PNNL-13501 - Pacific Northwest National Laboratory

Study Control Number: PN99061/1389
Real-Time Direct Surface Ultrasonic Holography
Robert Vail Harris, Jr., Byron B. Brenden, Gerald J. Posakony
Ultrasonic techniques are inherently well suited to nondestructive testing and characterizing the composition of materials.
Real-time ultrasonic images, or holograms, may be processed to show flaws and discontinuities in materials. This
technology has many practical applications in a variety of sciences.
Project Description
This project provided a basis for revolutionizing the
technology for ultrasonic nondestructive inspection of
metals and composite materials. By combining
technology from Pacific Northwest National Laboratory
and Idaho National Engineering and Environmental
Laboratory (INEEL), a new ultrasonic imaging system
could be developed capable of real-time imaging of
internal features of materials directly on the surface,
without the need for a water tank or bath and without the
use of radiation. This would dramatically enhance the
ability to detect and image flaws and discontinuities in
materials. It also has the potential for greatly enhancing
medical diagnostic imaging in the human body.
Results and Accomplishments
We determined that high-frequency ultrasonic wavefronts
and lower-frequency reflections from internal
discontinuities can be imaged, but presently attainable
levels of ultrasonic power and optical sensitivity are
insufficient to provide direct-surface ultrasonic imaging
of internal defects in bulk metals.
Solid Surface Imaging
The overall objective of this project is to produce realtime
ultrasonic images (ultrasonic holograms) of internal
features of an object by viewing its surface. We produced
images of ultrasound as it impinged on the surface of the
object. The next step was to make a block with suitable
internal discontinuities (artificial defects) and demonstrate
that the external surface images could be further
processed to reconstruct images of the internal
discontinuities. No work on liquid surface imaging was
planned or performed.
Higher Frequency
To obtain a resolution adequate to produce images of
internal defects in metal, the ultrasonic frequency had to
be increased by a factor of three. This entailed changes in
equipment for both transmission and detection.
Test Block Design
Two test blocks were fabricated of aluminum. Both had a
60 degree face to which the ultrasound transmitter was
clamped, 30-degree flat-bottomed holes to reflect the
ultrasound, and flat surfaces on which to observe the
transmitted and reflected ultrasound. One block had a
single hole, and the other had nine holes in an “F” pattern.
Transmission Results
Transmitted ultrasound was imaged on both blocks (“F”
block image, Figure 1). The spacing of the wavefronts
was consistent with the frequency, velocity, and
insonification angle. The transmitted waves did not show
evidence of interaction with the drilled holes. However,
the signal-to-noise ratio in the best images was 1:1, so the
effects of the interaction may have been masked by noise.
Reflection Results
No reflected high-frequency ultrasound was imaged,
although the presence of reflected ultrasound had been
detected using conventional ultrasonic receivers. For the
single hole, a bright or dark reflected circular spot should
have been observed, surrounded by contrasting diffraction
rings (Figure 2).
Sensors and Electronics 413