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

A digitally invertible universal amplifier for recording and processing of bioelectric signals

Indiana University-Purdue University Indianapolis (IUPUI)The recording and processing of bioelectric signals over the decades has led to the development of many different types of analog filtering and amplification techniques. Meanwhile, there have also been many advancements in the realm of digital signal processing that allow for more powerful analysis of these collected signals. The issues with present acquisition schemes are that (1) they introduce irreversible distortion to the signals and may ultimately hinder analyses that rely on the unique morphological differences between bioelectric signal events and (2) they do not allow the collection of frequencies in the signal from direct-current (DC) to high-frequencies. The project put forth aims to overcome these two issues and present a new scheme for bioelectric signal acquisition and processing. In this thesis, a system has been developed, verified, and validated with experimental data to demonstrate the ability to build an invertible universal amplifier and digital restoration scheme. The thesis is primarily divided into four sections which focus on (1) the introduction and background information, (2) theory and development, (3) verification implementation and testing, and (4) validation implementation and testing. The introduction and background provides pertinent information regarding bioelectric signals and recording practices for bioelectric signals. It also begins to address some of the issues with the classical and present methods for data acquisition and make the case for why an invertible universal amplifier would be better. The universal amplifier transfer function and architecture are discussed and presented along with the development and optimization of the characterization and the inversion, or restoration, filter process. The developed universal amplifier, referred to as the invertible universal amplifier (IUA), while the universal amplifier and the digital restoration scheme together are referred to as the IUA system. The IUA system is then verified on the bench using typical square, sine, and triangle waveforms with varying offsets and the results are presented and discussed. The validation is done with in-vivo experiments showing that the IUA system may be used to acquire and process bioelectric signals with percent error less than to 6% when post-processed using estimated characteristics of and when compared to a standard flat bandwidth high-pass cutoff amplifier

Wireless system for the measurement of bioelectric signals using capacitive electrodes

Català: Aquest projecte mostra el disseny i la implementació d'un sistema d'adquisició de senyals bioelèctriques mitjançant elèctrodes capacitius. El sistema, inalàmbric i a bateria, envia les dades a un ordinador per a la seva visualització o processament.Castellano: Este proyecto muestra el diseño y la implementación de un sistema de adquisición de señales bioeléctricas mediante electrodos capacitivos. El sistema, inalámbrico y a batería, envía los datos a un ordenador para su visualización o procesamiento.English: This project shows the design and implementation of an acquisition system for the measurement of bioelectric signals by means of capacitive electrodes. The system, which is wireless and battery powered, sends the data to a computer for its visualizations or processing

Towards Natural Control of Artificial Limbs

The use of implantable electrodes has been long thought as the solution for a more natural control of artificial limbs, as these offer access to long-term stable and physiologically appropriate sources of control, as well as the possibility to elicit appropriate sensory feedback via neurostimulation. Although these ideas have been explored since the 1960’s, the lack of a long-term stable human-machine interface has prevented the utilization of even the simplest implanted electrodes in clinically viable limb prostheses.In this thesis, a novel human-machine interface for bidirectional communication between implanted electrodes and the artificial limb was developed and clinically implemented. The long-term stability was achieved via osseointegration, which has been shown to provide stable skeletal attachment. By enhancing this technology as a communication gateway, the longest clinical implementation of prosthetic control sourced by implanted electrodes has been achieved, as well as the first in modern times. The first recipient has used it uninterruptedly in daily and professional activities for over one year. Prosthetic control was found to improve in resolution while requiring less muscular effort, as well as to be resilient to motion artifacts, limb position, and environmental conditions.In order to support this work, the literature was reviewed in search of reliable and safe neuromuscular electrodes that could be immediately used in humans. Additional work was conducted to improve the signal-to-noise ratio and increase the amount of information retrievable from extraneural recordings. Different signal processing and pattern recognition algorithms were investigated and further developed towards real-time and simultaneous prediction of limb movements. These algorithms were used to demonstrate that higher functionality could be restored by intuitive control of distal joints, and that such control remains viable over time when using epimysial electrodes. Lastly, the long-term viability of direct nerve stimulation to produce intuitive sensory feedback was also demonstrated.The possibility to permanently and reliably access implanted electrodes, thus making them viable for prosthetic control, is potentially the main contribution of this work. Furthermore, the opportunity to chronically record and stimulate the neuromuscular system offers new venues for the prediction of complex limb motions and increased understanding of somatosensory perception. Therefore, the technology developed here, combining stable attachment with permanent and reliable human-machine communication, is considered by the author as a critical step towards more functional artificial limbs

