Surface Profile Research Articles

Compact Single-Shot Dual-Wavelength Interferometry for Large Object Measurement with Rough Surfaces

Single-shot dual-wavelength interferometry offers a promising avenue for surface profile measurement of dynamic objects. However, current techniques employing pixel multiplexing or color cameras encounter challenges such as complex optical alignment, limited measurement range, and difficulty in measuring rough surfaces. To address these issues, this study presents a novel approach to single-shot dual-wavelength interferometry. By utilizing separated polarization illumination and detection, along with a monochromatic polarization camera and two slightly different wavelengths, this method enables the simultaneous recording of two frames of separated interferometric patterns. This approach facilitates straightforward optical alignment, expands measurement ranges, accelerates data acquisition, and simplifies data processing for dual-wavelength interferometry. Consequently, it enables online shape measurement of large dynamic samples with rough surfaces.

Experimental and numerical investigations of the water surface profile and wave extrema of supercritical flows in a narrow channel bend

Supercritical flows in channel bends, e.g., in steep streams, chute spillways, and flood and sediment bypass tunnels (SBTs), experience cross-waves, which undulate the free surface. The designs of these hydraulic structures and flood protection retaining structures in streams necessitate computing the locations and water depths of the wave extrema. This study numerically and experimentally investigates the water surface profiles along the sidewalls, the wave extrema flow depths, and their angular locations in a narrow channel bend model of the Solis SBT in Switzerland. The 0.2 m wide and 16.75 m long channel has a bend of 6.59 m radius and 46.5° angle of deviation. The tested flow conditions produced Froude numbers ≈ 2 and aspect ratios ranging from 1.14 to 1.83. Two-phase flow simulations were performed in OpenFOAM using the RNG k–ε turbulence closure model and the volume-of-fluid method. The simulated angular locations of the first wave extrema and the corresponding flow depths deviate marginally, within ± 6.3% and ± 2.1%, respectively, from the experimental observations, which signifies good predictions using the numerical model. Larger deviations, especially for the angular locations of the wave extrema, are observed for the existing analytical and empirical approaches. Therefore, the presented numerical approach is a suitable tool in designing the height of the hydraulic structures with bends and conveying supercritical flows. In the future, the model’s application shall be extended to the design of the height and location of retaining walls, embankments, and levees in steep natural streams with bends.

Fabrication and performance evaluation of a design for an extended depth-of-focus intraocular lens based on an improved sinusoidal profile

This study presents the fabrication and evaluation of a sinusoidal extended depth-of-focus (EDoF) intraocular lens (IOL) based on our previously proposed design approach. The power, through-focus MTF, and surface profile were measured using commercial instruments. Through-focus images of a United States Air Force (USAF) 1951 resolution target formed by the fabricated IOL were compared with Symfony and AR40E under monochromatic and polychromatic light using optical bench testing. Simulations assessed visual acuity (VA) of a pseudophakic model eye with the EDoF IOL, including evaluation of tilt and decentration effects. Results indicate that the base power, add power, and the through-focus MTF@50 lp/mm of the fabricated IOL at a 3 mm pupil size align with the design specifications. The extended-depth-of-focus and imaging performance for the far vision of the fabricated IOL under both monochromatic and polychromatic light conditions at a 3.0 mm pupil diameter is comparable to that of Symfony. In addition, the fabricated IOL exhibits a similar extended-depth-of-focus for three discrete wavelengths. The pseudophakic model eye with the designed EDoF IOL demonstrates a VA exceeding 0.1 logMAR within a defocus range of 2.44 D. The VA is tolerant to both IOL tilt and decentration. These findings demonstrate the promising potential of the sinusoidal EDoF IOL design for future applications in cataract surgery.

Investigation of a measurement-based dosimetry approach to beta particle-emitting radiopharmaceutical therapy nuclides across tissue interfaces.

