Low Ohmic Losses Research Articles

All-fiber high-order mode laser using a metal-clad transverse mode filter.

We propose and demonstrate an all-fiber laser with LP11 mode output. A transverse mode filter is designed and fabricated to suppress the fundamental mode and enable the fiber laser to oscillate in the second-order (LP11) transverse mode. The mechanism is to introduce relatively low ohmic loss for the TE01 mode and much higher ohmic losses for other modes through the loss of evanescent waves in the metal clad. The fiber laser operates at the center wavelength of 1053.9 nm with a narrow 3 dB linewidth of 0.019 nm. Four states of cylindrical vector mode with high modal purity are obtained through adjusting the intra-cavity polarization controller. This approach has great potentiality and scalability of realizing single high-order mode fiber laser, from which a wide range of applications could benefit.

Thermoplasmonic Response of Semiconductor Nanoparticles: A Comparison with Metals

AbstractA number of applications in nanoplasmonics utilize noble metals, gold (Au) and silver (Ag), as the materials of choice. However, these materials suffer from problems of poor thermal and chemical stability with significant dissipative losses under high‐temperature conditions. In this regard, semiconductor nanoparticles have attracted attention with their promising characteristics of highly tunable plasmonic resonances, low ohmic losses, and greater thermochemical stability. Here, the size‐dependent thermoplasmonic properties of semiconducting silicon and gallium arsenide nanoparticles are investigated to compare them with Au nanoparticles using Mie theory. To this end, experimentally estimated models of dielectric permittivity are employed. Among the various permittivity models for Au, the Drude–Lorentz (DL) and the Drude and critical points (DCP) models are further compared. Results show a redshift in the scattering and absorption resonances for the DL model while the DCP model presents a blueshift. A massive Drude broadening contributes strongly to the damping of resonances in Au nanoparticles at elevated temperatures. In contrast, the semiconductor nanoparticles do not exhibit significant deterioration in their scattering and absorption resonances at high temperatures. In combination with low dissipative damping, this makes the semiconductor nanoparticles better suited for high‐temperature applications in nanoplasmonics wherein the noble metals suffer from excessive heating.

Effect of Mode Transformation in THz Clinotron

Extension of the theory of a clinotron is developed by use of the scattering matrix of an oversized T-junction on the ends of a slow wave system. The matrix contains elements corresponding to the transformation of slow grating modes into fast ones and vice versa. Those fast waves with low ohmic losses provide strong resonant properties of a clinotron even in the case of strong attenuation of the surface mode. Results of the theoretical simulation are compared with experimental ones and obtained dependencies explain strong resonances in sub-THz clinotrons.

Shingling Technology For Cell Interconnection: Technological Aspects And Process Integration

Shingling technology is an extremely interesting development of cell interconnection in a photovoltaic module due to higher power densities at the same or lower cost, and increasing availability of suitable Electrically Conductive Adhesives (ECAs) and equipment. The shingling approach provides several advantages compared to standard modules, namely: lower ohmic losses, better area utilization, lower processing temperature, lower operating temperature resulting in enhanced energy yield, improved aesthetics. In this work, we demonstrate the performance gain obtained with shingling interconnection technology in terms of module output power and efficiency. Moreover, we describe the technological challenges for each step in the shingling assembly process flow.

How to calculate the pole expansion of the optical scattering matrix from the resonant states

We present a formulation for the pole expansion of the scattering matrix of open optical resonators, in which the pole contributions are expressed solely in terms of the resonant states, their wavenumbers, and their electromagnetic fields. Particularly, our approach provides an accurate description of the optical scattering matrix without the requirement of a fit for the pole contributions or the restriction to geometries or systems with low Ohmic losses. Hence, it is possible to derive the analytic dependence of the scattering matrix on the wavenumber with low computational effort, which allows for avoiding the artificial frequency discretization of conventional frequency-domain solvers of Maxwell's equations and for finding the optical far- and near-field response based on the physically meaningfull resonant states. This is demonstrated for three test systems, including a chiral arrangement of nanoantennas, for which we calculate the absorption and the circular dichroism.

