffold design and the three scaffold structures were combined into a single actuator module. This flipper actuator was capable of mimicking two different swimming gaits of the marine turtle with a single actuator, depending on the current pattern applied. The locomotion characteristics of the two swimming gaits were evaluated in terms of efficiency and swimming speed. An actuator design to increase actuating speed and deformation magnitude was also developed, which extended the range of actuating performance for the SMA-bending actuator. Use of a bundle of SMA wires with a small radius instead of a single, thick SMA wire improved the cooling efficiency of the wire and increased the actuating speed, up to 35 Hz. Also, because the natural frequency of the actuator could be controlled by the scaffold structure design, the resonance effect was used actively to increase the actuating deformation. With this, a scaffold design methodology to achieve the required natural frequency of the actuator was developed and confirmed with experimental data. Actuating performance underwater was also evaluated and a model to predict the appropriate actuator length for the best performance was proposed. As an application of the high-speed actuator, a fish mimetic robot capable of 10 Hz fin flapping was developed and its speed was measured. The actuator was also applied to flying wings to mimic the flapping motion of birds or insects by adding a mechanism for passive rotation.

Synthesis and Applications of Silica Aerogel Films/Bulks via Ambient Drying

김건수 연세대학교 2002 국내박사

에어로겔 (aerogels) 합성을 위한 표준적인 방법으로 알려진 고비용/고위험 초임계건조 대신에 저비용이면서 안전한 상압건조를 이용한 새로운 실리카 에어로겔 벌크/박막 제조 공정이 개발되었다. 또한 상압건조법으로 제조한 고집적 소자용 저유전 박막, 투명/단열 창유리 그레이징 및 저온형 에어로겔-PVB 복합단열재 등에 대한 합성 메커니즘 및 합성 조건에 따른 특성 변화를 규명하여 각 분야별 나노기공 실리카 에어로겔의 응용성을 최적화하였다. 본 연구에서 개발된 상압건조법은 크게 2 가지로 대별될 수 있는데, 첫째는 TEOS 를 가수분해/축중합하여 얻은 실리카 졸을 겔화시킨 습윤겔 속에 존재하는 IPA (isopropanol)를 nheptane 으로 치환한 후 상압건조하는 용매치환-상압건조법이다. 둘째는 물유리를 이온교환하여 제조한 실리카 졸을 겔화시켜 얻은 습윤겔을 IPA/TMCS/ n-hexane 용액에 넣었을 때 TMCS (trimethylchlorosilane) 와 기공수의 반응생성물 용액 간의 상분리에 의한 신속한 용매치환과 springback 효과를 일으키는 반응생성물 및 미반응 TMCS 에 의한 기공 표면의 -OH 기의 개질이 동시에 이루어져 상압건조를 가능케 하는 용매치환/표면개질-상압건조법이다. 단순 용매치환에 의한 상압건조법은 습윤겔 내의 나노기공을 통한 용매의 확산에 의해 이루어 지므로 박막 합성시에는 별문제가 없으나 벌크 합성의 경우에는 장시간을 요하는 단점을 갖고 있었다. 반면에 상분리에 의한 용매치환 속도는 나노기공 확산에 비해 빠르기 때문에 벌크 에어로겔 합성을 위해서는 용매치환/표면개질-상압건조법이 훨씬 효율적인 방법으로 평가되었다. 저유전 실리카 에어로겔 박막은 IPA 를 용매로 한 실리카졸을 p-Si (100) 웨이퍼 상에 스핀코팅하여 얻어진 습윤겔 박막을 용매치환-상압건조시켜 제조되었다. 건조 용매로 IPA 를 사용하여 제조한 실리카 박막의 두께와 유전상수는 건조 압력 [1160 psi (270 ℃) → 380 psi (200 ℃)]에 따라 각각 1100 nm 에서 350 nm 그리고 유전상수는 2.1 에서 3.6 까지 민감하게 변화되었다. 반면에 IPA 를 n-heptane 으로 치환한 후 건조한 경우에는 n-heptane 의 임계 압력과 상압 사이의 건조압력 범위 내에서는 압력에 무관하게 일정한 박막의 두께 (1350 nm), 기공율 (80 %) 및 낮은 유전상수 (2.0)를 갖는 저유전 박막을 합성할 수 있었다. 실리카 박막은 0.5 ∼ 1.0 μm 의 gap size 를 갖는 W-patterning 기판에 코팅시 100 %에 가까운 gap filling 과 평탄도를 가지므로 차세대 고집적 소자용 층간절연물질로써의 충분한 응용 가능성을 보여주었다. 실리카 에어로겔-스마트 그레이징 (aerogel-smart glazing)은 슬라이드 글라스에 IPA 를 용매로 한 실리카 졸을 침지 인상 또는 스핀 코팅하여 얻어진 습윤겔 박막을 저유전 실리카 박막시와 동일하게 용매치환-상압건조하므로써 제조할 수 있었다. 균일한 코팅막을 얻기 위한 최적의 졸의 점도, 침지 인상 속도와 스핀 코팅 속도는 각각 3 ∼ 5 cP, 10 ∼ 30 cm/min 그리고 3000 rpm 정도이었다. 