arXiv subjects

Xanthippi Zianni

Publications and source records attributed to Xanthippi Zianni.

3 recordsLinked to original sources

arXiv2025

Universal Scaling Formalism and Analytical Optimization Criterion for Multiscale Geometric Design of Thermoelectric Metamaterials

Thermoelectric (TE) generators can directly convert heat into electricity, but their performance is often constrained by limited temperature gradients. Here it is shown that width-modulated metamaterials with constrictions and expansions (constricted geometries) enhance temperature difference DT by reduced Transmissivity (Tr), a geometry-based parameter defined by the ratio of constriction to expansion cross-sections. A universal scaling behavior of transport and key TE efficiency metrics with Transmissivity is demonstrated, spanning from the nanoscale to the macroscale. Analytical formalism validated through finite element calculations for a range of modulation geometries reveals that DT, electrical and thermal resistances, efficiency, and power output are governed by a single scaling function, g(Tr), independent of carrier type, material, or operating conditions. This function represents the conductance of a constricted geometry relative to a uniform-width counterpart. The developed framework yields TE Performance Design Maps and an analytical criterion for optimal TE performance, with the maximum power density achieved at an optimal Transmissivity Tr_opt, determined by the condition that the functional g(Tr_opt) equals the Biot number, the dimensionless ratio hL/k of the convection coefficient h, the structure length L and the material thermal conductivity k. Transmissivity is established as a robust, multiscale design parameter - analogous to nature's hierarchical structures for optimized functionality. This work provides the theoretical framework for multiscale design and optimization of constricted geometries, thereby enabling systematic exploration of design strategies for next-generation TE modules based on advanced thermoelectric metamaterials.

physics.app-ph↗

arXiv2025

Optimal Geometric Design of Thermoelectric Metamaterials for Enhancing Power Generation: An Interpretative Approach

Thermoelectric metamaterials featuring width modulation through constrictions (constricted geometries) have emerged as a promising approach for improving heat management and thermoelectric performance. Through a combination of theoretical calculations, analytical formalism, and validation against experimental data, it is shown that thermoelectric performance in such geometries is governed by two fundamental mechanisms of pure geometrical origin: (i) a characteristic scaling behavior of resistance with Transmissivity, and (ii) the critical formation of the Constriction Thermal Resistance. Hourglass-shaped thermoelectric legs - identified as optimal in recent experiments - are found to exhibit the same underlying transport mechanisms observed in other constricted profiles, including single and multiple sharp constrictions. The commonly used Geometric Parameter is found to be insufficient for capturing the full influence of geometry on transport, whereas Transmissivity serves as a robust descriptor of constricted geometry, independent of material choice or device operating conditions. A universal scaling formalism is derived linking electrical and thermal resistances, along with key thermoelectric performance metrics, to the Transmissivity. A unified optimization framework is also developed for composite legs, incorporating both constricted material and contact electrodes. This framework indicates that previously reported performance gains may be largely attributed to contact resistance, rather than geometry alone. Transmissivity is established as a key geometric descriptor, enabling generalized design principles and global optimization criteria for enhancing thermoelectric power generation. This analysis elucidates new avenues in the design of thermoelectric metamaterials for efficient energy conversion.

physics.app-ph↗

arXiv2018

Thermal Conductance of a metallic dot Single-Electron Transistor

Dots are ideal systems to study fundamentals on heat transfer at the nanoscale and promising nanoscale heat-engines and thermal devices. Here, we report on the validation of our theoretical model on the thermal conductance of a metallic dot single-electron transistor (md-SET) by a recent experiment on the low-T thermal conductance. We compare with the experiment, we emphasize the physics interpretation and characteristic values and we apply the model to evaluate the operation the md-SET as heat-switch. Perfect agreement is shown between the calculated and the measured charge conductance G, heat conductance \k{appa} and the ratio \k{appa}/GT. The experimental findings confirm the theoretical predictions on the periodicity of the Coulomb oscillations in the classical regime, the low-T extreme values and the high-T limits of G and \k{appa}. The calculated conductances of the md-SET are presented in universal curves from low-T to high-T. It is shown that the md-SET can efficiently operate as a heat switch at temperatures , Ec being the charging energy of the dot.

cond-mat.mes-hall↗