Object Surface Research Articles

An alternative approach for detecting cavities in reinforced concrete structures using GPR A-scan data

This paper introduces an alternative approach for detecting cavities in reinforced concrete walls using Ground Penetrating Radar (GPR) A-scan data. GPR, leveraging electromagnetic waves, is extensively applied for cavity detection within structures. The nature of electromagnetic waves, significantly influenced by reflective media and attenuating through them, requires specialized analysis methods for data interpretation. Traditional methods often involve identifying and eliminating overlapping reflection patterns or adjusting signal magnitude at specific depths to isolate peak signals from the target object's surface, which can be subjective and complex. To overcome these challenges, this study proposes quantitatively assessing the presence of cavities by analyzing the integral area of A-scan data within suspected ranges. Observations indicate a substantial difference in reflection patterns between areas with and without cavities, showcasing the potential of this approach for quantitative cavity detection. This approach offers a more objective and quantitative basis for identifying cavities in reinforced concrete structures.

Object pose and surface material recognition using a single-time-of-flight camera

Object pose and surface material recognition using a single-time-of-flight camera

BimodalPS: Causes and Corrections for Bimodal Multi-Path in Phase-Shifting Structured Light Scanners.

Structured light illumination is an active 3D scanning technique based on projecting and capturing a set of striped patterns and measuring the warping of the patterns as they reflect off a target object's surface. As designed, each pixel in the camera sees exactly one pixel from the projector; however, there are multi-path situations where a camera pixel sees light from multiple projector positions. In the case of bimodal multi-path, the camera pixel receives light from exactly two positions, which occurs along a step edge where the edge slices through a pixel which, therefore, sees both a foreground and background surface. In this paper, we present a general mathematical model to address this bimodal multi-path issue in a phase-shifting or so-called phase-measuring-profilometry scanner to measure the constructive and destructive interference between the two light paths, and by taking advantage of this interference, separate the paths and make two decoupled depth measurements. We validate our algorithm with both simulations and a number of challenging real-world scenarios, significantly outperforming the state-of-the-art methods.

Air-coupled ultrasonic inspection of resin materials using single-probe vertical reflection method

Air-coupled ultrasonic inspection is a noncontact and convenient nondestructive testing method. However, its vertical reflection method using a single probe (i.e., pulse-echo mode) is known to be difficult to achieve, even though it is frequently used inspection mode in conventional contact or water immersion ultrasonic testing. This is because the reflectivity of ultrasonic waves at the boundary between air and the surface of inspection object is enormous, and faint signals received after transmitting into the object are difficult to detect. In this study, in order to achieve the air-coupled ultrasonic single-probe reflection method, transmitting chirp signals (waves with a linearly frequency modulation) with an appropriate window function and applying a pulse compression technique (a cross-correlation process between the received signal and a reference chirp signal) was examined, and its effectiveness was investigated through experiments for polystyrene specimens. Experimental results showed that the proposed method was effective in detecting faint reflection signals after propagating through the specimens, and that the difference in plate thickness could be detected by observing the change of the signal-receiving period of multiple reflection signals between the top and bottom surfaces of the specimens. These results demonstrate the feasibility of nondestructive testing using the air-coupled ultrasonic vertical reflection method and could show an important step toward its future practical applications.

Comparative study of phase retrieval algorithms for surface shape measurement by optical profilometry

Recent advances in optical sensors and information processing technology have granted a rapid progress in three-dimensional (3D) optical metrology, enabling highly accurate 3D inspection of complex-shaped objects. However, the 3D object surface estimation requires a phase recovery from so-called intensity fringe patterns of the tested objects. In this work, we present a comparative study of three most highlighted phase retrieval methods (phase shifting, Fourier transform and wavelet transform) using single or multiple acquired fringe patterns. Moreover, the phase retrieval methods performance is tested on additive and multiplicative noise based degraded fringe patterns, giving some qualitative and quantitative conclusions. Some experimental data are processed using Fourier transform and wavelet transform based algorithms to confirm accuracy of these two phase retrieval techniques.

