Substrate Thickness Research Articles

Modeling the partially detected backside reflectance of transparent substrates in reflectance microspectroscopy.

This article presents the development and validation of a thermal model for the Wire Arc Additive Manufacturing (WAAM) process. The model is based on the Finite Element Method (FEM) and is designed to predict the thermal distribution of the substrate where the welded bead is going to be deposited. To validate the thermal model, an experimentation process was carried out using three different substrate thicknesses (8, 10 and 30 mm), while varying key process parameters that influence heat input (such as deposition rate and travel speed). The simulation results were compared with experimental data by analyzing critical thermal parameters such as the area, height, and width of the heat affected zone (HAZ), as well as the melt pool dimensions. The HAZ geometry obtained from the thermal simulation showed strong agreement with experimental observations, confirming the model’s accuracy. Then, the model was extended to simulate a broader range of travel speed and deposition rate per sample thickness. This allowed for a more comprehensive study of how these parameters affect the thermal response of the substrate. The expanded dataset generated from the simulations was used to train a sequential artificial neural network and then compared with experimentation obtained results. The ANN model demonstrated reliable predictive performance across all cases, with the lowest error observed for the 30?mm substrate thickness due to its reduce extreme temperature gradients and transient thermal fluctuations. The novelty of this work lies in the integration of a validated FEM thermal model with a sequential ANN, enabling rapid and accurate prediction of thermal fields in WAAM process. Keywords: WAAM; HAZ; melt pool; FEM; ANN

Effect of AISe quantum dots synthesis method and TiO2 substrate thickness on the performance of quantum dots-sensitized solar cells

Abstract To compensate for the poor sensitivity of existing transformer vibration sensors and the deficiencies in transformer condition monitoring, this paper proposes a design of a frame-shaped convex micro-texture flexible graphene vibration sensor sensitive element. By constructing a frame-shaped micro-texture sensitive unit, combined with the constitutive model of superelastic materials, electrostatic coupling model, and structural mechanics model, a dynamic strain transfer model of the substrate under vibration load is established. The influence of micro-texture spacing and substrate thickness on the strain of the flexible sensor under the presence or absence of an electric field is investigated. The compression strain mechanism of the micro-texture in the flexible piezoresistive sensor is studied to explore the interaction between vibration load and electric load. Numerical simulations indicate that the micro-texture exhibits cantilever beam-type multi-order resonance characteristics, and the moment acting on the micro-texture increases with increasing spacing, while the stiffness decreases. The strain of the combined size micro-texture increases with the increase in micro-texture spacing, effectively increasing the contact area and improving the sensor sensitivity. This paper effectively increases the strain of the substrate and enhances the sensitivity of the flexible sensor through the coupling effect of mechanical and electric loads, and the distribution of moment and stiffness by combining sizes.

Purpose The purpose of this study is to develop a thermomechanical 3D transient model to analyze distortion, temperature history and residual stresses in a production cube fabricated by directed energy deposition using SS316L. In this paper, the process parameters have been optimized based on minimum residual stress and distortion. The developed finite element model successfully predicted the distortion. Design/methodology/approach The simulation phase consists of two thermal and mechanical models. In the thermal model, the Goldak function was utilized to apply focused laser energy. A twenty-layer wall configuration was employed to optimize manufacturing parameters, including laser power, the number of layers deposited before laser interruption, dwell time and substrate thickness. Findings Distortion levels were measured in both the x and y directions, achieving average errors of 4.07% and 12.32%, respectively. It was observed that the impact of the number of deposited layers, when the laser was continuously operated, was minimal. Furthermore, a modification of 67% in substrate thickness resulted in a notable 33% decrease in residual stresses. Additionally, the interaction between substrate thickness and laser power demonstrated the most significant influence on the reduction of residual stresses. The outcomes derived from the optimization utilizing the full factorial method demonstrated a 52% improvement in the average distortion of the final component. Originality/value The exploration of the concurrent influence of the specified parameters, coupled with the application of statistical optimization techniques aimed at minimizing residual stress and distortion within the proposed model, exemplifies the innovative aspects of this research.

