Accurate Thickness Measurements Research Articles

Ejecta Blankets at Small Craters on the Moon

Impact-derived ejecta covers most of the lunar surface, originating from recent impacts through to the beginning of the geologic record. Despite how common ejecta is, accurate measurements of ejecta thickness are difficult to obtain, and existing estimates of ejecta thickness vary widely. This study uses excavation by meter-scale impacts on the fresh ejecta blankets of larger, kilometer-scale impacts to make point measurements of ejecta thickness. We estimate ejecta thickness at the rims of 73 lunar craters (0.1–4.8 km diameter) and create isopach maps of ejecta thickness for three craters. We derive an equation for ejecta thickness, t=0.14±0.062R(0.77±0.080)r/R(−B) , where r is the horizontal distance from the center of the crater, R is the center-to-rim crater radius, and B describes the rate at which ejecta thickness decays with radial distance. Our average value for B (2.8 ± 0.1) is similar to previous work, though we observe that B can vary significantly within an ejecta blanket.

Numerical and experimental investigation on droplet entrainment mechanism and closed equations of two-fluid model

As a clean and low-carbon energy source, natural gas is an important force in achieving carbon peaking and carbon neutrality goals. Affected by the strong force of gas and liquid during mining and transportation, it exhibits the phenomenon of droplet entrainment. Entrained droplets change the properties of gas and liquid phases, which is crucial for accurate measurement of liquid film thickness, gas holdup, pressure drop and flow rates in natural gas pipelines. The measurement of entrained droplets has always been a focus and difficulty in the two-phase flow research field. Therefore, numerical simulation combined with experimental measurement are presented to study the droplet entrainment mechanism and closed equations of two-fluid model. The specific parameter settings for simulating horizontal gas–liquid annular flow based on numerical method are discussed, and effective simulation of droplet entrainment and deposition in annular flow is achieved. By comparing liquid film thickness and wave velocity from the simulation results with the experimental results, the correctness of the simulation method is verified. Then, the mechanism and dynamic evolution process of entrained droplets in annular flow are revealed, and the generation and deposition characteristics of entrained droplets are studied. As a result, the closed equations of two-fluid model such as droplet velocity, gas–liquid interface velocity, and gas–liquid interface friction factor are established. The proposed two-fluid model is validated using dual mode ultrasound and differential pressure sensors, demonstrating its good applicability and extrapolation.

Achieving highly accurate cavity thickness measurements in fabric compaction

The compaction of a fabric reinforcement in a Universal Testing Machine (UTM) allows to determine the achievable fiber volume fraction across a wide range of pressures, a valuable information for composite manufacturing. As seen in the first international compressibility benchmark, inaccuracies in the fabric stack thickness measurement, the approach to compliance correction and the non-parallelism between compaction plates resulted in highly inaccurate compression curves. In this paper, the different variability sources affecting indirect thickness methods, based on the machine displacement, and direct methods with laser sensors are presented and its impact on the accuracy is estimated. In conclusion, both thickness measurement methods produced similar results; however, the thickness measured by direct methods experienced more variability due to minor changes in the rig’s displacement or the orientations between plates, combined with other sources of variability such as external interferences or vibrations from the compaction plate which led to variations in measurement precision throughout the tests.

Experimental determination of reference intensity ratio essential for accurate thickness measurement of HfO2 ultrathin films by XPS

When measuring the thickness of ultrathin overlayer films using X‐ray photoelectron spectroscopy (XPS), accurate values of the reference intensity ratio (R0) and the effective attenuation length (L) are essential. By definition, R0 is the peak intensity ratio for an overlayer and the substrate in “bulk” phases. Two issues need to be addressed in experimental determining R0 for ultrathin films: (i) How might a contamination layer on the sample used for measuring peak intensities impact R0? And (ii) do differences in the structure or chemistry of an ultrathin film make it inappropriate to determine R0 using bulk forms of the overlayer? In this study, we demonstrate the experimental determination of the R0 for an ultrathin HfO2 film on a Si(100) substrate with a 2 nm SiO2 layer. The values of R0 were determined using (i) the bulk materials of the HfO2 film and substrate and (ii) the ultrathin HfO2 films after different cleaning treatments. The results show that the R0 determined by the ultrathin films is higher than that determined by the bulk materials. Also, keeping the same level of carbonaceous contamination on the sample surface by cleaning as much as possible is essential for an accurate experimental determination of R0. In addition, the effective attenuation length was obtained using samples with known thicknesses measured by X‐ray reflectometry. The thicknesses and uncertainty budget of the ultrathin HfO2 films were then evaluated.

