Sample Thickness Measurement Research Articles

Line spectroscopic reflectometry for rapid and large-area thickness measurement.

Thickness measurements in the range of 0.1-1 mm over large optically transparent layers are essential in various manufacturing applications. However, existing non-contact measurement methods, which typically measure a single point or a few points at a time, fall short in their suitability for inline area measurement. Here, we introduce line spectroscopic reflectometry (LSR), an approach that extends the point measurement of traditional SR to line measurement, enabling rapid thickness measurement over large areas. By combining line beam illumination and line spectroscopy, LSR can measure 2048 points simultaneously, thereby boosting the measurement speed by two thousand times. We detail the measurement principle and the optical design in the near-infrared regime, and demonstrate thickness measurements of single-layered and double-layered samples over a measurement line length of up to 68 mm. Furthermore, we showcase the inline area measurement capability of LSR through one-dimensional sample scanning, with measurement rates limited only by camera readout rates.

Methodology for estimation of undeformed thickness of arterial tissues

Soft tissue sample thickness measurement is one of the major sources of differences between mechanical responses published by different groups. New method for the estimation of unloaded sample thickness of soft tissues is proposed in this study. Ten 30 × 30 mm and ten 20 × 20 mm samples of porcine anterior thoracic aortas were loaded by gradually increased radial force. Their deformed thickness was then recorded in order to generate a pressure-thickness response. Next, the limit pressure to which the response can be considered linear was estimated. Line was fitted to the linear part of the curve and extrapolated towards zero pressure to estimate unloaded thickness (7 kPa fit). For comparison, data near zero pressure were fitted separately and extrapolated towards zero (Near Zero fit). The limit pressure for the linearity of the response was around 7 kPa. The Unloaded thickness for 30 × 30 mm samples was 2.68 ± 0.31 mm and 2.68 ± 0.3 mm for Near Zero fit and 7 kPa fit, respectively. The Unloaded thickness for 20 × 20 mm samples was 2.60 ± 0.35 mm and 2.59 ± 0.35 mm for Near Zero fit and 7 kPa fit, respectively. The median of thickness difference between smaller and larger samples was not found statistically different. Proposed method can estimate unloaded undeformed sample thickness quickly and reliably.

Optoelectronic frequency-modulated continuous-wave terahertz spectroscopy with 4\u2009THz bandwidth

Broadband terahertz spectroscopy enables many promising applications in science and industry alike. However, the complexity of existing terahertz systems has as yet prevented the breakthrough of this technology. In particular, established terahertz time-domain spectroscopy (TDS) schemes rely on complex femtosecond lasers and optical delay lines. Here, we present a method for optoelectronic, frequency-modulated continuous-wave (FMCW) terahertz sensing, which is a powerful tool for broadband spectroscopy and industrial non-destructive testing. In our method, a frequency-swept optical beat signal generates the terahertz field, which is then coherently detected by photomixing, employing a time-delayed copy of the same beat signal. Consequently, the receiver current is inherently phase-modulated without additional modulator. Owing to this technique, our broadband terahertz spectrometer performs (200 Hz measurement rate, or 4 THz bandwidth and 117 dB peak dynamic range with averaging) comparably to state-of-the-art terahertz-TDS systems, yet with significantly reduced complexity. Thickness measurements of multilayer dielectric samples with layer-thicknesses down to 23 µm show its potential for real-world applications. Within only 0.2 s measurement time, an uncertainty of less than 2 % is achieved, the highest accuracy reported with continuous-wave terahertz spectroscopy. Hence, the optoelectronic FMCW approach paves the way towards broadband and compact terahertz spectrometers that combine fiber optics and photonic integration technologies.