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

Diseño e implementación de un Sistema embebido

This article presents the design and implementation of an embedded system called TES ROv2.0 non-invasive, capable of capturing and transmitting relevant biomedical signals such as: electrocardiography signals, heart rate, oxygen saturation in the blood and arterial pressure with the Support from the Clinical Information System called "SARURO", in which a detailed process of these biomedical signals is visualized and carried out by a doctor or specialist, without direct contact with the patient. Therefore, researchers have been able to affirm that integrated systems are tools that offer great versatility in the medical information market, allowing acquisition, adaptation, transformation in remote places, without linking operation to a single communication alternative, making the Telemonitoring system more versatile in its functionality to transmit over WPAN, WLAN, LAN and CELULARE networks.Este articulo presenta el diseño e implementación de un sistema embebido llamado TES ROv2.0 no invasivo, capaz de capturar y transmitir señales biomédicas relevantes como: las señales de electrocardiografía, frecuencia cardíaca, la saturación de oxígeno en la sangre y la presión arterial con el apoyo del  Sistema de Información clínico llamado "SARURO", en el cual se visualiza y efectúa un proceso detallado de estas señales biomédicas por parte de un médico o especialista, sin el contacto  directo con el paciente. Por tanto, los investigadores han podido afirmar que los sistemas integrados son herramientas que ofrecen una gran versatilidad en el mercado de la información médica, lo que permite la adquisición, adaptación, transformación en lugares remotos, sin ligar el funcionamiento a una única alternativa de comunicación, haciendo al sistema de telemonitorización más versátil en su funcionalidad para transmitir por redes WPAN, WLAN, LAN y CELULARES

Improving the mechanistic study of neuromuscular diseases through the development of a fully wireless and implantable recording device

Neuromuscular diseases manifest by a handful of known phenotypes affecting the peripheral nerves, skeletal muscle fibers, and neuromuscular junction. Common signs of these diseases include demyelination, myasthenia, atrophy, and aberrant muscle activity—all of which may be tracked over time using one or more electrophysiological markers. Mice, which are the predominant mammalian model for most human diseases, have been used to study congenital neuromuscular diseases for decades. However, our understanding of the mechanisms underlying these pathologies is still incomplete. This is in part due to the lack of instrumentation available to easily collect longitudinal, in vivo electrophysiological activity from mice. There remains a need for a fully wireless, batteryless, and implantable recording system that can be adapted for a variety of electrophysiological measurements and also enable long-term, continuous data collection in very small animals. To meet this need a miniature, chronically implantable device has been developed that is capable of wirelessly coupling energy from electromagnetic fields while implanted within a body. This device can both record and trigger bioelectric events and may be chronically implanted in rodents as small as mice. This grants investigators the ability to continuously observe electrophysiological changes corresponding to disease progression in a single, freely behaving, untethered animal. The fully wireless closed-loop system is an adaptable solution for a range of long-term mechanistic and diagnostic studies in rodent disease models. Its high level of functionality, adjustable parameters, accessible building blocks, reprogrammable firmware, and modular electrode interface offer flexibility that is distinctive among fully implantable recording or stimulating devices. The key significance of this work is that it has generated novel instrumentation in the form of a fully implantable bioelectric recording device having a much higher level of functionality than any other fully wireless system available for mouse work. This has incidentally led to contributions in the areas of wireless power transfer and neural interfaces for upper-limb prosthesis control. Herein the solution space for wireless power transfer is examined including a close inspection of far-field power transfer to implanted bioelectric sensors. Methods of design and characterization for the iterative development of the device are detailed. Furthermore, its performance and utility in remote bioelectric sensing applications is demonstrated with humans, rats, healthy mice, and mouse models for degenerative neuromuscular and motoneuron diseases

