Three-dimensional Finite Element Method Simulations Research Articles

A Computational Study of Solid Si Target Dynamics under ns Pulsed Laser Irradiation from Elastic to Melting Regime

The dynamic behavior of solid Si targets irradiated by nanosecond laser pulses is computationally studied with transient, thermοmechanical three-dimensional finite element method simulations. The dynamic phase changes of the target and the generation and propagation of surface acoustic waves around the laser focal spot are provided by a finite element model of a very fine uniformly structured mesh, able to provide high-resolution results in short and long spatiotemporal scales. The dynamic changes in the Si material properties until the melting regime are considered, and the simulation results provide a detailed description of the irradiated area response, accompanied by the dynamics of the generation and propagation of ultrasonic waves. The new findings indicate that, due to the low thermal expansion coefficient and the high penetration depth of Si, the amplitude of the generated SAW is small, and the time and distance needed for the ultrasound to be generated is higher compared to dense metals. Additionally, in the melting regime, the development of high nonlinear thermal stresses leads to the generation and formation of an irregular ultrasound. Understanding the interaction between nanosecond lasers and Si is pivotal for advancing a wide range of technologies related to material processing and characterization.

Phase change material integrated cooling for transient thermal management of electronic devices

Phase change materials (PCM) used to buffer temperature swings in electronic devices have the potential to improve reliability and shrink the volume and weight of the thermal management system. Although PCMs have high latent heat of phase transitions between solid and liquid, they are only effective near their melting temperature. The limited temperature range of operation constrains their effective cooling performance to narrow operating conditions and presents a challenge for designing PCM integrated thermal management solutions that can operate over a broader range of power inputs and cooling conditions. This paper studies the effect of diverse operating conditions on the cooling performance on PCM-integrated power devices. We use a Field's metal-impregnated copper foam composite as our thermal buffer with an effective cooling capacity of 109.8 kJ/(m2·K0.5·s0.5), and integrate it with a circuit board-mounted top-cooled gallium nitride (GaN) device that undergoes transient operation. We measure the junction temperature of the device in response to different heating conditions, including single pulse and pulse train profiles, showing that the PCM can reduce the junction temperature swing as much as 21.3% when compared to a copper reference heat spreader, with a maximum temperature reduction of 9.2%. To analyze the physics of heat transfer within the device under varying operating conditions, we developed a three-dimensional finite element method (FEM) simulation of the PCM-integrated device and validated it with our measurements. We observe key attributes of the heat flow within the PCM-integrated device depending on different heating conditions and the phase change dynamics. Finally, we develop a reduced-order model (ROM), validated by both measurements and FEM simulations, which enables fast calculations of temperature response and enables PCM optimization.

Role of Microstructures in the Dielectric Properties of PVDF-Based Nanocomposites Containing High-Permittivity Fillers for Energy Storage.

Polymer-based nanocomposites containing inorganic ferroelectric inclusions, typically ABO3 perovskites, have emerged as innovative dielectric materials for energy storage and electric insulation, potentially coupling the high breakdown strength (BDS) and easy processing of polymers with the enhancement of dielectric constant provided by the ferroelectric phase. In this paper, experimental data and three-dimensional finite element method (3D FEM) simulations were combined to shed some light on the effect of microstructures on the dielectric properties of poly(vinylidene fluoride) (PVDF)-BaTiO3 composites. The existence of particle aggregates or touching particles has a strong effect on the effective dielectric constant and determines an increase of the local field in the neck region of the ferroelectric phase with a detrimental effect on the BDS. The distribution of the field and the effective permittivity are very sensitive to the specific microstructure considered. The degradation of the BDS can be overcome by coating the ferroelectric particles with a thin shell of an insulating oxide with a low dielectric constant, such as SiO2 (εr = 4). The local field is highly concentrated on the shell, while the field in the ferroelectric phase is reduced almost to zero and that on the matrix is close to the applied one. The electric field in the matrix becomes less homogeneous with increasing the dielectric constant of the shell material, as happens with TiO2 (εr = 30). These results provide a solid background to explain the enhanced dielectric properties and the superior BDS of composites containing core-shell inclusions.