합성 실리카 에어로겔 박막의 기공율, 굴절율 및 열전도도는 각각 78.8 ∼ 83.4 %, 1.076 ∼ 1.097 과 0.016 ∼ 0.017 W/(m·K) 정도였으며, 실리카 에어로겔-스마트 그레이징 (에어로겔 층 두께 0.16 ∼ 10 μm)은 슬라이드 그라스에 비해 12 % 정도 높은 광 투과도와 낮은 열전도도 (1.473 ∼ 1.682 W/(m·K))을 가짐을 알 수 있었다. 에어로겔 박막 두께와 열전도도와의 상관 관계식으로부터 박막의 두께가 100 μm 인 에어로겔-스마트 그레이징의 열전도도는 코팅을 하지 않은 유리에 비해 약 10 배 정도 낮은 값을 가질 것으로 예측할 수 있었다. 용매치환/표면개질-상압건조법으로 합성한 실리카 에어로겔 벌크는 95 %의 고기공율, 795 m^2/g 의 고비표면적 및 0.028 W/(m·K)의 낮은 열전도도를 가졌으며, 350 ℃ 까지 소수성을 유지하였다. 에어로겔의 어려운 성형성과 낮은 기계적 강도를 보완하기 위하여 실리카 에어로겔 입자와 PVB 혼합체를 150 ℃ 와 0.28 MPa 하에서 열간성형함으로써 저온형 실리카 에어로겔-PVB 복합단열재를 제조할 수 있었다. 에어로겔 (0.128 g/㎤)과 PVB (0.235 g/㎤)의 밀도 차이 때문에 건식 혼합 시에는 에어로겔 함량을 70 vol% 이상 증가시키지 못하였으나, 습식 혼합에서는 90 vol%까지 증가시킬 수 있었다. 더욱이 건식/습식 혼합법으로 97.5 vol%까지 증가시킬 수 있어서 열전도도를 현저히 낮출 수 있었다. 복합단열재의 밀도, 열전도도 및 기계적 강도는 에어로겔 부피 함량의 증가에 따라 각각 1.09 에서 0.19 g/㎤, 0.12 에서 0.03 W/(m·K), 그리고 46.5 에서 0.15 MPa 까지 감소하였으며, 특히 복합체의 기계적 강도는 측정할 수 없을 정도의 낮은 강도를 갖는 순수 실리카 에어로겔에 비해 상당히 증진되었다. New synthetic processes of silica aerogel films/bulks in conjunction with cost-effective/safe ambient drying techniques, instead of a capital intensive/dangerous supercritical drying technique which is known as a standard method, have been developed. The applicabilities of nanoporous silica aerogels, prepared by the ambient drying techniques, to low-dielectrics for integrated circuits, transparent/insulating window glazing, and low-temperature insulations were also optimized through investigating property changes of aerogels depending on synthetic mechanisms and conditions. The ambient drying processes developed in this study are basically divided into two types. The first one is the solvent exchange-ambient drying (AD) technique in which IPA (isopropanol) in wet gels prepared from TEOS (tetraethoxysilane) and IPA is exchanged with n-heptane, followed by ambient drying. The other process is the solvent exchange/surface modification-ambient drying (SMAD) technique. The silica sols used in this technique were prepared cost-effectively via ion exchange of waterglass solutions. The wet gels of these sols could be rapidly dried at ambient conditions by expelling water solution of reaction products out of the inside pore according to the phase separation mechanism. At the same time, the surfaces were modified through reacting surface -OH groups with TMCS (trimethylchlorosilane) and byproducts, consequently, showed the springback effects attributed to repulsive forces between modified surface -CH_(3) groups in drying steps. Since simply exchanging of solvent in the first technique is slowly proceeded by solvent diffusion through nanopores in wet gels, the solvent exchange-ambient drying might be suitable to synthesize thin films but not to synthesize bulks because of long diffusion time. On the other hand, the SMAD technique has shown to be more effective for synthesizing aerogel bulks, because the solvent exchange rate via phase separation is even faster than the pore diffusion rate. Low-dielectric silica aerogel films could be synthesized via solvent exchange-ambient drying of wet gel films that were obtained by spin-coating the IPA based silica sol on a p-Si (100) wafer. Using IPA as a drying solvent, the