Cho, Younho; IEEE; Hongerholt, D.D. & Rose, J.L.

Lamb Wave Scattering Analysis for Reflector Characterization

IEEE Trans on Ultrasonics..., Vol 44, No 1, Jan 1997, pp 44-52

Abstract: The potential use of guided waves for defect characterization is studied. The influence of defect shape and size on transmitted and reflected fields is considered. Using the hybrid boundary element technique, the reflection modes are numerically calculated and compared to experimental data. Selecting the aspect ratio as a shape parameter for various defects, the transmission and reflection coefficients are measured for certain guided wave modes input to the defect. The influence of defect size is then studied by monitoring the transmission and reflection coefficients for defects of various shapes and depths. The studies presented indicate that defect characterization is possible if a proper mode selection criteria can be established. The suitable features related to transmission and reflection coefficient data can also be used for algorithm development and implementation purposes of defect characterization.

Clark, AV; Fortunko, CM; Lozev, MG; Schaps & Renken

Determination of Sheet Steel Formability Using Wide Band Electromagnetic-Acoustic Transducers

Res Nondest Evaluation Vol 4 No 3 1992 pp.165-182

Abstract: An electromagnetic- acoustic transducer (EMAT) system was used in conjunction with a "sampled" CW signal-processing method to generate, receive, and process longitudinal and shear waves in thin steel sheets. Using the system, swept frequency measurements were made up to 7.5 MHz. To relate the measurements to sheet steel formability, a dimensionless frequency ratio, K, was computed from the resonant frequencies. From theoretical considerations, K should be related to a measure of sheet steel formability, F. This parameter is traditionally measured by plastically deforming uniaxial tension specimens. Good correlation was found between K and F for a set of steel sheet representative of those typically used to produce automobile body parts.

Clark, AV, Fuchs, P Schaps, SR

Fatigue Load Monitoring in Steel Bridges with Rayleigh Waves

Journal of Nondestructive Evaluation Vol 14 No 3 1995 pp 83-98

Abstract: Fatigue load monitoring is a useful tool for safety assessment of highway bridges. Monitoring has been conventionally done using strain gauges. Installation of these gauges is labor-intensive and requires safety precautions. Noncontact electro-magnetic-acoustic transducers (EMATs) offer an attractive alternative. EMATs were used to transmit and receive Rayleigh Waves (RW). Changes in time of flight of RF due to the acoustoelastic effect can in principle be used to monitor stresses resulting from vehicular traffic. We have performed proof-of-concept experiments to demonstrate the feasibility of this approach. Specimens were subjected to bending to simulate the load environment in bridges. RW EMATs were used to measure the relatively low stresses (less than 14 Mpa) typically experienced by bridge girders. The signal-to-noise ratio achievable with our system should allow adequate stress resolution for fatigue load monitoring. Factors which could impede technology transfer were considered. The primary obstacle appears to be variability in time of flight (TOF) due to magnetostriction. If the magnetic state is changed (e.g. by scanning of the EMATs) the TOF can change, even at constant stress. We have characterized this effect. If a proper installation procedure is followed, fatigue load monitoring with RW EMATs is feasible.

Fortunko, CM; Petersen, GL; Chick, BB; Renken; Preis

Absolute Measurements of Elastic-Wave Phase and Group Velocities in Lossy Materials

Rev Sci Instr 63 (6) June 1992 pp 3477-3486

Abstract: Traditional methods of determining phase and group velocities are often inadequate for many thick-section materials that exhibit greater than 30 dB, frequency-dependent propagation losses across the passband of the transducer. This article describes a measurement method that addresses the problem. Our method is mechanized as a pulsed, swept-frequency interferometer. The method's accuracy and reliability are enhanced by a combination of circuit-design methods which remove circuit related measurement errors and compensate for diffraction. First we describe the foundations of our measurement method and its mechanization. Then we describe the signal-processing procedures, used to calibrate the instrumentation and to determine the absolute phase and group velocities. To illustrate the method, we determine phase velocities in a very lossy, 50 mm thick, glass/epoxy specimen in the 0.3-1.3 MHz region.

Hein, I.A.; Novakofski, J.A. & O'Brien, W.D.

