High Ohmic Losses Research Articles

Ultra‐Wideband Terahertz Integrated Polarization Multiplexer

AbstractPolarization‐division multiplexing is crucial for increasing channel capacity and spectral efficiency in communications. A key component is the polarization multiplexer, which combines or separates signals with orthogonal polarizations. Existing planar multiplexers lack an ultrawide band for terahertz communications. While microwave‐inspired orthomode transducers (OMTs) provide broadband operation, they suffer from high ohmic loss and bulkiness at terahertz frequencies. Optical integrated polarization beam splitters (PBSs) offer low loss and good integrability but have narrow bandwidths. This work presents a substrateless all‐silicon polarization multiplexer based on tapered directional couplers and air‐silicon effective mediums, integrated monolithically on a compact footprint. The device demonstrates a 37.8% fractional bandwidth, an average insertion loss of 1 dB, and a polarization extinction ratio above 20 dB over 225–330 GHz. This superior performance is enabled by the anisotropy of the effective medium claddings, affecting the two orthogonal guided modes differently. The multiplexer enables simultaneous two‐channel terahertz fiber communications with polarization diversity. It supports aggregated data rates up to 155 and 190 Gbit with bit error rates below hard‐ and soft‐decision forward‐error‐correction limits, respectively. This advancement holds promise for 6G terahertz integrated systems with enhanced channel capacities.

Past, present, and future of hybrid plasmonic waveguides for photonics integrated circuits

This article addresses the past, present, and future status of hybrid plasmonic waveguides (HPWs). It presents a comprehensive review of HPW-based photonic integrated circuits (PICs), covering both passive and active devices, as well as potential application of on-chip HPW-based devices. HPW-based integrated circuits (HPWICs) are compatible with complementary metal oxide semiconductor technology, and their matched refractive indices enables the adaptation of existing fabrication processes for silicon-on-insulator designs. HPWs combine plasmonic and photonic waveguide components to provide strong confinement with longer propagation length Lp of HP modes with nominal losses. These HPWs are able to make a trade-off between low loss and longer Lp, which is not possible with independent plasmonic and photonic waveguide components owing to their inability to simultaneously achieve low propagation loss with rapid and effective all-optical functionality. With HPWs, it is possible to overcome challenges such as high Ohmic losses and enhance the functional performance of PICs through the use of multiple discrete components. HPWs have been employed not only to guide transverse magnetic modes but also for optical beam manipulation, wireless optical communication, filtering, computation, sensing of bending, optical signal emission, and splitting. They also have the potential to play a pivotal role in optical communication systems for quantum computing and within data centers. At present, HPW-based PICs are poised to transform wireless chip-to-chip communication, a number of areas of biomedical science, machine learning, and artificial intelligence, as well as enabling the creation of densely integrated circuits and highly compact photonic devices.

Investigating Temperature-Dependent Dynamics of SEI Growth and Battery Degradation