The Influence of Microstructure Characteristics on Thickness Measurement of TBCs Using Terahertz Time-Domain Spectroscopy

Thermal barrier coatings (TBCs) exhibit excellent thermal insulation capabilities, proving crucial in enhancing the performance of turbine blades. Accurate measurement of TBC thickness is pivotal for the quality control and health monitoring of turbine blades. However, the absence of suitable non-destructive testing (NDT) methods poses a challenge in ensuring precise quality control and health assessment of TBCs. This study investigates the efficacy of terahertz time-domain spectroscopy (THz-TDS) in measuring TBCs thickness, specifically focusing on the microstructure characteristics of the top coat (TC), including grain morphology, internal porosity, surface roughness, and agglomerates. The findings emphasize the significance of grain morphology in determining thickness measurement due to the varied terahertz wave propagation modes. Moreover, the study involved polishing EB-PVD and APS samples to mitigate surface roughness. This process revealed a discernible linear correlation between reduced surface roughness and decreased measurement errors. The slopes of the error reduction curves ranged from 0.59 to 1.7 for EB-PVD and 2.17 to 5.79 for APS samples. Furthermore, the research observed THz light scattering within internal pores, resulting in diminished outgoing energies and subsequent increments in measurement errors.

Measuring Thermal Conductivity of Single Thickness Fibrous Gas Diffusion Layers Using Transient Plane Source Method

