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Publications

Publications by CRIIS

2004

A wireless RF CMOS mixed-signal interface for soil moisture measurements

Authors
Morais, R; Valente, A; Couto, C; Correia, JH;

Publication
SENSORS AND ACTUATORS A-PHYSICAL

Abstract
This paper describes a wireless RF CMOS interface for soil moisture measurements. The interface basically comprises a Delta-Sigma (DeltaSigma) modulator for acquiring an external sensor signal, and a RF section where data is transmitted to a local processing unit. The DeltaSigma modulator is a single-bit, second-order modulator and it is implemented using switched-capacitors techniques in a fully-differential topology. With a sampling frequency of 423.75 kHz and an oversampling ratio (OSR) of 256, the modulator achieves a dynamic range of 98.7 dB (16.1 bit). The output of the modulator is applied to a counter, as a first-order decimation filter, and the result is stored. Prior to transmission, data is encoded as a pulse width modulated signal and assembled in a frame containing preamble and checksum control fields. This frame is then transmitted through a power amplifier operating at 433.92 MHz in class-E mode. To evaluate the DeltaSigma modulator performance, the bitstream was acquired and transferred to a personal computer to perform digital filtering and decimation using MATLAB. The soil moisture sensor is based on dual-probe heat-pulse (DPHP) method and is implemented by using an integrated temperature sensor and a heater. After applying a heat-pulse for a fixed period of time, the temperature rise, that is a function of soil moisture, generates a differential voltage that is amplified and applied to the mixed-signal interface input. The described interface can also be used with other kinds of environmental sensors in a wireless sensors network. The CMOS mixed-signal interface has been implemented in a single-chip using a standard CMOS 0.7 mum process (AMI C07M-A, n-well, 2 metals and 1 poly).

2004

Fractional-order position/force robot control

Authors
Ferreira, NMF; Machado, JAT; Cunha, JB;

Publication
ICCC 2004: SECOND IEEE INTERNATIONAL CONFERENCE ON COMPUTATIONAL CYBERNETICS, PROCEEDINGS

Abstract
This paper presents the implementation of fractional-order algorithms both for hybrid and cascade position/force control of robotic manipulators. The system performance and robustness is analyzed in the time and frequency domains. The effects joint backlash and flexibility are also investigated.

2004

Population size and processing time in a genetic algorithm

Authors
Reis, C; Machado, JAT; Cunha, JB;

Publication
ICCC 2004: SECOND IEEE INTERNATIONAL CONFERENCE ON COMPUTATIONAL CYBERNETICS, PROCEEDINGS

Abstract
This paper presents several experiments with a genetic algorithm (GA) for designing combinational logic circuits. The study addresses the population size and the processing time for achieving a solution in order to establish a compromise between the two parameters. Furthermore, it is also investigated the use of different gate sets for designing the circuits namely RISC and CISC like gate sets.

2004

Recursive parameter estimation of dynamical systems under closed loop control

Authors
Cunha, JB;

Publication
Proceedings of the 23rd IASTED International Conference on Modelling, Identification, and Control

Abstract
Real time parameter estimation of dynamic models operating in closed loop control is a crucial issue to implement industrial adaptive controllers. Parameter estimation must be seen as one of the key elements to solve a system identification problem, which involves also an experiment design, the selection of a model structure, and the model validation. This paper describes some approaches to compute the transfer function parameters of time-varying systems under closed loop control. To point the limitations and advantages of each method, with focus on robustness and quality of the model estimates, the techniques are applied to compute the parameters of a time varying discrete system, with known structure, under PI- Proportional-Integral control.

2004

An indirect variable structure model reference adaptive control applied to the speed control of a three-phase induction motor

Authors
de Oliveira, JB; de Araujo, AD;

Publication
PROCEEDINGS OF THE 2004 AMERICAN CONTROL CONFERENCE, VOLS 1-6

Abstract
In this paper an indirect approach to the variable structure model reference adaptive control (VS-MRAC) is proposed. This approach is applied to the speed control of a three-phase induction motor. In the direct approach, the switching laws are designed for the parameters of the controller, and in this case the main difficulty is to find the bounds which must be used in the control laws. On the other hand, in the indirect approach, the switching laws are designed for the plant parameters, which are uncertain, but their bounds can be easily found, since they are related to physical parameters of the system. The idea is to design an indirect variable structure approach and to apply it to the speed control of a three-phase induction motor.

2004

Performance of Piptatherum miliaceum (Smilo grass) in edaphic Pb and Zn phytoremediation over a short growth period

Authors
Garcia, G; Faz, A; Cunha, M;

Publication
INTERNATIONAL BIODETERIORATION & BIODEGRADATION

Abstract
In a general screening of some mining areas in SE Spain for wild and autochthonous plant species with the potential to accumulate zinc and lead, of which some classified as accumulators were able to accumulate large concentrations of metal ( > 1000 mg kg(-1)) dry matter. Several Mediterranean taxa showed moderately enhanced heavy-metal accumulation and tolerance, e.g. Piptathertan miliacetall (L.) Cosson, or Smilo grass. This could be considered a Pb hyperaccumulator, being most efficient at removing and accumulating Ph from contaminated soil, and also efficient in Zn extraction. When soils were polluted with both metals, accumulation of Ph was greater. Results indicated that concentration of metal in the plant was directly correlated with that of the soil, although the transfer factors for Ph and Zn were not high. Most plants remained healthy for 3 weeks after introduction of pollutants.

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