Several studies have contributed to the current understanding of the temperature-dependent behavior of solid-electrolyte interphase (SEI) formation in lithium-ion batteries and its impact on battery capacity and lifespan. Liu et al. developed a thermal-electrochemical model that revealed the complex interplay between diffusivity, reaction kinetics, and temperature on SEI growth1. Leng et al. presented an electrochemistry-based electrical model to examine the temperature's effect on battery aging2. Alipour et al. reviewed temperature-dependent electrochemical properties3, while Lubhani Mishra et al. provided a detailed physics-based analysis of battery degradation and temperature inhomogeneities4. These studies collectively indicate higher temperatures accelerating and promoting growth of compact and less permeable SEI structures leading to an increase in capacity loss and cell resistance, and lower temperatures resulting in slow ionic transport through the SEI also causing higher ohmic loss. In the present work, we study SEI growth and resulting effect on battery capacity fade using continuum scale modeling under the assumption of constant battery cell temperature as well as considering actual dynamically changing temperature data from experiments. SEI growth under these two considerations is compared and the comparison is used in determining scenarios where considering dynamically varying temperature is crucial for accuracy. The detailed analysis of the internal states from the simulation results contributes to the understanding of the effect of the thermal dynamics on battery cell degradation due to SEI growth. To achieve these objectives, a physics-based model, specifically the Single Particle Model (SPM), is utilized. The model uses temporal temperature data obtained from past experimental studies as well as temperature dependent properties of SEI provided in the literature as inputs for this investigation. The ultimate aim of this study is to better understand how temperature influences SEI characteristics, thereby contributing to improved battery performance and longevity across diverse thermal environments. References Liu, L., Park, J., Lin, X., Sastry, A. M., & Lu, W. (2014). A thermal-electrochemical model that gives spatial-dependent growth of solid electrolyte interphase in a Li-ion battery. Journal of power sources, 268, 482-490.Leng, F., Tan, C. M., & Pecht, M. (2015). Effect of temperature on the aging rate of Li-ion battery operating above room temperature. Scientific reports, 5(1), 12967.Alipour, M., Ziebert, C., Conte, F. V., & Kizilel, R. (2020). A review on temperature-dependent electrochemical properties, aging, and performance of lithium-ion cells. Batteries, 6(3), 35.Mishra, L., Subramaniam, A., Jang, T., Garrick, T. R., & Subramanian, V. R. (2022, October). Model Development for Temperature-Dependent Degradation in Large Format Lithium-Ion Batteries. In Electrochemical Society Meeting s 242 (No. 28, pp. 1075-1075). The Electrochemical Society, Inc.

Multiple hybrid Spp-Tamm modes in Ag grating/DBR microcavity

High confinement of surface plasmon polariton (SPP) have important applications in many aspects. However, access to high-Q resonant modes in metal cavity have many difficulties because of high Ohmic losses, large radiative losses and limited cavity designs. The Tamm mode is another surface plasmonic mode which has a high Q value but poor confinement. Here, we present a grating Tamm structure in which both nonradiative and radiative damping are suppressed, enabling excitation of high-Q and high confinement of hybrid SPP-Tamm mode. Theoretical analysis and simulations show that the proposed structure supports six resonance modes. By manipulating the geometric parameters of the metal grating, the multiple hybrid SPP-Tamm resonances could be well-defined and tuned with wavelength tuning sensitivity up to 1 nm. These results are promising for potential applications such as multiplexing, multi-frequency sensing and imaging.

High performance THz metasurface sensor based on modified-SWCNTs film for femtomolar protein detection

Terahertz (THz) metasurface sensor plays an important role in environmental monitoring, biomedical diagnostics, and materials science. However, most traditional THz metasurfaces for trace biological substance detection either suffer from high ohmic loss, or cannot achieve ultra-low concentration detection at the femtomolar level, which limits the application range of THz metasurfaces. Here, we propose a novel metasurface based on modified single-walled carbon nanotubes (SWCNTs) film for specific detection of SAA protein in femtomolar concentration. By modifying the SWCNTs film with concentrated sulfuric acid and introducing functionalized gold nanoparticles (Au-NPs), not only the non-resonant loss of the SWCNTs film was greatly reduced, but also the specific selection of trace SAA proteins was achieved. We experimentally demonstrated that the sensitivity of this THz metasurface sensor for SAA protein detection is 37.5 GHz/fM. In contrast to conventional metal or dielectric metasurfaces, because the unique mesh-like structure of the SWCNTs film can greatly increase the interaction between trace substances and the sensor, this new modifiable metasurface can achieve the lowest detection limit of 0.1 fM, which has increased by an order of magnitude. Our results provide a new and promising method for THz metasurfaces to realize high-performance biosensors.

Superscattering of electromagnetic waves from subwavelength dielectric structures

Superscattering, corresponding to the scattering cross section of a scatterer being significantly larger than its single-channel limit, has attracted increasing attention due to its huge potential for practical applications. The realization of superscattering relies on the overlapping of multiple resonance modes in a scatterer. Accordingly, superscattering phenomena have been observed primarily in alternating plasmonic/dielectric layered structures which support surface plasmons. However, such systems suffer from high Ohmic loss due to the excitation of surface plasmons, hindering broader application of the plasmonic/dielectric hybrid systems. On the other hand, subwavelength structures based on high permittivity dielectric materials (such as ferroelectric ceramics) offer expansive opportunities to realize electric and magnetic resonances at microwave and THz frequencies. Here, based on optimization methods involving mode analysis, we numerically demonstrate superscattering from individual multilayered dielectric cylinders. The maximum scattering cross section achieved is determined by the collective contributions from several resonance modes excited in a complex cylinder. Our results reveal that a combination of mode analysis and a custom optimization method can enable efficient designs of complex dielectric structures exhibiting exotic scattering responses.