Metal-dielectric hybrid nanoantennas for efficient frequency conversion at the anapole mode.

Background: Dielectric nanoantennas have recently emerged as an alternative solution to plasmonics for nonlinear light manipulation at the nanoscale, thanks to the magnetic and electric resonances, the strong nonlinearities, and the low ohmic losses characterizing high refractive-index materials in the visible/near-infrared (NIR) region of the spectrum. In this frame, AlGaAs nanoantennas demonstrated to be extremely efficient sources of second harmonic radiation. In particular, the nonlinear polarization of an optical system pumped at the anapole mode can be potentially boosted, due to both the strong dip in the scattering spectrum and the near-field enhancement, which are characteristic of this mode. Plasmonic nanostructures, on the other hand, remain the most promising solution to achieve strong local field confinement, especially in the NIR, where metals such as gold display relatively low losses.Results: We present a nonlinear hybrid antenna based on an AlGaAs nanopillar surrounded by a gold ring, which merges in a single platform the strong field confinement typically produced by plasmonic antennas with the high nonlinearity and low loss characteristics of dielectric nanoantennas. This platform allows enhancing the coupling of light to the nanopillar at coincidence with the anapole mode, hence boosting both second- and third-harmonic generation conversion efficiencies. More than one order of magnitude enhancement factors are measured for both processes with respect to the isolated structure.Conclusion: The present results reveal the possibility to achieve tuneable metamixers and higher resolution in nonlinear sensing and spectroscopy, by means of improved both pump coupling and emission efficiency due to the excitation of the anapole mode enhanced by the plasmonic nanoantenna.

Two-Dimensional Multimode Terahertz Random Lasing with Metal Pillars

Random lasers employing multiple scattering and interference processes in highly disordered media have been studied for several decades. However, it remains a challenge to achieve a broadband multimode random laser with high scattering efficiency, particularly at long wavelengths. Here, we develop a new class of strongly multimode random lasers in the terahertz (THz) frequency range in which optical feedback is provided by multiple scattering from metal pillars embedded in a quantum cascade (QC) gain medium. Compared with the dielectric pillars or air hole approaches used in previous random lasers, metal pillars provide high scattering efficiency over a broader range of frequencies and with low ohmic losses. Complex emission spectra are observed with over 25 emission peaks across a 0.4 THz frequency range, limited primarily by the gain bandwidth of the QC wafer employed. The experimental results are corroborated by numerical simulations that show the lasing modes are strongly localized.

Driving force behind electrochemical performance of microbial fuel cells fed with different substrates

The performance of miniaturized microbial fuel cells operating with five different substrates (acetate, lactate, glucose and octanoate) were studied with the aim to identify the reason for its different performance. In all cases, the COD removal rate was about 650 mg COD L−1 d−1. However, the bio-electrochemical performance of the MFC was very different, showing the MFC fed with acetate the best performance: 20 A m−2 as maximum current density, 2 W m−2 of maximum power density, 0.376 V of OCV and 12.6% of CE. In addition, the acetate showed the best bio-electrochemical performance in the polarization curves and cyclic voltammetries. These polarization curves were modelled and the key to explain the better electrical performance of acetate was its lower ohmic losses. When working with acetate, its ohmic losses were one log-unit below those attained by the other substrates. These lower ohmic losses were not associated to the electrolyte conductivity of the fuel but to the lower ohmic loses of the biofilm generated.

