Simultaneous Measurement Of Thickness Research Articles

Simultaneous measurement of thickness and ultrasonic wave velocity using a combination of laser-generated multiple wave modes in the thermoelastic regime

ABSTRACT This paper introduces a reliable laser ultrasonic technique without damage to the surface in the thermoelastic regime that provides a one-side access method for simultaneously determining the thickness and ultrasonic wave velocity by employing multiple wave modes. Initially, this study determines the optimal separated distance between two laser beams to achieve an effective signal-to-noise ratio of the employed wave modes. Subsequently, a pre-established ratio of 0.95 for the velocity of skimming longitudinal waves and longitudinal waves enables the simultaneous calculation using a combination of the skimming longitudinal wave, reflected shear wave, and mode-converted longitudinal wave in a single measurement. Experiments were carried out on various plane plates made of aluminium alloy 6061, ranging in thickness from 4 to 20 mm, demonstrating a high accuracy in thickness measurement, with a maximum absolute error of 0.05 mm. Compare the results of ultrasonic wave velocity measurements with theoretical calculations, the maximum absolute error is 32 m/s and 80 m/s for longitudinal wave and shear wave, respectively.

Simultaneous measurement of thickness and group refractive index in birefringent crystals

In order to measure the group refractive index and thickness of birefringent crystals simultaneously, a method based on spectral-domain interferometry is proposed. The optical path of each reflection layer of birefringent crystal is converted into spectral interference fringe of corresponding frequency by the principle of spectral-domain interferometry, and the accurate optical path calculation is realized by fast Fourier transform and Hanning-windowed energy centrobaric method. A two-step measurement method was designed to measure the crystal thickness and group refractive index of ordinary ( o ) and extraordinary ( e ) light synchronously by comparing the changes of the optical path before and after the insertion of the sample. The comparison between experimental and theoretical results of LiNbO3 crystals shows that the accuracy of the thickness measured by this system is better than 1 μm and the relative error of the group refractive index is better than 0.15%. The measurement method is simple to implement and has high precision, which is of practical significance for realizing the rapid and high-precision measurement of optical parameters of birefringent crystals.

Simultaneous Measurement of Thickness and Group Refractive Index Based on Differential White Light Interferometry

Simultaneous measurement of thickness and refractive index is an important quality control scheme in high-end fabrication. However, the precise measurement of large-range thickness is still technically difficult. In this paper, we propose a high-precision simultaneous measurement method of thickness and group refractive index using differential white light interferometry. Using the bi-directional white light interferometer with a high dynamic range, we can get access to the optical paths on both sides of the specimen. We evaluate the performance of the proposed method by measuring specimens of three different materials, with different thicknesses ranging from 200 μm to 2000 μm. The measurement data are in good agreement with the nominal thickness, and the standard deviations of repeated measurements are ≤0.009 μm and ≤1.63×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> RIU for thickness and group refractive index respectively. In addition, we evaluate the impact of the temperature change on the group refractive index. A quasi-linear relationship between group refractive index and temperature is observed, and the slope of linear fit of silicon specimen around 20 °C is about 3.29×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> RIU/°C@1310 nm. We also analyze and summarize the main factors which may introduce uncertainty in the measurement results. The expanded uncertainties ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> =2) of measured thickness and group refractive index are ≤4.21×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> μm and ≤7.84×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> RIU respectively. The repeatability and uncertainty of group refractive index measurement both decrease as the thickness of specimen increases.

Simultaneous measurement of thickness and sound velocity of porous coatings based on the ultrasonic complex reflection coefficient

The ultrasonic pulse-echo method is widely adopted in measuring coating thickness via parameter inversion of the reflection coefficient. However, the ultrasonic application to thermal barrier coatings (TBCs, as typically applied on aero-engine blades) remains a challenge, as the porous structure significantly attenuates sonic propagation, which is also difficult to characterize. In this article, a method that effectively addresses this issue without the need of the wave attenuation coefficient is presented. Specifically, the complex ultrasonic reflection coefficient can help calculate the coating-induced phase shift, which is found to linearly vary against the ultrasonic wave frequency. The slope of this linear function, depending on the structural porosity, enables simultaneous measurements of both the sound velocity and the thickness of the coating. Moreover, the effectiveness of the proposed method is verified by acoustic finite element simulations and experimental measurements of 8YSZ thermal barrier coatings.

