A simple control technique for series resonant converters

A control strategy for series resonant converters, based on the control of the state space trajectory, is proposed. Its simple implementation allows high frequency applications and requires only resonant current sensing. Quite linear and load independent control characteristics are obtained. Simulated and experimental results show good steady-state stability, fast dynamic response for wide reference step variations, and well-controlled converter start-up     

Simple digital control improving dynamic performance of powerfactor preregulators

This paper presents the practical implementation of a fully digital control for boost power factor preregulators (PFPs). The control algorithm, which is simple and fast, provides a significant improvement in the system's dynamic performance compared to the usual analog control techniques. The paper discusses the design criteria and the actions taken for the implementation of the digital control, which is performed by means of a standard microcontroller (Siemens 80C166). The effectiveness of the approach is assessed by experimental tests     

Electrochemical anticorrosion performance evaluation of Al2O3 coatings deposited by MOCVD on an industrial brass substrate

Alumina (Al₂O₃) coatings of different thickness were deposited on OT59 brass substrate (BS) using the metal organic chemical vapour deposition (MOCVD) technique to evaluate the corrosion performance by EIS measurements. The used precursor was dimethyl-aluminium-isopropoxide. Electrochemical characterizations of the deposited films were performed in a standard very aggressive acidic solution (aerated 1N H₂SO₄ at 25 °C up to 168 h of immersion time) by means of direct current method (Tafel curves) and electrochemical impedance spectroscopy (EIS). The Rutherford backscattering spectroscopy (RBS) indicated that the films are very pure with the correct Al₂O₃ stoichiometry, while the IR absorption spectra showed that the films did not contain any OH groups. The surface film morphology was investigated by atomic force microscopy (AFM) and displayed a globular texture. The films were very smooth, with a maximum root mean square roughness, for example, of 14 nm for a 0.96 μm thick coating. The EIS data confirmed, as expected, that a 2.40 μm Al₂O₃ layer ensures the best corrosion protection after 168 h of immersion in the very acidic environment used.     

A microfluidic optical beam steerer

This paper reports the fabrication and characterization of a prototype microfluidic device that can act as a periodic beam steerer. The prototype is formed by a simple T-junction followed by a serpentine channel that allows generation of a periodical segmented flow of air and water bubbles. If light hits the channel wall with a suitable angle, it can be either transmitted or reflected by the segmented flow, giving rise to an alternating beam steerer. The duty cycle, switching frequency, and overall stability and reproducibility of this prototype system are presented and discussed.     

QFD: The problem of comparing technical/engineering design requirements

An approach based on multiple-criteria decision aid (MCDA) methods has been introduced for the prioritization of technical/engineering design requirements during the quality function deployment (QFD) process. The proposed method allows the avoidance of the rigid procedure under which the relationship matrix coefficients are turned from an ordinal into a cardinal scale. A comparison analysis is carried out between the traditional approach and the proposed one. A numerical example is also provided so as to highlight the main differences between the two methods.     

Nanoconfined mixed Li and Mg borohydrides as materials for solid state hydrogen storage

Several mixtures of LiBH₄ and Mg(BH₄)₂ borohydrides in different stoichiometric ratios (1:0, 2:1, 1:1, 1:2, 0:1), prepared by high energy ball milling, have been investigated with X-ray powder diffraction and thermal programmed desorption (TPD) volumetric analysis to test the dehydrogenation kinetics in correlation with the physical mixture composition. Afterwards mixed and unmixed borohydrides were dispersed on high specific surface area ball milled graphite by means of the solvent infiltration technique. BET and statistical thickness methods were used to characterize the support surface properties, and SEM micrographs gave a better understanding of the preparation techniques. It has been observed by TPD volumetric measurements that the confinement of the reactive borohydrides on the nanoporous supports leads to a lower dehydrogenation temperature compared to unsupported borohydrides. Moreover, a further decrease of the dehydrogenation temperature has been observed by increasing the specific surface area of the support and the pores volume and by using the prepared mixtures instead of pure materials. The dehydrogenation process seems to be favoured by the heterogeneous nucleation on the graphite surface of decomposition products or intermediate phases from melted liquid borohydrides.     

S‐N curves in the very‐high‐cycle fatigue regime: statistical modeling based on the hydrogen embrittlement consideration

The continuous increment of durability and reliability requirements for many machinery components is significantly enhancing the research activity in the Very‐High‐Cycle Fatigue (VHCF) characterization of metallic materials, in particular of high‐strength steels for critical structural applications. According to the model, the VHCF strength of high‐strength steels can be estimated from the projected area of the ‘Optically Dark Area’ (ODA), which plays a key role in the VHCF response of high‐strength steels: more than 95% of the total VHCF life is consumed in the ODA formation, with crack growing even though the Stress Intensity Factor (SIF) is below the threshold for crack growth. Following the hydrogen embrittlement theory proposed by Murakami, hydrogen is supposed to assist crack growth within the ODA. The present paper proposes a general SIF formulation for the analytical model of the hydrogen assisted crack growth within the ODA. Starting from the general SIF formulation, a general expression for the material fatigue limit is obtained in the paper. The statistical method for the estimation of the parameters involved in the proposed model is finally illustrated in the paper and numerically applied to an experimental dataset.     

Single-stage current-fed DC-DC converter with time-sharing controlof output voltage and input current

A single-stage current-fed DC/DC power converter structure and control strategy for simultaneous control of output voltage and current flowing in the input inductor are described. This configuration is suitable for high power-density applications because it results in reduced converter size and power loss. A very fast control-to-output response is obtained, together with stable operation even for large load and reference variations. Static and dynamic converter performances are investigated and design criteria given. Experimental results obtained on a prototype are also reported     

Analog VLSI synaptic matrices as building blocks for neuralnetworks

An associative memory circuit that may let designers expand neural networks around a matrix of analog synapses is described. The architecture of the chip and its basic cell are discussed, and some SPICE simulation results are presented and compared with measures provided by the first prototype. In particular, the linearity and dynamic response of the complete chip, which includes an array of 25 synapses and two address decoders used for programming the weights, are examined     

ESD sensitivity of a GaAs MMIC microwave power amplifier

The EOS/ESD sensitivity of the main circuit blocks of a complete GaAs multi-stage power amplifier for microwave applications was investigated under HBM, MM and TLP regimes. Hard breakdown failure modes were identified due to passive components failure. The high current injection state of active components was also analyzed.