Metal‐Dielectric Nanocavity for Real‐Time Tracing Molecular Events with Temperature Feedback

AbstractPlasmonic nanoparticles coupled with metallic films forming nanometer scale cavities have recently emerged as a powerful tool for enhancement of light‐matter interaction. Despite high efficiency for sensing and light emission, such nanocavities exhibit harmful and uncontrolled optical heating which limits the ranges of light intensities and working temperature. In contrast to plasmonic nanoparticles, all‐dielectric counterparts possess low Ohmic losses, high temperature stability along with a strong temperature‐dependent Raman response. Here, we demonstrate that a silicon nanoparticle coupled with a thin gold film can serve as a multifunctional metal‐dielectric (hybrid) nanocavity operating up to 1200 K. Resonant interaction of light with such nanocavity enables molecular sensing, heat‐induced molecular events (protein unfolding), and their real‐time tracing with a nanoscale thermometry through the monitoring enhanced Raman scattering both from the nanoparticle and analyzed molecules. We model numerically the thermo‐optical properties of the hybrid nanocavity and reveal two alternative regimes of operation ‐ with and without strong optical heating while other functionalities are preserved. We believe that the concept of the multifunctional hybrid nanocavities holds great potential for diverse photochemical and photophysical applications.

Advanced low-temperature ceramic nanocomposite fuel cells using ultra high ionic conductivity electrolytes synthesized through freeze-dried method and solid-route

Low ionic conductivity and slow reaction kinetics often limit the performance of a ceramic nanocomposite fuel cell (CNFC). Here, we report a novel synthesis method, freeze-dried method, to achieve a record high ionic conductivity for nanocomposite electrolytes (>0.5 S/cm) based on Ce0.85Sm0.15O2 (SDC) and a eutectic mixture of Na2CO3, Li2CO3, K2CO3 (NLK). The highest ionic conductivity (0.55 S/cm) was reached by increasing the carbonate content of the electrolyte to 35 wt%. For the sake of comparison, the nanocomposite electrolytes were also prepared through solid-route. Composite anodes and cathodes for complete fuels were prepared from NiO and La0.6Sr0.4Co0.2Fe0.8O3 (LSCF), respectively using both solid-route and freeze-dried nanocomposite electrolytes. Complete fuel cells manufactured from these nanocomposite materials produced ∼1.1 W/cm2 at 550 °C. The EIS measurements revealed low ohmic losses (0.18 Ω cm2) and even lower charge transfer resistance (0.05 Ω cm2). In addition, it was found that the open-circuit-voltage (OCV) of the CNFCs improved from 1.1 V to 1.2 V when a mixture of air and CO2 was supplied as compared to the case when only air was supplied at the cathode. Finally, high temperature X-ray diffraction (HT-XRD) revealed stable structures of SDC, NiO and LSCF up to 600 °C, which shows the thermal stability of these fuel cell materials.

Morphology and Structure of Solid Oxide Fuel Cell (SOFC) Components Fabricated by Spray Pyrolysis