Computer Simulations of Dual-Antenna Microwave Ablation and Comparison to Experimental Measurements

Single-antenna microwave ablation (MWA) is mainly used to treat small tumors less than 3 cm in diameter. To obtain a larger coagulation zone in a single ablation, a dual-antenna ablation approach was proposed. A three-dimensional finite element method (FEM) simulation model of parallel dual-antennas was developed. Ex vivo experiments at 50 W for 8 min were performed to verify the model. Both the temperature changes in tissue and the size of the coagulation zone were recorded. The effects of dual-antenna spacing, heating power, and blood perfusion on the coagulation zone were analyzed. Fifteen experiments were carried out. The errors between the mean measurements and simulated results at the set temperature points were 1.08 °C, 0.95 °C, and 2.1 °C, respectively. For the same conditions, the blood perfusion of 1.0, 1.5, and 3.0 kg/(m3·s) can result in a reduction in the coagulation volume by 18.4%, 25.4%, and 42.5%. As the spacing increased, the coagulation zone of each antenna started to fuse together later and the resulting integral coagulation zone became larger. Dual-antenna MWA is expected to be used for the treatment of tumors larger than 5 cm in diameter.

Self-Aligning Capability of IPT Pads for High-Power Wireless EV Charging Stations

This article studies magnetic forces between transmitter (Tx) and receiver (Rx) coils in an inductive power transfer (IPT) system aiming to use those forces to align the coils and, consequently, improve power transfer. Due to its popularity, the analysis is conducted on a series–series compensated IPT system with planar spiral coils. The proposed method utilizes the bifurcation operation mode of the system and unloaded resonating receiver to maximize attractive force between magnetic couplers. Three-dimensional finite-element method simulations indicate that high-power IPT systems can develop enough attractive force to align coils even under nominal current. Regardless of the coil shape, e.g., spiral or Double-D (DD), the attractive forces tend to align the coils. Hence, a smart charging station can be devised based on self-aligning capability. Furthermore, this article proposes a mechanical structure to facilitate the attractive lateral force for the alignment of high power applications, i.e., wireless fast-charging stations. The forces are analyzed, modeled, and simulated for a 100-kW IPT system with an operating frequency of 20 kHz, while the self-aligning capability is experimentally verified on a downscale 11-kW prototype.

Temperature increase in STT-MRAM at writing: A fully three-dimensional finite element approach

The writing process in spin transfer torque magnetoresistive random access memories (STT-MRAM) is facilitated by elevated temperatures. In this work we investigate the temperature distribution and development in the free layer (FL) of an STT-MRAM during switching. With our fully three-dimensional (3D) finite element method simulation approach, we numerically solve the heat transport equation coupled to the electron, spin, and magnetization dynamics and demonstrate that the FL temperature is highly inhomogeneous due to the non-uniform magnetization of the FL during switching for an STT-MRAM with large magnetic tunnel junction (MTJ) diameter. While the average temperature in the FL can be obtained based on an average current density and an averaged potential drop across the tunnel barrier, a fully 3D model is required to evaluate the large local temperature variations. The temperature variations in the FL further increase, when realistic device structures with an MTJ coated by a passivation layer and contacted to broad electrodes are considered. Lowering the FL thermal conductivity increases the temperature variations even further. However, the variations are strongly reduced with the decrease of the MTJ diameter.

Enlarged tensile strain at edge of flexible substrate due to anticlastic curvature

Understanding the mechanical strain imposed on flexible electronics during bending is an essential consideration for the robust design of devices. In general, the bending behavior of flexible electronics is analyzed such that the cross-sectional mechanical strain distribution is the same along the width direction. However, even though a single curvature is applied to the cross section, the anticlastic curvature occurs along the width owing to the Poisson's ratio effect along the width. In this study, we analyze the effect of the anticlastic curvature on the maximum tensile strain of a flexible substrate because it is critical to the fracture of brittle films on the substrate. The strain distributions at the center and edge of a bent 75 μm-thick polyethylene terephthalate (PET) substrate are measured using the microscale digital image correlation (DIC) method. The anticlastic curvature effect on the maximum tensile strain of the bent substrate is analyzed through a three-dimensional finite element method (FEM) simulation. Results of DIC analysis and FEM simulation show that the maximum tensile strain at the edge of the substrate is larger than that at the center of the substrate owing to the anticlastic curvature. The enlarged tensile strain at the edge of a flexible substrate is experimentally validated by bending a laser patterned hard-coated PET substrate.

