Geometrical Influences Research Articles

Hybrid 3D Printing of a Nature‐Inspired Flexible Self‐Adhesive Biopatch for Multi‐Biosignal Sensing

AbstractBioinspired skin adhesives are promising alternatives to traditional glue‐based skin patches for use in various skin‐attachable devices. However, the typical nano‐/microfabrication of these bioinspired microstructures provides limited manufacturing freedom over their performance, constraining their versatility and customization for widespread use. In this study, a hybrid 3D printing approach for fabricating a permeable skin patch is developed with adhesive miniaturized octopus‐like suckers (AMOS) for biosignal monitoring. The design and geometrical influences are investigated on the adhesion strength under different skin conditions (i.e., dry, wet, and hairy), permeability, and durability as well as proposed a biocompatible, stretchable, highly permeable, reusable, and conformable biopatch. Unlike commercially available biopatches that use chemical adhesives, the adhesion strength of an AMOS patch is customizable, does not cause skin irritation, and is comfortable for the wearer when worn for extended durations. The biopatch is tested in electromyogram, electrooculogram, and electrocardiogram signal measurement during a hand‐cycling experiment over extended durations that confirms its potential in extreme sport events. In addition to biosignal monitoring, 3D‐printed AMOS patches have broad applicability across various skin‐interfacing devices, including glucose and sweat monitoring, drug delivery, and wound healing. This approach offers a promising and highly customizable manufacturing solution for unlocking next‐generation skin‐attachable technologies.

Review of Biosensors Based on Plasmonic-Enhanced Processes in the Metallic and Meta-Material-Supported Nanostructures.

Surface plasmons, continuous and cumulative electron vibrations confined to metal-dielectric interfaces, play a pivotal role in aggregating optical fields and energies on nanostructures. This confinement exploits the intrinsic subwavelength nature of their spatial profile, significantly enhancing light-matter interactions. Metals, semiconductors, and 2D materials exhibit plasmonic resonances at diverse wavelengths, spanning from ultraviolet (UV) to far infrared, dictated by their unique properties and structures. Surface plasmons offer a platform for various light-matter interaction mechanisms, capitalizing on the orders-of-magnitude enhancement of the electromagnetic field within plasmonic structures. This enhancement has been substantiated through theoretical, computational, and experimental studies. In this comprehensive review, we delve into the plasmon-enhanced processes on metallic and metamaterial-based sensors, considering factors such as geometrical influences, resonating wavelengths, chemical properties, and computational methods. Our exploration extends to practical applications, encompassing localized surface plasmon resonance (LSPR)-based planar waveguides, polymer-based biochip sensors, and LSPR-based fiber sensors. Ultimately, we aim to provide insights and guidelines for the development of next-generation, high-performance plasmonic technological devices.

Flexible CNT/silicon piezo-resistive strain sensors geometrical influences on sensitivity for human motion detection

Flexible CNT/silicon piezo-resistive strain sensors geometrical influences on sensitivity for human motion detection

Dynamic crushing of composite coupons: An experimental and numerical study

Dynamic crushing of composites is studied proposing an optimised experimental design: flat, millimetre-scale specimens reduce geometrical influences and facilitate detailed numerical studies. Crushing behaviour is investigated on a universal testing machine and a drop-tower at varying loading rates using two different force measurement techniques. The results show a decrease in the maximum stress and absorbed energy at elevated rates due to a higher extent of delamination, caused by strain-rate-induced increase of intralaminar damage property values. The experiments are simulated in an explicit finite element solver with different through-thickness discretisation, showing that a stacked-laminate model is incapable of reproducing the crushing response at high velocities. However, a discrete-ply model is capable of describing the main failure mechanisms and energy absorption for all loading rates. Further improvement of the model’s predictive capability could be achieved by adding a plasticity formulation in the ply material model.