An Improved Boundary Element Method for Predicting Half-Space Scattered Noise Combined with Permeable Boundaries

The boundary element method is widely used in practical engineering problems, especially in the field of acoustics. For flow-induced noise, the main target of acoustic calculations is to solve the wave equation with the flow field information. However, the sound field distribution of noncompact structures in half-space is especially complex because of the strong scattering effect, while the object surface boundary integration often brings a large workload and generates numerical singularities. In this paper, an improved boundary element method for predicting the aeroacoustic noise of noncompact structures is proposed, which can consider the characteristic distribution of sound field induced by complex structures in half-space. The smooth permeable boundary surrounding the object is used as the integration boundary, while the scattering effect of the ground boundary is investigated by combining the mirror Green’s function method, and the numerical prediction of aeroacoustic noise is carried out for the dipole source and NACA0012 airfoil in half-space. Numerical results show that the far-field noise obtained by using the permeable surface is consistent with that obtained by integrating the direct object boundary under the influence of ground boundary scattering. The mirror image Green’s function method is able to finely capture the ground scattering effect, which has a significant effect on the sound field as the frequency increases.

Coverage Planning for UVC Irradiation: Robot Surface Disinfection Based on Swarm Intelligence Algorithm.

Ultraviolet (UV) radiation has been widely utilized as a disinfection strategy to effectively eliminate various pathogens. The disinfection task achieves complete coverage of object surfaces by planning the motion trajectory of autonomous mobile robots and the UVC irradiation strategy. This introduces an additional layer of complexity to path planning, as every point on the surface of the object must receive a certain dose of irradiation. Nevertheless, the considerable dosage required for virus inactivation often leads to substantial energy consumption and dose redundancy in disinfection tasks, presenting challenges for the implementation of robots in large-scale environments. Optimizing energy consumption of light sources has become a primary concern in disinfection planning, particularly in large-scale settings. Addressing the inefficiencies associated with dosage redundancy, this study proposes a dose coverage planning framework, utilizing MOPSO to solve the multi-objective optimization model for planning UVC dose coverage. Diverging from conventional path planning methodologies, our approach prioritizes the intrinsic characteristics of dose accumulation, integrating a UVC light efficiency factor to mitigate dose redundancy with the aim of reducing energy expenditure and enhancing the efficiency of robotic disinfection. Empirical trials conducted with autonomous disinfecting robots in real-world settings have corroborated the efficacy of this model in deactivating viruses.

Single-Shot 3D Reconstruction via Nonlinear Fringe Transformation: Supervised and Unsupervised Learning Approaches.

The field of computer vision has been focusing on achieving accurate three-dimensional (3D) object representations from a single two-dimensional (2D) image through deep artificial neural networks. Recent advancements in 3D shape reconstruction techniques that combine structured light and deep learning show promise in acquiring high-quality geometric information about object surfaces. This paper introduces a new single-shot 3D shape reconstruction method that uses a nonlinear fringe transformation approach through both supervised and unsupervised learning networks. In this method, a deep learning network learns to convert a grayscale fringe input into multiple phase-shifted fringe outputs with different frequencies, which act as an intermediate result for the subsequent 3D reconstruction process using the structured-light fringe projection profilometry technique. Experiments have been conducted to validate the practicality and robustness of the proposed technique. The experimental results demonstrate that the unsupervised learning approach using a deep convolutional generative adversarial network (DCGAN) is superior to the supervised learning approach using UNet in image-to-image generation. The proposed technique's ability to accurately reconstruct 3D shapes of objects using only a single fringe image opens up vast opportunities for its application across diverse real-world scenarios.

The die for the production of the hammered kaptorgas from Kouřim, Central Bohemia

Kaptorgas were small trapezoidal boxes with lids worn by women and girls in early medieval central Europe as magic or protective amulets. The paper presents a new find of a bronze cast die for hammering the front side of kaptorgas, which was excavated at the Nad Dolnicí settlement site located in the hinterland of the important central Bohemian hillfort of Kouřim. The die was used to produce type 1A kaptorgas with a motif of a four-legged eared gryphon with an indication of a wing and a tail ending in a floral decorative element. Although kaptorgas with this particular motif have not been recorded in Bohemia, it has analogies in Bulgaria and Poland. Based on the stylistic assessment of this originally Mediterranean motif and the chronology of type IA kaptorgas in Bohemia, the die can be dated to the 10th and beginning of the 11th century. X-Ray fluorescence analysis and elemental mapping of the object's surface show that it was made from bronze with a significant lead admixture and a small admixture of zinc. The die is discussed in terms of the spread of Mediterranean motifs and their adaptation by local craftsmen.

