Download - A B C S Scan Olympus
-
8/12/2019 A B C S Scan Olympus
1/6
Inspection & Measurement Systems
Knowledge
Intro to Ultrasonicspan> Phased Array
by Tom Nelligan and Dan Kass
Many people are familiar with the medical applicationsof ultrasonic imaging, in which high frequency sound waves are used to create
highly detailed cross-sectional pictures of internal organs. Medical sonograms are commonly made with specialized multi-element
transducers known as phased arrays and their accompanying hardware and software. But the applications of ultrasonic phased array
technology are not limited to medical diagnosis. In recent years, phased array systems have seen increasing use in industrial settings to
provide new levels of information and visualization in common ultrasonic tests that include weld inspection, bond testing, thickness
profiling, and in-service crack detection. This paper provides a brief introduction to how phased array systems work and how they can
be employed in industrial ultrasonic nondestructive testing.
What is a phased array system?
Conventional ultrasonic transducers for NDT commonly consist of either a singleactive element that both generates and receives high
frequency sound waves, or two paired elements, one for transmitting and one for receiving. Phased array probes, on the other hand,
typically consist of a transducer assembly with from 16 to as many as 256 small individual elements that can each be pulsed separately.
These may be arranged in a strip (linear array), a ring (annular array), a circular matrix (circular array), or a more complex shape. As is
the case with conventional transducers, phased array probes may be designed for direct contact use, as part of an angle beam
assembly with a wedge, or for immersion use with sound coupling through a water path. Transducer frequencies are most commonly in
the range from 2 MHz to 10 MHz. A phased array system will also include a sophisticated computer-based instrument that is capable of
driving the multi-element probe, receiving and digitizing the returning echoes, and plotting that echo information in various standard
formats. Unlike conventional flaw detectors, phased array systems can sweep a sound beam through a range of refracted angles or
along a linear path, or dynamically focus at a number of different depths, thus increasing both flexibility and capability in inspection
setups.
Typical phased array probe assemblies
Typical multi-element construction
How do they work?
In the most basic sense, a phased array system utilizes the wave physics principle of phasing, varying the time between a series of
outgoing ultrasonic pulses in such a way that the individual wave fronts generated by each element in the array combinewith each other
to add or cancel energy in predictable ways that effectively steer and shape the sound beam.
This is accomplished by pulsing the individual probe elements at slightly different times. Frequently the elements will be pulsed in
groups of 4 to 32 in order to improve effective sensitivity by increasing aperture, which reduces unwanted beam spreading and enables
sharper focusing. Software known as a focal law calculator establishes specific delay times for firing each group of elements in order to
generate the desired beam shape, taking into account probe and wedge characteristics as well as the geometry and acoustical
properties of the test material. The programmed pulsing sequence selected by the instrument's operating software then launches a
number of individual wave fronts in the test material. These wave fronts in turn combine constructively and destructively into a single
primary wave front that travels through the test material and reflects off cracks, discontinuities, back walls, and other material
boundaries like any conventional ultrasonic wave. The beam can be dynamically steered through various angles, focal distances, and
focal spot sizes in such a way that a single probe assembly is capable of examining the test material across a range of different
perspectives. This beam steering happens very quickly, so that a scan from multiple angles or with multiple focal depths can be
performed in a small fraction of a second.
The returning echoes are received by the various elements or groups of elements and time-shifted as necessary to compensate for
varying wedge delays and then summed. Unlike a conventional single element transducer, which will effectively merge the effects of all
beam components that strike its area, a phased array transducer can spatially sort the returning wavefront according to the arrival time
and amplitude at each element. When processed by instrument software, each returned focal law represents the reflection from a
particular angular component of the beam, a particular point along a linear path, and/or a reflection from a particular focal depth. The
echo information can then be displayed in any of several formats.
Home About Us Careers Site Map Global Si te
Home> Knowledge> Theory > Introduction to Olympus Technologies
ENGLISH
o to Ultrasonic Phased Array / Olympus http://www.olympus-ims.com/en/ultrasonics/intro-to-pa/
6 28/2/2012 3:57 PM
-
8/12/2019 A B C S Scan Olympus
2/6
Example of angled beam generated by flat probe by means of variable delay
Example of focused linear scan beam
What do the images look like?
