Search Results (6)

Substrate-free epidermal antennas promise imperceptible and long-term wearable sensing, yet their electromagnetic performance is fundamentally constrained by the properties of ultrathin conductors. In this work, gold nanomesh is employed for the first time as the radiating conductor of a substrate-free epidermal tattoo antenna operating in the UHF RFID band. Owing to its RF-thin nature, the nanomesh behavior is governed by sheet resistance rather than skin-depth effects, imposing a strict upper bound on achievable radiation efficiency. By combining surface-impedance modeling, full-wave simulations, and on-body experiments, we demonstrate that ohmic losses set a geometry-independent limit on the realized gain of on-skin antennas. An inductively coupled loop architecture is optimized to approach this bound while ensuring mechanical robustness and impedance stability. Measurements on phantoms and human subjects confirm the predicted performance limits within a few decibels, enabling reliable UHF RFID read ranges up to 30–40 cm under standard regulatory constraints. Full article

This study presents a novel approach to manufacture a rigid printed circuit board (PCB) using sustainable polymers. Current PCBs use a fossil-fuel-based substrate, like FR4. This presents recycling challenges due to its composite nature. Replacing the substrate with an environmentally friendly alternative leads to a reduction in negative impacts. Polylactic acid (PLA) and Polyhydroxybutyrate (PHB) biopolymers are used in this study. These two biopolymers have low melting points (130–180 °C, and 170–180 °C, respectively) and cannot withstand the high temperature soldering process (up to 260 °C for standard SAC (SnAgCu, tin/silver/copper) lead free solder processes). Our approach for replacing the PCB substrate is applying the PLA/PHB carrier substrate at the end of the PCB manufacturing process using injection molding technology. This approach involves all the standard PCB processes, including wet etching of the Cu conductors, and component assembly with SAC solder on a thin flexible polyimide (PI) foil with patterned Cu conductors and then overmolding the biopolymer onto the foil to create a rigid base. This study demonstrates the functionality of two test circuits fabricated using this method. In addition, we evaluated the adhesion between the biopolymer and PI to achieve a durable PCB. Moreover, we performed two different end-of-life approaches (debonding and composting) as a part of the end-of-life consideration. By incorporating biodegradable materials into PCB standard manufacturing, the CO₂ emissions and energy consumption are significantly reduced, and installation costs are lowered. Full article

Carbon nanotubes (CNTs) are well known for their outstanding field emission (FE) performance, facilitated by their unique combination of electrical, mechanical, and thermal properties. However, if the substrate of choice is a poor conductor, the electron supply towards the CNTs can be limited, restricting the FE current. Furthermore, ineffective heat dissipation can lead to emitter–substrate bond degradation, shortening the field emitters’ lifetime. Herein, temperature-stable titanium nitride (TiN) was deposited by plasma-enhanced atomic layer deposition (PEALD) on different substrate types prior to the CNT growth. A turn-on field reduction of up to 59% was found for the emitters that were generated on TiN-coated bulk substrates instead of on pristine ones. This observation was attributed exclusively to the TiN layer as no significant change in the emitter morphology could be identified. The fabrication route and, consequently, improved FE properties were transferred from bulk substrates to free-standing, electrically insulating nanomembranes. Moreover, 3D-printed, polymeric microstructures were overcoated by atomic layer deposition (ALD) employing its high conformality. The results of our approach by combining ALD with CNT growth could assist the future fabrication of highly efficient field emitters on 3D scaffold structures regardless of the substrate material. Full article

Mo(001) and Mo(011) layers with thickness d = 4–400 nm are sputter-deposited onto MgO(001) and α-Al₂O₃(11$\overline{2}$0) substrates and their resistivity is measured in situ and ex situ at room temperature and 77 K in order to quantify the resistivity size effect. Both Mo(001) and Mo(011) layers are epitaxial single crystals and exhibit a resistivity increase with decreasing d due to electron surface scattering that is well described by the classical Fuchs and Sondheimer model. Data fitting yields room temperature effective electron mean free paths λ^*= 14.4 ± 0.3 and 11.7 ± 0.3 nm, respectively, indicating an anisotropy with a smaller resistivity size effect for the Mo(011) orientation. This is attributed to a smaller average Fermi velocity component perpendicular to (011) surfaces, causing less surface scattering and a suppressed resistivity size effect. First-principles electronic structure calculations in combination with Boltzmann transport simulations predict an orientation dependent transport with a more pronounced resistivity increase for Mo(001) than Mo(011). This is in agreement with the measurements, confirming the effect of the Fermi surface shape on the thin-film resistivity. The predicted anisotropy ${\lambda }_{001}^{*}$/${\lambda }_{011}^{*}$ = 1.57 is in reasonable agreement with 1.66 and 1.23 measured at 77 and 295 K. The overall results indicate that the resistivity size effect in Mo is relatively small, with a measured product of the bulk resistivity times the effective electron mean free path ρ_oλ^* = (7.7 ± 0.3) and (6.2 ± 0.2) × 10⁻¹⁶ Ωm² for Mo(001) and Mo(011) layers. The latter value is in excellent agreement with the first-principles-predicted ρ_oλ = 5.99 × 10⁻¹⁶ Ωm² and is 10% and 40% smaller than the reported measured ρ_oλ for Cu and W, respectively, indicating the promise of Mo as an alternate conductor for narrow interconnects. Full article

Radio frequency energy harvesting (RFEH) and wireless power transfer (WPT) are increasingly seen as a method of enabling sustainable computing, as opposed to mechanical or solar EH WPT does not require special materials or resonators and can be implemented using low-cost conductors and standard semiconductor devices. This work revisits the simplest antenna design, the wire monopole to demonstrate the lowest-footprint, lowest-cost rectifying antenna (rectenna) based on a single Schottky diode. The antenna is fabricated using a single Litz-wire silk-coated thread, embroidered into a standard textile substrate. The rectifier is fabricated on a compact low-cost flexible printed circuit board (PCB) using ultra-thin polyimide copper laminates to accommodate low-footprint surface mount components. The antenna maintains its bandwidth across the 868/915 MHz license-free band on- and off-body with only −4.7 dB degradation in total efficiency in human proximity. The rectenna achieves up to 55% RF to DC efficiency with 1.8 V DC output, at 1 mW of RF power, demonstrating its suitability as a power-supply unit for ultra-low power e-textile nodes. Full article

In this study, the stress analysis of YBCO/CeO₂/YSZ/CeO₂/Ni architextured materials under cryogenic conditions was carried out for coated conductor applications. YBCO/CeO₂/YSZ/CeO₂ multilayer films were fabricated on Ni tape substrate using reel-to-reel sol-gel and Pulse Laser Deposition (PLD) systems. The microstructural evolution of high temperature superconducting YBCO film and buffer layers with CeO₂/YSZ/CeO₂ configuration grown on textured Ni tape substrates were investigated by a Scanning Electron Microscope (SEM). SEM observations revealed that crack-free, pinhole-free, continuous superconducting film and buffer layers were obtained by solgel and PLD systems. The thermal distribution in the each layer was calculated using the classical lamination theory in the temperature range of 25 to -270°C in liquid helium media. The residual stresses occurred during the manufacturing are neglected therefore, all the residual stresses are assumed to be zero at 25°C. Different thermal expansion coefficients and modulus of elasticity bring about the thermal stresses in the layers. Full article