Directional Pattern Research Articles

Overview of Vivaldi Antenna Selection for Through-Wall Radar Applications

This paper analyzes broadband antennas, with a special focus on Vivaldi antennas, for their suitability for through-wall radar applications. It assesses various antenna designs, emphasizing high gain, wide impedance bandwidth, and effective wall penetration capabilities. Vivaldi antennas are superior due to their broad bandwidth, high gain, and directional radiation patterns. This study further explores structural optimizations, feeding techniques, and performance enhancement strategies to refine Vivaldi antenna designs for through-wall radar systems. Through a comparative analysis and technical evaluation, this paper highlights Vivaldi antennas’ potential for improving through-wall radar systems’ imaging and sensing capabilities. This presents a pathway for future ultra-wideband advancements.

Advanced Laser Techniques for the Development of Nature-Inspired Biomimetic Surfaces Applied in the Medical Field

This review focuses on the innovative use of laser techniques in developing and functionalizing biomimetic surfaces, emphasizing their potential applications in the medical and biological fields. Drawing inspiration from the remarkable properties of various natural systems, such as the water-repellent lotus leaf, the adhesive gecko foot, the strong yet lightweight spider silk, and the unique optical structures of insect wings, we explore the potential for replicating these features through advanced laser surface modifications. Depending on the nature and architecture of the surface, particular techniques have been designed and developed. We present an in-depth analysis of various methodologies, including laser ablation/evaporation techniques, such as Pulsed Laser Deposition and Matrix-Assisted Pulsed Laser Evaporation, and approaches for laser surface structuring, including two-photon lithography, direct laser interference patterning, laser-induced periodic surface structures, direct laser writing, laser-induced forward transfer, and femtosecond laser ablation of metals in organic solvents. Additionally, specific applications are highlighted with the aim of synthesizing this knowledge and outlining future directions for research that further explore the intersection of laser techniques and biomimetic surfaces, paving the way for advancements in biomedical applications.

Reinforced Magnetic-Responsive Electro-Ionic Artificial Muscles by 3D Laser-Induced Graphene Nano-Heterostructures.

Efficient ion transport and enriched responsive modals via modulating electrochemical properties of conductivity and capacitance are essential for soft electro-ionic actuators. However, cost-effective and straightforward approaches to achieve expedited fabrication of active electrode materials capable of multimodal-responsiveness remain limited. Herein, this work reports the one-step ultrafast laser direct patterning method, to readily synthesize electro- and magneto-active electrode material, derived from the unique cobalt-phosphorus co-doped core-shell heterostructures within 3D graphene frameworks, for fulfilling the dual-mode responsive electro-ionic actuators. The designed nanofiber-structured heterointerfaces across electrodes and electrolytes further promote highly efficient electron/ion transfer. The developed soft actuator exhibits superior actuation performance of peak-to-peak displacement to 13.08mm under an ultra-low ±0.5V, with doubled direct current deflection under 200 mT at 1V, an ultrafast response of 1.38 s and long-term stability (>90% retention for ≈106000 cycles), even detectable bending to ≈280µm under exceptional ±10mV. The promising demonstration of promoting differentiation and proliferation of stem cells under mechanical strain and electrical stimuli, sheds more light as well on the possibility of facilitating biomedical soft robotics with ultrahigh actuation performance.

Theoretical Substantiation of Methods for Reducing the Near-Side Radiation of Antennas for an Earth Satellite Communication Station

Within the framework of this article, various methods of reducing the lateral radiation of the antenna are considered, which mainly relate to the angular directions directly adjacent to the direction of the main radiation of the antenna for an earth satellite communication station. The relevance of this issue is beyond doubt, since it is the behavior of the antenna's diagrammatic orientation in this area that most significantly determines the electromagnetic compatibility of various satellite communication systems. The presence of axial shading leads to a significant increase in the near side lobes. The specified deformation of directional properties in a certain plane can be eliminated by using an additional radiator, the phase center of which in this plane coincides with the phase center of the antenna. Shadow radiation compensation is carried out only in a beam of regions close to the plane perpendicular to the straight line connecting the centers of the main and auxiliary antennas. The angular compensation area can be significantly expanded if the phase centers of the main and auxiliary antennas are combined. This rather trivial conclusion is still waiting for its non-trivial technical implementation. Wide-angle compensation of lateral radiation is proposed to be carried out by two auxiliary antennas located parallel to the suppression plane. The best results can be obtained by optimizing the opening shape of the auxiliary radiators. Studies show that the optimal variant of the directional pattern occurs when the mentioned irradiators are made in the form of rectangles with a length of 0,295 and a height of 0,117 from the opening radius of the main antenna, and the distribution in the openings of the auxiliary antennas is cosine-shaped. In this case, it is possible to suppress the radiation level to -40 dB.

