Characteristics of Eddy Current Attenuation and Thickness Measurement of Metallic Plate

In eddy current testing, the law of attenuation of eddy current(EC) is of great concern. In conductive half space under the excitation of uniform magnetic field, the EC density decreases exponentially in the depth direction. However, in conductor with finite thickness tested by coil, the distribution of EC in the depth direction is more complicated. This paper studies the characteristics of EC attenuation in metallic plate of finite thickness. Simulation results show that there is an EC reflection at the bottom of plate, which changes the law of EC attenuation. A new concept, namely the equivalent attenuation coefficient, is proposed to quantify the speed of EC attenuation. The characteristics of EC attenuation are utilized to explain the nonmonotonic relation between coil voltage and plate thickness. Procedure of selecting frequency is discussed. Thereafter, measurement of plate thickness is carried out and accurate result is obtained.

Thickness Measurement of Insulation Coating by NIR Spectrometry Based on Boosting-KPLS

A novel thickness measurement method for surface insulation coating of silicon steel based on NIR spectrometry is explored.The NIR spectra of insulation coating of silicon steel were collected by acousto-optic tunable filter(AOTF) NIR spectrometer.To make full use of the effective information of NIR spectral data,discrete binary particle swarm optimization(DBPSO) algorithm was used to select the optimal wavelength variates.The new spectral data,composed of absorbance at selected wavelengths,were used to create the thickness quantitative analysis model by kernel partial least squares(KPLS) algorithm coupled with Boosting.The results of contrast experiments showed that the Boosting-KPLS model could efficiently improve the analysis accuracy and speed.It indicates that Boosting-KPLS is a more accurate and robust analysis method than KPLS for NIR spectral analysis.The maximal and minimal absolute error of 30 testing samples is respectively-0.02 μm and 0.19 μm,and the maximal relative error is 14.23%.These analysis results completely meet the practical measurement need.

CONTAMINATION LINE METHOD AND COMPARISON OF FOIL THICKNESS MEASUREMENT METHODS IN TRANSMISSION ELECTRON MICROSCOPY

The paper briefly introduces the Contamination Line Method for foil thickness measurement in transmission electron microscopy and compares it with four conventional methods: the convergent beam diffraction method, the contamination spot method, the methods hased on characteristic X-ray emission and continuous X-ray emission on the application, aperation and accuracy etc.

Monitoring of the Corrosion on a Steel Sheet-pile Marine Breakwater by Systematic Thickness Measurements

In Quepos,Pacific of Costa Rica,it was finished on 2010 the first phase of a marina,including two mix breakwaters,with rubble mound(rocks and concrete units),and 25 circular steel sheet piles cofferdam cells,filled with sand and gravel.The maintenance plan,considers tracking sheet pile corrosion,comparing'actual'against expected rates,checking structural limits,and programming countermeasures if accelerated corrosion is identified.Specific control sections,along the breakwaters,both inside and outside the basin,were established.In each section,thicknesses were measured every meter from the top of the steel cell to seabed using an ultrasonic equipment,and an underwater transducer.Both land crew,and divers for submerged portions,were used.The measurements campaigns are for several years from 2011 to 2016.Sectors of the breakwater with varied corrosion attack levels could be differentiated.Also,corrosion rates and lifespans were estimated,both general for the structures,and specific for each section and level.In turn,this allowed to identify maintenance priorities,defining sites where measures of corrosion protection should initiate,as well,to have confidence in the structural capacity and safety of the breakwaters.

Histogram method for reliable thickness measurements of graphene films using atomic force microscopy(AFM)

Atomic force microscopy（AFM） is a commonly used technique for graphene thickness measurement.However, due to surface roughness caused by graphene itself and variation introduced in AFM measurement, graphene thickness is difficult to be accurately determined by AFM. In this paper, a histogram method was used for reliable measurements of graphene thickness using AFM. The influences of various measurement parameters in AFM analysis were investigated. The experimental results indicate that significant deviation can be introduced using various order of flatten and improperly selected measurement parameters including amplitude setpoint and drive amplitude. At amplitude setpoint of 100 mV and drive amplitude of 100 m V, thickness of 1 layer（1L）, 2 layers（2L） and 4 layers（4L） graphene were measured.The height differences for 1L, 2L and 4L were 1.51 ± 0.16 nm, 1.92 ± 0.13 nm and 2.73 ± 0.10 nm, respectively. By comparing these values, thickness of single layer graphene can be accurately determined to be0.41 ± 0.09 nm.

Double sinusoidal phase modulating laser diode interferometer for thickness measurements of transparent plates

A double sinusoidal phase modulating (SPM) laser diode interferometer for thickness measurements of a transparent plate is presented. A carrier signal is given to the interference signal by using a piezoelectric transducer, and the SPM interferometry is applied to measure the thickness of a transparent plate. By combining the double-modulation technique with the Bessel function ratio method, the measurement error originating from Sight intensity fluctuations caused by the modulation current can be decreased greatly. The thicknesses of a glass parallel plate and a quartz glass are measured in real time, and the corresponding experimental results are also given.

