Pierre Mathys

Ohmic losses calculation in SMPS transformers: numerical study of Dowell's approach accuracy

The paper compares two methods for ohmic losses calculation in switch-mode power supply transformers: Dowells 1D approach and 2D finite element method simulations (validated by measurements). Dowells method underestimates losses at the fundamental frequency for foil windings, whereas harmonic losses are generally overestimated (depending on conductor type). More significant differences are found with high leakage inductance transformers.

A closed-form formula for 2D ohmic losses calculation in SMPS transformer foils

A new closed-form formula aimed at calculating ohmic losses in switch-mode power supply transformers is presented. It is based on intensive 2D finite element method simulation. Only valid for one-layer-foil windings at the moment, it accurately covers cases where the classical Dowells formula significantly underestimated the losses.

Detection of obstructive apnea events in sleeping infants from thoracoabdominal movements

The aim of the study was to determine whether in infants, the evaluation of thoracoabdominal movements alone, with no measurement of airflow, could be used to identify obstructive sleep apnea events (OA). Two different methods were used: first, we initially quantified thoracoabdominal asynchrony. Although 79.3% of OAs showed a significant increase of thoracoabdominal asynchrony, only 10.9% of the events scored by the identification of phase opposition were true OAs. Next, we developed two artificial neural networks (ANNs) as classifiers for the study of the thoracoabdominal signals. The first network was trained to locate obstructive and central apnea events. It correctly detected 75% of the OAs; however, only 6.2% of the detected events were true OAs. When a second network was used, OAs could not be discriminated from other portions of the signals showing similar phase characteristics. It was concluded that the information available in uncalibrated signals of thoracic and abdominal respiratory movements was insufficient to unambiguously detect OA events in sleeping infants.

Reduction of power line interference using active electrodes and a driven-right-leg circuit in electroencephalographic recording with a minimum number of electrodes

Unwanted power line interference is one of the most common problems in electroencephalographic recording. This paper examines how the use of active electrodes together with a driven-right-leg circuit can significantly improve interference reduction, even when the same electrode is used for common and reference which is attractive because it saves an electrode. General conclusions about the active electrodes and the driven-right-leg circuits were obtained thanks to a prototype that uses the same electrode for both common and reference. Measurements were performed both on a subject and on an electrical equivalent model.

Two-dimensional analysis of the edge effect field and losses in high-frequency transformer foils

In design of high-frequency magnetic devices, various approaches have been used to provide calculation tools that are able to predict winding losses, including skin effect and proximity effect, in their two-dimensional (2-D) aspects. Up to now, these approaches have been mainly focused on giving quantitative results for specific cases. Because the final purpose of designers is not to perform single calculations, but to obtain optimal designs, we have looked for a complementary approach providing more general 2-D guidelines and understanding of the phenomena. In this paper, we examine the case of a foil winding undergoing edge effect, a typical situation where classical one-dimensional theories underestimate the real losses. Using a 2-D closed-form formula we developed in a previous work and the associated database of 400 2-D numerical models, we systematically analyze the dependence of the 2-D field and the corresponding extra losses with the geometrical design variables describing the dimension and position of the winding.

Quantification of Motion Artifact Rejection Due to Active Electrodes and Driven-Right-Leg Circuit in Spike Detection Algorithms

Identification of spikes in the EEG plays an important role during the diagnosis of neurological disorders, such as epilepsy. Automatic spike detection (ASD) is attractive because it reduces the diagnostic time and improves objectivity of the scoring. Unfortunately, automatic detection is sometimes confounded by artifacts, particularly motion artifacts, which can be frequent in ambulatory recording, in the ICU, when recording from restless patients or children, etc. EEG systems have recently been improved by using active electrodes and driven-right-leg circuits (DRL) to reduce motion artifacts. However, the performances of ASD algorithms, both with unimproved and improved EEG systems, are difficult to quantify in patients because of poor reproducibility of the results. In this paper, a test setup was used to evaluate the performance of active electrodes and DRL, and assess if they can be complemented or substituted by a spike detection algorithm in avoiding motion artifact. Results show that motion artifacts can largely degrade spike detection when a traditional EEG system is used, whereas an EEG fitted with active electrodes and a DRL allows high-quality detection. When using a traditional EEG, the choice of a spike detection algorithm has a large influence on detection quality.

A novel approach to the generation and optimization of three-level PWM wave forms for induction motor inverters

The application of three-level pulsewidth modulation (PWM) to voltage source inverters feeding three-phase induction motors is considered. A subharmonic modulation method using two modulating waves is introduced. It is particularly well adapted to the elimination of specific harmonic bands. Systematic optimization of precalculated waveforms with respect to loss factor, shows that three-level PWM is very well suited to harmonic reduction. Transient behavior is discussed. It is concluded that three-level PWM yields significant improvements compared with two-level PWM, especially in high-power (gate-turn-off) GTO applications where the high DC link voltage requires a series connection of the switches.<<ETX>>

Silicone rubber encapsulation for an endoscopically implantable gastrostimulator

Gastrointestinal stimulator implants have recently shown positive results in treating obesity. However, the implantation currently requires an invasive surgical procedure. Endoscopy could be used to place the gastric stimulator in the stomach, hence avoiding the riskier surgery. The implant then needs to go through the oesophagus and be located inside the stomach, which imposes new design constraints, such as miniaturization and protecting the electronic circuit against the highly acidic environment of the stomach. We propose to protect the implant by encapsulation with silicone rubber. This paper lists the advantages of this method compared to the more usual approach of a hermetic enclosure and then presents a method to evaluate the underwater adhesive stability of six adhesive/substrate couples, using repeated lap-shear tests and an elevated temperature to accelerate the ageing process. The results for different adhesive/substrate couples tested, presented on probability plots, show that FR4 and alumina substrates with MED4-4220 silicone rubber are suitable for a first implantable prototype. We then compare these with the predicted lifetimes of bonds between historical standard silicone rubber DC3140 and different substrates and describe the encapsulation of our gastrostimulator.

Eddy current losses in SMPS transformers round wire windings: a semi-analytical closed-form formula

We provide a new closed-form formula that instantly calculates the 2D high-frequency ohmic losses (skin and proximity effects) in round wire windings. It has been obtained by overwriting the classical definition (shown to be erroneous) of the layer copper factor introduced in 1D analytical theories. Compared to similar previous formulas, the average error is divided by a factor of thousand. Experimental validation is provided

Planar transformer technology applied to AC/DC conversion

Magnetic components play an important role in the technological evolution towards increased power density of AC/DC power converters. Planar transformers provide several advantages that have to be balanced with the latest evolution of more classical transformer technology. This paper analyses the interest of using planar transformer for AC/DC power conversion. Results of the implementation of a planar transformer in a 600 W AC/DC converter illustrate the analysis.