1,721,069 research outputs found
A Multilevel Synchronized Optical Pulsed Modulation for High Efficiency Biotelemetry
No full textThe paper describes the design, implementation, and characterization of a novel multilevel synchronized pulse position modulation paradigm for high efficiency optical biotelemetry links. The entire optoelectronic architecture has been designed with the aim to improve the efficiency of the data transmission and decrease the overall power consumption that are key factors for the fabrication of implantable and wearable medical devices. By employing specially designed digital architectures, the proposed modulation technique automatically transmits more than one bit per symbol together with the reference clock signal enabling the decoding process of the received coded data. In the present case, the paper demonstrates the capability of the modulation technique to transmit symbols composed by 3 and 4 bits. This has been achieved by developing a prototype of an optical biotelemetry system implemented on an FPGA board that, making use of 500 ps laser pulses, operates under the following two working conditions: (i) 40 MHz clock signal corresponding to a baud rate of 40 Mega symbol per second for symbols composed by 3 bits; (ii) 30 MHz clock signal corresponding to a baud rate of 30 Mega symbol per second for symbols composed by 4 bits. Thus, for both these two configurations the transmission data rate is 120 Mbps and the measured BER was lower than 10^(-10). Finally, the power consumption was found to be 1.95 and 1.8 mW and the resulting energy efficiencies were 16.25 and 15 pJ/bit for transmitted symbols composed by 3 and 4 bits/symbol, respectively
Implantable Biosensor for Brain Dopamine using Microwire-Based Electrodes
No full textThis paper systematically demonstrates the feasibility of wirelessly monitoring dopamine concentration in the brain with an implantable biosensor. The biosensor was realized using microwires, and then, the dopamine concentration was measured in-vitro ranging from 0.3 μM to 2 μM, corresponding to the physio-pathological concentration range in human brain. The obtained results were used to design and optimise a full-custom CMOS sensor interface for in-vivo dopamine monitoring. The key component of this interface is a potentiostat with a maximum power consumption of 10.24 μW in a 10 kHz sampling frequency. The CMOS interface automatically subtracts the background current up to 2.34 μA. The obtained sensitivity in dopamine detection has been evaluated in 150 μA/μM, with a Limit of Detection (LoD) of 33 nM, thus being suitable for dopamine monitoring in human brain.SCI-STI-S
Fast-Response Paradigm of Si Photodiode Array to Increase the Effective Sensitive Area of Detectors in Wireless Optical Biotelemetry Links
No full textExploiting CMOS Technology to Enhance the Performance of ISFET Sensors
Full text linkThis paper presents a novel method for fabricating ISFET devices in unmodified CMOS technologies. Conventional CMOS ISFETs utilise the protective passivation coating as the sensing membrane, with the sensed potential being coupled down to the floating MOS gate via a stack of conducting and insulating layers. The proposed structure minimises the use of these layers by exploiting the passivation opening mask, normally intended for bondpad openings. Parasitic effects such as reduced transconductance and trapped charge within the floating gate structure are minimised, resulting in a lower VT and improved chemical transconductance efficiency. Other characteristics including chemical sensitivity, reference leakage current and noise power are at comparable levels with conventional CMOS-based ISFET devices.Published versio
Real-time neural signal processing and low-power hardware co-design for wireless implantable brain machine interfaces
Full text linkIntracortical Brain-Machine Interfaces (iBMIs) have advanced significantly over the past
two decades, demonstrating their utility in various aspects, including neuroprosthetic control
and communication. To increase the information transfer rate and improve the devices’
robustness and longevity, iBMI technology aims to increase channel counts to access more
neural data while reducing invasiveness through miniaturisation and avoiding percutaneous
connectors (wired implants). However, as the number of channels increases, the raw data
bandwidth required for wireless transmission also increases becoming prohibitive, requiring
efficient on-implant processing to reduce the amount of data through data compression or
feature extraction.
The fundamental aim of this research is to develop methods for high-performance neural spike processing co-designed within low-power hardware that is scaleable for real-time
wireless BMI applications. The specific original contributions include the following:
Firstly, a new method has been developed for hardware-efficient spike detection, which
achieves state-of-the-art spike detection performance and significantly reduces the hardware
complexity. Secondly, a novel thresholding mechanism for spike detection has been introduced. By incorporating firing rate information as a key determinant in establishing the spike
detection threshold, we have improved the adaptiveness of spike detection. This eventually
allows the spike detection to overcome the signal degradation that arises due to scar tissue
growth around the recording site, thereby ensuring enduringly stable spike detection results.
