On lag controllers: Design and implementation

Sometimes it is inconvenient or expensive to open the loop of a system to insert lag controllers-for instance, when this system is an open-loop system. A new controller structure where the loop is not opened, and that allows the design of lag controllers as in the case where one can open the loop, is presented. This result can be used by educators in undergraduate courses that deal with classic control system theory, because it allows a better comprehension of the concept of lag compensation and provides a new method for its design and implementation. An example illustrates the application of the proposed method.

Low voltage four-quadrant current multiplier: An improved topology for n-well CMOS process

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

A high dynamic range method for the direct readout of a dynamic phase change in homodyne interferometers

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Low voltage four-quadrant current multiplier: an improved topology for n-well CMOS process

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Structural Health Monitoring in Smart Structures Through Time Series Analysis

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Optimal and robust modal control of a flexible structure using an active dynamic vibration absorber

This paper is concerned with feedback vibration control of a lightly damped flexible structure that has a large number of well-separated modes. A single active electrical dynamic absorber is used to reduce a particular single vibration mode selectively or multiple modes simultaneously. The absorber is realized electrically by feeding back the structural acceleration at one position to a collocated piezoceramic patch actuator via a controller consisting of one or several second order lowpass filters. A simple analytical method is presented to design a modal control filter that is optimal in that it maximally flattens the mobility frequency response of the target mode, as well as robust in that it works within a prescribed maximum control spillover of 2 dB at all frequencies. Experiments are conducted with a free-free beam to demonstrate its ability to control any single mode optimally and robustly. It is also shown that an active absorber with multiple such filters can effectively control multiple modes simultaneously.

Síntese, sinterização e caracterização de ferritas à base de Ni-Zn

Were synthesized different ferrites NixZn1-xFe2O4 (0,4 ≤ x ≤ 0,6) compositions by using citrate precursor method. Initially, the precursors citrates of iron, nickel and zinc were mixed and homogenized. The stoichiometric compositions were calcined at 350°C without atmosphere control and the calcined powders were pressed in pellets and toroids. The pressed material was sintered from 1100º up to 1200ºC in argon atmosphere. The calcined powders were characterized by XRD, TGA/DTG, FTIR, SEM and vibrating sample magnetometer (VSM). All sintered samples were characterized using XRD, SEM, VSM and measurements of magnetic permeability and loss factor were obtained. It was formed pure ferromagnetic phase at all used temperatures. The Rietveld analyses allowed to calculate the cations level occupation and the crystallite size. The analyses obtained nanometric crystals (12-20 nm) to the calcined powder. By SEM, the sintered samples shows grains sizes from 1 to 10 μm. Sintered densities (ρ) were measured by the Archimedes method and with increasing Zn content, the bulk density decrease. The better magnetization results (105-110 emu/g) were obtained for x=0,6 at all sintering temperatures. The hysteresis shows characteristics of soft magnetic material. Two magnetization processes were considered, superparamagnetism at low temperature and the magnetic domains formation at high temperatures. The sintered toroids presents relative magnetic permeability (μr) from 7 to 32 and loss factor (tanδ) of about 1. The frequency response of toroids range from 0,3 kHz to 0,2 GHz. The composition x=0,5 presents both greater μr and tanδ values and x=0,6 the most broad range of frequency response. Various microstructural factors show influence on the behavior of μr and tanδ, such as: grain size, porosity across grain boundary and inside the grain, grain boundary content and domain walls movement during the process of magnetization at high frequency studies (0,3kKz 0,2 GHz)

