Design of a CMOS closed-loop system with applications to bio-impedance measurements

This paper proposes a method for impedance measurements based on a closed-loop implementation of CMOS circuits. The proposed system has been conceived for alternate current excited systems, performing simultaneously driving and measuring functions, thanks to feedback. The system delivers magnitude and phase signals independently, which can be optimized separately, and can be applied to any kind of load (resistive and capacitive). Design specifications for CMOS circuit blocks and trade-offs for system accuracy and loop stability have been derived. Electrical simulation results obtained for several loads agree with the theory, enabling the proposed method to any impedance measurement problem, in special, to bio-setups including electrodes.Ministerio de Ciencia e Innovación TEC2007-6807

Developments in static and pulsed magnetic field systems for detection of magnetic resonance in non-uniform magnetic fields

The evolution of wearable diagnostic devices and more importantly, increasing consumer awareness, have demanded advancements in sensing mechanisms, sensor data analysis and data processing. Magnetics technologies such as current sensing, actuation, switching, navigation and data recording have all evolved technologically with the demand of lower operational power and long-term system stability. However, none of these advancements, have incorporated operations in low magnetic fields since these fields are non-uniform, vary spatially and provide low data resolution. In this work, the possibility of sensor operations in low non-uniform magnetic fields is explored. Magnetic fields produced by neodymium iron boron permanent magnets are studied, simulated and tested with portable pulsed field generation systems to demonstrate the capability of detecting magnetic resonance signals in non-uniform DC magnetic fields. Advances in detection capabilities in non-uniform fields will allow multiple new application areas to develop, potentially revolutionizing medical diagnostic procedures. In this dissertation, we analyze different aspects of a portable magnetic resonance sensor system in detail. We first study magnetic fields produced by different permanent magnet geometries. The spatial magnetic field variations in the magnet\u27s exterior are simulated using finite element methods. In particular, regions of localized field uniformity in the magnet\u27s exterior are identified for ring magnet geometries. Various modifications to ring magnets such as magnet dimensions, inclusion of magnetic inserts, placement of multiple magnets and their orientations are simulated to identify the optimal geometry with maximum magnetic flux density in locally uniform regions. We next consider the generation of pulsed magnetic fields using portable electronic circuits. Pulsed magnetic fields are needed to initiate the magnetic resonance process. Thus, pulsed fields are used alongside the static fields in magnetic resonance measurements. We discuss design considerations for creating portable pulsed magnetic field circuits, delivering upto 10 A of current at operational frequencies ranging from 2 - 5 MHz, via design of two prototype circuits. Both these prototype devices rely on application of pulsed sinusoidals to switching devices connected to inductors. A combination of the static and pulsed magnetic fields constitutes the NMR sensing and detection system that is used to study ferromagnetic and paramagnetic materials. We present measurements from ferromagnetic materials placed in non-uniform magnetic fields with applications in oil-well industry. We also present measurements of paramagnetic materials within organic media. These measurements validate applicability of such portable sensor systems, thereby ushering in varied possibilities for future portable magnetic resonance measurements in low and non-uniform magnetic fields

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

Dynamic Power Management for Neuromorphic Many-Core Systems

This work presents a dynamic power management architecture for neuromorphic many core systems such as SpiNNaker. A fast dynamic voltage and frequency scaling (DVFS) technique is presented which allows the processing elements (PE) to change their supply voltage and clock frequency individually and autonomously within less than 100 ns. This is employed by the neuromorphic simulation software flow, which defines the performance level (PL) of the PE based on the actual workload within each simulation cycle. A test chip in 28 nm SLP CMOS technology has been implemented. It includes 4 PEs which can be scaled from 0.7 V to 1.0 V with frequencies from 125 MHz to 500 MHz at three distinct PLs. By measurement of three neuromorphic benchmarks it is shown that the total PE power consumption can be reduced by 75%, with 80% baseline power reduction and a 50% reduction of energy per neuron and synapse computation, all while maintaining temporary peak system performance to achieve biological real-time operation of the system. A numerical model of this power management model is derived which allows DVFS architecture exploration for neuromorphics. The proposed technique is to be used for the second generation SpiNNaker neuromorphic many core system

Genetic algorithms

Genetic algorithms are mathematical, highly parallel, adaptive search procedures (i.e., problem solving methods) based loosely on the processes of natural genetics and Darwinian survival of the fittest. Basic genetic algorithms concepts are introduced, genetic algorithm applications are introduced, and results are presented from a project to develop a software tool that will enable the widespread use of genetic algorithm technology