Terahertz radar with all-dielectric leaky-wave antenna

Terahertz radars based on leaky-wave antennas are promising for the realization of radar systems with high resolution over short ranges. This type of radar relies on spatial frequency mapping to realize a wide field of view without mechanical actuation or electrical beam steering. Previously, integrated leaky-wave antennas based on metallic wave confinement have been implemented, but the high ohmic losses limit the realized antenna gain, which is essential for extending the range of such a system when limited power is available. Here, we demonstrate an all-dielectric leaky-wave antenna fabricated monolithically from silicon and then apply leaky-wave radar techniques to realize a terahertz radar system capable of real-time data acquisition. Through this all-dielectric approach, we can avoid metallic losses, achieving an experimentally measured maximum realized gain of 25 dBi and a 34.3° 3-dB field-of-view while utilizing established and scalable fabrication techniques essential for the wide-spread adoption of terahertz technologies. We foresee this technique being applied to a variety of real-time radar applications, and here we demonstrate two potential use-cases: multi-object tracking and differentiation of liquids.

Design of Bipolar Membranes to Increase CO Formation Rates in Bicarbonate Electrolysers at Low Voltage

The electrolysis of bicarbonate solutions offers a direct route for converting alkaline CO2 capture solutions into value-added products. Alkaline CO2 capture exploits the reaction of CO2 with OH- to form aqueous HCO3-, which can be converted back into CO2 in-situ ( i-CO2) by protons sourced from a bipolar membrane (BPM). Bicarbonate electrolysis is currently too energy intensive to be economically viable, with the largest energy input coming from the voltage drop across the membrane. BPMs are usually thicker than monopolar membranes, causing high Ohmic losses and limited water transport to the water dissociation junction. This causes the membrane to dry out and require excessively high voltages to operate at high current densities. To date, little research has been directed towards designing BPMs for bicarbonate electrolysis. Our work focuses on designing BPMs with low voltage drops while keeping the amount of i-CO2 suppliedto the cathode high. In this study, we present custom-made BPMs that enable bicarbonate electrolysis at a current density of 100 mA cm-2 and a cell voltage < 3 V, with cell voltage remaining < 10 V at current densities in excess of 1 A cm-2. We also demonstrate a correlation between a thicker cation exchange layer and higher i-CO2 generation and elucidate the cause of this phenomenon.

Plasmonic synergism in tailored metal–carbon interfaces for real-time single molecular level sniffing of PFOS and PFOA

Generating plasmonic hot-spots through engineering of nanoscale interfaces offers exciting opportunities towards point-of-care analytical detection. The mutual trade-off between ultra-high sensitivity, specificity and reliability are major drawbacks for practical applicability with real-time samples. Fundamentally these originate from low photonic mode density, high ohmic losses, temporally fluctuating and chemically indistinguishable nature of electromagnetic hot-spots. This work describes synergism of metallic plasmons from tailored interfaces of Ag-Au nanoalloys with conical nanocavities of nanocarbon florets (NCF), leading to strong metal-dielectric interfacial coupling. Such, Ag-Au-NCF nanohybrid delivers an unprecedented 1517-fold enhancement in surface-plasmon coupled directed emission (SPCE) of Rhodamine B (RhB) leading to robust (relative standard deviation, RSD < 10 %) single-molecular-level detection of spectroscopically-silent perfluoroalkyl substances (PFAS). The limit-of-detection demonstrated (PFOS = 0.005 ppt) is one-thousand times better than WHO recommendation and surpasses all existing reports. The specific cation–anion interactions between RhB and PFAS are substantiated through density functional calculations that concur with experimental findings. Finally, the emission from this SPCE platform can be visually tracked through a smartphone camera over wide range of PFOS concentrations (0.005–5000000 ppt) in water samples (lake, river, tap, drinking and ocean) and blood-plasma, offering transformative opportunities in analytical sciences.