Effects of the substrate thickness and chip area on the light extraction efficiency of chip-scale liquid cup encapsulated AlGaN-Based deep-ultraviolet light-emitting diodes

This paper presents a compact two-port MIMO antenna designed for 0.1—1 THz applications. The antenna features a multi-stage notched microstrip patch, fed by a 50-ohm line with a 0.02 mm feed width, built on a polyimide substrate (thickness: 0.04mm, εr=4.3, loss tangent=0.004). With a footprint of $$0.4\times 0.79$$ mm2, it resonates at 0.372 THz and 0.762 THz, offering bandwidths of 20 GHz and 60 GHz. Simulations using HFSS v15 show return losses of –30.73 dB and –31.76 dB, VSWRs of 1.06 and 1.05, and high gains of 5.00 dBi and 13.30 dBi. The design ensures strong isolation (ECC<0.02), making it suitable for compact, high-gain THz MIMO systems.

This study focuses on analyzing the characteristics of a microlens array produced by 3D diffusion lithography and the characteristics of the optical system based on the arrangement of the lenses. The microlens array, with an 85 μm pitch, 2.1 mm focal length, and 1 μm sag, was designed to match the numerical aperture of a 10×, 0.25 NA objective lens. Photoresist, aluminum, and photoresist layers were deposited onto a silicon substrate. After patterning with a photomask, the aluminum layer was etched to form a metal mask for subsequent diffusion lithography. The use of a metal mask improved the uniformity of the mold of the microlens array. A microlens array was replicated using polydimethylsiloxane, and the characteristics of this lens were very close to the design values, with an average pitch of 86.02 μm, sag of 1.078 μm, and substrate thickness of 1.067 mm. In addition, the Strehl ratio had a median value of 0.975, indicating excellent performance. The microlens array was integrated into two configurations: plenoptic camera module 1, in which the microlens array was directly attached to the sensor, and plenoptic camera module 2, in which it was mounted separately. A comparative analysis of the spatial resolution and depth of field of both modules revealed that both configurations achieved the same spatial resolution of 7.8 μm. However, plenoptic camera module 2 provided a wider depth of field than plenoptic camera module 1, allowing for clear imaging over a broader depth range.

Modern semiconductor device technology expands to new application fields and increasing integrability even to hybrid system approaches. Thus, membrane technologies emerge to be a new standard for light-emitting devices as well. However, the fabrication of membranes often results in a shift of the emission wavelength of the active region compared to the as-deposited structure, especially when containing quantum dots (QDs). In this study, we investigate the wavelength shift of an AlGaInP heterostructure with InP QDs during the GaAs substrate removal step. For this, the substrate of a fivefold InP QD layer is selectively etched in such a way that a single sample provides areas with different remaining substrate thicknesses in a range within 1 μm. With photoluminescence measurements, a continuous blueshift of the emission spectrum of the QD ensemble can be observed. We explain these findings by the change of the strain within the entire structure, which impacts the confinement energies within the QDs.

ABSTRACTWe present a wideband curved patch antenna with direct coplanar microstrip feeding. The patch substrate is derived from a solid of revolution generated using a parabolic profile that rests on a planar substrate. The proposed antenna takes advantage of the local increase in substrate thickness in the patch region to improve the reflection coefficient bandwidth. This design reduces substrate losses in comparison with conventional patch antennas printed on a thick dielectric substrate (key for bandwidth improvement). Indeed, in our case, the thick (curved) substrate is limited to the patch region, whereas the surrounding substrate can be made as thin as necessary, depending on the operating frequency, dielectric permittivity, and loss tangent. The presented configuration exhibits a reflection coefficient bandwidth of 32%, increasing the bandwidth of state‐of‐the‐art patch antennas fed by coplanar microstrip lines by over 50%. The achieved operating bandwidth is even comparable to that of several coaxial probe‐fed configurations, which, although undesirable for integrated implementations, typically offer a larger bandwidth due to greater flexibility in accessing the optimal feeding point, as seen in stacked and suspended‐substrate patch antennas. The proposed configuration represents a significant advancement for patch antennas suitable for integrated implementation and intended as elements in planar arrays with direct coplanar microstrip feeding.

