Development and Characterization of Ear-EEG for Real-Life Brain-Monitoring

Functional brain monitoring methods for neuroscience and medical diagnostics have until recently been limited to laboratory settings. However, there is a great potential for studying the human brain in the everyday life, with measurements performed in more realistic real-life settings. Electroencephalography (EEG) can be measured in real-life using wearable EEG equipment. Current wearable EEG devices are typically based on scalp electrodes, causing the devices to be visible and often uncomfortable to wear for long-term recordings. Ear-EEG is a method where EEG is recorded from electrodes placed in the ear. The Ear-EEG supports non-invasive long-term recordings of EEG in real-life in a discreet way. This Ph.D. project concerns the characterization and development of ear-EEG for real-life brain-monitoring. This was addressed through characterization of physiological artifacts in real-life settings, development and characterization of dry-contact electrodes for real-life ear-EEG acquisition, measurements of ear-EEG in real-life, and development of a method for mapping cortical sources to the ear. Characterization of physiological artifacts showed a similar artifact level for recordings from ear electrodes and temporal lobe scalp electrodes. Dry-contact electrodes and flexible earpieces were developed to increase the comfort and user-friendliness of the ear-EEG. In addition, electronic instrumentation was developed to allow implementation in a hearing-aid-sized ear-EEG device. Ear-EEG measurements performed in real-life settings with the dry-contact electrodes, were comparable to temporal lobe scalp EEG, when referenced to a Cz scalp electrode. However, the recordings showed that further development of the earpieces and electrodes are needed to obtain a satisfying recording quality, when the reference is located close to or in the ear. Mapping of the electric fields from well-defined cortical sources to the ear, showed good agreement with previous ear-EEG studies and has the potential to provide valuable information for future development of the ear-EEG method. The Ph.D. project showed that ear-EEG measurements can be performed in real-life, with dry-contact electrodes. The brain processes studied, were established with comparable clarity on recordings from temporal lobe scalp and ear electrodes. With further development of the earpieces, electrodes, and electronic instrumentation, it appears to be realistic to implement ear-EEG into unobtrusive and user-friendly devices for monitoring of human brain processes in real-life

Wearable System Based on Ultra-Thin Parylene C Tattoo Electrodes for EEG Recording

In an increasingly interconnected world, where electronic devices permeate every aspect of our lives, wearable systems aimed at monitoring physiological signals are rapidly taking over the sport and fitness domain, as well as biomedical fields such as rehabilitation and prosthetics. With the intent of providing a novel approach to the field, in this paper we discuss the development of a wearable system for the acquisition of EEG signals based on a portable, low-power custom PCB specifically designed to be used in combination with non-conventional ultra-conformable and imperceptible Parylene-C tattoo electrodes. The proposed system has been tested in a standard rest-state experiment, and its performance in terms of discrimination of two different states has been compared to that of a commercial wearable device for EEG signal acquisition (i.e., the Muse headset), showing comparable results. This first preliminary validation demonstrates the possibility of conveniently employing ultra-conformable tattoo-electrodes integrated portable systems for the unobtrusive acquisition of brain activity

Evaluation of a Behind-the-Ear ECG Device for Smartphone based Integrated Multiple Smart Sensor System in Health Applications

In this paper, we present a wireless Multiple Smart Sensor System (MSSS) in conjunction with a smartphone to enable an unobtrusive monitoring of electrocardiogram (ear-lead ECG) integrated with multiple sensor system which includes core body temperature and blood oxygen saturation (SpO2) for ambulatory patients. The proposed behind-the-ear device makes the system desirable to measure ECG data: technically less complex, physically attached to non-hair regions, hence more suitable for long term use, and user friendly as no need to undress the top garment. The proposed smart sensor device is similar to the hearing aid device and is wirelessly connected to a smartphone for physiological data transmission and displaying. This device not only gives access to the core temperature and ECG from the ear, but also the device can be controlled (removed and reapplied) by the patient at any time, thus increasing the usability of personal healthcare applications. A number of combination ECG electrodes, which are based on the area of the electrode and dry/non-dry nature of the surface of the electrodes are tested at various locations near behind the ear. The best ECG electrode is then chosen based on the Signal-to-Noise Ratio (SNR) of the measured ECG signals. These electrodes showed acceptable SNR ratio of ~20 db, which is comparable with existing tradition ECG electrodes. The developed ECG electrode systems is then integrated with commercially available PPG sensor (Amperor pulse oximeter) and core body temperature sensor (MLX90614) using a specialized micro controller (Arduino UNO) and the results monitored using a newly developed smartphone (android) application

