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Torsional wave transduction in magnetostrictive wire
RESEARCH AND DEVELOPMENT Torsional wave transduction wire
in magnetostrictive
Torsional elastic waves are of interest in the following applications: nondispersive wire delay-lines;1 determining the shear modulus in solid specimens;* monitoring polymerization 3 (by looking at the damping effect on the waves); and occasionally in ultrasonic thermometry.4 Electroacoustic transduction methods for generating and detecting torsional ultrasonic waves in magnetostrictive wires include the Scarrott-Naylor mode conversion 1 from tangentially-welded extensional wave members, the Wiedemann effect,5 in which an axial current produces circumferential magnetization, and the Fowler effectP observed by twisting a magnetostrictive wire previously magnetized in the axial direction only. Segmented or specially polarized piezoelectric elements have also been used to generate and detect torsional waves.7 Recently, experiments have been carried out with previously coiled ‘remendur’ magnetostrictive alloy wire (Co-Fe-Va), straightened by a commercial process to produce the line shown in Fig.1. The line was intended for use in certain experiments on sound velocity and attenuation, primarily with extensional waves.879y10 However, as is clear from Fig.2, torsional waves were strongly excited too. Both wave types, in fact, reverberated in the ‘specimen’
Waveguide transducer Fig. 1 Straightened magnetostrictive line. Waveguide -1.5 mm diameter x 2 m long. The specimen (0.75 mm diameter x 50 mm long) was centerless-ground
(0.75 mm diameter x 50 mm long) and led to the question: by what mechanism are the torsional waves produced? It appears that the mechanism by which torsional ultrasonic waves are transduced mainly depends on a twisting action in the straightening process. In this process the wire uncoils and zig-zags through several pairs of off-axis jaws which are rotating rapidly as a unit. Rotating at about 1 000 rpm, these sliding jaws revolve a portion of the wire in a bicycle-pedal-like manner, imparting a regular helical pattern to the surface of the wire passing through. This pattern suggests that although the wire emerges quite straight from the jaw station, it nevertheless has experienced some twisting. The regularity of the helix further suggests that the twisting is rather uniform along the wire’s length. It was observed that in wire thus straightened, the torsional transduction effect was relatively uniform and permanent. For example, the magnetization was not erased by applied axial fields generated by a six-layer coil (about 400 turns) with pulse currents up to 0.5 A (H,,, NN16 kA-turns m-l). But this field was sufficient to erase the Wiedemann effect when produced by the method of Tzannes.S It was also observed that, in the straightened wire, magnetization was not erased by impact, one year of aging on a shelf, or moderate heating. The effect is reproducible, in that it was observed in 15 wires similarly processed. After heating above ‘remendur’s’ Curie point (-980°C) room temperature tests showed that the effect for torsional waves had been destroyed. However, this heating did not destroy the Joule effect, which magnetostrictively accounts for extensional waves that are observed againafter cooling below the Curie point. Readers who wish to further explore these magnetostrictive transduction effects are invited to borrow transducers from Mr L. C. Lynnworth of Panametrics Inc. Experiments may readily be undertaken using an encircling solenoidal coil 12.7 mm long, containing six layers of 34-gauge wire, energized by current pulses of -0.5 A x 3 ps, at a repetition rate of 50 or 60 pulses per second. Standard equipment for conducting such experiments is available lo (Fig.3). A stub transducer is conveniently bonded or welded to stainless steel or other lead-in wires of similar impedance and diameter. This may be used to measure Young’s and shear moduli and Poisson’s ratio in specimen materials which are not magnetostrictive,11112 or for other applications. L. C. Lynnworth, Panametrics Inc, 221 Crescent Street, Waltham, Massachusetts 02 154, USA
Torsional waves
Extensional waves
Fig.2 Extensional and torsional echoes in the specimen of Fig.1. The different time interval between echoes is due to the lower velocity of torsional waves by comparison with extensional waves. The relative amplitude differences between echoes of the two modes are due to the respective wave impedances depending on the diameter ratio to the second and fourth powers. Delayed oscilloscope sweep is 100 ps per division
ULTRASONICS.