The long-term decoding performance, as a consequence, has also been improved notably.
Thirdly, the relationship between spike detection performance and neural decoding accuracy has been investigated to be nonlinear, offering new opportunities for further reducing
transmission bandwidth by at least 30% with minor decoding performance degradation.
In summary, this thesis presents a journey toward designing ultra-hardware-efficient spike
detection algorithms and applying them to reduce the data bandwidth and improve neural
decoding performance. The software-hardware co-design approach is essential for the next
generation of wireless brain-machine interfaces with increased channel counts and a highly
constrained hardware budget.
The fundamental aim of this research is to develop methods for high-performance neural spike processing co-designed within low-power hardware that is scaleable for real-time wireless BMI applications. The specific original contributions include the following:
Firstly, a new method has been developed for hardware-efficient spike detection, which achieves state-of-the-art spike detection performance and significantly reduces the hardware complexity. Secondly, a novel thresholding mechanism for spike detection has been introduced. By incorporating firing rate information as a key determinant in establishing the spike detection threshold, we have improved the adaptiveness of spike detection. This eventually allows the spike detection to overcome the signal degradation that arises due to scar tissue growth around the recording site, thereby ensuring enduringly stable spike detection results. The long-term decoding performance, as a consequence, has also been improved notably. Thirdly, the relationship between spike detection performance and neural decoding accuracy has been investigated to be nonlinear, offering new opportunities for further reducing transmission bandwidth by at least 30\% with only minor decoding performance degradation.
In summary, this thesis presents a journey toward designing ultra-hardware-efficient spike detection algorithms and applying them to reduce the data bandwidth and improve neural decoding performance. The software-hardware co-design approach is essential for the next generation of wireless brain-machine interfaces with increased channel counts and a highly constrained hardware budget.Open Acces
Methods and devices for chronically-reliable packaging of implantable neural microsystems
Full text linkThe current landscape of neurotechnology is thriving with a wide variety of systems and devices to study the brain and treat diseases associated with the nervous system. However, many patients who live every day with a prosthetic limb or with the consequences of a spinal cord injury are still waiting for a solution that could restore their abilities to move freely. In this regard, no established clinical solution exists at the moment, and the majority of the systems proposed and developed by the scientific community fail to translate to commercial products, mainly due to the lack of consistent chronic performances.
The design of an implantable system that can reliably work over decades is still a great challenge. The objective of this thesis is to explore the issues that impede long term operation, and to provide possible methods and solutions in the aspects regarding packaging and encapsulation of chronic implantable devices for cortical recording.
With such goal in mind, the following work starts by presenting a review of neural implantable devices, with an emphasis on the challenges they face when dealing with chronic implantation. The original contributions presented in the subsequent technical chapters are summarized here:
• The identification of a method to assess the level of hermeticity of a micro-packaged implantable device. The proposed solution is the use of a custom designed relative humidity sensor, to detect the presence of water molecules inside the packaged device. The full design of the sensor is described in detail, from the mathematical modelling of the sensing element to the readout circuit architecture, with focus on reducing the circuit footprint, as required by the specific application. The use of a commercially available sensor is also explored for the realization of a bench top hermeticity testing platform, by measuring its ability to withstand the temperatures required in the sealing process of an implantable micro-package.
• The quantification of the damages due to corrosion that occur on a silicon-based device encapsulated with a polymer coating. This has been achieved by designing dedicated test structures, and observing their behaviour in accelerated life tests, that have demonstrated the reliability of silicon substrates for chronic implantable devices. The use of an industry standard CMOS process increases the significance of the results. The idea of equipping implantable devices with self-diagnostic capabilities has also been explored. Two instrumentation circuits are proposed to monitor in real time the diffusion of water molecules within an implanted integrated circuit. real time the diffusion of water molecules within an implanted integrated circuit.
• The development of an overall structure and fabrication method for the realization of a fully autonomous, wireless, millimetre-sized neural implant, focusing on the hermeticity of the embedded electronics and on the use of penetrating microwires for cortical recording of local field potentials. The mechanical structure of the implant is presented in detail, and a first prototype is realized, together with a dedicated platform to speed up the assembly of the probes.