Ultrasound Data Acquisition System Design for Collecting High Quality RF Data from Beef Carcasses in the Slaughterhouse Environment

Abstract: Ultrasound has considerable potential to accurately and precisely grade beef. Currently beef quality grades (taste and tenderness) and yield grades (amount of meat) are assigned by a human who visually inspects and subjectively assigns a grade to a beef carcass. The ultimate goal of this work is an automated and objective grading process. The current phase of the work is not to construct an ultrasound gradin device but rather to determine which of these ultrasound related and derived quantities best correlate to each grade. In order to make this determination, an ultrasound data acquisition system capable of acquiring large amounts of high-quality RF data from beef carcasses has been constructed. This paper presents the engineering concepts and construction details of an ultrasound data acquisition device to be used as a research tool for this application.

Hirao, M; Ogi, H.; Fukuoka, H

Advanced Ultrasonic Method for Measuring Rail Axial Stresses with Electromagnetic Acoustic Transducer

Res Nodest Eval (1994) 5 pp. 211-223

Abstract: This paper explores the feasibility of the acoustoelastic birefringence method for monitoring the axial stresses in the railroad rails. An electromagnetic-acoustic transducer (EMAT) is incorporated with a superheterodyne-phase-sensitive detector to accomplish noncontacting stress measurements. Two different measurement techniques are employed and compared to each other, both of which use the polarized shear waves propagating transversely to the rail axis. One is the pulsed resonance spectroscopy technique applied to the web, where the surfaces are nearly parallel to each other and support the thickness oscillations. The other method detects the small phase shift that occurs along with the stress application. The compressive axial load was raised up to 60 tons with the Shinkansen (bullet train) rail samples, which exceeds the buckling load of long rails. Both techniques showed a linear response to stress with a sufficient sensitivity and robustness, which promise the development of a practical railroad maintenance technology. The effects of the liftoff and the residual stress distribution are determined.

Hirao, M; Ogi, H

Electromagnetically excited Acoustic Resonance for Evaluating Attenuation Coefficient and Grain Size in Polycrystalline Metals

App Phys Lett 64 (17) 25 April 1994 pp 2217-2219

Abstract: An experiment on an acoustic resonance spectrometer for evaluating attenuation characteristics and grain size of polycrystalline metals is described. A noncontacting electromagnetic acoustic transducer is excited to establish a shear-wave ringing in a plate sample and the amplitude spectrum is obtained by sweeping the driving rf frequency through the resonances. At each resonance the time constant, or the attenuation coefficient, whose frequency dependence is finally related to the w\average grain size through the Rayleigh scattering theory. This nondestructive evaluation agreed with the photomicrographic examination to an accuracy of 6 micrometers for a relatively narrow distribution of grain size in low carbon steels.

Hirao, M; Fukuoka, H; Fujisawa, K; Muryama, R

On-Line Measurement of Steel Sheet r-Value Using Magnetostrictive-Type EMAT

Journal of NDE Vol 12 No 1 1993 pp 27-32

Abstract: An ultrasonic on-line system to measure r values in cold rolled steel sheets has been developed with electromagnetic acoustic transducers (EMATs). These EMATs are composed of meanderline coils and electomagnets and operate with magnetostrictive mechanism. The EMAT instrument measures propagation times of the fundamental symmetrical Lamb wave at a low frequency and relates them to the r values through a calibrated regression curve. Preliminary tests indicate that the on-line monitoring of r is quite feasible with a standard deviation of 0.07 for various low carbon steel sheet; the thicknesses range from 0.5 mm to 2.5 mm. The measuring time is 20 msec per data. The liftoff is allowed to 5 mm with 2 mm thick sheet. The r evaluation is independent of the line speed up to 325 m/min. These promising results promote installation of ultrasonic r value measurement systems in steel production lines.

Hirao, M; Ogi, H; Fukuoka, H

Resonance EMAT system for Acoustoelastic Stress Measurement in Sheet Metals

Rev Sci Instr 64 (11) Nov 1993 pp 3198-3205

Abstract: A practical method of acoustoelastic stress measurement based on electromagnetic acoustic resonance is presented. This overcomes fundamental limitations of conventional procedures and exhibits the stress resolution to 0.1 Mpa for thin aluminum plates and the spatial resolution to several millimeter square in a noncontacting operation. The proposed method successfully combines an electromagnetic acoustic transducer (EMAT) and a superheterodyne phase-sensitive detector. An EMAT is excited by a high power rf burst in the 0.5-20 MHz range and generates ultrasonic oscillations in a plate through a Lorentz force mechanism. The signals in the plate are then received by this same MEAT and analyzed for the amplitude spectrum using swept-frequency phase-sensitive detection circuitry. The resonance frequencies can be determined for longitudinal and shear modes simultaneously. To illustrate the resonance spectrum technique, experimental results are shown for the measurement of a two dimensional stress field in a thin aluminum plate. Liftoff sensitivity is also determined.

