Photonic platform for bioelectric signal acquisition on wearable devices

Programa doutoral em BioengenhariaAmong all physiological functions, bioelectric activity may be considered one of the most important, since it is the backbone of many wearable technologies used for health condition diagnostic and monitoring. The existent bioelectric recording devices are difficult to integrate on wearable materials, mainly due to the number of electrical interconnections and components required at the sensing places. Photonic sensors have been presented in the medical field as a valuable alternative where features like crosstalk and attenuation, electromagnetic interference and integration constitute a challenge. Furthermore, photonic sensors have other advantages such as easy integration into a widespread of materials and structures, multiplexing capacity towards the design of sensing networks and long lifetime. The aim of this work was to develop a multi-parameter bioelectric acquisition platform based on photonic technologies. The platform includes electro-optic (EO) and optoelectronic (OE) stages, as well as standard filtering and amplification. The core sensing technology is based on a Mach-Zehnder Interferometer (MZI) Modulator, which responds to the bioelectric signal by modulating the input light intensity. Only optical fibers are used as interconnections, and the subsequent signal conditioning and processing can be centralized in a common processing unit. The photonic and OE modules were designed to guarantee bioelectric signal detection using parameters compatible with existing technologies. Several considerations were made regarding noise-limiting factors, unstable operation and sensitivity. The EO modulator of choice was a Lithium Niobate (LiNbO3) MZI modulator. The EO modulator was selected given its versatile geometry and potential to perform differential measurements and easiness to convert the resultant optical modulated signal into electrical values. The OE conversion module developed includes a transimpedance amplifier (TIA), a notch and bandpass filter. In order to prevent a phenomenon called gain-peaking, the TIA was properly compensated, to insure a stable TIA operation and simultaneously avoid output signal oscillation. The performance of the TIA circuit was improved considering DC currents of 1.3 mA, which resulted in an additional high-pass filtering block. This allowed for a transimpedance gain of 1x105 V/A. The filtering stage was designed for removing unwanted signal artifacts, and included two bandpass filters (0.2 – 40 Hz; 5 - 500 Hz) and a notch filtered centered at 50 Hz and with 34 dB of attenuation. The photonic platform prototype performance was evaluated, covering linearity, frequency response and sensitivity. Results have shown that the combination of the photonic and OE stages had a flat 60 dB frequency over the frequency range of 0.3 Hz to 1 kHz. With regard to system linearity, it was verified a linear relationship between the voltage input and output signal, with a gain of 60 dB. These results indicated a correct biasing of the MZI modulator. In order to study the minimum detected fields that can be achieved using the developed prototype, the filtering and amplification stages were also considered. The characterization was performed with an overall gain of 4000 V/V (72 dB) and the photonic platform showed sufficient sensitivity to detect signals as low as 20 μV. To assess the bioelectric signal acquisition performance, the developed photonic platform was tested in a real scenario through the acquisition of different bioelectric signals – Electrocardiogram (ECG), Electroencephalogram (EEG) and electromyogram (EMG). The results were compared with signals obtained from standard platforms using the same conditions. The developed photonic platform demonstrated the capability of recording signals with relevant and clinical content, providing enough sensitivity, frequency response and artifact removal. The photonic platform showed good results in various clinical scenarios, such as the evaluation of normal heart and muscle functions, as well as monitoring the consciousness state of patients. As a final conclusion, a photonic platform for bioelectric signal acquisition was developed and tested; its