TPU-assisted adhesive PDMS film for dry or underwater environments

Adhesive polymer films with anisotropic properties on either side have attracted tremendous interest for biomedical and engineering applications. However, developing an innovative solution that provides effective adhesion under both dry and wet conditions remains a considerable challenge. In this study, we devised a novel process for creating adhesive films by casting polydimethylsiloxane (PDMS) onto a thermoplastic polyurethane (TPU) substrate. During the curing process, the PDMS layer in contact with the TPU was lightly cross-linked, which significantly increased adhesion. The catalytic reaction used for polymerization was regulated by the TPU, which is known to adsorb metal ions. This adhesive PDMS film (APF) demonstrated outstanding adhesion on various substrates under dry and underwater conditions and maintained adhesion even after repeated use. In practical applications, the APF proved to be an effective waterproof patch by adhering to the surfaces of objects submerged in water.

A 3D Reconstruction Method Based on Homogeneous De Bruijn-Encoded Structured Light

Structured light three-dimensional reconstruction is one of the important methods for non-contact acquisition of sparse texture object surfaces. Variations in ambient illumination and disparities in object surface reflectance can significantly impact the fidelity of three-dimensional reconstruction, introducing considerable inaccuracies. We introduce a robust method for color speckle structured light encoding, which is based on a variant of the De Bruijn sequence, termed the Homogeneous De Bruijn Sequence. This innovative approach enhances the reliability and accuracy of structured light techniques for three-dimensional reconstruction by utilizing the distinctive characteristics of Homogeneous De Bruijn Sequences. Through a pruning process applied to the De Bruijn sequence, a structured light pattern with seven distinct color patches is generated. This approach ensures a more equitable distribution of speckle information.

An assessment of 2-D and 3-D interest point detectors in volumetric images

Many interest point detectors have been designed so far to work in two dimensional (2-D) images. However, expansion of these detectors into the third dimension for three dimensional (3-D) images can refine their representational power. This paper presents how the Harris corner, LoG filtering-based blob, and salient regions detectors can be expanded to find interest points in volumetric images handling multiple slices collectively. Performances of 2-D and 3-D detector implementations were assessed both qualitatively and quantitatively with value combinations of different parameters using metrics such as F1-score, localization error, and repeatability in binary images of twenty 3-D object models from the Princeton Shape Benchmark (PSB). Computation of F1-score and localization error depended on some manually marked ground truth points, while repeatability measurement was according to the proximity of the detected point sets. The 3-D detectors were evaluated as more successful in capturing distinctive and sparse interest points on 3-D object surfaces in qualitative analyses. Despite having greater computational complexities, most of the 3-D detectors yielded better average F1-score, localization accuracy, and repeatability given uniqueness constraint on the matched points in quantitative analyses. Therefore, the 3-D detectors appear preferable when longer working durations or sparser representations would not constitute any disadvantage.

Analysis of the Surface of Historic Fabric from the Auschwitz-Birkenau State Museum after Treatment with Ethanol Mist Used to Eliminate Microorganisms Harmful to Human Health.

the aim of the work was to present the changes occurring on the model and historical cotton surface of cotton resulting from disinfection with 90% ethanol mist. Samples of historical materials consisted of fabric elements from suitcases stored in A-BSM. A mist of 90% ethanol was applied for 15 s at a distance of 16 cm from the surface. The spectra of cotton samples before and after ethanol application were recorded using Fourier transform infrared spectroscopy (FTIR-ATR). Analyses of the surface layers were performed using X-ray photoelectron spectroscopy (XPS). the decontamination performed did not show any significant differences in the chemical composition and surface structure of cotton before and after the use of 90% ethanol mist. Ethanol mist, which eliminates microorganisms from the historical surface, does not cause significant changes to the surface of historical objects.