Experimental research of the stress-strain state when drawing aluminum-copper bimetal parts rectangular in plan

The stress-strain state of the aluminum-copper bimetal blank flange was studied when extracting boxes rectangular in plan. The studies were carried out using the grid method with assumptions about the material isotropy and incompressibility; uniform deformation within each cell; monotonous deformation, plane stress and three-dimensional strain state, while elastic strains were neglected. A CAD modeling program was used to minimize coordinate grid measurement errors and reduce the time for processing the information obtained. The blanks were rectangles of certain sizes with an explosion-welded AD aluminum and M4 copper layers subjected to preliminary heat treatment before the drawing operation. Rectangular blanks were successively drawn to a height of 10 mm with grid and test sample thickness measurements after drawing. Blank samples were photographed with the same focal length and loaded into the application program. In the program, coordinate points were applied to grid nodes with the distances and coordinates of these points measured before and after strain. According to measurement results, the highest strain was observed in the blank corner areas where compressive stresses increased from the angle bisector to the walls. These stresses led to bimetallic blank stratification and corrugations formed along the copper layer. 20 blanks were drawn, and corrugation was observed on the flange in each case. Varying the hold-down pressure from 0.25 to 0.5 MPa gave no positive results. The highest strain intensity is observed at the end part of the box flange, and this value decreases by 20 % at the approach to the die hole. The effect of angular shear stresses leads to a discontinuity in the transition zone featuring by the presence of an intermetallic layer with reduced plastic properties.

Introducing a low-cost tool for 3D characterization of pitting corrosion in stainless steel

Herein, we propose an approach to three-dimensional (3D) reconstruction of corroded samples to have access to information about the shape, diameter, volume, depth, and spatial distribution of pits. For this purpose, a 304 stainless steel sample, after exposure to controlled corrosion conditions, was submitted to a sequence of polishing, surface image acquisition, and sample thickness measurement. This allows the 3D reconstruction of the sample using computational tomography. The analyses of the two-dimensional and the reconstructed three-dimensional images made it possible to evaluate all the geometric parameters of the pits as well as to compare these data with the electrochemical measurements recorded during the corrosion process.

A preliminary study on the preparation of seamless tubular bacterial cellulose-electrospun nanofibers-based nanocomposite fabrics

Due to various production stages involved, textiles and clothing industry is known for causing carbon dioxide emissions, water pollution, soil erosion and huge waste generation. It is a need of the hour to seek for natural, renewable, and bio-degradable fabrication materials and environmentally friendly production methods. This study proposes an eco-friendly approach to prepare bacterial cellulose/electrospun nanofibers membrane-based hybrid non-woven fabrics using in-situ self-assembly method. This fabrication method enables bacterial cellulose cultivation on nanofibrous membrane support to create custom-made seamless tubular hybrid fabrics in desirable dimensions, to be used for various textile applications with minimized material wastage. As-prepared nano-composite fabric was characterized using SEM, X-ray diffraction, and FTIR. FTIR and X-ray diffraction results confirmed the presence of bacterial cellulose in the composite structure. SEM analysis showed as the bacterial cellulose cultivates, its nanofibrils penetrate and grow into empty voids of membrane's structure, which results in secure binding and interlocking of electrospun nonofibers. Sample thickness and weight gain measurements after the modification were found to be approx. 33.90% and 39.02%, respectively. Reduced surface hydrophobicity, water uptake, and increased tensile strength might contribute towards better fabric performance and comfort. Overall, this study suggests an eco-friendly approach to prepare nano-composite fabrics that might be used for bio-textiles and related applications.

Monte Carlo simulation and theoretical calculation of SEM image intensity and its application in thickness measurement

The intensity profiles of backscattered and secondary electrons from a pure Mg sample have shown a variation with sample thickness and acceleration voltage in the range of 5–30 kV, depending on the specimen holder used. The intensities of backscattered electron (BSE) and secondary electron (SE) signals increases with the sample thickness until saturation when using a scanning transmission electron microscopy (STEM) holder with a closed tube below the sample. However the SE signal increases to the maximum and then decreases with the sample thickness when using a transmission Kikuchi diffraction (TKD) holder with no shielding below the sample whereas the BSE signal again increases until saturation. The influence of the holder on the SE signals is caused by the fact that secondary electrons emitted from the bottom surface could be detected only when using the TKD holder but not the STEM holder. The experimental results obtained are consistent with the Monte Carlo simulation results. Application of the magnitude of the SE and BSE signals to measurement of sample thickness has been considered and the BSE image profile shows a reasonably good accuracy.