Simultaneous microscopic imaging of thickness and refractive index of thin layers by heterodyne interferometric reflectometry (HiRef)

The detection of spatial or temporal variations in very thin samples has important applications in the biological sciences. For example, cellular membranes exhibit changes in lipid composition and order, which in turn modulate their function in space and time. Simultaneous measurement of thickness and refractive index would be one way to observe these variations, yet doing it noninvasively remains an elusive goal. Here we present a microscopic-imaging technique to simultaneously measure the thickness and refractive index of thin layers in a spatially resolved manner using reflectometry. A coherent laser beam, focussed by a high-numerical-aperture microscope objective and reflected by the sample, is measured using its heterodyne interference with a reference in order to determine the amplitude and phase of the reflected field and thus the complex reflection coefficient. Comparing the results with the theoretically calculated reflection of a thin layer under coherent illumination of high numerical aperture by the microscope objective, the refractive index and thickness of the layer are determined. We present results on a layer of polyvinylacetate with a thickness of approximately 80 nm. These results have a precision better than 10% in the thickness and better than 1% in the refractive index. The measured refractive index is consistent with literature values, and the measured thickness is close to measurements of the same sample by quantitative differential interference contrast. We discuss the significance of these results and the possibility of performing accurate measurements on nanometric layers. Notably, the shot-noise limit of the technique is below 0.5 nm in thickness and 0.0005 in refractive index for millisecond measurement times.

Simultaneous Measurement of Thickness and Elastic Properties of Thin Plastic Films by Means of Ultrasonic Guided Waves.

Ultrasonic guided waves are already used for material characterization. The advantage of these waves is that they propagate in the plane of a plate and their propagation characteristics are sensitive to properties of the material. The objective of this research was to develop an ultrasonic method that could be used to measure the properties of thin plastic polyvinylchloride films (PVC). The proposed method exploits two fundamental Lamb wave modes, A0 and S0, for measurement of a thin film thickness and Young’s modulus. The Young’s modulus is found from the measured phased velocity of the S0 mode and the film thickness from the velocities of both A0 and S0 modes. By using the proposed semi-contactless measurement algorithm, the Young’s modulus and thickness of different thickness (150 µm and 200 µm) PVC films were measured. The uncertainty of thickness measurements of the thinner 150 µm PVC film is 2% and the thicker 200 µm PVC film is 3.9%.

Simultaneous measurement of thickness and permittivity using microwave resonator‐based planar sensor

This article presents a microwave sensor for dielectric characterization and thickness measurement of solid materials. The proposed sensor incorporates an interdigital capacitor (IDC) and a split-ring resonator to create an intense electric field, allowing it to efficiently interact with a sensing material. IDC parameters such as width and gap of the finger and length and gap of the electrode are optimized to enhance the material characterization sensitivity. The microwave resonant sensor structure is designed to operate at 1.8 GHz, making it applicable to measure permittivity and thickness of solid materials. The proximity of the material to be sensed influences the field distribution of the developed sensor, which, in turn, enables the simultaneous measurement of permittivity and thickness based on variations in a resonant frequency. Experimental results reveal that the highest sensitivity value reaches 113.4 MHz/mm and 47.6 MHz/∆εr for permittivity of the solids, when the thickness is between 0 and 1 mm. Furthermore, the developed sensor demonstrates a high accuracy (99.6%) and adequate accuracy (87.6%) for both real and imaginary permittivity, respectively. The developed microwave resonant sensor also shows excellent resolution for permittivity (0.04716) and thickness (0.1314), validating its high-performance for measuring permittivity and thickness for various solids.