Otimização da síntese de nanoferritas de nizn dopada com cobre e cobalto

Different compositions of Ni0,5-xCuxZn0,5Fe2O4 and Ni0,5-xCoxZn0,5Fe2O4 0 ≤ x ≤ 0.3 were synthesized ferrite y the citrate precursor method. The stoichiometric compositions were calcined in air at 350°C and then pressed into pellets and toroids. The pressed samples were sintered at temperatures of 1000, 1050 and 1100°C/3h in air control at the speed of heating and cooling. The calcined powders were characterized by XRD, TGA / DTG, FTIR, SEM and vibrating sample magnetometry (VSM) and the sintered samples by XRD, SEM, MAV, density and measurements of permeability and magnetic losses. There was pure phase formation ferrimagnetism applied at all temperatures except for A-I composition at all sintering temperatures and A-II only at a temperature of 1100°C. Crystallite sizes were obtained by Rietveld analysis, nanometer size from 11 to 20 nm for the calcined powders. For SEM, the sintered samples showed grain size between 1 and 10 micrometers. Bulk density (ρ) of sintered material presented to the Families almost linear behavior with increasing temperature and a tendency to decrease with increasing concentration of copper, different behavior of the B Family, where the increase in temperature decreased the density. The magnetic measurements revealed the powder characteristics of a soft ferrimagnetic material. Two processes of magnetization were considered, the superparamagnetism at low temperatures (350°C) and the formation of magnetic domains at higher temperatures. Obtaining the best parameters for P and B-II magnetic ferrites at high temperatures. The sintered material at 1000°C showed a relative permeability (μ) from 50 to 800 for the A Family and from 10 to 600 for the B Family. The samples sintered at 1100°C, B Family showed a variation from 10 to 1000 and the magnetic loss (tan δ) of A and B Families, around of 1. The frequency response of the toroidal core is in the range of 0.3 kHz. Several factors contribute to the behavior of microstructure considering the quantities μ and tan δ, such as the grain size, inter-and intragranular porosity, amount of grain boundary and the aspects of the dynamics of domain walls at high frequencies.

Aspectos metodológicos relacionados aos sistemas manométricos utilizados em estudos hemodinâmicos

Atualmente, diante das técnicas atuais, a manometria tem sido relegada a plano secundário durante a cateterização cardíaca. No entanto, ainda fornece importantes informações para identificação e avaliação das doenças cardiovasculares. Os dados coletados durante os exames possibilitam a obtenção de variáveis quantitativas e qualitativas, as quais podem ser comparadas aos padrões normais. Os sistemas manométricos são compostos por transdutor, amplificador e registrador, que, em conjunto, devem espelhar com fidelidade a morfologia e os valores das variáveis analisadas. Para atingir esse objetivo, é necessário desempenho adequado de todos os componentes. Se uma determinada informação é de extrema relevância, o operador deve gastar tempo suficiente para obtê-la de maneira inequívoca. Assim, o operador deve estar familiarizado com os sistemas manométricos e com as fontes de erro relacionadas com as técnicas de registro, cateteres, conectores e fluidos. Com os fundamentos analisados neste manuscrito, salientamos que deve ser dispensada atenção às ondas de pressão usadas nas interpretações da fisiopatologia das doenças cardiovasculares.

Analytical study of the nonlinear behavior of a shape memory oscillator: Part II-resonance secondary

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Admittance and dielectric spectroscopy of polycrystalline semiconductors

This text discusses about advantageous, powerful and limitations of admittance and dielectric spectroscopy in the characterization of polycrystalline semiconductors. In the context of polycrystalline semiconductors or dielectric materials, the admittance or dielectric frequency response analyses are shown to be sometimes more useful than impedance spectra analysis, mainly because information on the capacitances or deep trap states are possible to be monitored from admittance or dielectric spectra as a function of dopant concentration or annealing effects. The majority of examples of the application of admittance or dielectric analysis approach were here based on SnO2- and ZnO-based polycrystalline semiconductors devices presenting nonohmic properties. Examples of how to perform the characterization of Schottky barrier in such devices are clearly depicted. The approach is based on findings of the true Mott-Schottky pattern of the barrier by extracting the grain boundary capacitance value from complex capacitance diagram analysis. The equivalent circuit of such kind of devices is mainly consistent with the existence of three parallel elements: the high-frequency limit related to grain boundary capacitances, the complex incremental capacitance at intermediate frequency related to the deep trap relaxation and finally at low frequency region the manifestation of the conductance term representing the dc conductance of the multi-junction device. (c) 2007 Elsevier Ltd. All rights reserved.

A linearly tunable low-voltage CMOS transconductor with improved common-mode stability and its application to (gm)-C filters