Epitaxially Grown Silicon Nanowires with a Gold Molecular Adhesion Layer for Core/Shell Structures with Compact Mie and Plasmon Resonances.

Noble-metal plasmonic nanostructures have attracted much attention because they can support deep-subwavelength optical resonances, yet their performance tends to be limited by high Ohmic absorption losses. In comparison, high-index dielectric materials can support low-loss optical resonances but do not tend to yield the same subwavelength optical confinement. Here, we combine these two approaches and examine the dielectric-plasmonic resonances in dielectric/metal core/shell nanowires. Si nanowires were grown epitaxially from (111) substrates, and direct deposition of Au on these structures by physical vapor deposition yielded nonconformal Au islands. However, by introduction of a molecular adhesion layer prior to deposition, cylindrical Si/Au core/shell nanostructures with conformal metal shells were successfully fabricated. Examining these structures as optical cavities using both optical simulations and experimental extinction measurements, we found that the structures support Mie resonances with quality factors enhanced up to ∼30 times compared with pure dielectric structures and plasmon resonances with optical confinement enhanced up to ∼5 times compared with pure metallic structures. Interestingly, extinction spectra of both Mie and plasmon resonances yield Fano line shapes, whose manifestation can be attributed to the combination of high quality factor resonances, Mie-plasmon coupling, and phase delay of the background optical field. This work demonstrates a bottom-up synthetic method for the production of freestanding, cylindrically symmetric semiconductor/metal core/shell nanowires that enables the efficient trapping of light on deep-subwavelength length scales for varied applications in photonics and optoelectronics.

Insights into the effect of drying temperature on catalyst layer structure and PEM water electrolysis performance

The drying process of the membrane electrode assembly (MEA) has a significant impact on the structure of catalyst layer (CL) and the performance of proton exchange membrane water electrolysis (PEMWE). However, there is a lack of research on the relationship between drying temperature, CL structure, and performance. In this study, we investigated the drying process to regulate the CL microstructure, and the relationship between CL structure and water electrolysis performance was confirmed. As the drying temperature increased from 70 °C to 110 °C, the morphology of the CL changed from dense to loose due to differences in solvent evaporation rate. Specifically, the pore volume fractions of the CL (Vvoid) increased from approximately 0 to 27%. Electrochemical tests revealed that the dense CL structure formed at lower drying temperatures increased activation and mass transfer losses, while the aggregated CL structure formed at higher drying temperatures resulted in high ohmic loss. Consequently, the MEA dried at 90 °C exhibited the best water electrolysis performance, achieving a voltage of 1.78V at a current density of 2.0 A cm−2. The Vvoid was found to 18%, while the wet ionomer volume fraction (Vion,wet) was 50%. Furthermore, the durability test demonstrated that the MEA dried at 90 °C exhibited a voltage rate of −25 μV h−1 after 200 h of continuous current operation. The stable cell voltage was still observed even after 1000 intermittent start-stop operations, indicating excellent durability. This study provides valuable insights for optimizing the preparation process of MEA to enhance the structure of the CL and improve the PEMWE. It also presents a viable approach towards the commercialization of PEMWE.

Hydrocarbon-based membranes cost-effectively manage species transport and increase performance in thermally regenerative batteries

Low-temperature heat (T<130°C) can be utilized by thermally regenerative batteries (TRBs) for power production, allowing the thermal energy to be converted to storable chemical potential energy. However, TRBs suffer from high ohmic losses and ammonia crossover, which has slowed their development. In this study, we examined how the use of six different membranes influenced TRB performance, determined the most influential membrane parameters, and identified promising membrane candidates that cost-effectively increase TRB performance. Of the six membranes examined, an inexpensive, hydrocarbon CEM (Selemion CMVN) had low ammonia crossover without compromising resistance, resulting in good performance across all metrics studied. A thin anion exchange membrane (Sustainion, 50 microns) showed a high peak power density of 82 mW cm−2 due to low resistance, but the average power density and energy density were low due to high ammonia flux. Full discharge curves using Selemion CMVN provided an average power density of 26 ± 7 mW cm−2 with an energy density of 2.9 Wh L−1, which were large improvements on previous TRBs. A techno-economic analysis showed that Selemion CMVN had the lowest levelized cost of storage ($410 per MWh) at an applied current density of 50 mA cm−2.

