The Development of a Capacitance-Based Biotelemetry System for Implantable Applications

Most modern biomedical implants implement some form of communications link between the implant and the outside world. This biotelemetry link has many requirements such as data bandwidth and power consumption. Designing an appropriate link that meets these requirements is one of the most significant engineering challenges associated with these implants. Communications methods that are currently used for this link include standard Radio Frequency (RF) approaches, inductively coupled approaches, and load modulation approaches. This thesis describes the development of a unique capacitance-based biotelemetry system for implantable applications. This system consists of two distinct parts: the implanted transmitter and the external body-mounted receiver. The prototype transmitter is based on a custom Application Specific Integrated Circuit (ASIC) fabricated using the AMI 1.5µ process. This ASIC encodes and transmits predetermined data packets by driving two electrodes in a slew-controlled manner, all contained within a biocompatible material. The receiver consists of charge-sensitive amplifier front end using a discriminator to distinguish individual bits. A Field Programmable Gate Array (FPGA) decodes the transmitted data and relays it to a PC- based LabVIEW interface. Test results using a saline-based human tissue model are presented

Advanced sensors technology survey

This project assesses the state-of-the-art in advanced or 'smart' sensors technology for NASA Life Sciences research applications with an emphasis on those sensors with potential applications on the space station freedom (SSF). The objectives are: (1) to conduct literature reviews on relevant advanced sensor technology; (2) to interview various scientists and engineers in industry, academia, and government who are knowledgeable on this topic; (3) to provide viewpoints and opinions regarding the potential applications of this technology on the SSF; and (4) to provide summary charts of relevant technologies and centers where these technologies are being developed

Low-noise electronic readout for high-throughput, portable biomolecular detection in microchannel arrays

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2006.Includes bibliographical references (leaves 57-58).There's not much that can be done to make research easier - but excitement and passion are two key elements of success, and two of the many things I have learned from my advisor, Scott Manalis. It has been (and will continue to be) an awesome opportunity that I am especially thankful for, to work in nanoscale sensing with him. Perhaps the next best thing to a great advisor is having friends to work with who are equally as excited as me, more experienced, and many times smarter. I am forever indebted to all the members of the lab who have contributed to my biggest asset - knowledge. Special respect to those who bestow humour with the facts: Nebojsa, Johnson, Mike, Phil, and of course Thomas without whom I would have been in the lab a lot longer and in Europe a lot less. Thanks for coming to lab with a smile and for helping me leave with one. Places like MIT are excellent institutions, mostly because of their students. I am thankful to all of the graduate students in other labs which are always glad to give some words of advice or spend a few hours explaining something not so trivial to me. Especially to those in Professor Rahul Sarpeshkar's laboratory, especially Soumya and Scott. I am also very lucky to have great friends outside of the lab, for constant support, empathy and for bettering my overall well-being. Also to those who have come into my life and left at some point, I have gained so many more things from you than you may realize. Finally, to those who have probably contributed the most to my research success - without a single formula or circuit diagram, my family: Habibullah, Rosemin and Alizahra. You made me realize that as with life, struggle is the meaning of research. Defeat or victory is in the hands of God, but struggle itself is man's duty and should be his joy.by Rumi Chunara.S.M

Carbon Based Nanoelectromechanical Resonators.

