A review of solar energy harvesting electronic textiles

An increased use in wearable, mobile, and electronic textile sensing devices has led to a desire to keep these devices continuously powered without the need for frequent recharging or bulky energy storage. To achieve this, many have proposed integrating energy harvesting capabilities into clothing: solar energy harvesting has been one of the most investigated avenues for this due to the abundance of solar energy and maturity of photovoltaic technologies. This review provides a comprehensive, contemporary, and accessible overview of electronic textiles that are capable of harvesting solar energy. The review focusses on the suitability of the textile-based energy harvesting devices for wearable applications. While multiple methods have been employed to integrate solar energy harvesting with textiles, there are only a few examples that have led to devices with textile properties

Soft Materials for Wearable/Flexible Electrochemical Energy Conversion, Storage, and Biosensor Devices

none6Next-generation wearable technology needs portable flexible energy storage, conversion, and biosensor devices that can be worn on soft and curved surfaces. The conformal integration of these devices requires the use of soft, flexible, light materials, and substrates with similar mechanical properties as well as high performances. In this review, we have collected and discussed the remarkable research contributions of recent years, focusing the attention on the development and arrangement of soft and flexible materials (electrodes, electrolytes, substrates) that allowed traditional power sources and sensors to become viable and compatible with wearable electronics, preserving or improving their conventional performances.openBocchetta, P.; Frattini, D.; Ghosh, S.; Mohan, A.M.V.; Kumar, Y.; Kwon, Y.Bocchetta, P.; Frattini, D.; Ghosh, S.; Mohan, A. M. V.; Kumar, Y.; Kwon, Y

Study on Buckling of Stiff Thin Films on Soft Substrates as Functional Materials

abstract: In engineering, buckling is mechanical instability of walls or columns under compression and usually is a problem that engineers try to prevent. In everyday life buckles (wrinkles) on different substrates are ubiquitous -- from human skin to a rotten apple they are a commonly observed phenomenon. It seems that buckles with macroscopic wavelengths are not technologically useful; over the past decade or so, however, thanks to the widespread availability of soft polymers and silicone materials micro-buckles with wavelengths in submicron to micron scale have received increasing attention because it is useful for generating well-ordered periodic microstructures spontaneously without conventional lithographic techniques. This thesis investigates the buckling behavior of thin stiff films on soft polymeric substrates and explores a variety of applications, ranging from optical gratings, optical masks, energy harvest to energy storage. A laser scanning technique is proposed to detect micro-strain induced by thermomechanical loads and a periodic buckling microstructure is employed as a diffraction grating with broad wavelength tunability, which is spontaneously generated from a metallic thin film on polymer substrates. A mechanical strategy is also presented for quantitatively buckling nanoribbons of piezoelectric material on polymer substrates involving the combined use of lithographically patterning surface adhesion sites and transfer printing technique. The precisely engineered buckling configurations provide a route to energy harvesters with extremely high levels of stretchability. This stiff-thin-film/polymer hybrid structure is further employed into electrochemical field to circumvent the electrochemically-driven stress issue in silicon-anode-based lithium ion batteries. It shows that the initial flat silicon-nanoribbon-anode on a polymer substrate tends to buckle to mitigate the lithiation-induced stress so as to avoid the pulverization of silicon anode. Spontaneously generated submicron buckles of film/polymer are also used as an optical mask to produce submicron periodic patterns with large filling ratio in contrast to generating only ~100 nm edge submicron patterns in conventional near-field soft contact photolithography. This thesis aims to deepen understanding of buckling behavior of thin films on compliant substrates and, in turn, to harness the fundamental properties of such instability for diverse applications.Dissertation/ThesisPh.D. Mechanical Engineering 201

Pop-Up Stretchable Sensor Designs Using Multiphysics Modeliing

Stretchable electronic devices are critical for the future of wearable sensor technology, where existing rigid and non-flexible devices severely limit the applicability of them in many areas. Stretchable electronics extend flexible electronics one step further by introducing significant elastic deformation. Stretchable electronics can conform to curvy geometries like human skin which enables new applications such as fully wearable electronics whose properties can be tuned through mechanical deformation. Much of the effort in stretchable electronics has focused on investigation of the optimum fabrication method to make a trade-off between the manufacturing cost and acceptable performance. Here in this thesis a novel pop-up strain sensor design is introduced and tested.This technique is simple to use and can be applied to almost all available materials such as metals, dielectrics, semiconductors and different scales from centi-meter to nanoscale. Using this method three main electronic devices have been designed for different applications. The first category is pop-up antennas that are able to reconfigure their frequency response with respect to the mechanical deformation by out of plane displacement. The second category is pop-up frequency selective surface which similarly can change its frequency behaviour due to applied strain. This ability to accommodate the applied stress by three-dimensional (3D) deformation, making these devices ideal for strain sensing applications such as vapor sensing or on skin mountable sensors. Using the advantage of RFID technology in terms of wireless monitoring, the third category has been introduced which is a pop-up capacitor sensor integrating with an RFID chip to detect finger joint bending that can help those patients who are recovering after stroke. The proposed devices have been modelled using COMSOL Multiphysics and Extensive evaluations of the prototype system were conducted on purpose-built laboratory scale test rigs. Both results are in good correlation which makes them applicable for sensing purposes

