ACOUSTOGRAPHY NDE OF COMPOSITES
Tel. 847-215-8884 or 847-309-5869 e-mail: firstname.lastname@example.org
Acoustography* is a full-field, area inspection
technique similar to radiography.
heart of the acoustography method is a novel two-dimensional (2-D), super
high-resolution proprietary ultrasound area detector called AO sensor that converts
ultrasound directly into a visual image, which can then be electronically
captured using a digital camera for computer storage and image
Ultrasonic (AO-TTU) inspection, the test specimen is
ultrasonically illuminated using a sound source from one side. The ultrasound beam is differentially
attenuated as it propagates through the test specimen, casting an ultrasonic
“shadow” that is instantly converted into a visual image by the AO sensor.
acoustography inspection methods are
performed similarly to conventional UT, employing a water tank system.
Acoustography is also being adapted for single-sided (pulse-echo) inspection (AO-RMU) testing without an immersion tank.
*Nondestructive Testing Handbook,
2nd Edition: vol.9, Special Nondestructive Testing Methods, Columbus,
OH, American Society for Nondestructive Testing (1995), p278-284.
Image formation Principle
The geometrical resolution capability of the acoustography
ultrasonic image can be assessed using classical diffraction theory.
An opaque target (e.g. defect) is recognizable as long as
the distance, L, between the target and the plane of
detection (i.e. AO sensor) is less than R, the Fresnel or Near Field Diffraction length, which is given by (**):
D= target diameter
l = ultrasound wavelength
in the test material
where c is the ultrasound velocity in the test material and fis the ultrasound frequency of the illuminating ultrasound plane waves.
The Acoustic Contrast Ration of the geometrically-detected defect depends on:
ACR= Ad / Am
Ad= Defect Attenuation
Am=Test material Attenuation
**Hecht, "Optics," 2nd Ed., Pub. Addison Wesley, 1987, pp 396.
HIGH RESOLUTION ULTRASOUND DETECTOR
How defect becomes visible
A 2D x-ray like ultrasound detector, called Acousto-Optic Sensor (AO sensor), is used to detect and instantly convert the the ultrasound image of the defect into a corresponding optical (visual) image.
The AO sensor has a super high, x-ray film like, resolution because ultrasound is sensed by a continuous layer of a proprietary "mesophase" material; sensing molecules of the layer are on the order of liquid crystal material with sensing molecules ~20 Angstroms. Therefore, the geometrically detected defect is converted into a visual image with high resolution.
The defect becomes optically visible because the ultrasonically-exposed region (ultrasound image) becomes birefringent, which induces a brightness change under polarized light. The degree of brightness change depends on the ultrasonic intensity. Therefore, the ultrasonic image, which is a distribution of ultrasonic intensity, gets converted into a corresponding optical image with brightness variations corresponding to ultrasonic variations.