3D Printed High Performance Silver Mesh for Transparent Glass Heaters through Liquid Sacrificial Substrate Electric-Field-Driven Jet

Microwave-transparent metallic metamaterials for autonomous driving safety

Maintaining the surface transparency of protective covers using transparent heaters in extreme weather is imperative for enhancing safety in autonomous driving. However, achieving both high transmittance and low sheet resistance, two key performance indicators for transparent heaters, is inherently challenging. Here, inspired by metamaterial design, we report microwave-transparent, low-sheet-resistance heaters for automotive radars. Ultrathin (approximately one ten-thousandth of the wavelength), electrically connected metamaterials on a millimetre-thick dielectric cover provide near-unity transmission at specific frequencies within the W band (75-110 GHz), despite their metal filling ratio exceeding 70 %. These metamaterials yield the desired phase delay to adjust Fabry-Perot resonance at each target frequency. Fabricated microwave-transparent heaters exhibit exceptionally low sheet resistance (0.41 ohm/sq), thereby heating the dielectric cover above 180 °C at a nominal bias of 3 V. Defrosting tests demonstrate their thermal capability to swiftly remove thin ice layers in sub-zero temperatures.

Bandgap reduction and efficiency enhancement in Cs2AgBiBr6 double perovskite solar cells through gallium substitution

Lead-free halide double perovskite (LFHDP) Cs2AgBiBr6 has emerged as a promising alternative to traditional lead-based perovskites (LBPs), offering notable advantages in terms of chemical stability and non-toxicity. However, the efficiency of Cs2AgBiBr6 solar cells faces challenges due to their wide bandgap (Eg). As a viable strategy to settle this problem, we consider optimization of the optical and photovoltaic properties of Cs2AgBiBr6 by Gallium (Ga) substitution. The synthesized Cs2Ag0.95Ga0.05BiBr6 is rigorously characterized by means of X-ray diffraction (XRD), UV-vis spectroscopy, and solar simulator measurements. XRD analysis reveals shifts in peak positions, indicating changes in the crystal lattice due to Ga substitution. The optical analysis demonstrates a reduction in the Eg, leading to improvement of the light absorption within the visible spectrum. Importantly, the Cs2Ag0.95Ga0.05BiBr6 solar cell exhibits enhanced performance, as evidenced by higher values of open circuit voltage (Voc), short-circuit current (Jsc), and fill factor (FF), which are 0.94 V, 6.01 mA cm-2, and 0.80, respectively: this results in an increased power conversion efficiency (PCE) from 3.51% to 4.52%. This research not only helps to overcome film formation challenges, but also enables stable Cs2Ag0.95Ga0.05BiBr6 to be established as a high-performance material for photovoltaic applications. Overall, our development contributes to the advancement of environmentally friendly solar technologies.

Flexible Embedded Metal Meshes by Sputter-Free Crack Lithography for Transparent Electrodes and Electromagnetic Interference Shielding

A facile and novel fabrication method is demonstrated for creating flexible poly(ethylene terephthalate) (PET)-embedded silver meshes using crack lithography, reactive ion etching (RIE), and reactive silver ink. The crack width and spacing in a waterborne acrylic emulsion polymer are controlled by the thickness of the polymer and the applied stress due to heating and evaporation. Our innovative fabrication technique eliminates the need for sputtering and ensures stronger adhesion of the metal meshes to the PET substrate. Crack trench depths over 5 μm and line widths under 5 μm have been achieved. As a transparent electrode, our flexible embedded Ag meshes exhibit a visible transmission of 91.3% and sheet resistance of 0.54 Ω/sq as well as 93.7% and 1.4 Ω/sq. This performance corresponds to figures of merit (σDC/σOP) of 7500 and 4070, respectively. For transparent electromagnetic interference (EMI) shielding, the metal meshes achieve a shielding efficiency (SE) of 42 dB with 91.3% visible transmission and an EMI SE of 37.4 dB with 93.7% visible transmission. We demonstrate the highest transparent electrode performance of crack lithography approaches in the literature and the highest flexible transparent EMI shielding performance of all fabrication approaches in the literature. These metal meshes may have applications in transparent electrodes, EMI shielding, solar cells, and organic light-emitting diodes.

