Energy autonomous wearable sensors for smart healthcare: a review

Energy Autonomous Wearable Sensors (EAWS) have attracted a large interest due to their potential to provide reliable measurements and continuous bioelectric signals, which help to reduce health risk factors early on, ongoing assessment for disease prevention, and maintaining optimum, lifelong health quality. This review paper presents recent developments and state-of-the-art research related to three critical elements that enable an EAWS. The first element is wearable sensors, which monitor human body physiological signals and activities. Emphasis is given on explaining different types of transduction mechanisms presented, and emerging materials and fabrication techniques. The second element is the flexible and wearable energy storage device to drive low-power electronics and the software needed for automatic detection of unstable physiological parameters. The third is the flexible and stretchable energy harvesting module to recharge batteries for continuous operation of wearable sensors. We conclude by discussing some of the technical challenges in realizing energy-autonomous wearable sensing technologies and possible solutions for overcoming them

Multilayer films for coloured glazed solar collectors

In this work a solution to the problem of black colour appearance which dominates the external aspect of buildings covered by solar thermal collectors is proposed. Multilayered thin films on the glass surface, consisting of oxides materials such as SiO2, Al2O3, TiO2 or a mixture of these oxides were deposited by reactive magnetron sputtering on glass and their optical properties were examined. As the interface between the sputtered layers on glass emerged as important, the interfaces formed between TiO2 and SiO2 and between Al2O3 and SiO2 were studied by X-ray photoelectron spectroscopy. The reflectivity of the film on glass system was shown to be a narrow band in the visible region while the rest of the sunlight is transmitted through the glass due to the use of a near zero absorption materials. In addition, the desired colour of the reflected light in the visible range was obtained by adapting the oxide film thicknesses. Such optical properties besides the film’s stability as demonstrated in accelerated ageing tests make the coloured glazing aesthetically pleasing and suitable as a cover glass for thermal solar collectors

Enzymatic Sensor Based on Dye Sensitized TiO₂ Electrode for Detection of Catechol in Water

n/

Towards Low Cost and Low Temperature Capacitive CO2 Sensors Based on Amine Functionalized Silica Nanoparticles

Hybrid materials based on inorganic particles and an organic polymer were developed and used as an efficient sensing material for carbon dioxide (CO2). The sensing material consists of fumed silica that is functionalized with an organic polymer, polyethylenimine, by means of the impregnation method. The organic polymer is effectively immobilized around the silica nanoparticles and confirmed by infrared spectroscopy. Thermogravimetric analysis proves the thermal stability of the sensing material. CO2 capacitive sensors operating at temperatures lower than 70 °C were fabricated by depositing a thin layer of hybrid sensing material on interdigitated gold electrodes. Impedance spectroscopy explored the sensing capability of the hybrid organic–inorganic material towards CO2 in the presence of different relative humidity levels, as well as its stability and reversibility. This strategy to couple organic and inorganic materials as a sensing layer for CO2 paves the way for the design of a low-cost CO2 sensor

Capacitive CO2 sensor

The objective of the present paper is to provide a concept for a chemical sensor having a small size, a low power consumption and a high reliability for sensing CO2 under different humidity levels at atmospheric pressure, while maintaining a long term stability under working conditions. A high temperature regeneration process of the sensing layer is unneeded to ensure a long term stability of the sensing material. This objective is achieved by using a hybrid organic-inorganic nanomaterial, consisting of inorganic nanoparticles functionalized with an amine-based polymer

Smart capacitive CO2 sensor

A capacitive gas sensor with a highly selective, sensitive and reversible sensing layer for detecting CO2 at atmospheric pressure was developed. The sensor operating temperature is less than 60 degrees C. The sensing layer consists of a hybrid material. We report an interdigitated transducer coated with a hybrid organic-inorganic nanomaterial as a sensitive layer. It is shown that the nanocomposite can detect CO2 gas in the range of interest for environmental sensing between 500 to 3000 ppm at moderate low temperature. Furthermore, the response and recovery times are below 2min. The reported results demonstrate the capability of the newly developed sensor to be used as a CO2 gas detector in several applications such as indoor monitoring, security, gas leakage and medical diagnostic

Microwave plasma assisted process for cleaning and deposition in future semiconductor technology

The epitaxial growth of silicon layers is an important step in the fabrication of semiconductor devices. For conventional silicon epitaxy, high temperatures, up to 900 °C are necessary. However, in future, semiconductor technology epitaxy processes at lower temperatures are required to increase the integration density. The goal of this study was to investigate microwave plasma assisted processes for the selective removing of thin silicon oxide, the cleaning of silicon surfaces and the depositing of high quality silicon films. The main focus was to apply these processes for low temperature epitaxy. All processes, such as oxide removal, cleaning and deposition, were done in one chamber and with microwave plasma assistance. In order to remove silicon dioxide, the etching behavior of hydrogen, fluorine, and hydrogen/fluorine plasma was studied. It was shown, that with hydrogen/fluorine plasma, the best selectivity of oxide to silicon was reached. The deposition process of silicon was studied by growing μc-Si films. The process was characterized and optimized by spectral ellipsometry. After a successful characterization of all process steps, silicon epitaxy layers have been grown with in-situ removal of native oxide and in-situ surface cleaning. The temperature for all process steps was reduced below 450 °C

Method to study water diffusion into polymers

We designed and realized a low cost relative humidity (RH) capacitive sensor having an interdigitated transducer coated with a cheap sensing material working at room temperature (polyimide). Thermally perturbed diffusion of water molecules into the polyimide layer is studied by heating the sensor locally and measuring the sensor capacitance change. The swelling and deswelling model is applied to determine the time constant of involved processes. This simple method, using an evaluation kit developed by our group, to measure the sensor capacitance and to study the diffusion process of water molecules into polyimide could be generalized to analyze the gas diffusion processes into polymer based sensing layer generally used in the field of gas chemical sensors