Numerical Investigation of Plastic Strain Homogeneity during Equal-Channel Angular Pressing of a Cu-Zr Alloy

A three-dimensional finite element method (3D FEM) simulation was carried out using ABAQUS/Explicit software to simulate multi-pass processing by equal-channel angular pressing (ECAP) of a circular cross-sectional workpiece of a Cu-Zr alloy. The effective plastic strain distribution, the strain homogeneity and the occurrence of a steady-state zone in the workpiece were investigated during ECAP processing for up to eight passes. The simulation results show that a strain inhomogeneity was developed in ECAP after one pass due to the formation of a corner gap in the outer corner of the die. The calculations show that the average effective plastic strain and the degree of homogeneity both increase with the number of ECAP passes. Based on the coefficient of variance, a steady-state zone was identified in the middle section of the ECAP workpiece, and this was numerically evaluated as extending over a length of approximately 40 mm along the longitudinal axis for the Cu-Zr alloy.

Analytical model of the acoustic response of nanogranular films adhering to a substrate

A one-dimensional (1D) mechanical model for nanogranular films, based on a structural interface, is presented. The analytical dispersion relation for the frequency and lifetimes of the acoustics breathing modes is obtained in terms of the interface layer thickness and porosity. The model is successfully benchmarked both against three-dimensional finite element method simulations and experimental photoacoustic data on a paradigmatic system available from the literature. A simpler 1D model, based on an homogenized interface, is also presented and its limitations and pitfalls discussed at the light of the more sophisticated pillar model. The pillar model captures the relevant physics responsible for acoustic dissipation at a disordered interface. Furthermore, the present findings furnish to the experimentalist an easy-to-adopt, benchmarked analytical tool to extract the interface layer physical parameters upon fitting of the acoustic data. The model is scale invariant and may be deployed, other than the case of granular materials, where a patched interface is involved.

Free vibration and buckling characteristics of functionally graded beams with triply periodic minimal surface architecture

This work presents models to studies the free vibration and buckling characteristics of functionally graded porous (FGP) beam with triply periodic minimal surfaces including Primitive, Diamond, IWP, and Gyroid using Euler’s beam theory. The models take into account the effect of the neutral axis dislocation during both vibration and buckling mode. The porous density is considered to be functionally graded along the vertical direction following the practical fabrication of architected structures. The effective stiffness is proposed in form of the three-degree polynomials and their coefficients are found by fitting the discrete data from three-dimensional finite element method (3D FEM) simulation of architected TPMSs with a wide range of porosity. The condition of gradient index is derived based on the power rule to make this work practical. 3D FEM simulations for FGP beam are carried out to validate against the present model in terms of natural frequency and neutral axis deviation to mid-plane with good agreements observed. It is found that three-degree polynomial is a good form to express the effective stiffness over the large range of porosity. In addition, the gradient index, beam dimension, architected material types, and base materials are found to affect significantly the free vibrational and buckling behaviors of beam.

Analytical design and experiment of radial inductive displacement sensor with full-bridge structure for magnetic bearings

In magnetic bearing systems, the air gap between the stator and the rotor is generally measured with an eddy current displacement sensor. However, the inductive displacement sensor (IDS) is a preferred choice due to its structural consistency with magnetic bearings, which contributes to a compact system design. While most of the reported IDS research studies are based on three-dimensional finite element method (3D FEM) simulation and the IDS of such studies is designed with a half-bridge structure, in this paper, a higher sensitivity IDS with a full-bridge structure is proposed. To optimize the response of the sensor, an accurate theoretical analysis method is presented for the sensor based on the Schwarz-Christoffel transformation, which is used for compensating fringe effects of sensor inductance. Compared to traditional 3D FEM simulation, fast sensor design and optimization can be achieved with the proposed method. Experimental results agree well with theoretical predictions. The sensitivity of the proposed sensor is nearly 15.5 mV/μm, and the displacement resolution is better than 1 µm.

Analysis of Stresses in Metal Sheathed Thermocouples in High-Temperature Flows

Flight and ground test applications for in-flow and near-wall flow temperature sensing demand robust and accurate sensing, making thermocouple sensors attractive. Even for these extremely well-developed sensors, an accurate prediction of stresses within thermocouple sheaths for custom-configured probes remains a topic of great concern for ensuring an adequate lifetime of sensors. In contemporary practice, high-fidelity simulations must be run to prove survivability, albeit at significant time and expense. Given the resources it takes to run high-fidelity simulations, rapid optimization of sensor configurations is often impossible or, at a minimum, impractical. The developments presented in this paper address the need for high-temperature sensor structural predictions that are compatible with rapid design iteration. The derivation and implementation of a new analytical, low-order model to predict stresses within the sheath of a thermocouple are provided. The analytical model is compared to three-dimensional elastic finite element method simulations as well as experimental data from a simplified configuration. The low-order model sheath stress predictions, which are critical to probe survival, are in excellent agreement with the numerically simulated results and experimental results with root-mean-squared percentage errors of approximately 1.2 and 2.6%, respectively, thus, validating the model.