This work proposes devices and methods for the realization of miniaturized neural implantable devices, stressing the importance of chronic reliability and emphasizing the need for a design approach that keeps in mind the clinical applications of future neural interfaces.Open Acces
Thermally controlled lab-on-PCB for biomedical applications
Full text linkThis paper reports on the implementation and
characterisation of a thermally controlled device for
in vitro
biomedical applications, based on standard Printed Circuit Board
(PCB) technology. This is proposed as a low cost alternative
to state-of-the-art microfluidic devices and Lab-on-Chip (LoC)
platforms, which we refer to as the thermal Lab-on-PCB concept.
In total, six different prototype boards have been manufactured
to implement as many mini-hotplate arrays. 3D multiphysics
software simulations show the thermal response of the modelled
mini-hotplate boards to electrical current stimulation, highlight-
ing their versatile heating capability. A comparison with the
results obtained by the characterisation of the fabricated PCBs
demonstrates the dual temperature sensing/heating property of
the mini-hotplate, exploitable in a larger range of temperature
with respect to the typical operating range of LoC devices. The
thermal system is controllable by means of external off-the-shelf
circuitry designed and implemented on a single-channel control
board prototype
Enhancing selectivity of minimally invasive peripheral nerve interfaces using combined stimulation and high frequency block: from design to application
Full text linkThe discovery of the excitable property of nerves was a fundamental step forward in our knowledge of the nervous system and our ability to interact with it. As the injection of charge into tissue can drive its artificial activation, devices have been conceived that can serve healthcare by substituting the input or output of the peripheral nervous system when damage or disease has rendered it inaccessible or its action pathological. Applications are far-ranging and transformational as can be attested by the success of neuroprosthetics such as the cochlear implant. However, the body’s immune response to invasive implants have prevented the use of more selective interfaces, leading to therapy side-effects and off-target activation. The inherent tradeoff between the selectivity and invasiveness of neural interfaces, and the consequences thereof, is still a defining problem for the field.
More recently, continued research into how nervous tissue responds to stimulation has led to the discovery of High Frequency Alternating Current (HFAC) block as a stimulation method with inhibitory effects for nerve conduction. While leveraging the structure of the peripheral nervous system, this neuromodulation technique could be a key component in efforts to improve the selectivity-invasiveness tradeoff and provide more effective neuroprosthetic therapy while retaining the safety and reliability of minimally invasive neural interfaces.
This thesis describes work investigating the use of HFAC block to improve the selectivity of peripheral nerve interfaces, towards applications such as bladder control or vagus nerve stimulation where selective peripheral nerve interfaces cannot be used, and yet there is an unmet need for more selectivity from stimulation-based therapy. An overview of the underlying neuroanatomy and electrophysiology of the peripheral nervous system combined with a review of existing electrode interfaces and electrochemistry will serve to inform the problem space. Original contributions are the design of a custom multi-channel stimulator able to combine conventional and high frequency stimulation, establishing a suitable experimental platform for ex-vivo electrophysiology of the rat sciatic nerve model for HFAC block, and exploratory experiments to determine the feasibility of using HFAC block in combination with conventional stimulation to enhance the selectivity of minimally-invasive peripheral nerve interfaces.Open Acces
Embedded platform for electrical neural stimulation
No full textTese de mestrado integrado em Engenharia Biomédica e Biofísica, apresentada à Universidade de Lisboa, através da Faculdade de Ciências, 2015Atualmente, o número de tecnologias baseadas em neuro-estimulação está em crescimento, crescimento este que é promovido pelo facto de a neuro-estimulação ser uma área de investigação de elevado interesse devido às várias áreas de possível aplicação, tais como a terapia e tratamento, reabilitação e próteses. Na área da terapia e tratamentos, a possível aplicação da neuro-estimulação está relacionada com a neuro-regulação de órgãos do corpo humano, aplicação que tem sido vista já no campo dos distúrbios do sistema nervoso, tais como a doença de Parkinson e a epilepsia, no tratamento de dor crónica, no controlo do funcionamento cardíaco {no qual se insere uma das tecnologias mais conhecidas, o pacemaker { e está ainda a ser investigada para o controlo da libertação de insulina e a absorção renal de sais. Na área da reabilitação, a aplicação da neuro-estimulação tem sido vista em casos de lesões na medula espinal onde a utilização da técnica de estimulação eléctrica funcional, ou FES de Funcional Electrical Stimulation, resultou na recuperação de algumas funções motoras e de controlo de certos órgãos. Relativamente à área das próteses, a neuro-estimulação tem um papel muito importante principalmente no desenvolvimento de próteses funcionais, permitindo que estas próteses não só reajam a informação vinda do sistema de nervoso, realizando os movimentos desejados pelo utilizador, como também forneçam informação ao mesmo, permitindo assim que haja um mecanismo de feedback da prótese, aumentando assim a restituição que esta pode dar ao seu utilizador, tanto a nível funcional como emocional. Uma das mais conhecidas próteses que recorrem à neuro-estimulação é o implante coclear que permite uma recuperação parcial da capacidade auditiva recorrendo para isso a um conjunto de microfones no ouvido externo que deteta o som e o transmite à unidade de processamento que por sua vez transforma o som em impulsos eléctricos que são direccionados para eléctrodos no interior da cóclea e que irão estimular os nervos auditivos.