Solid oxide fuel cells are expected to play a significant role in the future energy sector mainly due to their inherent high efficiency and low pollutants emissions. These devices typically operate above 800°C by means of a solid oxide electrolyte, typically yttria stabilized zirconia (YSZ) that conducts oxygen ions at sufficiently high conductivities at these temperatures. The cathode is exposed to air or pure oxygen which is reduced to O2 -. State of the art cathodes are based on the perovskite lanthanum strontium manganite La0.9Sr0.1MnO3 (LSM) in a mixture with YSZ which exhibits adequate electronic conductivity at 1000°C, is stable under oxidizing conditions and has a good thermal expansion match with YSZ. The anodic electrode is exposed to the fuel mixture that can even consist of CO which is normally, deleterious for other types of fuel cells. In fact, one major advantage of SOFCs is their suitability to oxidize conventional hydrocarbons and/or biofuels which renders them ideal candidates in connection with renewable sources (see Figure 1). Due to the difference in the oxygen chemical potential between the anode and the cathode, part of the free energy of the oxidation reaction is converted directly to electricity. State of the art anodes, have been based on Ni due to its low cost, again in a mixture with YSZ1. Oxidizing directly (i.e. without an intermediate reforming step) conventional hydrocarbons in SOFCs offers a number of advantages that relate to the existing infrastructure for these fuels that in this case, can be used more efficiently and environmentally consciously until their reserves are depleted. Nickel cermets, however, have to be replaced with other types of mixed conducting (i.e. ionic and electronic) electrodes that do not catalyze carbon formation such ascomposite anodes of the type Cu/CeO2 /YSZ2or materials based on lanthanum chromate such as the perovskite (La0.75Sr0.25)Cr0.5Mn0.5O3 -δ (LSCM)3. High materials and fabrication costs have prevented wide commercialization of these type of fuel cells and, thus, research efforts have been intensified in recent years by many laboratories that address the above issues. Regarding fabrication, there exist two major categories of techniques, namely conventional which are based on a particulate approach and deposition which entail the formation of cell components on a support via a physical and/or chemical process. The latter offer the advantage of in situ and directly controlling final particle size and morphology by appropriately tuning the characteristics of the physicochemical processes involved during deposition. The purpose of this research is to explore the potential of the spray pyrolysis (SP) technique which is a deposition technique for the fabrication of SOFC components of flat plate geometry. It involves spraying of an appropriate solution of ionic salts on a suitable substrate at certain temperature for the production of oxides in film form4. The technique has the potential for the fabrication of electrolytic films with low thickness resulting in lower ohmic losses and for the fabrication of all the cell components in situ. It also offers great flexibility in terms of materials selection and processing parameters to fabricate suitable electrodes and electrolytes for SOFCs. In the present work, we focus on the effect of the substrate temperature and solution concentration on the final morphology of anodic, cathodic and electrolytic films fabricated by SP using environmentally friendly aqueous solutions. Results are presented of the application of this method for the production of anodic film cermets such as Cu-CeO2, Co-CeO2 and Cu-La0.75Sr0.25Cr0.5Mn0.5O3-δ (Cu-LSCM) on dense YSZ substrates. In addition, cathodic electrodes of La0.75Sr0.25MnO3 (LSM) on dense YSZ and porous LSM substrates were fabricated. Finally, YSZ films as well as composite structures of the type Cu-LSCM/YSZ were deposited on porous LSM pellets. The effort is concentrated to identify optimized processing conditions that lead to good adhesion.The produced films were characterized by X-ray diffraction and scanning electron microscopy (SEM).

Thermally Sprayed Large Tubular Solid Oxide Fuel Cells and Its Stack: Geometry Optimization, Preparation, and Performance

In this study, we develop a large tubular solid oxide fuel cells design with several cells in series on a porous cermet support, which has many characteristics such as self-sealing, low Ohmic loss, high strength, and good thermal expansion coefficient matching. Here, we investigate aspects of the cell design, manufacture, performance, and application. Firstly, the cell length and number of cells in series are optimized by theoretical analysis. Then, thermal spraying is applied as a cost-effective method to prepare all the cell components. Finally, the performance of different types of cells and two types of stacks is characterized. The maximum output power of one tube, which had 20 cells in series, reaches 31 and 40.5 W at 800 and 900 °C, respectively. Moreover, the output power of a stack assembled with 56 tubes, each with ten cells in series, reaches 800 W at 830 °C. The excellent single tube and cell stack performance suggest that thermally sprayed tubular SOFCs have significant potential for commercialized application.

Optimized design of polarizers with low ohmic loss and any polarization state for the 28 GHz QUEST ECH/ECCD system

In a high-power long-pulse millimeter-wave transmission line for electron cyclotron heating and current drive (ECH/ECCD), the ohmic loss on the grooved mirror surface of polarizers is one of the important issues for reducing the transmission loss. In this paper, the ohmic loss on the mirror surface is evaluated in simulated real-scale polarizer miter bends for different groove parameters under a linearly-polarized incident wave excitation. The polarizers with low ohmic loss are optimally designed for a new 28GHz transmission line on the QUEST spherical tokamak. The calculated optimum ohmic loss is restricted to only less than 1.5 times as large as the theoretical loss for a copper flat mirror at room temperature. The copper rounded-rectangular grooves of the polarizers were relatively easy to make smooth in mechanical machining and the resultant surface roughness was not more than 0.15μm, which is only 0.38 times as large as the skin depth. The combination of the designed elliptical polarizer and the polarization rotator can also realize any polarization state of the reflected wave.