3D-FEM Simulation of Hot Rolling Process and Characterization of the Resultant Microstructure of a Light-Weight Mn Steel

Computational simulation has become more important in the design of thermomechanical processing since it allows the optimization of associated parameters such as temperature, stresses, strains and phase transformations. This work presents the results of the three-dimensional Finite Element Method (FEM) simulation of the hot rolling process of a medium Mn steel using DEFORM-3D software. Temperature and effective strain distribution in the surface and center of the sheet were analyzed for different rolling passes; also the change in damage factor was evaluated. According to the hot rolling simulation results, experimental hot rolling parameters were established in order to obtain the desired microstructure avoiding the presence of ferrite precipitation during the process. The microstructural characterization of the hot rolled steel was carried out using optical microscopy (OM), scanning electron microscopy (SEM) and X-ray diffraction (XRD). It was found that the phases present in the steel after hot rolling are austenite and α′-martensite. Additionally, to understand the mechanical behavior, tensile tests were performed and concluded that this new steel can be catalogued in the third automotive generation.

Phase Change Material Heat Sink for Transient Cooling of High-Power Devices

This paper reports a heat sink that uses a composite phase change material (PCM) made from a copper foam infused with a Field's metal eutectic alloy that melts at 60°C to achieve both high cooling and the ability to buffer transient temperature spikes. We integrate this composite PCM heat sink with circuit board mounted gallium nitride (GaN) devices that dissipate heat flux as large as 50 W/cm2. To design the PCM heat sink and understand its behavior, we developed a three-dimensional finite element method (FEM) simulation of the integrated assembly. We fabricated and characterized five composite PCM heat sink devices, where each device had a different PCM thermal buffer. The thermal buffers had varying Cu volume fraction and thickness. The PCM heat sinks were integrated with top-cooled or bottom-cooled GaN devices on printed circuit boards. Measurements of PCM heat sink performance showed that during phase change, the device junction temperature was reduced by 10-20°C compared to a solid Cu reference heat sink, depending on the device heating power which was as high as 6 W. The PCM heat sink cooling time was increased by up to 2X compared to a solid Cu heat sink of the same geometry. Finally, we developed and validated a reduced order resistance-capacitance (RC) circuit model that can guide the design of future PCM heat sinks. This work demonstrates the potential for PCM heat sinks to be integrated with high power GaN devices and shows methods for the design and modeling of PCM heat sinks.

Определение LC-параметров корпусов ИМС с помощью электромагнитного моделирования

At the IC design phase it is required to consider all possible factors to ensure the produced device’s compliance with specified requirements. For instance, it is necessary to select an optimum package and to lower its impact on IC’s final characteristics. Electromagnetic simula-tion is widely used to calculate electrical parameters of the electric motors, printed circuit boards, and microcircuits. In this work, full-wave three-dimensional finite element method simulation in frequency domain was used to characterize LGA package. S-parameters matrix obtained by modeling was converted to an equivalent RLGC transmission line model to determine the electrical parameters of the package – self-capacitance and inductance of the leads, mutual capa-citance of the adjacent leads, – on which the package bandwidth and crosstalk depend. Correct-ness of the obtained results was confirmed by comparison with the measurements results. It has been found that discrepancy between the results of modeled and measured capacitance was less than 5 %. The inductance modeling results turned out to be less accurate, which, however, is not significant for low and medium frequency applications.

Sensorless attitude estimation of three-degree-of-freedom actuator for image stabilization

Space recognition is a crucial issue for autonomous systems such as unmanned aerial vehicles, walking robots, and autonomous cars. These systems are necessary to obtain information using a camera while moving. However, reduction in recognition accuracy and system size increase has created problems. To solve these problems, we proposed the three-degree-of-freedom (DOF) actuator for image stabilization. This paper proposes a novel initial position estimation method and sensorless attitude estimation method for the three-DOF actuator to further downsize and reduce weight. The effectiveness of the proposed methods is verified by a magnetic field analysis, using a three-dimensional finite element method and numerical simulations.

