Challenges in Design and Fabrication of Flexible/Stretchable Carbon- and Textile-Based Wearable Sensors for Health Monitoring: A Critical Review

To demonstrate the wearable flexible/stretchable health-monitoring sensor, it is necessary to develop advanced functional materials and fabrication technologies. Among the various developed materials and fabrication processes for wearable sensors, carbon-based materials and textile-based configurations are considered as promising approaches due to their outstanding characteristics such as high conductivity, lightweight, high mechanical properties, wearability, and biocompatibility. Despite these advantages, in order to realize practical wearable applications, electrical and mechanical performances such as sensitivity, stability, and long-term use are still not satisfied. Accordingly, in this review, we describe recent advances in process technologies to fabricate advanced carbon-based materials and textile-based sensors, followed by their applications such as human activity and electrophysiological sensors. Furthermore, we discuss the remaining challenges for both carbon- and textile-based wearable sensors and then suggest effective strategies to realize the wearable sensors in health monitoring

A sensor technology survey for a stress aware trading process

The role of the global economy is fundamentally important to our daily lives. The stock markets reflect the state of the economy on a daily basis. Traders are the workers within the stock markets who deal with numbers, statistics, company analysis, news and many other factors which influence the economy in real time. However, whilst making significant decisions within their workplace, traders must also deal with their own emotions. In fact, traders have one of the most stressful professional occupations. This survey merges current knowledge about stress effects and sensor technology by reviewing, comparing, and highlighting relevant existing research and commercial products that are available on the market. This assessment is made in order to establish how sensor technology can support traders to avoid poor decision making during the trading process. The purpose of this article is: 1) to review the studies about the impact of stress on the decision making process and on biological stress parameters that are applied in sensor design; 2) to compare different ways to measure stress by using sensors currently available in the market according to basic biometric principles under trading context; and 3) to suggest new directions in the use of sensor technology in stock markets

Performance evaluation of textile based passive RFID antennas as wearable sensors

Conformal and stretchable wearable sensors provide real-time information about individual's health conditions. There are a lot of vital signs and parameters of the human body that are supposed to be sensed by the sensors like, body movement, body temperature, Electrocardiogram (ECG), Electroencephalogram (EEG) etc. Hence, there are a lot of health tracking devices available in the market for different purposes. One of the most important sensors are the hydration/moisture/humidity sensors. These sensors are required for the health fitness and for the medical care of the patients. However, as far as the skin sensors are concerned, they are facing one important challenge, which is to have better contact with the body to have better results to analyze as well as providing ease and comfort to the patient/user. In this work, Radio frequency identification technology (RFID) has been used to achieve and overcome the challenge. Since RFID is a prevailing technology in which a microchip in a label used to transmit data when the label is exposed to radio waves. RFID technology can easily be understood by the concept of student cards used in our university where student cards are working as the Tag and the readers planted on the door slots read them. The data/information read by the reader is stored in the database for every specific tag (transponder), to be accessed it later. Passive Ultra-High Frequency (UHF) RFID tags are here used as moisture sensors. The tags for the mentioned challenged used here for different application as stated before, are specifically textile tags. There are two types of textiles (Substrate) that have been used; cotton, which is organic in nature and stretchable synthetic textile, which is a mixture of viscose and polyester. The IC chip containing the information is attached to the antenna that is designed on the substrate which is acting as a Tag (Sensor), one with glue and the other with embroidery. The most specific part is the tag is embroidered with silver thread, which is conductive in nature. Hence embroidery is the fabrication method as well as the vital part of making the tags. The embroidery is accomplished with the help of domestic sewing machine. To get different results, different embroidery designs have been used; single line (less dense), horizontal embroidery and vertical embroidery. Moreover, six tags are fabricated using cotton substrate and two tags are fabricated using stretchable substrate, both substrates have IC antenna attached with sewing as well as glue as mentioned before. When the fabricated sensors (Tags) were tested in the anechoic chamber, all the sensors have different behavior with different read ranges as well as different peak frequencies. The objective was to test the humidity/moisture evaluation on the sensors. Hence, the sensors were very well exposed to the moisture and were tested again. The sensors with less dense embroidery (Single Line) were wetter than the dense embroidery (vertical and horizontal designs), hence, making the frequency more affected in terms of putting the frequency at a lower level in the less dense embroidered sensors than the dense ones. After being dried up, after 48 hours, the sensors were almost back the initial read range values. Therefore, the frequency difference between the initial read ranges and the moist read ranges is of vital importance and all the tags are having different behaviors. As the tags are textile in nature and are embroidered like a simple cloth, they are easy to wear and have very better contact with the body to have better results in terms of moisture evaluation. So further fabrication technique in the prospect of UHF RFID has multiple applications e.g. wounds sensor inside the bandages, soil moisture sensor, moisture/humidity leakage sensor etc. Hence, they have very vital advantages, which include that they are passive, cost-effective, and simple