Quantitative coating thickness determination using a coefficient-independent hyperspectral scattering model

BackgroundHyperspectral imaging is a technique that enables the mapping of spectral signatures across a surface. It is most commonly used for surface chemical mapping in fields as diverse as satellite remote sensing, biomedical imaging and heritage science. Existing models, such as the Kubelka-Munk theory and the Lambert-Beer law also relate layer thickness with absorption, and in the case of the Kubelka-Munk theory scattering, however they are not able to fully describe the complex behavior of the light-layer interaction.MethodsThis paper describes a new approach for hyperspectral imaging, the mapping of coating surface thickness using a coefficient-independent scattering model. The approach taken in this paper is to model the absorption and scattering behavior using a developed coefficient-independent model, calibrated using reference sample thickness measurements performed with optical coherence tomography.ResultsThe results show that this new model, by considering the spectral variation that can be recorded by the hyperspectral imaging camera, is able to measure coatings of 250 μm thickness with an accuracy of 11 μm in a fast and repeatable way.ConclusionsThe new coefficient-independent scattering model presented can successfully measure the thickness of coatings from hyperspectral imaging data.

Effects of Coil Diameter in Thickness Measurement Using Pulsed Eddy Current Non-destructive Testing

Non-destructive testing (NDT) techniques are used in industry to evaluate the properties of a material, component or structure without causing any permanent damage. Among the techniques, pulsed eddy current (PEC) NDT is regarded as a new technique where a broadband pulse excitation is used, as opposed to single frequencies employed in conventional eddy current NDT. In this study, a 2D axisymmetric electromagnetic model of a PEC probe has been developed and it has been used to study the effects of the excitation coil diameter on the performance of PEC probes in sample thickness measurement. A PEC system has also been built to validate the model. Aluminium plates are used as the sample and they can be stacked up to replicate thickness from 1 mm to 10 mm. The results show that there is a very good correlation between the simulation and experimental results, with an average error of less than 10%. The results also suggest that the larger the diameter of the excitation coil, the deeper the penetration and therefore the larger the thickness measurement range. It has also been shown that although the larger diameters have deeper penetration, the smallest diameter has the highest sensitivity if normalization is not used. These conclusions indicate that coil diameter is an important parameter in a PEC probe design for thickness measurement applications.

The effect of thickness measurement on numerical arterial models

Several optical-based techniques for measuring the sample thickness (ST) of soft tissues have been proposed in the literature to overcome the limits of hand-operated procedures. However, ST measurement still remains arbitrary. The stress calculated during an experimental procedure, usually based on a constant thickness value for all samples, cannot be considered representative of the actual stress experienced by the tissue. Therefore, a new optical methodology to measure ST is proposed and compared to four different thickness estimations. A simplified aortic geometry, under physiologic pulsatile conditions, is used to assess the impact of ST measurement on stress predictions. An additional computational model investigates the effect of such thickness values on critical pressure levels that may instigate aneurysm formation in a homogeneous or artificially modified geometry. Comparing the results obtained for the application of a pulsatile load, wall stress values associated to minimum ST are at least 24kPa inferior to maximum ST. Critical pressure values appear to be inversely proportional to ST estimation: simulations, associated to maximum ST, predict aneurysm formation for pressure levels at least 7kPa inferior to minimum ST outcomes. Finally, the role of the strain-energy function used to fit the experimental data is demonstrated to be fundamental for predictions of aneurysm formation.

Three-point bending setup for piezoresistive gauge factor measurement of thin-film samples at high temperatures.

We present a new method for measuring the piezoresistive gauge factor of a thin-film resistor based on three-point bending. A ceramic fixture has been designed and manufactured to fit a state-of-the-art mechanical testing apparatus (TA Instruments Q800). The method has been developed to test thin-film samples deposited on silicon substrates with an insulating layer of SiO2. The electrical connections to the resistor are achieved through contacts in the support points. This insures that the influence of the electrical contacts is reduced to a minimum and eliminates wire-bonding or connectors attached to the sample. During measurement, both force and deflection of the sample are recorded simultaneously with the electrical data. The data analysis extracts a precise measurement of the sample thickness (<1% error) in addition to the gauge factor and the temperature coefficient of resistivity. The sample thickness is a critical parameter for an accurate calculation of the strain in the thin-film resistor. This method provides a faster sample evaluation by eliminating an additional sample thickness measurement or alternatively an option for cross checking data. Furthermore, the method implements a full compensation of thermoelectrical effects, which could otherwise lead to significant errors at high temperature. We also discuss the magnitude of the error sources in the setup. The performance of the setup is demonstrated using a titanium nitride thin-film, which is tested up to 400 °C revealing the gauge factor behavior in this temperature span and the temperature coefficient of resistivity.