Owing to their light mass and high Young’s modulus, carbon nanotubes (CNTs) and graphene are promising candidates for nanoelectromechanical resonators capable of ultrasmall mass and force sensing. Unfortunately, the mass sensitivity of CNT resonators is impeded by the low quality factor (Q) caused by intrinsic losses. Therefore, one should minimize dissipations or seek an external way to enhance Q in order to overcome the fundamental limits. In this thesis, I first carried out a one-step direct transfer technique to fabricate pristine CNT nanoelectronic devices at ambient temperature. This process technique prevents unwanted contaminations, further reducing surface losses. Using this technique, CNT resonators was fabricated and a fully suspended CNT p-n diode with ideality factor equal to 1 was demonstrated as well. Subsequently, the frequency tuning mechanisms of CNT resonators were investigated in order to study their nonlinear dynamics. Downward frequency tuning caused by capacitive spring softening effect was demonstrated for the first time in CNT resonators adopting a dual-gate configuration. Leveraging the ability to modulate the spring constant, parametric amplification was demonstrated for Q enhancement in CNT resonators. Here, the simplest parametric amplification scheme was implemented by modulating the spring constant of CNTs at twice the resonance frequency through electrostatic gating. Consequently, at least 10 times Q enhancement was demonstrated and Q of 700 at room temperature was the highest record to date. Moreover, parametric amplification shows strong dependence on DC gate voltages, which is believed due to the difference of frequency tunability in different vibrational regimes. Graphene takes advantages over CNTs due to the availability of wafer-scale graphene films synthesized by chemical vapor deposition (CVD) method. Thus, I also examined graphene resonators fabricated from CVD graphene films. Ultra-high frequency (UHV) graphene resonators were demonstrated, and the Qs of graphene resonators are around 100. Future directions of graphene resonators include investigating the potential losses, exploring the origin of nonlinear damping, and demonstrating parametric amplification for Q enhancement.Ph.D.Electrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/91487/1/chungwu_1.pd