Substrate thickness variation on the frequency response of microstrip antenna for mm-wave application

Microstrip patch antennas are extensively utilized in modern communication systems because of their small size and simple fabrication process. Among the different patch geometries, triangular patches offer size reduction compared to their rectangular and circular counterparts, making them suitable for space-constrained applications. This study focuses on the design and analysis of an equilateral triangular microstrip antenna (ETMSA) using proximity coupled feed with a triangular slot, targeting optimal performance at 2.2 GHz. The antenna is constructed using two FR4 substrates of identical permittivity but different thicknesses (h1 and h2), with a 50-ohm microstrip line feed positioned between them. The aim is to determine the optimal values of patch surface area, slot dimensions, and upper substrate thickness to achieve maximum bandwidth, minimal return loss, and ideal voltage standing wave ratio (VSWR). Simulations and measurements confirm that the antenna achieves a 120 MHz bandwidth achieving a return loss of –42 dB and a VSWR of 1.03, demonstrating excellent agreement. These results confirm the antenna's effectiveness for fixed-beam applications in wireless communication systems, highlighting its potential for efficient and compact antenna solutions.

Abstract In this study, a compact and cost-effective Frequency Selective Surface (FSS) unit cell absorber is proposed to mitigate electromagnetic interference in the sub-6 GHz 5G bands, specifically targeting the n77 (3.3–4.2 GHz), n78 (3.3–3.8 GHz), and n79 (4.4–5.0 GHz) frequency ranges. The absorber structure, fabricated on an FR-4 substrate, was designed through a systematic geometric optimization of patch dimensions and substrate thickness to enhance absorption performance via inductive-capacitive resonance tuning. Simulation and experimental results show strong agreement, with a maximum absorption rate of 98% at 4.2 GHz and over 80% absorption between 3.5 GHz and 4.7 GHz. The structure also demonstrates robust angular stability up to 60°, making it suitable for practical applications requiring directional reliability. Compared to existing designs, the proposed FSS absorber offers superior absorption efficiency, simpler fabrication, and enhanced angular resilience. This work contributes a practical and validated solution for targeted EMI suppression in 5G-enabled electronic systems.

Abstract Hybrid SAC-LTS solder joints are widely adopted in SMT processes due to their ability to lower reflow temperatures, thereby limiting package warpage and improving reliability. However, accurately predicting their thermomechanical performance remains challenging due to the complex relation between dynamic Bi diffusion during thermal exposure and paste-to-ball volume ratio, as well as the effects of package design parameters such as die size, die thickness, substrate and PCB thickness. Prior FEA models attempted to capture Bi diffusion effects but often oversimplified Bi diffused layer geometries or did not capture plasticity while modeling those layers. Moreover, the influence of key package design parameters was not explored. This study refines FEA modeling by incorporating curved Bi diffusion layers and a viscoplastic Anand model to better represent their mechanical behavior. It evaluates the effects of paste-to-ball volume ratio, die size, die thickness, PCB thickness, and component substrate thickness on plastic work accumulation in the critical solder joints, enabling a more precise thermal fatigue life (TFL) assessment. Results confirm that curved Bi diffusion layers can effectively capture plastic work distributions and failure locations. Also, it was found that a paste-to-ball volume ratio of 0.50 maximizes TFL - which aligns with a prior experimental study. Moreover, the study reveals that die size and thickness are dominant factors in TFL. These findings refine the approach of the reliability assessments of hybrid SAC-LTS solder joints using FEA and provide insights for optimizing next-generation packaging solutions with hybrid joints.

