EP0479918A1 - Method and apparatus for photoinductive imaging - Google Patents
Method and apparatus for photoinductive imagingInfo
- Publication number
- EP0479918A1 EP0479918A1 EP19900911486 EP90911486A EP0479918A1 EP 0479918 A1 EP0479918 A1 EP 0479918A1 EP 19900911486 EP19900911486 EP 19900911486 EP 90911486 A EP90911486 A EP 90911486A EP 0479918 A1 EP0479918 A1 EP 0479918A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- specimen
- probe
- eddy
- localized
- current probe
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y15/00—Nanotechnology for interacting, sensing or actuating, e.g. quantum dots as markers in protein assays or molecular motors
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N25/00—Investigating or analyzing materials by the use of thermal means
- G01N25/72—Investigating presence of flaws
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/72—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables
- G01N27/82—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables for investigating the presence of flaws
- G01N27/90—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables for investigating the presence of flaws using eddy currents
- G01N27/9013—Arrangements for scanning
- G01N27/902—Arrangements for scanning by moving the sensors
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R35/00—Testing or calibrating of apparatus covered by the other groups of this subclass
Definitions
- the present invention relates to the photoinductive imaging, and in particular, to the use of eddy-current probes and thermal-waves to image a specimen or a response pattern for an eddy-current probe.
- Eddy-current probes have been used as a form of nondestructive evaluation (NDE). By monitoring the change in inductance of the eddy-current probe as it is scanned over material, information regarding the structure of the material can be derived. Eddy- current probes are valuable because they are noncontacting, can be relatively small in size, and are relatively inexpensive. The major limitations for such probes are that they can only be used with conductive materials and their information is reliable only for new surface regions or thin plates. Also, the spatial resolution of eddy current probes is limited by the size of the probe.
- Eddy-current probes have poor reproducibility in probe behavior from probe to probe. Additionally, it is generally necessary to have access to a large number of different sized, shaped, constructed, and operating probes for various tasks. For example, a different probe would be needed for different frequencies of operation. A further example is the need for a larger probe for a larger area of investigation.
- a further object of the present invention is to provide a means and method as above described which is nondestructive, and can be economically and efficiently incorporated into instrumentation.
- Eddy- current probes are widely known to be used for NDE flaw detection. It has been found that photoinductive imaging also has application to flaw detection which may represent an improvement over utilizing solely eddy-current probe detection. By utilizing photoinductive imaging, it is possible to improve the spatial resolution capabilities above that of eddy current probes alone.
- a further object of the present invention is to provide a means and method as above described which is useful in flaw detection of materials.
- the present invention is related to a means and method of photoinductive imaging for conductive materials, generally as to near surface layers of the materials or to thin plate or sheet materials or thin conductive films on non-conducting or partially- conducting substrates.
- the means and method of the present invention are useful in calibrating eddy- current probes, mapping the response of eddy-current probes, or for nondestructive imaging of materials for use in, for example, flaw detection.
- An eddy-current probe is positioned adjacent to the specimen.
- the specimen can either be one which is to be analyzed or imaged, or can be a flaw-free control specimen used for calibration purposes.
- the probe and specimen can remain stationary while a source of localized heating is raster scanned on the opposite side of the specimen to create localized thermal waves and heating in the specimen coincident with the probe.
- Readings of the eddy-current probe are then recorded over time to create a map or image of the variation of eddy-current probe electrical impedance with respect to the raster scan. This procedure creates basically an image or map of the response pattern for the particular probe. By viewing the response pattern, characteristics of the probe can be discerned nd the probe can be calibrated.
- the eddy-current probe and localized heating source are raster scanned across the specimen.
- the specimen and eddy current probe can remain stationary while the localized heating source is raster scanned across the specimen.
- the output of the eddy-current probe is then recorded to produce an image of that portion of the specimen which was raster scanned. Because any flaws in the material will result in variations in temperature change as compared to portions of the material that are not flawed, the image will produce a map of that portion of the specimen showing, with good positional resolution, location of the flaws such as occlusions, holes, cracks, and the like.
- Figure 1 is a schematic view of one embodiment of a system for photoinductive imaging.