Advanced Interfaces for HMI in Hand Gesture Recognition

The present thesis investigates techniques and technologies for high quality Human Machine Interfaces (HMI) in biomedical applications. Starting from a literature review and considering market SoA in this field, the thesis explores advanced sensor interfaces, wearable computing and machine learning techniques for embedded resource-constrained systems. The research starts from the design and implementation of a real-time control system for a multifinger hand prosthesis based on pattern recognition algorithms. This system is capable to control an artificial hand using a natural gesture interface, considering the challenges related to the trade-off between responsiveness, accuracy and light computation. Furthermore, the thesis addresses the challenges related to the design of a scalable and versatile system for gesture recognition with the integration of a novel sensor interface for wearable medical and consumer application

Every sign of life

Thesis (Ph. D.)--Massachusetts Institute of Technology, School of Architecture and Planning, Program in Media Arts and Sciences, 2003.MIT Institute Archives copy: pages 151-[182] bound in reverse order.Includes bibliographical references (p. 142-150).Every Sign of Life introduces an approach to and motivational schema for personal health monitoring. It is an exploration of how to make information collected by personal health-monitoring devices fun and engaging, and consequently more useful to the non-specialist. In contrast to the common methodology of adding game elements to established biofeedback systems, the Every Sign of Life approach is to design and build games that use biosensor information to effect the game environment. This work tests the hypothesis that fun (the joy of learning, achieving, competing, etc.) is a way to achieve the goal of self-efficacy; to induce people to take care of their own health by altering their habits and lifestyles. One result is a basic architecture for personal health-monitoring systems that has led to an approach to the design of sensor peripherals and wearable computer components called "Extremity Computing." This approach is used to redefine biosensor monitoring from periodic to continuous (ultimately saving data over a lifetime). Another result is an approach to adding implicit biofeedback to computer games. This has led to a new genre of games called "Bio-Analytical Games" that straddles the boundary between sports and computer games. A series of studies of how to present health information to children and adults have demonstrated the ability of consumers to use bioinformatics without involving professionals.by Vadim Gerasimov.Ph.D

Assessment of trends in the cardiovascular system from time interval measurements using physiological signals obtained at the limbs