SEPTEMBER
1972
Acknowledgement This work was supported in part by the Acoustics Branch of the US Office of Naval Research under contract NOOO14-71C-0050. The author gratefully acknowledges helpful discussions with K. A. Fowler and E. P. Papadakis of Panametrics concerning the mechanism of torsional wave transduction in twisted magnetostrictive wire. The co-operation of
195
the informers...
.___^.~
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and Laser
Technology
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.
[PC science and technology press
196
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vol.
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The approach throughout is international all publications from IPC Science and Technology Press, although published in English, are international in content and international in readership.
-
The journals are authoritative - written by scientists and engineers for scientists and engineers and backed up by the expertise of editorial advisory boards of internationally recognized experts -the informers.
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ULTRASONICS.
SEPTEMBER
1972
Ponapulser pulse genemtor
r-f-J
Pulse transit time in specim3
V---i
A
r---------t
8 9 10
11
12
Proceedings of the sixth symposium on temperature-Its measurement and control in science and industry (1972) Tzannes, N. S. IEEE Tram on Sonics and Ultrasonics 2 (July 1966) 33 Fowler, K. A. private communication (22 January 1969) May, J. E. Physical acoustics - Principles and methods vol 1 part A, edited by W. P. Mason (Academic Press, New York and London 1964) 429 Lawrence Jr, F. W. MIT research report R65-05 AD471325 (1965) Fowler, K. A. et al. Proceedings of the sixth temperature measurements conference, Hawthorne, California (April 1969) 191 Lynnworth, L. C. Materials Evaluation 2 (February 197 1) 27A; 10 (October 1972) to be published Greif, R. Elementary experiments in mechanical engineering, edited by K. N. Astill (February 1971) 105 - available from Professor F. Landis, New York University, New York 10453 Panametrics data sheet UTD-2 (April 1970) Lynnworth, L. C. et al. IEEE Trans Nucl Sci 1 (February 1971) 351 US patent 3 633 424 (11 January 1972) Lynnworth, L. C. Ultrasonics 4 (October 1969) 254
Volume flow meter for steady and unsteady flow
Initial pulse a
Interface
echo
End echo
Current methods usually rely on the measurement of velocity rather than total flow-rate. Furthermore, velocity measuring instruments such as pitot tubes or hot-wire anemometers are themselves indirect devices which infer the velocity from some other quantity. The frequency response of such pitot probes is poor, and both instruments cause some blockage of the flow by their physical presence.
b Fig.3 a - block diagram of the experiment; in the present experiments
b - transducer
used
J. Parchini and his staff at Watertown Wire Products Company, Watertown, Massachusetts is also appreciated. References 1
2 3 4
Bradfield, G. National Physical Laboratory (UK) memorandum, PHYS/U8-1952 (Elasticity symposium, 20 March 1952) Brockelsby, C. F., Palfreeman, J. S., Gibson, R. W. Ultrasonic delay lines, chapter 6 (Butterworths, London 1963) Lynnworth, L. C. et al. Ultrasound propagation measurements and applications, Ini JNdt (to be published) Papadakis, E. P. Ultrasound and polymerization, Panametrics Inc tech memo no 7 UR-93 (January 1971) 1 Lynnworth, L. C. et al. Proceedings of the 1970 ultrasonics symposium, IEEE Cat No 7OC69SU (1971) 83
ULTRASONICS.
The rate of volume flow is a fundamental quantity of all ducted aerodynamic systems. Unfortunately it is a very difficult quantity to measure, even in steady (ie, not timedependent) conditions. When the flow is time-dependent, the difficulties are compounded to such an extent that little reliance can be placed upon existing methods of measurement.
