Thermoelastic damping in micromechanical and nanomechanical resonators
Notice bibliographique
Résumé
Thermoelastic damping (TED) is a fundamental mechanism of material damping in which energy is dissipated by the irreversible conduction of heat across thermoelastic temperature gradients within an oscillating structure. The first studies of TED were conducted over 85 years ago. Since that time, thermoelastic damping has been extensively studied, especially when it became clear in 1990 that TED can be a major mechanism of damping in microelectromechanical systems (MEMS). Nevertheless, as revealed by a careful survey of the literature, many aspects of TED remain to be investigated and understood. In this thesis, four such topics are addressed using a combination of analytical and numerical techniques.For monolithic beams, thermoelastic damping can be computed using a closed-form expression. Similar expressions were lacking for flexural-mode bilayer resonators, consisting of a substrate coated with a thin film, which are widely used in MEMS. To fill this gap in knowledge, a closed-form expression was developed for calculating TED in bilayers, and the formula was used to explore the nature and structure of the thermoelastic dissipation over several decades of frequency in a large set of materials and structures. This exploration showed that TED exhibits a rich variety of spectral features and provided useful information into the existence of multiple well-resolved dissipation peaks. Previously, numerical studies of TED in plates and membranes had concluded that TED can be decreased by subjecting the structures to in-plane tensile stresses. To gain a better understanding of the underlying mechanisms, simple closed-form analytical formulas were developed for the energy dissipated per cycle (ÎW) and TED for nanomembranes subjected to uniform biaxial, in-plane, tensile stresses. The results show that the effects of stress on dissipation are quite subtle: depending on the frequency, ÎW can increase, remain constant, or decrease when the structure is stressed in tension. The majority of the literature on TED is based on a linear analysis of damping. The sparse literature on nonlinear TED focuses on nonlinearities that have their origins in large deformations (that is, geometrical nonlinearities) or due to interactions with other energy domains (for example, electromechanical nonlinearities in electrostatically-actuated microresonators). In this thesis, a new type of dissipative nonlinearity (also called thermal nonlinearity) is studied. A finite-difference scheme was developed to solve the nonlinear governing equation and explore the effects of the dissipative nonlinearity on TED in stress-free silicon microcantilever beams and highly-stressed silicon nitride nanomembranes.Finally, the thesis considers an emerging topic in studies of TED, namely, computing dissipation using large-scale atomistic simulations. Classical molecular dynamics was used to simulate damping in the longitudinal-mode of single-crystal nickel resonators. Isothermal simulations were performed using the Nosé-Hoover thermostat to control the temperature. A protocol was devised for estimating the specific damping capacity and phase angle by identifying the factors that must be considered while selecting simulation parameters, and establishing criteria for convergence and linearity.
Récupéré en direct depuis OpenAlex et désinversé. Les résumés ne sont pas conservés dans cette base de données : les index inversés représentent 8,6 Go des 9,3 Go de texte de la base, et le serveur dispose de 13 Go libres.
Comment cette classification a été obtenuedéplier
Prédiction distillée sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Apprise à partir de 10 348 étiquettes directes de Codex et de 10 348 étiquettes directes de Gemma. Le mode candidate est l'union des têtes enseignantes seuillées; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont ni des étiquettes humaines ni des étiquettes directes de modèles de pointe.
Scores Codex et Gemma par catégorie
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,001 | 0,001 |
| Méta-épidémiologie (sens strict) | 0,001 | 0,001 |
| Méta-épidémiologie (sens large) | 0,001 | 0,000 |
| Bibliométrie | 0,001 | 0,001 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,001 | 0,000 |
| Intégrité de la recherche | 0,001 | 0,002 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,000 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule tête enseignante, pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».