In a proton exchange membrane fuel cell (PEMFC), the gas diffusion layer (GDL) is a porous material placed between the flow field plates and the catalyst layer. Its primary responsibility is to distribute reactants evenly across the surface of the catalyst layer while allowing for the removal of excess water and heat produced during operation. The GDL is typically made of a carbon-based material, such as carbon paper or carbon cloth, which is treated with polytetrafluoroethylene (PTFE) to become hydrophobic. This treatment allows it to repel water and facilitate the transport of gases such as hydrogen and oxygen during operation. The thermal conductivity of the GDL plays a crucial role in managing the heat and water of PEMFCs.The Guarded Heat Flow (GHF) technique is a well-established steady-state method for measuring the thermal conductivity of carbon fiber papers. This is achieved by testing two different thicknesses of a material that have an identical structure [1-3]. Using this two-thickness method, as per ASTM standard C177-19e1 [4], enables the bulk thermal conductivity to be deconvoluted from the thermal contact resistance at the interface between the sample and the measurement device's surface (an interfacial phenomenon). However, materials with identical structures for two-thickness measurements are not always available for commercial GDLs. In this study, we compare the transient plane source (TPS) thin film method, which measures the thermal conductivity of single thickness GDL samples, with the two-thickness GHF method for measuring thermal conductivity.In this study, GDL samples with the same bulk structure and manufactured in two thicknesses were used: Sigracet series 24BA and 34BA with original thicknesses of 190 µm and 280 µm, respectively. A custom-built Thickness Under Compression and Resistance Under Compression machine (TUC-RUC) was utilized to measure the thickness of the samples under loads ranging from 0.35 MPa to 2 MPa. The thickness under compression was measured for five samples (25.4 mm diameter) of each type of GDL. The standard deviation for each sample thickness was below 4%. As shown in Fig. 1, the stress-strain response of the GDL samples was measured and analyzed to assess the similarity in their mechanical structures. Consistent with the assumptions that both samples have the same structure, the GDL samples with two different thicknesses displayed identical stress-strain behavior under compression, as shown by the curve-fit for stress-strain behavior in proposed Fig. 1.The thermal conductivity of the samples was measured using both the TPS thin films method, as per ISO 2207-2:2022 [5], and the GHFM. On the TPS, three samples of each type of GDL were measured three times. The measured thermal conductivities increased with compression, ranging from 0.15 to 0.47 W/mK, with a standard deviation of less than 5% for each measurement. The results from the TPS technique for a single thickness of GDL were compared with the two-thickness measurements conducted using the GHFM, as shown in Figure 2. The GHFM tests were conducted on three samples of each type of GDL at five compressive loads, and the standard deviation on the deconvoluted thermal conductivity was less than 7% for each measurement. The values measured by the two techniques were found to be in good agreement, with a relative difference of within 6%. This study demonstrates that the transient plane source (TPS) method, when combined with an accurate thickness measurement technique, is a precise technique for determining the bulk thermal conductivity of commercial GDLs produced in a single thickness.[1] H. Sadeghifar, N. Djilali, and M. Bahrami, “Effect of Polytetrafluoroethylene (PTFE) and micro porous layer (MPL) on thermal conductivity of fuel cell gas diffusion layers: Modeling and experiments,” Journal of Power Sources, vol. 248, pp. 632–641, Feb. 2014, doi: 10.1016/j.jpowsour.2013.09.136.[2] M. Ahadi, M. Andisheh-Tadbir, M. Tam, and M. Bahrami, “An improved transient plane source method for measuring thermal conductivity of thin films: Deconvoluting thermal contact resistance,” International Journal of Heat and Mass Transfer, vol. 96, pp. 371–380, May 2016, doi: 10.1016/j.ijheatmasstransfer.2016.01.037.[3] E. Sadeghi, N. Djilali, and M. Bahrami, “Effective thermal conductivity and thermal contact resistance of gas diffusion layers in proton exchange membrane fuel cells. Part 1: Effect of compressive load,” Journal of Power Sources, vol. 196, no. 1, pp. 246–254, Jan. 2011, doi: 10.1016/j.jpowsour.2010.06.039.[4] “Test Method for Steady-State Heat Flux Measurements and Thermal Transmission Properties by Means of the Guarded-Hot-Plate Apparatus.” ASTM International. Doi: 10.1520/c0177-19e01.[5] “ISO22007-2, Plastics-determination of thermal conductivity and thermal diffusivity-part 2: transient plane heat source (hot disc) method”, 2022. Figure 1

Age and sex related change in tooth enamel thickness of maxillary incisors measured by cone beam computed tomography

BackgroundTo measure adequate enamel thickness of maxillary incisors in planning enamel reduction for a porcelain laminate veneer restoration in relation to chronological age and sex by using cone beam computed tomography (CBCT) in an Iraqi subpopulation.MethodsFrom 81 CBCT images, 324 maxillary incisors were examined. Enamel thickness was measured at both mesial and distal regions of the tooth in three different levels: cervical, middle, and incisal (occlusal) 1/3 at a sagittal section. Measurements were made for the following tooth areas using CBCT: facial enamel thickness at 1, 3, and 5 mm from the cementoenamel junction (CEJ), palatal enamel thickness at 5 mm from the CEJ (5 mm P), facial and palatal enamel thickness at the incisal edge (IFP), mid incisal enamel thickness (IET), and the incisal edge enamel-pulp distance (IEPD). Relationships of enamel thickness with age and sex were evaluated using Independent t-test, Mann–Whitney U-test and the Pearson correlation coefficient, a simple linear regression analysis used for statistical analysis.ResultsSignificant differences (P < 0.05) were found in terms of an inverse association between enamel thickness and chronological age at all measurements above the CEJ and the regression model for the mid-incisal enamel thickness was (R2 of 0.4). In contrast, there was an increase in IFP, palatal, and IPED enamel thickness with age. Also, significant differences were found in enamel thickness between males and females, the enamel being thicker in females in relation to facial enamel thickness, enamel palatal thickness above CEJ and IET, while for IEPD, the enamel thickness was greater in males compared to females.ConclusionThe measurements for enamel thickness outcome variables in relation to chronological age revealed significant differences for each measured distance and there were statistically significant differences in enamel thickness between males and females at all measurements except at IFP. These results demonstrate that CBCT can be used for noninvasive, accurate measurements of enamel thickness in both sex.