In this work, we present and evaluate a technique for performing interface 
measurements of beta particle-emitting radiopharmaceutical therapy agents in solution.
APPROACH: Unlaminated EBT3 film was calibrated for absorbed dose to water using a NIST 
matched x-ray beam. Custom acrylic source phantoms were constructed and placed above 
interfaces comprised of bone, lung, and water equivalent materials. The film was placed 
perpendicular to these interfaces and measurements for absorbed dose to water using solutions of 
90Y and 177Lu were performed and compared to Monte Carlo absorbed dose to water estimates 
simulated with EGSnrc. Surface and depth dose profile measurements were also performed.
MAIN RESULTS: Surface absorbed dose to water measurements agreed with predicted results 
within 3.6 % for 177Lu and 2.2 % for 90Y. The agreement between predicted and measured absorbed 
dose to water was better for 90Y than 177Lu for depth dose and interface profiles. In general, 
agreement within k = 1 uncertainty bounds was observed for both radionuclides and all interfaces. 
An exception to this was found for the bone to water interface for 177Lu due to the increased 
sensitivity of the measurements to imperfections in the material surfaces.
SIGNIFICANCE: This work demonstrates the feasibility of using radiochromic film for 
performing absorbed dose to water measurements on beta-emitting radiopharmaceutical therapy 
agents across material interfaces.

Hydraulic-based optimization algorithm for the design of stormwater drainage networks

Stormwater drainage networks are designed to reduce the risk of rainwater damage to the served area. The purpose of optimizing a stormwater drainage system is to reduce overall construction costs and to meet hydraulic design requirements. Currently, designs that rely on software or manual calculations are limited by the available time and the designer’s capabilities. In fact, manual optimization for large networks consumes a lot of time and effort, and there is no guarantee that the optimal design is reached, also it is subject to human errors. In recent years, several researchers have focused on creating optimization design algorithms specifically for sewer and storm networks, such as genetic algorithm (GA), linear programming (LP), heuristic programming (HP),…etc. However, these studies were limited to covering one or two design parameters and constraints. Additionally, in some studies, the hydraulic performance of the designed network was not treated in a proper way, especially the water surface profile effects. So, the main objective of the study is to develop an effective hydraulic-based optimization algorithm (HBOA) that can dynamically get the optimal design with minimum total cost for a given storm network layout and meet all hydraulic requirements. To achieve this, a MATLAB code is created and coupled with SewerGEMS software that automatically simulates all expected optimization scenarios based on network hydraulic performance. The HBOA is validated economically and hydraulically using two benchmark examples from the literature. According to the economic validation, the total network cost generated by HBOA was the lowest when compared to the optimization methods found in the literature. During the hydraulic evaluation, it was observed that the optimization algorithm (GA-HP) used in the literature for the benchmark examples does not meet the hydraulic requirements where the networks are flooded, whereas HBOA meets the hydraulic requirements with minimal overall network cost. Also, the HBOA is applied to four real stormwater drainage networks that were already designed, constructed, and optimized manually. The four redesigned real cases using HBOA revealed a cost reduction of about 15% compared to the original designs, while consuming a few hours for the design and optimization processes. Finally, the developed HBOA is a robust, time-efficient, and cost-effective optimization and hydraulic design tool which could be used in the design of stormwater drainage networks with different design constraints with minimal human interference.

Ion beam figuring for X-ray mirrors: history, state-of-the-art and future prospects.

Synchrotron light sources require X-ray optics with extremely demanding accuracy for the surface profile, with less than 100 nrad slope errors and sub-nanometre height errors. Such errors are challenging to achieve for aspheres using traditional polishing methods. However, post-polishing error correction can be performed using techniques such as ion beam figuring (IBF) to improve optics to the desired quality. This work presents a brief overview of the history of IBF, introduces some of the challenges for obtaining such demanding figure errors, and highlights the work done at several in-house IBF facilities at synchrotron light sources worldwide to obtain state-of-the-art optical quality.

Application of laboratory micro X-ray fluorescence devices for X-ray topography

It is demonstrated that high-resolution energy-dispersive X-ray fluorescence mapping devices based on a micro-focused beam are not restricted to high-speed analyses of element distributions or to the detection of different grains, twins and subgrains in crystalline materials but can also be used for the detection of dislocations in high-quality single crystals. Si single crystals with low dislocation densities were selected as model materials to visualize the position of dislocations by the spatially resolved measurement of Bragg-peak intensity fluctuations. These originate from the most distorted planes caused by the stress fields of dislocations. The results obtained by this approach are compared with laboratory-based Lang X-ray topographs. The presented methodology yields comparable results and it is of particular interest in the field of crystal growth, where fast chemical and microstructural characterization feedback loops are indispensable for short and efficient development times. The beam divergence was reduced via an aperture management system to facilitate the visualization of dislocations for virtually as-grown, non-polished and non-planar samples with a very pronounced surface profile.

