US 5,629,865 AGranted

Pulse-echo ultrasonic imaging method for eliminating sample thickness variation effects

AssigneeThe United States of America as represented by the Administrator of the National Aeronautics and Space Administration

InventorDon J. Roth

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Abstract

A pulse-echo, immersion method for ultrasonic evaluation of a material which accounts for and eliminates nonlevelness in the equipment set-up and sample thickness variation effects employs a single transducer and automatic scanning and digital imaging to obtain an image of a property of the material, such as pore fraction. The nonlevelness and thickness variation effects are accounted for by pre-scan adjustments of the time window to insure that the echoes received at each scan point are gated in the center of the window. This information is input into the scan file so that, during the automatic scanning for the material evaluation, each received echo is centered in its time window. A cross-correlation function calculates the velocity at each scan point, which is then proportionalized to a color or grey scale and displayed on a video screen.

Claims15

Dependent claims

A pulse-echo, immersion method for ultrasonic evaluation of a material, employing automatic scanning and digital imaging to obtain an image of a property of said material, wherein said material is held in a holding apparatus which is positioned in an immersion liquid over an acoustic reflector, said reflector having an acoustic impedance which is greater than that of said liquid, and wherein nonlevelness in said holding apparatus and material thickness are accounted for and eliminated, said method comprising:

(i) ultrasonically scanning said material at a plurality of scan points and receiving the first and second echoes, each of which is a complete waveform, reflected off the back surface of said material and the first echo reflected off the front surface of said reflector both with and without the presence of said material;
(ii) adjusting the time delay for each said received echo from each said scan point during said scanning in (i) above, gating each said received echo so that it is centered within its respective time window;
(iii) automatically scanning said material at said scan points to receive said first and second back surface echoes and said two front surface echoes using the information obtained in (ii) above, so that each echo received from each scan point during said automatic scanning is centered within its time window;
(iv) digitizing each echo received during said automatic scanning and determining the time delay between said first two successive sample back surface echoes, 2.tau., and the time delay, .DELTA.t, between the two different reflector front surface echoes received at each scan point during said automatic scanning and calculating the wave velocity, using a cross correlation function, at each said scan point from ##EQU3## where c is the speed of the ultrasonic wave transmitted in said liquid, and
(v) scaling the velocity values obtained in (iv) to corresponding proportional color or grey scale values and displaying the resulting image.

2 more elements

A pulse-echo, immersion method for ultrasonic evaluation of a material employing a single transducer, automatic scanning and digital imaging to obtain an image of a property of said material, wherein said material has a uniform thickness variation and is positioned in an immersion liquid between said transducer and an accoustic reflector, said method comprising:

(I) accounting for and eliminating nonlevelness in the set-up and said material thickness variation by;
(a) performing a preliminary scan along both the x-and y-directions of the material to provide slant correction factors which are input into a computer to account for said nonlevelness and thickness variation during the subsequent automatic scanning for said material evaluation in (ii) below;
(b) adjusting the time delay during said preliminary scan for any received echoes which are not centered in the scan time window, so that each received echo is centered in its time window;
(ii) automatically scanning said material at a plurality of scan points in both the x- and y-directions to receive the first and second back surface echoes and front surface echoes with and without the presence of said material between said transducer and reflector using the information obtained in (i) above, so that each echo received from each scan point during said automatic scanning is centered within its time window;
(iii) digitizing each echo received during said automatic scanning and determining the time delay between said first two successive sample back surface echoes, 2.tau., and the time delay, .DELTA.t, between the two different reflector front surface echoes received at each scan point during said automatic scanning and calculating the wave velocity at each said scan point from ##EQU4## where c is the speed of the ultrasonic wave transmitted in said liquid, and
(iv) scaling the velocity values obtained in (iii) to corresponding proportional color or grey scale values and displaying the resulting image.

3 more elements

Dependencies are inferred from the claim text.