A Wideband Contactless Electrical Impedance Tomography System

This work focuses on the development of a wideband contactless electrical impedance tomography (EIT) system. The system is developed from the aspects of the multifrequency capacitively coupled electrical impedance tomography (CCEIT) hardware, the impedance calculation model and the system evaluation. The hardware includes a 12-electrode CCEIT sensor, 6 sensing modules, a data acquisition module, and a personal computer (PC). The impedance calculation model is established by combining the mechanism modeling of the integrated circuits (ICs) and the empirical modeling of the measurement data with the least squares (LS) method. Experiments were carried out to evaluate the developed system, including the signal-to-noise ratio (SNR), the impedance measurement accuracy and the imaging performance. Experimental results show that the system achieves an SNR above 65.00 dB for the frequencies up to 20 MHz. Impedance measurement results indicate that the system has good impedance measurement accuracy at frequencies below 10 MHz and acceptable impedance measurement accuracy at 10 MHz - 20 MHz. It has particularly good performance at several specific frequencies, which can also serve as a high-performance single-frequency contactless EIT device. Imaging results show that the spectroscopic images reconstructed by the developed system are consistent with the actual distributions. Few types of research on contactless multifrequency EIT systems have been reported. So, this work is of great significance for further development and practical application of the newly emerged contactless EIT technique

Bioimpedance and bone fracture detection: A state of the art

Bioimpedance measurements are used increasingly in health applications because bioelectric parameters have been associated with anatomical and physiological properties, thus enabling to distinguish medical conditions. For bone fracture diagnostics, nevertheless, there is no established non-invasive method. Ex vivo studies and In vivo bioimpedance procedures, both invasive and non-invasive, on mammalians long bones are associated with promising results. In this work, out of a total of 568 papers, we reviewd 59 articles that mention long bone integrity by electric properties, be it Bioimpedance Analysis, Electrical Impedance Spectroscopy or Electrical Impedance Tomography. The papers are described in three sections, "Ex vivo measurements", "In vivo invasive measurements" and "In vivo non-invasive measurements". This review allows to establish the basics to planning the development of new technology to detect bone fracture via bioimpedance measurements.Fil: Dell'osa, Antonio Héctor. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Tierra del Fuego. Instituto de Desarrollo Economico E Innovacion; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Bioingeniería. Laboratorio de Medios e Interfases; ArgentinaFil: Felice, Carmelo Jose. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Bioingeniería. Laboratorio de Medios e Interfases; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Simini, Patricio. Universidad de la Republica. Facultad de Ingeniería; Urugua

Design, implementation and test of a fast impedance spectroscopy measurement system for biomedical applications

This project offers a detailed explanation on the design, implementation, and measures to characterize the hardware and firmware programmed for the acquisition of the electrical impedance spectra. It includes from the signal generation, which is based on the use of a multifrequency signal, to the acquisition and signal processing. All have been implemented using the development board RedPitaya. Moreover, all the process of signal generation, signal acquisition and processing so as the results calculation is done inside the commented RedPitaya board. The communication between the board and the computer is handled through SSH via ethernet port. Finally, this project also includes a brief script implemented in MatLab which objective is just to represent the acquired results from the board. To conclude, characterization measures are made to verify the system specifications

Development of real-time cellular impedance analysis system

The cell impedance analysis technique is a label-free, non-invasive method, which simplifies sample preparation and allows applications requiring unmodified cell retrieval. However, traditional impedance measurement methods suffer from various problems (speed, bandwidth, accuracy) for extracting the cellular impedance information. This thesis proposes an improved system for extracting precise cellular impedance in real-time, with a wide bandwidth and satisfactory accuracy. The system hardware consists of five main parts: a microelectrode array (MEA), a stimulation circuit, a sensing circuit, a multi-function card and a computer. The development of system hardware is explored. Accordingly, a novel bioimpedance measurement method coined digital auto balancing bridge method, which is improved from the traditional analogue auto balancing bridge circuitry, is realized for real-time cellular impedance measurement. Two different digital bridge balancing algorithms are proposed and realized, which are based on least mean squares (LMS) algorithm and fast block LMS (FBLMS) algorithm for single- and multi-frequency measurements respectively. Details on their implementation in FPGA are discussed. The test results prove that the LMS-based algorithm is suitable for accelerating the measurement speed in single-frequency situation, whilst the FBLMS-based algorithm has advantages in stable convergence in multi-frequency applications. A novel algorithm, called the All Phase Fast Fourier Transform (APFFT), is applied for post-processing of bioimpedance measurement results. Compared with the classical FFT algorithm, the APFFT significantly reduces spectral leakage caused by truncation error. Compared to the traditional FFT and Digital Quadrature Demodulation (DQD) methods, the APFFT shows excellent performance for extracting accurate phase and amplitude in the frequency spectrum. Additionally, testing and evaluation of the realized system has been performed. The results show that our system achieved a satisfactory accuracy within a wide bandwidth, a fast measurement speed and a good repeatability. Furthermore, our system is compared with a commercial impedance analyzer (Agilent 4294A) in biological experiments. The results reveal that our system achieved a comparable accuracy to the commercial instrument in the biological experiments. Finally, conclusions are given and the future work is proposed