Nonbulk motion system for simultaneously measuring the refractive index and thickness of a sample using tunable optics and spatial signal processing-based Gaussian beam imaging.

This paper presents a novel approach to simultaneously measuring the thickness and refractive index of a sample. The design uses an electronically controlled tunable lens (ECTL) and a microelectromechanical-system-based digital micromirror device (DMD). The method achieves the desired results by using the DMD to characterize the spatial profile of a Gaussian laser beam at different focal length settings of the ECTL. The ECTL achieves tunable lensing through minimal motion of liquid inside a transparent casing, whereas the DMD contains an array of movable micromirrors, which make it a reflective spatial light modulator. As the proposed system uses an ECTL, a DMD, and other fixed optical components, it measures the thickness and refractive index without requiring any motion of bulk components such as translational and rotational stages. A motion-free system improves measurement repeatability and reliability. Moreover, the measurement of sample thickness and refractive index can be completely automated because the ECTL and DMD are controlled through digital signals. We develop and discuss the theory in detail to explain the measurement methodology of the proposed system and present results from experiments performed to verify the working principle of the method. Refractive index measurement accuracies of 0.22% and 0.2% were achieved for two BK-7 glass samples used, and the thicknesses of the two samples were measured with a 0.1mm accuracy for each sample, corresponding to a 0.39% and 0.78% measurement error, respectively, for the aforementioned samples.

Simple Method for Non Contact Thickness Gauge using Ultrasonic Sensor and Android Smartphone

The aim of this research is to develop simple method for non contact thickness gauge using ultrasonic sensor and android smartphone. This system is constructed using ultrasonic sensor HY-SRF05, microcontroller ATMEGA328, bluetooth module and android smartphone. Ultrasonic sensor transmits ultrasonic pulses in the form of waves and recieves back the pulses after the waves are reflected by an object. The time duration of ultrasonic between transmition and reception is calculated as distance between sensor and sample. The method of for thickness measurement adhere sample on holder infront of ultrasonic sensor. The Thickness measurement of sample is calculated base on distance beetwen sensor to holder (fixed barrier) and sample to sensor. The zero position of measurement is distance of sensor to holder. The data of thickness is sent via bluetooth and received by the Android application. Android Application uses to display measurement is designed base on MIT App Inventor for Android (AIA) platform. The measurement results show a fairly high degree of accuracy is 99.978%. DOI: http://dx.doi.org/10.11591/telkomnika.v15i1.7187

Sample Thickness Measurement with THz-TDS: Resolution and Implications

The accuracy of any measurement with terahertz time-domain spectroscopy (THz-TDS) depends strongly on knowing and supplying the precise sample thickness when processing the raw terahertz data. Sample thickness usually is estimated using other (non-THz) metrology and invariably involves some degree of uncertainty. It turns out that the terahertz data itself typically also contains information regarding sample thickness. However, there is limited systematic work addressing the following questions: What is the best method for extracting sample thickness from THz-TDS data? And, what is the thickness resolution obtainable with THz-TDS? In this study we demonstrate how these questions can be answered in general by answering them for a specific example: undoped silicon wafers. We determine the accuracy with which the exact thickness of nominally 500 μm silicon wafers can be measured using transmission mode THz-TDS. We analyze and compare the resolution of 5 different approaches for determining sample thickness using THz-TDS data, including two new methods and three methods proposed in the literature. The quantitative results and analyses of methods we present will be useful in developing far-infrared optical metrology. Conversely the quantitative results presented can be used to relate uncertainty in sample thickness to uncertainty in the measured terahertz data both in the time domain and frequency domain (phase and amplitude). Finally, a precise understanding of the relationship between sample thickness and THz-TDS data can be used to formulate superior THz-TDS data work-up methodologies.

