Amplitude Of Reflection Coefficient Research Articles

A Method for Ultrasonic Characterization of Density, Thickness and Velocity of Homogeneous Coating

This paper provides a nondestructive method for determination of the density, thickness and velocity of homogeneous coating from an inversion of experimental ultrasonic reflection coefficient amplitude spectrum (URCAS). The detailed analyses of the inverse algorithm and sensitivity of URCAS to the density, thickness and velocity are presented, and the sensitivity is identified as a basis for selecting the experimental data used in inversion. An example of the method and experimental measurement for comparison was given for an epoxy coating with the thickness of 0.277 mm. The relative errors between the inversion and reference value of the density, thickness and velocity were found to be 0.5 %, 3.97 %, and 0.97 %, respectively.

Measurement of the dielectric constant of thin films by terahertz time-domain spectroscopic ellipsometry

We present a reflection-type terahertz time-domain spectroscopic ellipsometry (THz-TDSE) technique for measuring the complex dielectric constants of thin-film materials without replacement of the sample. THz-TDSE provides complex dielectric constants from the ratio of the complex amplitude reflection coefficients between p- and s-polarized THz waves. The measured dielectric constants of doped GaAs thin films show good agreement with predictions of the Drude model, even though the film thickness is of the order of a tenth of the penetration depth of the THz waves. In addition, we demonstrate the measurements of soft-phonon dispersion in SrTiO(3) thin films deposited on a Pt layer. The obtained dielectric constants agree well with the predictions of a generalized harmonic oscillator model.

Nondestructive Evaluation of SCC on the Surface of Ni-Base Alloy by Microwaves

To detect stress corrosion cracking (SCC) and evaluate its depth on the surface of Ni-base alloys, a microwave microscope was employed. An open-ended coaxial line sensor was used to increase the spatial resolution. The working frequency was 110 GHz and the standoff distance between the sensor and the sample was 60 μm. The shape of SCC was obtained by microwave imaging. By measuring the amplitude of reflection coefficient, detection of SCC was achieved. To evaluate SCC depth, the attenuation constant of microwave in the crack was decided by comparing the measured microwave signal with the depth of a reference SCC obtained by destructive testing. Finally, the distribution of the depth of another SCC was evaluated by the proposed equation with the obtained attenuation constant.

OS1716 積層複合材料における超音波伝搬挙動に及ぼす層間界面の影響(OS17-4 複合材料,OS-17 先端材料システムの力学とメゾスケールモデリング)

The influence of the interlaminar interfaces on the longitudinal wave propagation behavior in a multilayered composite material immersed in water is investigated through FEM analysis. Spring boundary conditions are applied to each interface and different interfacial stiffnesses are considered by varying the spring constants. The results of amplitude reflection coefficient of the laminate are compared with those obtained by the transfer matrix method. Good agreement is observed between the results of FEM and the transfer matrix method. Reflection coefficient strongly depends on frequency. It is also found that there exists a stop band, a frequency range in which the reflection coefficient is near or equal to unity, and that this became wider as the interfacial stiffness decreases. From the short-time Fourier transform of waveform data, waves reflected by each interface are found to contain a frequency range corresponding to the stop band.

Interpretation of Fano lineshape reversal in the reflectivity spectra of photonic crystal slabs

Resonant coupling of light to leaky modes of a photonic crystal slab leads to asymmetric Fano lineshapes in the reflectivity spectra. The generally accepted picture, for a lossless system, is that the sign of the real-valued parameter q controls the asymmetry of a Fano resonance. For the reflectivity of a symmetric slab this situation occurs if the amplitude reflection coefficient of the slab goes through zero. In this article, we show that it is also possible to change the asymmetry of a resonance by angle tuning without reaching a condition of zero amplitude. Moreover, we show that the picture of a real-valued parameter q that controls the asymmetry is incomplete.