thickness and the dielectric constant of silica films significantly changed from 1100 nm to 350 nm and from 2.1 to 3.6, respectively, with the drying pressure of [1160 psi (270 ℃) → 380 psi (200 ℃)]. However, when IPA in pores was exchanged with n-heptane followed by AD technique, the aerogel films had 1350 nm thickness, 80 % porosity, and 2.0 dielectric constant, regardless of drying pressure. The degree of planarization and the gap filling capability on 0.7 μm tungsten patterning wafer were excellent. It was proved that the ambient-dried aerogel films have a possibility of an application to IMD materials in the next generation of semiconductor devices beyond the giga level. A silica aerogel-smart glazing has been prepared by solvent exchange-ambient drying of wet gel films obtained by dip-/spin-coating of the silica sol on a glass slide, in the same manner as described above. The optimum values of the sol viscosity, the dip-/spin-coating rate for obtaining uniform coating layers were 3 ∼ 5 cP, 10 ∼ 30 cm/min, and 3000 rpm, respectively. The porosities, the refractive indices, and the thermal conductivities of the aerogel films were found to be in the range of 78.8 ∼ 83.4 %, 1.076 ∼ 1.097, and 0.016 ∼ 0.017 W/(m·K), respectively, and the aerogel-smart glazing (aerogel layer thickness 0.16 ∼ 10 μm) showed 12 % higher transmittance and lower thermal conductivities (1.473 ∼ 1.682 W/(m·K)) than those of the glass slide (1.705 W/(m·K)). From the correlation between the aerogel film thickness and the thermal conductivity of the aerogel-smart glazing, the thermal conductivity of the aerogel-smart glazing with 100 μm thickness was predicted to be 0.2 W/(m·K), which is about 10 times lower than that of the glass slide. Silica aerogel bulks with 95 % porosity, 795 ㎡/g specific surface area, and 0.028 W/(m·K) thermal conductivity could be cost-effectively manufactured via solvent exchange/surface modification-ambient drying of wet gels prepared from waterglass based silica sols. They had the hydrophobic surface up to 350 ℃. In order to complement a poor forming ability and a low mechanical strength of silica aerogels, aerogel-PVB composites for low temperature insulation were manufactured by hot pressing under 150 ℃ and 0.28 MPa. Because of a difference in aerogel (0.128 g/㎤) and PVB densities (0.235 g/㎤), when dry mixing was carried out, the aerogel-PVB composites containing the aerogel above 70 vol% could not be manufactured, but the wet mixed composites involving 90 vol% aerogel could be manufactured. Moreover, when dry and wet mixing (dual mixing) were simultaneously conducted, the thermal conductivity of the composites could significantly be lowered as the aerogel volume fraction could be increased to 97.5 vol%. As the aerogel volume fraction increased, the density, the thermal conductivity, and the mechanical strength of the composites decreased from 1.09 to 0.19 g/㎤, from 0.12 to 0.03 W/(m·K), and from 46.5 to 0.15 MPa, respectively. In particular, the mechanical strength of the composite was significantly improved in comparison with that of pure aerogels which could not be measured due to weak porous structure.