application in wearable health systems was demonstrated.De todas as funções fisiológicas, a actividade bioeléctrica é considerada uma das mais importantes, uma vez que representa a base para muitos sistemas vestíveis, utilizados para monitorização e diagnóstico no sector médico. Os dispositivos existentes - baseados em aquisição electronica - apresentam algumas desvantagens essencialmente relacionadas com a dificuldade de integração em materiais vestíveis, a quantidade de interligações e os componentes necessários nos locais de medição. Os sensores fotónicos têm vindo a ser cada vez mais utilizados no sector médico, uma vez que conseguem ultrapassar as desvantagens de atenuação e interferência electromagnética. Para além disso, este tipo de sensores apresenta uma fácil integração em diversos materiais, durabilidade e capacidade de multiplexagem, especialmente concebidas para redes de sensores. O principal objectivo da presente tese foi desenvolver uma plataforma de aquisição de biopotenciais baseada em sensores fotónicos. A plataforma inclui um bloco responsável por efectuar a conversão electro-óptica (EO) do biopotencial medido, assim como a optoelectrónica (OE) necessária para transformar o sinal óptico para o domínio electrico. A tecnologia que está na base do mecanismo de transdução desta plataforma consiste em moduladores Mach-Zehnder (MZI), cujo princípio é modular a intensidade da luz em resposta a um sinal electrico. As interconexões e transdução são efectuadas apenas por fibra óptica, sendo que o processamento e acondicionamento do sinal pode ser centralizado numa unidade de processamento transversal a todos os sinais. Os módulos correspondentes aos blocos EO e OE foram desenvolvidos de forma a garantir a detecção do biopotencial utilizando características compatíveis com a tecnologia disponível. Foram efectuadas várias considerações relativamente aos factores que limitam o funcionamento adequado da plataforma fotónica, mais especificamente no que diz respeito a níveis de ruído, instabilidade e resolução. O modulador EO seleccionado foi um MZI de niobato de litio (LiNbO3). A escolha deste modulador teve como principal motivo a possibilidade de efectuar medições diferenciais, geometria versátil e a facilidade de converter o sinal óptico resultante para o domínio eléctrico. Os módulos de conversão OE desenvolvidos incluem um amplificador de transimpedância (TIA) e filtros passa-banda e notch. Para assegurar o funcionamento estável do TIA e evitar um fenóneno designado por gain-peaking (ganho de pico), foi necessário compensar devidamente o circuito. A performance do TIA desenvolvido foi optimizada para currentes DC na ordem dos 1.3 mA, resultando na adição de um filtro passa-alto de forma a atingir ganhos de transimpedância de 1x105 V/A. Os blocos de filtragem para remover as componentes de interferencia indesejados incluiram dois filtros passa-banda (0.2 – 40 Hz; 5 – 500 Hz) e um filtro notch centrado nos 50 Hz filtered e com um factor de atenuação de 34 dB. O protótipo da plataforma fotónica, mais especificamente o modulo EO e OE (saída do TIA) foi submetido a diferentes testes com o principal objectivo de caracterizar o desempenho do sistema ao nível da resposta em frequência, linearidade e resolução. Os resultados obtidos demonstratam uma resposta em frequência com um agama dos 0.3 Hz aos 1 kHz com um ganho de 60 dB. Relativamente à linearidade, foi demonstrado que a relação entre o sinal de entrada (biopotencial) e o sinal à saída do TIA apresentam uma relação linear. Os testes realizados para confirmar o mínimo sinal detectado pela plataforma fotónica desenvolvida foram efectuados incluindo os estágios de filtragem e amplificação, resultando num ganho global de 4000 V/V. O sinal minimo detectável foi de 20 μV, a uma frequência de 10 Hz. Por último, a plataforma desenvolvida foi testada em cenários reais na aquisição de diferentes biopotenciais – Electrocardiograma (ECG), Electroencefalograma (EEG) e Electromiograma (EMG). Os resultados obtidos foram comparados com plataformas convencionais nas mesmas condições. A plataforma fotónica apresentou boa capacidade para adquirir biopotenciais com conteúdo clinico relevante, assegurando a sensibilidade, resposta em frequência e remoção de artefactos desejável

