Digital imaging technology assessment: Digital document storage project

An ongoing technical assessment and requirements definition project is examining the potential role of digital imaging technology at NASA's STI facility. The focus is on the basic components of imaging technology in today's marketplace as well as the components anticipated in the near future. Presented is a requirement specification for a prototype project, an initial examination of current image processing at the STI facility, and an initial summary of image processing projects at other sites. Operational imaging systems incorporate scanners, optical storage, high resolution monitors, processing nodes, magnetic storage, jukeboxes, specialized boards, optical character recognition gear, pixel addressable printers, communications, and complex software processes

Piezoelectric Transducers Based on Aluminum Nitride and Polyimide for Tactile Applications

The development of micro systems with smart sensing capabilities is paving the way to progresses in the technology for humanoid robotics. The importance of sensory feedback has been recognized the enabler of a high degree of autonomy for robotic systems. In tactile applications, it can be exploited not only to avoid objects slipping during their manipulation but also to allow safe interaction with humans and unknown objects and environments. In order to ensure the minimal deformation of an object during subtle manipulation tasks, information not only on contact forces between the object and fingers but also on contact geometry and contact friction characteristics has to be provided. Touch, unlike other senses, is a critical component that plays a fundamental role in dexterous manipulation capabilities and in the evaluation of objects properties such as type of material, shape, texture, stiffness, which is not easily possible by vision alone. Understanding of unstructured environments is made possible by touch through the determination of stress distribution in the surrounding area of physical contact. To this aim, tactile sensing and pressure detection systems should be integrated as an artificial tactile system. As illustrated in the Chapter I, the role of external stimuli detection in humans is provided by a great number of sensorial receptors: they are specialized endings whose structure and location in the skin determine their specific signal transmission characteristics. Especially, mechanoreceptors are specialized in the conversion of the mechanical deformations caused by force, vibration or slip on skin into electrical nerve impulses which are processed and encoded by the central nervous system. Highly miniaturized systems based on MEMS technology seem to imitate properly the large number of fast responsive mechanoreceptors present in human skin. Moreover, an artificial electronic skin should be lightweight, flexible, soft and wearable and it should be fabricated with compliant materials. In this respect a big challenge of bio-inspired technologies is the efficient application of flexible active materials to convert the mechanical pressure or stress into a usable electric signal (voltage or current). In the emerging field of soft active materials, able of large deformation, piezoelectrics have been recognized as a really promising and attractive material in both sensing and actuation applications. As outlined in Chapter II, there is a wide choice of materials and material forms (ceramics: PZT; polycrystalline films: ZnO, AlN; polymers and copolymers: PVDF, PVDF-TrFe) which are actively piezoelectric and exhibit features more or less attractive. Among them, aluminum nitride is a promising piezoelectric material for flexible technology. It has moderate piezoelectric coefficient, when available in c-axis oriented polycrystalline columnar structure, but, at same time, it exhibits low dielectric constant, high temperature stability, large band gap, large electrical resistivity, high breakdown voltage and low dielectric loss which make it suitable for transducers and high thermal conductivity which implies low thermal drifts. The high chemical stability allows AlN to be used in humid environments. Moreover, all the above properties and its deposition method make AlN compatible with CMOS technology. Exploiting the features of the AlN, three-dimensional AlN dome-shaped cells, embedded between two metal electrodes, are proposed in this thesis. They are fabricated on general purpose Kapton™ substrate, exploiting the flexibility of the polymer and the electrical stability of the semiconductor at the same time. As matter of fact, the crystalline layers release a compressive stress over the polymer, generating three-dimensional structures with reduced stiffness, compared to the semiconductor materials. In Chapter III, a mathematical model to calculate the residual stresses which arise because of mismatch in coefficient of thermal expansion between layers and because of mismatch in lattice constants between the substrate and the epitaxially grown films is adopted. The theoretical equation is then used to evaluate the dependence of geometrical features of the fabricated three-dimensional structures on compressive residual stress. Moreover, FEM simulations and theoretical models analysis are developed in order to qualitative explore the operation principle of curved membranes, which are labelled dome-shaped diaphragm transducers (DSDT), both as sensors and as piezo-actuators and for the related design optimization. For the reliability of the proposed device as a force/pressure sensor and piezo-actuator, an exhaustive electromechanical characterization of the devices is carried out. A complete description of the microfabrication processes is also provided. As shown in Chapter IV, standard microfabrication techniques are employed to fabricate the array of DSDTs. The overall microfabrication process involves deposition of metal and piezoelectric films, photolithography and plasma-based dry and wet etching to pattern thin films with the desired features. The DSDT devices are designed and developed according to FEM and theoretical analysis and following the typical requirements of force/pressure systems for tactile applications. Experimental analyses are also accomplished to extract the relationship between the compressive residual stress due to the aluminum nitride and the geometries of the devices. They reveal different deformations, proving the dependence of the geometrical features of the three-dimensional structures on residual stress. Moreover, electrical characterization is performed to determine capacitance and impedance of the DSDTs and to experimentally calculate the relative dielectric constant of sputtered AlN piezoelectric film. In order to investigate the mechanical behaviour of the curved circular transducers, a characterization of the flexural deflection modes of the DSDT membranes is carried out. The natural frequency of vibrations and the corresponding displacements are measured by a Laser Doppler Vibrometer when a suitable oscillating voltage, with known amplitude, is applied to drive the piezo-DSDTs. Finally, being developed for tactile sensing purpose, the proposed technology is tested in order to explore the electromechanical response of the device when impulsive dynamic and/or long static forces are applied. The study on the impulsive dynamic and long static stimuli detection is then performed by using an ad hoc setup measuring both the applied loading forces and the corresponding generated voltage and capacitance variation. These measurements allow a thorough test of the sensing abilities of the AlN-based DSDT cells. Finally, as stated in Chapter V, the proposed technology exhibits an improved electromechanical coupling with higher mechanical deformation per unit energy compared with the conventional plate structures, when the devices are used as piezo-actuator. On the other hand, it is well suited to realize large area tactile sensors for robotics applications, opening up new perspectives to the development of latest generation biomimetic sensors and allowing the design and the fabrication of miniaturized devices

