Method for evaluating a material on a remote side of a partition using ultrasonic measurements

A method for evaluating a material on a remote side of a partition separating a first domain from a second domain, the method comprising:

• disposing at least one ultrasonic transmitter and a plurality of ultrasonic receivers in longitudinally spaced-apart relationship along a first side of the partition in the first domain;
• activating the at least one ultrasonic transmitter to propagate a transmitted signal that hits the partition at an oblique incidence and excites, inside the partition, ultrasonic waveforms that comprise propagated quasi leaky-Lamb waves constituting an extensional wave and a flexural wave having respective symmetric and antisymmetric zero-order modes within the partition, wherein the spaced-apart receivers record the ultrasonic waveforms;
• processing the recorded ultrasonic waveforms to determine a measured phase velocity of the flexural wave propagating through the second domain on the second side of the partition from a longitudinal position of a first receiver to a longitudinal position of a second receiver that is located more remote from the transmitter than the first receiver and whose separation from the first receiver is known;
• computing a theoretical phase velocity of the flexural wave propagating through the second domain;
• and
• establishing that the second domain contains a solid if the measured phase velocity deviates from the theoretical phase velocity by an amount that is not accountable by noise alone;
• wherein establishing that the second domain contains a solid comprises:
• processing the recorded ultrasonic waveforms to calculate the group velocity of the flexural wave propagating through the second domain;
• identifying a perturbation in the group velocity plot when group velocity is plotted in the frequency domain and identifying a first critical frequency at which the perturbation occurs;
• and
• comparing the theoretical phase velocity at the first critical frequency to a predetermined threshold to determine if the second domain contains a liquid or a solid.