Fluorescence-Based Calibration Model for In-Situ Measurement of Micro-scaled Lubricant Thickness Distribution at Indentation Interface

This study proposes a model for the measurement of microscale liquid film thickness distribution using fluorescence signals. The interfacial conditions between the tool and the workpiece in mechanical machining are important for understanding these phenomena and mechanisms. In this study, indentation tests with transparent tools were used to observe interfaces; however, it was challenging to obtain the signal from a thin fluorescent liquid film on smooth and steeply inclined surfaces. Therefore, fluorescence-based measurement, such as laser-induced fluorescence, was employed. To measure the absolute thickness of the thin fluorescent film, calibration of the measurement system is necessary. Therefore, a theoretical model was proposed considering the multiple reflections of excitation light and fluorescence at the inclined surface between the indenter and workpiece. By measuring the profile of the surface topography of the indented workpiece and comparing the results with those measured by a surface profiler, the validity of the proposed calibration method and the performance of this measurement system were demonstrated. The measured surface profiles, including scratches of 2–4 µm, were in good agreement, demonstrating the validity of the proposed method.

3D Profile Reconstruction and Internal Defect Detection of Silicon Wafers Using Cascaded Fiber Optic Fabry-Pérot Interferometer and Leaky Field Detection Technologies

Abstract Wafer quality control is one of the important processes to improve the yield rate of semiconductor products. Profile quality and defects in the wafer are two key factors that should be taken into consideration. In this research, we introduce a method that measures the profile of the upper surface and the thickness of the wafer at the same time using an optical fiber cascaded Fabry-Pérot interferometer working at wavelength of 1550 nm. Therefore, the 3D profile of the wafer can be reconstructed directly. Testing results show that both accuracy and precision of the Fabry-Pérot interferometer are within a nanometer scale. Defects, especially those embedded inside the wafer, will be detected by monitoring the leaky field with treating wafers as slab waveguides. With the leaky field detection, defects on the lower surface of the wafer were successfully detected by monitoring the leaky field above the upper surface of the wafer. Compared with traditional methods such as radiographic testing (RT) or computed tomography (CT) testing, the proposed methods provide a cost-effective alternative for wafer quality evaluation.

Accuracy Improvement of a Multi-ring Beam Structured Inner Surface Measurement: via Novel Calibration Methodology and Light Source Optimization

Abstract Parts with a large depth-to-diameter ratio play a critical role in the military, aerospace, and automotive industries. However, accurately measuring their inner surface profile remians challenging owing to the lack of adequate and accurate sensors. We developed a multi-ring structured light system to obtain three-dimensional data of inner contours, such as inner diameters, which are crucial for ensuring component performance and safety. In this study, we proposed three simple yet effective techniques to improve the multi-ring beam structured measurement system. First, we designed a distortion correction method to calibrate the imaging system. Second, a two-step calibration approach was used to calibrate the multi-ring projection. Meanwhile, we benchmarked the effects of different light sources on image speckles. The calibration results demonstrated that the coefficient of determination (R-2) used for line fitting exceeded 0.999. Moreover, the measurement experimental results show that the uncertainty of less than 10 µm and the smallest measurable pipe inner diameter can reach 15 mm, demonstrating that our methods are promising for improving the accuracy of structured light optical sensing systems. This system satisfies the measurement requirements and can be immediately utilized to meet the high demand for inner contour measurements in industrial applications.

