Geometrical Dependency Research Articles

Concept for a geometry-insensitive high-field magnetic resonance detector

AbstractWe introduce an inverse design methodology for a new class of eigenfrequency-invariant metamaterial-resonators, targeting nuclear magnetic resonance detection at ultra-high $$\mathbf {B_0}$$ B 0 field, and operating at two specified frequencies selected from within the 100-1500 MHz range. The primary optimisation goal is to maximise the magnetic field intensity and uniformity within a liquid sample, while the electric energy should be kept to a minimum level to reduce dielectric heating or quadrupolar moment excitation effects. Due to the symmetric geometry requirement of the cavity, a demultiplexer is also designed to direct each discrete resonant signal to another predetermined output port of the resonator. In order to reduce the geometrical dependency of the resonance frequency, a bespoke metamaterial is used for the cavity host. Therefore, an additional optimisation problem for a unit cell domain is defined to seek a proper material layout for the host region of the resonators. Given the sensitivity of the frequency domain, the optimisation process is effectively regulated through the utilisation of both a Helmholtz filter and a projection method. It is found that considerable improvements of the resonator quality factor can be obtained through this optimisation process.

Geometrical parameter dependency of non-Markovian and quantum speed limit measures in the spontaneous emission dynamics of a qubit near a plasmonic nanodisk

Geometrical parameter dependency of non-Markovian and quantum speed limit measures in the spontaneous emission dynamics of a qubit near a plasmonic nanodisk

Global Observations of Tropospheric Bromine Monoxide (BrO) Columns From TROPOMI

AbstractBromine monoxide (BrO) plays an important role in tropospheric chemistry. The state‐of‐the‐science TROPOspheric Monitoring Instrument (TROPOMI) offers the potential to monitor atmospheric composition with a fine spatial resolution of up to 5.5 × 3.5 km2. We present here the retrieval of tropospheric BrO columns from TROPOMI. We implement a stratospheric correction scheme using a climatological approach based on the latest GEOS‐Chem High Performance chemical transport model, and improve the tropospheric air mass factor calculation with TROPOMI surface albedo data accounting for the geometrical dependency. Our product presents a good level of consistency in comparison with measurements from ground‐based zenith‐sky differential optical absorption spectroscopy (r = 0.67), aircrafts (r = 0.46), and satellites (similar spatial distributions of BrO columns). Furthermore, our retrieval captures BrO enhancements in the polar springtime with values up to 7.8 × 1013 molecules cm−2 and identifies small‐scale emission sources such as volcanoes and salt marshes. Based on TROPOMI data, we probe a blowing snow aerosol bromine mechanism in which the snow salinity is reduced to better match simulation and observation. Our TROPOMI tropospheric BrO product contributes high‐resolution global information to studies investigating atmospheric bromine chemistry.

Numerical elastic fracture analysis of SENT test specimen subjected to non-linear loading

Crack characterization of any component depends on specimen type and geometry, material properties, and loading pattern. The geometrical and material property dependency of crack description is well established in literature, but loading pattern influence is limited to classical Mode-I, II and III types. Here, an effort is made to relate the crack stress state for different load pattens and crack length to specimen width, (a/W) using 2D and 3D linear elastic fracture analysis. The crack stress state is characterized by KI and T-stress in the present analysis using ABAQUS software. The non-uniform load patterns were defined by a non-linear stress distribution term σ (x). The stress distributions applied on the crack faces and were classified as constant, linear, parabolic, and cubic. The a/W varied as 0.2, 0.4, 0.6, and 0.8 to account the in-plane dimension effect on crack driving parameters. The 3D normalized KI and T-stress magnitudes were directly proportional to a/W. The normalized KI magnitudes decreased in the stress distribution order of constant, linear, parabolic and cubic. 3D normalized KI and T-stress values represented the real stress state of the crack. To ease the complex computational simulations, simple equations were proposed to estimate the normalized KI and T-stress for the different load patterns and a/W. To avoid the conservatism in component design, an attempt is made to represent the real load patterns through constraint inclusiveness in the 3D fracture analysis.

