Miguel Angel Mayosky

AC-coupled front-end for biopotential measurements

AC coupling is essential in biopotential measurements. Electrode offset potentials can be several orders of magnitude larger than the amplitudes of the biological signals of interest, thus limiting the admissible gain of a dc-coupled front end to prevent amplifier saturation. A high-gain input stage needs ac input coupling. This can be achieved by series capacitors, but in order to provide a bias path, grounded resistors are usually included, which degrade the common mode rejection ratio (CMRR). This paper proposes a novel balanced input ac-coupling network that provides a bias path without any connection to ground, thus resulting in a high CMRR. The circuit being passive, it does not limit the differential dc input voltage. Furthermore, differential signals are ac coupled, whereas common-mode voltages are dc coupled, thus allowing the closed-loop control of the dc common mode voltage by means of a driven-right-leg circuit. This makes the circuit compatible with common-mode dc shifting strategies intended for single-supply biopotential amplifiers. The proposed circuit allows the implementation of high-gain biopotential amplifiers with a reduced number of parts, thus resulting in low power consumption. An electrocardiogram amplifier built according to the proposed design achieves a CMRR of 123 dB at 50 Hz.

Sliding Mode Strategy for PEM Fuel Cells Stacks Breathing Control Using a Super-Twisting Algorithm

A second-order sliding mode strategy to control the breathing subsystem of a polymer electrolyte membrane fuel cell stack for transportation applications is presented. The controller is developed from a design model of the plant derived from open literature, and well suited for the design of second-order sliding mode strategies. Stability issues are solved using a super twisting algorithm. The resulting approach exhibits good dynamic characteristics, being robust to uncertainties and disturbances. Simulations results are provided, showing the feasibility of the approach.

A novel fully differential biopotential amplifier with DC suppression

Fully differential amplifiers yield large differential gains and also high common mode rejection ratio (CMRR), provided they do not include any unmatched grounded component. In biopotential measurements, however, the admissible gain of amplification stages located before dc suppression is usually limited by electrode offset voltage, which can saturate amplifier outputs. The standard solution is to first convert the differential input voltage to a single-ended voltage and then implement any other required functions, such as dc suppression and dc level restoring. This approach, however, yields a limited CMRR and may result in a relatively large equivalent input noise. This paper describes a novel fully differential biopotential amplifier based on a fully differential dc-suppression circuit that does not rely on any matched passive components, yet provides large CMRR and fast recovery from dc level transients. The proposed solution is particularly convenient for low supply voltage systems. An example implementation, based on standard low-power op amps and a single 5-V power supply, accepts input offset voltages up to /spl plusmn/500 mV, yields a CMRR of 102dB at 50 Hz, and provides, in accordance with the AAMI EC38 standard, a reset behavior for recovering from overloads or artifacts.

A transconductance driven-right-leg circuit

Biopotential measurements are very sensitive to electromagnetic interference (EMI). EMI gets into the acquisition system by many ways, both as differential and common mode signals, driven-right-leg circuits (DRL) are widely used to reduce common mode interference. This paper reports an improvement on the classic DRL. The proposed circuit uses a transconductance amplifier to drive the patients body. This configuration has some interesting properties, which provide an extended bandwidth for high-frequency EMI rejection (such as fluorescent lights interference). The improvement is around 20 dB for frequencies of few kilohertz and the circuit is easy to compensate for stability. A comparative analysis against a typical DRL is presented, the results obtained have been experimentally tested.

Sliding-mode control of PEM fuel cells

Introducing Fuel Cells.- Basics of PEM Fuel Cells.- Fundamentals of Sliding Mode Control Design.- Assessment of SOSM Techniques Applied to Fuel Cell Control.- Control-oriented Modelling and Experimental Validation of a PEMFC Generation System.- SOSM Controller for the PEMFC Generation System: Design and Implementation.- Closing Remarks.

Control-Oriented Modeling and Experimental Validation of a PEMFC Generation System

An experimentally validated control-oriented model that reproduces the most typical features of a laboratory proton exchange membrane fuel cell generation system, is presented in this paper. The proposed representation is a 7th order fully analytical nonlinear model of ordinary differential equations, primarily focused on the system gases dynamics. The complete model is developed following a modular procedure, combining theoretical modeling techniques and empirical analysis based on experimental data. The presented methods can be used as a general modeling guideline for control-oriented purposes, being possible to adapt to other fuel-cell-based systems with similar characteristics.

Two-electrode biopotential measurements: power line interference analysis

In this paper, an analysis of power line interference in two-electrode biopotential measurement amplifiers is presented. A model of the amplifier that includes its input stage and takes into account the effects of the common mode input impedance Z/sub C/ is proposed. This approach is valid for high Z/sub C/ values, and also for some recently proposed low-Z/sub C/ strategies. It is shown that power line interference rejection becomes minimal for extreme Z/sub C/ values (null or infinite), depending on the electrode-skin impedances unbalance /spl Delta/Z/sub E/. For low /spl Delta/Z/sub E/ values, minimal interference is achieved by a low Z/sub C/ strategy (Z/sub C/=0), while for high /spl Delta/Z/sub E/ values a very high Z/sub C/ is required. A critical /spl Delta/Z/sub E/ is defined to select the best choice, as a function of the amplifiers Common Mode Rejection Ratio (CMRR) and stray coupling capacitances. Conclusions are verified experimentally using a biopotential amplifier specially designed for this test.

Behavioral control through evolutionary neurocontrollers for autonomous mobile robot navigation

This paper deals with the study of scaling up behaviors in evolutive robotics (ER). Complex behaviors were obtained from simple ones. Each behavior is supported by an artificial neural network (ANN)-based controller or neurocontroller. Hence, a method for the generation of a hierarchy of neurocontrollers, resorting to the paradigm of Layered Evolution (LE), is developed and verified experimentally through computer simulations and tests in a Khepera^^^(R) micro-robot. Several behavioral modules are initially evolved using specialized neurocontrollers based on different ANN paradigms. The results show that simple behaviors coordination through LE is a feasible strategy that gives rise to emergent complex behaviors. These complex behaviors can then solve real-world problems efficiently. From a pure evolutionary perspective, however, the methodology presented is too much dependent on users prior knowledge about the problem to solve and also that evolution take place in a rigid, prescribed framework. Mobile robots navigation in an unknown environment is used as a test bed for the proposed scaling strategies.

A single supply biopotential amplifier

A biopotential amplifier for single supply operation is presented. It uses a Driven Right Leg Circuit (DRL) to drive the patients body to a DC common mode voltage, centering biopotential signals with respect to the amplifiers input voltage range. This scheme ensures proper range operation when a single power supply is used. The circuit described is especially suited for low consumption, battery-powered applications, requiring a single battery and avoiding switching voltage inverters to achieve dual supplies. The generic circuit is described and, as an example, a biopotential amplifier with a gain of 60 dB and a DC input range of +/-200 mV was implemented using low power operational amplifiers. A Common Mode Rejection Ratio (CMRR) of 126 dB at 50 Hz was achieved without trimming.

A practical approach to electrode-skin impedance unbalance measurement

Unbalance between electrode-skin impedances is a major problem in biopotential recordings, leading to increased power-line interference. This paper proposes a simple, direct method to measure that unbalance at power-line frequency (50-60 Hz), thus allowing the determination of actual recording conditions for biopotential amplifiers. The method is useful in research, amplifier testing, electrode design and teaching purposes. It has been experimentally validated by using both phantom impedances and real electrode-skin impedances.