Cardiovascular diseases are an increasing source of concern in modern societies due to their increasing prevalence and high impact on the lives of many people. Monitoring cardiovascular parameters in ambulatory scenarios is an emerging approach that can provide better medical access to patients while decreasing the costs associated to the treatment of these diseases. This work analyzes systems and methods to measure time intervals between the electrocardiogram (ECG), impedance plethysmogram (IPG), and the ballistocardiogram (BCG), which can be obtained at the limbs in ambulatory scenarios using simple and cost-effective systems, to assess cardiovascular intervals of interest, such as the pulse arrival time (PAT), pulse transit time (PTT), or the pre-ejection period (PEP). The first section of this thesis analyzes the impact of the signal acquisition system on the uncertainty in timing measurements in order to establish the design specifications for systems intended for that purpose. The minimal requirements found are not very demanding yet some common signal acquisition systems do not fulfill all of them while other capabilities typically found in signal acquisition systems could be downgraded without worsening the timing uncertainty. This section is also devoted to the design of systems intended for timing measurements in ambulatory scenarios according to the specifications previously established. The systems presented have evolved from the current state-of-the-art and are designed for adequate performance in timing measurements with a minimal number of active components. The second section is focused on the measurement of time intervals from the IPG measured from limb to limb, which is a signal that until now has only been used to monitor heart rate. A model to estimate the contributions to the time events in the measured waveform of the different body segments along the current path from geometrical properties of the large arteries is proposed, and the simulation under blood pressure changes suggests that the signal is sensitive to changes in proximal sites of the current path rather than in distal sites. Experimental results show that the PAT to the hand-to-hand IPG, which is obtained from a novel four-electrode handheld system, is correlated to changes in the PEP whereas the PAT to the foot-to-foot IPG shows good performance in assessing changes in the femoral PAT. Therefore, limb-to-limb IPG measurements significantly increase the number of time intervals of interest that can be measured at the limbs since the signals deliver information from proximal sites complementary to that of other measurements typically performed at distal sites. The next section is devoted to the measurement of time intervals that involve different waves of the BCG obtained in a standing platform and whose origin is still under discussion. From the relative timing of other physiological signals, it is hypothesized that the IJ interval of the BCG is sensitive to variations in the PTT. Experimental results show that the BCG I wave is a better surrogate of the cardiac ejection time than the widely-used J wave, which is also supported by the good correlation found between the IJ interval and the aortic PTT. Finally, the novel time interval from the BCG I wave to the foot of the IPG measured between feet, which can be obtained from the same bathroom scale than the BCG, shows good performance in assessing the aortic PAT. The results presented reinforce the role of the BCG as a tool for ambulatory monitoring since the main time intervals targeted in this thesis can be obtained from the timing of its waves. Even though the methods described were tested in a small group of subjects, the results presented in this work show the feasibility and potential of several time interval measurements between the proposed signals that can be performed in ambulatory scenarios, provided the systems intended for that purpose fulfill some minimal design requirements.Les malalties cardiovasculars són una tema de preocupació creixent en societats modernes, degut a l’augment de la seva prevalença i l'elevat impacte en les vides dels pacients que les sofreixen. La mesura i monitoratge de paràmetres cardiovasculars en entorns ambulatoris és una pràctica emergent que facilita l’accés als serveis mèdics i permet reduir dràsticament els costos associats al tractament d'aquestes malalties. En aquest treball s’analitzen sistemes i mètodes per la mesura d’intervals temporals entre l’electrocardiograma (ECG), el pletismograma d’impedància (IPG) i el balistocardiograma (BCG), que es poden obtenir de les extremitats i en entorns ambulatoris a partir de sistemes de baix cost, per tal d’avaluar intervals cardiovasculars d’interès com el pulse arrival time (PAT), pulse transit time (PTT) o el pre-ejection period (PEP). En la primera secció d'aquesta tesi s’analitza l’impacte del sistema d’adquisició del senyal en la incertesa de mesures temporals, per tal d’establir els requeriments mínims que s’han de complir en entorns ambulatoris. Tot i que els valors obtinguts de l’anàlisi no són especialment exigents, alguns no són assolits en diversos sistemes habitualment utilitzats mentre que altres solen estar sobredimensionats i es podrien degradar sense augmentar la incertesa en mesures temporals. Aquesta secció també inclou el disseny i proposta de sistemes per la mesura d’intervals en entorns ambulatoris d’acord amb les especificacions anteriorment establertes, a partir de l’estat de l’art i amb l’objectiu de garantir un correcte funcionament en entorns ambulatoris amb un nombre mínim d’elements actius per reduir el cost i el consum. La segona secció es centra en la mesura d’intervals temporals a partir de l’IPG mesurat entre extremitats, que fins al moment només s’ha fet servir per mesurar el ritme cardíac. Es proposa un model per estimar la contribució de cada segment arterial per on circula el corrent a la forma d’ona obtinguda a partir de la geometria i propietats físiques de les artèries, i les simulacions suggereixen que la senyal entre extremitats és més sensible a canvis en arteries proximals que en distals. Els resultats experimentals mostren que el PAT al hand-to-hand IPG, obtingut a partir d’un innovador sistema handheld de quatre elèctrodes, està fortament correlacionat amb els canvis de PEP, mentre que el PAT al foot-to-foot IPG està correlat amb els canvis en PAT femoral. Conseqüentment, l’ILG entre extremitats augmenta de manera significativa els intervals d’interès que es poden obtenir en extremitats degut a que proporciona informació complementària a les mesures que habitualment s’hi realitzen. La tercera secció està dedicada a la mesura d’intervals que inclouen les ones del BCG vertical obtingut en plataformes, de les que encara se’n discuteix l’origen. A partir de la posició temporal relativa respecte altres ones fisiològiques, s’hipostatitza que l’interval IJ del BCG es sensible a variacions del PTT. Els resultats experimentals mostren que la ona I del BCG és un millor indicador de l’ejecció cardíaca que el pic J, tot i que aquest és el més utilitzat habitualment, degut a la bona correlació entre l’interval IJ i el PTT aòrtic. Finalment, es presenta un mètode alternatiu per la mesura del PTT aòrtic a partir de l’interval entre el pic I del BCG i el peu del foot-to-foot IPG, que es pot obtenir de la mateixa plataforma que el BCG i incrementa la robustesa de la mesura. Els resultats presentats reforcen el paper del BCG com a en mesures en entorns ambulatoris, ja que els principals intervals objectiu d’aquesta tesi es poden obtenir a partir de les seves ones. Tot i que els mètodes descrits han estat provats en grups petits de subjectes saludables, els resultats mostren la viabilitat i el potencial de diversos intervals temporals entre les senyals proposades que poden ésser realitzats en entorns ambulatoris, sempre que els sistemes emprats compleixin els requisits mínims de disseny.Postprint (published version