Ultrasensitive dual-band terahertz metasurface sensor based on all InSb resonator

Terahertz (THz) metasurface sensors have recently received considerable attention. We report an ultrasensitive dual-band metasurface (DBM) sensor in this work. The reported DBM sensor is a micro-rod periodic structure based on all InSb semiconducting material. The DBM is realized for the dual-band resonance behaviour at 1.911 THz and 1.985 THz. The corresponding Q factor for the DBM sensor is obtained at the higher side, around 174.36 and 181.11 at room temperature (T = 300 K). The geometrical parameters dependency for the resonance frequency of the proposed DBM is analysed and reported. Further, the refractive index sensitivity is observed by varying the surrounding’s refractive index from 1.00 to 1.05 (aqueous glucose solution). It is reported that, at room temperature, the proposed DBM sensor shows a sensitivity of 1800 GHz/RIU and 1900 GHz/RIU at the corresponding resonance frequencies 1.911 THz and 1.985 THz respectively. The temperature sensitivity of the proposed DBM is also explored and reported. Furthermore, the figure of merit (FOM) of the proposed DBM sensor is 164 and 173 respectively at corresponding resonance frequencies. So, the reported DBM structure could also find potential applications in the THz region as sensors, detectors, and other optoelectronic devices.

Stimulation efficiency of an actuator driven piston at the biological interface to the inner ear

Direct acoustic cochlear stimulation uses piston motion to substitute for stapes footplate (SFP) motion. The ratio of piston to stapes footplate motion amplitude, to generate the same loudness percept, is an indicator of stimulation efficiency. We determined the relationship between piston displacement to perceived loudness, the achieved maximum power output and investigated stapes fixation and obliteration as confounding factors. The electro-mechanical transfer function of the actuator was determined preoperatively on the bench and intraoperatively by laser Doppler vibrometry. Clinically, perceived loudness as a function of actuator input voltage was calculated from bone conduction thresholds and direct thresholds via the implant. The displacement of a 0.4 mm diameter piston required for a perception equivalent to 94 dB SPL at the tympanic membrane compared to normal SFP piston displacement was 27.6–35.9 dB larger, consistent with the hypothesis that the ratio between areas is responsible for stimulation efficiency. Actuator output was 110 ± 10 eq dB SPLFF @1Vrms ≤ 3 kHz and decreased to 100 eq dB SPLFF at 10 kHz. Output was significantly higher for mobile SFPs but independent from obliteration. Our findings from clinical data strongly support the assumption of a geometrical dependency on piston diameter at the biological interface to the cochlea.

Mimicking the Human Tympanic Membrane: The Significance of Scaffold Geometry.

The human tympanic membrane (TM) captures sound waves from the environment and transforms them into mechanical motion. The successful transmission of these acoustic vibrations is attributed to the unique architecture of the TM. However, a limited knowledge is available on the contribution of its discrete anatomical features, which is important for fabricating functional TM replacements. This work synergizes theoretical and experimental approaches toward understanding the significance of geometry in tissue-engineered TM scaffolds. Three test designs along with a plain control are chosen to decouple some of the dominant structural elements, such as the radial and circumferential alignment of the collagen fibrils. In silico models suggest a geometrical dependency of their mechanical and acoustical responses, where the presence of radially aligned fibers is observed to have a more prominent effect compared to their circumferential counterparts. Following which, a hybrid fabrication strategy combining electrospinning and additive manufacturing has been optimized to manufacture biomimetic scaffolds within the dimensions of the native TM. The experimental characterizations conducted using macroindentation and laser Doppler vibrometry corroborate the computational findings. Finally, biological studies with human dermal fibroblasts and human mesenchymal stromal cells reveal a favorable influence of scaffold hierarchy on cellular alignment and subsequent collagen deposition.

Influence of a local short-term heat treatment on the formability of orbital formed functional components

Conventional processes like shearing dispose a lack in efficiency and formability to manufacture functional components with a high geometric variety. A possibility to allow the efficient and sustainable manufacturing is the application of innovative forming operations like orbital forming. Thus, a strain-hardened component with a load-adapted thickness profile can be manufactured in a single-stage process. Thereby, the control of the material flow could be identified as major challenge due to the three-dimensional stress and strain state. In order to reduce the parts weight and simultaneously guarantee the same level of performance, conventional steel is substituted by lightweight materials such as precipitation hardenable aluminum alloys. However, new challenges arise due to the reduced formability of aluminum compared to conventional steel. In recent research, the potential of a short-term heat treatment to enlarge the formability could be shown. The presented process locally reduces the materials strength, thus allowing a control of the material flow by the interaction between softened areas and areas, which offer the initial conditions. In this contribution, the influence on the formability of orbital formed components manufactured out of the precipitation hardenable aluminum alloy EN AW 6016 by a local short-term heat treatment is investigated. Different geometry-based heat treatment layouts are applied in order to maximize the thickening on different radial positions. The potential to enhance the formability is evaluated by comparing geometrical and mechanical properties of the components manufactured in the conventional process route and with a previous heat treatment. The analysis of radial cross-sections and the hardness distribution reveals the positive influence of the heat treatment but also points out the geometrical dependency of the effect due to the characteristic material flow in orbital forming.