3D printed negative stiffness meta-structures with superior energy absorption and super-elastic shape-recovery features

The aim of this paper is to create novel 3D cubic negative stiffness (NS) structures (NSSs) with superior mechanical performances such as high energy absorption, shape recovery, super-elasticity, and reversibility. The conceptual design is based on an understanding of geometrical influences, non-linear buckling-type instability, snap-through mechanism, elasto-plastic deformation growth and plastic hinges. A finite element (FE) based computational model with an elasto-plastic material behavior is developed to design and analyze NSSs, saving time, material, and energy consumption. Material samples and meta-structures are 3D printed by selective laser sintering printing method. Material properties are determined via mechanical testing revealing that the printing process does not introduce much anisotropy into the fabricated parts. Experimental tests are then conducted to study the behavior of novel designs under loading–unloading cycles verifying the accuracy of the computational model. A good correlation is observed between experimental and numerical data revealing the high accuracy of the FE modeling. The structural model is then implemented to digitally design and test NSSs. Effects of the geometrical parameters of the negative stiffness members under three cyclic loading are investigated, and their implications on the non-linear mechanical behavior of NSSs under cyclic loading are put into evidence, and pertinent conclusions are outlined. In addition, the dissipated energy and loss factor values of the designed structures are studied and the proposed unit cell is presented for the energy absorbing systems. The results show that the structural and geometry of energy absorbers are key parameters to improve the energy absorption capability of the designed structures. This paper is likely to fill a gap in the state-of-the-art NS meta-structures and provide guidelines that would be instrumental in the design of NSS with superior energy absorption, super-elasticity and reversibility features.

How to Create Trusted Tribological Characterization Data of Soft Polymers as Input for FEM Simulations?

Soft polymers such as the investigated polyurethane, characterized by low Young's moduli and prone to high shear deflection, are frequently applied in pneumatic cylinders. Their performance and lifetime without external lubrication are highly determined by the friction between seal and shaft and the wear rate. FEM simulation has established itself as a tool in seal design processes but requires input values for friction and wear depending on material, load, and velocity. This paper presents a tribological test configuration for long stroke, reciprocating movement, allowing the generation of data which meet the requirements of input parameters for FEM simulations without the geometrical influences of specific seal profiles. A numerical parameter study, performed with an FEM model, revealed the most eligible sample geometry as a flat, disc-shaped sample of the polymer glued on a stiff sample holder. At the same time, the study illustrates that the sensitivity of the contact pressure distribution to Poisson's ratio and CoF can be minimized by the developed and verified setup. It ensures robust, reliable, and repeatable experimental results with uniform contact pressures and constant contact areas to be used in databases and FEM simulations of seals, enabling upscaling from generically shaped samples to complex seal profiles.

Analysis of the flow through the blowhole of twin-screw machines with different rotor profiles using dimensionless numbers

To ensure safe operation, gaps in a screw machine are essential. Some are relatively easy to adjust, like front and housing gaps, while it is more difficult, if they depend directly on the selected rotor profile shape, such as the inter-lobe clearance and the blowhole. Consideration of mass flow rates through those clearances is crucial to predict operation conditions or design screw machines. When using chamber model simulations, it is common to calculate idealized, theoretical mass flow rates and to combine them with a flow coefficient which represents the effect of e.g. friction losses. This paper deals with the flow coefficient of the blowhole, which is formed by the two rotors and the housing cusp. Therefore, a set of dimensionless numbers is used, including physical and geometrical influences on the flow coefficient. The real mass flow rate of an ideal gas (e.g. air) through the blowhole is calculated by CFD-simulations. The dimensionless numbers are systematically varied to identify their specific influences on the gained mass flow rates.

Investigations on the fatigue behaviour of welded-in stiffeners with gaps

The paper deals with investigations on the fatigue resistance of welded-in stiffeners with gaps. The presented investigations aim to specify limits of acceptable imperfections in terms of gaps in welds, as these do not reduce the fatigue strength in all cases. Finite-element simulations applying the effective notch stress concept have been conducted and confronted with fatigue test results from a detailed fatigue test database. Several geometrical influences regarding the fatigue behaviour of welded-in stiffeners with gaps were analysed and evaluated by performing a numerical study. Finally, interesting details of welded-in stiffeners were worked out and presented, in order to be tested experimentally in a future fatigue test program. It can be concluded that the effective notch stress concept is in fact a valuable tool to assess influences on the fatigue behaviour of the presented detail. The weld toe of the stiffener proves to be the relevant failure location in all investigated configurations, the weld root on the other hand is irrelevant. While the section size has a minor influence on the fatigue strength of the welded-in stiffener, the distance of the weld toes is the main influencing characteristic. The gap size does not play a major role for the fatigue resistance, which is why gaps with a certain size could be accepted in practice. This aspect will be confirmed in the future by conducting additional experimental fatigue tests.

