This paper is focused on a homogenization-based multiscale topology optimization (TO) framework with explicit de-homogenization for the design of graded pin-fin heat sinks subject to conjugate heat transfer. The proposed approach enables the design of diverse pin-fin geometries, and facilitates practical implementation through direct computer-aided design (CAD) model generation using explicit geometry feature representation. The proposed framework consists of three steps. Surrogate models for effective thermal conductivity and fluid permeability are first constructed using numerical homogenization and artificial neural networks. These models are then incorporated with cell rotations and macroscopic design variables to build the material property model, which is subsequently used to define and solve the TO problem. Finally, explicit de-homogenization is employed to restore optimized pin-fin microstructures using CAD feature representation, allowing direct generation of manufacturable CAD models. The effectiveness of the proposed framework is validated through a quantitative comparison of three benchmark heat sink designs using full three-dimensional (3D) numerical simulations. This comparison confirms that a multiscale heat sink design outperforms conventional (uniform fin, size-optimized fin, and macro-topology optimized fin) approaches by achieving a balanced configuration through effective flow redistribution. In addition, the practical applicability of the framework is established through additional examples including a Pareto front investigation for trade-off analysis and the direct generation of a 3D CAD model for additive manufacturing (AM).

This paper presents a robust multi-objective genetic algorithm (MOGA) optimization of the novel CONDIV manifold heatsink for external airflow environments. The converging-diverging (CONDIV) manifold is designed to protect internal heatsinks from debris-laden flows while maintaining high thermal performance. Previous studies relied on simple parametric sweeps for only a limited exploration of the design space of external manifolds, limiting the discovery of optimal designs. Here, a comprehensive MOGA framework is implemented, combining 3D computational fluid dynamics (CFD) simulations validated against experiments. Seven geometric parameters are optimized to simultaneously minimize thermal resistance and pumping power, maximizing the coefficient of performance (COP). The design of experiments (DOE) is generated via Latin hypercube sampling (LHS), and a response surface model is constructed to approximate heatsink performance. The MOGA efficiently explores the design space, yielding a Pareto front of optimal solutions. Best compromise solutions (BCSs) are selected and verified through CFD. Results show that MOGA-optimized designs consistently outperform previous CONDIV and baseline plate-fin heatsinks, achieving up to 33% higher COP and 4.3% greater heat flux than previous CONDIV-H design and 42.4% higher mean COP than the baseline plate-fin heatsink. Detailed flow analyzes reveal that optimized BCSs improve airflow into internal channels and improve flow uniformity, resulting in superior thermal management. This demonstrates the strong potential of MOGA-driven optimization for advanced manifold heatsink applications in electrified transport.

Ultrasound power transfer enables the wireless charging of implantable medical devices by utilizing an energy harvester to convert incoming ultrasound into electrical energy. Most harvesters rely on Lead Zirconate Titanate (PZT) crystals for energy conversion, but since PZTs are rigid and dense ceramics, scaling them up to harvest more energy produces heavier devices that are impractical for medical applications. This study presents a metamaterial-enhanced ultrasound energy harvester (Meta-UEH) that integrates a small PZT crystal with a locally resonant metamaterial, which concentrates ultrasound energy onto the PZT and thus improves its energy harvesting performance. The metamaterial is flexible, lightweight, and entirely passive, making it well-suited for medical applications, while increasing the power of harvested electricity by more than double. Experimental and simulation results confirm that the Meta-UEH achieves enhanced efficiency even under reverberation or deformation, benefiting from standing waves that form between transducers and the metamaterial, with harvested electrical power reaching up to 350% of that obtained without the metamaterial and standing wave. The underlying mechanisms behind the improvement are analyzed, revealing that the improvement is not specific to PZTs but can also be applied to other ultrasound-electricity conversion methods, such as piezoelectric and triboelectric nanogenerators.