A neuro-estimulação é então um procedimento baseado na estimulação de células excitáveis, como os neurónios, recorrendo para isso à utilização de eléctrodos, com o objectivo de iniciar ou inibir um potencial de acção. Esta possibilidade de iniciar um estímulo nervoso através de estímulos externos deve-se ao facto da activação e propagação de um sinal neural ser um fenómeno eletroquímico. Este fator torna possível o desenvolvimento de tecnologias que resultem numa maior, ou menor, recetividade da célula a um estímulo através da promoção de alterações do meio em que estão inseridas as células excitáveis ou de propriedades da membrana das mesmas. O desenvolvimento de tecnologias que recorram à neuro-estimulação está dependente de um estudo profundo dos tipos e estratégias de estimulação de forma a obter a estratégia que seja mais eficaz, segura e eficiente, sendo que esta varia de situação para situação, dependendo de fatores como o local de aplicação e mesmo o resultado que se espera do estímulo. Por estes motivos têm de ser realizados estudos comparativos válidos entre estratégias de estimulação e, para um estudo deste tipo ser valido, os vários estudos devem ser feitos nas mesmas condições com distâncias temporais preferencialmente curtas. Assim sendo, no âmbito da neuro-estimulação recorrendo a estímulos eléctricos, criou-se a necessidade de desenvolver sistemas que permitissem uma mais rápida variação dos parâmetros de estimulação comparativamente à montagem experimental clássica. De forma a cumprir estes requisitos, vários sistemas de rápida configuração de parâmetros tem vindo a ser propostos. O projeto relatado nesta Tese de Mestrado, desenvolvido durante um estágio de seis meses no Centre for Bio-Inspired Technologies, Imperial College London, apresenta-se então como uma plataforma de neuro-estimulação eléctrica para a realização de estudos comparativos tendo em vista a optimização da estratégia de estimulação, com o objectivo de ser uma versão melhorada dos sistemas já disponíveis. Esta plataforma é composta por três principais componentes: uma interface utilizador-sistema, que permite ao utilizador configurar a estimulação como pretende controlando características como o tipo de onda, a amplitude, a duração, a frequência, entre outros; um microcontrolador e uma placa de estimulação, em que o primeiro controla o segundo de acordo com o que foi configurado pelo utilizador sendo que a placa têm a responsabilidade de gerar e aplicar um estímulo eléctrico. O principal objetivo deste projeto era então desenvolver uma plataforma de neuro-estimulação eléctrica capaz de gerar e aplicar uma estimulação eléctrica bipolar com capacidade de equilíbrio de cargas, podendo fazê-lo através de quatro canais de estimulação. Ao mesmo tempo era objetivo que esta fosse pequena, de baixo custo, eficaz, eficiente, de fácil utilização proporcionando um maior leque de possibilidades de configuração comparativamente aos sistemas já desenvolvidos e que pudesse também ser facilmente recriado, alterado e, eventualmente, melhorado. Os resultados obtidos de testes realizados demonstraram que esta plataforma opera corretamente nos dois principais aspetos do seu funcionamento, nomeadamente a capacidade de gerar uma estimulação de acordo com todos os parâmetros tal como configurados pelo utilizador e a capacidade de cumprir os propósitos de equilíbrio de cargas após estimulação, em todos os tipos de ondas definidos. Existem no entanto ainda algumas limitações no funcionamento da plataforma. Estas limitações estão relacionadas com a amplitude máxima de estimulação que o sistema é capaz de aplicar, mais especialmente a amplitude máxima do output do DAC utilizado e também a amplitude máxima que o amplificador operacional escolhido consegue por no seu output; com a existência de algumas imprecisões temporais na aplicação do estímulo, resultantes do tempo de execução de algumas funções por parte do microcontrolador; com o consumo energético e ainda o facto de a ligação entre o computador e o microcontrolador ser feita através de um cabo USB, o que limita a mobilidade que se pode ter durante o trabalho experimental. Comparativamente a plataformas de estimulação eléctrica configuráveis existentes, o sistema aqui desenvolvido apresenta diversas vantagens. Para além de vantagens como baixo custo e facilidade de recriação, esta plataforma tem também um maior número de parâmetros da estimulação que o utilizador pode configurar e também permite uma estimulação através de quatro canais, de três formas diferentes: utilizando apenas um canal, utilizando mais do que um canal ao mesmo tempo ou ainda mais do que um canal de forma sequencial. No entanto, alguns dos sistemas já existentes não apresentam as limitações acima referidas e como tal os desafios futuros desta placa passam por ultrapassar essas limitações.Nowadays, neuro stimulation technologies have grown to reach a wide range of applications