Design and performance evaluation of smart shoes using EAP and composite sensors

정인준 중앙대학교 대학원 2023 국내석사

골절된 긴 뼈에 대한 기계적 자극은 뼈 치유 과정에 큰 영향을 미친다. 따라서 환자의 보행을 실시간으로 모니터링하는 것은 골절 부위에 작용하는 힘의 정도를 추정하고 제어하는 데 유용하다. 이를 위해 본 논문에서는 족압 등 보행 상태를 모니터링할 수 있는 자가발전 스마트 신발을 소개한다. PVDF(Polyvinylidene fluoride) 리본과 전도성 섬유 테이프로 구성된 기능성 리본 유닛은 에너지 하베스터와 보행 패턴 모니터링을 위한 동적 센서에 사용된다. 에너지 하베스터로서 최적의 리본 유닛 수와 유효 연신율을 결정하기 위해 표준 인장 시험 및 반복되는 전기-기계적 시험을 수행하였고, 리본 구성에 따른 출력 전압 및 에너지 저장 능력을 실험적으로 조사하였다. 기능성 리본 유닛의 에너지 하베스팅 효율을 높이기 위해 경량 카본 복합소재 프레임을 설계하여 스마트 슈즈 내부의 뒤꿈치 부위에 설치하고 3개의 리본 유닛을 체결하였다. 성능 테스트에서 에너지 하베스팅을 통해 커패시터에 충분히 저장될 전력을 생성하였고, 최종적으로 리튬 이온 배터리에 성공적으로 저장되었다. 또한 족압과 관련한 데이터를 확인하는 압력 센서에 대한 연구가 수행되었다. 그리드 타입 정하중 센서는 기능성 전도성 필름과 리본형 전극으로 구성된 전도성 리본 유닛으로 구성되었다. 여러 개의 전도성 리본 유닛이 직교 배열 형태로 배열되고, 전극이 교차된 영역에서 압력 센서가 작동한다. 그리드 센서의 감지 성능을 확인하고자 센서의 전체 감지 범위에 대해 압력에 따른 전기 저항 변화를 정밀하게 측정하였다. 리본 유닛을 동하중 센서로 활용하여 보행 속도와 보행 패턴을 확인하는 연구도 수행되었다. 리본형 압력 센서를 깔창에 장착하고 블루투스 연결을 통해 휴대폰으로 신호를 전달했다. 실시간 족압 정보는 전체 보행 주기 동안 수집되어 환자의 연속적인 하중 조건을 파악하게 된다. 이것은 뼈 치유 시뮬레이션을 위한 핵심 데이터로 사용될 수 있다. Mechanical stimulation of fractured long bones has a great effect on the bone healing process. Therefore, real-time monitoring of the patient's gait is useful for estimating and controlling the degree of force acting on the fracture site. To this end, this paper introduces self-powered smart shoes that can monitor walking conditions such as foot pressure. Functional ribbon units composed of polyvinylidene fluoride (PVDF) ribbons and conductive textile tapes are used in energy harvesters and dynamic sensors for gait pattern monitoring. To determine the optimal number of ribbon units and effective elongation as an energy harvester, standard tensile tests and repeated electro-mechanical tests were performed, and output voltage and energy storage capacity according to ribbon configurations were experimentally investigated. To increase the energy harvesting efficiency of the functional ribbon unit, a lightweight carbon composite frame was designed and installed on the heel of the smart shoe, and three ribbon units were fastened. In the performance test, energy harvesting generated enough power to be stored in a capacitor and was finally successfully stored in a lithium-ion battery. In addition, a study was conducted on a pressure sensor that checks data related to foot pressure. The grid-type static load sensor is composed of a conductive ribbon unit composed of a functional conductive film and a ribbon-type electrode. A plurality of conductive ribbon units are arranged in an orthogonal arrangement, and a pressure sensor operates in an area where the electrodes cross each other. To check the sensing performance of the grid sensor, the electrical resistance change according to the pressure was precisely measured for the entire sensing range of the sensor. A study was also conducted to check the walking speed and walking pattern by using the ribbon unit as a dynamic load sensor. A ribbon-type pressure sensor was attached to the insole and the signal was transmitted to a mobile phone through a Bluetooth connection. Real-time foot pressure information is collected during the entire gait cycle to determine the patient's continuous load condition. This can be used as key data for bone healing simulation.