Guorong Song

Fabrication of broadband poly(vinylidene difluoride-trifluroethylene) line-focus ultrasonic transducers for surface acoustic wave measurements of anisotropy of a (1 0 0) silicon wafer

This paper investigates a new method for fabrication of broadband line-focus ultrasonic transducers by sol-gel spin-coating the poly(vinylidene difluoride-trifluroethylene) [P(VDF-TrFE)] copolymer film on a concave fine-polished beryllium copper backing. The ferroelectric hysteresis loops of the P(VDF-TrFE) films spin-coated from different molar ratios of VDF/TrFE, 77/23 and 55/45, were measured to select the better mixture. Owing to the better acoustic matching to water, compared with lead zirconate titanate (PZT), the fabricated transducers show relatively wide bandwidth of approximately 50 MHz with high central frequency of 60 MHz obtained at the focal plane when a fused-quartz acts as a reflecting target. Each one of the two finished transducers has a focal length of 5mm and a full aperture angle of 90°. After applying the specially developed digital signal processing algorithm to the defocusing experiment data, which is called V(f,z) analysis method based on two-dimensional fast Fourier transform (2-D FFT), the operating frequency can extend from several MHz to over 90 MHz. Surface acoustic wave (SAW) velocities of a typical (100) silicon wafer was measured along various directions between [100] and [010] to represent the anisotropic features.

Measurement of circumferential Lamb waves using a line-focus poly(vinylidene fluoride) transducer and cross correlation waveform analysis.

This paper presents a method for measuring circumferential Lamb waves propagating on a cylindrically curved thin plate. The measurement is carried out using a wideband and line-focused poly(vinylidene fluoride) transducer along with a defocusing waveform measurement method. After synthesizing the acquired waveforms, interference patterns can be obtained and a cross correlation method is developed to accurately extract the wave velocity as a function of wave frequency. Using three stainless steel thin plates of different thicknesses (100, 150, and 300 μm) and a radius of curvature of 10 mm, dispersion curves for several fundamental and higher order modes of circumferential Lamb waves are simultaneously determined. Theoretical dispersion curves are also calculated and compared with their experimental counterparts. Very good agreements are observed, which concludes the measurement accuracy of this measurement method.

Vibro-acoustic modulation technique for micro-crack detection in pipeline

For the poor sensitivity of traditional ultrasonic technique for micro crack detection, a kind of nonlinear ultrasonic technique, vibro-acoustic modulation technique, is used for micro crack detection in pipes. The influence of the frequency and amplitude of vibration on the modulation index (MI) is experimentally investigated. The experiment results prove that the vibro-acoustic modulation technique can be used for crack detection in pipes. The modulation index is influenced by the frequency and amplitude of vibration, therefore it is important to choose the appropriate parameters in order to get higher sensitivity in crack detection.

Vibration modulated Lamb waves for structure health monitoring

In this paper, Lamb wave health monitoring in plate structure for detection of nonlinear contact scatter is conducted using vibration modulation technique. The low frequency vibration varies the interface area within the contact defect; therefore the amplitude and phase of high frequency Lamb waves reflected from the contact defect will be modulated. By time-frequency analysis of modulated Lamb wave series, the nonlinear responses at frequency of vibration are extracted out and used for defect imaging. It was shown that the nonlinear Lamb wave imaging method based on vibration modulation can effectively characterize and locate the nonlinear contact defects.

Modelling guided waves in layered media materials using the state-vector formalism and legendre polynomial method