OPTIMIZATION OF TIME-RESPONSE AND AMPLIFICATION FEATURES OF EGOTs FOR NEUROPHYSIOLOGICAL APPLICATIONS

In device engineering, basic neuron-to-neuron communication has recently inspired the development of increasingly structured and efficient brain-mimicking setups in which the information flow can be processed with strategies resembling physiological ones. This is possible thanks to the use of organic neuromorphic devices, which can share the same electrolytic medium and adjust reciprocal connection weights according to temporal features of the input signals. In a parallel - although conceptually deeply interconnected - fashion, device engineers are directing their efforts towards novel tools to interface the brain and to decipher its signalling strategies. This led to several technological advances which allow scientists to transduce brain activity and, piece by piece, to create a detailed map of its functions. This effort extends over a wide spectrum of length-scales, zooming out from neuron-to-neuron communication up to global activity of neural populations. Both these scientific endeavours, namely mimicking neural communication and transducing brain activity, can benefit from the technology of Electrolyte-Gated Organic Transistors (EGOTs). Electrolyte-Gated Organic Transistors (EGOTs) are low-power electronic devices that functionally integrate the electrolytic environment through the exploitation of organic mixed ionic-electronic conductors. This enables the conversion of ionic signals into electronic ones, making such architectures ideal building blocks for neuroelectronics. This has driven extensive scientific and technological investigation on EGOTs. Such devices have been successfully demonstrated both as transducers and amplifiers of electrophysiological activity and as neuromorphic units. These promising results arise from the fact that EGOTs are active devices, which widely extend their applicability window over the capabilities of passive electronics (i.e. electrodes) but pose major integration hurdles. Being transistors, EGOTs need two driving voltages to be operated. If, on the one hand, the presence of two voltages becomes an advantage for the modulation of the device response (e.g. for devising EGOT-based neuromorphic circuitry), on the other hand it can become detrimental in brain interfaces, since it may result in a non-null bias directly applied on the brain. If such voltage exceeds the electrochemical stability window of water, undesired faradic reactions may lead to critical tissue and/or device damage. This work addresses EGOTs applications in neuroelectronics from the above-described dual perspective, spanning from neuromorphic device engineering to in vivo brain-device interfaces implementation. The advantages of using three-terminal architectures for neuromorphic devices, achieving reversible fine-tuning of their response plasticity, are highlighted. Jointly, the possibility of obtaining a multilevel memory unit by acting on the gate potential is discussed. Additionally, a novel mode of operation for EGOTs is introduced, enabling full retention of amplification capability while, at the same time, avoiding the application of a bias in the brain. Starting on these premises, a novel set of ultra-conformable active micro-epicortical arrays is presented, which fully integrate in situ fabricated EGOT recording sites onto medical-grade polyimide substrates. Finally, a whole organic circuitry for signal processing is presented, exploiting ad-hoc designed organic passive components coupled with EGOT devices. This unprecedented approach provides the possibility to sort complex signals into their constitutive frequency components in real time, thereby delineating innovative strategies to devise organic-based functional building-blocks for brain-machine interfaces.Nell’ingegneria elettronica, la comunicazione di base tra neuroni ha recentemente ispirato lo sviluppo di configurazioni sempre più articolate ed efficienti che imitano il cervello, in cui il flusso di informazioni può essere elaborato con strategie simili a quelle fisiologiche. Ciò è reso possibile grazie all'uso di dispositivi neuromorfici organici, che possono condividere lo stesso mezzo elettrolitico e regolare i pesi delle connessioni reciproche in base alle caratteristiche temporali dei segnali in ingresso. In modo parallelo, gli ingegneri elettronici stanno dirigendo i loro sforzi verso nuovi strumenti per interfacciare il cervello e decifrare le sue strategie di comunicazione. Si è giunti così a diversi progressi tecnologici che consentono agli scienziati di trasdurre l'attività cerebrale e, pezzo per pezzo, di creare una mappa dettagliata delle sue funzioni. Entrambi questi ambiti scientifici, ovvero imitare la comunicazione neurale e trasdurre l'attività cerebrale, possono trarre vantaggio dalla tecnologia dei transistor organici a base elettrolitica (EGOT). I transistor organici a base elettrolitica (EGOT) sono dispositivi elettronici a bassa potenza che integrano funzionalmente l'ambiente elettrolitico attraverso lo sfruttamento di conduttori organici misti ionici-elettronici, i quali consentono di convertire i segnali ionici in segnali elettronici, rendendo tali dispositivi ideali per la neuroelettronica. Gli EGOT sono stati dimostrati con successo sia come trasduttori e amplificatori dell'attività elettrofisiologica e sia come unità neuromorfiche. Tali risultati derivano dal fatto che gli EGOT sono dispositivi attivi, al contrario dell'elettronica passiva (ad esempio gli elettrodi), ma pongono comunque qualche ostacolo alla loro integrazione in ambiente biologico. In quanto transistor, gli EGOT necessitano l'applicazione di due tensioni tra i suoi terminali. Se, da un lato, la presenza di due tensioni diventa un vantaggio per la modulazione della risposta del dispositivo (ad esempio, per l'ideazione di circuiti neuromorfici basati su EGOT), dall'altro può diventare dannosa quando gli EGOT vengono adoperati come sito di registrazione nelle interfacce cerebrali, poiché una tensione non nulla può essere applicata direttamente al cervello. Se tale tensione supera la finestra di stabilità elettrochimica dell'acqua, reazioni faradiche indesiderate possono manifestarsi, le quali potrebbero danneggiare i tessuti e/o il dispositivo. Questo lavoro affronta le applicazioni degli EGOT nella neuroelettronica dalla duplice prospettiva sopra descritta: ingegnerizzazione neuromorfica ed implementazione come interfacce neurali in applicazioni in vivo. Vengono evidenziati i vantaggi dell'utilizzo di architetture a tre terminali per i dispositivi neuromorfici, ottenendo una regolazione reversibile della loro plasticità di risposta. Si discute inoltre la possibilità di ottenere un'unità di memoria multilivello agendo sul potenziale di gate. Viene introdotta una nuova modalità di funzionamento per gli EGOT, che consente di mantenere la capacità di amplificazione e, allo stesso tempo, di evitare l'applicazione di una tensione all’interfaccia cervello-dispositivo. Partendo da queste premesse, viene presentata una nuova serie di array micro-epicorticali ultra-conformabili, che integrano completamente i siti di registrazione EGOT fabbricati in situ su substrati di poliimmide. Infine, viene proposto un circuito organico per l'elaborazione del segnale, sfruttando componenti passivi organici progettati ad hoc e accoppiati a dispositivi EGOT. Questo approccio senza precedenti offre la possibilità di filtrare e scomporre segnali complessi nelle loro componenti di frequenza costitutive in tempo reale, delineando così strategie innovative per concepire blocchi funzionali a base organica per le interfacce cervello-macchina

Development and modelling of a versatile active micro-electrode array for high density in-vivo and in-vitro neural signal investigation

