Harnessing energy for wearables: a review of radio frequency energy harvesting technologies

Wireless energy harvesting enables the conversion of ambient energy into electrical power for small wireless electronic devices. This technology offers numerous advantages, including availability, ease of implementation, wireless functionality, and cost-effectiveness. Radio frequency energy harvesting (RFEH) is a specific type of wireless energy harvesting that enables wireless power transfer by utilizing RF signals. RFEH holds immense potential for extending the lifespan of wireless sensors and wearable electronics that require low-power operation. However, despite significant advancements in RFEH technology for self-sustainable wearable devices, numerous challenges persist. This literature review focuses on three key areas: materials, antenna design, and power management, to delve into the research challenges of RFEH comprehensively. By providing an up-to-date review of research findings on RFEH, this review aims to shed light on the critical challenges, potential opportunities, and existing limitations. Moreover, it emphasizes the importance of further research and development in RFEH to advance its state-of-the-art and offer a vision for future trends in this technology

Energy harvesting from human and machine motion for wireless electronic devices

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Novel electronic stretchable materials for future medical devices

L’electrònica convencional basada en el silici te grans dificultats a l’hora de ser implementada en dispositius electrònics que estiguin en contacte amb les corbes i las plasticitat dels teixits del cos humà. Futures aplicacions mèdiques como la pell electrònica, sistemes de alliberació de fàrmac transdèrmic o nous bio-sensors requereixen de sistemes electrònics capaços de ser doblegats, retorçats o enrotllats en superfícies corbes. Tot i els prometedors resultats mostrats por la investigació en electrònica flexible, no hi ha aplicacions comercials directes dins de l’àrea mèdica. La dependència de components només presents en l’electrònica convencional limita el complet desenvolupament d’aquests dispositius posant de manifest la necessitat de trobar nous materials en aquest camp. Amb l’objectiu de potenciar nous sistemes electrònics flexibles, en aquest treball es proposen noves estratègies per proveir de flexibilitat als materials utilitzats en electrònica sense perdre de vista la directa aplicabilitat. Primerament, s’ha estudiat l’aplicació de polímers conductors mitjançant impressió inkjet. Aquesta tecnologia permet l’obtenció de films polimèrics molt fins sobre sistemes flexibles més complexos. Anant un pas més enllà, s’han desenvolupat noves metodologies per poder depositar polímers conductors sobre substrats elastomèrics mantenint el bon rendiment elèctric. Aquesta part culmina amb l’estudi d’un nou polielectròlit per la síntesis del polipirrol basat en l’àcid hialurònic modificat amb grups dopamina. Aquest polielectròlit aporta noves propietats que milloren l’adaptabilitat del polipirrol obtenint nanosuspensions estables que poden ser depositades directament sobre substrats elastomèrics. Centrant-nos en los materials metàl·lics de la electrònica, s’ha desenvolupat un mètode per la deposició selectiva de plata conductora sobre substrats elastomèrics. Les pistes fabricades amb aquest procediment han demostrat un comportament de galga extensomètrica sota deformació mecànica. Finalment la aplicabilitat de las estratègies desenvolupades ha estat avaluada per veure como es poden aplicar en dispositius mèdics actuals y futurs tals como sensors fisiològics, galgas extensomètriques portables para seguiment o nous stents de tràquea electrònics.La implementación de la electrónica convencional basada en el silicio en dispositivos electrónicos que entren en contacto con la plasticidad y las curvas de los tejidos del cuerpo humano presenta serias dificultades. Futuras aplicaciones médicas como la piel electrónica, sistemas de liberación de fármaco transdérmico o nuevos bio-sensores requieren sistemas electrónicos capaces de ser doblados, retorcidos o enrollados en superficies curvas. A pesar de los prometedores resultados mostrados por la investigación en electrónica flexible, muy pocas tecnologías se han visto adaptadas en una aplicación comercial dentro del área médica. Problemas como la dependencia de componentes solo presentes en la electrónica convencional limita el completo desarrollo de estos dispositivos poniendo de manifiesto la necesidad de encontrar nuevos materiales en este campo. Con el objetivo de potenciar nuevos sistemas electrónicos flexibles, este trabajo propone nuevas estrategias para aportar flexibilidad a los materiales empleado para la electrónica sin perder de vista su aplicabilidad. Primeramente, se ha estudiado la aplicación de polímeros conductores usando impresión inkjet. Esta tecnología permite la obtención de films poliméricos muy delgados sobre sistemas flexibles más complejos. Dando un paso más allá, se han desarrollado nuevas metodologías para poder depositar polímeros conductores sobre substratos elastómericos manteniendo un buen rendimiento eléctrico. Esta parte culmina con el estudio de un nuevo polielectrolito para la síntesis del polipirrol basado en el ácido hyaluronico modificado con dopamina. Este polielectrolito aporta nuevas propiedades que mejoran la adaptabilidad del polipirrol obteniendo nanosuspensiones estables que pueden ser depositadas directamente sobre substratos elastómeros. Estudiando también los materiales metálicos en la electrónica, se ha desarrollado un método para la deposición selectiva de plata conductora sobre substratos elastómeros. Las pistas fabricadas con este procedimiento han mostrado un interesante comportamiento de galga extensométrica cuando son sometidas a una deformación. Finalmente, la aplicabilidad de las estrategias desarrolladas ha sido evaluada para ver cómo se puede aplicar en dispositivos médicos actuales y futuros tales como sensores fisiológicos, galgas extenso métricas portables para seguimiento o nuevos stents traqueales electrónicos.Conventional electronics based in rigid and planar silicon wafers presents several difficulties to be implemented in systems where a direct contact with the soft and curved geometries of the tissues of the human body is required. The future medical devices such as electronic skin, transdermal drug delivery systems or novel wearable biosensors requires electronic materials with the ability to be twisted, folded and conformably wrapped onto arbitrarily curved surfaces. Despite the promising results on stretchable electronic research, the applications have not yet been translated into commercial medical devices. The dependence of components still only present in conventional silicon electronics limits the full development of the stretchable strategies, revealing the need for new materials in this field. Aiming to potentiate new electronic stretchable systems, this works proposes novel strategies to provide stretchability to electronic materials always having in mind the final application. Firstly, the study of conducting polymers to be deposited using ink jet printing have been performed. This kind of implementation allows the formation of conductive thin films on more complex flexible systems. Going further, it has been developed novel methodologies using plasma treatments to fabricate conducting polymeric coating on stretchable substrate with good electrical performance. The culmination of this part consisted in the synthesis of polypyrrole with a novel polyelectrolyte based on a hyaluronic acid modified with dopamine groups that allows stable nanosuspension able to directly form a film onto stretchable substrates. Focusing on metallic materials, conductive silver deposition on selective stretchable substrate have been developed. The electrical performance under mechanical deformation revealed strange gauge sensor behaviour of the silver paths with promising applicability in the medical device. Finally, the applicability of the approaches developed in this work have been studied to evaluate its suitability on actual and future applications in the field of medical devices such as physiological sensors, wearable strain gauge sensors or tracheal stent able to monitor deformations