White light interferometry with spectral-temporal demodulation for large-range thickness measurement

Film thickness measurement can be realized using white light interferometry,but it is challenging to guarantee high precision in a large range of thicknesses.Based on scanning white light interferometry,we propose a spectral-temporal demodulation scheme for large-range thickness measurement.The demodulation process remains unchanged for either coatings or substrate-free films,while some adjustments are made according to the estimated optical thickness.Experiments show that the single-point repeatabilities for 500 nm SiO_(2) coating and 68μm substrate-free Si film are no more than 0.70 nm and 1.22 nm,respectively.This method can be further developed for simultaneous measurement of surface profile and film thickness.

Employing a Cerenkov detector for the thickness measurement of X-rays in a scattering background

The variation in environmental scattering background is a major source of systematic errors in X- ray inspection and measurement systems. As the energy of these photons consisting of environmental scattering background is much lower generally, the Cerenkov detectors having the detection threshold are likely insensitive to them and able to exclude their influence. A thickness measurement experiment is designed to verify the idea by employing a Cerenkov detector and an ionizing chamber for comparison. Furthermore, it is also found that the application of the Cerenkov detectors is helpful to exclude another systematic error from the variation of low energy components in the spectrum incident on the detector volume.

Nondestructive determination of film thickness with laser-induced surface acoustic waves

The application of surface acoustic waves（SAWs） for thickness measurement is presented. By studying the impact of film thickness h on the dispersion phenomenon of surface acoustic waves, a method for thickness determination based on theoretical dispersion curve v（ fh） and experimental dispersion curve v（ f） is developed. The method provides a series of thickness values at different frequencies f, and the mean value is considered as the final result of the measurement. The thicknesses of six interconnect films are determined by SAWs, and the results are compared with the manufacturer＇s data.The relative differences are in the range from 0.4% to 2.18%, which indicates that the surface acoustic wave technique is reliable and accurate in the nondestructive thickness determination for films. This method can be generally used for fast and direct determination of film thickness.

A Semi-Automatic Thickness Inspection Technique for Marine Propellers

This paper describes the design and development of a Semi-Automatic Precision Caliper System to measure the thickness of an outboard marine engine propeller blade. Several commonly used methods for measuring the thickness of a propeller blade are reviewed in this paper. These include the P rops Scan, 3D Vision System and Black Dog. However, the operating practices and availability of different facilities in industry necessitate a more cost-effect ive approach. An alternative method using a Semi-Automatic Precision Caliper S ystem is therefore proposed. Details of the design criteria, principles of oper ation as well as the testing and verification of the system are presented. The paper concludes that the Semi-Automatic Precision Caliper System is a low cost and effective method for measuring the thickness of a propeller.

Nonlinear phase error analysis of equivalent thickness in a white-light spectral interferometer

A white light spectral interferometry based on a Linnik type system was established to accurately measure the thin film thickness through transparent medium.In practical work,the equivalent thickness of a beam splitter and the mismatch of the objective lens introduce nonlinear phase errors.Adding a transparent medium also increases the equivalent thickness.The simulation results showthat the equivalent thickness has a significant effect on thin film thickness measurements.Therefore,it is necessary to perform wavelength correction to provide a constant equivalent thickness for beamsplitters.In the experiments,some pieces of cover glasses as the transparent medium were added to the measured beam and then a standard thin film thickness of 1052.2±0.9 nm was tested through the transparent medium.The results demonstrate that our system has a nanometer-level accuracy for thin film thickness measurement through transparent medium with optical path compensation.

Novel method for simultaneous measurement of film thickness and mass fraction of urea–water solution

Quantitative knowledge of the film thickness and mass fraction of the urea-water solution is very crucial in many practical applications. Film thickness or mass fraction can only be determined individually by conventional measurement techniques. We develop a novel measurement method to measure the film thickness and mass fraction of ure^water solution simultaneously. The absorption coefficients of urea-water solution （5 50 wt%） are measured, a pair of optimized wavelengths is then chosen to achieve high measurement sensitivity. Cross validation is also performed and uncertainties of the technique are smaller than 0.68% for thickness measurements and 1.86% for mass fractions.

