In Case You Missed It
Characteristic Impedance
“Identifying and Modeling Resonance-Related Fluctuations on the Experimental Characteristic Impedance for PCB and On-Chip Transmission Lines”
Authors: Yojanes Rodríguez-Velásquez, et. al.
Abstract: It is well known that the fluctuations in experimentally obtained characteristic impedance versus frequency curves are associated with resonances originated by standing waves bouncing back and forth between the transitions at the transmission line terminations. In fact, microwave engineers are aware of the difficulty to completely remove the parasitic effect of these transitions, which makes obtaining smooth and physically expected frequency-dependent curves for the characteristic impedance a tough task. Here, the authors point out for the first time that these curves exhibit additional fluctuations within the microwave range due to standing waves taking place within the transition itself. Experimental verification was carried out by extracting this fundamental parameter from measurements performed on on-chip and printed circuit board (PCB) lines using probe pad adapters and coaxial connectors. The authors demonstrate that the lumped circuit approach to represent the transitions lacks validity when the additional fluctuations due to the connectors become apparent, and they propose a new model including transmission line effects within the transition. (Electronics, July 2023, https://doi.org/10.3390/electronics12132994)
Solder Fatigue
“Low-Cycle Fatigue Life Assessment of SAC Solder Alloy Through a FEM-Data Driven Machine Learning Approach”
Authors: Vicente-Segundo Ruiz-Jacinto, et. al.
Abstract: This paper aims to present the novel stacked machine learning approach (SMLA) to estimate low-cycle fatigue (LCF) life of SAC 305 solder across structural parts. Using the finite element simulation (FEM) and continuous damage mechanics (CDM) model, a fatigue life database is built. The stacked machine learning (ML) model’s iterative optimization during training enables precise fatigue predictions (2.41% root mean square error [RMSE], R2 = 0.975) for diverse structural components. Outliers are found in regression analysis, indicating potential overestimation for thickness transition specimens with extended lifetimes and underestimation for open-hole specimens. Correlations between fatigue life, stress factors, nominal stress and temperature are unveiled, enriching comprehension of LCF, thus enhancing solder behavior predictions. (Soldering & Surface Mount Technology, September 2023, https://doi.org/10.1108/SSMT-08-2023-0045)
Sustainability
“Functional Composites by Programming Entropy-Driven Nanosheet Growth”
Authors: Emma Vargo, et. al.
Abstract: Nanomaterials must be systematically designed to be technologically viable. Driven by optimizing intermolecular interactions, current designs are too rigid to plug in new chemical functionalities and cannot mitigate condition differences during integration. Despite extensive optimization of building blocks and treatments, accessing nanostructures with the required feature sizes and chemistries is difficult. Programming their growth across the nano-to-macro hierarchy also remains challenging, if not impossible. To address these limitations, researchers should shift to entropy-driven assemblies to gain design flexibility, as seen in high-entropy alloys, and program nanomaterial growth to kinetically match target feature sizes to the mobility of the system during processing. Here, following a micro-then-nano growth sequence in ternary composite blends composed of block-copolymer-based supramolecules, small molecules and nanoparticles, the authors successfully fabricate high-performance barrier materials composed of more than 200 stacked nanosheets (125nm sheet thickness) with a defect density less than 0.056μm−2 and about 98% efficiency in controlling the defect type. Contrary to common perception, polymer-chain entanglements are advantageous to realize long-range order, accelerate the fabrication process (<30 min.) and satisfy specific requirements to advance multilayered film technology. This study showcases the feasibility, necessity and unlimited opportunities to transform laboratory nanoscience into nanotechnology through systems engineering of self-assembly. (Nature, November 2023, https://doi.org/10.1038/s41586-023-06660-x)
Thermal Transistors
“Electrically Gated Molecular Thermal Switch”
Authors: Man Li, et. al.
Abstract: Controlling heat flow is a key challenge for applications ranging from thermal management in electronics to energy systems, industrial processing and thermal therapy. Progress has generally been limited, however, by slow response times and low tunability in thermal conductance. In this work, the authors demonstrate an electronically gated solid-state thermal switch using self-assembled molecular junctions to achieve excellent performance at room temperature. In this three-terminal device, heat flow is continuously and reversibly modulated by an electric field through carefully controlled chemical bonding and charge distributions within the molecular interface. The devices have ultrahigh switching speeds above 1MHz, have on/off ratios in thermal conductance greater than 1300%, and can be switched more than 1 million times. The authors anticipate that these advances will generate opportunities in molecular engineering for thermal management systems and thermal circuit design. (Science, Nov. 2, 2023, https://www.science.org/doi/10.1126/science.abo4297) 