Practical Multi-Mesh Registration for Few-View Poly-Chromatic X-Ray Inspection

Accurate 3D mesh registration is essential in many industrial applications of X-ray imaging, as it allows quality assessment and inspection of manufactured objects. Conventional methods rely mainly on time-consuming and expensive X-ray computed tomography (X-CT) or ancillary camera systems. Instead, we propose a novel approach for efficient 3D multi-mesh registration in few-view industrial X-ray imaging scenarios. Our approach harnesses the capabilities of CAD-ASTRA, an X-ray mesh projector, compatible with the ASTRA toolbox and popular GPU libraries such as CuPy and PyTorch, for the simulation of X-ray projec tions from a known object surface mesh. As a differentiable program, CAD-ASTRA allows iterative improvement of the objects’ position in space by back-propagation of a differentiable measure of the projection error. The potential of this approach is demonstrated through tests on simultaneous multiple object registration in a poly-chromatic imaging, even in cases where the spectral characteristics of the imaging system are unknown. Results from a diverse set of real experiments highlight the efficacy of mesh registration, achieving successful registrations even when only two projections at a 10∘\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^\\circ $$\\end{document} angle relative to the scanning system center are available. The mesh projector facilitates resource-efficient registration in industrial applications with few viewpoints, thereby reducing the demand for resources and eliminating the need for X-CT reconstruction.

One‐step synthesis of a spongy flexible substrate for surface enhanced Raman spectroscopy comprising a silver nanoparticles‐loaded poly(amidoamine) dendrimer crosslinked with glutaraldehyde

AbstractA composite comprising a silver nanoparticles‐loaded poly(amidoamine) (PAMAM) dendrimer crosslinked with glutaraldehyde (PAMAM/AgNPs) is synthesized using a one‐step method under vortex at room temperature. The structure of glutaraldehyde‐crosslinked PAMAM dendrimer is characterized using FTIR and high‐resolution magic angle spinning–carbon 13 nuclear magnetic resonance (HRMAS 13C NMR) spectroscopy. The crosslinking structure ensures the uniformity and stability of the Ag nanoparticles, and the flexibility of the PAMAM/AgNPs composite. X‐ray diffraction (XRD) analysis and energy dispersive spectroscopy (EDS) confirm the formation of Ag nanoparticles in the PAMAM/AgNPs composite. Scanning electron microscopy (SEM) and three‐dimensional (3D) micro‐Raman images reveal the coarsely porous 3D micro‐structure of the PAMAM/AgNPs composite. This unique micro‐3D architecture provides the PAMAM/AgNPs composite with spongy flexibility and a swab‐like nature, which is advantageous for the rapid and effective absorption of liquid samples on the surfaces of objects. Surface enhanced Raman spectroscopy (SERS) indicates that the detection limits of both rhodamine 6G (R6G) and thiram are 1.0 × 10−5 mol L−1, and the SERS enhancement factor of R6G is determined to be 1.35 × 104. The spongy flexible PAMAM/AgNPs SERS substrate therefore has potential for use in Raman active compound detection.

3D scanning of daguerreotypes

Daguerreotypes are historical photographic images made on mirror-like metallic plates. These are heritage objects whose shape cannot be measured with invasive techniques, like contact probes, but the high reflectivity of their surfaces makes the use of non-invasive, 3D-measuring optical techniques challenging. Moreover, the dark areas resulting from their degradation produce a very high contrast, which add extra difficulties to their measurement. In the last few years, several strategies have been developed to overcome the limitations of optical techniques when measuring reflective metallic surfaces. Many of these solutions are not applicable to the study of cultural heritage artifacts, as they are invasive. We attempted the use of conoscopic holography in a 3D-scanning system using a double-exposure strategy. This is a promising option for 3D measuring of daguerreotypes, as we experimentally demonstrated in this work. We present the results obtained from the analyses of two 19th-century daguerreotypes with different superficial conditions. The double-exposure allowed us to obtain high-quality data from the entire object surface. This enabled the measurement of micro-scale details related to the manufacturing process and/or to the corrosion deposits. The proposed methodology can be exploited to monitor the overall health of highly reflective metallic objects but also the outcomes of some conservation treatments, such as cleaning.