Evaluation of the Feasibility of the Prediction of the Surface Morphologiesof AWJ-Milled Pockets by Statistical Methods Based on Multiple Roughness Indicators

Improvement of the surface quality of machined parts is essential in order to avoid excessive and costly post-processing. Although non-conventional processes can efficiently carry out the machining of difficult-to-cut materials with high productivity, they may also, for various reasons, be related to increased surface roughness. In order to optimize the surface quality of generated surfaces in a reliable way, surface profiles obtained during these processes must be adequately modeled. However, given that most studies have focused on Ra or Rz indicators or are based on the assumption of a normal distribution for the profile heights, relevant models cannot accurately represent the surface characteristics that exist in a real machined surface with a high degree of accuracy. Thus, in the present study, a new modeling approach based on the use of a statistical probability distribution for the surface profile height is proposed. After six different distributions were evaluated on the basis of a three-stage procedure involving different roughness indicators pertaining to the abrasive waterjet (AWJ) milling of pockets, it was found that, although it is not possible to model the nominal values of every roughness parameter simultaneously, in several cases, it is possible to approximate the values of critical indicators such as Ra, Rz, Rsk, Rku and Rp/Rv ratio by Weibull distribution with a sufficient degree of accuracy.

A wind tunnel study of the effects of vegetation structural characteristics on the airflow field

Implementing vegetation is the preferred measure for controlling soil wind erosion. The physical variations in the wind velocity profile, such as the friction wind velocity (u*), aerodynamic roughness (z0), zero-plane displacement (d) and drag coefficient (Cd), are key to understanding soil wind erosion on vegetation-covered surfaces. However, the lack of systematic and in-depth research in the literature has led to significant controversy and uncertainty. Based on the wind tunnel data of wind velocities at 18 different heights near the ground surface for four plant heights (H = 5, 10, 15, and 20 cm) and densities (ds = 27, 46, 97, and 193 N/m2) and six free stream velocity (u∞ = 6, 8, 10, 12, 14, and 16 m/s) scenarios, the relationships among u*, z0, d, the parameters of u∞ and the vegetation structural characteristics, including the plant height (H), density (ds), and lateral cover (λ), are investigated in this paper. The conclusions are as follows: (1) The near-surface wind velocity profiles of the vegetation-covered surface can be divided into three segments with little variation in the wind velocity with height, a rapid increase in the wind velocity with height, and close to the free stream velocity. Their corresponding heights ranged from the surface to heights of 0.5 – 0.75H, 0.5 – 0.75H to 50 cm, and exceeding the height of 50 cm, respectively. (2) The zero-plane displacement increased with the plant height and density but decreased with the free stream velocity. The relationship between them can be expressed by Eq. (5). (3) The friction wind velocity of the vegetation-covered surface increased with the plant height, density, and free stream velocity. The relationship between them can be expressed by Eq. (6). The drag coefficient increased rapidly at first and then slowly decreased with increasing lateral cover, which satisfied the equation Cd = 0.00155 + 0.0111λ/(λ + 0.124). (4) The aerodynamic roughness increased with the plant height and density but decreased with the free stream velocity. The aerodynamic roughness of the vegetation-covered surface under different free stream velocities and lateral cover conditions can be expressed by Eq. (8). The study results are a basis for the modeling of the dynamics of wind erosion on vegetation-covered surfaces.

Discriminative spatial localisation in confocal reflectance and carbon dots-based fluorescence imaging using mixed-mode endoscopic scanner

Carbon dots (CDs)-based fluorescence imaging with confocal reflectance effectively localises labelled structures with clear sample visualization. Yet, integrating these modalities into single-fibre cantilever-based endoscopic scanners poses challenges. Thus, we present an endoscopic scanner with a mixed-mode fibre cantilever for dual modalities imaging. The cantilever features two-attached fibre construction for multiple illumination and detection channels without additional optical components. The measured lateral and axial resolutions are 5.81 and 6.52 µm, respectively with field-of-view of 408 × 488 µm. The fluorescence detection capability was first verified using fluorescent microspheres and CD-embedded polymer film, followed by confocal reflectance and CDs-based fluorescence imaging on labelled fibrous network and plant samples. The results demonstrate the complementary strengths of confocal reflectance, which extracts surface profiles, and CDs-based fluorescence, which captures fluorescence signals, leading to precise localization of fluorescence signals within the sample. Switching modality schemes at the scanner’s back-end enables implementation of different modalities.

