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Concept

Forme d'onde

La forme d'onde d'un signal est la représentation graphique de l'évolution de l'amplitude instantanée d'une onde physique périodique ou aléatoire en fonction du temps. Il peut s'agir d'une onde mécanique ou d'une onde électromagnétique. La représentation d'une forme d'onde utilise le principe des coordonnées cartésiennes, avec le temps en abscisse et l'amplitude en ordonnée. Une forme d'onde peut être observée avec un oscilloscope à bande passante appropriée lorsqu'il s'agit d'un signal électrique direct ou issu de capteurs. Elle est omniprésente dans les fenêtres des logiciels d'enregistrement et de traitement audio. Parmi ceux-ci, certains permettent de dessiner ou de redessiner à l'écran des formes d'onde. Cette fonction est parfois utilisée comme traitement audio pour reconstruire la forme d'onde lorsque des parasites, visibles sous forme de brèves irrégularités, affectent la qualité sonore. La forme d'onde à évolution la plus progressive est la sinusoïde. C'est la plus simple.

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Onde

vignette|Propagation d'une onde. Une onde est la propagation d'une perturbation produisant sur son passage une variation réversible des propriétés physiques locales du milieu. Elle se déplace avec un

Amplitude

En physique classique, on nomme amplitude la mesure scalaire (une coordonnée) d’un nombre positif caractérisant l’ampleur des variations d'une grandeur. Le plus souvent il s'agit de l'écart maximal

Oscilloscope

thumb|Un oscilloscope. Un oscilloscope, ou oscillographe, est un instrument de mesure destiné à visualiser un signal électrique, le plus souvent variable au cours du temps. Il permet d'observer les v

MR derived volumetric flow rate waveforms of internal carotid artery in patients treated for unruptured intracranial aneurysms by flow diversion technique

Ricardo Alberto Corredor Jerez

Little is known about the hemodynamic disturbances induced by the cerebral aneurysms in the parent artery and the effect of flow diverter stents (FDS) on these latter. A better understanding of the aneurysm-parent vessel complex relationship may aid our understanding of this disease and to optimize its treatment. The ability of volumetric flow rate (VFR) waveform to reflect the arterial compliance modifications is well known. By analyzing the VFR waveform and the pulsatility in the parent vessel, this study aimed to test the hypotheses that (1) intracranial aneurysms might disrupt the blood flow of the parent vessel and (2) the treatment by FDS might have measurable corrective effect on these changes. Ten patients followed for unruptured intracranial aneurysms treated by FDS and ten healthy volunteers as control group were included in this study. Two-dimensional quantitative phase-contrast magnetic resonance imaging (MRI) was performed on each patient on the ICA artery upstream and downstream to the aneurysm, and on each volunteer at similar locations. The aneurysms altered significantly the parent vessel pulsatility and this effect was correlated to their volume. The aneurysms treatment by FDS allowed for the restoration of a normally modulated flow and pulsatility correction in the parent vessel.

2015

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Study of the enhanced electricity output of a sliding droplet-based triboelectric nanogenerator for droplet sensor design

Jürgen Brugger, Xia Liu, Wei Xu

Triboelectric nanogenerators are establishing themselves as promising candidates for realizing high-efficient energy harvesting from largely available droplets. However, the conventional droplet-based liquid-solid triboelectric nanogenerator (DLS-TENG) has energy conversion efficiency of only ~ 2 × 10−5%. Here, an optimized structure of DLS-TENG with an additional top electrode is proposed aiming to increase the energy conversion from mechanical energy of sliding droplets into electricity. A peak short circuit current output is obtained up to 0.48 μA, which represents an increase of about 1000 times comparing to the same device working in single-electrode mode. The relationship between the time-domain current waveform and the movement of the droplet is analyzed in details using the equivalent circuit model to study the unique features of the electricity output from sliding motion. Critical parameters, including the dripping frequency, droplet releasing height and the liquid property, are discussed to reveal the dominant factor to maximize the triboelectric output from droplet sliding. Demonstrations of applications in droplet detecting with high accuracy and microfluidic sensor offer new significant insights into the design of triboelectric microfluidic and droplet sensors.

2022

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Spatial covariance improves BCI performance for late ERPs components with high temporal variability

Ruslan Aydarkhanov, Ricardo Andres Chavarriaga Lozano, Lucian Andrei Gheorghe, Marija Uscumlic

Objective. Event Related Potentials (ERPs) reflecting cognitive response to external stimuli, are widely used in brain computer interfaces. ERP waveforms are characterized by a series of components of particular latency and amplitude. The classical ERP decoding methods exploit this waveform characteristic and thus achieve a high performance only if there is sufficient time- and phase-locking across trials. The required condition is not fulfilled if the experimental tasks are challenging or if it is needed to generalize across various experimental conditions. Features based on spatial covariances across channels can potentially overcome the latency jitter and delays since they aggregate the information across time. Approach. We compared the performance stability of waveform and covariance-based features as well as their combination in two simulated scenarios: 1) generalization across experiments on Error-related Potentials and 2) dealing with larger latency jitter across trials. Main results. The features based on spatial covariances provide a stable performance with a minor decline under jitter levels of up to ± 300 ms, whereas the decoding performance with waveform features quickly drops from 0.85 to 0.55 AUC. The generalization across ErrP experiments also resulted in a significantly more stable performance with covariance-based features. Significance. The results confirmed our hypothesis that covariance-based features can be used to: 1) classify more reliably ERPs with higher intrinsic variability in more challenging real-life applications and 2) generalize across related experimental protocols.

2020

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MICRO-211: Analog circuits and systems

This course introduces the analysis and design of linear analog circuits based on operational amplifiers. A Laplace early approach is chosen to treat important concepts such as time and frequency responses, convolution, and filter design. The course is complemented with exercises and simulations.

COM-302: Principles of digital communications

This course is on the foundations of digital communication. The focus is on the transmission problem (rather than being on source coding).

MICRO-461: Low-power radio design for IoT

The basic function of an IoT node is to collect data and send it through a wireless channel to the cloud. Since the power consumption of an IoT node is largely dominated by the wireless communication, it is therefore key to understand the trade-offs faced when designing the radio.