Electrospinning piezoelectric fibers for biocompatible devices

The field of nanotechnology has been gaining great success due to its potential in developing new generations of nanoscale materials with unprecedented properties and enhanced biological responses. This is particularly exciting using nanofibers, as their mechanical and topographic characteristics can approach those found in naturally occurring biological materials. Electrospinning is a key technique to manufacture ultrafine fibers and fiber meshes with multifunctional features, such as piezoelectricity, to be available on a smaller length scale, thus comparable to subcellular scale, which makes their use increasingly appealing for biomedical applications. These include biocompatible fiber-based devices as smart scaffolds, biosensors, energy harvesters, and nanogenerators for the human body. This paper provides a comprehensive review of current studies focused on the fabrication of ultrafine polymeric and ceramic piezoelectric fibers specifically designed for, or with the potential to be translated toward, biomedical applications. It provides an applicative and technical overview of the biocompatible piezoelectric fibers, with actual and potential applications, an understanding of the electrospinning process, and the properties of nanostructured fibrous materials, including the available modeling approaches. Ultimately, this review aims at enabling a future vision on the impact of these nanomaterials as stimuli-responsive devices in the human body

A mechanically-guided approach to three-dimensional functional mesostructures towards unconventional applications

Controlled formation of three-dimensional functional mesostructures (3DFMs) has broad engineering implications in biomedical devices, microelectromechanical systems (MEMS), optics, and energy storage. Most existing 3D techniques, however, not only lack compatibility with essential electronic materials (silicon, metals, ceramics) that exist in solid-state or crystalline forms, but also produce in a slow and inefficient manner. This is in stark contrast to the planar technologies widely adopted by the modern semiconductor industry. I propose to solve these challenges by a novel 3D assembly strategy based on the planar technologies, which involves precisely controlled 2D-to-3D transformations via the substrate-induced mechanical buckling. This lithography-based, mechanically-guided 3D approach is compatible with virtually any engineering thin films including semiconductors, metals, and polymers, applies to a wide range of length scales and geometries and produces in a high throughput. In this dissertation, I present strategies that combine fabrications and mechanics to achieve a set of complex 3D geometries. I also study the potentials of the 3DFMs in micro-robotics. I further demonstrate the unique applications in energy harvesting, bio-integrated systems, and nanoscale sensing. The results may enlighten the development of advanced, multi-functional 3D electronic micro-systems inaccessible to other 3D techniques

Mechanical energy harvesting and self-powered electronic applications of textile-based piezoelectric nanogenerators: a systematic review

Environmental pollution resulting from fossil fuel consumption and the limited lifespan of batteries has shifted the focus of energy research towards the adoption of green renewable technologies. On the other hand, there is a growing potential for small, wearable, portable electronic devices. Therefore, considering the pollution caused by fossil fuels, the drawbacks of chemical batteries, and the potential applications of small-scale wearables and portable electronic devices, the development of a more effective lightweight power source is essential. In this context, piezoelectric energy harvesting technology has attracted keen attention. Piezoelectric energy harvesting technology is a process that converts mechanical energy into electrical energy and vice-versa. Piezoelectric energy harvesters can be fabricated in various ways, including through solution casting, electrospinning, melt spinning, and solution spinning techniques. Solution and melt-spun filaments can be used to develop woven, knitted, and braided textile-based piezoelectric energy harvesters. The integration of textile-based piezoelectric energy harvesters with conventional textile clothing will be a key enabling technology in realising the next generation smart wearable electronics. This review focuses on the current achievements on textile based piezoelectric nanogenerators (T-PENGs), basic knowledge about piezoelectric materials and the piezoelectric mechanism. Additionally, the basic understanding of textiles, different fabrication methods of T-PENGs, and the strategies to improve the performance of piezoelectric nanogenerators are discussed in the subsequent sections. Finally, the challenges faced in harvesting energy using textile based piezoelectric nanogenerators (T-PENGs) are identified, and a perspective to inspire researchers working in this area is presented

Flexible sensors—from materials to applications

Flexible sensors have the potential to be seamlessly applied to soft and irregularly shaped surfaces such as the human skin or textile fabrics. This benefits conformability dependant applications including smart tattoos, artificial skins and soft robotics. Consequently, materials and structures for innovative flexible sensors, as well as their integration into systems, continue to be in the spotlight of research. This review outlines the current state of flexible sensor technologies and the impact of material developments on this field. Special attention is given to strain, temperature, chemical, light and electropotential sensors, as well as their respective applications