Optimizing FDM process parameters: predictive insights through taguchi, regression, and neural networks

Fused deposition modelling (FDM) is a popular additive manufacturing process used for rapid prototyping and the production of complex geometries. Despite its popularity, FDM’s susceptibility to variations in numerous process parameters can significantly impact the quality, design, functionality, and mechanical properties of 3D printed parts. This study explores thirteen FDM process parameters and their influence on the mechanical properties of polylactic acid (PLA) polymer, encompassing surface roughness, warpage, tensile and bending strength, elongation at break, deformation, and microhardness. The optimum parameters were identified alongside key contributors by applying the Taguchi method, signal-to-noise ratios, and analysis of variances (ANOVA). Notably, specific FDM parameters significantly affect the surface profile, with layer thickness contributing 32.65% and fan speed contributing 8.59% to the observed variations. Similarly, warping values show notable influence from nozzle temperature (29.53%), wall thickness (16.74%), layer thickness (16.56%), and retraction distance (12.80%). Tensile strength is primarily determined by wall thickness (31.83%), followed by infill percentage (26.73%) and infill pattern (16.18%). Elongation at break predominantly correlates with wall thickness (44.82%), with a supplementary contribution from nozzle temperature (10.90%). Microhardness lacks a dominant parameter. Bending strength variations primarily arise from layer thickness (38%), wall thickness (37.6%), and infill percentage (9.17%). Deformation tendencies are influenced by layer thickness (19.20%), print speed (11.37%), wall thickness, and fan speed (10.9% each). The optimized dataset of FDM process parameters was then employed in two prediction models: multiple-regression and artificial neural network (ANN). Evaluation based on the correlation coefficient (R2) and root mean squared error (RMSE) indicates that the ANN model outperforms the multiple-regression approach. The results indicate that precise control of FDM parameters, coupled with ANN predictions, facilitates the fabrication of 3D printed parts with the desired mechanical characteristics.

Design and implementation of dynamic beam shaping in high power laser processing by means of a Deformable Mirror

Optimising the laser intensity distribution in high power laser processes, such as laser welding, laser cladding or laser hardening, can be used to tailor the local thermal fields and thermal cycles which, in turn, determine the final process results. Deformable Mirrors allow to dynamically shape the beam profile and previous studies showed their potential. However, only limited flexibility in achievable beam shapes is shown at higher power levels. In addition the relation between desired laser intensity profiles and required mirror surface profiles is nontrivial. In this work the design and implementation of a dynamic beam shaping system, capable of handling high laser powers (up to 1 kW), is presented and evaluated. To that end, several distinctly different laser intensity profiles are defined, corresponding mirror surfaces are determined and realised with the beam shaping system. Measurements of the laser intensity profiles were compared with laser intensity profiles simulated using a previously presented mathematical framework and showed a good agreement. From the measurements it was concluded that the setup is suitable for high laser powers (up to 1 kW) and is characterised by large depth of focus (<14% change in dimensions at a distance of 100 mm from the focal plane).

Surface morphology of API 5L X65 pipeline steel processed by ultrasonic impact peening: An integrated experimental and computational study

Ultrasonic impact peening (UIP) is a highly effective surface engineering technique to improve material durability through peening-induced surface plastic deformation. These improvements are determined by not only the generation of surface compressive residual stresses but also the alteration of surface morphological features. In literature, researchers have focused primarily on the average roughness (Sa) to understand the morphology changes induced by UIP. From the surface engineering perspective, in addition to Sa, other surface morphological characteristics play key roles in determining material durability, particularly surface skewness (Ssk) and surface kurtosis (Sku), which describe the asymmetrical distribution of surface profiles and the sharpness of peak features, respectively. In this study, surface morphological characteristics of API 5L X65 pipeline steel processed by UIP are investigated with a focus on the effects of processing parameters on Sa, Ssk, and Sku. The results indicate that the optimized UIP conditions lead to the preparation of surfaces with valley structures as the dominant feature accompanied by blunt peaks, resulting in the elimination of stress concentration sites towards enhanced material durability. In addition, surface hardness, residual stresses, and peening-induced deformation depth are measured. Furthermore, to gain a comprehensive understanding of the material response and the underlying mechanisms driving surface morphological alterations by UIP, a finite element method (FEM)-based model is developed. By investigating the effect of process parameters (peening amplitude, peening cycles, and pin size) on the surface deformation depth and stress/strain distribution, a correlation between these process variables with surface characteristics is established.

