Normalized State-Space Models for Resonant Rectifiers

In AC-DC power conversion, the input source features: time dependence and phase angle, combined with the complexity of resonant circuits, lead to solutions that are difficult to obtain. In this sense, an analysis and design methodology of resonant rectifiers is proposed, in which, iterative numerical solutions are replaced by analytic solutions with the help of computer algebra systems. The method allows obtaining the AC-to-DC transfer function, the quality factor, the phase angle and the resonance frequency. A case study for the Class-E zero-derivative voltage switched resonant rectifier is performed. Experimental results are shown in order to validate the theoretical approach

Ultrasound Piezo-Harvester Energy Transfer Systems for MachineTool Sensor-Charger Applications

Ultrasound energy transfer systems can be an alternative for sensor-chargers aiming batteryreplacement avoidance and can be used in machine tool applications. An ultrasound input source canbe used to send an acoustic signal through a machine. The signal is received by an ultrasound receiverbased on piezoelectric component and should be converted into an electrical signal to supply or chargethe sensor. Notwithstanding, for rotating machines, an air gap must be considered between the inputsource and the machine tool part. This paper deals with the acoustic-electrical energy transferconsidering the changes in the propagation media of the ultrasound. Theoretical results are verified bymeans of an experimental setup

Modeling and Design of a Linear-Assisted Zeta Conveter

Linear-assisted switching (PWM) converters have advantages over single switching topologies, mainly because of the reduction or elimination of bulky output capacitors and ultra-fast dynamical response. In this paper, a linear-assisted zeta converter is presented. The linear regulator circuit is composed by three bipolar transistors and an operational amplifier, which drives the transistor based on the error between the output voltage and its reference. The modeling of the whole circuit is presented, as well as a design example. The modeling of the zeta converter is similar to the conventional topology modeling, except the fact that the linear regulator current is considered as an extra state that substitutes the state regarding the output capacitor voltage. The zeta converter can be designed independently of the linear regulator circuit and simulations are used to validate the static operation of the overall topology. Experimental results confirm in practice the ripple compensation of the main zeta converter, where extra current is provided by the main converter, in order to drive the linear regulator that is responsible for the ripple compensation

Influence of a heating device and adhesive temperature on bond strength of a simplified ethanol-based adhesive system

Abstract Introduction Increased adhesive temperature has been reported to promote solvent evaporation, reduce viscosity, and improve monomeric permeation into dentin. Objective The aim of this study was to determine the influence of different heating methods on the microtensile bond strength of an etch-and-rinse adhesive to dentin. Material and method Twenty-four caries-free extracted human third molars were transversally sectioned to expose a flat dentinal surface. The samples were etched with 37% phosphoric acid gel and divided into three groups (n = 8): 1) Control - the adhesive system (Adper Single Bond 2; 3M ESPE) was applied at room temperature; 2) Warming device - the adhesive was warmed to 37°C in a custom device before application; and 3) Warm air - the adhesive was warmed to 50°C with an air jet after application on dentin. The specimens were restored with a composite resin (Filtek Z250 A2, 3M ESPE) and prepared for microtensile bond strength testing, after 24 h in water storage. The data were subjected to one-way ANOVA and Tukey's test (p 0.05). The mean bond strength values in the control, the warming device, and the warm air groups were 48.5 (± 5.2), 40.35 (± 4.9), and 47.2 (± 5.3) MPa, respectively (p = 0.05). Conclusion The different heating methods had no significant influence on the immediate microtensile bond strength of an etch-and-rinse ethanol-based adhesive to dentin