Igarashi, B., Alers, GA., Purtscher, PT.

An Ultrasonic Measurement of Magnetostriction

1997 IEEE Ultrasonics Symposium

Abstract: The amplitudes of shear horizontal plate waves generated by EMATs (electromagnetic acoustic transducers) are measured to obtain estimates of the magnetostriction of a steel specimen. The wave amplitude is linked to magnetostriction through an existing model that is modified in the present work to extend its applicability to a broader range of magnetic fields. Measurements with intermediate levels of EMAT currents yield estimates that best agree with strain-gage measurements of the magnetostriction.

Johnson, W; Auld, BA; Alers, GA

Spectroscopy of Resonant Torsional Modes in Cylindrical Rods Using Electromagnetic-Acoustic Transduction

Abstract: Two ultrasonic techniques employing electromagnetic acoustic transduction are presented for performing measurements of the resonance torsional frequencies and Q of solid cylindrical metallic rods. One of these techniques uses long radio frequency pulses to drive the sample into resonance and the other uses continuous wave excitation. Measurements are performed on an aluminum alloy. Since the transduction involves no mechanical coupling, the background damping is low; the Q is 1.2 x 10⁵ at 755 kHz with the sample simply supported on its side. The shear velocity is determined with an accuracy of better than 2 parts in 10⁴(limited by the uncertainty in the sample radius).

Jung, J.K., Seo, Y.M., Choh, S.H., Park, Y.M. and Song, S.K.

¹⁴N NQR Relaxation in Mixed Complex system [(CH₂)₆N₄]_1-x [NaNO₂]_x

Jrnl of the Korean Physical Society, Vol 32, feb 1998, pp. S665-S668

Abstract: ¹⁴N nuclear quadrupole resonance (NQR) of the mixed system, [(CH₂)₆N₄]_1-x[NaNO₂]_x(x=0.0, 0.17, 0.29, 0.52, 0.80, 0.91) have been investigaed at room temperature. Both ¹⁴N NQR frequencies v_o of [(CH₂)₆N₄]-matrix and v₊(v_-) of NaN0₂-matrix in [(CH₂)₆N₄]_1-x[NaNO₂]_x do not depend on x and are the same as those in pure (CH₂)₆N₄and NaN0₂, respectively. On the other hand, the spin-lattice relaxation times for v_o, v₊, and v_-in (CH₂)₆N₄ and NaN0₂, respectively, increase systematically with the increasing impurity concentration. This change can be explained in terms of the activation energy.

Kawashima, K; Wright, OB

Resonant Electromagnetic Excitation and Detection of Ultrasonic Waves in Thin Sheets

Journ App Physics Vol 72 No 10 15 Nov 1992 pp 4830-4839

Abstract: A unified theory of the simultaneous electromagnetic excitation and detection of ultrasonic waves traveling in the through-thickness direction in conducting sheets in the presence of a static magnetic field is presented. What to our knowledge are the highest-frequency room temperature measurements of this type are described for aluminum sheets of thickness as low as 20 micrometers for frequencies up to 120 MHz. Maxwell's equations are solved for the geometry of a planar current sheet above a conducting sheet with sinusoidal time variation. It is shown how, from the solution of a single fourth order differential equation for the magnetic vector potential, the coupled electromagnetic and elastic wave problem can be solved analytically. The effective transfer impedance is evaluated, a measure of the ultimate efficiency of the combined excitation and detection process. At acoustic resonance its amplitude is inversely proportional to the sum of the ultrasonic attenuation of the sample and the attenuation arising from the electromagnetic-elastic coupling. This high frequency resonant method should open up a wide range of new applications for the nondestructive evaluation of thickness, ultrasonic attenuation, binding and delamination of thin sheets and coatings in the sub-10 micrometer to 1 mm thickness range.

Morgan, K.; Dayton, P.; Klibanov, S.; Brandenburger, G.; Kaul, S.; Wei, K. & Ferrara, K.

Properties of contrast agents insonified at frequencies above 10 MHz.

1996 IEEE Ultrasonics Symposium, pp 1127-1130

Abstract: WE compare the properties of contrast agents following insonation in the 3-7 MHz range with the properties observed at higher frequencies, in order to differentiate the properties associated with insonation near resonance. In addition, to map small blood vessels located in deeper tissues, such as those within the retina and within lymph nodes, contrast-enhanced imaging at high frequencies may be desirable. Increasing the echo intensity with a frequency transducer, and thus improve the spatial resolution of the vascular map. With these goals in mind, we explore the properties of ultrasonic echoes from contrast agents at 38 MHz and compare these properties to those at lower frequencies.