Quantitative study of 3.0T MRI on the thickness of knee joint cartilage in healthy young people

To explore 3.0T MRI accurate measurement of knee cartilage thickness in healthy youth provides reliable anatomical parameters for quantitative diagnosis of osteoarthritis and accurate osteotomy of joint replacement. From January 2013 to December 2013, 30 healthy young volunteers including 14 males and 16 females with an average age of (25.8±2.4) years old ranging from 22 to 33 years were recruited in Changchun, Jilin Province, and a 3.0T MRI scan was performed on the bilateral knee joints of each volunteer. The cartilage thickness was measured on the lateral femoral condyle (LFC), medial femoral condyle (MFC), lateral tibial plateau (LTP) and medial tibial plateau (MTP). In four regions of the knee joint:LFC, MFC, LTP and MTP, whether young men or women, there was no significant difference in cartilage thickness between the left and right knee joints (P>0.05). There were significant differences in knee cartilage thickness between healthy young men and women (P<0.05). In the same sex group, LFC cartilage thickness was thinner in the middle, thicker in front and rear;MFC cartilage thickness was the thinnest in front and gradually thickening from the front to the rear; LTP cartilage thickness was thickest in the middle, second in the rear and thinnest in the front;MTP cartilage thickness was the thinnest in the front, was relatively uniform in the middle and rear and thicker than that in the front. In Northeast China, among healthy adults aged 22 to 33, gender difference may be an important factor in the difference of cartilage thickness in various regions of the knee joint. Regardless of whether male or female healthy young people, the cartilage thickness of the entire knee joint is unevenly distributed, but there is no significant difference in cartilage thickness in the same area between the left and right knee joints.

Ultrasonic Thickness Measurement Method and System Implementation Based on Sampling Reconstruction and Phase Feature Extraction.

The existing ultrasonic thickness measurement systems require high sampling frequencies for echo signal acquisition, leading to complex circuit designs and high costs. Moreover, extracting the characteristics of ultrasonic echo signals for accurate thickness measurement poses significant challenges. To address these issues, this paper proposes a method that utilizes conventional sampling frequencies to acquire high-frequency ultrasonic echo signals, overcoming the limitations of high-frequency data acquisition imposed by the Nyquist-Shannon sampling theorem. By employing an improved sampling reconstruction technique, the multi-cycle sampling signals are reconstructed and rearranged within a single cycle, effectively increasing the equivalent sampling frequency. Additionally, a combination of coarse estimation using fast Fourier transform (FFT) and precise phase extraction using the moving sine fitting algorithm is proposed for accurate thickness measurement, resolving the limitations of common thickness measurement methods such as peak detection, envelope detection, and Hilbert autocorrelation in terms of low measurement accuracy. Experimental results obtained from thickness measurements on 45 steel ultrasonic test blocks within the range of 3 mm to 20 mm indicate a measurement error of ±0.01 mm, while for thicknesses ranging from 1 mm to 50 mm, the measurement error is ±0.05 mm.

Automated measurement of lamellar thickness in human bone using polarized light microscopy

Lamellar bone formed in individuals with moderate and severe osteogenesis imperfecta (OI) is often composed of lamellae that are structurally abnormal. Measuring the thickness of these lamellae can be helpful in assessing the effect of specific collagen and collagen-related mutations on OI bone synthesis.Manual measurement of lamellar thicknesses in large quantities is very time consuming. The method for automated measurement described in this article utilizes an image processing script to identify the average thickness of multiple lamellae automatically from histologic images of bone. This allows for faster measurements that are less prone to human error and can account for variability in the thickness of a lamella along its length.•OI and control bone samples are prepared per the glycol methacrylate resin (JB-4 plastic) technique and viewed using polarized light microscopy.•Ideal bone regions for measurement are identified using specific qualitative criteria designed to ensure uniform and accurate thickness measurements.•The method was validated with dataset containing 211 lamellae from control bone and 212 lamellae from OI bone.