Impedance Spectroscopy

This book covers new advances in the field of impedance spectroscopy including fundamentals, methods and applications. It releases selected extended and peer reviewed scientific contributions from the International Workshop on Impedance Spectroscopy (IWIS 2017) focussing on detailed information about recent scientific research results in electrochemistry and battery research, bioimpedance measurement, sensors, system design, signal processing

A Low Total Harmonic Distortion Sinusoidal Oscillator Based on Digital Harmonic Cancellation Technique

Sinusoidal oscillator is intensively used in many applications, such as built-in-self-testing and ADC characterization. An innovative medical application for skin cancer detection employed a technology named bio-impedance spectroscopy, which also requires highly linear sinusoidal-wave as the reference clock. Moreover, the generated sinusoidal signals should be tunable within the frequency range from 10kHz to 10MHz, and quadrature outputs are demanded for coherent demodulation within the system. A design methodology of sinusoidal oscillator named digital-harmonic-cancellation (DHC) technique is presented. DHC technique is realized by summing up a set of square-wave signals with different phase shifts and different summing coefficient to cancel unwanted harmonics. With a general survey of literature, some sinusoidal oscillators based on DHC technique are reviewed and categorized. Also, the mathematical algorithm behind the technique is explained, and non-ideality effect is analyzed based on mathematical calculation. The prototype is fabricated in OnSemi 0.5um CMOS technology. The experimental results of this work show that it can achieve HD2 is -59.74dB and HD3 is -60dB at 0.9MHz, and the frequency is tunable over 0.1MHz to 0.9MHz. The chip consumes area of 0.76mm2, and power consumption at 0.9MHz is 2.98mW. Another design in IBM 0.18um technology is still in the phase of design. The preliminary simulation results show that the 0.18um design can realize total harmonic distortion of -72dB at 10MHz with the power consumption of 0.4mW. The new design is very competitive with state-of-art, which will be finished with layout, submitted for fabrication and measured later

Acoustic Simulation and Characterization of Capacitive Micromachined Ultrasonic Transducers (CMUT)

Ultrasonic transducers are used in many fields of daily life, e.g. as parking aids or medical devices. To enable their usage also for mass applications small and low- cost transducers with high performance are required. Capacitive, micro-machined ultrasonic transducers (CMUT) offer the potential, for instance, to integrate compact ultrasonic sensor systems into mobile phones or as disposable transducer for diverse medical applications. This work is aimed at providing fundamentals for the future commercialization of CMUTs. It introduces novel methods for the acoustic simulation and characterization of CMUTs, which are still critical steps in the product development process. They allow an easy CMUT cell design for given application requirements. Based on a novel electromechanical model for CMUT elements, the device properties can be determined by impedance measurement already. Finally, an end-of-line test based on the electrical impedance of CMUTs demonstrates their potential for efficient mass production

A Low Total Harmonic Distortion Sinusoidal Oscillator Based on Digital Harmonic Cancellation Technique

Sinusoidal oscillator is intensively used in many applications, such as built-in-self-testing and ADC characterization. An innovative medical application for skin cancer detection employed a technology named bio-impedance spectroscopy, which also requires highly linear sinusoidal-wave as the reference clock. Moreover, the generated sinusoidal signals should be tunable within the frequency range from 10kHz to 10MHz, and quadrature outputs are demanded for coherent demodulation within the system. A design methodology of sinusoidal oscillator named digital-harmonic-cancellation (DHC) technique is presented. DHC technique is realized by summing up a set of square-wave signals with different phase shifts and different summing coefficient to cancel unwanted harmonics. With a general survey of literature, some sinusoidal oscillators based on DHC technique are reviewed and categorized. Also, the mathematical algorithm behind the technique is explained, and non-ideality effect is analyzed based on mathematical calculation. The prototype is fabricated in OnSemi 0.5um CMOS technology. The experimental results of this work show that it can achieve HD2 is -59.74dB and HD3 is -60dB at 0.9MHz, and the frequency is tunable over 0.1MHz to 0.9MHz. The chip consumes area of 0.76mm2, and power consumption at 0.9MHz is 2.98mW. Another design in IBM 0.18um technology is still in the phase of design. The preliminary simulation results show that the 0.18um design can realize total harmonic distortion of -72dB at 10MHz with the power consumption of 0.4mW. The new design is very competitive with state-of-art, which will be finished with layout, submitted for fabrication and measured later