Non-contact thin-film sheet conductance measurement based on the attenuation of low frequency electric potentials

Conductivity is a fundamental property of materials; in particular the precise quantification of electrical sheet resistance is essential for the development of electronic thin-film devices. Conventionally, resistive probes are used to perform the corresponding measurements. However, non-invasive methods are more desirable as they minimize the required sample preparation, as well as geometrical influences. Existing non-contact conductivity measurements mostly rely on the transmission of electromagnetic waves through conductive thin-films. Hence, they only characterize translucent samples at high frequencies. We present an alternative technique based on the attenuation of low frequency 10 kHz electric fields. The approach is used to quantify the field-effect induced conductivity variation of a flexible indium-gallium-zinc-oxide semiconductor film. A custom-built high-impedance electrometer is used to capacitively measure the attenuation of an alternating electric field passing through the film. The obtained data is discussed and related to the absolute conductivity with the aid of two bespoke models describing the impedance mismatch between the sample and its surroundings. The sheet conductivity is modulated and measured from 660 nS to 116 µS while conventional DC current/voltage measurements serve as a reference. Both methods show a high degree of correlation to the reference measurements. Unlike techniques based on light, the low frequency signal used here resembles quasi-static characteristics, and enables the direct measurement of DC parameters.

Numerical and databased investigations on the fatigue of cruciform joints with gaps

The paper deals with investigations on the fatigue resistance of the load-carrying cruciform joint with gaps. The aim is to define limits of specific acceptable imperfections, since these do not always necessarily affect the fatigue strength. Different geometrical influences on the fatigue strength of the load-carrying cruciform joint with gaps are analysed numerically. Numerical simulations comprise effective notch stress calculations, which have been compared to fatigue test results from literature, documented in a fatigue test database. A larger gap in combination with a smaller weld size leads to the unfavourable failure at the weld root. For the specific geometrical configurations, borderline functions defining the failure location on the basis of local weld geometry have been defined. Finally, the most interesting configurations are presented, which will be tested experimentally in a subsequent fatigue test program.

A New In Situ and Operando Measurement Method to Determine the Electrical Conductivity of the Negative Active Material in Lead-Acid Batteries during Operation

The electrical conductivity of the negative active material in lead-acid batteries has been found to significantly influence the properties of the electrode. Though several publications have addressed this subject, essential information on the conductivity evolution during cycling as well as the influence of additives could yet not be elucidated, even though specific knowledge could support the enhancement of existing lead-acid battery technology. In this study, a novel measurement setup is presented which enables the in-situ and operando measurement of the electrical resistance of bulk electrodes during operation based on the implementation of a four-point probe setup into a laboratory electrode. A comprehensive evaluation of the measurement setup is conducted using the negative electrode of a lead-acid battery as a test material. The experimental results are supported by numerical simulations in order to reflect and include all relevant geometrical and electrical influences from the measurement setup. A direct correlation between active material resistance and conductivity can be established, including the influence of the vertical position of the four-point probes. Finally, the evolution of the discharge capacity, electrical resistance and electrical conductivity of the negative electrode is studied over ten C 5 cycles and correlated to well-known structural developments within the active material.

Soft x-ray tomograms are consistent with the magneto-hydrodynamic equilibrium in the Wendelstein 7-X stellarator

Soft x-ray tomograms are inferred from experimental data obtained during the recent operational phases of the superconducting, optimized stellarator Wendelstein 7-X. It is shown that the reconstructed soft x-ray emission profiles of the plasma are consistent with the numerically calculated magneto-hydrodynamic equilibrium of Wendelstein 7-X. In order to obtain reliable tomograms, the full chain of electrical and geometrical influences on the x-ray observation has to be taken into account. This has been achieved by formulation and application of an extended forward model. The forward model has been verified using phantom data derived from surrogate tomograms.