Composite Structured Surfaces for Durable Dropwise Condensation

Dropwise condensation of steam on hydrophobic substrates has a 10X higher heat transfer coefficient compared to filmwise condensation. To promote dropwise condensation, low surface energy hydrophobic coatings (polymers) are typically utilized. The low intrinsic thermal conductivity (k < 1 W/(m·K)) of polymers, coupled with high heat transfer coefficient of dropwise condensation (100 kW/(m2·K)), necessitates that the coating be thin (< 1µm) in order to avoid reducing the overall heat exchanger conductance. However, thin polymeric films easily degrade. The two opposing requirements result in the need for optimization between the durability (thick coating) and the heat transfer (thin coating). To enable high thermal conductivity in thicker coatings, we develop metal-polymer structured surfaces. By using porous structures as inter-connected heat-conducting backbones that are filled with hydrophobic materials, we enable tuning of the coating effective thermal conductivity and surface energy. Three metal structures were studied; micro/nanowires, inverse opals, and sintered spheres. Heat transfer performance was calculated using three-dimensional finite element method simulations with two distinct boundary conditions; convection at the walls and isothermal walls. Interestingly, the overall conductance shows up to 40% difference depending on the boundary condition used in calculating the composite coating effective thermal conductivity. We use our model to predict the heat transfer performance as a function of metal fraction by volume and by surface area for condensation. By coupling our thermal simulations with a previously verified analytical model for predicting wetting behavior on heterogeneous surfaces, we propose a regime map to predict dropwise-to-filmwise transition. Our work not only forms a starting point for the development of durable dropwise condensing surfaces, it identifies important considerations needed for computing effective thermal conductivity of composites.

Ultrahigh sensitive gas sensors based on slotted photonic wire-based structures including optical microcavities

In this paper, we investigated two-dimensional (2D) and three-dimensional (3D) finite element method (FEM) simulations to provide ultrasensitive gas sensors based on silicon-on-insulator (SOI) slotted photonic wire structures in the mid-IR spectral region, tuned for the wavelength 3.392 $$\upmu \hbox {m}$$. The proposed optical microstructures have the ability to detect methane gas in the environment in addition to sensing the gas flux from the hole/slot regions with a very high sensitivity ($${S} = 2.97$$) through a very high confinement of the electric field in the photonic wire slot region that leads to an increase in the interaction of light with gas. To further boost the sensitivity of the SOI slotted photonic wire structure to the methane gas, we designed an optical microcavity in the photonic crystal (PhC) slotted structure. This microcavity can sense the smallest methane gas level $$(0.36062\,\upmu \hbox {m}^{2})$$ with high sensitivity ($${S}= 27.45$$), by means of strengthening the high-quality factor cavity mode and reduction of effective modal volumes. In addition, the ultra-wide bandgap ($$1.9\,\upmu \hbox {m}$$) obtained from Bragg mirrors of the simulated microcavity structures can facilitate us to extend the sensing in a wide range of wavelengths.

Revealing Plasmonic Property Similarities and Differences Between a Nanoparticle on a Metallic Mirror and Free Space Dimer Nanoparticle

Conventionally, in plasmonics, experimentally developed nanoparticle on a metallic mirror design is used to mimic the free space dimer metallic nanoparticles. Numerous theoretical simulations considering free space dimer were carried out and their plasmonic properties were applied to nanoparticle on a metallic mirror design. In this work, with the help of three-dimensional finite element method simulation we directly compared the free space dimer and nanoparticle on a metallic mirror designs and analyzed their plasmonic properties. Although there are similarities in their generalized near field enhancement properties, we observe significant differences as well. With the help of three-dimensional surface charge density mappings, we explain the origin of these differences, as cross-sectional amplitude of electric field profiles has limitation in understanding such complex plasmonic mode(s). We hope our study will be helpful in understanding the origin of complex plasmonic modes, and sub-wavelength optical properties for the development of the efficient light devices.

A grain level model for deformation and failure of ultrafine-grained tungsten

Ultrafine-grained tungsten (UFG W) produced by severe plastic deformation technology has many potential applications due to its high strength and ductility. To reveal the mechanism for the high ductility of UFG W, the deformation and failure behaviors of coarse-grained tungsten (CG W) and UFG W have been compared based on a three-dimensional crystal plastic finite element method (CPFEM) simulation. Cohesive element method has been utilized to model the behavior of grain boundaries (GBs). Both plastic deformation in grain interiors and grain boundary opening have been observed in different periods of deformation in UFG W. It is concluded that the high GB density and elongated microstructure in the UFG W suppress crack propagation, decrease the stress concentration and impurity concentration on GBs, therefore enhance the ductility of the material.