AVA seismic reflectivity analysis in carbon dioxide accumulations: Sensitivity to CO2 phase and saturation

Abstract Seismic monitoring of sequestered carbon dioxide (CO 2 ) in underground deposits is a matter of growing importance. The subsurface monitoring of this greenhouse gas is possible due to the marked contrast between the physical properties of natural reservoir fluids and those of carbon dioxide after the injection. This technique makes necessary the investigation of appropriate seismic indicators to link seismic attributes to petrophysical properties, composition and state of the rock as well as pore-fluid type and in-situ physical conditions. With this motivation in mind, we use a Biot–Gassmann formulation to model the theoretical P-wave amplitude reflection coefficients vs. angle of incidence in the seismic range when a planar P-wave strikes the interface between a caprock and a porous sandstone which has its pore space saturated by a mixture of CO 2 with brine or oil at different states (supercritical, liquid and gas). The effects of dissolution of CO 2 in oil and the existence of a saturation threshold, above which a free CO 2 phase develops, are included in the computations. Attention is particularly focused on the sensitivity of the classic best-fit amplitude variations with angle coefficients, to different degrees of CO 2 saturation. We conclude from this analysis that the changes in seismic AVA attributes between 30 and 40 degrees can be useful to infer bounds on the CO 2 saturation degree, to detect the presence of immiscible CO 2 phase and, in some cases, to infer the physical state of the accumulations.

Reflection of electromagnetic plane waves in a long-wavelength approximation from a multilayer system of anisotropic transparent films on non-absorbing isotropic medium

The reflection of s- and p-polarised electromagnetic plane waves from an N-layer system of anisotropic dielectric films upon transparent homogeneous substrate is investigated in the long-wavelength approximation. The analytical expressions are obtained for the amplitude reflection (transmission) coefficients, reflectances (transmittances), and ellipsometric angles of an anisotropic multilayer thin-film system. All analytical results are in agreement with the numerical solution of the reflection problem for anisotropic stratified medium. The possibilities of using obtained expressions for resolving the inverse problem for ultrathin anisotropic films upon isotropic substrates are discussed.

Simultaneous determination of the coating thickness and its longitudinal velocity by ultrasonic nondestructive method

The ultrasonic reflection coefficient amplitude spectrum (URCAS) has been extended to obtain the coating thickness and its longitudinal velocity at the same time on thick substrates. A model was set up first to represent the ultrasonic waves reflected from a coating system at normal incident, and the expression of URCAS was derived in order to obtain the coating thickness and velocity. Then, an inverse algorithm based on the Gauss–Newton method was introduced to determine the thickness and velocity by comparing the theoretical and measured URCAS. Experimental validation was conducted on the homogeneous epoxy coatings on the aluminum substrates and inhomogeneous ZrO2−7wt%Y2O3 (YSZ) coatings on the superalloy substrates. The relative errors of the thickness and velocity measurement were in the ranges of 2.15–2.35% and 2.67–4.40% for epoxy coatings, and between 5.33–5.96% and 8.95–9.66% for YSZ coatings. It is concluded that the URCAS combined with inversion technique can be applied to obtain the thickness and longitudinal velocity of coatings simultaneously.

C208 マイクロ波によるNi基合金溶接部表面の応力腐食割れの非破壊評価(亀裂の検査・モニタリング技術-(2),OS5 保全・設備診断技術),動力エネルギーシステム部門20周年,次の20年への新展開)

To detect stress corrosion cracking (SCC) and evaluate its depth on the surface of Ni-base alloys, a microwave microscope was employed. An open-ended coaxial line sensor was used to increase the spatial resolution. The working frequency was 110GHz and the standoff distance between the sensor and the sample was 60μm. The shape of SCC was obtained by microwave imaging. By measuring the amplitude of reflection coefficient, detection of SCC was achieved and V-shaped and W-shaped characteristic signal was obtained. The distribution of SCC depth along the crack length was evaluated using the measured amplitude of reflection coefficient.

S0301-1-2 マイクロ波によるNi基合金溶接部表面の応力腐食割れの計測・評価([S0301-1]欠陥の診断および治癒)

In this paper, we report results of measuring stress corrosion cracking (SCC) and evaluating its depth on the surface of Ni-base alloys, utilizing microwaves. An open-ended coaxial line sensor was used to increase the spatial resolution. The working frequency was 110 GHz and the standoff distance between the sensor and the sample was 60 μm. The distribution of SCC was obtained by microwave imaging. By measuring the amplitude of reflection coefficient, detection of SCC was achieved and V-shaped and W-shaped characteristic signal was obtained. The equation to evaluate SCC depth was proposed. Consequently, the distribution of SCC depth along the crack length was evaluated using the measured amplitude difference.

Omnidirectional constant transmission and negative Brewster angle at planar interfaces associated with a uniaxial medium

This paper presents our detailedly theoretical analyses on omnidirectional constant transmission and negative Brewster angle at planar interfaces associated with a uniaxial medium. The amplitude reflection and transmission coefficients at planar interfaces associated with uniaxial media are derived by examining the boundary condition and the dispersion relation. It is found that under certain conditions, the coefficients are constants independent of the incident angle. Another interesting phenomenon is that an interface between isotropic and uniaxial media can exhibit negative refraction under Brewster condition. Our results offer considerable potential device applications of uniaxial media.