Wall slip of highly concentrated non-Brownian suspensions in pressure driven flows: A geometrical dependency put into a non-Newtonian perspective

Wall slip quantification using the classical Mooney slip analysis has produced physically unreasonable results for many complex fluids. Over the past decades, the assumption that the slip velocity is solely dependent on the wall shear stress has therefore been questioned. In this contribution, the influence of the radius of cylindrical dies on the wall slip velocity of highly concentrated non-Brownian suspensions in a high-pressure capillary rheometer is re-examined, by varying the rheology of the liquid phase. Water- and oil-based suspensions (solid volume fraction ~ 0.60, D4,3 ~ 5 µm) are made using liquid phases that have different flow indices (n = 0.22 – 1.00) and a variation in their thickener concentration (25 g/L – 350 g/L). All classical Mooney plots showed negative y-intercepts and the fit worsened with decreasing flow index. A modification to the Mooney analysis is proposed that includes a geometrical dependency of the slip velocity that scales with the flow index of the liquid phase. Proposed modified Mooney plots not only show positive y-intercepts, but also show a good fit (R2 > 0.99) over the entire range of shear rates (10 – 640 s − 1) and corresponding wall shear stresses. The geometrical dependency is thought to arise from the shear stress gradient within the extrusion die.

Geometrical scale dependency of thin film solid oxide fuel cells

To study the geometrical scale dependency of thin film solid oxide fuel cells (SOFCs), we fabricated three thin films SOFCs which have the same cross-sectional structure but different electrode areas of 1 mm2, 4 mm2 and 9 mm2. Since the activation and ohmic losses of SOFCs depend on their active region, we examined the variations of the power density of the cells with a Pt/YSZ/Pt structure and simulated the power density variations using the COMSOL software package.

Experimental Analysis of Performance Variation on Thin Film Solid Oxide Fuel Cell with Different Cathode Area Sizes

To study the geometrical scale dependency of thin film solid oxide fuel cells (SOFCs), we fabricated three thin films SOFCs with the same cross-sectional structure but with different electrode areas of 1, 4 and 9 ㎟. Since the activation and ohmic losses of SOFCs depend on their active region, we examined the variations of the power density of the cells with a Pt (anode)/sputtered YSZ/Pt (cathode) structure. We found that a cathode electrode with a low aspect ratio may suffer from high ohmic and activation losses because of the geometrical scale dependency.

Active Control of Geometrically Nonlinear Vibrations of Laminated Composite Beams Using Piezoelectric Composites by Element-Free Galerkin Method

In this article, active control of geometrically nonlinear transient vibrations in laminated composite beams has been demonstrated using an advanced piezoelectric composite (PZC) layer as the active layer with a proper control strategy. A nonlinear mesh free (MF) model is derived for analyzing the dynamic characteristics of the laminated composite beams integrated with the PZC patch based on the element-free Galerkin (EFG) method within the framework of a layer wise beam theory considering transverse shear deformations. The Von Kármán type nonlinear strain–displacement relationships are considered for formulating the coupled electromechanical nonlinear MF model. Both in-plane and transverse actuation by the PZC layer have been taken into consideration for deriving the model. Various geometrical shapes of the PZC layers have been considered for the analysis to understand the geometrical shape dependency of the PZC layer in attenuating vibration in the structure. The numerical results indicate that the PZC layer significantly improves the dynamic characteristics of the laminated beams by suppressing the geometrically nonlinear transient vibrations induced in them. It has been also noticed that the irregular shaped PZC patches like triangular PZC patches perform better as compared to the regular rectangular PZC patches in alleviating vibration the structure.