Development and evaluation of a calibration free exhaustive coulometric detection system for remote sensing.

Most quantitative analytical measurement techniques require calibration to correlate signal with the quantity of analyte. The purpose of this study was to employ exhaustive coulometry, an implementation of coulometric analysis in a stopped-flow, fixed-volume, thin-layer cell, to attain calibration-free measurements that would directly benefit intervention-free analysis systems designed for remote deployment. This technique capitalizes on the short diffusion lengths (\u3c 100 µm) to dramatically reduce the time for analysis (\u3c 30 sec). For this work, a thin-layer fluidic cell was designed in software, fabricated via CNC machining, and evaluated using Ferri/Ferrocyanide {Fe(CN)63-/4-} as a model analyte. The 2 µL fixed volume incorporated an oval, 8mm by 4 mm, thin-film gold electrode sensor with an integrated Ag|AgCl pseudo-reference electrode. The flow cell area matched the shape of the sensor, with a volume set by the thickness of a laser-cut silicone rubber gasket (~80 µm). A semi-permeable membrane isolated the working electrode and counter electrode chambers to prevent analyte diffusion. A miniaturized custom potentiostat was designed and built to measure reaction currents ranging from 10 mA to 0.1 nA. Software was developed to perform step voltammetry as well as cyclic voltammetry analysis for verifying electrode condition and optimal redox potential levels. Experimentally determined oxidation/reduction potentials of -100 mV and 400 mV, respectively, were applied to the working electrode for sample concentrations ranging from 50 µM to 10,000 µM. The current generated during the reactions was recorded and the total charge captured at each concentration was obtained by integrating the amperograms. When compared to the expected charge for a 2 µL sample, the total charge vs. concentration plots displayed a near perfect linearity over the full concentration range, and the expected charge (100 % converted) was reached within 20 seconds. The reaction currents ideally should have decayed to background levels, but exhibited constant offset values slightly larger than the background signal, a phenomenon assumed to be lingering residual flow from sample injection. After adding rigid tubing and external valves, the thin-layer cell was shown to remain within 6% of the theoretical charge after 200 seconds. Continued development of this system will offer the possibility of remote, calibration-free determinations of real-world analytes such mercury and lead