A versatile all-channel stimulator for electrode arrays, with real-time control

Over the last few decades, technology to record through ever increasing numbers of electrodes has become available to electrophysiologists. For the study of distributed neural processing, however, the ability to stimulate through equal numbers of electrodes, and thus to attain bidirectional communication, is of paramount importance. Here, we present a stimulation system for multi-electrode arrays which interfaces with existing commercial recording hardware, and allows stimulation through any electrode in the array, with rapid switching between channels. The system is controlled through real-time Linux, making it extremely flexible: stimulation sequences can be constructed on-the-fly, and arbitrary stimulus waveforms can be used if desired. A key feature of this design is that it can be readily and inexpensively reproduced in other labs, since it interfaces to standard PC parallel ports and uses only off-the-shelf components. Moreover, adaptation for use with in vivo multi-electrode probes would be straightforward. In combination with our freely available data-acquisition software, MeaBench, this system can provide feedback stimulation in response to recorded action potentials within 15 ms

Textile Concentric Ring Electrodes for ECG Recording Based on Screen-Printing Technology

[EN] Among many of the electrode designs used in electrocardiography (ECG), concentric ring electrodes (CREs) are one of the most promising due to their enhanced spatial resolution. Their development has undergone a great push due to their use in recent years; however, they are not yet widely used in clinical practice. CRE implementation in textiles will lead to a low cost, flexible, comfortable, and robust electrode capable of detecting high spatial resolution ECG signals. A textile CRE set has been designed and developed using screen-printing technology. This is a mature technology in the textile industry and, therefore, does not require heavy investments. Inks employed as conductive elements have been silver and a conducting polymer (poly (3,4-ethylenedioxythiophene) polystyrene sulfonate; PEDOT: PSS). Conducting polymers have biocompatibility advantages, they can be used with flexible substrates, and they are available for several printing technologies. CREs implemented with both inks have been compared by analyzing their electric features and their performance in detecting ECG signals. The results reveal that silver CREs present a higher average thickness and slightly lower skin-electrode impedance than PEDOT: PSS CREs. As for ECG recordings with subjects at rest, both CREs allowed the uptake of bipolar concentric ECG signals (BC-ECG) with signal-to-noise ratios similar to that of conventional ECG recordings. Regarding the saturation and alterations of ECGs captured with textile CREs caused by intentional subject movements, silver CREs presented a more stable response (fewer saturations and alterations) than those of PEDOT: PSS. Moreover, BC-ECG signals provided higher spatial resolution compared to conventional ECG. This improved spatial resolution was manifested in the identification of P1 and P2 waves of atrial activity in most of the BC-ECG signals. It can be concluded that textile silver CREs are more suitable than those of PEDOT: PSS for obtaining BC-ECG records. These developed textile electrodes bring the use of CREs closer to the clinical environment.Grant from the Ministerio de Economia y Competitividad y del Fondo Europeo de Desarrollo Regional. DPI2015-68397-R (MINECO/FEDER). This work was also supported by the Spanish Government/FEDER funds (grant number MAT2015-64139-C4-3-R (MINECO/FEDER)).Lidon-Roger, JV.; Prats-Boluda, G.; Ye Lin, Y.; Garcia Casado, FJ.; Garcia-Breijo, E. (2018). Textile Concentric Ring Electrodes for ECG Recording Based on Screen-Printing Technology. Sensors. 18(1):300-314. https://doi.org/10.3390/s18010300S30031418

Waterproof ECG Electrode Design

This project was undertaken with the goal of creating an electrode for an ECG that would work underwater. There is a specific need for an underwater electrode to detect the onset of Decompression Sickness (DCS) in deep water SCUBA diving. DCS is an extremely dangerous ailment that can lead to permanent harm and death. Electrocardiogram (ECG) can be used to diagnose DCS in divers. The combination of an electrode that records ECG underwater could lead to the elimination of the threat of DCS to divers. This project attempts to accomplish the elimination of DCS