SEPTEMBER
1972
At the National Physical Laboratory an instrument is being developed to overcome many of these problems. The principle of operation is that a narrow ultrasonic beam projected across the duct is convected downstream by a distance which is proportional to the flow rate. The constant of proportionality is the speed of sound in the duct, so that no calibration is necessary if that speed is known. Furthermore, it is not necessary to insert any part of the instrument into the flow, so that no significant disturbance is caused to the quantity being measured. The theory of operation is quite simple. A reciprocating piston will radiate sound as a narrow beam, provided that the frequency is high enough for the wavelength to be small by comparison with the piston diameter. Such a beam directed across an air duct will cause highly localized acoustic pressure at its point of impingement on the opposite wall. But, as shown in Fig.4, the beam is convected downstream and the point of impingement is moved by a distance D, given by 1 u(x) D= / -& where u(x) = local velocity of the fluid 1 = diameter of the duct = velocity of sound and a
197
in magnetostrictive
Torsional elastic waves are of interest in the following applications: nondispersive wire delay-lines;1 determining the shear modulus in solid specimens;* monitoring polymerization 3 (by looking at the damping effect on the waves); and occasionally in ultrasonic thermometry.4 Electroacoustic transduction methods for generating and detecting torsional ultrasonic waves in magnetostrictive wires include the Scarrott-Naylor mode conversion 1 from tangentially-welded extensional wave members, the Wiedemann effect,5 in which an axial current produces circumferential magnetization, and the Fowler effectP observed by twisting a magnetostrictive wire previously magnetized in the axial direction only. Segmented or specially polarized piezoelectric elements have also been used to generate and detect torsional waves.7 Recently, experiments have been carried out with previously coiled ‘remendur’ magnetostrictive alloy wire (Co-Fe-Va), straightened by a commercial process to produce the line shown in Fig.1. The line was intended for use in certain experiments on sound velocity and attenuation, primarily with extensional waves.879y10 However, as is clear from Fig.2, torsional waves were strongly excited too. Both wave types, in fact, reverberated in the ‘specimen’
Waveguide transducer Fig. 1 Straightened magnetostrictive line. Waveguide -1.5 mm diameter x 2 m long. The specimen (0.75 mm diameter x 50 mm long) was centerless-ground
(0.75 mm diameter x 50 mm long) and led to the question: by what mechanism are the torsional waves produced? It appears that the mechanism by which torsional ultrasonic waves are transduced mainly depends on a twisting action in the straightening process. In this process the wire uncoils and zig-zags through several pairs of off-axis jaws which are rotating rapidly as a unit. Rotating at about 1 000 rpm, these sliding jaws revolve a portion of the wire in a bicycle-pedal-like manner, imparting a regular helical pattern to the surface of the wire passing through. This pattern suggests that although the wire emerges quite straight from the jaw station, it nevertheless has experienced some twisting. The regularity of the helix further suggests that the twisting is rather uniform along the wire’s length. It was observed that in wire thus straightened, the torsional transduction effect was relatively uniform and permanent. For example, the magnetization was not erased by applied axial fields generated by a six-layer coil (about 400 turns) with pulse currents up to 0.5 A (H,,, NN16 kA-turns m-l). But this field was sufficient to erase the Wiedemann effect when produced by the method of Tzannes.S It was also observed that, in the straightened wire, magnetization was not erased by impact, one year of aging on a shelf, or moderate heating. The effect is reproducible, in that it was observed in 15 wires similarly processed. After heating above ‘remendur’s’ Curie point (-980°C) room temperature tests showed that the effect for torsional waves had been destroyed. However, this heating did not destroy the Joule effect, which magnetostrictively accounts for extensional waves that are observed againafter cooling below the Curie point. Readers who wish to further explore these magnetostrictive transduction effects are invited to borrow transducers from Mr L. C. Lynnworth of Panametrics Inc. Experiments may readily be undertaken using an encircling solenoidal coil 12.7 mm long, containing six layers of 34-gauge wire, energized by current pulses of -0.5 A x 3 ps, at a repetition rate of 50 or 60 pulses per second. Standard equipment for conducting such experiments is available lo (Fig.3). A stub transducer is conveniently bonded or welded to stainless steel or other lead-in wires of similar impedance and diameter. This may be used to measure Young’s and shear moduli and Poisson’s ratio in specimen materials which are not magnetostrictive,11112 or for other applications. L. C. Lynnworth, Panametrics Inc, 221 Crescent Street, Waltham, Massachusetts 02 154, USA
Torsional waves
Extensional waves
Fig.2 Extensional and torsional echoes in the specimen of Fig.1. The different time interval between echoes is due to the lower velocity of torsional waves by comparison with extensional waves. The relative amplitude differences between echoes of the two modes are due to the respective wave impedances depending on the diameter ratio to the second and fourth powers. Delayed oscilloscope sweep is 100 ps per division
ULTRASONICS.
