Piezoelectric Detection Method Research Articles

Measurement of Absolute Acoustic Nonlinearity Parameter Using Laser-Ultrasonic Detection

The absolute acoustic nonlinearity parameter β is defined by the displacement amplitudes of the fundamental and second-order harmonic frequency components of the ultrasonic wave propagating through the material. As β is a sensitive index for the micro-damage interior of industrial components at early stages, its measurement methods have been actively investigated. This study proposes a laser-ultrasonic detection method to measure β. This method provides (1) the β measurement in a noncontact and nondestructive manner, (2) inspection ability of different materials without complex calibration owing to direct ultrasonic displacement detection, and (3) applicability for the general milling machined surfaces of components owing to the use of a laser interferometer based on two-wave mixing in the photorefractive crystal. The performance of the proposed method is validated using copper and 6061 aluminum alloy specimens with sub-micrometer surface roughness. The experimental results demonstrated that the β values measured by the proposed method for the two specimens were consistent with those obtained by the conventional piezoelectric detection method and the range of previously published values.

Investigating peculiarities of piezoelectric detection methods for acoustic plate waves in material characterisation applications

Abstract Acoustic waves in plates have proven a viable tool for testing and material characterisation purposes. There are a multitude of options for excitation and detection of theses waves, such as optical and piezoelectric systems. While optical systems, with thermoelastic excitation and interferometric detection, have the benefit of being contactless, they usually require rather complex and expensive experimental setups. Piezoelectric systems are more easily realised but require direct contact with the specimen and usually have a limited bandwidth, especially in case of piezoelectric excitation. In this work, the authors compare the properties of piezoelectric and optical detection methods for broad-band acoustic signals. The shape (e. g. the displacement) of a propagating plate wave is given by its frequency and wave number, allowing to investigate correlations between mode shapes and received signal strengths. This is aided by evaluations in normalised frequency and wavenumber space, facilitating comparisons of different specimens. Further, the authors explore possibilities to utilise the specific properties of the detection methods to determine acoustic material parameters.

Simplified detection of cavitation threshold in control valves

For industrial monitoring of fluid flows, the transition from a single-phase flow to a cavitation regime is most commonly determined by a microphone that measures the sound emitted in the vicinity of critical constrictions such as in the opening of the control valves. To measure the cavitation threshold, we developed an analogue and robust piezoelectric detection method. The evaluation of this method on the reference test orifice plate and on a chosen control valve shows that it eliminates the sound noise of an industrial environment, largely removes the subjectivity of the operator and enables a more detailed observation of the cavitation phenomenon.

Relative measurement of the acoustic nonlinearity parameter using laser detection of an ultrasonic wave

The relative acoustic nonlinearity parameter β' is defined by the amplitudes of the fundamental and second-order harmonic components in the detected ultrasonic wave signal, in which a piezoelectric transducer is conventionally used for detection. Although it is not identical to the absolute parameter β defined by the displacement amplitudes, β' has been widely used for the relative comparison between the same materials since its ratio is identical to that of the absolute parameter when the detected signal amplitude is proportional to the displacement amplitude. However, β cannot be replaced by β' for the comparison between different materials due to the difference of respective acoustic impedance. This study aims to show that a laser detection method using a photorefractive interferometer can be used for the relative comparison of acoustic nonlinearity between different materials because its output is independent of the acoustic impedance. To demonstrate, two similar materials, Al6061-T6 and Al2024-T4, and one different material, copper, were tested. Experimental results showed that the ratio β 2024 / β 6061 , measured via the proposed method and the conventional piezoelectric detection method, were in good agreement with the references. However, in the case of β Cu / β 6061 , only the proposed method showed good agreement with the references.