The status of textile-based dry EEG electrodes

Electroencephalogram (EEG) is the biopotential recording of electrical signals generated by brain activity. It is useful for monitoring sleep quality and alertness, clinical applications, diagnosis, and treatment of patients with epilepsy, disease of Parkinson and other neurological disorders, as well as continuous monitoring of tiredness/ alertness in the field. We provide a review of textile-based EEG. Most of the developed textile-based EEGs remain on shelves only as published research results due to a limitation of flexibility, stickability, and washability, although the respective authors of the works reported that signals were obtained comparable to standard EEG. In addition, nearly all published works were not quantitatively compared and contrasted with conventional wet electrodes to prove feasibility for the actual application. This scenario would probably continue to give a publication credit, but does not add to the growth of the specific field, unless otherwise new integration approaches and new conductive polymer composites are evolved to make the application of textile-based EEG happen for bio-potential monitoring

Intimate interfaces in action: assessing the usability and subtlety of emg-based motionless gestures

Mobile communication devices, such as mobile phones and networked personal digital assistants (PDAs), allow users to be constantly connected and communicate anywhere and at any time, often resulting in personal and private communication taking place in public spaces. This private -- public contrast can be problematic. As a remedy, we promote intimate interfaces: interfaces that allow subtle and minimal mobile interaction, without disruption of the surrounding environment. In particular, motionless gestures sensed through the electromyographic (EMG) signal have been proposed as a solution to allow subtle input in a mobile context. In this paper we present an expansion of the work on EMG-based motionless gestures including (1) a novel study of their usability in a mobile context for controlling a realistic, multimodal interface and (2) a formal assessment of how noticeable they are to informed observers. Experimental results confirm that subtle gestures can be profitably used within a multimodal interface and that it is difficult for observers to guess when someone is performing a gesture, confirming the hypothesis of subtlety

Entwicklung einer berührungslosen EEG-Mütze mittels kapazitiver Elektroden

Non-contact capacitive electrodes for bioelectric diagnostics provide an interesting alternative to classical galvanically coupled electrodes. Such a low cost diagnostic system can be applied without preparation time and in mobile wireless environments. For even higher user comfort textile capacitive electrodes are preferable. In this work, a comprehensive model for the electronic noise properties and frequency dependent responses of PCB-based, as well as textile non-contact capacitive electrodes, is presented. A thorough study of the influence of the electrical components on the resulting noise properties of these electrodes, is provided by independently measuring the corresponding noise spectra. The most important low frequency noise source of capacitive electrode is the necessary high input bias resistance. By comparing the noise measurements with the theoretical noise model of the electrode, it is concluded that the surface of the electrode contributes to an additional 1/f-power noise. It is also found that the highest possible coupling capacitance is most favorable for low noise behavior. Therefore, we implemented electrodes with electrically conducting fabric surfaces. With these electrodes, it is possible to enlarge the surface of the electrode while simultaneously maintaining a small distance between the body and the electrode over the whole surface area, thus maximizing the capacitance. We also show that the use of textile capacitive electrodes, reduces the noise considerably. Furthermore, this thesis describes the construction of a capacitive non-contact textile electroencephalography measuring hat (cEEG hat) with seven measuring channels. This hat benefits from the low noise characteristics of the integrated developed textile capacitive electrodes. The measured noise spectrum of this cEEG hat shows low noise characteristics at low frequencies. This fulfills many requirements for measuring brain signals. The implemented cEEG hat is comfortable to wear during very long measurements and even during sleep periods. In contrast to common methods, the cEEG hat provides a possibility of measuring EEG signal during sleep outside laboratories and in the comfort of home. EEG sleep measurements shown in this work, are recorded inside a normal apartment. The possibility of brain computer interface application is also shown by measuring steady state visually evoked potentials (SSVEP) at different frequencies.Berührungslose, kapazitive Elektroden für bioelekrische Untersuchungen stellen eine interessante Alternative zu klassischen galvanisch gekoppelten Elektroden dar. Ein solches preisgünstiges Diagnosesystem kann ohne lange Vorbereitungszeit und in mobilen Umgebungen eingesetzt werden. Für gesteigerten Tragekomfort sind textile Elektroden von Vorteil. In dieser Arbeit wird eine umfassende Beschreibung der elektronischen Rauscheigenschaften und des frequenzabhängigen Verhaltens von sowohl platinenbasierten, als auch textilen kapazitiven Elektroden vorgestellt. Die Einflüsse aller elektronischen Komponenten auf die resultierenden Rauscheigenschaften werden durch Messungen der entsprechenden Rauschspektren untersucht. Die wichtigste niederfrequente Rauschquelle kapazitiver Elektroden stellt der notwendige und zugleich hohe Bias-Eingangswiderstand dar. Durch Vergleich der gemessenen Rauschspektren mit dem theoretischen Modell wird die Oberfläche der Elektroden als eine zusätzliche 1/f-Rauschquelle identifiziert. Dabei ist die größtmögliche Kopplungskapazität vorteilhaft für ein niedriges Rauschen. Deshalb setzen wir im Folgenden Elektroden aus elektrisch leitfähigen Textilien ein. Mit diesen Elektroden ist es möglich, die Oberfläche der Elektrode unter gleichzeitiger Beibehaltung eines kleinen Abstandes zum Körper zu vergrößern. Dies maximiert wiederum die Kapazität. Wir zeigen zudem, dass die Verwendung textiler kapazitiver Elektroden die Rauscheigenschaften deutlich verbessert. Desweiteren wird in dieser Arbeit die Konstruktion eines kapazitiven, berührungslosen EEG-Helmes (cEEG-Mütze) mit sieben Kanälen beschrieben. Dieser Helm profitiert von den guten Rauscheigenschaften der zuvor entwickelten und hier integrierten textilen Elektroden. Die gemessenen Rauschspektren zeigen ein niedriges Rauschen im unteren Frequenzbereich. Dies erfüllt viele Voraussetzungen für die Messung von Gehirnsignalen. Die erstellte cEEG-Mütze lässt sich während langer Messzeiten und Schlafperioden angenehm tragen. Im Gegensatz zu herkömmlichen Methoden ermöglicht sie Messungen außerhalb von Laboratorien und im gewohnten Umfeld. Alle in dieser Arbeit gezeigten Schlafmessungen wurden in einer normalen Wohnung aufgezeichnet. Außerdem wird die Einsatzmöglichkeit für sogenannte ”Gehirn-Computer-Schnittstellen” anhand der Messung von ”steady state visually evoked potentials” (SSVEP) Signalen bei verschiedenen Frequenzen demonstriert