Instrumentación para neuroprótesis vestibles

La tesis pretende contribuir al conocimiento en adquisición de biopotenciales mediante técnicas no invasivas con aplicación a neuroprótesis (NPs). Las NPs son dispositivos que, interactuando con el cuerpo humano, permiten recuperar o reemplazar capacidades perdidas o disminuidas incrementando drásticamente la comodidad e independencia de las personas. Por lo tanto es de interés que las NPs se utilicen de forma muy sencilla y sin asistencia profesional, en correspondencia con el paradigma de los sistemas ``vestibles''. El objetivo general de la tesis es desarrollar etapas de instrumentación que permitan adquirir biopotenciales útiles a las NPs en forma robusta en las condiciones de medida impuestas por los sistemas vestibles. Por lo tanto, se desarrollan sistemas de adquisición de señal mixta en el estado del arte como plataformas para validar los modelos y circuitos de acondicionamiento propuestos, y se diseñan, implementan y verifican experimentalmente circuitos de acondicionamiento analógico que permiten enfrentar este desafío. En primer lugar, se desarrolla un circuito de realimentación de modo común con ganancia aumentada como estrategia general para la robustez frente a interferencia electromagnética. En segundo lugar se proponen electrodos activos para la medición de señales de electromiograma, desarrollando herramientas de análisis e implementando amplificadores para electrodos de múltiples contactos. Finalmente, los electrodos secos son el factor clave del registro de biopotenciales en sistemas vestibles. Por lo tanto, se desarrolla un electrodo activo con impedancia de entrada aumentada utilizando bootstrap de fuente y conservando una topología de baja complejidad.This thesis contributes to the topic of non-invasive biopotential acquisition techniques applied to Neuroprostheses (NPs). NPs are technological devices that, through interaction with the body, allow to recover or replace lost or diminished capabilities, thus dramatically increasing the comfort and independence of a person. It is desirable for NPs to be able to be used in a simple manner without professional assistance, in correspondence with the paradigm of wearable devices. The general objective of the thesis is to develop instrumentation circuits which allow to acquire the biopotential signals that NPs need robustly, even under the measurement conditions imposed by wearable systems. Therefore, state of the art mixed-signal acquisition systems are developed as a platform upon which models and conditioning circuits can be validated, and a set of analog conditioning circuits are designed, implemented, and experimentally tested. First, a common mode feedback circuit with increased gain is developed as a general strategy for increased robustness against electromagnetic interference. Next, active electrodes for electromyography signal measurement are proposed. An analysis tool as well as an implementation alternative for multiple-input electrodes are proposed. Finally, dry-contact electrodes are a key factor in wearable biopotential measurements. Hence, an active electrode with increased input impedance is developed using power supply bootstrapping and a low complexity topology.Facultad de Ingenierí

