Front Side Research Articles

An Ultra‐Thin Dual‐Polarized Bandpass Frequency Selective Surface for 2.45‐/5.8‐GHz ISM Bands

ABSTRACTThis paper presents the design of a single‐layer, double‐sided frequency selective surface (FSS) with bandpass characteristics at the S‐band (2.45 GHz) and C band (5.8 GHz) for sub‐6‐GHz Industrial Scientific and Medical (ISM) bands. The proposed FSS is based on the concept of complementary FSS that produces additional resonant modes. The FSS is constructed using an ultra‐thin microwave laminate with a thickness of 0.00076λeff calculated at the C‐band. The solid patch on the front side of the FSS unit cell is composed of an octagonal ring connected to four spiral arms while the slotted region on the rear side is complementary to the geometry on the front side. The unit cell size of the proposed FSS element is 0.087λeff × 0.087λeff. The FSS has an ultra‐low profile with at least 40% size reduction compared to the state‐of‐the‐art. The FSS element offers 11.12% (288 MHz) and 11.45% (650 MHz) at 2.45 GHz and 5.8 GHz, respectively, at x‐polarization while 5.8% (142 MHz) and 5.9% (342 MHz) bandwidth in the y‐polarization. The FSS element has a rotational symmetric structure offering enhanced polarization stability and angular independent operation for oblique incidences up to 80°. Furthermore, FSS operation is stable, which is evaluated and presented. The prototype bandpass FSS is fabricated, and the simulation results are validated in real‐time using experiments.

Regulation of Wide Bandgap Perovskite by Rubidium Thiocyanate for Efficient Silicon/Perovskite Tandem Solar Cells.

Developing high-quality wide bandgap (WBG) perovskites with ≈1.7eV bandgap (Eg) is critical to couple with silicon and create efficient silicon/perovskite tandem devices. The sufferings of large open-circuit voltage (VOC) loss and unstable power output under operation continuously highlight the criticality to fully develop high-quality WBG perovskite films. In this study, rubidium and thiocyanate as additive regulators in WBG perovskites are incorporated, significantly reducing non-radiative recombination, ion-migration, and phase segregation. The optimized 1.66 eV Eg perovskite solar cells achieved state-of-art 1.3V VOC (0.36V deficit), and delivered a stabilized power conversion efficiency of 24.3%, along with good device stability (20% degradation (T80) after over 994h of operation under 1 sun at ≈65°C). When integrated with a flat front side silicon cell, silicon/perovskite two-terminal tandem device (30% efficient) is obtained with a 1.97V VOC, and T90 operational lifetime of more than 600h at room temperature.

A novel multifunctional chiral metasurface with asymmetric transmission

The multiband, multifunctional chiral metasurface with asymmetric transmission exhibits significant potential for diverse applications in modern communication systems, ranging from enhanced signal modulation and polarization control to advanced beam steering and compact antenna design. This research presents a versatile and advanced chiral metasurface operating at multiple bands with diverse functionalities, including asymmetric transmission. The proposed metasurface effectively transforms an incoming Linearly Polarized (LP) wave into a Circularly Polarized (CP) wave. Additionally, it functions as a 90° polarization rotator for the incident LP wave. The design starts with an element of a 2 × 2 supercell comprising a Square Split Ring Resonator (SSRR) and an I-shaped resonator. The right diagonal elements of a supercell undergo scaling down, giving rise to a rotational asymmetry. Chirality is introduced into the design, and cross polarization conversion is enhanced by rotating all four elements by 90° relative to each other. On the back side of the substrate, each element undergoes a 90° rotation compared to its counterpart on the front side, realizing the asymmetric transmission feature. The incorporation of multiband and multifunctional features within a single supercell equips the subject chiral metasurface to be utilized in various engineering applications.

Pixelation method for the FARCOS array

A pixelation method addresses the challenge of accurately assigning coordinates to each particle that impinges on the detector area. The pixelation method used for the analysis of the data acquired with Double-Sided Silicon Strip Detectors of the Femtoscope ARray for COrrelations and Spectroscopy FARCOS is described here. The application of the pixelation method requires several tasks to be performed. First, the coincidence in the detection time of the particles of front and back signals allows the elimination of spurious events. The second fundamental operation is the recovery of inter-strip events obtained comparing the energies of detected front and back side signals in all possible configurations. Two-alpha coincidences are analysed and the 8Beg.s. resonance is observed to compare the energy resolution of recovered inter-strip events with that of single-strip events. Using this pixelation method, a 41 ± 8% improvement in the efficiency of detecting three-alpha particles was achieved.