Low-Noise Micro-Power Amplifiers for Biosignal Acquisition

There are many different types of biopotential signals, such as action potentials (APs), local field potentials (LFPs), electromyography (EMG), electrocardiogram (ECG), electroencephalogram (EEG), etc. Nerve action potentials play an important role for the analysis of human cognition, such as perception, memory, language, emotions, and motor control. EMGs provide vital information about the patients which allow clinicians to diagnose and treat many neuromuscular diseases, which could result in muscle paralysis, motor problems, etc. EEGs is critical in diagnosing epilepsy, sleep disorders, as well as brain tumors. Biopotential signals are very weak, which requires the biopotential amplifier to exhibit low input-referred noise. For example, EEGs have amplitudes from 1 μV [microvolt] to 100 μV [microvolt] with much of the energy in the sub-Hz [hertz] to 100 Hz [hertz] band. APs have amplitudes up to 500 μV [microvolt] with much of the energy in the 100 Hz [hertz] to 7 kHz [hertz] band. In wearable/implantable systems, the low-power operation of the biopotential amplifier is critical to avoid thermal damage to surrounding tissues, preserve long battery life, and enable wirelessly-delivered or harvested energy supply. For an ideal thermal-noise-limited amplifier, the amplifier power is inversely proportional to the input-referred noise of the amplifier. Therefore, there is a noise-power trade-off which must be well-balanced by the designers. In this work I propose novel amplifier topologies, which are able to significantly improve the noise-power efficiency by increasing the effective transconductance at a given current. In order to reject the DC offsets generated at the tissue-electrode interface, energy-efficient techniques are employed to create a low-frequency high-pass cutoff. The noise contribution of the high-pass cutoff circuitry is minimized by using power-efficient configurations, and optimizing the biasing and dimension of the devices. Sufficient common-mode rejection ratio (CMRR) and power supply rejection ratio (PSRR) are achieved to suppress common-mode interferences and power supply noises. Our design are fabricated in standard CMOS processes. The amplifiers’ performance are measured on the bench, and also demonstrated with biopotential recordings