In vivo characterisation of field pea stem wall thickness using optical coherence tomography

BackgroundModern field pea breeding faces a significant challenge in selecting lines with strong stems that resist lodging. Traditional methods of assessing stem strength involve destructive mechanical tests on mature stems after natural senescence, such as measuring stem flexion, stem buckling or the thickness of dry stems when compressed, but these measurements may not correspond to the strength of stems in the living plant. Optical coherence tomography (OCT) can be used as a noncontact and nondestructive method to measure stem wall thickness in living plants by acquiring two- or three-dimensional images of living plant tissue.ResultsIn this proof-of-principle study, we demonstrated in vivo characterisation of stem wall thickness using OCT, with the measurement corrected for the refractive index of the stem tissue. This in vivo characterisation was achieved through real-time imaging of stems, with an acquisition rate of 13 milliseconds per two-dimensional, cross-sectional OCT image. We also acquired OCT images of excised stems and compared the accuracy of in vivo OCT measurements of stem wall thickness with ex vivo results for 10 plants each of two field pea cultivars, Dunwa and Kaspa. In vivo OCT measurements of stem wall thickness have an average percent error of − 3.1% when compared with ex vivo measurements. Additionally, we performed in vivo measurements of both stem wall thickness and stem width at various internode positions on the two cultivars. The results revealed that Dunwa had a uniform stem wall thickness across different internode positions, while Kaspa had a significantly negative slope of − 0.0198 mm/node. Both cultivars exhibited an increase in stem width along the internode positions; however, Dunwa had a rate of increase of 0.1844 mm/node, which is three times higher than that of Kaspa.ConclusionsOur study has demonstrated the efficacy of OCT for accurate measurement of the stem wall thickness of live field pea. Moreover, OCT shows that the trends of stem wall thickness and stem width along the internode positions are different for the two cultivars, Dunwa and Kaspa, potentially hinting at differences in their stem strength. This rapid, in vivo imaging method provides a useful tool for characterising physical traits critical in breeding cultivars that are resistant to lodging.

Metal film thickness measurement using phase linearity feature for immunity to lift-off effect

In eddy current (EC) thickness measurements, the presence of the lift-off effect will significantly impact the measurement signal, leading to inaccuracies. It has been reported that the phase signal demonstrates a certain level of immunity to the lift-off effect compared to the amplitude signal, as its variation in response to lift-off is relatively less prominent. However, it should be noted that the phase is not entirely unaffected by the lift-off effect. In this paper, a linear relationship between the tangent of the phase angle and the lift-off has been found, termed the phase linear feature. Firstly, the phase linear feature was validated through theoretical derivations and experimental investigations. Subsequently, a new method of thickness measurement based on the fixed lift-off deviation was proposed by using this feature, and a corresponding double-coil sensor was also designed. Finally, to validate the proposed method, measurements of aluminum and copper films were carried out using the developed measurement system under different lift-off distances. The experimental results demonstrate that the measurement relative error of the proposed method remains within 5% in the 0–3 mm lift-off range. This indicates that the proposed method can provide accurate thickness measurements and is independent of the lift effect. Furthermore, the proposed method also has the advantages of single-frequency excitation, simplicity of the sensor, and straightforward relationship between features and thickness. Therefore, this study presents an effective solution for practical online thickness measurement.