This paper presents the research and development results of circularly polarised antennas used in radio frequency identification (RFID) systems. Such antennas play a crucial role in improving reliability, orientation independence and reading range of RFID systems in industry, transport and logistics. The frequency range under consideration is 860-900 MHz (UHF), which is widely used for passive RFID technologies due to its favorable propagation characteristics and compatibility with international standards. A printed antenna from FEIG ELECTRONIC GmbH (Germany) was used as a reference for the developed antenna. This paper presents the results of a similar antenna but without the use of a symmetry transformer. The elimination of this component reduces the overall design complexity, improves manufacturability and minimizes manufacturing cost, making the design more suitable for mass deployment. The printed dipole was developed on a 1.6 mm thick FR4 substrate with a relative dielectric constant of 4.3 and a dielectric loss tangent of 0.02. The dimensions of the developed printed dipole correspond to 332 mm × 34 mm × 1.6 mm. The printed dipole and the overall design of the developed RFID antenna were pre-simulated in the software environment “CST Studio Suite”, which allows accurate simulation of the electromagnetic behavior. This modelling step was necessary to optimize the input matching, radiation efficiency and circular polarization characteristics. The frequency of the designed antenna was 868 MHz (|S11| < -10 dB). and the radiated power was measured to be -11.7 dBm. The layout of the printed dipole was designed using Altium Designer software. The prototype assembly proceeded following model-based and electromagnetic simulation techniques. A Spectrum Rider FPH spectrum analyzer conducted test measurements which supported the theoretical prediction results. The proposed framework demonstrates great promise as an inexpensive solution with high detection efficiency for modern RFID systems operating in diverse conditions.

Over the past few years, naturally sourced bioactive molecules have drawn increased attention for their antioxidant capacity and wide-ranging health effects. At the same time, interest in eco-friendly extraction approaches has risen sharply. Atmospheric Room Temperature Plasma (ARTP), a novel non-thermal pretreatment method, has emerged as a promising green technology due to its minimal environmental impact, cost-effectiveness, and superior extraction efficiency compared to conventional methods. In this study, ARTP pretreatment—optimized across variables such as treatment distance, substrate thickness, power, nitrogen flow, and duration—was combined with ultrasonic-assisted extraction to enhance the recovery of bioactive compounds from Moringa oleifera leaves. Both techniques were optimized using Response Surface Methodology (RSM). Under optimal conditions, the extract yielded a total polyphenol content of approximately 40 mg gallic acid equivalents per gram of dry weight. Antioxidant activity, assessed via ferric-reducing antioxidant power (FRAP) and DPPH radical scavenging assays, reached ~280 and ~113 μmol ascorbic acid equivalents per gram dry weight, respectively, and the ascorbic acid content was ~5.3 mg/g. These findings highlight the potential of ARTP as an effective and sustainable pretreatment method for producing high-value phytochemical extracts, with promising applications in the food, pharmaceutical, and cosmetic industries.

To improve the ballistic resistance of hydrogen storage tank-grade 316L austenitic stainless steel (ASS) plates that are prone to shear plugging failure under blunt projectile impact, this study proposes a non-bonded bilayer protective configuration: covering the 316L ASS substrate with a thin front layer of 2024-T351 aluminum alloy (AA) plate. Ballistic impact tests were performed on monolithic 5 mm thick 316L ASS plates and bilayer targets composed of a 2.05 mm thick 2024-T351 AA plate and a 5 mm thick 316L ASS substrate (total thickness: 7.05 mm), using a single-stage light gas gun combined with high-speed photography. Parallel explicit dynamics models were established using ABAQUS/Explicit, incorporating a modified Johnson–Cook constitutive model and a Lode-dependent Modified Mohr–Coulomb (MMC) fracture criterion, thereby enabling rigorous mutual validation between experimental results and numerical simulations. Results demonstrate that the addition of a mere 2.05 mm thick aluminum alloy front layer significantly enhances the ballistic limit velocity (BLV) of the 5 mm thick 316L stainless steel target plate, increasing it from 167.5 m/s to 250.7 m/s. The enhancement mechanism is closely related to the transition in the failure mode from localized shear plugging to a combination of bulging, dishing, and plugging. This shift substantially improves the structure’s overall plastic deformation capacity and energy dissipation efficiency. This research provides an effective solution and establishes a reliable experimental–numerical benchmark for the lightweight, impact-resistant design of hydrogen storage tanks.