Long-term in vivo monitoring of gliotic sheathing of ultrathin entropic coated brain microprobes with fiber-based optical coherence tomography

Objective. Microfabricated neuroprosthetic devices have made possible important observations on neuron activity; however, long-term high-fidelity recording performance of these devices has yet to be realized. Tissue-device interactions appear to be a primary source of lost recording performance. The current state of the art for visualizing the tissue response surrounding brain implants in animals is immunohistochemistry + confocal microscopy, which is mainly performed after sacrificing the animal. Monitoring the tissue response as it develops could reveal important features of the response which may inform improvements in electrode design. Approach. Optical coherence tomography (OCT), an imaging technique commonly used in ophthalmology, has already been adapted for imaging of brain tissue. Here, we use OCT to achieve real-time, in vivo monitoring of the tissue response surrounding chronically implanted neural devices. The employed tissue-response-provoking implants are coated with a plasma-deposited nanofilm, which has been demonstrated as a biocompatible and anti-inflammatory interface for indwelling devices. We evaluate the method by comparing the OCT results to traditional histology qualitatively and quantitatively. Main results. The differences in OCT signal across the implantation period between the plasma group and the control reveal that the plasma-type coating of otherwise rigid brain probes (glass) only slightly improve the glial encapsulation in the brain parenchyma indicating that geometrical or mechanical influences are dominating the encapsulation process. Significance. Our approach can long-term monitor and compare the tissue-response to chronically-implanted neural probes with and withour plasma coating in living animal models. Our findings provide valuable insigh to the well acknowledged yet not solved challenge.

Geometrical Influences on the Vibration of Layered Plates

This paper aims to study the influence of different geometric properties and support conditions on the vibration of layered plates of nonuniform thickness under shear deformation theory. The layered plates are supposed to have arbitrarily nonuniform thickness as linear, exponential, and sinusoidal. The spline approximation is used to approximate translational and angular displacement functions. Eigen frequency parameters are calculated by solving eigenvalue problem. The geometrical influences such as number of lay-ups, different ply orientations, each ply consisting of different material, side-to-thickness ratio, and aspect ratio are taken into consideration to examine the frequency variation of plates for two different support conditions.

Geometrical and thermal influences on a bacterial cellulose based sensing element for acceleration measurements

The need for a sustainable economy necessitates new environmentally friendly production technologies as well as devices that can be easily recycled, disposed of, and, finally, degraded, without any release of pollutants to the environment. In this context, bacterial cellulose (BC) has recently been investigated as an intriguing solution for the creation of green motion sensors. BC has excellent mechanical properties, and it is fully biodegradable and greener than the more common plant-derived cellulose. In this paper, we investigate the influence of geometry and environmental temperature on BC based sensing elements. More specifically, the influence of these quantities on a previously investigated BC-based accelerometer are reported. An experimental campaign and the characterization of the proposed green device for several geometries (from 7 to 22 mm of length) and various temperatures (from 5 °C to 55 °C) is addressed, obtaining very intriguing results.

Design principles for a single-process 3d-printed accelerometer – theory and experiment

Fused-filament fabrication, one of the most accessible additive manufacturing technology, has already been used to manufacture piezoresistive static/quasistatic strain sensors, force sensors and wind sensors. Recent research showed that fused-filament fabrication could also be used for the manufacturing of dynamic sensors. However, the anisotropic mechanical and piezoresistive behaviour, the heterogeneity, the large number of process parameters and the large number of possible geometrical designs open up numerous design options for manufacturing. Additionally, a small size is difficult to achieve due to the relatively low geometrical tolerances and the resolution of fused-filament fabrication. This paper is focused on the design principles of a single-process, fused-filament fabricated, uni-axial accelerometer with a piezoresistive sensing element. The anisotropic piezoresistive behaviour is researched for the maximum sensitivity in the measured acceleration direction and the minimal cross-axis sensitivity for the perpendicular axes. The analytical accelerometer model is based on a Bernoulli-Euler beam and is used to understand the frequency and the geometrical influences of the piezoresistive accelerometer with a beam-shaped sensing element and an attached intertial mass. Finally, a small-sized (22 × 22 × 15 mm3), single-axis, prototype accelerometer, with an approximately linear response up to-425 Hz and a low cross-axis sensitivity was manufactured. The derived principles can be used for further optimisation of the developed prototype sensor and as a foundation for the derivation of design principles for other types of fused-filament fabricated accelerometers, including 3-axis accelerometers. keyword: accelerometer; piezoresistivity; additive manufacturing; fused filament fabrication; dynamic sensor; 3D printing.

