Location

Brunswick, ME

Start Date

1-1-1990 12:00 AM

Description

In ultrasonic nondestructive evaluation (NDE) studies, impulse response is often used to evaluate internal defects. Under the far-field Born approximation [1], the impulse response can be written as the product of the second derivative of the area function with respect to the coordinate along the line-of-sight and a scattering constant which depends on the material properties as well as scattering directions [2]. The line-of-sight is a straight line along the illumination direction for pulse-echo tests, and the area function is an artificial time domain waveform equal to the target cross-sectional area intersected by an imaginary transverse plane travelling along the line-of-sight. Hence the double integration of the impulse response yields the product of the area function and the scattering constant. This product is also known as the ramp function response or the ramp response. Dividing the ramp response by its integral results the area function per volume of the target (normalized area function) [2] thus eliminating the unknown scattering constant. Since the area function (or its normalized form) contains the geometric information about the target, it has been employed in studies of both radar [3–5] and ultrasonic signal imaging [6]. In this paper, an ultrasonic CT algorithm is develped, using the area function from the Born approximation previously suggested by Tam [7]. A similar imaging technique for radar signals can be found in an earlier work done by Das and Boerner [5].

Book Title

Review of Progress in Quantitative Nondestructive Evaluation

Volume

9A

Chapter

Chapter 2: Advanced Techniques

Section

A: Computed Tomography

Pages

439-446

DOI

10.1007/978-1-4684-5772-8_54

Language

en

File Format

application/pdf

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Jan 1st, 12:00 AM

Area Function Imaging in Two-Dimensional Ultrasonic Computerized Tomography

Brunswick, ME

In ultrasonic nondestructive evaluation (NDE) studies, impulse response is often used to evaluate internal defects. Under the far-field Born approximation [1], the impulse response can be written as the product of the second derivative of the area function with respect to the coordinate along the line-of-sight and a scattering constant which depends on the material properties as well as scattering directions [2]. The line-of-sight is a straight line along the illumination direction for pulse-echo tests, and the area function is an artificial time domain waveform equal to the target cross-sectional area intersected by an imaginary transverse plane travelling along the line-of-sight. Hence the double integration of the impulse response yields the product of the area function and the scattering constant. This product is also known as the ramp function response or the ramp response. Dividing the ramp response by its integral results the area function per volume of the target (normalized area function) [2] thus eliminating the unknown scattering constant. Since the area function (or its normalized form) contains the geometric information about the target, it has been employed in studies of both radar [3–5] and ultrasonic signal imaging [6]. In this paper, an ultrasonic CT algorithm is develped, using the area function from the Born approximation previously suggested by Tam [7]. A similar imaging technique for radar signals can be found in an earlier work done by Das and Boerner [5].