압전형 수신 기법을 이용한 초음파 절대변위진폭 측정

음향 비선형 파라미터는 입사시킨 기본주파수 성분의 변위 진폭 크기와 재료의 비선형성에 의하여 발생된 2차 고조파 성분의 변위 진폭 크기의 비로 정의된다. 본 연구에서는, 압전소자 방식을 이용한 초음파 절대변위진폭 측정의 타당성을 확인하고자, 이 기법을 통해 초음파가 입사된 SUS316 시편의 절대변위진폭을 측정하였다. 또한 비교를 위해, 레이저를 통한 패브리패럿 방식의 간섭계를 이용하여 동일 시편에 대한 절대변위진폭을 측정하였다. 두 가지 기법을 통한 실험 결과는 서로 잘 일치하는 경향을 보였으며, 특히 압전형 수신 기법의 경우 기존의 레이저 변위측정기법에 비하여 반복 측정의 안정성이 우수한 것으로 나타났다. 이 결과로부터 압전형 수신 기법은 기존 레이저 측정 기법에 비하여 과정이 복잡하지만, 미세변위를 더 안정적으로 측정할 수 있어 음향 비선형 파라미터의 측정에 유리할 것으로 기대된다. A nonlinear ultrasonic parameter is defined by the ratio of displacement amplitude of the fundamental frequency component to that of the second-order harmonic frequency component. In this study, the ultrasonic displacement amplitude of an SUS316 specimen was measured via a piezo-electric-based method to identify the validity of piezo-electric detection method. For comparison, the ultrasonic displacement was also determined via a laser-based Fabry-Pérot interferometer. The experimental results for both measurements were in good agreement. Additionally, the stability of the repeated test results from the piezo-electric method exceeded that of the laser-interferometric method. This result indicated that the piezo-electric detection method can be utilized to measure a nonlinear ultrasonic parameter due to its excellent stability although it involves a complicated process.

Quantitative evaluation of strength degradation by using linear-nonlinear ultrasonic techniques

The ultrasonic nonlinear parameter, β, has been known as effective for the evaluation of material degradation, and its correlation with material degradations such as thermal aging, fatigue, creep, and plastic deformation has been reported. However, most studies were limited to the relative measurements that is effective only for the relative comparison and not able to evaluate the degradation in quantitative. To overcome this limit, this study proposes a new algorithm which is able to evaluate the quantitative strength degradation. The proposed method mainly consists of four steps: 1) Measure the linear elastic modulus (E) from the longitudinal and shear wave velocities by using pulse echo method. 2) Measure the absolute ultrasonic nonlinear parameter, β, by using piezoelectric detection method. 3) Construct the stress-strain curve by substituting the measured linear elastic modulus (E) and absolute ultrasonic nonlinear parameter β to the nonlinear stress-strain equation. 4) Estimate the 0.01% offset yield strain and yield strength. The yield strengths estimated by the proposed technique in the heat-treated Al6061-T6 and SA508 showed good agreement with the yield strength obtained by tensile test. Consequently, the proposed method makes the quantitative evaluation of strength degradation using ultrasonic measurement possible. [This research was supported by the National Research Foundation of Korea (NRF) grant funded by the Korean government (NRF-2013M2A2A9043241).]

Absolute measurement of ultrasonic non-linearity parameter at contact interface

Non-linear interaction of waves with contact interfaces has been widely applied in non-destructive evaluation fields such as bonding quality evaluation, and the detection of closed microcracks and composite delamination. This paper proposes an absolute measurement of the ultrasonic non-linearity parameter using a piezoelectric detection method for two aluminum alloy blocks of different lengths. The results of a two-dimensional finite element method model verified by models for hard and soft contact interfaces, depending on the interface property, were compared with the measured non-linearity parameter. The measured values show good agreement with the modelled results, indicating good potential for measuring the non-linearity parameter at interfaces experimentally and numerically.

Features of photoacoustic transformation in microporous nanocrystalline silicon

Results of a study of the photoacoustic transformation in microporous nanocrystalline silicon are described. The amplitude-frequency and phase-frequency characteristics of the photoacoustic signal from microporous silicon samples on a monocrystalline substrate exposed to illumination at various wavelengths are experimentally determined. Informative response was measured by the gas-microphone and piezoelectric detection methods. In terms of the proposed mathematical model, it is shown that the difference in the parameters of the photoacoustic signal for different wavelengths of exciting radiation is attributed to a shift of the fundamental absorption edge in nanocrystalline silicon. It is pointed out that the piezoelectric detection method is more sensitive to changes in the thermophysical and optical parameters of the porous layer.