AIRBORNE AND MOBILE LIDAR, WHICH SENSORS FOR WHICH APPLICATION?

Abstract. The UAV mapping industry expanded tremendously during the last five years. Thanks to miniaturization, automation and advertising, this technology may give a wrong impression that mapping of certain quality is as simple as clicking few buttons on a PC. Moreover, with a large and continuously increasing offer of hardware and software, the identification of the right tools is not easy, especially when aiming at certain standard. In this respect, the mapping with LiDAR is more delicate than with a camera due to a lower level of redundancy within the process of orientation/georeferencing and somewhat higher threshold on the size/weight per performance ratio within these sensors. This fact motivated us to present a practical benchmark evaluating a popular small LiDAR sensor in realistic conditions for intrinsic parameters such as noise or capacity to penetrate canopy, as well as the “low-weight” inertial technology in terms of geometrical influences on the resulting point cloud. The practical limitations are indeed considerably lower than those specified by the manufacturers or tested in laboratory conditions. These should be considered together with other “mapping-productivity” factors that are summarized in the last part of this study.

Computational Design and Synthesis of a Deeply Red-Shifted and Bistable Azobenzene.

We computationally dissected the electronic and geometrical influences of ortho-chlorinated azobenzenes on their photophysical properties. X-ray analysis provided the insight that trans-tetra-ortho-chloro azobenzene is conformationally flexible and thus subject to molecular motions. This allows the photoswitch to adopt a range of red-shifted geometries, which account for the extended n → π* band tails. On the basis of our results, we designed the di-ortho-fluoro di-ortho-chloro (dfdc) azobenzene and provided computational evidence for the superiority of this substitution pattern to tetra-ortho-chloro azobenzene. Thereafter, we synthesized dfdc azobenzene by ortho-chlorination via 2-fold C–H activation and experimentally confirmed its structural and photophysical properties through UV–vis, NMR, and X-ray analyses. The advantages include near-bistable isomers and an increased separation of the n → π* bands between the trans- and cis-conformations, which allows for the generation of unusually high levels of the cis-isomer by irradiation with green/yellow light as well as red light within the biooptical window.

Computation of Global and Local Mass Transfer in Hollow Fiber Membrane Modules

Computational fluid dynamics (CFD) provides a flexible tool for investigation of separation processes within membrane hollow fiber modules. By enabling a three-dimensional and time dependent description of the corresponding transport phenomena, very detailed information about mass transfer or geometrical influences can be provided. The high level of detail comes with high computational costs, especially since species transport simulations must discretize and resolve steep gradients in the concentration polarization layer at the membrane. In contrast, flow simulations are not required to resolve these gradients. Hence, there is a large gap in the scale and complexity of computationally feasible geometries when comparing flow and species transport simulations. A method, which tries to cover the mentioned gap, is presented in the present article. It allows upscaling of the findings of species transport simulations, conducted for reduced geometries, on the geometrical scales of flow simulations. Consequently, total transmembrane transport of complete modules can be numerically predicted. The upscaling method does not require any empirical correlation to incorporate geometrical characteristics but solely depends on results acquired by CFD flow simulations. In the scope of this research, the proposed method is explained, conducted, and validated. This is done by the example of CO2 removal in a prototype hollow fiber membrane oxygenator.

Influence of Geometry of Twisted Tape Insert on Heat Transfer Augmentation

Heat exchangers are commonly used devices in several industrial applications owing to their high performance in transferring the heat from the hot nature to cold nature. Heat exchangers are necessary for saving energy, there are lots of methods implied to increase the thermal performance of heat transfer device by changing the surface of the flow area of the fluids.in most of the methods there is an insertion in the flow passage like twisted tape or blocks to make a disturb in the flow. Mainly these twisted tapes have a vital role in the heat transfer characters. In this present paper the various techniques used in increasing the heat transfer with the insertion of twisted tape and its geometrical influences on the performance of heat transfer were studied and reported.