Capillary-driven two-phase micro-cooler is a promising thermal management solution for passive cooling in highheat-flux electronics applications. In this study, we have developed an area-scalable two-phase capillary-driven cooler that integrates a silicon pin array coated with copper inverse opal (CIO) wick with a copper wire mesh 3D manifold over a 5 x 5 mm2 heated area and utilizes water as the working fluid. We achieved a critical heat flux of ti 650 Wcm- 2, and two-phase heat transfer coefficients ti 1 MWm- 2 degrees C- 1. We consider three different wick structures (a planar CIO layer, a sparse square pin array coated with CIO layer, and a dense square pin array coated with CIO layer), three inlet flow rates of 5, 10, and 15 g(min)- 1, and two types of copper wire mesh 3D manifolds with different spacings between neighboring wire mesh layers of 550 and 650 & micro;m, respectively. The two-phase heat transfer at critical heat flux (CHF) for CIO wick layer on sparse and dense silicon pin array increases by ti 47% and ti 120%, respectively, compared to that of the baseline planar CIO wick. This enhancement in the two-phase heat flux is directly correlated to the increase in the effective (extended) silicon (wick) surface area. Our systematic study concludes that the CHF values are limited by the wick structures rather than the copper wire mesh 3D manifold for baseline planar CIO wick and sparse silicon pin array covered with CIO layer. However, for the dense silicon pin fins covered with CIO layer, either the wick or the copper wire mesh manifold could be limiting the CHF; further study of the micro-coolers with larger heated footprint is required to understand the limiting factor. Furthermore, it is found that the 3D manifold with a center-to-center wire-mesh spacing of 550 & micro;m (9 wire meshes) exhibit better coolant supply across the wick, showing a higher CHF, compared to the 3D manifold with a center-to-center wire-mesh spacing of 650 & micro;m (8 wire meshes), owing to the larger number of parallel wire-mesh capillary pathways (9 vs. 8) and the shorter maximum lateral distance (ti 275 & micro;m vs. ti 325 & micro;m) from the nearest mesh to the wick. Finally, we provided a comprehensive performance review of the capillary-based micro-coolers with and without 3D manifolding scheme to benchmark the present work. The next generation of copper wire mesh manifold will be optimized to cover large, heated area as well as improving the permeability of the copper wire mesh to support high two-phase heat flux.

Future data centers will employ large-area (greater than 25 mm x 25 mm), high-heat-flux (greater than 1 kW/cm2) central processing unit (CPU) and graphics processing unit (GPU) devices. Such devices, or chips, will necessitate aggressive cooling solutions, including two-phase cooling. In this work, we explore the potential of indium solder as a thermal interface material (TIM) for directly bonding cold plates to chips, providing a lowthermal-resistance pathway. By eliminating the need for multiple TIM layers, this approach enhances thermal efficiency while mitigating stresses by minimizing the coefficient of thermal expansion (CTE) and stiffness mismatch within the device stackup. We performed thermal-mechanical modeling of the device stack-up to analyze the temperature and stress maps. Our numerical results indicate that the highly viscoplastic and compliant nature of the indium solder TIM prevents excessive thermally induced built-in stress in the device after cooling postreflow. Furthermore, the numerical results clarify that the thickness of an additional copper-tungsten (CuW) layer, as a CTE alleviating component between the cold plate and device, can be minimized as its role is minor in preventing thermally induced stress, and in fact this layer increases package conductive thermal resistance. Thus, optimal thermal-mechanical performance for such large-area devices might be achieved through a minimal indium solder TIM thickness without such intermediary stress mitigation layers.

External airflow plays a crucial role in thermal management across many vehicle types, often relying on forced convection through plate-fin heatsinks. However, this airflow frequently contains dust, particles, and foreign object debris (FOD), which can cause wear, clogging, and damage to conventional heatsinks. This study introduces a novel three-dimensional (3D) manifold architecture specifically designed to mitigate the impact of FOD on air-cooled heatsinks in harsh environments. Unlike traditional manifolds that channel all airflow through an internal heatsink, the proposed design features a unique 'multi-path' configuration: portion of the air is drawn through the internal heatsink, while the remainder may flow directly through the manifold itself. This approach improves resilience to debris-laden flows compared to conventional manifolds. The proposed manifold, referred to as 'CONDIV', is constructed from angled fins arranged to form an array of converging-diverging channels, which generate alternating high and low pressure regions when exposed to external airflow. This pressure differential effectively draws a portion of external airflow through the protected internal heatsink while allowing debris and the remaining air to pass through the manifold directly, minimizing obstruction and reducing the risk of clogging. A comprehensive parametric optimization of the manifold and heatsink geometries was conducted using 3D simulations in ANSYS Fluent. Results demonstrate that the 'CONDIV' manifold achieves higher performance coefficients compared to traditional plate-fin heatsinks of equivalent mass. In fully ducted flow scenarios, the proposed design can attain 8.3-32.6% higher base heat fluxes, and 3.4-22.5% improvements when flow bypass is allowed. These findings highlight the potential of this innovative manifold architecture to enhance vehicle cooling performance in challenging environments involving debris-laden airflow.