Ogi, H; Hirao, M; Honda, T; Fukuoka, H

Ultrasonic diffraction from a transducer with arbitrary geometry and strength distribution

J Acoust Soc Am 98 (2) Pt 1 Aug 1995 pp 1191-1198

Abstract: The exact solution to the Hemholtz equation with a Dirichlet boundary condition is obtained to study three-dimensional ultrasonic diffraction phenomena and derive the numerical data of amplitude loss and the phase shift for correcting induced errors. Calculation is made for near field diffraction, for the rectangular transducers, and for the transducers with strength distribution on the radiating area. In the near field, where the wavelength and the propagation distance are comparable with each other, the longitudinal and shear waves undergo different diffraction. For transducers having a noncircular shape and a strength distribution on the area, both the amplitude loss and the phase shift experience different tendencies from the classical work on the circular piston source. Use of diffraction data specific to each measurement condition is then necessary to correct the errors. The calculated results are verified for pulse-echo measurements using a shear wave electromagnetic acoustic transducer.

Ogi, Hirotsugu;Hirao, Masahiko; Honda, Takashi

Ultrasonic attenuation and grain-size evaluation using electromagnetic acoustic resonance

J Acoust Soc Am 98 (1) July 1995 pp 458-464

Abstract: Electromagnetic Acoustic resonance is applied for determining the frequency dependence of the ultrasonic attenuation and the average grain size of low-carbon steels. Use of a noncontacting electromagnetic acoustic transducer (EMAT ) makes it possible to isolate the attenuation within the plate specimens. The method relies on the Lorentz force mechanism to couple the EMAT to the specimen surfaces and then eliminates the other losses, which may otherwise occur with the contacting piezoelectric transducers. The measurement is independent of the EMAT used, the specimen thickness, the surface condition, the lift-off, etc., and is stable because of the noncontacting nature. First, the resonant frequencies are measured, to the accuracy of 10 Hz, by sweeping the operating frequency and obtaining the amplitude spectrum over a band in the 0.5-20 MHz range. The ringing signals are excited and received by a shear wave EMAT and then processes with a superheterodyne receiver. Second, the attenuation coefficient as a function of the resonant frequency is determined. At each resonant frequency, the output signal rings down exponentially with time and the attenuation coefficient is obtained from the time constant by fitting an exponential decay to them. After correcting for the diffraction effect, the average grain size is obtained from the fourth-power term in the frequency dependence. The final results are favorably compared with the average of the three- dimensional grain-size distribution of steels.

Ogi, H. and Hirao, M

Ultrasonic Noise Relaxation for Evaluating Thermal aging Embrittlement of Duplex Stainless Steels

Res Nondest Evaluation Vol 9 No 3 1997 pp 171-180

Abstract: A noncontact ultrasonic method is presented to evaluate the thermal aging embrittlement of the cast duplex stainless steels, which uses the shear-wave backscattering noise detected by an electromagnetic acoustic transducer (EMAT). Duplex stainless steel is a highly damping material, and the pulse-echo measurement for the velocity and attenuation is unavailable. High damping comes from the scattering at boundaries between austenitic and ferritic phases. But, since little energy is absorbed in the material, the elastic waves impinged by an EMAT last in the the sample for a long period (in the order of 10 ms) and are received by the same EMAT as a slowly decaying backscattering noise. The relaxation time coefficient is calculated by integrating the digitized noise signal and is correlated with the aging time. It clearly discriminates four duplex stainless steels aged for 0, 300, 1000, and 3000 h at 673K. The noise decays in a shorter time as the aging period increases. The difference of the noise relaxation rate is interpreted by the phase decomposition of ferrite into Cr-rich (alpha)' phase and Fe-rich (alpha) phase as supported by transmission electron microscopy (TEM).

Park, Y.M., Song, S.K., Jung, J.K., Seo, Y.M. and Choh, S.H.

¹⁴N NQR Investigations of the Mixed Complex Systems; [NaNO₂] _1-x[ANO₃]_x:A=K, Na

Jrnl of the Korean Physical Society, Vol 32, Feb 1998, pp. S690-S692

Abstract: Temperature dependence of the ¹⁴N NQR frequency and line width were investigated in the nonisostructural mixed systems [NaNO₂] _1-x[ANO₃]_x with A=K and Na for the temperature range 77 K- 360 K. The results of the line width measurements show a cross over for the impurity induced lattice defects from the fast motion to the static rigid lattice behaviour at around 175 K on decrease of temperature. Above 290 K, on approaching the transition temperature, the critical line broadening caused by the flipping of the NO^-₂ ions becomes weaker with increasing ANO₃ content. Comparing with the spin-lattice relaxation data this phenomenon seems to be associated with the enhancement of the activation energy for the flipping of NO^- ₂ due the presence of lattice defects.