- Figure 2 is a diagramatic representation of the process of photoinductive imaging.
- Figures 3a-3d relate to photoinductive imaging of two blackened strips positioned upon an aluminum specimen ( Figures 3c and 3d);
- Figure 3a showing the image of magnitude of the eddy-current probe versus time;
- Figure 3b showing the image of phase shift versus time.
- Figures 4a and 4b represent photoinductive imaging of the response pattern for two different eddy-current probes.
- Figure 5 is a theoretical representation of photoinductive imaging for a thin sheet specimen having a small hole.
- Figures 6a and 6b are depictions of an actual raster scan on a specimen with a hole.
- Figure 6a scanning the specimen location without the hole;
- Figure 6b representing a scan across the location of the hole.
- Figure 7 is a perspective representation of a photoinductive image produced according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
- a photoinductive imaging system 10 is shown schematically.
- a specimen 12 comprised of a thin sheet of conductive material such as metal foil, is positioned adjacent an eddy-current probe 14 such as are well known within the art.
- the eddy-current probe 14, in this embodiment, and specimen 12 are positioned in a holder, such as is well within the skill of those of ordinary skill in the art, which in turn is connected to an X-Y translator 16.
- Translator 16 serves to move probe 14 and specimen 12 according to instructions from a microcomputer 18.
- An argon-ion laser 20 produces a beam 22 which passes through a chopper mechanism 24.
- a very localized or small area of specimen 12 is therefore impacted directly by beam 22 creating thermal waves which heat up specimen 12 at that localized area, penetrating to a depth dependent on the chopping frequency.
- Chopper 24 is controllable for various frequencies and modulates beam 22 of laser 20.
- An eddy-scope such as is well known in the art, is connected to the coil 30 of eddy-current probe 14. Eddy-scope 28 is in turn connected to lock in amplifier 32. The lock in amplifier 32 is synchronized to chopper 24.
- the signal from the eddy-scope 28 analyzed by the lock-in amplifier 32 results in a magnitude component and a phase component.
- Each of these components is sent to separate volt meters 34 and 36 respectively from lock in amplifier 32.
- the analog output signals of volt meters 34 and 36 are summed with a signal from a vertical position sensor and fed to the vertical channels of x-y recorders 38 and 40 such as a linear variable differential transformer (lvdt).
- the horizontal channels of x-y recorders 38 and 40 are fed with a signal from a horizontal position sensor.
- the signal at x-y recorders 38 and 40 presents the modulation of the impedance of the eddy-current probe 14 and is synchronized with the chopped laser beam 22.
- the signal also represents an image of the sample at the location of probe 14.
- the x-y translator 16 moves the combined probe and specimen in a computer-controlled manner through the beam 22. It is to be understood that this movement could be in any reasonable manner, but conventionally is raster-scanned so that a reliable and discernible image can be obtained.
- FIG. 2 diagramatically depicts the specifics of the photoinductive imaging method using the system 10 of Figure 1.
- Thermal waves are generated in specimen 12 (metal foil) by focusing the modulated laser beam 22 on one side of specimen 12 causing localized temperature-induced fluctuations in the specimen 12's conductivity. These fluctuations are synchronously detected with an eddy-current probe 14 placed on the opposite side of specimen 12. It is to be understood, however, that the probe could be positioned on the same side of specimen 12. Both the thermal diffusion length and the electromagnetic skin depth are large compared to specimen 12 thickness. Raster scanning of beam 22 across specimen 12 allows photoinductive imaging of thermally absorping features on specimen 12.
- Eddy-current signals offer excellent spatial resolution whereas thermal waves can enhance this resolution and utilize the simple, small, non-contact eddy-current detectors. Improved detectability of flaws such as surface-smeared cracks can be achieved.
- Figures 3a and 3b show the magnitude and phase images obtained when a nominal one watt laser beam 22, focused on a 30 micrometer j ⁇ m) diameter spot is raster scanned across an aluminum foil specimen 12 (20 ⁇ thick) which has two black ink strips on its surface (see Figure 3c and 3d) to simulate the presence of a flaw structure.