Simultaneous measurement of thickness and lift-off using the tangential component of magnetic flux density in pulsed eddy current testing

The pulsed eddy current (PEC) technique is commonly used in the petrochemical and power generation industries to measure two parameters: the degree of pipe wall corrosion and the thickness of the insulation shield. These two parameters can be evaluated by examining the thickness of conductive materials and the lift-off distance, respectively. To explore a possible technique for simultaneously measuring the thickness and the lift-off, the present study envisaged the development of a PEC testing method based on detecting the tangential component of the magnetic flux density. The tangential component of the magnetic flux density was excited by two racetrack-type coils injecting currents in opposite directions that were picked up by a magnetic sensor. The slope in logarithmic scale and the time-to-peak of the magnetic signal were verified to characterise the features of the thickness and the lift-off, respectively. By analysing the simulation and experimental results, the feasibility of simultaneously measuring the thickness and the lift-off was demonstrated.

Rivulet structures formation, rupture and heat transfer in the falling liquid films

The evolution of three-dimensional waves into thermocapillary-wave structures, rivulets deflection, heat transfer enhancement and rupture vertically falling water film at heating were studied. Characteristics of the film flow were determined experimentally using simultaneous measurements of thickness and temperature fields on the falling heated liquid film surface (LIF and IR scanner). The amplitudes and velocities of waves, amplitudes of rivulet deflection, temperature fluctuations on the film surface, frequency spectra and pulsation energies were determined. Several different types of instability were registered on the surface of the heated fluid film: 3D hydrodynamic and thermocapillary A, B and C instabilities. The thermocapillary structures of type A arise in the residual layer behind the front of the wave, leading to an increase in the amplitude of the waves and rivulets deflection amplitudes. It is shown that the heat flux of rupture increases and intensity of heat transfer enhances due to an increase in the surface waves and rivulet deflection amplitudes.

Non-destructive simultaneous measurement of thickness and elastic modulus by laser ultrasonic method

Non-destructive simultaneous measurement of thickness and elastic modulus by laser ultrasonic method

Simultaneous Measurement of Thickness and Permittivity by Means of the Resonant Frequency Fitting of a Microstrip Line Ring Resonator

A simultaneous measurement method of the thickness and permittivity of a thin and uniform material which is attached onto the top of a sensor structure is presented. The sensor utilizes the fundamental and harmonic frequencies of a microstrip line ring resonator structure. The thickness and permittivity of a material under test are calculated from two simultaneous equations at the fundamental and second-harmonic frequencies. Fitting equations to calculate the peak resonant frequencies with respect to the thickness and permittivity are also derived. The structure is implemented with a microstrip line on the front side of a TLY-5A substrate and coplanar waveguide access lines on the backside. The permittivity and thickness of the test material are successfully measured simultaneously.

Accurate and simultaneous measurement of thickness and refractive index of thermally evaporated thin organic films by surface plasmon resonance spectroscopy.

We demonstrate that Surface Plasmon Resonance spectroscopy can be used for the accurate and simultaneous determination of the thickness and refractive index of transparent thin thermally deposited organic films. The experimental approach is based on a two-metal deposition or a two-thickness method. These methods have been applied to an encapsulated sample containing a thin film of commercial tris(8-hydroxyquinoline) (Alq3). The accuracy of the measurement depends on the control of the film deposition process and suggests the use of SPR spectroscopy as inexpensive and valuable metrology tool for small molecule organic thin films.

Simultaneous Measurements of Thickness and Temperature Profile of the Lubricant Film at Chip-tool Interface during Machining Process Using Luminescent Sensors

Simultaneous measurements of thickness and temperature profile of the lubricant film at chip-tool interface during machining have been studied in this experimental programme. Conventional techniques such as thermography can only provide temperature measurement under controlled environment in a laboratory and without the addition of lubricant. The present study builds on the capabilities of luminescent sensors in addition to direct image based observations of the chip-tool interface. A suite of experiments conducted using different types of sensors are reported in this paper, especially noteworthy are concomitant measures of thickness and temperature of the lubricant.

Simultaneous measurement of thickness and refractive index based on rotation incidence angle

A method for simultaneous measurement of geometric thickness and refractive index of an optical wafer is presented. By using a fiber optic Mach–Zehnder interferometer (MZI) with a free space, the transmission spectrum of a MZI for the optical wafer at different incidence angle is interrogated, and the geometric thickness and the refractive index of the optical wafer are measured simultaneously. With the transmission spectrum, we can obtain a clear interferogram with a high visibility no matter how small the measurement range of the refractive index. Therefore the proposed technique possesses a broad measurement range and low cost. The experimental results show that the maximum errors of the geometric thickness and the refractive index are only 0.007 mm and 0.008, respectively, and that a broad measurement from 1.316 to 3.503 can be achieved.