To meet the increasing demand for higher power density in compact spaces, significant advancements are being made in power electronics, including the development of three-dimensional (3D) integrated packages. However, the 3D integration of power electronics presents several challenges, including effective in-plane and through-plane heat transfer and removal, plus reliable high-temperature layer-to-layer stack bonding technologies. Addressing these challenges requires innovative package assembly solutions, ensuring robust performance and scalability. This study presents a cost-effective and scalable copper (Cu) metal coating process for electronics packaging with adjustable properties, ranging from microporous to dense Cu, achieved by varying the metal particle size. This coating is produced using a "slurry cast" method, where a copper particle slurry is applied to the target surface/feature and reduced at 160 degrees C, forming a porous or dense copper layer and/or structure. The coating's thickness, particle size, and porosity can be easily controlled to meet the specific requirements of a vertically integrated 3D power package. To demonstrate the versatility of the slurry-cast structures, we explored their use in three different integration applications: a low-temperature processable planar bonding layer, a large diameter through via to demonstrate it's prospective to use for making Through Silicon Via (TSV) for efficient cross-plane heat conduction, electrical connectivity and a novel phase change cooling structure for heat removal. The results show that the slurry-cast process has the potential to be applied in a range of future 3D power electronics packaging applications.

The thermal management of planar magnetic inductor or transformer components is a critical factor in increasing the power density and enhancing the performance plus reliability of power electronics. This paper comprehensively investigates the thermal management of printed circuit board (PCB)-based planar inductors used in high-power converters through active liquid cooling. The study specifically explores embedded cooling technology to improve the heat dissipation efficiency of a planar inductor design. Three cooling configurations are analyzed: 1) a baseline case with single-sided active liquid cooling of the component package; 2) an improved case with double-sided liquid cooling of the package; and 3) a novel proposed method utilizing hybrid double-sided cooling with embedded liquid cooling of the component. Thermal modeling and simulation results are presented for all three cases to evaluate their effectiveness in dissipating heat. The initial numerical results demonstrate that the proposed hybrid cooling technique significantly enhances thermal performance by reducing hot spots inside the planar magnetic component and provides more uniform temperature distribution across the inductor windings. This method shows promise for high-power density applications where efficient thermal management is essential.

It is well known that pin-fin arrays can significantly improve the convective heat transfer of air-cooled heat sinks due to a large surface area enhancement from the fins. Such pin-fin heat sink designs serve as a promising solution for addressing a wide range of electronic device thermal management needs in both computing and energy conversion applications. However, air movers (e.g., axial fans or centrifugal pumps) that are used to drive and control air flow typically generate noise that tends to have spectral characteristics with specific resonances in the general range of 100 Hz to 10 kHz. Often it is desirable to attenuate such noise using additional sound absorbers, ducting, or grills. Here, we numerically investigate heat sinks with hybrid pin-fin/absorber-fin array designs subject to air jet impingement that simultaneously address heat transfer and noise attenuation. For the hybrid-fin array, Helmholtz resonators are employed for acoustic absorber fins that are then interleaved with more traditional heat sink pin fins whose phononic characteristics are not often discussed for noise mitigation. Through numerical studies, it is shown that the designed acoustic absorber fins effectively reduce the noise level at target frequencies over an acoustic spectrum that mimics a representative rotating axial fan. We further demonstrate that these frequencies can be changed by varying geometrical parameters of the hybrid pin-fin/absorber-fin array. Regarding heat transfer, thermal-fluid conjugate models are utilized to quantify the performance of a standard pin-fin heat sink versus the hybrid pin-fin/absorber-fin heat sink design. Our findings open new possibilities for further optimizing multifunctional hybrid-fin array-based heat sinks considering both thermal and acoustic performance.