Addressing the efficiency loss and degradation of triple cation perovskite solar cells via integrated light managing encapsulation

Here, we present a holistic encapsulation method for perovskite solar cells to address both optical performance losses at the air-cell interface as well as intrinsic and extrinsic stability challenges. Our one-step method provides shielding to PSCs from oxygen and moisture-induced degradation as well as in situ patterning for light management. As a result of embedding the antireflective coating onto the front side of the cell, the power conversion efficiency (PCE) of the PSCs was increased from 14.1 ± 0.8 % to 15.6 ± 0.8 %, indicating an 8 % relative improvement. Moreover, the encapsulated devices kept their initial performance after 90 % relative humidity and water immersion tests. The outdoor exposure test showed no degradation for the encapsulated cells after 24 h of resting at −17 °C and maximum wind speeds of 7 m/s on average. Additionally, the encapsulation strategy was instrumental in mitigating oxygen and humidity-induced degradation during ISOS-LC tests, retaining up to 80 % of the initial performance for the encapsulated devices after 360 h. This research establishes in situ encapsulation and patterning as a promising solution for reducing optical losses and extrinsic instabilities in PSCs. The choice of flexible encapsulant enables it to be used for both rigid and flexible PSCs in a wide range of applications.

Poly(l-lactic acid) Janus Shape Memory Membranes with Uniform Vertically Penetrative Channels and Slit Pores for Enhanced Fog Collection: Synergistic Effect of Transport through Membranes and Sequential Sliding Behaviors of Water Droplets.

In this work, poly(l-lactic acid) (PLLA) Janus shape memory membranes with uniform vertically penetrative channels (SMEUVs) with slit pores have been fabricated with the help of template-assisting spray-coating and uniaxial tension at high temperature. During fog collection, superhydrophobic and hydrophilic surfaces act as the front (fog-facing) side and back side, respectively, in which the structural characteristics play essential roles. On one hand, the vertically penetrative channels in SMEUVs and the special pore geometry contribute to lower resistance, accelerating the transport of captured water through membranes (from the superhydrophobic side to the hydrophilic side). On the other hand, the movement of water droplets along the back side has been guided by the oriented structures of slit pores, promoting the detachment of droplets from the hydrophilic surface. Their synergistic effect removes captured water in a timely manner and provides fresh sites for the subsequent nucleation of water, enhancing fog collection performance. As a result, the optimal specimen (Janus SMEUVs with a draw ratio of 2.5, placed in the parallel direction) exhibits a much higher water collection rate (∼6×) relative to references (superhydrophobic and hydrophilic membranes). Our results are significant for sustainable development in view of both fog collection in arid regions and the biodegradability of PLLA.

Effects of electron beam and atomic oxygen irradiation on hypervelocity - Impact tested / polyimide coated carbon fiber-reinforced plates

In a low-Earth orbit, space debris orbit at approximately the first cosmic velocity. When space debris strike a spacecraft, ejecta (fragments) from the spacecraft are widely scattered. The reduction in the number of ejecta (fragments caused by impact) must also be considered when selecting spacecraft materials. The authors’ group has previously examined the size of ejecta (fragments) and reduction in the number of ejecta. In general, the mechanical properties of polymer materials and CFRP plates may be damaged by space environments, such as radiation (gamma rays and electron beams (EBs)), atomic oxygen (AO), ultraviolet rays, temperature, and thermal cycling. The authors suggested an anti-AO coating/polyimide CFRP as a material resistant to space environments. The effects of EB and AO irradiation on the fracture behavior and ejecta of anti-AO coating/polyimide CFRP were examined for hypervelocity impacts. The results of static three-point flexural tests were compared with the fracture behavior and ejecta. A two-stage light-gas gun was used for the impact tests. Spherical projectiles formed of aluminum alloy 2017-T4 with a diameter of 1.6 mm were used. Photographs of the ejecta scattered in front of each polyimide CFRP plate were captured from the side using a high-speed video camera. The number and weight of the ejecta on the front side and perforation holes were examined.