Petersen,GL; Chick, BB; Fortunko, CM; Hirao, M

Resonance Techniques for Elastic-Wave velocity Determination in Thin Metal Plates

Rev Sci Instr 65 (1) Jan 1994 pp 192-198

Abstract: The principles of operation of a new pulsed ultrasonic resonance spectrometer are presented. The system incorporates: (1) the use of electromagnetic acoustic transducers (EMATs), (2) a method of obtaining acoustic signals similar to the sampled continuous wave scheme described by Bolef and Miller, (3) the Clark method of recording line shapes, and (4) a high power gated rf amplifier and a unique implementation of superheterodyne and quadrature phase sensitive detection circuitry. The result is a spectrometer capable of measuring both shear and longitudinal ultrasonic velocities in very thin samples with mu\ch greater reproducibility then other pulse methods. It has also applicability in measuring attenuation and other physical properties such as composite material bonding that can be accessed using ultrasound. Experimental results of tests using EMATs in the 0.1-20 MHz range on thin (1.27 and 2.49 mm thick) aluminum sheets are presented.

Schramm, Raymond E., Szelazek, Jacek, and Clark, A Van

Ultrasonic Measurement of Residual Stress in the Rims of Inductively Heated Railroad Wheels

Materials Evaluation Vol 54 No 8, August 1996, pp 929-934

Abstract: Residual stresses in railroad wheels may change from compressive to tensile during use, a potentially hazardous condition that could cause wheel failure. Until recently, US regulation called for the measurement of a discoloration, revealing past heating that sometimes leads to unsafe stress. Quantitative measurement by ultrasonic methods is an attractive alternative. Stress causes small changes in sound velocity. This report covers an extensive series of ultrasonic tests on ten cast steel wheels; two were as-manufactured, while the others received induction heating to generate stresses similar to in service wheels. Measurements with two different ultrasonic instruments gave comparable results. Furthermore, ultrasonic measurements correlated well with a simple destructive evaluation. This suggests a useful method for inspection and maintenance.

Sohn, C.W., Jung, J.K., Seo, Y.M., Choh, S.H., Park, Y.M. and Song, S.K.

Impurity Effects on ¹⁴N NQR in Mixed Systems; [(CH₂)₆N₄]_1-x [KNO₃]_x and [(CH₂)₆N₄]_1-x[SC(NH₂)₂]_x

Jrnl of the Korean Physical Society, Vol 32, Feb 1998, pp. S639-S642

Abstract: X-ray diffraction in ¹⁴N NQR have been investigated at room temperature in mixed systems, [(CH₂)₆N₄]_1-x [KNO₃]_x and [(CH₂)₆N₄] _1-x [SC(NH₂)₂]_{x ,} grown by evaporating mixed solutions. The results of x-ray pattern in both systems show that introducing [KNO₃ or SC(NH₂)₂] impurity into (CH₂)₆N₄ leads to a formation of impurity cluster in the cubic phase of (CH₂)₆N₄. The spin-lattice relaxation time (T₁) of 14N NQR in (CH₂)₆N₄ matrix in two mixed systems were measured. In both systems T₁ tends to increase with impurity content. The change of T₁ due to impurity is explained by the increase in the activation energy for reorientational motion of (CH₂)₆N₄ molecules. Impurity effects of local molecular dynamics in two mixed systems are also discussed and compared to those from the hydrated HMT.

Xing Li; Zuoqing Wang;Cheng Kuei Jen; Martin Viens; David Cheeke

Ultrasonic Thin-Walled Tube Wave Structure for Sensing Devices

IEEE transactions on Ultrasonics... Vol 43 No 2 Mar 96 pp 331-336

Abstract: Theoretical and experimental investigations of thin-walled tube acoustic wave devices for gravimetric sensing applications are presented. Integrated sensor configurations have been demonstrated by employing a sol-gel processed thin piezoelectric lead zirconate titanate (PZT) film. This was coated coaxially on stainless steel tubes and interdigital transducers (IDT) fabricated as the transmitter and receiver on the curved tube surfaces. We have observed tube waves along both the axial and circumferential directions between 1 and 6.6 MHz. We have also analyzed the mass sensitivities of different modes propagating along the tubes and shown that high mass sensitivity can be achieved by keeping the tube wall thin.