High-performance electronics are continuously demanding cooling of higher heat fluxes. Phase-change cooling, including pool boiling, is a useful approach to address this challenge; however, competition between liquid and vapor flows generally limit the heat fluxes that can be dissipated. A range of strategies to control these flows have been investigated previously, including capillary guides. Here a manifold structure formed from a metallic mesh is investigated to control the disposition of liquid and vapor phases above a pool fed boiling surface enhanced with porous structures. Copper mesh forms defined liquid flow paths, using capillary action to guide and distribute liquid evenly over the heated surface, along with open channels to facilitate vapor escape. The mesh provides a novel structure for liquid guidance that imposes low resistance to liquid flow while occluding a minimal area of heated surface underneath. The manifold performance is characterized in boiling fed by a pool of water above a laser-textured aluminum nitride heat dissipation surface with pin-fin structures having heights of 110 mu m and spacing of 30 mu m with a heated area of 5 mm x 5 mm. A maximum heat flux of 490 W/cm2 is reached with the manifold in the pool fed configuration, representing an increase of more than 65% over the porous pin fin surface alone. The maximum stable superheat observed for the manifold of 36 K is 14 K higher than that for the porous surface without the manifold. The factors limiting performance of the manifold are analyzed. High superheat is attributed to partial flooding of the boiling surface as suggested by the reduction in superheat using external suction. Similar systems and structures for enhanced two-phase cooling are compared.

Engineered microporous structures have received much attention in high-heat-flux electronics cooling due to their high thermal conductivity and permeability, and large surface area for heat transfer, but are susceptible to boiling-induced thermal degradation. This study investigates the efficacy of nickel inverse opals (NiIOs) in mitigating structural degradation caused by corrosion-assisted erosion during pool boiling with water as the working fluid. First, we compared the reliability of NiIOs to copper inverse opals (CuIOs) for a 3-day pool boiling test at constant heat flux. The NiIOs demonstrated superior resistance to thermal degradation due to their inherent corrosion resistance and mechanical strength. Subsequently, we conducted a more controlled experiment to show the effect of heat flux on the degradation of the NiIOs while excluding the effect of temperature variations. Pool boiling tests of 20-mu m-thickness NiIOs covering an area of similar to 11 x 11 mm2 with a 2.5 x 2.5 mm2 heater at the center were conducted at heat flux levels of 20%, 40%, and 60% of the critical heat flux (CHF) for 3 days. The NiIOs subjected to heat flux levels of 20% and 40% CHF showed minimal degradation, while the sample subjected to 60% CHF showed erosion on the top surface due to higher bubble formation and departure rate. These results show the potential of NiIOs as a promising solution for long-term thermal management in high-power electronic devices, although design considerations for maximum allowable heat flux are necessary for reliable operation.

Sustainable and energy-efficient cooling is crucial for managing high-performance computing architectures within the rapidly expanding data center industry. Here, we introduce a novel capillary-driven two-phase microcooler that eliminates the need for conventional pump-based cooling schemes. The device integrates thinfilm boiling in silicon micropin fin wicks (six geometric variations) with a copper 3D wiremesh manifold (two spacings), representing a new approach that combines self-regulated capillary liquid supply with nearly complete vapor phase separation. Using deionized water, the optimized wick achieved a critical heat flux of 486 W/cm2 at a low superheat of Delta Tsat = 7 degrees C, corresponding to a two-phase thermal resistance of R(y)tp= 1.8 mm2- degrees C/W, while ensuring nearly complete liquid-vapor separation (vapor quality -0.9). The microcooler offers design flexibility that allows any combinations of wick and manifold materials 9silicon or copper) as well as area and performance scalability toward larger heated footprints and higher heat fluxes (-1 kW/cm2) and heat transfer coefficients (-106 W/m2- degrees C). These findings establish capillary-driven two-phase cooling as a transformative pathway for the thermal management of high-end microelectronics and energy-efficient data centers.