- the black regions cause increased laser heating similar to what occurs in the presence of flaws such as voids.
- Figure 3a shows the magnitude image signal increases in the black regions corresponding to a temperature induced resistivity increase resulting in a higher eddy-current probe 14 impedance.
- the dip structure in the magnitude image at the center of the left strip is due to a bare metal region.
- the phase image contrast of Figure 3b is believed to be primarily due to a noise reduction mechanism.
- the images were acquired with laser modulation and eddy-current probe frequencies of 13 hertz (Hz) and 100 kilohertz (kHz) respectively resulting in the thermal-wave decay length and electromagnetic skin depth being considerably larger than the sample thickness of 20 ⁇ i. This specimen was fixed to the eddy-current probe during imaging and the laser beam raster scanned across the specimen.
- the length of the black bar in Figures 3c and 3d is 1 mm.
- the lock in amplifier 32 sensitivity was 6 mV with a time constant of 125 ms. It is to be understood that system 10 could operate by either moving the specimen and probe in combination with respect to laser beam 22, or scanning the beam 22 across the fixed specimen and probe. In either case, the images of Figures 3a and 3b are possible because the sensitive area of the probe 14 was considerably larger than the image area.
- Figure 5 depicts a theoretical calculation of the signal for an aluminum foil specimen having a small hole directly under a single turned coil of an eddy-current probe, with the laser beam 22 scanned across the foil specimen. The outline of the small hole can clearly be seen.
- Figure 6a shows a single line of the raster scan through a portion of the specimen away from the hole.
- Figure 6b shows a single line scan directly through the hole.
- Figure 6b shows the sharp edges of the hole depicting the high resolution of the present invention.
- the structure in the signal at the edges of the hole, which is uneven, is believed to be caused by scratches in the ink coating from the needle that was used to make the hole.
- Resolution is believed to be better than eddy-current probe detection alone.
- the resolution is dominated by the size of the probe.
- the resolution is governed by the size of the thermal spot or, as in this case, by the diameter of the laser focal spot.
- the foil specimen was blackened to improve absorption of the laser energy.
- Figure 7 shows in composite form a gold film 32 which was deposited on a layer of glass 34.
- the letters "NDE” in outline form were written on top of the gold film as shown in figure 7.
- the three dimensional photoinductive image 36 shown underneath plate 34 in the diagrammatic view of figure 7, was derived.
- the black ink as with the black stripes in figures 3A-D, alter the conductivity measurements as the probe and localized heating spot were scanned across plate 34.
- the three dimensional images of the letters "NDE" are clearly shown in image 36.
- the present invention can be useful in imaging thermally absorping features or voids or flaws or cracks. It is also believed that the present system is applicable to not only very thin sheets or foils, but could also be used with thicker materials. The capability for imaging was also found to have valuable applicability to calibrating or mapping the response of eddy-current probes.
- the system of 10 of Figure 1 is utilized.
- the specimen 12 consists of a calibration fixture.
- the calibration fixture can be, for example, thin plates of the same material the probe will be used to inspect, curved fixtures if the probe is designed to inspect holes such as bolt holes, or fixtures made from specially sensitive material such as magnetic materials near a phase transition or semiconducting materials, or metals with a large temperature coefficient of conductivity, if that is the use to which the probe is to be put.
- special fixtures could be designed to mimic the geometry the probe is intended to inspect.
- the localized heating source again such as laser beam 22 would then be operated to induce a small, localized region of changed conductivity in the calibration fixture. This region of perturbed conductivity is then scanned over the fixture while recording the variation in eddy-current probe 14's electrical i pedence, producing a map of the probe's response pattern.
- the response pattern is then used for calibration purposes, or for other uses.
- Figures 4a and 4b depict two maps of response patterns for two different eddy-current probes.
- Figure 4a shows the response pattern for a two megahertz (MHz) probe
- Figure 4b shows the pattern for a 100 kilohertz (kHz) probe.
- the patterns directly characterize each probe. As can be seen by comparing Figures 4a and 4b, the maximum strength of response and the shape of the pattern are clearly distinguishable. This is useful in selecting a probe for a particular use.