The Investigation and Implementation of electrical Impedance Tomography Hardware System

Electrical impedance tomography (EIT) is a medical imaging technology that provides a tomographic representation of the distribution of electrical impedance within the body. As the electrical impedance varies for different body tissues, it is possible to characterize tissues from the images and to detect physiological events. EIT systems have been developed from applying a single signal frequency to a range of frequencies. Imaging at multiple frequencies significantly improves the ability to characterize and differentiate heterogeneity within the region of interest. Applications of EIT are limited by its poor resolution as a consequence of limited number of electrodes and lack of independently published measurements. In a practical EIT system design the parallel structure is normally adopted as it provides a real time monitoring structure. However, there is a difficulty in expanding to a 2-dimensitional or 3-dimensitional high resolution imaging system, as the number of electrodes increase. In this thesis, a serial structure spectrum EIT system has been investigated and developed. Modelling of the electrical circuit has shown that the system bandwidth is degraded primarily by the signal transmission in the coaxial cable and multiplexer. To remove the capacitive effect of these components, a distribute system concept has been developed. The concept uses active electrodes in which a current source and a front end amplifier are embedded in the electrode which makes direct contact with the tissue being measured. The active electrode is based on the Howland current source. The required high output impedance of Howland current source can be realised by matching the two resistor arms. However, from the electrical equivalent circuit analysis the actual output impedance of this circuit was found to be degraded by the op-amp' s limited open loop gain, especially at higher frequencies. To solve the problem, the author describes in detail a novel method of compensating for the above effects. Subsequent circuit tests showed significant improvement after the compensation. Further, to improve the small signal noise ratio a programmable gain amplifier to adapt the frame data measurement was developed. These developments have led to the feasibility of active electrodes. The thesis describes in detail the development, of the MK2 EIT system which is presented as the output of this research

Faisabilité d’un récepteur Galileo SDR bi-fréquence à échantillonnage direct pour l’Aviation Civile