Nonlinearity modulation based multiple Fano resonance and multi-spectral switching in a nanoplasmonic waveguide-coupled cavity system

Dual and multiple asymmetric Fano resonance are theoretically explored in a subwavelength plasmonic cavity-coupled waveguide system incorporated with a third order Kerr nonlinear medium. The degree of asymmetry and the number of multiple resonances are controlled by an external pump beam which modulates the Kerr permittivity thereby dictating the resonant behavior. Electromagnetically induced transparency in plasmonic systems, referred to as plasmon induced transparency, is a special case of Fano resonance and plays a key role for the occurrence of multiple Fano excitations. Plasmon induced transparency appears as induced reflectance dips when analyzed in reflection mode. Though geometrical dependency of dual and multiple Fano effect is demonstrated, the main interest and importance is focused on the generation and manipulation of multiple Fano resonances by intensity modulation of the pump beam and its application in multispectral switching and quality factor tuning at a fixed operating frequency.

Geometrical Effect Dependency on the On-State Characteristics in 5.6 kV 4H-SiC BJTs

The influence of varying the emitter-base geometry, i.e., the emitter width (WE), emitter contact–emitter edge distance (Wn), and base contact–emitter edge (Wp) on the on-state characteristics in 5.6 kV implantation free 4H-SiC BJTs are investigated. The BJTs present a clear emitter size effect pointing out that surface recombination has a significant influence on current gain (β). The results show that the influence of varying Wp on the β is higher than Wn. A distance of 3 μm between emitter contact and base contact to the emitter edge (Wn = Wp = 3 μm) is the optimized value to have a BJT with a high β, and low on-resistance (RON) at a given WE.

A general formulation of an analytical model for the elastic–plastic behaviour of a spot weld finite element

A general formulation of an analytical procedure for the evaluation of the elastic–plastic behaviour of spot welded joints is presented. The procedure is based on a model of spot weld region shaped by a circular plate having variable thickness and having a central rigid nugget representing the spot weld. A closed form solution of the original analytical approach allows to define the displacement of the rigid nugget, when an axial load is applied on the plate, though plasticity and large displacements are present. The so defined spot weld region model has to be used as the basis to extend the capability of a spot weld element in FE analysis when plasticity and large displacements are in effect. As well as presented in previous works, the procedure is completely general; the accuracy on geometrical parameters dependency is now improved and the strain hardening material characteristics has been introduced.Furthermore the constraints influence of the sheet metal surrounding the spot on elastic–plastic behaviour is investigated and evaluated, in order to generalize the plastic contribution on spot weld stiffness. Even if the theoretical framework is non-trivial, the formulation of the proposed procedure is straightforward and it can be easily implemented as an add-on of a FE code.The results, obtained by applying the general analytical procedure to some examples of spot welded joints, precisely match those obtained modelling spot weld region by FEA.

Tailoring of the flip effect in the orientation of a magnet levitating over a superconducting torus: Geometrical dependencies

In a previous study, a general local model was used in order to demonstrate the apparition of a flip effect in the equilibrium orientation of a magnet when it is over a superconducting torus. This effect can be easily used in devices such as binary position detectors for magneto-microscopy, contactless sieves or magnetic levels amongst others. We present an initial study useful to design devices based on the flip effect between magnets and torus superconductors. It demonstrates that varying different geometrical parameters the flip effect point can be fixed. Also, it can be observed that increasing the inner radius of the torus elevates the flip effect point. A magneto-mechanical explanation of this phenomenon is exposed. For an increment of cross-section diameter occurs the same behavior. There are linear piecewises in the geometrical dependency functions that can be used for a more accurate fitting of the flip effect point.

Effect of thermal and mechanical properties variations on microcantilever mass sensor performance

Ensuring desirable performance for piezoelectric microcantilever sensors constitutes a crucial research subject particularly for the applications such as detection of biochemical entities, virus particles or human biomarkers. However, these sensors’ performance may be affected by the environmental conditions such as temperature variation, and/or the uncertainty in the material properties. The objective of this study is to explore Young modulus uncertainty of microcantilever’s structural layer, thermo-mechanical and geometrical temperature dependency effects, on the natural frequency, bias and sensitivity of microcantilever mass sensors. These effects have been investigated for different sensor lengths and resonant modes. Also, a temperature compensation method which omits the need for bulky non-contact thermometers or fabrication of built-in temperature sensor has been proposed. As theoretical model, Euler–Bernoulli beam theory has been employed and solved by Galerkin expansion procedure. Using this model, it is demonstrated that the sensitivity of microcantilever sensor decreases with increasing the added mass. The microcantilever sensor sensitivity operating at the second resonant mode has been improved almost five times comparing to the first mode sensitivity regardless of microcantilever length. The simulation results show that temperature variation causes thermal frequency shift which in turn introduces a significant mass bias far beyond the sensors’ minimum detectable mass. This mass bias is constant for a given microcantilever in its first and second resonant mode. Additionally, the effect of temperature variation on the sensitivity of the given mass sensors is negligible. However, it has been shown that the variations in sensors sensitivity due to uncertainty of Young modulus remain constant for different lengths and two resonant modes of the microcantilever sensor.