Evaluation of Concrete Fatigue Damage with Elastic Wave-based Measurement Techniques

Fatigue damage is a progressive and permanent change in the internal material structure due to cyclic loading. The cyclic loads can be due to wind, waves, temperature variation, and traffic loads. Each cyclic load application introduces micro-damages that accumulate to induce failure. Detecting these micro-damages requires sensitive measuring techniques. Hence this research compares the sensitivity of different measuring techniques applied to fatigue experiments of concrete. The applied NDT are the passive acoustic emission technique (AET) and active ultrasonic measurements. In addition, linear variable differential transformers (LVDTs) are applied as a reference measurement. Accordingly in this research, cylindrical concrete samples are subjected to monotonic and cyclic Brazilian splitting tests. The cylinders are 100 mm in diameter and 150 mm in length. The cyclic load is applied to these samples with a loading frequency of 5 Hz. During the tests, the damage evolution is monitored with AET, ultrasonic measurements and LVDTs. There are eight AE sensors attached to the sample. The two LVDTs are positioned at the center of the sample's front and back side. Besides passively monitoring the acoustic emissions, the AET sensors are also used to do active ultrasonic measurements. The research reports the comparison conducted on the deformations and cracks measured with the LVDTs, the damage growth identified with the AET, and the change in the ultrasonic pulse velocity measurements. In addition, the study also presents the damage analysis capacity of the methods across different types of loading: monotonic, constant amplitude, and stepped fatigue loading. The comparison shows that combination of AET and ultrasonic velocity measurement is a sensitive indicator for damage growth.

Effect of Gasket Wear Rate on Hydraulic Performance and Internal Flow of Multistage Centrifugal Pump with Floating Impellers

Abstract The sealing gaskets of multistage centrifugal pumps are prone to wear during operation. This study investigates the influence of gasket wear rate on hydraulic performance and internal flow field through numerical simulations. As the wear rate of the gasket increases, both the efficiency and head coefficient of the pump gradually decrease. When the gasket is completely worn out, the efficiency decreases by 5.6% and the head coefficient decreases by 9.5% compared to the unworn gasket condition. Analysis of the internal flow field reveals that the front side chamber is most significantly affected by gasket wear. As the gasket wears, the flow velocity within the front side chamber increases gradually, and the high-entropy production zone expands, thereby affecting the hydraulic performance of the pump. The findings of this study provide practical engineering insights for enhancing the operational performance of multistage centrifugal pumps.

High performance Bi-facial dye sensitized solar cells developed using MXenes assisted novel photoelectrode design

A new device architecture of bi-facial dye sensitized solar cell (DSSC) is designed, fabricated by use of novel photoelectrode design contains MXenes. The developed bi-facial DSSC witnessed higher power conversion efficiency (PCE) of 12.82 % with short-circuit current density (JSC) of 27.46 mA/cm2. The DSSC revealed 9.74 % of PCE by front side illumination and 4.57 % by back side illuminations. The results motivated to develop mini-module of series connected 12 test cells, which results in 13.34 % of PCE.

Optimizing strategy of bifacial TOPCon solar cells with front-side local passivation contact realized by numerical simulation

The tunnelling oxide passivation contact (TOPCon) solar cells have been impressive in the global photovoltaic (PV) market originating from their high efficiency and stability. However, it exhibits significant recombination losses due to its boron diffusion, laser damage and metal-semiconductor contact on front side. The bifacial TOPCon structure demonstrates massive potential in the improvement of passivation and contact performance with the premise that it can solve the parasitic absorption of polycrystalline silicon (poly-Si). In this study, the localized poly finger structure with excellent optics and passivation performance is designed in the front side of bifacial solar cells to compare with traditional TOPCon and full-area poly passivation devices. The theoretical efficiency and detailed power loss analysis in our simulation reveal that suppressing the recombination of FSF (front surface field) and the contact area is the crucial strategy to improve device performance, with optimized efficiency of 26.62 % and FF of 85.16 %. These results indicate that the route of BJ (back junction) structure containing localized selective contact and full coverage high-quality passivation holds potential in realizing both high Jsc and Voc for FBC (front and back contact) solar cells, featuring great instructive significance for future industrialization of PV production.