In most typical flaw detection and thickness gaging applications, the ultrasonic test data will be based on time and amplitude information
derived from processed RF waveforms. These waveforms and the information extracted from them will commonly be presented in one or
more of four formats: A-scans, B-scans, C-scans, or S-scans. This section shows some examples of image presentations from both
conventional flaw detectors and phased array systems.
A-Scan displaysAn A-scan is a simple RF waveform presentation showing the time and amplitude of an ultrasonic signal, as commonly provided by
conventional ultrasonic flaw detectors and waveform display thickness gages. An A-scan waveform represents the reflections from one
sound beam position in the test piece. The flaw detector A-scan below shows echoes from two side-drilled holes in a steel reference
block. The columnar sound beam from a common single-element contact transducer intercepts two out of the three of the holes and
generates two distinct reflections at different times that are proportional to the depth of the holes.
Generalized beam profile Straight beam A-scan image
A single-element angle beam transducer used with a conventional flaw detector will generate a beam along one angular path. While
beam spreading effects will cause the beam diameter to increase with distance, the area of coverage or field of vision of a conventional
angle beam will still basically be limited to one angular path. In the example below, a 45 degree wedge at one fixed position is able to
detect two of the side-drilled holes in the test block because they fall within its beam, but it is not possible to detect the third without
moving the transducer forward.
Generalized beam profile Angle beam A-scan image
A phased array system will display similar A-scan waveforms for reference, however in most cases they will be supplemented by
B-scans, C-scans, or S-scans as seen below. These standard imaging formats aid the operator in visualizing the type and position of
flaws in a test piece.
B-Scan displaysA B-scan is an image showing a cross-sectional profile through one vertical slice of the test piece, showing the depth of reflectors with
respect to their linear position. B-scan imaging requires that the sound beam be scanned along the selected axis of the test piece, either
mechanically or electronically, while storing relevant data. In the case below, the B-scan shows two deep reflectors and one shallower
reflector, corresponding to the positions of the side drilled holes in the test block. With a conventional flaw detector, the transducer must
be moved laterally across the test piece.
o to Ultrasonic Phased Array / Olympus http://www.olympus-ims.com/en/ultrasonics/intro-to-pa/
6 28/2/2012 3:57 PM
-
8/12/2019 A B C S Scan Olympus
3/6
Generalized beam profile Typical b-scan image showing relative hole depth
A phased array system, on the other hand, can use electronic scanning along the length of a linear array probe to similarly create a
cross-sectional profile without moving the transducer:
Electronic linear scan (B-scan) image showing relative hole position and depth across the length of a linear array
C-Scan displays
A C-scan is a two dimensional presentation of data displayed as a top or planar view of a test piece, similar in its graphic perspective to
an x-ray image, where color represents the gated signal amplitude at each point in the test piece mapped to its x-y position. With
conventional instruments, the single-element transducer must be moved in an x-y raster scan pattern over the test piece. With phased
array systems, the probe is typically moved physically along one axis while the beam electronically scans along the other. Encoders will
normally be used whenever precise geometrical correspondence of the scan image to the part must be maintained, although unencoded
manual scans can also provide useful information in many cases.
The images that follow show C-scans of a reference block made with a conventional immersion scanning system with a focused
immersion transducer, and with a portable phased array system using an encoded hand scanner and a linear array. While the graphic
resolution is not fully equivalent, there are other considerations. The phased array system is field portable, which the conventional
system is not, and costs about one-third the price. Additionally, the phased array image was made in a few seconds, while the
conventional immersion scan took several minutes.
o to Ultrasonic Phased Array / Olympus http://www.olympus-ims.com/en/ultrasonics/intro-to-pa/
6 28/2/2012 3:57 PM
-
8/12/2019 A B C S Scan Olympus
4/6
General ized beam profi le and direction of motion Conventional C-scan image showing hole position
General ized beam profi le and direction of motion Phased array C-scan image showing hole position
S-Scan displays
An S-scan or sectorial scan image represents a two-dimensional cross-sectional view derived from a series of A-scans that have been
plotted with respect to time delay and refracted angle. The horizontal axis corresponds to test piece width, and the vertical axis to depth.