The research studied ZnO thin films containing 3 at.% sulphur (S) on silicon (1 μm) through Geant4 simulations for radiation analysis. Analysis of ZnO thin films (400 nm) doped with 3 at.% sulphur (S) on a 1 μm thick silicon substrate through Monte Carlo simulation platform Geant4 considered energy absorption together with particle penetration depth and ionization and secondary electron generation and optical property changes as the study examined different electron radiation energies from 3 keV to 10 keV. The ZnO:S layer absorbed most of the incoming electron energy in the 3-5 keV range which produced increases in defects near the surface while ionization occurred. When electrons used 9-10 keV energies they penetrated the full substrate layer which caused silicon to receive most of the energy absorption. The highest change in parameters occurred at the film-substrate junction when the energy reached 7 keV. All modeling findings demonstrated that the total absorbed energy together with secondary electron production and defect density reaching up to 10⁷ increased rapidly with electron energy acceleration. The decrease in optical properties occurs because defects exist at different depths while energy absorption takes place. Electrical and optical characteristics of ZnO:S/Si can be regulated through electron irradiation procedures according to this research. Results from this study will function as fundamentals for creating sensors and optoelectronic devices and protective coatings which operate effectively under high radiation conditions.

Mechanotransduction plays a pivotal role in shaping cellular behavior including migration, differentiation, and proliferation. To investigate this mechanism more accurately further, this study came up with a novel elastomeric substrate with a stiffness gradient using a sugar-based replica molding technique combined with a two-layer PDMS system. The efficient water solubility of candy allows easy release, creating a smooth substrate. By adjusting the substrate's thickness, the optimal effective gradient length for the study is achievable. Additionally, adjusting substrate thickness precisely controls stiffness, from very soft to hard-tissue-like rigidity. Atomic force microscopy characterization confirmed a continuous stiffness gradient on three commonly used PDMS mixtures, 1:30, 1:50, and 1:75, demonstrating the versatility of this method for fabricating and tuning substrates to mimic various tissue environments. In cellular experiments, 3T3 fibroblast cells exhibited a significant migratory response toward the 1:50/1:75 two-layer stiffness gradient, with cells migrating preferably in stiffer directions. Its cost-effectiveness, smooth surface, and ability to regulate gradient substrates with varied stiffness via different PDMS combinations are key advantages. By precisely replicating physiologically relevant mechanical microenvironments, this method advances mechanobiology research and facilitates modeling of stiffness-guided cellular behaviors, paving the way for reliable tissue engineering and regenerative medicine studies.

Two-dimensional materials provide a rich platform to explore phenomena such as emerging electronic and excitonic states, strong light-matter coupling, and new optoelectronic device concepts. The optical response of monolayers is entangled with the substrate on which they are grown or deposited on, often a two-dimensional material itself. Understanding how the properties of the two-dimensional monolayers can be tuned via the substrate is therefore essential. Here we employ angle-resolved reflectivity and photoluminescence spectroscopy on highly ordered molecular monolayers on hexagonal boron nitride (hBN) to systematically investigate the angle-dependent optical response as a function of the thickness of the hBN flake. We observe that light reflection and emission occur in a strongly directed fashion and that the direction of light reflection and emission is dictated by the hBN flake thickness. Transfer matrix simulations reproduce the experimental data and show that optical interference effects in hBN are at the origin of the angle-dependent optical properties. While our study focuses on molecular monolayers on hBN, our findings are expected to be general and relevant for any 2D material placed on top of a substrate given the ubiquitous presence of optical interferences. Our findings demonstrate the need to carefully choose substrate parameters for a given experimental geometry but also highlight opportunities in applications such as lighting technology, where the direction of light emission can be controlled via substrate thickness.