Feasibility Examination of the Field Multi-focal Metallography Method (FMM) for Characterisation of Metallic Marine Artefacts

Field multi-focal metallography (FMM) is a development of field metallographic replication (FMR). It is an innovative minimally destructive technique that facilitates high-resolution metallographic observations of metallic object surfaces, regardless of their orientation to the optical axis of the microscope. Several artefacts retrieved during underwater excavations (a bronze powder chamber, a stud-link anchor chain, a winch, a heart-shaped shackle, a deadeye strap with a futtock plate, and an iron stud-link chain controller) were examined. The FMM results were compared with conventional metallography, where the sampling process inflicts substantial damage to the item. This FMM trial produced results of comparable quality to conventional metallography for both the bronze and the ferrous objects. It revealed the microstructure of the archaeological objects with minimal damage. The FMM method was shown to be a suitable tool for the study of ancient metal objects retrieved from shipwrecks.

MsSVT++: Mixed-Scale Sparse Voxel Transformer With Center Voting for 3D Object Detection.

Accurate 3D object detection in large-scale outdoor scenes, characterized by considerable variations in object scales, necessitates features rich in both long-range and fine-grained information. While recent detectors have utilized window-based transformers to model long-range dependencies, they tend to overlook fine-grained details. To bridge this gap, we propose MsSVT++, an innovative Mixed-scale Sparse Voxel Transformer that simultaneously captures both types of information through a divide-and-conquer approach. This approach involves explicitly dividing attention heads into multiple groups, each responsible for attending to information within a specific range. The outputs of these groups are subsequently merged to obtain final mixed-scale features. To mitigate the computational complexity associated with applying a window-based transformer in 3D voxel space, we introduce a novel Chessboard Sampling strategy and implement voxel sampling and gathering operations sparsely using a hash map. Moreover, an important challenge stems from the observation that non-empty voxels are primarily located on the surface of objects, which impedes the accurate estimation of bounding boxes. To overcome this challenge, we introduce a Center Voting module that integrates newly voted voxels enriched with mixed-scale contextual information towards the centers of the objects, thereby improving precise object localization. Extensive experiments demonstrate that our single-stage detector, built upon the foundation of MsSVT++, consistently delivers exceptional performance across diverse datasets.

A screening method for heavy metals in consumer goods using reactive desorption electrospray ionization mass spectrometry.

Contamination of everyday goods with heavy metals such as nickel, cadmium, and lead known to be hazardous to the health of customers is an ongoing problem. Here, a mass spectrometric screening method based on reactive desorption electrospray ionization (DESI) is presented for the analysis of metals in consumer goods such as jewelry, tableware, and paintings. The method detects oxidized species of lead, nickel, cadmium, copper, and iron from the surface of objects without sample preparation. Positively charged metal ions form singly and doubly negatively charged complexes with ethylenediaminetetraacetic acid added to the DESI solvent, which are analyzed by a mass spectrometer. Qualitative and quantitative performance of the method was elucidated with metal salt standards. Subsequently, authentic samples were analyzed qualitatively. Reactive DESI-MS was able to detect lead and cadmium in eight out of nine consumer goods. For tableware, these heavy metals were found to be localized in the print as determined by reactive DESI imaging. In addition, mockup paintings generated from modern and historical pigments of Pb, Cu, Cd, and Fe in various media (acrylic binder, egg tempera, and linseed oil) were measured to show the suitability of the method for art authentication and conservation. The developed method expands the range of analytes accessible by DESI-MS to metal ions. Hence, DESI becomes a suitable ionization technique for an increasing number of analyte classes, which are of interest in chemical screening of consumer goods.

Microfacet rendering with diffraction compensation

AbstractThe traditional microfacet rendering models usually only consider the straight propagation of light and do not take into account the diffraction effect when calculating the radiance of outgoing light. However, ignoring the energy generated by diffraction can lead to darker rendering results when the object's surface has many small details. To address this issue, we introduce a diffraction energy term in the microfacet model to compensate for the energy loss caused by diffraction. Starting from the Fresnel‐Kirchhoff diffraction theorem, we combine it with the Cook‐Torrance model. By incorporating the computed diffraction radiance into the outgoing radiance of the microfacet, we obtain a diffraction‐compensated BRDF (Bidirectional Reflectance Distribution Function) model. Experimental results demonstrate that our proposed method has a significant effect in compensating for outgoing light and produces more realistic rendering results.