Machine learning-enabled thickness estimation of thin coatings on carbon fibre composites using microwaves

Accurate thickness measurement of thin coatings (typically 50–500 μm) on carbon fibre-reinforced polymer composites is a major challenge in the manufacturing and maintenance processes of modern aircraft. Different from the conventional material-dependent technique for prediction, a machine learning-enabled strategy with an artificial neural network configuration is used with no requirement of prior knowledge of the type of coating or substrate under test. In the test, an open microwave cavity resonator sensor is directly placed on a coated composite, and any variation of the coating material, coating thickness and conductivity of the composite alters the resonance frequency. Principal component analysis is employed in the signal pre-processing for the dimensionality reduction of the raw measurement data. In terms of the root-mean-square error, the maximum value for the calibration approach is approximately 15 μm and that for the machine learning-based approach is 12 μm. The sensor system developed enables real-time on-site assessment of coated composite structures and thus offers a new approach for non-destructive evaluation 4.0 with improved efficiency, accuracy and automation.

Real Aperture Continuous Terahertz Imaging System and Spectral Refinement Method

In order to meet the increasing demand of non-destructive testing (NDT) in engineering practice, a continuous terahertz NDT platform based on linear scanning has been developed, with a center frequency of 154 GHz and a bandwidth of 56 GHz. This system combines frequency modulation continuous wave (FMCW) radar technology with a continuous scanning structure, as well as a data acquisition platform to provide a non-contact detection method; this is highly efficient and compensates for the shortcomings of traditional methods such as microwave, X-ray, ultrasonic, and others in safety inspection and special detection. In addition, a signal processing method of spectral refinement and correction is proposed in this paper for accurate thickness measurement. The results show that the method has a high accuracy for ABS, PVC, and ceramic matrix composites. By extracting the characteristic parameters, the detection and imaging of prefabricated defects, such as debonding and bubbles in composite materials, have been successfully achieved. This helps to evaluate the internal state of the inspected object more intuitively and further meets the requirements of industrial NDT.

Imaging and investigation with PLIF40 for improved film thickness measurements in annular flow

Gas–liquid annular flow occurs frequently in industrial production processes, and the accurate measurement of film thickness is essential for applying its mass and heat transfer properties. The non-invasive planar laser-induced fluorescence (PLIF) method is widely employed in annular flow investigation. However, both methods of PLIF90 and PLIF70 (the measurement angles between laser and camera are set to 90°and 70°) suffer from total reflection. In this paper, the effect of measurement angle on total reflection, measurement accuracy, and robustness are quantitatively investigated. Accordingly, a PLIF40 method is proposed, which minimizes the influence of total reflection by reducing the measurement angle to 40°. Sub-pixel-based edge detection and liquid film smoothing algorithms are developed to accurately identify liquid films with missing edge details, resulting in a measurement error of 0.09 mm. The flow structure is qualitatively diagnosed by waveform reconstruction and wave height extraction combined with the film thickness distribution. Furthermore, the prediction models for average film thickness are established and compared with the classical prediction models to demonstrate the accuracy and reliability of PLIF40.

Some practical NDE and QC Applications of Time Domain Terahertz Technology

This is an introductory talk, which will briefly discuss the principles of the generation and measurement of terahertz energy, look at its interaction with different materials and show how these principles can be employed to perform inspections of a wide variety of nonconductive materials, including single or multi-layer plastic structures and coatings on both conductive and nonconductive substrates. Terahertz technology, using electromagnetic waves situated between microwaves and the far infra-red, is another ‘tool in the box’ enabling accurate measurement of layer thickness, location of metallic inserts, and detection of discontinuities in materials and configurations that are unsuited for ‘conventional’ inspection approaches. Terahertz investigations are non-harmful, non-contact and normally can be applied from one side of a part. This talk will discuss the applicability of this technology to several practical applications in the aerospace, manufacturing, energy, construction and oil and gas industries. This includes applications where the technology has been implemented into production, and others where it has been investigated, shown to be feasible, but not yet implemented due to external factors. We will also mention its application in several ‘cultural heritage’ investigations. Brief details of equipment used will be discussed and an outline case study showing development of a technique and the accuracy which can be obtained will be presented.