Synthesizing source directivity using DeepONet room acoustic predictions

Incorporating source directivity when simulating spatial room impulse responses for virtual environments is crucial for achieving natural results. Directly injecting the directional source as the initial condition for a wave equation to solve would require re-running a numerical solver for each new directivity pattern, source position or orientation. Here we show that learned surrogate models can lead to large efficiency benefits if such variation shall be simulated. Although training such models is a computationally expensive process, performing inference over them is typically fast. Here we show how to exploit that property by training a deep neural operator network (DeepONet) only using omni-directional sources, and predicting the pressure on a variable grid of points, to which directivity filters are applied to generate arbitrary patterns. We show the fit of directictivity patterns to their re-synthesized versions from the output of a DeepONet.

On the influence of AVAS directivity on electric vehicle speed perception

Electric vehicles (EVs) typically produce minimal noise at low driving speeds, increasing the risk of accidents for pedestrians and other vulnerable road users. Therefore, regulations require EVs to use acoustic vehicle alerting systems (AVAS) that emit artificial warning sounds. Investigating the human response to these AVAS sounds requires laboratory listening experiments, often based on auralizations. One of the challenges when auralizing electric vehicles is to include AVAS radiation directivity. However, it is currently unknown how this directivity affects the perception of a vehicle passing by and whether an accurate reproduction is necessary for auralizations. We present a study on the influence of AVAS directivity on perceived vehicle speed, comparing different radiation patterns in combination with narrowband and tonal AVAS signals in a paired comparison listening experiment with 31 participants. The results show that AVAS radiation directivity can significantly influence the perception of vehicle pass-by speed, with a tendency for omnidirectional patterns to be perceived slower than more directional patterns. Additionally, most participants consistently rated either the tonal or the narrowband noise AVAS signal as faster throughout most comparisons. This indicates that AVAS signal type can affect vehicle speed perception with a subjective preference between tonal and narrowband noise AVAS.

ANÁLISE DO COMPORTAMENTO EROSIVO E CARACTERIZAÇÃO SEDIMENTOLÓGICA DA BARRA ARENOSA NA FOZ DO RIO ITABAPOANA, PRESIDENTE KENNEDY-ES

The state of Espírito Santo, despite being the smallest in the Southeast region, presents a significant diversity in the variations between the effects of retrogradation and coastal progradation. This dynamic is influenced by a complex interplay of variable factors, such as coastal geomorphology, hydrodynamics, and geology, which directly affect coastal cities and their development. The objectives of this study are to understand the phenomenon of coastal erosion and to analyze the morphological behavior of the sandy bar at the mouth of the Itabapoana River and at Praia das Neves, generating relevant information for the preservation of the coastal environment and minimizing material losses in urban areas adjacent to the sea. This work used tools such as the Ground Penetrating Radar (GPR) for the interpretation of radarfacies, as well as remote sensing and satellite image geoprocessing methodologies, combined with sedimentological characterization studies applied to Environmental Geology. The integration of GPR data revealed a complex sedimentary dynamic, with reflectors that indicate the progradation of beach deposits, as well as eolian, fluvial and marine influences, observing the presence of filled paleochannels and fluvial deposits. The analysis of satellite images allowed us to identify variations in the morphology of the beach and the location of the sandy bar at the mouth of the Itabapoana River, which shows migration patterns in a north-south direction. The compilation of the results suggests that coastal erosion in the region is cyclical, alternating between moments of progradation and retrogradation throughout the analyzed period, reflecting a complex coastal environment that involves climatic factors and marine and fluvial dynamics. The sediments analyzed were well selected, ranging from fine to medium fraction, with heavy fine sediments from the Araçuaí-Ribeira Orogen, showing low textural maturity.

Modelling structure-borne sound and radiation of submerged structures at high frequencies

Predicting the vibroacoustic behaviour of structures in contact with water and at high frequencies can be a complex task due to the fluid-structure interaction. Computation time increases with frequency and the complexity of the structure. Being able to predict the sound radiated by a naval vehicle in contact with water could help in improving passengers' comfort as well as the impact on the marine fauna. We use a prediction method called Dynamic Energy Analysis (DEA), so far emloyed mainly to assess the vibrational energy levels in the structure itself. DEA is a phase-space based ray tracing method determining energy densities in terms of the ray densities in a structure. The method can be applied on FEM-meshes and thus needs no SEA type substructuring. We expand the DEA methodology here to take into account radiation into the fluid in contact with the structure. From structure borne DEA calculations, we can determine directional sound radiation patterns both inside and outside the structure. We will demonstrate the new technique using some simple model systems.