Simultaneous measurement of thickness and refractive index by a single-channel self-mixing interferometer

The authors introduce a new method for the simultaneous measurement of thickness d and refractive index n of transparent slabs and thin films. The method is based on the optical phase shift measured by a single-channel, self-mixing interferometer (SMI) as a function of the angle of incidence on the sample. The authors use a motorised rotating stage to apply an angular scan up to ±65° to the sample. Then, the authors analyse the derivative of phase difference with respect to the rotation angle, apply a standardisation and fit it to the theoretical expression and after a few iterations they are able to simultaneously determine n and d, with a typical accuracy of 0.02 and 1%, respectively.

P‐32: Simultaneous Measurements of Thickness of Filled Cholesteric LC Cell and the Average Refractive Index

AbstractA novel method for simultaneous measurement of an average refractive index of the cholesteric LC cell and a cell gap of the filled LC cell has been proposed. It is based on spectrum analysis of light mirror reflected from a LC cell at different angles. This method can be applied to other types of liquid crystal cells and easily implemented in commercial instruments.

A high-frequency eddy current method for the thickness measurement of thin metallic foils using ferrite-core transmission systems

An eddy current system is described that allows the simultaneous measurement of thickness and electrical conductivity of thin nonmagnetic foils. The transmission coil systems used in the experiments consist of two coils with ferrite-cup cores. Because of the high measurement frequencies (up to 60 MHz), a special shielding of the coils including metallic meshes between coil and test-foil is necessary. The measured frequency responses of amplitude and phase angle are compared to the results of finite-element calculations, and excellent agreement is found for different test-foils with thickness between 10 and 200 μm. The optimization of the coil shape and the influence of the coil-to-coil spacing is discussed, and two alternatives for the reduction of the position sensitivity of the ferrite-core system are proposed. Finally, an inversion procedure that permits the fast and accurate estimation of thickness and conductivity from the complex output voltage is presented.

Simultaneous Measurement of Thickness and Temperature of Oil Film by Laser Induced Fluorescence.

A new simultaneous measurement method of temperature and thickness for lubricating oil film was proposed. In this method, two fluorescent dyes with different fluorescent spectrum and temperature characteristics were dissolved in oil and excited by same laser light. The temperature was obtained by the intensity ratio of fluorescence and the oil film thickness was obtained by the intensity of fluorescence. The 488 nm light of Ar Laser was used as a light source. From the experiments, Coumarin 6 and DCM were selected as appropriate fluorescent dye for this method. The fluorescence from Coumarin 6 in PAO increases with temperature and that from DCM in PAO decreases with temperature, and the intensity ratio of each dye changes greatly with temperature. It was confirmed that, by using the combination of Coumarin 6 and DCM with PAO, this method can he applied to measure the temperature and thickness of oil film in the temperature range from 60°C to 140°C.

分光計測を利用した膜厚と屈折率の同時測定

分光計測を利用した膜厚と屈折率の同時測定

Fast Simultaneous Thickness Measurements of Gold and Nickel Layers on Copper Substrates

The thickness of nickel and gold films plated on a copper substrate has been determined by measuring the intensity of various fluorescent lines excited in reflection by a 50-kV tungsten X-ray source. An exploratory system has been constructed which can simultaneously measure the thickness of the gold and nickel layers on an area of 125 × 175 μm. Thickness of gold from 0.2 μm to 5 μm and from 0.3 μm to 1.5 μm of nickel can be measured to an accuracy of ±6 percent in the gold films and ±10 percent in the nickel films in about 20 seconds, including the measurement and calculation. The equations describing the attenuation of the incident radiation, the primary and secondary excitation of fluorescence radiation in the films, and the attenuation of the fluorescence radiation in the films have been determined for the case of nickel and gold films on copper substrates and for indium and gold films on copper substrates and are solved by a computer in the system. The method could be extended to other multilayer systems.