Fused Silica와 Al2024-T4의 비선형 파라미터 측정

금속 재료의 비선형 파라미터는 고유한 물성치로서 기본주파수의 음압의 크기(<TEX>$A_1$</TEX>)과 2차고조파의 음압의 크기(<TEX>$A_2$</TEX>)을 측정하면 산정할 수 있다. 하지만, 실험적으로 <TEX>$A_1$</TEX>과 <TEX>$A_2$</TEX>를 측정하는 것은 매우 복잡한 변환 과정이 필요하기 때문에 현재 많은 연구자들이 비선형 파라미터의 절대값을 측정하지 않고, 전압 변화를 관찰하는 비선형 파라미터의 상대값을 측정하고 있다. 하지만, 비선형 파라미터 상대값으로는 재료의 물성치를 대변할 수가 없기 때문에, 열화도에 따른 시편 측정에만 사용할 수 있는 제약이 있다. 따라서 본 연구에서는 정전용량 측정기법(capacitive detector)보다는 비용이 적게 소모되고 현장 적용이 가능한 압전형 수신기법(piezoelectric detection)을 이용하여 비선형 파라미터의 절대값을 측정하기 위한 시스템을 구축하였다. <TEX>$A_1^2vsA_2$</TEX> 그래프로 시스템의 선형성을 검증하고 시험편인 fused silica와 Al2024-T4에 대한 비선형 파라미터를 측정하였다. Nonlinearity parameter is an inherent property of materials measuring fundamental acoustic amplitude(<TEX>$A_1$</TEX>) and second harmonic amplitude(<TEX>$A_2$</TEX>). However, measurement of <TEX>$A_1$</TEX> and <TEX>$A_2$</TEX> has complex calibration procedure, many researchers prefer to measure relative nonlinearity parameter rather than absolute nonlinearity parameter. But, relative nonlinearity parameter is only detect materials degradation with various degradation samples, it is limited application in determining third order elastic constants of materials. Therefore, in this study, the piezoelectric detection method is adopted to measure absolute nonlinearity parameter due to experimental simplicity compare to capacitive detector. Linearity of measurement system is verified by <TEX>$A_1^2vsA_2$</TEX> plot, and we measured ultrasonic nonlinearity parameters of fused silica and Al2024-T4.

Determination of a quantum efficiency of AII–BVIcompounds on the basis of photoacoustic spectra

The method of determination of the quantum efficiency η of irradiative relaxation processes in semiconductors is introduced and discussed. The correlation of the amplitude photoacoustic spectra in the high absorption region with the annealing process is used to estimate the values of η. The values of η, both for as grown and annealed crystals were determined and have been discussed. The results are presented for microphone and piezoelectric detection methods.

Photoacoustic microscopy of coal macerals

Photoacoustic microscopy, in which laser-light energy absorbed by coal macerals is converted into thermal energy, has recently emerged as an in-situ technique for coal maceral characterization. By employing two possible detection modes, different thermal properties can be measured and correlated with the material properties of the coal macerals. For the piezoelectric detection method, the photoacoustic signal is proportional to aB pc , where a is the coefficient of thermal expansion, B is the bulk modulus, p is the mass density, and c is the specific heat capacity of the maceral. The second method employs a gas microphone where the photoacoustic signal is proportional to l √Kpc , where K is the thermal conductivity. Photoacoustic data gathered by both methods on vitrinite and pseudovitrinite macerals from Appalachian basin coals agree with values predicted from known values of a, B, p and c. Data indicate that the thermal-elastic and thermal-conductance properties vary in a systematic manner from low- to high-rank coals. Throughout the entire rank range up to 92% carbon, vitrinite exhibits a significantly different photoacoustic response than pseudovitrinite. The photoacoustic measurements reflect the chemical composition and molecular structure of the individual coal macerals.

Photoacoustics and Photoacoustic Spectroscopy

The recognized leader in the modern development of the field presents both theory and applications. Begins with a historical account, covers gas-phase photoacoustic spectroscopy and detection and the theory of condensed phase photoacoustics, and provides a comprehensive survey of applications, from spectroscopy and chemistry analysis to medical applications and thermal analysis. Treats, for the first time, recent work in high-resolution gas spectroscopy, liquid studies, piezoelectric detection methods, thermal processes, depth profiling, and photoacoustic microscopy.