Design and Analysis of Wireless Power Transmission (2X1) MIMO Antenna at 5G - Frequencies for Applications of Rectenna Circuits in Biomedical

This research presents the design and analysis of a 5G harvesting energy Circuit (MIMO-rectenna) to receive wireless power at Sub-6 frequencies (5.6 GHz) as a power source for some medical devices carried by a patient and moved from one place to another, whether they are diagnostic or therapeutic devices. This concept aims (MIMO-rectenna) to increase the likelihood of obtaining electricity from the ambient field by harvesting energy at 5G- frequencies. The tiny MIMO (2x1) antenna measuring 30 by 40 mm2 is the antenna portion of this rectenna. It has been built and tested to operate at Sub-6 frequency, or 5.6 GHz, for wireless power transmission applications related to 5G technology. The MIMO antenna has parameters of E = 4.4, h = 1.6 mm, and tand = 0.025 when printed on an FR4 substrate. A significant section of the antenna's rear was removed to carry out the broadband process, and the material's front side was composed of a series of circular slits. In this antenna, the parasitic approach was employed to decrease the mutual coupling between two ports by creating an inverted T with precise dimensions. The CST software 2024 was used to assist with the design and simulation results of this MIMO antenna. It was discovered through the simulation that the mutual coupling for these ports, 𝑆12and 𝑆21, is equal to -51.476 dB, and that the S-parameters, 𝑆11, 𝑆22, equal -22 dB. That is, there is very little signal loss while switching from the first port to the second and vice versa. This antenna's rectifier comprised an AC-to-DC conversion circuit, a DC filter, and an impedance-matching network. With the use of ADS software 2024, this rectenna's design and simulation results were completed. The greatest conversion efficiency of this rectenna at the frequency of 5.6 GHz is determined to be between 65 % and 65.01% for load resistance between 12 KΩ and 15 KΩ at an input power of 14 dBm.

View Factors Approach for Bifacial Photovoltaic Array Modeling: Bifacial Gain Sensitivity Analysis

Abstract Bifacial modules are highly valued in the global photovoltaic market since they are able to receive sunlight from both sides and can generate up to 10–30% additional energy compared to monofacial ones. They are integrated into various sectors, including building and notably Agrivoltaics. In this work, a coupled optical–thermal–electrical model was developed in matlab to simulate the energy performance and bifacial gain for a ground-raised bifacial system. The model allows optimization as a function of the photovoltaic (PV) system and bifacial module characteristics. A fixed, south-facing bifacial PV arrays composed of three rows assumed installed in Agadir, Morocco, is considered. The optical model is based on an analytical determination of view factors using the cross-string rule. These enable the determination of irradiances received by both sides of modules, which are subsequently used to evaluate energy yield of the system. Model validation was carried out based on various statistical metrics by comparing our results with simulation results generated by various softwares. The comparison shows a very good agreement, notably with 3dbifacialvf (R2 = 1, root-mean-square error (RMSE) = 0.03 W/m2 and R2 = 0.96, RMSE = 12.4 W/m2) for front and rear side irradiance, respectively. The DC energy generated by the system differs by less than 1% compared to pvsyst results. Sensitivity analysis revealed that all system parameters, particularly ground albedo, positively affect the bifacial gain. The bifacial gain increased from 10.6% to 20.1% as the ground albedo increased from 0.25 to 0.5.

Unveiling the origin of metal contact failures in TOPCon solar cells through accelerated damp-heat testing