Van der Waals Materials for Applications in Nanophotonics

AbstractNumerous optical phenomena and applications have been enabled by nanophotonic structures. Their current fabrication from high refractive index dielectrics, such as silicon (Si) or gallium phosphide (GaP), pose restricting fabrication challenges while metals, relying on plasmons and thus exhibiting high ohmic losses, limit the achievable applications. An emerging class of layered, so‐called van der Waals (vdW), crystals is presented as a viable nanophotonics platform in this work. The dielectric response of 11 mechanically exfoliated thin‐film (20–200 nm) vdW crystals is extracted, revealing high refractive indices up to n = 5, pronounced birefringence up to Δn = 3, sharp absorption resonances, and a range of transparency windows from ultraviolet to near‐infrared. Nanoantennas are subsequently fabricated on silicon dioxide (SiO2) and gold, utilizing the compatibility of vdW thin films with a variety of substrates. Pronounced Mie resonances are observed due to the high refractive index contrast on SiO2, leading to a strong exciton‐photon coupling regime as well as largely unexplored high‐quality‐factor, hybrid Mie‐plasmon modes on gold. Additional vdW‐material‐specific degrees of freedom in fabrication are further demonstrated by realizing nanoantennas from stacked twisted crystalline thin‐films, enabling control of nonlinear optical properties, and post‐fabrication nanostructure transfer, important for nano‐optics with sensitive materials.

RCS Reduction on Patterned Graphene-Based Transparent Flexible Metasurface Absorber

A metasurface absorber consisting of patterned graphene sandwich structure, transparent flexible polyvinyl chloride (PVC) dielectric layer, and indium tin oxide (ITO) bottom plate is proposed in microwave band. The graphene layer is patterned as periodic strip bands with the same rectangular holes. The radar cross section (RCS) characteristics are studied by simulation and experiment. The results indicate that the proposed transparent flexible metasurface shows more than 10 dB RCS reduction in dual band, wideband, and single band when the sheet resistance ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$R_{s}$ </tex-math></inline-formula> ) of graphene is 70, 240, and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$350~\Omega $ </tex-math></inline-formula> /sq, respectively. For <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$R_{s} = 240\,\,\Omega $ </tex-math></inline-formula> /sq, RCS reduction in the conformal case is better than 10 dB in 8.52–16.98 GHz, and corresponding relative bandwidth is 66.35%. The regulation characteristics are attributed to the strong interference at the resonant frequency or in the broadband. It effectively captures the incident electromagnetic (EM) waves in the metasurface, and the incident wave energies are dissipated with high ohmic loss. Moreover, the RCS suppression ability of the conformal metasurface becomes better with the increase of curvature radius when the metasurface size is fixed. The proposed metasurface initiates a new way for research and development of multifunctional metasurface devices, which has important application in EM stealth in microwave band.

Designing Gadolinium-doped ceria electrolyte for low temperature electrochemical energy conversion

Reducing the operational temperature of solid oxide fuel cells (SOFC) is vital to improving their durability and lifetime. However, a traditional SOFC suffers from high ohmic and polarization losses at low temperatures, leading to poor performance. Gadolinium-doped ceria is the best ionic conductor for SOFC at lower temperatures. The present work envisages the GDC as an electrolyte for applying low-temperature solid oxide fuel cells (LT-SOFCs). So, in this regard, herein, GDC is synthesized through a wet chemical co-precipitation technique as a functional electrolyte layer fixed between two symmetrical porous electrodes NCAL (Ni0.8Co0.15Al0.05LiO2). Due to the improved surface properties of the synthesized GDC, particles perform better than commercially available GDC. The synthesized GDC electrolyte shows an impressive fuel cell performance of 569 mW/cm2 and a high ionic conductivity of 0.1 S/cm at a shallow temperature of 450 °C. Moreover, the fuel cell device utilizing the synthesized GDC remained stable for 150 h of operation at a high current density of 110 mA/cm2 at 450 °C. The high conduction mechanism has been proposed in detail. The results show that excellent fuel cell performance, high ionic conductivity, and better stability can be achieved at exceptionally low enough temperatures. Also, the proposed work suggests that new electrolytes can be designed for developing advanced low-temperature fuel cell technology.