- a response pattern can be used to calibrate the probe or to analyze probe quality.
- Probe qualitity can be assessed by translating or rotating the probe with respect to the calibration fixture.
- the probe's magnetic field (its fundamental physical characteristic) can also be determined quantitatively from the response pattern.
- the photoinductive images of the response pattern for the probes in Figures 4a and 4b show the characteristic circular-shaped pattern expected for the current distribution in the conductive calibration fixture, which mirrors the pattern of the magnetic field. From patterns such as Figures 4a and 4b, information relevant to probe calibration could be obtained such as follows. For example, the symmetry of the pattern can reveal any tilting or defects in the probe construction. The relative vertical displacement of the pattern is proportional to the probe's field strength; so greater vertical displacement indicates a stronger field, or more sensitive probe. The actual quantitative strength of the probe's magnetic field per unit excitation current could also be obtained from the vertical displacement.
- localized changes in the conductivity of the specimen or calibration fixture can be easily created by a variety of means. Examples include, but are not limited to, laser beams, focused electromagnetic radiation (even an ordinary beam of light from an incandescent light source), electron or other particle beams, or x-ray beams can be used to locally heat the surface which in turn causes the change in the local conductivity. Thick parts or specimens can also be scanned by using an equipment configuration such that the eddy current probe and the laser beam are incident from the same side.
- Hot spot localization can be affected by modulating the heat input to the specimen or calibration fixture.
- a chopper was used to modulate the laser beam.
- modulation can be accomplished with electrical pulses rather than a chopper, or by an acoustic optic modulator, as is well known in the art. Other methods are possible. It is to be understood that careful selection of the modulation frequency limits the size of the hot spot to a size much less than the size of the probe, which is important.
- An optional enhancement would be to connect a CRT to display the image or probe map. Another option would be to add controls to vary the frequency of operation and to adjust the sensitivity of the display.
- the system could also have connection means for easy communication of the probes to the system by having different plug-in modules or the like.
- the source of heat such as a laser beam
- the probe measuring conductants can be positioned on opposite sides of the specimen, or they can be on the same side.
- Figures 1 and 2 show them on opposite sides.
- both could be on the same side, for example, when used on thicker materials, by utilizing conductivity probe which can accommodate the source of heat to be directed to the specimen within its operable field range.
- An example would be a coil with a number of turns whereby a sufficient gap exists or could be created between two turns to allow passage of a focused laser beam or some other type of narrowed heat source.
- An example of another type of narrowed heat source would be the use of fiber optics to direct energy such as a laser beam to a localized area of the specimen. Fiber optics could be used instead of a lense to narrow the width and localize the heat source. As is well known in the art, an optical fiber coupler could receive the chopped laser beam and channel it into a fiber optic which could physically pass through the probe, such as an eddy current probe, and direct the laser beam to the specimen.
- a heating source could be an argon-ion laser available from Spectra Physics, Mountain View, California under product model 2010;
- the beam chopper could be a HMS light beam chopper, model 222 from Ithaco, Ithaca, New York.
- the lense to focus the laser beam could be any simple positive lense; and preferably a microscope objective to get a small spot size.
- the eddy scope could be such as is available under model NDT-19 from Nortec of Kennewick, Washington; and the eddy current probe also could be obtained from Nortec.
- the x-y translator such as is known in the art, could be a daedal roller bearing translator table and can be computer controlled.
- the x-y recorders are available from companies such as Hewlett Packard.
- the lock-in amplifiers could be model 5206 from EG&G/Princeton Applied Research, Princeton, New Jersey. Volt meters are such as is well known in the art.
- the microcomputer could be any general type of microcomputer such as an IBM PC. An example of how the present invention can improve upon methods such as using solely eddy current probes is with respect to detecting smear cracks.
- cracks smeared by grinding or peening basically shortcircuit eddy currents which reduces signal strength and thus reduces the accuracy and reliability of detection using solely eddy current probes.
- the heating source such as the laser heats the specimen over the crack to a greater extent then the surrounding area. This produces greater signal strength.