Detection of surface defect on flexible printed circuit via guided box improvement in GA-Faster-RCNN network

Industrial defect detection is a critical aspect of production. Traditional industrial inspection algorithms often face challenges with low detection accuracy. In recent years, the adoption of deep learning algorithms, particularly Convolutional Neural Networks (CNNs), has shown remarkable success in the field of computer vision. Our research primarily focused on developing a defect detection algorithm for the surface of Flexible Printed Circuit (FPC) boards. To address the challenges of detecting small objects and objects with extreme aspect ratios in FPC defect detection for surface, we proposed a guided box improvement approach based on the GA-Faster-RCNN network. This approach involves refining bounding box predictions to enhance the precision and efficiency of defect detection in Faster-RCNN network. Through experiments, we verified that our designed GA-Faster-RCNN network achieved an impressive accuracy rate of 91.1%, representing an 8.5% improvement in detection accuracy compared to the baseline model.

Omnidirectional Printing of PEDOT:PSS for High-Conductivity Spanning Structures

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), a prominent conducting polymer, holds significance in both industry and academia. However, prevailing fabrication techniques struggle to build spanning features of PEDOT:PSS with both high electrical conductivity and fine resolution due to layerwise assembly in the xy plane. Here, we report an "omnidirectional printing and secondary doping" strategy to construct spanning, filamentary and out-of-plane 3D PEDOT:PSS with high conductivity. The pristine PEDOT:PSS suspension is homogeneously concentrated to form a printable ink with high solids (∼15 wt %) consisting of entangled PEDOT:PSS nanofibrils. Such ink shows a high storage modulus G' (43531 Pa) and a high yield stress τy (4325 Pa), thereby enabling omnidirectional printing. Secondary doping with sulfuric acid or other polar solvents is used to induce a synergetic process of PSS loss, conformational change, phase separation, and crystallinity enhancement in the printed structures, resulting in a remarkable enhancement of conductivity in dehydrated (65,378 S/m) and swollen (7190 S/m) states. As a proof-of-concept, 2D grids with a feature size of 15 μm and 3D overhanging arches are fabricated for high-performance transparent glass heaters and 3D interconnection, respectively. This work promises great potential for the development of advanced flexible electronics, wearable devices, and bioelectronics.

Boosting water evaporation via continuous formation of a 3D thin film through triple-level super-wicking routes

Capillary-fed thin-film evaporation via micro/nanoscale structures has attracted increasing attention for its high evaporation flux and pumpless liquid replenishment. However, maximizing thin-film evaporation has been hindered by the intrinsic trade-off between the heat flux and liquid transport. Here, we designed and fabricated nanostructured micro-steam volcanoes on copper surfaces featuring triple-level super-wicking routes to overcome this trade-off and boost water evaporation. The triple-level super-wicking routes enable the continuous formation of a 3D thin film for highly efficient evaporation by continuous self-driven liquid replenishment and extending the thin-film region. The micro-steam volcanoes increased the surface area by 225%, improving the evaporation rate by 141%, with a rapid self-pumping water transport speed up to 80 mm s-1. A remarkable solar-driven water evaporation rate of 3.33 kg m-2 h-1 under one sun vertical incidence was achieved, which is among the highest reported values for metal-based evaporators. When attached to electric-heating plates, the evaporator realized an electrothermal evaporation rate of 12.13 kg m-2 h-1. Moreover, it can also be used for evaporative cooling with enhanced convective heat transfer, reaching a 36.2 °C temperature reduction on a heat source with a heat flux of 6 W cm-2. This study promises a general strategy for designing thin-film evaporators with high efficiencies, low costs, and multi-functional compatibilities.

Development and Optimization of 3D-Printed Flexible Electronic Coatings: A New Generation of Smart Heating Fabrics for Automobile Applications

Textile-based Joule heaters in combination with multifunctional materials, fabrication tactics, and optimized designs have changed the paradigm of futuristic intelligent clothing systems, particularly in the automobile field. In the design of heating systems integrated into a car seat, conductive coatings via 3D printing are expected to have further benefits over conventional rigid electrical elements such as a tailored shape and increased comfort, feasibility, stretchability, and compactness. In this regard, we report on a novel heating technique for car seat fabrics based on the use of smart conductive coatings. For easier processes and integration, an extrusion 3D printer is employed to achieve multilayered thin films coated on the surface of the fabric substrate. The developed heater device consists of two principal copper electrodes (so-called power buses) and three identical heating resistors made of carbon composites. Connections between the copper power bus and the carbon resistors are made by means of sub-divide the electrodes, which is critical for electrical-thermal coupling. Finite element models (FEM) are developed to predict the heating behavior of the tested substrates under different designs. It is pointed out that the most optimized design solves important drawbacks of the initial design in terms of temperature regularity and overheating. Full characterizations of the electrical and thermal properties, together with morphological analyses via SEM images, are conducted on different coated samples, making it possible to identify the relevant physical parameters of the materials as well as confirm the printing quality. It is discovered through a combination of FEM and experimental evaluations that the printed coating patterns have a crucial impact on the energy conversion and heating performance. Our first prototype, thanks to many design optimizations, entirely meets the specifications required by the automobile industry. Accordingly, multifunctional materials together with printing technology could offer an efficient heating method for the smart textile industry with significantly improved comfort for both the designer and user.

