KEYWORDS: Transducers, Near field, Acoustics, Ultrasonics, Optics manufacturing, Safety equipment, Signal attenuation, Precision optics, Near field optics
Generally, the surface vibration velocity amplitude of a conventional rectangular acoustic probe is the same. Because of strong interference, the radiated sound field in the near-field is extremely uneven, and radiation side lobes appears in the far field, which are not conducive to its application in ultrasonic technology. A rectangular acoustic transducer with Gaussian vibration velocity distribution on the acoustic radiation surface can reduce or avoid the near field of extreme inhomogeneity and far-field side-lobe. So it can be used in medical ultrasound diagnosis and industrial nondestructive testing and can obtain better effect. In this paper, the radiated sound field of a rectangular transducer with Gaussian distribution of surface vibration velocity is calculated, theoretically. The medium is isotropic without attenuation. The center of the rectangular transducer is assigned as the origin of coordinates. And the plane of the surface is as XOY surface. Then the coordinate system is established. Using Rayleigh integral method, the calculation of the radiation sound field is carried out. Discussion of the acoustic field distribution including on the beam axis and the far field is carried out. It is found that the sound field distribution on the beam axis is closely related to the parameters of the transducer surface. The oscillation of the sound pressure on the beam axis can be avoided by adjusting the parameters. There is no side lobe in the far field. The study of this paper can provide a theoretical suggestion for the application of Gaussian rectangular transducer.
The research focuses on measuring body wave by continuous laser scanning along the surface of aluminum plate. The model of aluminum plate was established by finite element method. The temperature near the upper edge rises, and the temperature rise is small. In infinite large aluminum plates, there are transverse and longitudinal wave front, and the wave front velocity is affected by the velocity of the scanning laser source. Finally, the wave front in plate bottom is used to identify the wave front type, which is generated by scanning laser and determined by combining the relationships between wave velocity and scanning velocity and Bscan diagram.
Rectangular transducer is widely used in industrial non-destructive testing. Current studies generally assume that there is no attenuation in the medium. In this paper, the distribution characteristics of the radiated sound field in attenuation media of a rectangular transducer are theoretically calculated. Firstly, considering the attenuation of the medium, the analytical expression of sound field distribution in The Fresnel region is derived under the condition of Fresnel approximation. Secondly, the distribution characteristics of sound pressure on the beam axis are discussed. Finally, the sound pressure distribution in the far field is calculated using the Fraunhofer approximation and compared with the case without attenuation. This study provides an important reference for the method and process design of using rectangular transducer to detect attenuation materials.
The investigation focuses on analyzed the influence of periodic V-defects on wedge waves by laser ultrasound technique. Usually, wedge tip is almost non-perfect, which may bring in break and enormous economic losses. The wedge waveguide models with different periodic V-defects were established by using finite element method. We have observed multiple mode wedge waves in 20° wedge. The depth of defect is 0.1mm, and the periodic number are 1, 6, 12, and 24, respectively. Both reflected and transmitted waves are observed. And the low order reflected wave and transmitted wave modes separate from high order mode. As periodic number increase, the amplitude of reflected wave and transmitted wave decreased. By integrating the power spectra of the wedge waves, the energy distribution of these wedge waves of different periodic are analyzed. It is found that the energy has a fluctuation, which could be determined the location of defect. The energy has a gradually increase as the propagation before defect, and dramatic decrease after the defect. The results of this study can provide theoretical guidance for the positioning and size estimation of wedge defects.
The investigation focuses on measuring the influence of crack and its width on wedge waves propagating along wedge tip by using laser ultrasound technique. Usually, ideal wedge is almost non-existent, the non-perfect wedge may bring in break and enormous economic losses. Therefore, it is necessary to investigate the characteristic of wedge waves propagating along line wedge with cracks. The wedge waveguide models with different cracks were built by using finite element method. For 20° wedge, multiple mode wedge waves were observed through B-scan. The width of crack of rectangle shape is 0.1mm, and the width are 0.01mm, 0.05mm, 0.1mm, and 0.2mm, respectively. Both reflected and transmitted waves are observed. Due to the dispersion characteristics, we observed the reflected and transmitted A1, A2 mode. Meanwhile, A1 mode separated from the reflected and transmitted A2 mode are also obtained as the wedge wave mode propagating to crack. As the width diverse, it is found that the propagating of wedge waves is almost no change. This study can provide theoretical guidance for the positioning and size estimation of wedge cracks.
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 Fermat's 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.
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.
The research focuses on measuring the influence of V-defect on wedge waves propagating along line wedge tip by using laser ultrasound technique. Generally, wedge has more or less defect or damage on the tip, which may result in break and bring economic losses. Thus it is necessary to investigate characteristic of wedge waves propagating along line wedge with defect. The wedge waveguide models with different defect depth were built by using finite element method. Multiple mode wedge waves were observed through B-scan. The open of defect is 0.1mm, and the depth is 0.01mm, 0.05mm, 0.1mm, 0.2mm, and 0.3mm, respectively. It was seen that both reflected and transmitted waves were observed. Due to the dispersion characteristics, we observed the reflected and transmitted A1 mode separated from A2 mode, which can be used to determine the width of V-defect. Meanwhile, models of V-defect with different depth are also built. We had found that wedge waves are totally reflected and there is no transmitted wave observed as the depth is bigger than 0.3mm.
The research focuses on study the influence of truncations on the dispersion of wedge waves propagating along cylinder wedge with different truncations by using the laser ultrasound technique. The wedge waveguide models with different truncations were built by using finite element method (FEM). The dispersion curves were obtained by using 2D Fourier transformation method. Multiple mode wedge waves were observed, which was well agreed with the results estimated from Lagasse’s empirical formula. We established cylinder wedge with radius of 3mm, 20° and 60°angle, with 0μm, 5μm, 10μm, 20μm, 30μm, 40μm, and 50μm truncations, respectively. It was found that non-ideal wedge tip caused abnormal dispersion of the mode of cylinder wedge, the modes of 20° cylinder wedge presents the characteristics of guide waves which propagating along hollow cylinder as the truncation increasing. Meanwhile, the modes of 60° cylinder wedge with truncations appears the characteristics of guide waves propagating along hollow cylinder, and its mode are observed clearly. The study can be used to evaluate and detect wedge structure.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.