Measurement of Mucosal Thickness in Denture-bearing Area of Edentulous Mandible

Background： The thickness of the alveolar mucosa influences the probability of the occurrence of denture-induced irritations. Thick denture-supporting tissues offer relief from mucosal tenderness and ulcers; however, the uniformity of the thickness across the entire mandibular alveolar mucosa cannot be accurately determined in edentulous patients. This study aimed to assess the mucosal thickness of the denture-bearing area in the edentulous mandible. Methods： Twenty-seven edentulous patients underwent cone-beam computed tomography scanning, wherein the patients wore a record base to retract soft tissues away from the alveolar mucosa. The measured regions were the central incisor （1C）, lateral incisor （1L）, canine （Ca）, first premolar （P 1）, second premolar （P2）, first molar （M 1）, and second molar （M2） regions. The thickness was measured in the alveolar ridge crest （T）, buccal （B1-B4）, and lingual （L I-L4） alveolar ridge mucosa. The average thickness of the mucosa at buccal sides （B） and lingual sides （L） were also assessed. Results： The differences in the mucosal thickness between the left and right sides were not significant. In the Ca-M2 regions, T was the thickest, and L3 was the thinnest of all the measured points in the same regions. L was significantly less than B in posterior regions （P 〈 0.01 ）. On the other hand, M2 at L4 was thinnest of all the measured regions from Ca to M2 （P 〈 0.01）, and was thicker than IC, IL, P1, and P2 at B2. Conclusions： Since the mucosal thickness of denture-bearing area in the edentulous mandible is not uniform; the tissue surface of the denture base or custom tray should be selectively relieved, which may reduce the risk of denture-induced irritations.

Inverse problem of pulsed eddy current field of ferromagnetic plates

To determine the wall thickness, conductivity and permeability of a ferromagnetic plate, an inverse problem is established with measured values and calculated values of time-domain induced voltage in pulsed eddy current testing on the plate. From time-domain analytical expressions of the partial derivatives of induced voltage with respect to parameters,it is deduced that the partial derivatives are approximately linearly dependent. Then the constraints of these parameters are obtained by solving a partial linear differential equation. It is indicated that only the product of conductivity and wall thickness, and the product of relative permeability and wall thickness can be determined accurately through the inverse problem with time-domain induced voltage. In the practical testing, supposing the conductivity of the ferromagnetic plate under test is a fixed value, and then the relative variation of wall thickness between two testing points can be calculated via the ratio of the corresponding inversion results of the product of conductivity and wall thickness. Finally, this method for wall thickness measurement is verified by the experiment results of a carbon steel plate.

Effect of coating thickness on the calibration and measurement uncertainty of a wide-band liquid crystal thermography

The liquid crystal thermography is a high-resolution and non-intrusive optical technique for full-field temperature measurement.We present detailed calibration data for a wide-bandwidth thermochromic liquid crystal（TLC） to investigate the effect of the coating thickness on the hue-temperature characteristics and the measurement uncertainty of the TLC.It is found that the coating thickness has appreciable effect on the TLC hue-temperature curve.For TLC coatings with the thickness over 20μm,a thicker TLC coating shows a relatively smaller measurement uncertainty,but the effect of the coating thickness is non-distinctive on the measurement uncertainty.

Multi-frequency lateral shear interferometer system for simultaneous measurement of thickness and three-dimensional shape

This Letter demonstrates a novel lateral shear interferometer system for simultaneous measurement of three-dimensional （3D） shape and thickness of transparent objects. Multi-frequency fringe patterns can be created by tilting mirrors at different inclination angles. With a single camera, the multi-frequency fringes are recorded in one image. The phase-shift of the fringes can be generated synchronously only by moving a plane-parallel plate along an in-plane parallel direction. According to the feature of transparent materials, the thickness and 3D shape can be reconstructed simultaneously based on the relationship between the in-plane displacement and their characteristics. The experiment was conducted on a thin transparent film subjected to a shearing force, which verifies the feasibility of the proposed system.

Optimization of thickness uniformity of coatings on spherical substrates using shadow masks in a planetary rotation system

A model is developed to improve thickness uniformity of coatings on spherical substrates rapidly and au- tomatically using fixed shadow masks in a planetary rotation system. The coating thickness is accurately represented by a function composed of basic thickness, self-shadow effect, and shadow mask function. A type of mask with parabolic contours is proposed, and the thickness uniformity of coatings on spheri- cal substrates can be improved in a large range of ratios of clear aperture （CA） to radius of curvature （RoC） by optimizing shadow masks using a numerical optimization algorithm. Theoretically, the thick- ness uniformity improves to more than 97.5% of CA/RoC from -1.9 to 1.9. Experimentally, the thickness uniformities of coatings on a convex spherical substrate （CA/RoC = 1.53） and on a concave spherical substrate （CA/RoC=-1.65） improve to be better than 98.5% after corrected by the shadow masks.

Simultaneous quality improvement of the roughness and refractive index of SiC thin films

We deposite silicon carbide thin layers on cleaned Si（100） substrates using the plasma enhanced chemical vapor deposition method,and show that the RFTIR spectrum is periodic in the near and medium infrared ranges. It is shown that both the deposition rate and the uniformity of the thin films are decreased by increasing the substrate temperature,and that the refractive index is increased by increasing the substrate temperature.This shows that there is a trade-off between the quality improvement of the uniformity and refractive index.