Prediction and observation of regional infrasound from the OSIRIS REx re-entry capsule

Infrasonic signals produced by bolides and space debris passing through atmosphere are frequently observed at notable stand-off distances. The acoustic energy radiated from such objects is dominated by the aero-acoustic Mach cone which exhibits a highly directional radiation pattern dependent on the velocity of the object relative to the surrounding atmosphere. Recently, a mapping of the Mach cone geometry into acoustic ray tracing methods has enabled efficient regional simulation of infrasonic ensonification from such sources. In September 2023, the OSIRIS REx sample capsule returned to Earth as part of a NASA supported asteroid study and a number of institutions deployed sensors to measure geophysical signatures of the event. The anticipated capsule trajectory was combined with historical atmospheric data for September in the western United States to predict likely regional ensonification during re-entry. Los Alamos National Laboratory infrasound experts deployed microbarometer arrays in locations predicted to be ensonified and were able to identify signals with arrival times and direction-of-arrival consistent with the capsule re-entry. An overview of the predictions, field deployments, and identified signals will be presented.

Experimental validation of an hybrid analytical-numerical technique to estimate the directivity of ultrasonic piezoelectric actuators

The generation of guided waves is a common approach for structural health monitoring. The optimization of the excitation strategies very much benefits from the availability of efficient simulation tools. On the one hand, the application of finite elements (FEs) for the analysis of wave propagation problems leads to large models which tend to be computationally costly for optimization studies. On the other hand, semi-analytical approaches provide useful analytical expressions for parametric studies, but may lead to inaccurate estimations of tuning frequencies and directionality, especially at high frequencies. This is mostly because of the simplifying assumptions regarding the stress field at the interface between the actuator patches and the plate. An interesting methodology couples the analytical far-field solution of the plate response with a local FE model of the interface stresses between plate and patches. This method allows the analysis of complex actuation configurations for various purposes, such as directivity steering. In this contribution, we experimentally validate such hybrid FE-analytical technique. A Scanning Laser Doppler velocimeter is employed to retrieve both temporal and spatial Fourier Transforms on a polycarbonate plate, excited by piezoelectric patches, and the directivity patterns of the first symmetric and antisymmetric modes are compared to the numerical predictions.

Effect of Airfoil thickness on low-frequency gust-airfoil interaction noise

Interaction between turbulence and an airfoil is a significant aerodynamic noise source for many engineering applications when turbulence in the wake of upstream blades interacts with the leading edge of downstream blades. Modeling the oncoming turbulence as harmonic gusts is a common approach to studying the noise generated by turbulence-airfoil interaction. The airfoil can be considered a compact noise source, resulting in a dipole-like sound directivity pattern when the acoustic wavelength of gust-airfoil interaction is much larger than the airfoil chord length. However, the interaction becomes more complex when the acoustic wavelength is comparable to or smaller than the airfoil chord, as the airfoil cannot be treated as a compact source anymore and multiple lobes appear in the radiated sound directivity. This paper studies airfoil thickness effects using a computational aeroacoustics approach based on the spectral/hp element method for low-reduced frequency gusts. It is found that the sound pressure decreases with the increase of thickness for low reduced frequency gusts. To reveal its mechanism, a semi-analytical method and the convective FW-H equation are used for low reduced frequency to analyze the radiated noise. The interaction between sound sources on the airfoil surface is crucial for the thickness effect.

Direct Photo‐Crosslinking Patterning for High‐Performance 0D–2D Hybrid Photodetectors

AbstractHigh‐performance 0D–2D hybrid photodetectors integrated with a crosslinker for direct pattering of quantum dots on the large‐scale synthesized MoS2 layer are reported. In the patterned hybrid structure, QD layers are patterned with a resolution of up to 2 µm, ensuring high precision. Enhanced charge transfer from QDs to 2D materials is confirmed using PL quenching, TR‐PL, and UPS analysis. As a result, the QD/2D hybrid photodetectors with crosslinker‐assisted direct patterning demonstrated a remarkable photoresponsivity of ≈105 A W−1 and a specific detectivity of over 1011 Jones, attributed to the difference in built‐in potential. The crosslinker patterning of QDs opens up potential applications for the photodetectors in highly integrated image sensors and can be further extended to high‐resolution display industries, eliminating unnecessary fabrication processes.