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

Soft, curved electrode systems capable of integration on the auricle as a persistent brain–computer interface

Recent advances in electrodes for noninvasive recording of electroencephalograms expand opportunities collecting such data for diagnosis of neurological disorders and brain–computer interfaces. Existing technologies, however, cannot be used effectively in continuous, uninterrupted modes for more than a few days due to irritation and irreversible degradation in the electrical and mechanical properties of the skin interface. Here we introduce a soft, foldable collection of electrodes in open, fractal mesh geometries that can mount directly and chronically on the complex surface topology of the auricle and the mastoid, to provide high-fidelity and long-term capture of electroencephalograms in ways that avoid any significant thermal, electrical, or mechanical loading of the skin. Experimental and computational studies establish the fundamental aspects of the bending and stretching mechanics that enable this type of intimate integration on the highly irregular and textured surfaces of the auricle. Cell level tests and thermal imaging studies establish the biocompatibility and wearability of such systems, with examples of high-quality measurements over periods of 2 wk with devices that remain mounted throughout daily activities including vigorous exercise, swimming, sleeping, and bathing. Demonstrations include a text speller with a steady-state visually evoked potential-based brain–computer interface and elicitation of an event-related potential (P300 wave)

Non-invasive Electronic Biosensor Circuits and Systems

An aging population has lead to increased demand for health-care and an interest in moving health care services from the hospital to the home to reduce the burden on society. One enabling technology is comfortable monitoring and sensing of bio-signals. Sensors can be embedded in objects that people interact with daily such as a computer, chair, bed, toilet, car, telephone or any portable personal electronic device. Moreover, the relatively recent and wide availability of microelectronics that provide the capabilities of embedded software, open access wireless protocols and long battery life has led many research groups to develop wearable, wireless bio-sensor systems that are worn on the body and integrated into clothing. These systems are capable of interaction with other devices that are nowadays commonly in our possession such as a mobile phone, laptop, PDA or smart multifunctional MP3 player. The development of systems for wireless bio-medical long term monitoring is leading to personal monitoring, not just for medical reasons, but also for enhancing personal awareness and monitoring self-performance, as with sports-monitoring for athletes. These developments also provide a foundation for the Brain Computer Interface (BCI) that aims to directly monitor brain signals in order to control or manipulate external objects. This provides a new communication channel to the brain that does not require activation of muscles and nerves. This innovative and exciting research field is in need of reliable and easy to use long term recording systems (EEG). In particular we highlight the development and broad applications of our own circuits for wearable bio-potential sensor systems enabled by the use of an amplifier circuit with sufficiently high impedance to allow the use of passive dry electrodes which overcome the significant barrier of gel based contacts

A Hybrid-Powered Wireless System for Multiple Biopotential Monitoring

Chronic diseases are the top cause of human death in the United States and worldwide. A huge amount of healthcare costs is spent on chronic diseases every year. The high medical cost on these chronic diseases facilitates the transformation from in-hospital to out-of-hospital healthcare. The out-of-hospital scenarios require comfortability and mobility along with quality healthcare. Wearable electronics for well-being management provide good solutions for out-of-hospital healthcare. Long-term health monitoring is a practical and effective way in healthcare to prevent and diagnose chronic diseases. Wearable devices for long-term biopotential monitoring are impressive trends for out-of-hospital health monitoring. The biopotential signals in long-term monitoring provide essential information for various human physiological conditions and are usually used for chronic diseases diagnosis. This study aims to develop a hybrid-powered wireless wearable system for long-term monitoring of multiple biopotentials. For the biopotential monitoring, the non-contact electrodes are deployed in the wireless wearable system to provide high-level comfortability and flexibility for daily use. For providing the hybrid power, an alternative mechanism to harvest human motion energy, triboelectric energy harvesting, has been applied along with the battery to supply energy for long-term monitoring. For power management, an SSHI rectifying strategy associated with triboelectric energy harvester design has been proposed to provide a new perspective on designing TEHs by considering their capacitance concurrently. Multiple biopotentials, including ECG, EMG, and EEG, have been monitored to validate the performance of the wireless wearable system. With the investigations and studies in this project, the wearable system for biopotential monitoring will be more practical and can be applied in the real-life scenarios to increase the economic benefits for the health-related wearable devices

Wearable, Integrated EEG-fNIRS Technologies: A Review.