Converging Laser Generated Ultrasonic Waves using Annular Patterns Irradiation

We report on a contactless method to focus laser generated bulk and surface ultrasound waves in the thermo-elastic coupling mode by annular shaped illumination. By using a spatial light modulator (SLM) the beam profile of a pulsed picoseconds laser was shaped to annular forms flexibly and further rings with a thickness of 50 μm and a generation energy as low as 2 mJ were generated on the surface of aluminum plates. The annular shapes have been used to focus acoustic waves toward the center. In this work, a photorefractive adaptive interferometer set up based on Two-Wave Mixing in a fast BSO crystal was used to probe and detect the converging acoustic pulses at the center of the laser generated rings. By moving the detection point about 1 mm out of the ring epicenter, the amplitude of bulk and surface waves drop quickly which shows the converging evidence of the acoustic waves in the ring center. For a 3 mm thick aluminum plate, the ring size from 1 mm to 10 mm was scanned. The optimum ring diameter and the focal length of the acoustic waves along the central axis were found. Applications of this technique in subsurface defects detection as well as sample thickness measurement are investigated.

Sample thickness and quantitative concentration measurements in Br K-edge XANES spectroscopy of organic materials.

While XANES spectroscopy is an established tool for quantitative information on chemical structure and speciation, elemental concentrations are generally quantified by other methods. The edge step in XANES spectra represents the absolute amount of the measured element in the sample, but matrix effects and sample thickness complicate the extraction of accurate concentrations from XANES measurements, particularly at hard X-ray energies where the X-ray beam penetrates deeply into the sample. The present study demonstrates a method of quantifying concentration with a detection limit approaching 1 mg kg(-1) using information routinely collected in the course of a hard X-ray XANES experiment. The XANES normalization procedure unambiguously separates the signal of the absorber from any source of background. The effects of sample thickness on edge steps at the bromine K-edge were assessed and an empirical correction factor for use with samples of variable mass developed.

Spectroscopic method for measuring refractive index

A method for routine, but precise measurements of refractive index is described. The method is fast and accurate. It is based on the analysis of interference fringes, and uses positions of the fringe maxima and/or minima and a precise measurement of sample thickness to extract refractive index. An extremely dense dataset of refractive index values over the entire spectral range of interest can be routinely obtained.

Ultrasonic thickness measurement for aluminum alloy irregular surface parts based on spectral analysis

Ultrasonic methods of measuring the thin thickness in a non-parallel irregular surface sample require quite a high time resolution of the detection device. Ultrasonic resonance method based on spectral analysis was used for accurate thickness measurement of this kind irregular aluminum alloy sample. Aiming at performing successive measurement of the thicknesses of different positions of one sample, non-contact detection mode was selected by using 20 MHz water immersion ultrasonic focused transducer and ultrasonic PAC testing system with 3D location device. Multiple resonant thickness algorithm was set up, so that the thickness value can be calculated by multiple resonant frequencies. In order to obtain the precise multiple resonant frequencies, in spectral analysis, surface wave in time domain signal needs to be removed and the appropriate window of time domain signal was selected. A high measurement accuracy of ±15 μm can be achieved using this method. In addition, the effect of the transducer location error was investigated and the allowed transducer offset ±500 μm was determined.

Specified value based defect depth prediction using pulsed thermography

Several methods have been reported in the literature using pulsed thermography for quantitative measurement of defect depth or sample thickness. In this paper, based on the analysis of a theoretical one-dimensional solution of pulsed thermography, a new method was proposed to first multiply the original temperature decay with square root of the corresponding time to obtain a monotonically increasing function f. A specific time was obtained by setting f equals to a predefined value, the theoretical model shows that the obtained specific time has linear relation with square of defect depth, which was verified with the experimental results of one aluminum and one glass fiber reinforced polymer specimen machined with six flat-bottom wedges as simulated defects. This linearity can be used for defect depth prediction in pulsed thermography.

Method for improving terahertz band absorption spectrum measurement accuracy using noncontact sample thickness measurement

The terahertz absorption spectrum has a complex nonlinear relationship with sample thickness, which is normally measured mechanically with limited accuracy. As a result, the terahertz absorption spectrum is usually determined incorrectly. In this paper, an iterative algorithm is proposed to accurately determine sample thickness. This algorithm is independent of the initial value used and results in convergent calculations. Precision in sample thickness can be improved up to 0.1 μm. A more precise absorption spectrum can then be extracted. By comparing the proposed method with the traditional method based on mechanical thickness measurements, quantitative analysis experiments on a three-component amino acid mixture shows that the global error decreased from 0.0338 to 0.0301.