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

NASA Tech Briefs, June 1996

Topics: New Computer Hardware; Electronic Components and Circuits; Electronic Systems; Physical Sciences; Materials; Computer Programs; Mechanics; Machinery/Automation; Manufacturing/Fabrication; Mathematics and Information Sciences;Books and Reports

Aerosol-Jet Printed Nanocomposites for Flexible and Stretchable Thermoelectric Generators

Converting waste heat from the environment into usable electricity, via thermoelectric generators (TEGs) based on thermoelectric (TE) materials, is predicted to be one of the most promising renewable energy solutions of the future. TE materials produce a current when subjected to a temperature gradient as a result of the Seebeck effect, and are characterised by a TE figure of merit, ZT = S2σT/κ, where S is the Seebeck coefficient, σ is the electrical conductivity, T is the operating temperature, and κ is the thermal conductivity. TEGs can be used as an energy source for ‘small-power’ applications, such as wireless sensors and wearable devices. Nonetheless, traditional inorganic TE materials pose significant challenges owing to their high cost, toxicity, scarcity, and brittleness, particularly when it comes to applications requiring flexibility and/or stretchability. On the other hand, organic TE polymers are less expensive, environmentally friendly, and flexible. However, they typically suffer from poor TE performance due to their comparatively low S and σ. This thesis therefore seeks to explore solutions for high-performance and mechanically conformable TEGs based on organic-inorganic TE nanocomposites, adopting a material engineering approach to enhancing TE properties while ensuring the flexibility and/or stretchability of TEGs. In this work, a flexible and robust TEG based on a novel hybrid nanocomposite structure for harvesting energy from low-grade waste heat, has been successfully fabricated via a customised and scalable aerosol-jet printing (AJP) technique. Firstly, Bi2Te3 nanoparticles and Sb2Te3 nanoflakes were fabricated using a solvothermal synthesis approach, and their resulting morphological and microstructural properties were studied. They were then incorporated into a conducting polymer matrix poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) via the AJP method, resulting in well-dispersed TE nanocomposites on flexible polyimide substrates. These TE nanocomposites comprised Bi2Te3/Sb2Te3 nano-inclusions with higher S and σ embedded within a polymeric PEDOT:PSS matrix having lower κ. The compositions were dynamically tuned and controlled by the in-house developed in situ mixing method to optimise the resulting power factor (PF = S2σ). The AJP technique used in this work allows functional materials to be printed from inks with a wide range of viscosities and constituent particle sizes and shapes. The morphological and TE properties of AJ-printed nanocomposite structures were then evaluated as a function of the composition so that optimum ink formulation and printing conditions could be found to maximise the final TE performance. Importantly, these TE nanocomposites were found to be particularly stable and robust upon repeated flexing. They can be directly integrated into high-performance TEGs with minimal post-possessing treatment, making them particularly suitable for flexible TE applications. Subsequently, multiwall carbon nanotubes (MWCNTs) were introduced to enhance σ of AJ-printed nanocomposites, thereby achieving even higher PF values. A novel in situ mixing method was capable of simultaneously incorporating high-S Sb2Te3 nanoflakes and high-σ MWCNTs that could provide good inter-particle connectivity, to significantly enhance the TE performance of PEDOT:PSS. Rigorous flexing and fatigue tests also confirmed the excellent mechanical robustness and stability of these AJ-printed MWCNTs-based TE nanocomposites. The added MWCNTs have led to not only higher σ, but they also have improved the mechanical flexibility and fatigue robustness of the resulting nanocomposites. Since the ZT and PF of TE materials often have a strong dependence on temperature, a single TE material spanning a given temperature range is unlikely to have an optimal ZT or PF across the entire range, leading to the inefficient TEG performance. The temperature-dependent TE properties of AJ-printed TE nanocomposites were therefore studied as a function of the loading fraction, with a view to enhancing the overall TE performance of a TEG by varying its composition accordingly across a given temperature range. For the first time, compositionally graded thermoelectric composites (CG-TECs) have been developed and shown to improve TE performance over TEGs having a single composition across the same temperature range. The composition of the TE nanocomposite was systematically tuned along the length of the TEG in order to optimise the PF along the temperature gradient between which it operates. Lastly, the AJP technique was used to fabricate free-standing and stretchable TE structures, by printing serpentine patterns of the TE ink onto a sacrificial substrate that was subsequently removed. The TE performance and stretchability under different imposed mechanical conditions were evaluated, including testing for the reliability of prolonged stretching cycles. The CG-TEC concept was also incorporated into the stretchable structure to achieve further improvement of TE performance.China Scholarship Council and Cambridge Commonwealth, European and International Trus