Copper plasmonics with excitons

We investigate the propagation of surface plasmons (SPPs) in a thin layer of copper surrounded by copper oxide Cu$_2$O. It is shown that particularly strong excitons in Cu$_2$O can have considerable impact on plasmon propagation, providing many opportunities for plasmon-exciton and plasmon-plasmon interactions. It is demonstrated that by the use of sufficiently thin metal layer, one can excite the so-called long range plasmons (LRSPPs) which can overcome the inherently high ohmic losses of Cu as compared to usual plasmonic metals such as silver. Analytical results are confirmed by numerical calculations.

Multi-Scale Electrochemo-Mechanical Experiments on Thin Film Battery Materials

The application of a solid-electrolyte may enable the use of certain high energy density anodes like Li and Si and also circumvents the flammable liquid-electrolyte. However, all solid components introduce multiple solid-solid interfaces whose responses are strongly affected by the mechanical state of the region on both sides, which can be affected by a combination of applied stack pressure and cycling induced volumetric change1. Electrochemo-mechanical coupling (ECM) studies2 are a relatively new area for this society, especially with thin film structures,3 which provide high purity, uniformity, and controlled geometries for the reaction to take place. However, correctly interpreting ECM experimental results as well as explaining the fundamental failure mechanisms (i.e. cracking and dendrite propagation) requires careful experimental study of material mechanical properties and how electrochemical characteristics change with mechanical state4.In this work, we describe two experimental studies on sputter-deposited thin-film LixV2O5 electrodes, with a thickness of 1 µm on a Si wafer. A lateral cell design that has the two electrodes on a single plane on a substrate, is described to focus on a single electrode. An ionic liquid electrolyte (ILE) on the Si substrate is used instead of a solid electrolyte pellet to avoid high ohmic losses , and to focus on the mechanics of the LixV2O5. The ILE covers the two electrodes and serves as the ionic pathway. Lithium foil (or vapor-deposited Li metal) is placed on the wafer and serves as the Li source. The first study is conducted with a liquid electrolyte and compares the cell behaviors between stressed and unstressed states. An external mechanical load is applied to the whole electrode surface for a uniform force distribution. An important thermodynamic contribution of stress is the change in equilibrium potential, which can be measured as a function of applied stress on the electrode and may also affect charge transfer kinetics at the interface. The second experiment will focus on the composition modulated mechanical properties of LixV2O5 which is crucial for ECM modeling work. Here, we lithiate V2O5 electrodes to different amounts, remove the electrolyte to stop ionic transport, and then perform nanoindentation in an inert argon environment. The correlation between elastic moduli and x in LixV2O5 as well as the variation of equilibrium potential provide important parameters for building accurate ECM numerical models. Pasta, M., Armstrong, D., Brown, Z.L., Bu, J., Castell, M.R., Chen, P., Cocks, A., Corr, S.A., Cussen, E.J., Darnbrough, E., et al. (2020). 2020 roadmap on solid-state batteries. JPhys Energy 2, 032008.Wan, T.H., and Ciucci, F. (2020). Electro-chemo-mechanical modeling of solid-state batteries. Electrochim. Acta 331, 135355.Spencer Jolly, D., Ning, Z., Darnbrough, J.E., Kasemchainan, J., Hartley, G.O., Adamson, P., Armstrong, D.E.J., Marrow, J., and Bruce, P.G. (2020). Sodium/Na β″ Alumina Interface: Effect of Pressure on Voids. ACS Appl. Mater. Interfaces 12, 678–685.Cao, D., Sun, X., Li, Q., Natan, A., Xiang, P., and Zhu, H. (2020). Lithium Dendrite in All-Solid-State Batteries: Growth Mechanisms, Suppression Strategies, and Characterizations. Matter 3, 57–94.