This is the most common format for medical sonograms as well as for industrial phased array images. The sound beam sweeps through
a series of angles to generate an approximately cone-shaped cross-sectional image. It should be noted that in this example, bysweeping the beam the phased array probe is able to map all three holes from a single transducer position.
o to Ultrasonic Phased Array / Olympus http://www.olympus-ims.com/en/ultrasonics/intro-to-pa/
6 28/2/2012 3:57 PM
-
8/12/2019 A B C S Scan Olympus
5/6
Advanced NDT Solutions
Weld Inspection Solutions
Corrosion Inspection Solutions
Composite Inspection Solutions
Tube Inspection Solutions
Industrial Scanners
Aerospace Inspection Solutions
Flaw Detectors
Ultrasonic Flaw Detectors
Phased Array
Eddy Current Products
Eddy Current Array Products
BondMaster
Probes and Transducers
Pulser-Receivers
Integrated InspectionSystems
Bar Inspection Systems
Tube Inspection Systems
NDT Systems Instrumentation
Thickness Gages
Precision Thickness Gages
Corrosion Thickness Gages
Microscope Solutions
Laser Confocal Microscopes
Opto-digital Microscopes
Semiconductor & Flat Panel DisplayInspection Microscopes
Upright Metallurgical Microscopes
Inverted Metallurgical Microscopes
Modular Microscopes
Polarizing Microscopes
Measuring Microscopes
Stereo Microscopes
Objective Lenses
Digital Cameras
Image Analysis Software
Optical Metrology
Laser Confocal Microscopes
Measuring Microscopes
Interferometers
Lens Decenter Measurement Devices
Micro Spectrophotometer
Videoscopes, Borescopes
Industrial Videoscopes
Industrial Fiberscope
Industrial Rigid Borescopes
Light Sources
Turning tools
High Speed Video Cameras
i-SPEED LT
i-SPEED 2
i-SPEED TR
i-SPEED 3
i-SPEED FS
i-SPEED PL
i-SPEED Comparison
i-SPEED Video Examples
Innov-X XRF and XRDAnalyzers
Alloy QA/QC
Petrochemical & Power
Precious Metals
Scrap Recycling, Metal, Glass, &Plastics
Geochemistry & Mining
Oil & Concentrate Analyses
Environmental & IH
Consumer Products SafetyArchaeometry, Academic & R&D
Pharmaceutical & Nutraceutical
Government & Security
Applications Solutions Key
Applications
Application Notes
Applications Support
Support
Service Centers
PDF Library
Video Gallery
Software Downloads
Training Academy
Obsolete Products
ISO Certifications
MSDS Datasheets
A-Scan of a single angular component at left, composite sectorial scan at right. The cursor marking 49 degrees identifies the angularlocation of the displayed A-scan.
Where are phased array systems used?
Ultrasonic phased array systems can potentially be employed in almost any test where conventional ultrasonic flaw detectors have
traditionally been used. Weld inspection and crack detection are the most important applications, and these tests are done across a
wide range of industries including aerospace, power generation, petrochemical, metal billet and tubular goods suppliers, pipeline
construction and maintenance, structural metals, and general manufacturing. Phased arrays can also be effectively used to profile
remaining wall thickness in corrosion survey applications.
The benefits of phased array technology over conventional UT come from its ability to use multiple elements to steer, focus and scan
beams with a single transducer assembly. Beam steering, commonly referred to sectorial scanning, can be used for mapping
components at appropriate angles. This can greatly simplify the inspection of components with complex geometries. The small footprint
of the transducer and the ability to sweep the beam without moving the probe also aids inspection of such components in situations
where there is limited access for mechanical scanning. Sectorial scanning is also typically used for weld inspection. The ability to test
welds with multiple angles from a single probe greatly increases the probability of detection of anomalies. Electronic focusing permits
optimizing the beam shape and size at the expected defect location, thus further optimizing probability of detection. T he ability to focus
at multiple depths also improves the ability for sizing critical defects for volumetric inspections. Focusing can significantly improve signal-
to-noise ratio in challenging applications, and electronic scanning across many groups of elements allows for C-Scan images to be
produced very rapidly.
Further information on phased array technology and instrumentation is available from Olympus NDT. Contact us for details.
o to Ultrasonic Phased Array / Olympus http://www.olympus-ims.com/en/ultrasonics/intro-to-pa/
6 28/2/2012 3:57 PM
-
8/12/2019 A B C S Scan Olympus
6/6
Copyright 2011 OLYMPUS CORPORATION, All rights reserved. Terms Of Use| Privacy Statement
o to Ultrasonic Phased Array / Olympus http://www.olympus-ims.com/en/ultrasonics/intro-to-pa/