Custom-Shaped Carbon Xerogel Materials by 3D Printing

Sol–gel-based carbon xerogels possess very promising properties for pollution abatement, using processes that associate adsorption and on-site electrochemical oxidation. However, combining a high exterior surface area (for efficient diffusion) and a monolithic shape (necessary for electrochemical processes) poses challenges. In this work, the shape of monolithic carbon xerogels was contrived by the use of 3D-printed molds. Several parameters were optimized: the choice of mold design, the choice of plastic, the 3D printer parameters, the solvent, and the process of dissolving the plastic. A design combining fine sticks and plates made of ABS was printed; a sol–gel carbon xerogel monolith was synthesized in it, and the mold was removed by using a combination of acetone and pyrolysis. Dissolving the plastic could be carried out by placing the material on a metallic net and leaving the dissolved ABS to settle. The resulting carbon material exhibits a high exterior surface area and good strength, leading to potential uses in the aforementioned process. The research shows that 3D printing is an efficient method of parameter optimization in pre-industrialization research, thanks to its flexibility, low cost, and ease of use.

Improvement of the Geometric Accuracy for Microstructures by Projection Stereolithography Additive Manufacturing

Projection stereolithography creates 3D structures by projecting patterns onto the surface of a photosensitive material layer by layer. Benefiting from high efficiency and resolution, projection stereolithography 3D printing has been widely used to fabricate microstructures. To improve the geometric accuracy of projection stereolithography 3D printing for microstructures, a compensation method based on structure optimization is proposed according to mathematical analysis and simulation tests. The performance of the proposed compensation method is verified both by the simulation and the 3D printing experiments. The results indicate that the proposed compensation method is able to significantly improve the shape accuracy and reduce the error of the feature size. The proposed compensation method is also proved to improve the dimension accuracy by 21.7%, 16.5% and 19.6% for the circular, square and triangular bosses respectively. While the improvements on the dimension accuracy by 16%, 17.6% and 13.8% for the circular, square and triangular holes are achieved with the proposed compensation method. This work is expected to provide a method to improve the geometric accuracy for 3D printing microstructures by projection stereolithography.

In Situ Growth of a Metal-Organic Framework on Graphene Oxide for the Chemo-Photothermal Therapy of Bacterial Infection in Bone Repair

Bacterial infection with high morbidity (>30%) seriously affects the defect's healing after bone transplantation. To this end, chemotherapy and photothermal therapy have been utilized for antibacterial treatment owing to their high selectivity and minimal toxicity. However, they also face several dilemmas. For example, bacterial biofilms prevented the penetration of antibacterial agents and local temperatures (over 70 °C) caused by the photothermal therapy damaged normal tissue. Herein, a co-dispersion nanosystem with chemo-photothermal function was constructed via the in situ growth of zeolitic imidazolate framework-8 (ZIF-8) on graphene oxide (GO) nanosheets. In this nanosystem, GO generates a local temperature (∼50 °C) to increase the permeability of a bacterial biofilm under near-infrared laser irradiation. Then, Zn ions released by ZIF-8 seized this chance to react with the bacterial membrane and inactivate it, thus realizing efficient sterilization in a low-temperature environment. This antibacterial system was incorporated into a poly-l-lactic acid scaffold for bone repair. Results showed that the scaffold showed a high antibacterial rate of 85% against both Escherichia coli and Staphylococcus aureus. In vitro cell tests showed that the scaffold promoted cell proliferation.

Microstructure and Corrosion Behavior of Iron Based Biocomposites Prepared by Laser Additive Manufacturing

Iron (Fe) has attracted great attention as bone repair material owing to its favorable biocompatibility and mechanical properties. However, it degrades too slowly since the corrosion product layer prohibits the contact between the Fe matrix and body fluid. In this work, zinc sulfide (ZnS) was introduced into Fe bone implant manufactured using laser additive manufacturing technique. The incorporated ZnS underwent a disproportionation reaction and formed S-containing species, which was able to change the film properties including the semiconductivity, doping concentration, and film dissolution. As a result, it promoted the collapse of the passive film and accelerated the degradation rate of Fe matrix. Immersion tests proved that the Fe matrix experienced severe pitting corrosion with heavy corrosion product. Besides, the in vitro cell testing showed that Fe/ZnS possessed acceptable cell viabilities. This work indicated that Fe/ZnS biocomposite acted as a promising candidate for bone repair material.