Experimental and theoretical study of Al plasma under femtosecond laser pulses

The amplitude and phase of the complex reflection coefficient of a weak probe laser pulse from strongly coupled Al plasma created on the surface of a metallic target by pump femtosecond laser pulses with intensities I ≲ 1015 W cm−2 were measured using femtosecond interference microscopy. A theoretical model developed for the interaction of intense ultrashort laser pulses with solid targets on the basis of a two-temperature equation of state for an irradiated substance was used for numerical simulations of the dynamics of the formation and expansion of the plasma. A comparison of the experimental data with the simulated results shows that the model is suitable up to I ∼ 1014 W cm−2. At higher intensities of the heating laser pulse, lower values of the reflection coefficient amplitude of Al plasma are observed in the experiment.

A microcontroller-based microwave free-space measurement system for permittivity determination of lossy liquid materials

A microcontroller-based noncontact and nondestructive microwave free-space measurement system for real-time and dynamic determination of complex permittivity of lossy liquid materials has been proposed. The system is comprised of two main sections--microwave and electronic. While the microwave section provides for measuring only the amplitudes of reflection coefficients, the electronic section processes these data and determines the complex permittivity using a general purpose microcontroller. The proposed method eliminates elaborate liquid sample holder preparation and only requires microwave components to perform reflection measurements from one side of the holder. In addition, it explicitly determines the permittivity of lossy liquid samples from reflection measurements at different frequencies without any knowledge on sample thickness. In order to reduce systematic errors in the system, we propose a simple calibration technique, which employs simple and readily available standards. The measurement system can be a good candidate for industrial-based applications.

Complex flow and reflection of evanescent waves from a nanometer-sized hole in a cylindrical waveguide

The results of the theoretical studies on the leakage of the optical radiation through a truncated waveguide with a subwavelength-sized exit hole are reported. We develop a self-consistent approach for the description of the fields behavior by taking into account the transformation of the initial wave into all possible modes, which appear due to the influence of the exit aperture. Our approach allows us to evaluate the amplitude reflection coefficient for the initial evanescent wave and to establish its relationship with the impedance of an infinite waveguide and the impedance of the exit aperture coupling a truncated waveguide with a free space. We determine the complex flow through the exit hole and the transmission coefficient to the far-field zone and express them through the reflection coefficient. Special attention in the work is paid to the evaluation of specific dependencies of the reflection and transmission coefficients on the ratio of the aperture radius to the light wavelength, on the dielectric constants of the waveguide core and the surrounding matter, and on the type of the waveguide mode. It is demonstrated that in the case of a metallic matter at the exit of a waveguide there is a strong resonance enhancement in the amplitude of the reflected wave and in the resulting amplitude of the tangential component of the electric field.

Auto-calibration of ultrasonic lubricant-film thickness measurements

The measurement of oil film thickness in a lubricated component is essential information for performance monitoring and design. It is well established that such measurements can be made ultrasonically if the lubricant film is modelled as a collection of small springs. The ultrasonic method requires that component faces are separated and a reference reflection recorded in order to obtain a reflection coefficient value from which film thickness is calculated. The novel and practically useful approach put forward in this paper and validated experimentally allows reflection coefficient measurement without the requirement for a reference. This involves simultaneously measuring the amplitude and phase of an ultrasonic pulse reflected from a layer. Provided that the acoustic properties of the substrate are known, the theoretical relationship between the two can be fitted to the data in order to yield reflection coefficient amplitude and phase for an infinitely thick layer. This is equivalent to measuring a reference signal directly, but importantly does not require the materials to be separated. The further valuable aspect of this approach, which is demonstrated experimentally, is its ability to be used as a self-calibrating routine, inherently compensating for temperature effects. This is due to the relationship between the amplitude and phase being unaffected by changes in temperature which cause unwanted changes to the incident pulse. Finally, error analysis is performed showing how the accuracy of the results can be optimized. A finding of particular significance is the strong dependence of the accuracy of the technique on the amplitude of reflection coefficient input data used. This places some limitations on the applicability of the technique.

