Yiwei Mao

Investigation on interaction of Lamb waves and circumferential notch in pipe by means of wavelet transform

Mode analysis of Lamb waves propagating in an aluminum alloyed pipe is carried out using wavelet transform (WT). With the aid of the technique the interaction of Lamb waves with a circumferential notch is investigated. It is found that different Lamb wave modes propagating in the pipe can be distinguished clearly by means of wavelet transformation. Therefore, the mode conversion caused by existence of the notch has been unambiguously observed.

Second‐harmonic generation of interface waves

The second‐harmonic generation of leaky waves at the interface between glass and iron has been investigated. Fundamental frequency interface waves are excited by bulk shear waves, incident at the critical angle, and the generated second‐harmonic surface waves are detected by reradiated bulk shear waves. The amplitudes of the generated second harmonic obey the square law. The second‐harmonic generation decreases sharply as the incident and detection drive deviate from the critical angle.

Mode analysis of Lamb waves in hollow cylinder by means of 2-D Fourier transformation

The Lamb wave modes propagating along a hollow cylinder are analyzed by means of two-dimensional (2-D) FFT. The 2-D FFT system consists of a laser probe and a digital oscilloscope. The former implements the spatial and the latter implements the temporal sampling of the waveform. With the aid of this system, the Lamb wave modes propagating along an aluminum alloy tube are analyzed. Comparison between the experiments and calculations shows that the 2-D FFT can be effectively used to analyze quantitatively Lamb wave modes in hollow cylinders.

Switchable single mode Lamb wave transduction by means of both side excitation

Two identical interdigital transducers, deposited on both sides of the 127.86/spl deg/ Y-X LiNbO/sub 3/ plate symmetrically, were used to generate Lamb waves. For the case of electrically symmetrical connection of transducers, the S/sub 0/ mode was generated four or five times more strongly than that for the same transducer on one side, while the A/sub 0/ mode was reduced by about 10 dB. For antisymmetrical electric connection, the A/sub 0/ mode is strong and the S/sub 0/ mode is suppressed. Experiments on nonpiezoelectric medium glass with 121/spl deg/ Y-X LiNbO/sub 3/ on both sides showed a similar result. A delay line composed of such a structure has an insertion loss of only 3 dB.

An evaluation method of bonding strength at a bonded solid-solid interface by contact acoustic nonlinearity

This paper presents a nondestructive method to evaluate the bonding strength of the interface of bonded solid-solid. It is based on a contact acoustic nonlinearity (CAN) phenomenon produced by a bonded solid-solid interface when a longitudinal wave propagates through the interface. The CAN model is set up to depict a bonded state by the relationship between the bonding strength and the crack width in the interface and the CAN parameter described by the ratio, 2 21 / AA , between the amplitudes of the second harmonic and fundamental waves. According to this model, a nondestructive evaluation of the bonding strength can be established. When the CAN parameter and the crack width are measured, the bonding strength can be evaluated from the model. In this paper, experiments have been done to demonstrate the model and the bonding strengths of some samples are evaluated based on the CAN method, The results (the example of 10.2kg/cm 2 by CAN model) are well agree with the bonding strengths (9.9 kg/cm 2 ) measured by hanging clogs to destroy their interfaces.

Influence of electrical boundary conditions on Lamb wave propagation in piezoelectric plates

When a Lamb wave propagates in a piezoelectric plate, it may be governed by three kinds of electrical boundary conditions on two surfaces of the plate. They are: (1) both surfaces are electrically open (oo); (2) both are electrically shorted (ss); (3) one is open and the other is shorted (os). Under these conditions we calculated the dispersion curves of Lamb wave in Y-Z and 128/spl deg/ Y-X lithium niobate plates. The obvious influence of the electrical boundary conditions on Lamb wave propagation is found from the calculations. Especially, it is found that electromechanical coupling coefficient K/sup 2/ of Lamb wave can be evaluated simply from the velocity difference of Lamb wave under the conditions oo and ss.

Quantitative mode analysis of Lamb wave excited by interdigital transducers

In this paper the two-dimensional Fourier transformation technique is used to analyze quantitatively the modes of the Lamb wave. The Lamb waves are generated by IDTs on the 128/spl deg/ Y-X LiNbO/sub 3/ plate. The displacement out-off the plate surface is detected by a heterodyne laser probe. The waveform of the Lamb wave is probed at the interval of 0.1 mm along the direction of wave propagation and recorded by a digital oscilloscope. Total of 64 spatial-temporal samples are taken. A three-dimensional plot in k-f space of the Lamb wave is obtained by the two-dimensional Fourier transformation (DFT). The influence of exciting electrical signals on the purity of mode is investigated in this way.

A nonlinear interaction of two acoustic beams on the solid interface

Two incident ultrasonic shear wave beams of 7.5 MHz interact at glass‐metal interface, and the reflected longitudinal wave of 15 MHz normal to the interface are investigated. This effect is identified as a nonlinear interface effect and the sum frequency signal is the convolution of two input signals. The convolution efficiency is measured as about 106 dBm for glass‐iron interface. The observation reveals that the quality of interface bonding has a significant influence on the convolution output. So the nonlinear effect is found to be useful for implementation of convolution or nondestructive evaluation of bonding layer. Theoretical analysis and experimental measurements on the effect are presented in this letter.

Non-reciprocal wave propagation in one-dimensional nonlinear periodic structures

We study a one-dimensional nonlinear periodic structure which contains two different spring stiffness and an identical mass in each period. The linear dispersion relationship we obtain indicates that our periodic structure has obvious advantages compared to other kinds of periodic structures (i.e. those with the same spring stiffness but two different mass), including its increased flexibility for manipulating the band gap. Theoretically, the optical cutoff frequency remains unchanged while the acoustic cutoff frequency shifts to a lower or higher frequency. A numerical simulation verifies the dispersion relationship and the effect of the amplitude-dependent signal filter. Based upon this, we design a device which contains both a linear periodic structure and a nonlinear periodic structure. When incident waves with the same, large amplitude pass through it from opposite directions, the output amplitude of the forward input is one order magnitude larger than that of the reverse input. Our devised, non-reci...

Acoustic radiation force on a sphere in a progressive and standing zero-order quasi-Bessel-Gauss beam

HighlightsThe beam coefficients of the zero‐order quasi‐Bessel‐Gauss beam are proposed.The quasi‐Bessel‐Gauss beam can perform negative axial radiation forces.Beam width significantly influences the radiation force on sphere of bigger radius for quasi‐Bessel‐Gauss beam. Abstract By means of series expansion theory, the incident quasi‐Bessel‐Gauss beam is expanded using spherical harmonic functions, and the beam coefficients of the quasi‐Bessel‐Gauss beam are calculated. According to the theory, the acoustic radiation force function, which is the radiation force per unit energy on a unit cross‐sectional surface on a sphere made of diverse materials and immersed in an ideal fluid along the propagation axis of zero‐order quasi‐Bessel‐Gauss progressive and standing beams, is investigated. The acoustic radiation force function is calculated as a function of the spherical radius parameter Symbol and the half‐cone angle Symbol with different beam widths in a progressive and standing zero‐order Bessel‐Gauss beam. Simulation results indicate that the acoustic radiation forces with different waist radii demonstrate remarkably different features from those found in previous studies. The results are expected to be useful in potential applications such as acoustic tweezers. Symbol. No caption available. Symbol. No caption available.