Studying experimental variability in EEG and tDCS through uncertainty and sensitivity analyses

In neuroscience, simulating electric current in the head of a subject is of main interest for both electroencephalography (EEG) and transcranial direct current stimulation (tDCS). EEG is used to reconstruct the electric activity of the brain based on the measured electric potential on the scalp. On the other hand, tDCS consists in injecting a small electric current through the head of a subject to modulate the activity of a specific brain region. Such simulations rely heavily on the electric conductivity of the biological tissues composing the head. Unfortunately, there is currently no effective and non-invasive method to measure it accurately for each individual. Consequently, researchers and practitioners have to set arbitrary values chosen from the literature, despite the fact that this property has been shown to vary widely both inter- and intra-subject. The simulations also depend on the geometry of the tissues and on how they are modelled. In this thesis, we studied the influence of different skull models and of the electrical conductivity of the tissues on the EEG forward problem. We also analysed the effect of the uncertainty in the conductivity on the electric field induced in different regions of the brain by several stimulating electrode montages in tDCS. To support these experiments, we developed a python package named Shamo which provides the user with tools to perform mesh generation, current simulation, surrogate modelling and sensitivity and uncertainty analyses with a user-friendly API. It interfaces with industrial grade software to perform the computationally intensive tasks and is easy to use on distributed architectures. The present work describes both Shamo and the results that it helped to obtain for the different experiments.Dans le domaine des neurosciences, la simulation du courant électrique dans la tête d’un sujet est d’un intérêt majeur, tant pour l’électroencéphalographie (EEG) que pour la stimulation transcrânienne à courant continu (tDCS). L’EEG est utilisée pour reconstruire l’activité électrique du cerveau à partir du potentiel électrique mesuré sur le cuir chevelu. D’autre part, la tDCS consiste à injecter un petit courant électrique dans la tête d’un sujet pour moduler l’activité d’une région spécifique du cerveau. De telles simulations dépendent de la conductivité électrique des tissus biologiques composant la tête. Malheureusement, il n’existe actuellement aucune méthode efficace et non invasive pour la mesurer avec précision pour chaque individu. Par conséquent, les chercheurs et les praticiens doivent fixer des valeurs arbitraires choisies dans la littérature, malgré le fait qu’il a été démontré que cette propriété varie considérablement entre les sujets et à l’intérieur d’un même sujet. Les simulations dépendent également de la géométrie des tissus et de la façon dont ils sont modélisés. Dans cette thèse, nous avons étudié l’influence de différents modèles de crâne et de la conductivité électrique des tissus sur le problème direct de l’EEG. Nous avons également analysé l’effet de la conductivité sur le champ électrique induit dans différentes régions du cerveau par plusieurs montages d’électrodes en tDCS. Pour soutenir ces expériences, nous avons développé un package python nommé Shamo qui fournit à l’utilisateur des outils pour effectuer la génération de maillage, la simulation de courant, la génération de modèles de substitution et les analyses de sensibilité et d’incertitude avec une API simple. Il s’interface avec des logiciels de qualité industrielle pour effectuer les tâches de calcul intensif et est facile à utiliser sur des architectures distribuées. Ce travail décrit à la fois Shamo et les résultats que cet outil a permis d’obtenir pour les différentes expériences