An inverse opal (IO) structure is a highly ordered porous structure that has broad applications in fields, including optics, thermal management, and chemical catalysis. The morphology and properties of IO structures primarily depend on the sintering process applied to the IO spherical template. In this research, we provide a new fundamental understanding of the polystyrene template sintering process for IO structure formation through both experimental verification and polymer melt theory development. Through experiments, we investigated 15 sintering cases using three types of polystyrene templates formed from 3.0, 4.0, and 5.3 μm diameter colloidal particles to study the optimal sintering conditions for achieving self-organized and well-connected copper inverse opal (CIO) structures. The theory underlying a "generalized" version of the Mark-Houwink equation is applied for the first time to understand polystyrene bead template sintering and CIO formation. From experiments, it was found the square of the IO neck diameter-to-pore diameter ratio, (dn/dp)2, an important parameter to indicate the IO morphology, is proportional to the sintering time at the initial stage of sintering in agreement with the developed theory. The study also clarifies relationships among the polymer recipe weight-average-molecular weight (Mw), dn, and dp on the IO morphology. Specifically, the slope of the linear relation between (dn/dp)2 and the sintering time is proportional to (Mw1.34·dp)-1 under 100 °C process conditions, a commonly used sintering temperature. As a result, the morphology and features of the IO structure were well predicted using polystyrene templates with different properties. Findings from this research enable the design of IO structures for a range of applications using empirically fit coefficients in the Mark-Houwink equation.

Capillary-driven boiling using the microporous structures exhibits an exceptional two-phase heat transfer performance due to the presence of numerous nucleation sites and effective liquid-vapor separation. In addition, the high capillary pressure due to the small pore size enables passive liquid supply. Therefore, capillary-driven boiling is a promising candidate for energy-efficient microcoolers in high-heat-flux electronics. However, achieving area scalability is challenging due to significant viscous pressure losses along the wick, which hinder liquid transport across the boiling region. This limitation poses a major obstacle to contemporary large-area, high-performance chip cooling solutions and requires the development of the area-scalable capillary-driven two-phase cooler. In the present study, we have significantly improved the performance and expanded the cooling area of a capillary-driven micro-cooler with the augmented microporous layers over “sparse” and “dense” micro pin arrays to improve the two-phase heat transfer coefficient in conjunction with a capillary-based silicon open microchannel manifold (channel spacing of $\mathbf{5 7 0, 1 1 4 0}$ and $\mathbf{1 7 1 0 ~} \boldsymbol{\mu} \mathbf{m}$), for efficient liquid delivery and vapor extraction, targeting exit vapor quality, $x_{\mathrm{e}} \approx 1$. Infrared thermography is employed to characterize the spatial temperature distribution and to understand the underlying heat and mass transfer mechanism. To extract the contribution of the two-phase heat transfer from the applied heat flux, the flow rate at the drainages in the test vehicle is measured to estimate the boiling rate at the critical heat flux level. We demonstrated critical heat flux level $\approx 200 \mathrm{Wcm}^{-2}$ and a superheat of $\approx 4^{\circ} \mathrm{C}$, achieving heat transfer coefficient $\approx 430 \mathrm{kWm}^{-20} \mathrm{C}^{-1}$ and $x_{\mathrm{e}} \approx 1$ with minimum inlet flow rates of $5 \mathrm{~g}^{(\mathrm{min})^{-1}}$. Even a higher CHF level of $\approx 450 \mathrm{Wcm}^{-2}$ with superheat $\approx 7^{\circ} \mathrm{C}$, is achieved using inlet flow rate of $15 \mathbf{g}(\mathbf{m i n})^{-1}$ but with $x_{e} \approx 0.65$. The 3D manifold with microchannels spacing of $1140 \mu \mathrm{~m}$ provided the right balance of efficient liquid delivery for capillary wicking and open pathways for vapor extraction, showing the highest critical heat flux, given the same supplied flow rate. The two-phase cooler assisted by capillary-driven boiling in the previous studies typically supplied liquid across the perimeter of the wick, limiting their scalability and performance. The integration of a silicon microchannel manifold with a copper inverse opal porous layer overcomes these limitations by enhancing liquid flow distribution and preventing local dryout, enabling efficient two-phase heat transfer over larger areas. Therefore, the two-phase cooling scheme in this study demonstrates large-area capillary-driven boiling without compromising high heat transfer efficiency, making it a promising solution for contemporary high-performance chip cooling.

