Appendix A: Future Directions
A.7.3 Example for the Interaction of Structural, Aerodynamic,
9.3 Noncontact Ultrasonic Testing and Analysis of Materials
9.3.5 Perusal of NCU
material. An example of this is shown in Figure 9.59. Here we see the artificially embedded defects in a 4 mm thick panel of CFRP composite.
9.3.4.3 Single Transducer Pulse-Echo NCU
Under ambient conditions, it is very easy to obtain high-quality signals corresponding to the refl ection from the material surface
(Figure 9.60). By monitoring the amplitude and time of fl ight of surface refl ections, materials can be characterized for surface roughness, texture, etc. Figures 9.61 and 9.62 provide examples to this eff ect.
While highly desired, pulse-echo NCU technique to obtain the far side materials ref lection under ambient conditions is at best extremely arduous, if not impossible at the time of this writing. However, if the test is conducted under high air–gas pressure, then it is relatively easy to observe far side ref lections in pulse-echo NCU mode. Figure 9.63 shows an example of multiple thickness ref lections from 10 mm steel at 5 bar air pressure by using a special broadband 3 MHz transducer.
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FIGURE 9.52 Sintered alumina NCU transmission imaging and analysis of samples varying in density. Left : 65% (2.58 g/cc), middle: 70%
(2.8 g/cc), right: 77% (3.08 g/cc). Transducers: 500 kHz, 12.5 mm active diameter.
FIGURE 9.53 Fired silica refractory NCU imaging. Left : Defect-free. Right: Cracked. Transducers: 500 kHz, 12.5 mm active diameter.
FIGURE 9.54 Concrete NCU (200 mm) imaging showing internal defects. Transducers: Mixed 140 kHz.
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13 26 39 52 65 78 91 104 117 130 143 mm150
FIGURE 9.55 Oriented strand board (OSB) NCU imaging as a function of moisture content. Left to right: Dry, 30 min soak, 2 h soak, and 11 h soak. Transducers: 200 kHz. Note as the moisture content increases the NCU transmission decreases, which is more evident in the colored images.
FIGURE 9.56 Porous wood core NCU high-resolution imaging. Transducers: Mixed 1 MHz.
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170 mm
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120 96 72 48 24 0
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FIGURE 9.57 Cheddar cheese NCU imaging. Left : Reduced fat. Right: Extra sharp. It appears as the fat content in cheese increases so does the ultrasound attenuation. Transducers: 1 MHz, 12.5 mm active area diameter.
FIGURE 9.58 NCU T-R pitch-catch refl ection technique showing far side (bottom surface) refl ection from a material. In this case the bottom surface of 12.5 mm thick aluminum with 1 MHz transducers.
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FIGURE 9.59 Same side NCU image of a CFRP panel with embedded defects (left ). As a comparison, the right hand image shows similar image, but acquired by direct transmission mode. Transducers: 500 kHz, 12.5 mm active diameter.
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0 32 64 96 128 160 192 224 256 288 320 352mm380 0 32 64 96 128 160 192 224 256 288 320 352mm380
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FIGURE 9.60 NCU single transducer, pulse-echo technique showing surface refl ection signal from a material. In this case the surface of dense alumina with 3 MHz transducer.
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FIGURE 9.61 Very high-resolution NCU surface images of familiar objects generated by 3 MHz sharply focused transducer.
FIGURE 9.62 Surface imaging of other materials: Left : Semiconductor polishing pad showing surface roughness. Right: Fine celled polymer foam showing its texture, the details of which are more evident in color image.
and other applications. A partial list of these organizations is as following:
Iowa State University, United States
•
University of Bordeaux, France
•
University of Irvine at California, United States
•
University of Ancona, Italy
•
Institute of Technical Ceramics, Spain
•
Yamanashi University, Japan
•
California State University at Carson, United States
•
Katholieke Hogeschool (KATHO), Belgium
•
Katholieke University at Leuven, Belgium
•
Stanford University at Stanford, United States
•
University of Windsor, Canada
•
Fraunhofer Institute at Saarbrucken, Germany
•
Penn State University at University Park, United States
•
Queens University at Kingston, Canada
•
Warwick University,
• United Kindom
National Physical Laboratory,
• United Kindom
Los Alamos National Laboratory, United States
•
Gas Technology Institute, United States
•
Southwest Research Institute, United States
•
Nagoya Institute of Technology, Japan
•
Johns Hopkins University, United States
•
It is our hope that the materials and biomedical industries, research institutes, and government agencies take a serious look at the status of modern ultrasound, particularly NCU transducers and associated testing know-how and its necessity in solving important process and quality-related material testing needs.
Th e advantages of NCU are too numerous and far beyond con- ventional ultrasound to be ignored. We believe sooner it is applied for specifi c tasks along with increment in practical edu- cational foundation, better it would be for our complex socio- technical world.
References
1. Brunk, J.A., Ultrasonic nondestructive testing and materi- als characterization, this volume.
2. Fox, J.D., Khuri-Yakub, B.T., and Kino, G.S., High fre- quency wave measurements in air, 1983 IEEE Ultrasonics Symposium, pp. 581–592, 1983.
3. Bhardwaj, M.C., Modern ultrasonic transducers, Comm- ercial Catalog, Ultran Laboratories, Inc., 1986.
4. Yano, T., Tone, M., and Fukumoto, A., Range fi nding and surface characterization using high frequency air trans- ducer, IEEE Trans. UFFC, 34(2), 222–236, 1987.
5. Haller, M.I. and Khuri-Yakub, B.T., 1–3 composites for ultra- sonic air transducer, IEEE Ultrasonics Symposium, pp.
937–939, 1992.
6. Bhardwaj, M.C., Ultrasonic transducer for high transduc- tion in gases and method for non-contact transmission in solids, U.S. Patent 6,311,573, November 6, 2001. Japan Patent 3225050, August 24, 2001. European Cooperation Treaty, Pending. WIPO, PCT/US98/12537.
7. Bhardwaj, M.C., Non-destructive evaluation: introduction of non-contact ultrasound, Encyclopedia of Smart Materials, M. Schwartz ed., John Wiley & Sons, New York, pp. 690–714, 2002.
8. Bhardwaj, M.C., Gas matrix piezoelectric composite, U.S.
and international patents pending.
FIGURE 9.63 NCU single transducer, pulse-echo at high gas pressure. In this case, far side (bottom surface) refl ections from a 10 mm steel plate at 5 bar air pressure by using a broadband 3 MHz NCU transducer. (Reproduced from Gas Technology Institute, U.S.A.)
Transmitter/
receiver
High air/gas pressure
Test material
Tek Run
T
1
Ch1
T Trig’d
100mV M 4.00μs A Ext 397mV