Practical NDE and QC applications of time domain terahertz technology

This is an introductory talk, which will briefly discuss the principles of the generation and measurement of terahertz energy, look at its interaction with different materials and show how these principles can be employed to perform inspections of a wide variety of nonconductive materials, including single or multi-layer plastic structures and coatings on both conductive and nonconductive substrates. Terahertz technology, using electromagnetic waves situated between microwaves and the far infra-red, is another ‘tool in the box’ enabling accurate measurement of layer thickness, location of metallic inserts, and detection of discontinuities in materials and configurations that are unsuited for ‘conventional’ inspection approaches. Terahertz investigations are non-harmful, non-contact and normally can be applied from one side of a part. This talk will discuss the applicability of this technology to several practical applications in the aerospace, manufacturing, energy, construction and oil and gas industries. This includes applications where the technology has been implemented into production, and others where it has been investigated, shown to be feasible, but not yet implemented due to external factors. We will also mention its application in several ‘cultural heritage’ investigations. Brief details of equipment used will be discussed and an outline case study showing development of a technique and the accuracy which can be obtained will be presented.

Autonomous Ultrasonic Thickness Measurement of Steel Bridge Members Using a Climbing Bicycle Robot

This paper presents the development of a steel-climbing bicycle robot integrated with an ultrasonic sensing device towards autonomous thickness measurement of steel bridge members. The bicycle-like robot has two magnetic wheels controlled by two independent steering actuators, which navigates on various steel surfaces (flat, curved, rough, concave, and convex). The compact ultrasonic sensing device is capable of high-voltage pulse excitation, filtering/amplification of the received ultrasonic signal, and high-speed analog-to-digital conversions (up to 80 MHz). Along with the ultrasonic sensing device, the robot carries a dual element transducer, an automatic gel couplant dispenser, a position tracking sensor, and a camera. A mounting/retrieving mechanism of the transducer is designed to ensure the reliable contact of the transducer on steel surfaces. The camera view assists an operator to safely navigate the robot to measurement locations, properly dispense gel couplant, and firmly press the transducer on a measurement surface. The automated robot localization provides accurate thickness measurement locations, which are mapped real-time in three-dimensional (3D) space together with the robot’s travel path. We validate the performance of the developed system in several indoor and outdoor tests. Weblink to a supplementary video demonstrating the robot’s maneuverability and ultrasonic thickness measurements is available in the Data Availability Statement of this article.

A method for measuring and calibrating the thickness of thin films based on infrared interference technology

Transparent thin films are critical industrial components widely used in advanced optics, microelectronics and materials science, among other relevant fields. The rapid and stable measurement of sub-micron industrial film thickness is of particular importance. In this study, a novel method based on the principles of infrared interference and laser profilometry is proposed to calculate the periodogram of the original spectrum and accurately extract the maximum frequency. In addition, a high-precision, compact and low-cost thin-film thickness measurement and calibration system is developed. This system achieves accurate measurement of single-layer film thickness and adapts to correct errors caused by slight tilt due to mechanical vibration or misalignment during film placement. Experimental data show that, compared to conventional infrared interference thickness measurement systems, the use of the proposed maximum frequency extraction algorithm improves measurement accuracy by approximately 90% and stability by approximately 70%. Furthermore, even when measuring the thickness of films with inclined components, the use of the constructed thin film thickness measurement and calibration system provides equivalent results.

THzResNet: A Physics-Inspired Two-Stream Residual Network for Thermal Barrier Coating Thickness Measurement

The uneven and complicated porose microstructure of thermal barrier coatings (TBCs) brings a big challenge for accurate and reliable thickness measurement due to the resultant change of refractive index. In this work, a novel insight into the physics, the first two peaks are originally adopted as the preferred signal, and a physics-inspired two-stream deep learning framework, termed as the terahertz (THz) residual network (THzResNet) is proposed to accurately infer topcoat thickness by extracting refractive index online. Specifically, the division and reciprocal layers are figured out and incorporated into the first-stream, yielding the reciprocal of refractive index. Then, a product layer connects it with time-of-flight from the second-stream to generate topcoat thickness, which endows the THzResNet in accord with the THz physics. Finally, the experiments demonstrate the advantages of THzResNet in accuracy and efficiency. The presented approach allows for addressing the challenge for accurate thickness measurement of coatings with complicated microstructures.