Wearable biopotential measurement using the TI ADS1198 analog front-end and textile electrodes : signal conditioning and signal quality assessment

The development of mobile systems for monitoring bioelectric signals outside a hospital environment involves many challenges that do not arise when it is in a controlled environment, like a hospital. The dimensions of these systems are an important factor to consider in order to facilitate their use without interfering with the daily activities of individuals. The purpose of this work is the implementation of a single-supply battery-powered, low power ECG/EMG signal monitoring system based on the ADS1198 Analog Front-End from Texas Instruments. The system was designed to acquire ECG signals from three electrodes using the integrated Right-Leg-Drive (RLD) circuit from the ADS1198. The developed analog front-end was connected for testing purposes through the SPI interface to a NI-USB 8451 board and signals were acquired using LabVIEW. The circuit was tested in several situations and proved to provide high quality signals using textile integrated electrodes and conventional disposable gel electrodes.FEDER- “Programa Operacional Factores de Competitividade – COMPETE”, FCT - Fundação para a Ciência e a Tecnologia, projects PEst-C/CTM/UI0264/2011 and PTDC/EEA-ELC/70803/2006, and Instituto de Telecomunicaçõe

Multifunctional wearable epidermal device for physiological signal monitoring in sleep study

Sleep is the essential part of life. Thousands of people are suffering from different kinds sleep disorders. Clinical diagnosing and treating for such disorders are costly, painful and quite sluggish. To reach the demand many commercial products are into the market to encourage home based sleep studies using portable devices. These portable devices are limited in use, cannot be handled easily and quite costly. Advancements in technology miniaturized these portable devices to wearable devices to make them convenient and economical. Elastic, soft and thin silicon membrane with physical properties well matched with that of the epidermis provides conformal and robust contact with the skin. Integration of an elastic and flexible electronics to such a membrane provides an epidermal electronic system (EES) that can enhance the robustness in operation for electrophysiological signal measurement. Biocompatible and non-invasive over the skin are the advantages of this class of technology that lie beyond those available with conventional, point-contact electrode interfaces to the skin. Recording of various long-term physiological signals relevant in various sleep studies can be performed using this multifunctional device. Optimized design of EES for monitoring various physiological signals like surface electroencephalography (EEG), electrooculography (EOG) and electromyography (EMG) are presented in this project --Abstract, page iii

Polypyrrole (PPy) Coated Patterned Vertical Carbon Nanotube (pvCNT) Dry ECG Electrode Integrated with a Novel Wireless Resistive Analog Passive (WRAP) ECG Sensor

Polypyrrole (PPy) Coated Patterned Vertical Carbon Nanotube (pvCNT) Dry ECG Electrode Integrated with a Novel Wireless Resistive Analog Passive (WRAP) ECG Senso

Skin-Like Electronics for a Persistent Brain-Computer Interface

There exists a high demand for a continuous, persistent recording of non-invasive electroencephalograms in both clinical and research fields. Head-cap electrodes with metal conductors and conductive gels are widely used and considered as the gold standard for such measurement. This physical interface, however, is poorly suited to uninterrupted, long-term use due to the uncomfortable rigid electrodes, skin irritation due to the gel, and electrical degradation as the gel dries. These issues can be addressed by using a newly developed, dry form of electronics. Here, we briefly review a class of soft electronic technology in the aspects of mechanics, materials, and its capabilities for a long-term recording of electroencephalograms and a brain-computer interface (BCI). We summarize the progress in the development of a skin-like electronic system with a focus on key mechanical factors to achieve conformal skin contact. The design of hard electronics, integrated with soft membranes, uses deterministic fractal motifs to offer bending and stretching mechanics. We also introduce a most recent example of such electronics, an ‘auricle-integrated system’, which includes a strategy of conformal integration on the complex surface topology, a quantitative study of biocompatibility, and an application as a persistent BCI