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Abstract
Système d'imagerie photoinductive servant à la détection de défauts de matériaux et à étalonner des sondes de courant parasite. Ce système comprend notamment la mise en place de la sonde de courant parasite (14) à proximité d'une éprouvette (12) devant être analysée ou devant être utilisée comme dispositif d'étalonnage. Une source d'énergie thermique (20) est modulée et focalisée sur une région ponctuelle de l'éprouvette. On balaie ensuite au moins une partie de la région de détection de la sonde de courant parasite (14) à l'aide d'une source d'énergie thermique. Le signal provenant de la sonde de courant parasite (14) est enregistré; il peut décrire soit les composants thermo-influencés de l'éprouvette (12) soit la configuration de réaction de la sonde de courant parasite (14). L'enregistrement peut par conséquent être utilisé pour représenter par une image les défauts, les trous ou les formes physiques de l'éprouvette ou pour étalonner la sonde de courant parasite (14).Photoinductive imaging system used to detect material faults and to calibrate stray current probes. This system includes in particular the installation of the stray current probe (14) near a test piece (12) to be analyzed or to be used as a calibration device. A thermal energy source (20) is modulated and focused on a point region of the test piece. Then scanning at least part of the detection region of the stray current probe (14) using a thermal energy source. The signal from the stray current probe (14) is recorded; it can describe either the thermo-influenced components of the test piece (12) or the reaction configuration of the stray current probe (14). The recording can therefore be used to represent the defects, holes or physical shapes of the test piece or to calibrate the stray current probe (14).
Description
Claims
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US510112 | 1990-04-17 | ||
US07/510,112 US5019775A (en) | 1989-07-21 | 1990-04-17 | Calibrating an eddy-current-probe using a modulated thermal energy source |
Publications (2)
Publication Number | Publication Date |
---|---|
EP0479918A1 true EP0479918A1 (en) | 1992-04-15 |
EP0479918A4 EP0479918A4 (en) | 1993-09-29 |
Family
ID=24029419
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP19900911486 Withdrawn EP0479918A4 (en) | 1990-04-17 | 1990-07-20 | Method and apparatus for photoinductive imaging |
Country Status (3)
Country | Link |
---|---|
EP (1) | EP0479918A4 (en) |
JP (1) | JPH05500416A (en) |
WO (1) | WO1991016638A1 (en) |
Families Citing this family (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPH08105863A (en) * | 1994-10-05 | 1996-04-23 | Kobe Steel Ltd | Measuring apparatus for conductivity distribution of metal material |
CN101135680B (en) * | 2007-07-13 | 2011-04-20 | 东南大学 | Light-induction dielectrophoresis auxiliary unicellular dielectric spectrum automatic test equipment and testing method |
JP2015052467A (en) * | 2013-09-05 | 2015-03-19 | 国立大学法人東京工業大学 | Compound material inspection device and method |
JP1580264S (en) * | 2016-10-03 | 2020-06-29 | ||
JP1580265S (en) * | 2016-10-03 | 2020-06-29 |
Family Cites Families (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4513384A (en) * | 1982-06-18 | 1985-04-23 | Therma-Wave, Inc. | Thin film thickness measurements and depth profiling utilizing a thermal wave detection system |
US4578643A (en) * | 1983-11-18 | 1986-03-25 | Westinghouse Electric Corp. | Simulation apparatus for eddy current inspection techniques |
US4581576A (en) * | 1984-04-23 | 1986-04-08 | Hewlett-Packard Company | Nondestructive method for profiling imperfection levels in high resistivity semiconductor wafers |
-
1990
- 1990-07-20 JP JP51109090A patent/JPH05500416A/en active Pending
- 1990-07-20 EP EP19900911486 patent/EP0479918A4/en not_active Withdrawn
- 1990-07-20 WO PCT/US1990/004120 patent/WO1991016638A1/en not_active Application Discontinuation
Non-Patent Citations (2)
Title |
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No further relevant documents disclosed * |
See also references of WO9116638A1 * |
Also Published As
Publication number | Publication date |
---|---|
EP0479918A4 (en) | 1993-09-29 |
WO1991016638A1 (en) | 1991-10-31 |
JPH05500416A (en) | 1993-01-28 |
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