Experimental study on the membrane electrode assembly of a proton exchange membrane fuel cell: effects of microporous layer, membrane thickness and gas diffusion layer hydrophobic treatment

In this study, electrochemical impedance spectroscopy (EIS) is employed to analyze the influence of microporous layer (MPL), membrane thickness and gas diffusion layer (GDL) hydrophobic treatment in the performance of a proton exchange membrane (PEM) fuel cell. Results show that adding a MPL increases cell performance at low to medium current densities. Because lower ohmic losses are observed when applying a MPL, such improvement is attributed to a better hydration state of the membrane. The MPL creates a pressure barrier for water produced at the cathode, forcing it to travel to the anode side, therefore increasing the water content in the membrane. However, at high currents, this same phenomenon seems to have intensified liquid water flooding in the anode gas channels, increasing mass transfer losses and reducing the cell performance. Decreasing membrane thickness results into considerably higher performances, due to a decrease in ohmic resistance. Moreover, at low air humidity operation, a rapid recovery from dehydration is observed when a thinner membrane is employed. The GDL hydrophobic treatment significantly improves the cell performance. Untreated GDLs appear to act as water-traps that not only hamper reactants transport to the reactive sites but also impede the proper humidification of the cell. From the different designs tested, the highest maximum power density is obtained from that containing a MPL, a thinner membrane and treated GDLs.

Efficient complementary metamaterial element for waveguide-fed metasurface antennas.

We present a metamaterial element designed as an efficient radiator for waveguide-fed metasurface antennas. The metamaterial element is an electrically-small, complimentary electric-LC (cELC) resonator designed to exhibit large radiated power while maintaining low ohmic losses. The shape of the element is tapered to simultaneously achieve broadband operation and suppression of cross polarization radiation. Full-wave numerical studies at the K-band are conducted to examine its performance when etched into a microstrip line. In this configuration, the element shows a radiation efficiency of 90.2% and a fractional bandwidth of 8.7%. To investigate the potential benefits of the proposed element in two-dimensional platforms, the radiative characteristics of the element are calculated when the element is embedded in a dielectric-filled parallel-plate waveguide. This efficient metamaterial element has potential application as a building block for metasurface devices used in imaging, sensing, wireless power transfer, and wireless communication systems.

A Ridge-Loaded Sine Waveguide for $G$ -Band Traveling-Wave Tube

A novel slow-wave structure (SWS), named ridge-loaded sine waveguide (RLSWG), has been proposed to develop the wideband high-power terahertz traveling-wave tube (TWT). The slow-wave characteristics of the RLSWG SWS, including dispersion properties and interaction impedance, are analyzed by using the 3-D electromagnetic simulation software Ansoft high frequency structure simulator (HFSS). From our calculation, the average interaction impedance of the RLSWG SWS at 0.22 THz is 42.2% higher than the conventional SWG SWS. Meanwhile, the simulation results demonstrate that the RLSWG SWS possesses low ohmic losses and reflection. Moreover, the particle-in-cell (PIC) simulation results reveal that, with the cylindrical electron beam of 20.9 kV and 45 mA, the output power and electron efficiency of the RLSWG TWT at the typical frequency of 0.22 THz can reach 52.1 W and 5.54%, respectively. In addition, the 3-dB bandwidth of the RLSWG TWT exceeds 25 GHz. Compared with the SWG TWT, the RLSWG TWT has the shorter tube length and can generate the larger output power.