Investigation of the Temperature Effects on Copper Losses in Hairpin Windings

Today, an extensive electrification is occurring in all industrial sectors, with a special interest seen in the automotive and aerospace industries. The electric motor, surely, is one of the main actors in this context, and an ever-increasing effort is spent with the aim of improving its efficiency and torque density. Hairpin windings are one of the recent technologies which are implemented onto the stator of the electric motor. Compared to conventional random windings, it inherently features lower DC resistance, higher fill factor, better thermal performance, improved reliability, and an automated manufacturing process. However, its bottleneck is the high ohmic losses at high-frequency operations due to skin and proximity effects (AC losses), resulting in a negative impact on the temperature map of the machine. Nevertheless, while it is well-known that DC losses increase linearly with the operating temperatures, the AC losses trend needs further insight. This paper demonstrates that operating the machine at higher temperatures could be beneficial for overall efficiency, especially at high-frequency operations. This suggests that a paradigm shift is required for the design of electric motors equipped with hair-pin windings, which should therefore focus on a temperature-oriented approach. In addition, the effect of the rotor topology on AC losses, which is often overlooked, is also considered in this paper. The combination of these effects is used to carry out observations and, eventually, to provide design recommendations. Finite element electromagnetic and thermal evaluations are performed to prove the findings of this research.

Strong mode coupling-enabled hybrid photon-plasmon laser with a microfiber-coupled nanorod.

Laser based on single plasmonic nanoparticle can provide optical frequency radiation far beyond the diffraction limit and is one of the ultimate goals of nanolasers, yet it remains a challenge to be realized because of the inherently high Ohmic loss. Here, we report the direct observation of lasing in microfiber-coupled single plasmonic nanoparticles enabled by strong mode coupling. We show that, by strongly coupling a gold nanorod (GNR) with the whispering gallery cavity of a dye-doped polymer microfiber (with diameter down to 2.0 μm), the substantially enhanced optical coherence of the hybrid photon-plasmon mode and effective gain accumulated from the active microfiber cavity enable single-mode laser emission from the GNR at room temperature with a threshold as low as 2.71 MW/cm2 and a linewidth narrower than 2 nm.

Hybrid Manufacturing of a Single-Layer Ceramic Fuel Cell Utilizing 3D Printing and Laser Scribing

Single-layer ceramic fuel cells are developing as a promising fuel cell technology [1-3]. Since 3D printing can create both the dense and the porous structures with good mechanical and electrochemical properties, it has the potential to revolutionize the manufacturing of fuel cells. We recently reported a 3D printed single-layer ceramic fuel cell fabricated through an extrusion-based 3D printing, which generated a power density of 230 mW/cm2 at 550oC [1]. A comprehensive investigation into the influence of sintering temperatures ranging from 700oC to 1000oC assisted us in optimizing the density of the functional layer for acceptable electrochemical performance while maintaining adequate mechanical properties. We noticed that the performance of the single-layer cells was limited by the mass transport losses due to low porosity of the single-layer. The best printed cell suffered from a high ohmic loss (0.46 Ω.cm2) and a polarization loss (0.32 Ω.cm2) [1]. In this work, we used a hybrid of a 3D printer and a laser scriber to fabricate the patterned single-layer ceramic fuel cells. Interestingly, the performance of the patterned single-layer ceramic fuel cell was 30% better as compared to a conventional single-layer fuel cell without any patterns. The patterned structures on the surfaces of the cell obtained through the laser scribing, considerably improved the electrode processes. In the patterned 3D printed fuel cells, we studied several electrode materials such as CuFe2O4, LSCF, LSC, NiCoAlLi-oxide, and LiNiZn-oxide and synthesized pastes appropriate for extrusion-based 3D printing. The rheological characteristics of the pastes were investigated using several characterization techniques such as dynamic light scattering, viscometry and tensiometry. Electrochemical impedance spectroscopy and current-voltage measurements were used to assess the electrochemical performance of the cells. Furthermore, high-temperature XRD demonstrated the composite materials' excellent structural stability. To further understand the processes in the cells, additional spectroscopic and microscopic investigations (HR-TEM, SEM-EDX, XPS) were performed. Acknowledgement. Dr. Asghar thanks Academy of Finland (Grant No. 13322738, 13329016) and the Hubei overseas Talent 100 program for their support.