High-temperature (HT) proton exchange membrane (PEM) fuel cells (FC) offer key advantages for sustainable transportation, especially in heavy-duty applications, due to their improved thermal efficiency and water management. This study introduces an inverse design framework to develop flow field plates integrated with a gas diffusion layer (GDL), enabling scalable electrochemical performance from the unit cell to the plate level. A reduced-order, homogenization-based multiphysics model is developed to evaluate designs with approximately 1000x faster computation. Flow channel orientation is optimized using a tensor field method and dehomogenized into manufacturable geometries. Optimized designs, validated through high-fidelity 3D simulations, show up to 12% higher average current density and 88% lower pressure drop compared to conventional parallel and mesh configurations. To address fabrication challenges, solid-to-porous metal additive manufacturing is employed, producing monolithic structures that integrate flow channels with a porous metal GDL. Both numerical and physical tests confirm high permeability and improved power output compared to carbon-based GDLs. These findings highlight the effectiveness of combining advanced computational modeling with metal 3D printing to enhance the performance and manufacturability of high-temperature PEMFC, supporting their broader adoption in sustainable energy applications.

Plug-in electric vehicles (EVs) are reshaping the transportation energy landscape, providing a practical alternative to petroleum fuels for a growing number of applications. EV sales grew 55× in the past decade (2014–2024) and 6× since 2020, driven by technological progress enabled by policies to reduce transportation emissions as well as industrial plans motivated by strategic value of EVs for global competitiveness, jobs and geopolitics. In 2024, 22

As land, air, and sea-based transportation electrification expands, inverter technology is subject to a variety of domain-specific requirements. With such a diversity in requirements, prior learning may not transfer between domains to offer appropriate solutions. To keep pace with the quickly evolving power conversion landscape, efficient numerical methods are needed to assess the performance of a new technology and determine whether changes in the design paradigm are necessary. In this research, a categorical embedded Bayesian optimization approach is extended to generate Pareto-optimal solutions for both an electronics power module and associated cold plate using a sequential design approach. Each design problem is independently solved using three-dimansional (3D) multi-physics evaluation methods to measure the impact of both continuous and categorical design variable selections. It was observed that the probabilistic models accurately captured Pareto designs near the utopia point thus expanding the number of eligible designs for down-selection. Furthermore, such models showed improved convergence with a limited number of function calls motivating the use of Bayesian optimization approaches for the design acceleration of power modules and cold plates.

Modern computational resources have revolutionized the optimization of materials research for creating advanced photonic elements. These same computational resources are in such demand that alternative formats of compute technology are being pursued, which has reignited interest in photonic processing. This talk will review our progress towards the design of optical elements for a variety of applications. We have studied the optimization of meta-optical elements for metalense technology, the optimization of periodic metamaterials for image processing applications, and the exploration of unorthodox structural designs to miniaturize existing optical elements. All of these studies are driven by our motivation to pursue advanced technologies for the vehicle, including internal and external sensors, reduced power consumption, and the optical revolution of data management systems.

The demand for higher heat flux cooling is increasing as the use of power electronics continues to expand. Two-phase cooling approaches that are tightly integrated into electronic packages offer potential for high performance. Here we describe a method to produce microscale pillars directly in aluminum nitride using UV laser ablation that is compatible with existing substrates for power electronics packaging and offers high precision and short production time. The resulting structures show significantly enhanced performance in pool boiling compared to unmodified surfaces. Effectiveness in two-phase cooling is investigated in terms of critical heat flux, heat transfer coefficient, and thermal resistance. The micropillar structures achieve a maximum critical heat flux of 299 W/cm2 and heat transfer coefficients up to 20 W/cm2 K for cooled areas of 0.25 cm2 in deionized water. Performance is attributed to the effective capillary rewetting of the surface during boiling and increased surface area. Corrosion of the aluminum nitride surface by the water working fluid is observed and contributes to a slow degradation of the measured heat transfer coefficient. The potential for simple processing routes to allow tight integration of two-phase cooling of electronics more generally is considered.