Low-Loss Spoof Surface Plasmon Slow-Wave Transmission Lines With Compact Transition and High Isolation

The symmetric spoof surface plasmon (SSP)-based slow-wave transmission line (SW-TL) with compact transition, low ohmic loss, and low crosstalk between SW-TLs is proposed and investigated. First, the SSP cells are modeled by equivalent circuit elements. The proposed equivalent circuit model is appealing for the integration of SW-TLs with other microwave circuits. With the symmetricity, the SW-TLs are readily realized by a compact mode converter providing gradual impedance, momentum, and polarization matching from guided waves to spoof microwave plasmons. Then, simulation studies and experiments verify that the proposed SSP SW-TL features as low as half the ohmic loss of the traditional counterparts. After that, the low mutual coupling between the proposed SSP SW-TLs is numerically and experimentally substantiated and showed to be up to 10 dB lower than that between conventional microstrip TLs. The proposed low loss, highly isolated and compact SW-TL along with the reliable circuit model enables the further exploitation of promising spoof plasmon modes in microwave technology.

Ohmic resistance affects microbial community and electrochemical kinetics in a multi-anode microbial electrochemical cell.

Multi-anode microbial electrochemical cells (MxCs) are considered as one of the most promising configurations for scale-up of MxCs, but understanding of anode kinetics in multiple anodes is limited in the MxCs. In this study we assessed microbial community and electrochemical kinetic parameters for biofilms on individual anodes in a multi-anode MxC to better comprehend anode fundamentals. Microbial community analysis targeting 16S rRNA Illumina sequencing showed that Geobacter genus was abundant (87%) only on the biofilm anode closest to a reference electrode (low ohmic energy loss) in which current density was the highest among three anodes. In comparison, Geobacter populations were less than 1% for biofilms on other two anodes distant from the reference electrode (high ohmic energy loss), generating small current density. Half-saturation anode potential (EKA) was the lowest at -0.251 to -0.242 V (vs. standard hydrogen electrode) for the closest biofilm anode to the reference electrode, while EKA was as high as -0.134 V for the farthest anode. Our study proves that electric potential of individual anodes changed by ohmic energy loss shifts biofilm communities on individual anodes and consequently influences electron transfer kinetics on each anode in the multi-anode MxC.