Tunnel oxide passivated contact (TOPCon) solar cells are expected to dominate the global photovoltaic market in the coming decade thanks to rapid advancements in power conversion efficiency (PCE). However, there are concerns about the reliability of TOPCon modules, particularly in hot and humid conditions. The current module-level fundamental analysis strategies for TOPCon solar cells provide too slow feedback for rapid process development. This study explores the degradation of metal contacts in TOPCon solar cells under accelerated testing conditions of 85 °C and 85 % relative humidity (DH85). The degradation was induced by two commonly used sodium-related salts, sodium bicarbonate (NaHCO3) and sodium chloride (NaCl), in the testing of the solar cells. When applied to the front side, NaHCO3 caused a ∼5%relPCE reduction after 100-h DH85 exposure, while NaCl leads to a more significant ∼92%relPCE reduction. The primary cause of degradation is a considerable increase in series resistance (Rs), likely due to electrochemical reactions within the Ag/Al paste. When the salts are applied to the rear of the TOPCon solar cell, the degradation becomes more complex. NaHCO3 increases recombination and results in a deterioration of the contact, resulting in a ∼16%relPCE reduction after 100-h DH85 testing. Conversely, NaCl primarily causes a decline in open-circuit voltage (Voc) and a ∼4%relPCE loss. This manuscript primarily investigates degradation mechanisms related on the rear side, with a focus on significant oxidation occurring at the interface between Ag and Si. These findings highlight the susceptibility of TOPCon solar cells to contact corrosion, emphasizing the electrochemical reactivity of metallisation as a potential risk for long-term TOPCon module operation. This study provides crucial insights into TOPCon cell degradation mechanisms, which are essential for optimising performance and enhancing the long-term reliability of TOPCon modules.

Effects of die top system and trenches on large thin die mechanical robustness

Abstract Power MOSFET dies in the automotive industry are becoming larger (> 5 x 5 mm) and thinner (< 50 µm) to meet high-performance and lifetime requirements. Ensuring the mechanical robustness of these large ultrathin chips is crucial for reliable electronic devices and high-throughput packaging processes. The high aspect ratio and advanced chip designs incorporating trench technology present significant challenges in semiconductor assembly, packaging, and testing. This paper introduces an experimental front-end strategy aimed at strengthening the front side of large ultrathin dies using various die-top systems. Industry-equivalent 50 µm thick dummy power MOSFET dies were fabricated to evaluate the efficacy of different chip designs and materials, such as polyimide, in mitigating fracture risks. Fabrication-induced stresses and warpage in the device layers were measured using a thin-film stress measurement tool. Additionally, the frontside strength of the ultrathin dies was assessed using the three-point bending method, with the resulting data analyzed via two-parameter Weibull distribution plots. Results demonstrated that the deposition of 5 µm polyimide (PI) on the nitride die topside significantly increased die strength from 339 MPa to 760 MPa, with 5 µm PI proving more effective for die strengthening than 10 µm. The interaction between the metal-trench layer and the die was found to be critical to the robustness of ultrathin dies, influenced by the pattern and layout of the trenches. Die-top metallization designs, such as meandering patterns, showed promising improvements in die strength compared to standard designs. A proposed chip layout aims to maximize polyimide coverage for clip-bonded products on the die topside, leveraging its strengthening effect. The study also demonstrated that dummy reference chips can facilitate rapid and straightforward evaluation of extensive design experiments to identify robust chip designs.

Exploring the reaction mechanistic pathway for the sensing of G-Series nerve agent with Kemp's triacid derivative: A computational study

Kemp's triacid derivative have been reported as a candidate for sensing of nerve agents employing the photoinduced electron transfer (PET) processes. The sensor probe molecules were prepared with primary alcohol in very close proximity to a tertiary amine to acylate the alcohol with rapid intramolecular N-alkylation to produce quaternary ammonium salt. The reaction pathways for the formation of quaternary ammonium salt and isomethyl propyl phosphonate remain unexplored. In this report, the mechanistic pathways of G-series nerve agents sarin and its simulant diethylcholorophosphate (DCP) with Kemp's triacid derivatives has been explored computationally. The calculations performed with B3LYP-D3/6-311+G(d,p) level of theory in DCM solvent revealed that the reaction proceeds via intermolecular and intramolecular SN2 pathways. The probe molecule is sterically hindered, therefore, the frontside and backside SN2 reaction pathways have been examined. The computed results suggest that the first intermolecular SN2 reaction of Kemp's triacid derivatives (I &II) with sarin for the backside attack is energetically favored compared to the frontside attack and the following intramolecular SN2 reaction is a barrierless process. The calculations performed with simulant diethylcholorophosphate (DCP) and Kemp's triacid derivatives (I &II) show that the reactions are energetically more facile compared to the nerve agent sarin molecule. The Distortion-Interaction model and ΔNBOSteric analysis showed that the back side is energetically favored over the front side attack in such SN2 reactions. The designed Kemp's triacid derivative (II) with phosphorus center for sensing sarin and (DCP) suggests that the size of the hetero centers are important to facilitate the reaction in the probe molecule.