This thesis studies the relevance of DS (Direct Sampling) SDR (Software-Defined Radio) architectures applied to Galileo receivers in the specific context of Civil Aviation, characterized in particular by strict requirements of robustness to interference, in particular, interference caused by DME (Distance Measuring Equipment) or CW (Carrier Wave) signals. The Software Defined Radio concept renders the major tendency, inside the receiver, to move the demodulation part from an analog technology to digital signal processing, that is software. The choice of this kind of design is nearly generalized in new receiver architectures so it was considered the case in this work. The Direct Sampling method consists in digitizing the signal as close as possible to the antenna, typically after the LNA (Low-Noise Amplifier) and the associated RF (Radio Frequency) bandpass filter. So this technique does not use any conversion to an intermediate frequency, using as much as possible the bandpass sampling principle in order to minimize the sampling frequency and consequently the downstream computational costs. What is more, this thesis aiming at the greatest simplification of the analog part of the receiver, the decision was made to suppress the analog AGC (Automatic Gain Control) which equips the receivers of classical architecture. Only fixed gained amplifiers should precede the ADC (Analog to Digital Converter). This document exposes the work done to determine if these choices can apply to a multifrequency (E5a and E1 signals) Galileo receiver intended for a Civil Aviation use. The structure of the document reflects the approach used during this thesis. It progresses step by step from the antenna down to the digital signal, to be processed then by the SDR part. After an introduction detailing the problem to study and its context, the second chapter investigates the Civil Aviation requirements of robustness to interference a satellite navigation receiver must comply with. It is the basis which completely conditions the design process. The third chapter is devoted to the determination of the sampling frequency. Two sampling architectures are proposed: the first implements coherent sampling of the two E5a and E1 bands while the second uses separate sampling. In both cases the necessity to use extra RF filters is shown. The minimum attenuation to be provided by these filters is also specified. These requirements are strong enough to justify a feasibility investigation. It is the subject of chapter four where an experimental study, based on a SAW (Surface Acoustic Wave) filter chip available on the shelf, is related. The issue of the sampling clock jitter, of concern with the Direct Sampling technique because of the high frequency of the signal to digitize, is investigated in chapter five. Some simulation results are presented and a dimensioning of the quality of the sampling clock is proposed. In chapter six, quantization, a byproduct of digitization, is detailed. Precisely it is the calculation of the number of bits the ADC must have to digitally represent the whole dynamic of, not only the useful signal, but also of the potential interference. Considering the high binary throughput highlighted in chapters three and six, chapter seven evaluates the possibility to reduce the coding dynamic of the digital signal at the output of the ADC by means of compression functions. The last chapter is focused on the digital separation of the two E5a and E1 bands in the coherent sampling architecture presented in chapter two. Here also specifications of minimum attenuation are given. Lastly the conclusions synthesize the contributions of this thesis and proposes ideas for future work to enrich them and more generally the subject of DS-SDR Galileo receivers for Civil Aviation.Cette thèse étudie l’intérêt des architectures SDR (Software-Defined Radio) à échantillonnage direct pour des récepteurs Galileo dans le contexte particulier de l’Aviation Civile, caractérisé notamment par une exigence de robustesse à des interférences bien spécifiées, principalement les interférences causées par les signaux DME (Distance Measuring Equipment) ou CW (Carrier Wave). Le concept de Software Defined Radio traduit la migration toujours plus grande, au sein des récepteurs, des procédés de démodulation d’une technologie analogique à du traitement numérique, donc de façon logicielle. La quasi généralisation de ce choix de conception dans les architectures nouvelles nous a conduit à le considérer comme acquis dans notre travail. La méthode d’échantillonnage direct, ou Direct Sampling, quant à elle consiste à numériser les signaux le plus près possible de l’antenne, typiquement derrière le LNA (Low-Noise Amplifier) et les filtres RF (Radio Frequency) associés. Cette technique s’affranchit donc de toute conversion en fréquence intermédiaire, utilisant autant que possible le principe de l’échantillonnage passe-bande afin de minimiser la fréquence d’échantillonnage et en conséquence les coûts calculatoires ultérieurs. De plus cette thèse s’est proposée de pousser jusqu’au bout la simplification analogique en renonçant également à l’utilisation de l’AGC (Automatic Gain Control) analogique qui équipe les récepteurs de conception traditionnelle. Seuls des amplificateurs à gain fixe précéderont l’ADC (Analog to Digital Converter). Ce mémoire rend compte des travaux menés pour déterminer si ces choix peuvent s’appliquer aux récepteurs Galileo multifréquences (signaux E5a et E1) destinés à l’Aviation Civile. La structure du document reflète la démarche qui a été la notre durant cette thèse et qui a consisté à partir de l’antenne pour, d’étape en étape, aboutir au signal numérique traité par la partie SDR. Après une introduction détaillant le problème posé et le contexte dans lequel il s’inscrit, le deuxième chapitre étudie les exigences de robustesse aux interférences auquel doit se soumettre un récepteur de navigation par satellites destiné à l’Aviation Civile. Il s’agit de la base qui conditionne toute la démarche à suivre. Le troisième chapitre est consacré au calcul des fréquences d’échantillonnage. Deux architectures d’échantillonnage sont proposées. La première met en oeuvre un échantillonnage cohérent des deux bandes E5a et E1 tandis que la seconde implémente un échantillonnage séparé. Dans les deux cas, la nécessité de filtres RF supplémentaires précédant l’échantillonnage est mise en évidence. L’atténuation minimale que doivent apporter ces filtres est spécifiée. Ces spécifications sont suffisamment dures pour qu’il ait été jugé indispensable d’effectuer une étude de faisabilité. C’est l’objet du chapitre quatre où une approche expérimentale à base d’un composant disponible sur étagère a été menée. La problématique de la gigue de l’horloge d’échantillonnage, incontournable ici eu égard à la haute fréquence des signaux à numériser, est étudiée dans le chapitre cinq. Des résultats de simulation sont présentés et un dimensionnement de la qualité de l’horloge d’échantillonnage est proposé. Dans le chapitre six, la quantification, second volet de la numérisation, est détaillée. Il s’agit très précisément du calcul du nombre minimum de bits de quantification que doit exhiber l’ADC pour représenter toute la dynamique, non seulement du signal utile mais aussi des interférences potentielles. Au vu des débits de données conséquents mis en évidence dans les chapitres trois et six, le chapitre sept évalue la possibilité de réduire la dynamique de codage du signal à l’aide de fonctions de compression. Le dernier chapitre est focalisé sur la séparation numérique des bandes E5a et E1 dans l’architecture à échantillonnage cohérent introduite au chapitre deux. Ici aussi l’atténuation minimale que doivent apporter les filtres requis est spécifiée. Et finalement la conclusion synthétise les résultats obtenus et propose des idées de travaux complémentaires destinés à enrichir les contributions de cette thèse