The electrophysiological observation of neurological cells has allowed much knowledge to be gathered regarding how living organisms are believed to acquire and process sensation. Although much has been learned about neurons in isolation, there is much more to be discovered in how these neurons communicate within large networks. The challenges of measuring neurological networks at the scale, density and chronic level of non invasiveness required to observe neurological processing and decision making are manifold, however methods have been suggested that have allowed small scale networks to be observed using arrays of micro-fabricated electrodes. These arrays transduce ionic perturbations local to the cell membrane in the extracellular fluid into small electrical signals within the metal that may be measured. A device was designed for optimal electrical matching to the electrode interface and maximal signal preservation of the received extracellular neural signals. Design parameters were developed from electrophysiological computer simulations and experimentally obtained empirical models of the electrode-electrolyte interface. From this information, a novel interface based signal filtering method was developed that enabled high density amplifier interface circuitry to be realised. A novel prototype monolithic active electrode was developed using CMOS microfabrication technology. The device uses the top metallization of a selected process to form the electrode substrate and compact amplification circuitry fabricated directly beneath the electrode to amplify and separate the neural signal from the baseline offsets and noise of the electrode interface. The signal is then buffered for high speed sampling and switched signal routing. Prototype 16 and 256 active electrode array with custom support circuitry is presented at the layout stage for a 20 μm diameter 100 μm pitch electrode array. Each device consumes 26.4 μW of power and contributes 4.509 μV (rms) of noise to the received signal over a controlled bandwidth of 10 Hz - 5 kHz. The research has provided a fundamental insight into the challenges of high density neural network observation, both in the passive and the active manner. The thesis concludes that power consumption is the fundamental limiting factor of high density integrated MEA circuitry; low power dissipation being crucial for the existence of the surface adhered cells under measurement. With transistor sizing, noise and signal slewing each being inversely proportional to the dc supply current and the large power requirements of desirable ancillary circuitry such as analogue-to-digital converters, a situation of compromise is approached that must be carefully considered for specific application design

Communications Biophysics

Contains reports on six research projects.National Institutes of Health (Grant 2 P01 GM-14940-01)Joint Services Electronics Programs (U. S. Army, U.S. Navy, and U.S. Air Force) under Contract DA 28-043-AMC-02536(E)National Aeronautics and Space Administration (Grant NsG-496)National Institutes of Health (Grant 2 ROl NB-05462-03

Light-Addressing and Chemical Imaging Technologies for Electrochemical Sensing

Visualizing chemical components in a specimen is an essential technology in many branches of science and practical applications. This book deals with electrochemical imaging techniques based on semiconductor devices with capability of spatially resolved sensing. Two types of such sensing devices have been extensively studied and applied in various fields, i.e., arrayed sensors and light-addressed sensors. An ion-sensitive field-effect transistor (ISFET) array and a charge-coupled device (CCD) ion image sensor are examples of arrayed sensors. They take advantage of semiconductor microfabrication technology to integrate a large number of sensing elements on a single chip, each representing a pixel to form a chemical image. A light-addressable potentiometric sensor (LAPS), on the other hand, has no pixel structure. A chemical image is obtained by raster-scanning the sensor plate with a light beam, which can flexibly define the position and size of a pixel. This light-addressing approach is further applied in other LAPS-inspired methods. Scanning photo-induced impedance microscopy (SPIM) realized impedance mapping and light-addressable electrodes/light-activated electrochemistry (LAE) realized local activation of Faradaic processes. This book includes eight articles on state-of-the-art technologies of light-addressing/chemical imaging devices and their application to biology and materials science

Power system applications of fiber optics

Power system applications of optical systems, primarily using fiber optics, are reviewed. The first section reviews fibers as components of communication systems. The second section deals with fiber sensors for power systems, reviewing the many ways light sources and fibers can be combined to make measurements. Methods of measuring electric field gradient are discussed. Optical data processing is the subject of the third section, which begins by reviewing some widely different examples and concludes by outlining some potential applications in power systems: fault location in transformers, optical switching for light fired thyristors and fault detection based on the inherent symmetry of most power apparatus. The fourth and final section is concerned with using optical fibers to transmit power to electric equipment in a high voltage situation, potentially replacing expensive high voltage low power transformers. JPL has designed small photodiodes specifically for this purpose, and fabricated and tested several samples. This work is described