A semi-analytical framework for predicting far-field responses of complex elastic waves emitters

Applications of guided waves in various fields of engineering and science rely on elastic wave emitters for wave generation. Accurate prediction and understanding of the far-field responses of these wave emitters are crucial for the reliable and efficient application of guided waves-based technologies. In this paper, we propose a novel semi-analytical framework capable of predicting the far-field response of complex wave emitters of arbitrary shape and internal structure in any type of substrate. This framework is general, and is not confined to specific methods, enhancing its versatility. We applied the proposed semi-analytical framework to predict the directivity patterns of two different macro-fiber composite transducers, accurately modeled using their exact topologies. The framework’s validity was experimentally confirmed by comparing the predicted directivity patterns with the results obtained from experimental measurements.

Gain enhancement of compact CPW‐Fed ultra‐wideband antenna using an FSS reflector

AbstractIn this paper, an enhancement gain of compact CPW‐Fed antenna using a single layer frequency selective surfaces (FSSs) reflector for ultra‐wideband (UWB) applications is presented. A hexagonal CPW‐Fed antenna with a size of 30 × 30 mm2 is realized to provide a UWB bandwidth operation. In this study, a novel design of an FSS unit cell with reduction and a small size of 8 × 8 mm2 is proposed. It allows one to achieve a UWB band‐stop response between 3 and 11.5 GHz. The FSS reflector has 7 × 7 units with a total size of 56 × 56 mm2. This reflector is placed below the antenna at a distance of 20 mm. The main objective of this contribution is to improve the gain level of the antenna, where the proposed antenna achieves an improvement of realized gain of 6.2 dBi with increasing from 2.2 to 8.4 dBi. The antenna became more directive after the integration of the FSS reflector with a directional radiation pattern. The numerical and experimental results are in good concordance with the simulated one. This study is performed in terms of voltage standing wave ratio, radiation pattern, realized gain, and radiation efficiency.

Harm-to-Benefit Ratio of Fecal Immunochemical Test–Based Screening for Colorectal Cancer Given Prior Fecal Hemoglobin Concentrations

This study aimed to provide evidence on the harm-to-benefit ratio of fecal immunochemical test (FIT)-based colorectal cancer (CRC) screening by previous fecal hemoglobin (f-Hb) concentrations, as reflected in the number needed to screen (NNS) and number needed to scope (NNSc). Participants in up to 4 FIT screening rounds of the Dutch CRC screening program were included. The main outcomes of this study were the NNS and NNSc to detect 1 CRC and/or advanced neoplasia (AN) in screening rounds 2, 3, or 4, conditional on previous f-Hb concentrations. Outcomes were compared between participants using chi-square tests and logistic regression. In total, 2,428,883 study participants completed at least 2 consecutive FITs, 1,308,684 completed 3 FITs, and 150,958 completed 4 FITs. There were 31,400, 16,060, and 2007 ANs detected by round, respectively. The NNS for individuals with vs without a history of detectable f-Hb differed significantly irrespective of screening round. Individuals without detectable f-Hb in previous negative FITs had almost 9 times the NNS to detect 1 AN compared with those with detectable f-Hb (odds ratio, 8.71; 95% confidence interval, 8.51-8.92). A similar directional pattern was observed for NNSc, although the differences were smaller (odds ratio, 2.7; 95% confidence interval, 2.7-2.8). The harm-to-benefit ratio of FIT-based screening is substantially greater in individuals without vs with prior detectable f-Hb. Less intensive screening should be considered for this lower-risk group.

The Accuracy of Custom-Made Milled Metal Posts as Compared to Conventional Cast Metal Posts.

The aim of this study was to compare the fitting accuracy of custom-made metal posts and cores fabricated by half-digital and milling technique to that of conventional cast posts fabricated by direct technique. Sixteen extracted single-rooted teeth were endodontically treated followed by post space preparation. A direct resin post and core pattern was made for each tooth and used for the fabrication of two posts (n = 16). Each post resin pattern was digitized with a laboratory scanner and used for the fabrication of a milled cobalt-chrome (Co-Cr) alloy post, while the direct resin pattern, after scanning, was cast in a Co-Cr alloy to produce a cast post. Each post was seated on its respective tooth and evaluated using microcomputed tomography. The following variables were evaluated: total space volume between the post and root canal, the volume and distance of the apical gap between each post and the remaining apical root canal filling, as well as the distance and surface area of the space between the post and lateral root canal wall at four determined points along the length of each post. The results revealed that half-digital and milled posts had a statistically significantly higher total space volume (p < 0.05), apical gap volume (p < 0.02) and distance (p < 0.02), as well as a higher surface area of space between the post and root canal wall at the cervical area as compared to the cast post (p < 0.05). This study demonstrated that the fitting accuracy of cast posts was more accurate than posts fabricated with half-digital and milling technique.