Analytical Modeling and Thermodynamic Analysis of Robust Superhydrophobic Surfaces with Inverse-Trapezoidal Microstructures

A polydimethylsiloxane (PDMS) elastomer surface with perfectly ordered microstructures having an inverse-trapezoidal cross-sectional profile (simply PDMS trapezoids) showed superhydrophobic and transparent characteristics under visible light as reported in our previous work. The addition of a fluoropolymer (Teflon) coating enhances both features and provides oleophobicity. This paper focuses on the analytical modeling of the fabricated PDMS trapezoids structure and thermodynamic analysis based on the Gibbs free energy analysis. Additionally, the wetting characteristics of the fabricated PDMS trapezoids surface before and after the application of the Teflon coating are analytically explained. The Gibbs free energy analysis reveals that, due to the Teflon coating, the Cassie-Baxter state becomes energetically more favorable than the Wenzel state and the contact angle difference between the Cassie-Baxter state and the Wenzel state decreases. These two findings support the robustness of the superhydrophobicity of the fabricated Teflon-coated PDMS trapezoids. This is then verified via the impinging test of a water droplet at a high speed. The dependencies of the design parameters in the PDMS trapezoids on the hydrophobicity are also comprehensively studied through a thermodynamic analysis. Geometrical dependency on the hydrophobicity shows that overhang microstructures do not have a significant influence on the hydrophobicity. In contrast, the intrinsic contact angle of the structural material is most important in determining the apparent contact angle. On the other hand, the experimental results showed that the side angles of the overhangs are critical not for the hydrophobic but for the oleophobic property with liquids of a low surface tension. Understanding of design parameters in the PDMS trapezoids surface gives more information for implementation of superhydrophobic surfaces.

Thermoelastic stability analysis of imperfect functionally graded cylindrical shells

Elastic buckling analysis of imperfect FGM cylindrical shells under axial compression in thermal environments is carried out, using two different models for geometrical imperfections. The material properties of the functionally graded shell are assumed to vary continuously through the thickness of the shell according to a power law distribution of the volume fraction of the constituent materials, also temperature dependency of the material properties is considered. Derivation of equations is based on classical shell theory using the Sanders nonlinear kinematic relations. The stability and compatibility equations for the imperfect FGM cylindrical shell are obtained, and the buckling analysis of shell is carried out using Galerkin’s method. The novelty of the present work is to obtain closed form solutions for critical buckling loads of the imperfect FGM cylindrical shells, which may be easily used in engineering design applications. The effects of shell geometry, volume fraction exponent, magnitude of initial imperfections, and environment temperature on the buckling load are investigated. The results reveal that initial geometrical imperfections and temperature dependency of the material properties play major roles in dictating the bifurcation point of the functionally graded cylindrical shells under the action of axial compressive loads. Also results show that for a particular value of environment temperature, critical buckling load is almost independent of volume fraction exponent.

Calculation of field distortion by a large-gained avalanche in a gas counter

Simulation performed by using the continuity equation of electrons and positive ions is applied to examine the three-dimensional formation and the time evolution of an electron avalanche in a cylindrical gas counter. The field made by space charge is calculated exactly and concurrently by the relaxation method in the evolution. The gas multiplication for photon detection is consistently estimated for an Ar-based mixture by not using any adjustable parameter for geometrical dependency. Field distortion at the time of the finish of the evolution is studied systematically. The distortion is concentrated in a small region of angle in case of a large diameter of the anode. The shape of the distortion is calculated for several distributions of the initial charge. The distortion is enhanced by the distribution that occupies small area in the transverse plain in the avalanche. Change of the field distortion depending on the anode diameter and the initial charge distribution is shown quantitatively by these calculations. The transition to a streamer by the continuous supply of electrons is suggested to depend strongly on the charge distribution in an avalanche.