Estimation of ultrasound attenuation and dispersion using short time Fourier transform

Detection of metal, glass and plastic pieces in bottled beverages using ultrasound

To accomplish a high-resolution ultrasonic imaging without wetting a sample, the efficiency of the dry-contact ultrasonic transmission is discussed. In this study, a dry-contact interface is formed on a sample by inserting a thin film between water and a sample, and the pressure is working on the interface by evacuating the air between the film and the sample. A model of dry-contact ultrasonic transmission is presented to assess the signal loss accompanied with the transmission. From the determination of the signal loss caused by the transmission using various films, it was found that the higher frequency ultrasound is transmitted effectively into the sample by selecting an optimum film, which can keep the displacement continuity between the film and the sample during ultrasonic transmission. Finally, ultrasonic imaging with the sufficient signal-to-noise ratio (SNR) and high lateral resolution was performed on the delamination in a package and the jointing interface of the ball-grid-array package without wetting the packages.

Dry-contact technique for high-resolution ultrasonic imaging

An acoustic resonant spectroscopy technique for measuring the acoustic impedance, ultrasonic velocity, and density of micron-scale polymer films is developed. The method, which is based on spectral analysis, observes the acoustic resonance between water, the film, and a tungsten plate with high acoustic impedance in the frequency range of 20–70MHz. The interface between the film being examined and the plate is vacuum sealed, enabling us to characterize the low-density polyethylene film with acoustic impedances as low as about 1.9MNm−3s and the poly(vinyl chloride) film as thin as about 8μm. The error in the film density measurements is found to be less than 1%, and the validity of the technique is verified.

Acoustic resonant spectroscopy for characterization of thin polymer films

Multipass welds made in 316-L stainless steel are specific welds of the primary circuit in nuclear power plants. Their complex structure complicates ultrasonic assessment of their structural integrity : they present a heterogeneous anisotropy that modifies wave propagation (deviation and division of the beam, high attenuation, high grain noise…). In order to understand ultrasonic propagation in such media, a finite-element model called Athena was developed (INRIA-EDF). Athena predicts ultrasonic beam and particle's velocity in heterogeneous and anisotropic materials, but attenuation has still to be integrated to the code. Our work aims at providing realistic input data of attenuation compatible with the existing model by studying mechanisms leading to attenuation in anisotropic structures. Experimental measurements are made with two immersion techniques using longitudinal waves. Results are presented and compared with theoretical predictions of the literature.

Acoustical characterization of austenitic stainless steel welds for experimental and modeling NDT

A novel method to determine the acoustic impedance of membrane material

Evaluation of ultrasonic attenuation without invoking the diffraction correction separately

Ultrasonic longitudinal and shear wave velocities can be evaluated in cylindrical specimens using line contact with transducers. The present communication discusses various important aspects involved in the method regarding time of arrival, phase and height of the echoes.

Basant Kumar

Papers

A novel method to determine the acoustic impedance of membrane material

Evaluation of ultrasonic attenuation without invoking the diffraction correction separately

On the measurement of longitudinal and shear ultrasonic velocities