There has been considerable interest in applying electroencephalography (EEG) and functional near-infrared spectroscopy (fNIRS) simultaneously for multimodal assessment of brain function. EEG-fNIRS can provide a comprehensive picture of brain electrical and hemodynamic function and has been applied across various fields of brain science. The development of wearable, mechanically and electrically integrated EEG-fNIRS technology is a critical next step in the evolution of this field. A suitable system design could significantly increase the data/image quality, the wearability, patient/subject comfort, and capability for long-term monitoring. Here, we present a concise, yet comprehensive, review of the progress that has been made toward achieving a wearable, integrated EEG-fNIRS system. Significant marks of progress include the development of both discrete component-based and microchip-based EEG-fNIRS technologies; modular systems; miniaturized, lightweight form factors; wireless capabilities; and shared analogue-to-digital converter (ADC) architecture between fNIRS and EEG data acquisitions. In describing the attributes, advantages, and disadvantages of current technologies, this review aims to provide a roadmap toward the next generation of wearable, integrated EEG-fNIRS systems

Acquisition of subcortical auditory potentials with around-the-Ear cEEGrid technology in normal and hearing impaired listeners

Even though the principles of recording brain electrical activity remain unchanged since their discovery, their acquisition has seen major improvements. The cEEGrid, a recently developed flex-printed multi-channel sensory array, can be placed around the ear and successfully record well-known cortical electrophysiological potentials such as late auditory evoked potentials (AEPs) or the P300. Due to its fast and easy application as well as its long-lasting signal recording window, the cEEGrid technology offers great potential as a flexible and 'wearable' solution for the acquisition of neural correlates of hearing. Early potentials of auditory processing such as the auditory brainstem response (ABR) are already used in clinical assessment of sensorineural hearing disorders and envelope following responses (EFR) have shown promising results in the diagnosis of suprathreshold hearing deficits. This study evaluates the suitability of the cEEGrid electrode configuration to capture these AEPs. cEEGrid potentials were recorded and compared to cap-EEG potentials for young normal-hearing listeners and older listeners with high-frequency sloping audiograms to assess whether the recordings are adequately sensitive for hearing diagnostics. ABRs were elicited by presenting clicks (70 and 100-dB peSPL) and stimulation for the EFRs consisted of 120 Hz amplitudemodulated white noise carriers presented at 70-dB SPL. Data from nine bipolar cEEGrid channels and one classical cap-EEG montage (earlobes to vertex) were analysed and outcome measures were compared. Results show that the cEEGrid is able to record ABRs and EFRs with comparable shape to those recorded using a conventional capEEG recording montage and the same amplifier. Signal strength is lower but can still produce responses above the individual neural electrophysiological noise floor. This study shows that the application of the cEEGrid can be extended to the acquisition of early auditory evoked potentials

Dry EEG Electrodes

Electroencephalography (EEG) emerged in the second decade of the 20th century as a technique for recording the neurophysiological response. Since then, there has been little variation in the physical principles that sustain the signal acquisition probes, otherwise called electrodes. Currently, new advances in technology have brought new unexpected fields of applications apart from the clinical, for which new aspects such as usability and gel-free operation are first order priorities. Thanks to new advances in materials and integrated electronic systems technologies, a new generation of dry electrodes has been developed to fulfill the need. In this manuscript, we review current approaches to develop dry EEG electrodes for clinical and other applications, including information about measurement methods and evaluation reports. We conclude that, although a broad and non-homogeneous diversity of approaches has been evaluated without a consensus in procedures and methodology, their performances are not far from those obtained with wet electrodes, which are considered the gold standard, thus enabling the former to be a useful tool in a variety of novel applications.This work was supported by Nicolo Association for the R+D+i in Neurotechnologies for disability, the research project P11-TIC-7983, Junta of Andalucia (Spain) and the Spanish National Grant TIN2012-32030, co-financed by the European Regional Development Fund (ERDF). We also thank Erik Jung, head of the Medical Microsystems working group, at the Department of System Integration & Interconnection Technologies, Fraunhofer IZM (Berlin), for his support