This paper presents a new numerical approach for computing the phase velocity dispersion curves of the guided waves, from silicon wafers and layered aluminum-steel plates. By combining the state matrix with Legendre polynomial method, the theoretical framework of the state-vector formalism and Legendre polynomial (SVF-LP) method is constituted. Compared with the conventional Legendre polynomial method, when solving the high frequency-thickness products problem and the high truncate order (N), the drawbacks of modes extraction and the extremely time-consuming calculation are overcome. The characteristics of the higher order mode of the guided waves propagating in different materials are determined more precisely. In order to verify the validity and applicability of the state-vector formalism and Legendre polynomial method, two numerical case studies will be presented: (1) the study of guided waves propagating in the anisotropic material (silicon) in multiple crystal faces; (2) the study of guided waves propagating in the isotropic aluminum-steel plates. The accuracy and applicability of this proposed approach is verified by using the commercial Disperse software (Imperial College UK).This paper presents a new numerical approach for computing the phase velocity dispersion curves of the guided waves, from silicon wafers and layered aluminum-steel plates. By combining the state matrix with Legendre polynomial method, the theoretical framework of the state-vector formalism and Legendre polynomial (SVF-LP) method is constituted. Compared with the conventional Legendre polynomial method, when solving the high frequency-thickness products problem and the high truncate order (N), the drawbacks of modes extraction and the extremely time-consuming calculation are overcome. The characteristics of the higher order mode of the guided waves propagating in different materials are determined more precisely. In order to verify the validity and applicability of the state-vector formalism and Legendre polynomial method, two numerical case studies will be presented: (1) the study of guided waves propagating in the anisotropic material (silicon) in multiple crystal faces; (2) the study of guided waves pro...

Application of improved orthogonal polynomial method in calculating dispersion curves on layered semi-infinite structure

The stress at the boundary of adjacent layers is discontinuous when the conventional Laguerre orthogonal polynomial method is used to calculate the propagation characteristics of Rayleigh-like waves on a layered semi-infinite structure. This problem results in an error of wave velocity calculation, primarily when the mechanical properties of the adjacent layers differentiate significantly. Therefore, in this paper, the conventional Laguerre orthogonal polynomial method is improved to overcome the drawbacks. The Rayleigh-like dispersion curves of the semi-infinite structure are calculated by the improved method and verified by the partial wave method. The difference of the dispersion curves calculated by the conventional and the improved method can be observed significantly for the different adjacent materials. As a result of the expansion coefficients of the orthogonal polynomial, stress distribution is reconstructed, and the superiority of the improved method in dealing with the continuity problem of bou...

Method of Measuring Mechanical Properties for Semi-Infinite Coating Materials

At present coating materials are widely used in the field of aerospace, machinery, petroleum, chemical, nuclear power. The strength and failure analysis of coating is more and more important, at the same time the coating mechanical properties are critical for guiding the industrial electroplating. The elastic constant is one of the most important mechanical properties of parameters that are needed to be evaluated. The paper presents the measurement method of elastic constants for coating material based acoustic microscopy technology. The elastic constants of different thickness semi-infinite nickel coating materials are test by the V(f, z) analytical method, it’s a frequency domain method; which is to obtain the experimental dispersion curves. The mechanical properties of the nickel coating can be inversed by changing the longitudinal wave velocity and shear wave velocity of nickel coating to fit the theoretical dispersion curves with the experimental dispersion curves. The experimental results show the method is feasible, this study lays a foundation for evaluating mechanical properties for semi-infinite coating materials.

An Ultrasonic System for Detecting Channel Defects in Flexible Packages

Ultrasonic system was developed for detecting channel defects embedded in bonded 2-sheet flexible packages film. This hardware system consisted of spherically focused 22.66-MHz ultrasonic transducer, four-axis precision positioning system, NI PXI-bus embedded controller and ultrasonic pulser-receiver. The software system was designed based on the modularization, realized the echo signal on-line processing using ultrasonic backscattered echo envelope integral (BEEI) imaging method. Some experimental results were presented, and the BEEI-mode imaging of channel defect was shown. The system can be easily used to detect the channel defects in flexible packages.

A new method for measuring elastic constants of limited-size materials and the errors analysis

A new method of measuring elastic constants of limited-size materials is presented in this paper. The measurement is based on acoustic microscope technology. The material elastic constants are determined by measuring longitudinal wave and leak surface wave velocity simultaneously by the system with a line-focus PVDF transducer developed by ourselves. Based on the virtual instrument technology, a set of precise measure software was programmed. Experimental tests on three limited-size samples, aluminum, cuprum and steel, were carried out using the line-focus PVDF transducers and automatically measure software. The experimental results indicate that the ultrasonic measurement system can be used to determine the elastic constants of limited-size materials accurately. The main factors to affect the precision of elastic constants were discussed, including the measuring error of defocus distance, thickness and time interval. Take Youngs modulus of aluminum for an example, the qualitative analysis of the errors sources influence on the measure system was made. This method is suitable not only to measuring elastic constants of isotropy materials, but also those of anisotropic ones.