Effect of static compression on near-field tsunami waves: Three-dimensional solution

An analytical solution of three-dimensional surface wave profiles due to arbitrary spatio-temporal disturbance of a circular ocean bottom in a compressible ocean is obtained by incorporating the influence of the static ocean background compression under the assumptions of linearized water wave theory. Time-domain simulations of the surface profile in three dimensions and the pressure distribution within the water column for a circular uniform rise and tilt are shown. The corresponding animation movies depict the temporal evolution of the surface profile and pressure field inside the water column eloquently, which was not shown in earlier literature. The impact of static compression is also discussed through the simulations. A novel analytical expression of the potential function for a generic tilted motion (rmcos(mθ),m∈Z) of the circular ocean floor is derived. An efficient numerical code is developed to find surface elevation and pressure distribution, implementing the inverse Fourier integral as matrix multiplication. Validation is performed for the specific case of a rising flat ocean floor, showing the oscillations due to acoustic-gravity modes. Initially, a simplified problem of a flat rising ocean bottom is solved using the eigenfunction matching method, which involves finding a particular solution for the nonhomogeneous ocean bottom condition and the solution for its homogeneous counterpart. Solutions are obtained using a newly developed inner product between the depth-dependent functions. Later, a Green function technique is used to incorporate the impact of the arbitrary spatio-temporal motion of the circular portion of the ocean bed. The solution obtained from the eigenfunction matching method is utilized to obtain the analytical form of Green’s function and, eventually, an expression of surface elevation and pressure distribution inside the ocean water column.

A multi-sensor based online monitoring system for laser hot-wire surface cladding process

A multi-sensor online monitoring system, including a high-speed camera, a spectrometer, and an infrared camera, was developed to enhance the laser hot wire cladding process. This innovative process feeds a preheated wire, using a hot-wire power supply, into a shallow molten pool formed on the substrate surface by a rectangular diode laser beam. This study assesses the capability of the monitoring system to detect variations in cladding process conditions that significantly influence the geometry and quality of the clad layer. Specifically, the study involved four sets of laser hot-wire cladding experiments, altering substrate surface conditions, substrate thicknesses, laser powers, and scanning speeds. The real-time data from the three sensors were synchronized and analyzed in depth, focusing on the morphology and microhardness of the clad layers. A laser vision sensor was employed to examine the surface profile and roughness of the clads. The findings indicated that the crucial role of surface preparation in influencing the dynamics of the molten pool, subsequently affecting the geometry, dilution depth, and microhardness of the clads. The sensors demonstrated increased sensitivity to changes in surface conditions compared to variations in other conditions like substrate thickness, laser power, and scanning speed. A significant correlation was found between the dilution depth, clad height, surface roughness, and microhardness of the clad layer. These correlations are in response to adjustments in laser power, scanning speed, and surface preparation and can be reliably and rapidly detected by the multi-sensor system.

Design and development of an occlusion-free surface profile measurement device

The prevalent surface profile measurement techniques in the sub-millimetre measurement scale, based on active triangulation (such as laser scanners), stereo vision and photometric stereo, may miss certain parts of the surface of the object due to occlusion. Occlusion occurs in these techniques as they rely on a top-view configuration, where the illumination rays and the surface profile lie on the same plane. In this study, a surface profile measurement device is designed and developed, which can generate occlusion-free measurements by adopting a side-view configuration. This proposed measurement technique is tested on a few surfaces, and the results are presented.

Experimental investigation of the effects of debris on non-conforming contact stress

Debris widely exists in contact structures, affecting the reliability of structures. In this investigation, the effects of debris on the non-conforming contact stress are investigated through two-body and three-body contact experiments. According to the relationship between the contact length and debris length, debris is divided into long debris and short debris, which show different influences on the contact behaviors. The non-conforming contact stress is reconstructed based on full-field metrology and an inverse method. The evolution of contact stress induced by debris is analyzed with various parameters and contact surface profiles. Different factors, including debris material, debris length, debris thickness, plate material, and load amplitude, are considered in experiments. Their influence rules are discussed and summarized. The plate materials and short debris materials have coupling effects on the contact stress, which is associated with the deformation characteristics of the contact surface. The results provide an experimental reference for the research of non-conforming contact problems.