A linearly tunable low-voltage CMOS transconductor featuring a new adaptative-bias mechanism that considerably improves the stability of the processed-signal common,mode voltage over the tuning range, critical for very-low voltage applications, is introduced. It embeds a feedback loop that holds input devices on triode region while boosting the output resistance. Analysis of the integrator frequency response gives an insight into the location of secondary poles and zeros as function of design parameters. A third-order low-pass Cauer filter employing the proposed transconductor was designed and integrated on a 0.8-mum n-well CMOS standard process. For a 1.8-V supply, filter characterization revealed f(p) = 0.93 MHz, f(s) = 1.82 MHz, A(min) = 44.08, dB, and A(max) = 0.64 dB at nominal tuning. Mined by a de voltage V-TUNE, the filter bandwidth was linearly adjusted at a rate of 11.48 kHz/mV over nearly one frequency decade. A maximum 13-mV deviation on the common-mode voltage at the filter output was measured over the interval 25 mV less than or equal to V-TUNE less than or equal to 200 mV. For V-out = 300 mV(pp) and V-TUNE = 100 mV, THD was -55.4 dB. Noise spectral density was 0.84 muV/Hz(1/2) @1 kHz and S/N = 41 dB @ V-out = 300 mV(pp) and 1-MHz bandwidth. Idle power consumption was 1.73 mW @V-TUNE = 100 mV. A tradeoff between dynamic range, bandwidth, power consumption, and chip area has then been achieved.

A contribution for nonlinear structural dynamics characterization of cantilever beams

Successful experiments in nonlinear vibrations have been carried out with cantilever beams under harmonic base excitation. A flexible slender cantilever has been chosen as a convenient structure to exhibit modal interactions, subharmonic, superharmonic and chaotic motions, and others interesting nonlinear phenomena. The tools employed to analyze the dynamics of the beam generally include frequency- and force-response curves. To produce force-response curves, one keeps the excitation frequency constant and slowly varies the excitation amplitude, on the other hand, to produce frequency-response curves, one keeps the excitation amplitude fixed and slowly varies the excitation frequency. However, keeping the excitation amplitude constant while varying the excitation frequency is a difficult task with an open-loop measurement system. In this paper, it is proposed a closed-loop monitor vibration system available with the electromagnetic shaker in order to keep the harmonic base excitation amplitude constant. This experimental setup constitutes a significant improvement to produce frequency-response curves and the advantages of this setup are evaluated in a case study. The beam is excited with a periodic base motion transverse to the axis of the beam near the third natural frequency. Modal interactions and two-period quasi-periodic motion are observed involving the first and the third modes. Frequency-response curves, phase space and Poincaré map are used to characterize the dynamics of the beam.

Dynamic analysis of a new piezoelectric flextensional actuator using the J1-J4 optical interferometric method

Piezoelectric actuators are widely used in positioning systems which demand high resolution such as scanning microscopy, fast mirror scanners, vibration cancellation, cell manipulation, etc. In this work a piezoelectric flextensional actuator (PFA), designed with the topology optimization method, is experimentally characterized by the measurement of its nanometric displacements using a Michelson interferometer. Because this detection process is non-linear, adequate techniques must be applied to obtain a linear relationship between an output electrical signal and the induced optical phase shift. Ideally, the bias phase shift in the interferometer should remain constant, but in practice it suffers from fading. The J1-J4 spectral analysis method provides a linear and direct measurement of dynamic phase shift in a no-feedback and no-phase bias optical homodyne interferometer. PFA application such as micromanipulation in biotechnology demands fast and precise movements. So, in order to operate with arbitrary control signals the PFA must have frequency bandwidth of several kHz. However as the natural frequencies of the PFA are low, unwanted dynamics of the structure are often a problem, especially for scanning motion, but also if trajectories have to be followed with high velocities, because of the tracking error phenomenon. So the PFA must be designed in such a manner that the first mechanical resonance occurs far beyond this band. Thus it is important to know all the PFA resonance frequencies. In this work the linearity and frequency response of the PFA are evaluated up to 50 kHz using optical interferometry and the J1-J4 method.

On the dynamic behaviour of a nonlinear system weakly connected to a linear single degree-of-freedom system

This paper discusses the dynamic behaviour of a nonlinear two degree-of-freedom system consisting of a harmonically excited linear oscillator weakly connected to a nonlinear attachment that behaves as a hardening Duffing oscillator. A system which behaves in this way could be a shaker (linear system) driving a nonlinear isolator. The mass of the nonlinear system is taken to be much less than that in the linear system and thus the nonlinear system has little effect on the dynamics of the linear system. Of particular interest is the situation when the linear natural frequency of the nonlinear system is less than the natural frequency of the linear system such that the frequency response curve of the nonlinear system bends to higher frequencies and thus interacts with the resonance frequency of the linear system. It is shown that for some values of the system parameters a complicated frequency response curve for the nonlinear system can occur; closed detached curves can appear as a part of the overall amplitude-frequency response. The reason why these detached curves appear is presented and approximate analytical expressions for the jump-up and jump-down frequencies of the system under investigation are given.