including therapy and treatment, rehabilitation and prosthetics and its range continues to grow as it still represents an interesting area of research. Neurostimulation is based on stimulation of excitable cells, such as nerve cells, through the use of electrodes, with the purpose of achieving initiation or inhibition of an action potential. This interaction is possible due to the electrophysiological base of activation and propagation of a neural signal. This neural signal characteristic makes it possible to use external technologies to promote changes in the nerve cell membrane voltage potential or the environment surrounding it, which can lead to the initiation of a neural signal in the cell or simply to a higher, or lower, receptivity of the cell to a stimulus. The use of neuro stimulation technologies in referred areas and future possibility of use in other applications depends on research developments. An important point of this research is the stimulation strategy, more specifically, the characteristics that a stimulation pulse should have to optimize results towards the intended objective and minimize
safety risks. The present thesis reports a project developed during an internship at the Centre for Bio-Inspired Technologies, Imperial College London which consists in designing and building
a full system for the study of stimulation strategies. This full system includes a user interface in a computer, so that the user can choose the stimulus characteristics, such as waveform and amplitude, and define the intended strategy, such as repetition rate and inter-stimulus increasing or decreasing rate; and a microcontroller for control of stimulus application through a front-end stimulation-output circuit, which will be responsible for generation of programmed current-controlled stimulus. The measurement results verify that the main objectives of this project were accomplished, namely, the capacity to generate a stimulation that meets the parameters as configured by the user and the capacity to carry a charge-balanced stimulation in all the preset waveforms. However, some limitations were also found related namely with the maximum stimulation amplitude, the small time inaccuracy during stimulation, the power consumption and the fact that connection between the computer and microcontroller is done via USB, limiting the mobility of an experimental procedure using this system. The system developed here presents some advantages compared to existing systems, such as low cost, easy to build, higher number of parameters that can be configured and can apply stimulation through four channels and do it either with only one, with two or more at the same time or with two or more sequentially. However some of these existing systems do not present some of the limitations mentioned and the challenge on the future of this platform is to overcome these limitations
Brain machine interfaces: low power techniques for CMOS based system integration
Full text linkThe emergence of miniaturized electronic sensors for recording neural activity is opening up new opportunities for better health care and understanding brain function. The precise instrumentation for sensing these signals has been developed extensively, but no implantable system available today is capable of providing a high density recording structures that can be scaled to accommodate the large number of electrodes and processing neuroprosthetics need for functional limb replacement. The design of these systems is complicated by micro-volt levels of signal that contain convoluted mixtures of information. This demands highly accurate signal quantization and exhaustive processing that is constrained by the scarce power availability. The resulting difficulty in realizing viable solutions for chronic implants necessitates cutting-edge fabrication technologies and state-of-the-art circuit optimization techniques. This thesis presents the understanding behind optimizing these instrumentation systems in order to maximize the simultaneous sensing capabilities of brain machine interfaces that can be implanted wirelessly into living systems. These analytics enabled this work to outperform state of the art in terms of delivering high precision at 56 dB SINAD with a sub 0.01mm^2 silicon footprint and a 800 nW power budget by employing novel time-domain circuit techniques. This advancement will enable BMIs to be integrated & minimutrized using nanometre CMOS with extensive digital processing capabilities that are capable of decoding neural signals without supervision such that therapy in a fully implanted fashion. Moreover by introducing distributed processing architecture this work is the first to allows scalable fully reconfigurable functionality at the instrumentation interface for complex algorithmic operations while maintaining a power efficiency of 2.7μW per MIPS.Open Acces
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