Direct visualization of viscous dissipation and wetting ridge geometry on lubricant-infused surfaces

Drops are exceptionally mobile on lubricant-infused surfaces, yet they exhibit fundamentally different dynamics than on traditional superhydrophobic surfaces due to the formation of a wetting ridge around the drop. Despite the importance of the wetting ridge in controlling drop motion, it is unclear how it dissipates energy and changes shape during motion. Here, we use lattice Boltzmann simulations and confocal microscopy to image how the wetting ridge evolves with speed, and construct heatmaps to visualize where energy is dissipated on flat and rough lubricated surfaces. As speed increases, the wetting ridge height decreases according to a power law, and an asymmetry develops between the front and rear sides. Most of the dissipation in the lubricant ( >75%) occurs directly in front and behind the drop. The geometry of the underlying solid surface hardly affects the dissipation mechanism, implying that future designs should focus on optimizing the surface geometry to maximize lubricant retention.

Fresnel Diffraction Model for Laser Dazzling Spots of Complementary Metal Oxide Semiconductor Cameras.

Laser dazzling on complementary metal oxide semiconductor (CMOS) image sensors is an effective method in optoelectronic countermeasures. However, previous research mainly focused on the laser dazzling under far fields, with limited studies on situations that the far-field conditions were not satisfied. In this paper, we established a Fresnel diffraction model of laser dazzling on a CMOS by combining experiments and simulations. We calculated that the laser power density and the area of saturated pixels on the detector exhibit a linear relationship with a slope of 0.64 in a log-log plot. In the experiment, we found that the back side illumination (BSI-CMOS) matched the simulations, with an error margin of 3%, while the front side illumination (FSI-CMOS) slightly mismatched the simulations, with an error margin of 14%. We also found that the full-screen saturation threshold for the BSI-CMOS was 25% higher than the FSI-CMOS. Our work demonstrates the applicability of the Fresnel diffraction model for BSI-CMOS, which provides a valuable reference for studying laser dazzling.

A novel dual-band defected ground structure wearable microstrip patch antenna for breast tumor detection in biomedical applications

This paper presents a dual-band, low-profile wearable antenna for detecting breast tumors in biomedical applications. The antenna is designed on the FR4 substrate with an optimized dimension of 32 × 27.5 × 0.61 mm3. The compact rectangular patch is miniaturized by cutting the rectangular slots on the front side. The partial ground structure is used for moving the resonance frequency in the ISM band region and for giving the tripping result of the return loss. A breast phantom is created between the transmitter and receiver for detecting the tumor in the phantom model. The different sizes and positions of the tumor in the breast phantom provide different values of the return loss. The final optimized design of the antenna is operated at 2.43 GHz and 3.32 GHz with −35 and −24 return losses respectively. It has been observed from the simulated and measured results that the antenna has a negligible difference between the reflected coefficient, radiation pattern and gain. Afterward, the antenna is also checked for biocompatibility, which represents its good performance. The on-body analysis of the antenna represents a minor variation in the results. The Specific Absorption Ratio (SAR) value of the antenna is in the acceptable range as defined for the wearable device. It is a promising compact wearable antenna that can be used in biomedical applications.

Bilateral Production Shield Enabling Highly Efficient Perovskite Photovoltaics.

Enhancing the intrinsic stability of perovskite and through encapsulation to isolate water, oxygen, and UV-induced decomposition are currently common and most effective strategies in perovskite solar cells. Here, the atomic layer deposition process is employed to deposit a nanoscale (≈100nm), uniform, and dense Al2O3 film on the front side of perovskite devices, effectively isolating them from the erosion caused by water and oxygen in the humid air. Simultaneously, nanoscale (≈100nm) TiO2 films are also deposited on the glass surface to efficiently filter out the ultraviolet (UV) light in the light source, which induces degradation in perovskite. Ultimately, throughthe collaborative effects of both aspects, the stability of the devices is significantly improved under conditions of humid air and illumination. As a result, after storing the devices in ambient air for 1000h, the efficiency only declines to 95%, and even after 662h of UV exposure, the efficiency remains at 88%, far surpassing the performance of comparison devices. These results strongly indicate that the adopted Al2O3 and TiO2 thin films play a significant role in enhancing the stability of perovskite solar cells, demonstrating substantial potential for widespread industrial applications.