Xueping Jiang

Quantitative measurement of acoustic pressure in the focal zone of acoustic lens-line focusing using the Schlieren method.

This paper proposes a theory and method for quantitative measurement of the acoustic lens-line focusing ultrasonic (ALLFU) field in its focal spot size and acoustic pressure using the Schlieren imaging technique. Using Fourier transformation, the relationship between the brightness of the Schlieren image and the acoustic pressure was introduced. The ALLFU field was simulated using finite element method and compared with the Schlieren acoustic field image. The measurement of the focal spot size was performed using the Schlieren method. The acoustic pressure in the focal zone of the ALLFU field and the transducer-transmitting voltage response were quantitatively determined by measuring the diffraction light fringe intensity. The results show that the brightness of the Schlieren image is a linear function of the acoustic intensity when the acousto-optic interaction length remains constant and the acoustic field is weak.

Design of wedge structure with non-dispersive wedge wave propagation

This paper focuses on designing a structure using a laser ultrasound technique, wherein wedge waves can propagate without dispersion. First, the impact of curvature radius and truncations on the wedge waves are investigated using finite element method, and the dispersion curves are obtained using a two-dimensional Fourier transformation method. Subsequently, the propagation of non-dispersive wedge waves is realized via a special wedge shape, which was designed with a unique relationship between the curvature radius and truncation, and its correctness is validated using numerical simulation. Finally, experiments are performed to detect the wedge waves, wherein a pulsed laser is coupled with optical fiber excitation, and the waves are detected using an optical vibrometer.

Propagation of laser-generated visco-elastic Rayleigh-like waves in coatings

This paper reports on a study of the propagation characteristics of visco-elastic, Rayleigh-like waves in coatings. Beginning with the Kelvin model, the characterization equation and the normal displacement of visco-elastic Rayleigh waves in stratified half-space structures are derived and the influence of the visco-elastic modulus on dispersion and attenuation are discussed. The transient response of a visco-elastic Rayleigh wave is also simulated by means of Laplace and Hankel inversion transforms. The results are in good agreement with the theoretic predictions. It is believed the papers results and conclusions will provide insights and guidance for estimating visco-elastic parameters.

Schlieren visualization of leaky guided waves in a liquid immersion plate

In the ultrasonic testing of submarine pipelines by using guided waves, wave energy leakage is a main reason of signal decay. For overcoming the decrease of energy attenuation, the propagation of guided waves of immersion plates is studied in this paper. The dispersion equations of guided waves is numerically solved. Then the appropriated modes of which phase velocity are small or large are selected for optical Schlieren visualization and propagation of leaky waves is discussed. It is shown that selecting some modes of which imaginary part are small can retard guided wave decay and extend length of testing.

Delay time calculations for testing transverse defects of cylindrical surface artefacts with phased array ultrasonic

Bars or tubes are widely used in all kinds of equipment such as automobile shafts or power plant boilers. Effective detection of internal transverse defects is very important to the security of the equipment. In this paper, the time-delay algorithm for the detection by using the combination of a phased array ultrasonic probe and a wedge was discussed. Firstly, a coordinate system was established and the position of each element was calculated. The focal point position of phased array ultrasonic wave was specified. Secondly, based on the geometric acoustics assumption, the equation of the sound wave incident location of each element and its scope on the interface between wedges and artifacts were deduced by using Fermats principle. The numerical method was implied to solve the equations. And the delay time of each element of the array was computed. Finally, the computed delay time of each element was imported to the finite element model and the acoustic beam was simulated. The result shows that the detecting waves can be focused to the specified position by using the calculated delay time. This paper provides a method to calculate the delay time of each element of phased array probes for detecting the transverse defects of cylindrical surface artefacts.

Propagation characteristics of interface waves between a porous medium and a sediment-containing two-phase fluid

&NA; Based on the modified Biot theory of Johnson, the propagation characteristics of the various interface waves at an interface between a semi‐infinite fluid and a porous medium were studied. First, based on the characteristic equations of open‐pore and sealed‐pore, which were derived from the wave equations, time‐domain waveforms at the interface were obtained by inverse Fourier transform. The effects of the longitudinal frame modulus on the interface waves were investigated. For open‐pore and sealed‐pore, the effect of porosity on the propagation of the interface waves was studied; the porosity was found to strongly influence the true surface wave. Based on four ultrasonic suspension models—Utrick, Utrick‐Ament (UA), Harker–Temple (HT) and McClement, the pseudo‐Stoneley wave propagation characteristics were analyzed at the interface between the sediment‐containing two‐phase fluid and the porous medium solid. The effects of volume fraction and particle diameter on the phase velocity, attenuation coefficient and dispersion for the pseudo‐Stoneley and true surface wave were discussed, and the results demonstrated that the properties of the fluid strongly impacted the pseudo‐Stoneley wave but exerted very little effect on the true surface wave. The conclusions drawn in this paper could contribute to elucidate the parameters of sediment and porous media. HighlightsFocus on the effect of the fluid side characteristics on the interface waves.The porosity strongly influences the true surface wave. The sediment characteristics significantly influence the pseudo‐Stoneley wave.The conclusions drawn in this paper could contribute to elucidate the parameters of sediment and porous media.

Measurement of the sound pressure in the focal spot area of line-focus ultrasound field by Schlieren technique

Schlieren method is an effective method for studying the sound field in transparent medium which called phase objects. The method is used to research the acoustic field by analyzing the refractive index changes induced by the acoustic wave. Calculations of the sound pressure distribution radiated by the line-focus ultrasonic transducer are implemented, and the acoustic field in the focal spot area is obtained. Then the diffraction light intensity on the Fourier transform plane in a Schlieren system is calculated with two-dimensional Fourier transformation when the phase object is the ultrasonic wave. Because the light intensity of the different diffraction spots on the back focal plane of the transform lens depends on the sound pressure, the sound pressure in the focal spot area can be determined using Schlieren technique. A Schlieren system is set up. The images of the line-focus ultrasonic field are obtained and the sound pressure in its focal point area is measured non-invasively by measuring and compa...