Ultrasonic method and device for characterizing a medium

摘要

A probe including NE ultrasonic emitters and NR ultrasonic receivers is applied on the medium to be characterized. Each emitter is activated successively and each time signals are detected on the set of receivers during a time window. Each of the NE×NR signals detected is converted by temporal Fourier transformation to a sum of vibrational components each having its temporal frequency. For each frequency, a matrix NE×NR of complex amplitudes of vibrational components having this frequency is extracted. These matrices are decomposed into singular values, the smallest are eliminated, and the singular vectors associated with the singular values retained, a base of the space of the reception signals is formed, for each frequency. The contribution of each plane wave, characterized by its velocity, in this base is calculated. This contribution is represented in the form of a grey level in a frequency-propagation velocity reference system.

主权项

1. An ultrasonic method of characterization of a medium, comprising:
applying an ultrasonic excitation signal to the medium; detecting a response constituted by the ultrasonic signals received at several receiving sites located at different distances from an emission site where the ultrasonic excitation signal was applied; and extracting, from the ultrasonic signals received, a map of the modes that have been propagated, in a frequency-propagation velocity reference system, wherein for each receiving site, detection is performed successively for at least two different excitation signals, so that at least two responses, whose vibrational components are different and/or are added differently, pass each receiving site, wherein a matrix NE×NR of the energy levels and phase differences of the responses for NR different receiving sites and NE different emission signals is established for each frequency, thereby generating a matrix of initial frequency responses, and wherein the matrix of initial frequency responses is subjected to singular value decomposition, which results for each frequency in a base of singular vectors in the space of the excitations, and a base of singular vectors in the space of the waves that were propagated along the receivers, as well as singular values.