Direct patterning of electrical wiring on three-dimensional plastic substrate under ambient air conditions

Direct patterning of electrical wiring on three-dimensional plastic substrate under ambient air conditions

Splitting intensity tomography to image depth-dependent seismic anisotropy patterns beneath the Italian Peninsula and surrounding regions

The region between central Europe and the centre of the Mediterranean is characterised by complex tectonics and kinematics. Here, the interaction between thickened crust, subducting lithosphere and surrounding asthenosphere produces strong and pervasive anisotropy in the upper mantle. Shear wave splitting measurements, the most adopted method to image seismic anisotropy so far, when interpreted in a ray-based framework result in little or no depth resolution, hampering a correct image of the anisotropy distribution with depth. In this study, we aim to better constrain the depth-dependent seismic anisotropy beneath Italy and surrounding regions, by isolating for the first time the source region of anisotropy at different depths. To do that, we perform an anisotropy tomography, adopting the splitting intensity inversion method. It is entirely based on the finite-frequency effect in the splitting of SKS waves. We first computed the splitting intensity using SKS waves recorded at all available permanent and temporary stations over the region, obtaining a huge dataset of measurements used as an input for the tomographic inversion. The large-scale 3D model of seismic anisotropy obtained with the inversion shows a clear change of anisotropy properties in terms of fast polarisation direction and intensity for different depths, thus improving the characterization of the main sources of anisotropy in the mantle as a function of depth. Shallower layers (70–100 km depth) are characterised by a complex and variable oriented pattern of anisotropy fast direction and intensity, which becomes progressively more organised with depth (100–300 km). This pattern suggests a strong control exerted by the geometry and motion of the different slab segments and the large-scale asthenospheric flow generated by subduction and roll-back processes. The strength of anisotropy increases with depth, with high values affecting the bulge of the Alps and Apennines chains and the southern Tyrrhenian subduction system. On the contrary, weaker anisotropy characterises the transition zone from the Apennines to Alpine domains beneath the Po plain, and both the Adriatic and European domains.

Fabrication of Multiscale and Periodically Structured Zirconia Surfaces Using Direct Laser Interference Patterning

AbstractThe functionalization of zirconia surfaces by accurate and fast printing of periodical patterns embedding sub‐micrometric features is of great interest to many engineering fields and is yet to be explored. This study aims to assess the influence of the Direct Laser Interference Patterning processing parameters on the morphology and microstructure of zirconia surfaces using a 532 nm 10 ps‐pulsed laser source. Well‐defined linear structures with a period of 3 µm are successfully produced. Depending on the laser parameters, the structures are developed at or below the surface level, with higher depths (≈1 µm) being seen for increasing values of laser fluence and pulse overlap. Line‐like hierarchical structures with smaller interference spatial structures (3 µm period) and higher secondary structures with different periods (18, 15, and 12 µm) and heights (7, 5, and 3 µm, respectively) are also obtained on zirconia surface. Ablated regions presented few traces of molten material, nano‐droplets, and sub‐micrometric (&lt;1 µm) pores, while no (sub) micrometric cracks are detected. A slight amount of tetragonal to monoclinic phase transformation (≈5%) is detected by X‐ray diffractometry. A processability map for ps‐laser processing of zirconia is proposed based on the experimental data.

IR Hidden Patterns for Security Labels.

Authentication of a product's originality by anticounterfeiting labels represents a crucial point toward protection against forgery. Fast and scalable fabrication methods of original labels with a high degree of protection are in high demand for the protection of valuable goods. Here, we propose a simple strategy for fabrication of hidden security tags with IR luminescent readout by the direct femtosecond laser patterning of silicon-erbium-silicon sandwiched thin films. The choice of laser processing parameters makes possible the creation of random or quasi-regular self-organized surface nanotextures. The controlled laser-driven oxidation accompanying this process provides simultaneous regulation of the film's optical properties and spontaneous emission yield of the embedded Er atoms. The regimes are detected when optically similar patterned areas demonstrate different Er emission intensities, allowing us to create hidden security tags with facile readout at the C-band telecommunication wavelengths. The obtained results take another step toward the application of IR-luminescent erbium-based anticounterfeiting labels for covert and/or forensic security levels.