Morphology and Structure of SOFC Components Fabricated By Spray Pyrolysis

Solid oxide fuel cells are expected to play a significant role in the future energy sector mainly due to their inherent high efficiency and low pollutants emissions. These devices typically operate above 800°C by means of a solid oxide electrolyte, typically yttria stabilized zirconia (YSZ) that conducts oxygen ions at sufficiently high conductivities at these temperatures. The cathode is exposed to air or pure oxygen which is reduced to O2 -. State of the art cathodes are based on the perovskite lanthanum strontium manganite La0.9Sr0.1MnO3 (LSM) in a mixture with YSZ which exhibits adequate electronic conductivity at 1000°C, is stable under oxidizing conditions and has a good thermal expansion match with YSZ. The anodic electrode is exposed to the fuel mixture that can even consist of CO which is normally, deleterious for other types of fuel cells. In fact, one major advantage of SOFCs is their suitability to oxidize conventional hydrocarbons and/or biofuels which renders them ideal candidates in connection with renewable sources (see Figure 1). Due to the difference in the oxygen chemical potential between the anode and the cathode, part of the free energy of the oxidation reaction is converted directly to electricity. State of the art anodes, have been based on Ni due to its low cost, again in a mixture with YSZ[i]. Oxidizing directly (i.e. without an intermediate reforming step) conventional hydrocarbons in SOFCs offers a number of advantages that relate to the existing infrastructure for these fuels that in this case, can be used more efficiently and environmentally consciously until their reserves are depleted. Nickel cermets, however, have to be replaced with other types of mixed conducting (i.e. ionic and electronic) electrodes that do not catalyze carbon formation such as composite anodes of the type Cu/CeO2 /YSZ[ii] or materials based on lanthanum chromate such as the perovskite (La0.75Sr0.25)Cr0.5Mn0.5O3 -δ (LSCM)[iii]. High materials and fabrication costs have prevented wide commercialization of these type of fuel cells and, thus, research efforts have been intensified in recent years by many laboratories that address the above issues. Regarding fabrication, there exist two major categories of techniques, namely conventional which are based on a particulate approach and deposition which entail the formation of cell components on a support via a physical and/or chemical process. The latter offer the advantage of in situ and directly controlling final particle size and morphology by appropriately tuning the characteristics of the physicochemical processes involved during deposition. The purpose of this research is to explore the potential of the spray pyrolysis (SP) technique which is a deposition technique for the fabrication of SOFC components of flat plate geometry. It involves spraying of an appropriate solution of ionic salts on a suitable substrate at certain temperature for the production of oxides in film form[iv]. The technique has the potential for the fabrication of electrolytic films with low thickness resulting in lower ohmic losses and for the fabrication of all the cell components in situ. It also offers great flexibility in terms of materials selection and processing parameters to fabricate suitable electrodes and electrolytes for SOFCs. In the present work, we focus on the effect of the substrate temperature and solution concentration on the final morphology of anodic, cathodic and electrolytic films fabricated by SP using environmentally friendly aqueous solutions. Results are presented of the application of this method for the production of anodic film cermets such as Cu-CeO2, Co-CeO2 and Cu-La0.75Sr0.25Cr0.5Mn0.5O3-δ (Cu-LSCM) on dense YSZ substrates. In addition, cathodic electrodes of La0.75Sr0.25MnO3(LSM) on dense YSZ and porous LSM substrates were fabricated. Finally, YSZ films as well as composite structures of the type Cu-LSCM/YSZ were deposited on porous LSM pellets. The effort is concentrated to identify optimized processing conditions that lead to good adhesion. The produced films were characterized by X-ray diffraction and scanning electron microscopy (SEM). [i] Kiratzis N. E., Connor P., Irvine J. T. S.(2010) Preparation and characterization of copper based cermet anodes for use in solid oxide fuel cells at intermediate temperatures. J. Electroceram. 24:270-287. [ii] Park S.D., Vohs J.M., Gorte R.J. (2000) Direct oxidation of hydrocarbons in a solid-oxide fuel cell. Nature 404: 265-267. doi:10.1038/35005040 [iii] Plint S.M., Connor P.A., Tao S., Irvine J.T.S. (2006) Electronic transport in the novel SOFC anode material La1−xSrxCr0.5Mn0.5O3±δ. Solid State Ion. 177: 2005-2008. doi:10.1016/j.ssi.2006.02.025 [iv] Papastergiades E., Argyropoulos S., Rigakis N., Kiratzis N. E. (2009) Fabrication of ceramic electrolytic films by the method of solution aerosol thermolysis (SAT) for solid oxide fuel cells (SOFC). Ionics 15: 545-554. Figure 1

UV-LIGA microfabrication process for sub-terahertz waveguides utilizing multiple layered SU-8 photoresist

A microfabrication process based on UV LIGA (German acronym of lithography, electroplating and molding) is proposed for the fabrication of relatively high aspect ratio sub-terahertz (100–1000 GHz) metal waveguides, to be used as a slow wave structure in sub-THz vacuum electron devices. The high accuracy and tight tolerances required to properly support frequencies in the sub-THz range can be only achieved by a stable process with full parameter control. The proposed process, based on SU-8 photoresist, has been developed to satisfy high planar surface requirements for metal sub-THz waveguides. It will be demonstrated that, for a given thickness, it is more effective to stack a number of layers of SU-8 with lower thickness rather than using a single thick layer obtained at lower spin rate. The multiple layer approach provides the planarity and the surface quality required for electroforming of ground planes or assembly surfaces and for assuring low ohmic losses of waveguides. A systematic procedure is provided to calculate soft and post-bake times to produce high homogeneity SU-8 multiple layer coating as a mold for very high quality metal waveguides. A double corrugated waveguide designed for 0.3 THz operating frequency, to be used in vacuum electronic devices, was fabricated as test structure.The proposed process based on UV LIGA will enable low cost production of high accuracy sub-THz 3D waveguides. This is fundamental for producing a new generation of affordable sub-THz vacuum electron devices, to fill the technological gap that still prevents a wide diffusion of numerous applications based on THz radiation.