Microwave Detection of Longitudinal Crack and Identification of Its Location in Straight Pipe

A microwave NDT method based on guided electromagnetic wave is described in order to detect longitudinal crack and evaluate its location in steel pipe. To detect longitudinal crack in pipe, suitable guided-mode should be propagated in the inspected pipe with crack. For this purpose, first and dominant circular TE11-mode is sent to the system by using a mode-converter. Mode-converter is used to convert rectangular TE10-mode to the circular TE11-mode. A network analyzer, which is a generator and receiver of the microwaves designed to process the magnitude and phase of the reflected and transmitted waves was used to generate continues signal and to measure the amplitude of reflection coefficient. The goal of this investigation is to demonstrate the capability of this technique for detecting longitudinal cracks in piping system with high speed. More emphasis is put on the evaluation of crack location by measuring time of flight (TOF) of the reflected waves from the crack. The results for two crack locations at several plunger positions either in frequency domain or time domain for measuring TOF of the waves are presented. The experimental results of TOF are compared with calculations to show that by knowing TOF of the reflected wave, it is possible to predict crack locations. The evaluated results of TOFs are shown to agree well with the calculated ones and crack locations can be estimated with error less than 0.13%.

Transmission and reflection of the evanescent waves from a nanometric exit hole in a cylindrical waveguide

The results of theoretical considerations of the electromagnetic-field behavior in a truncated cylindrical waveguide with a subwavelength-sized exit hole are reported. We develop a self-consistent approach to the description of the transverse-magnetic (TM) and transverse-electric (TE) fields inside the waveguide and in the free space behind the exit aperture of the waveguide. The approach takes into account the transformation of the initial wave into all possible modes that appear upon reflection from the exit aperture of the waveguide. It allows us to evaluate the amplitude reflection coefficients for the evanescent TM and TE waves and express them in terms of the impedance of an infinite waveguide and the impedance of the exit aperture at the interface of the truncated waveguide and the free space. We determine the complex optical flow through a nanometric hole and the transmission coefficient to the far-field zone and express them through the reflection coefficient. It is shown that the reflection and transmission coefficients strongly depend on the ratio of the aperture radius to the light wavelength, the dielectric constants of the waveguide core and the surrounding matter, and the type of waveguide modes. It is demonstrated that, in the case of a metallic matter at the waveguide exit, there is a strong enhancement in the amplitude of the reflected wave and, hence, in the resulting amplitude of the tangential component of the electric field. This enhancement is a result of the plasmon-supported effects in a metallic substrate.

A study on the interval between longitudinal modes of Fabry-Perot cavity composed of fiber Bragg gratings

The characteristics of transmission spectrum of the Fabry-Perot (F-P) cavity composed of two fiber Bragg gratings (FBG) are analyzed detailedly in this paper. The influencing factors of the position of the longitudinal mode are pointedout. The relationship and difference between the FBG F-P cavity and normal F-P cavity are discussed. The phase factor of the amplitude reflection coefficient in the range of the FBG main lobe is simulated linearly using the effective mirror surface model. The effective length of the FBG is defined and the expression of the effective length is obtained. Furthermore， the effective length of the FBG is brought into the equivalent cavity length of the FBG F-P cavity. The interval between longitudinal modes of the FBG F-P cavity is calculated using the equivalent cavity length. Both the numerical simulation and experimental results show that the interval calculated using the equivalent cavity length accords well with the true interval between longitudinal modes of the FBG F-P cavity.

Wide angle X‐ray dynamical diffraction by deformed crystals: recurrence relations

AbstractDynamical wide‐angle multiwave X‐ray diffraction from a deformed crystal was considered, for the special case when no more than one strong reflection occurs at a time. The obtained set of equations can be transformed to the Takagi two‐beam approximation if the scattering vector is close to a vector of the reciprocal lattice. The new formalism was employed to obtain recurrence relations for the amplitude reflection coefficient corresponding to laterally homogeneous multilayer structures for the case of coplanar Bragg diffraction. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Unambiguous reconstruction of the complex amplitude reflection coefficient of a laterally homogeneous crystal using analyser-based phase-contrast imaging

A theoretical approach is developed to invert analytically a hard X-ray analyser-based phase-contrast image of a known weak object to recover the complex amplitude reflection coefficient (ARC) of a laterally homogeneous crystal. Numerical simulations test the method to recover the ARC from two systems of interest: a thick perfect crystal and a linearly strained thin film. For the latter model, a kinematical diffraction approximation was used to recover the one-dimensional deformation profile from the ARC.