SEPTEMBER
1972
Acknowledgement This work was supported in part by the Acoustics Branch of the US Office of Naval Research under contract NOOO14-71C-0050. The author gratefully acknowledges helpful discussions with K. A. Fowler and E. P. Papadakis of Panametrics concerning the mechanism of torsional wave transduction in twisted magnetostrictive wire. The co-operation of
195
the informers...
.___^.~
Optics
and Laser
Technology
Scientists, engineers and managers are confronted every day by
.
[PC science and technology press
196
new discoveries new techniques new technologies new materials The informers - journals from IPC Science and Technology Press - give them the information they need - up-to-date, thorough, precisely tailored to their wants.
vol.
3
no, 2
The approach throughout is international all publications from IPC Science and Technology Press, although published in English, are international in content and international in readership.
-
The journals are authoritative - written by scientists and engineers for scientists and engineers and backed up by the expertise of editorial advisory boards of internationally recognized experts -the informers.
Journals - current awareness bulletins conference proceedings - each one contains the right balance of content for its particular readership: abstracts applications articles book reviews case studies conference reports
design data equipment evaluations news coverage patents surveys research papers review articles etc
Please write for details to: The Subscription Manager
IPC Science and Technology
Press
IPC House, 32 High Street, Guildford, Surrey, U.K.
ULTRASONICS.
SEPTEMBER
1972
Ponapulser pulse genemtor
r-f-J
Pulse transit time in specim3
V---i
A
r---------t
8 9 10
11
12
Proceedings of the sixth symposium on temperature-Its measurement and control in science and industry (1972) Tzannes, N. S. IEEE Tram on Sonics and Ultrasonics 2 (July 1966) 33 Fowler, K. A. private communication (22 January 1969) May, J. E. Physical acoustics - Principles and methods vol 1 part A, edited by W. P. Mason (Academic Press, New York and London 1964) 429 Lawrence Jr, F. W. MIT research report R65-05 AD471325 (1965) Fowler, K. A. et al. Proceedings of the sixth temperature measurements conference, Hawthorne, California (April 1969) 191 Lynnworth, L. C. Materials Evaluation 2 (February 197 1) 27A; 10 (October 1972) to be published Greif, R. Elementary experiments in mechanical engineering, edited by K. N. Astill (February 1971) 105 - available from Professor F. Landis, New York University, New York 10453 Panametrics data sheet UTD-2 (April 1970) Lynnworth, L. C. et al. IEEE Trans Nucl Sci 1 (February 1971) 351 US patent 3 633 424 (11 January 1972) Lynnworth, L. C. Ultrasonics 4 (October 1969) 254
Volume flow meter for steady and unsteady flow
Initial pulse a
Interface
echo
End echo
Current methods usually rely on the measurement of velocity rather than total flow-rate. Furthermore, velocity measuring instruments such as pitot tubes or hot-wire anemometers are themselves indirect devices which infer the velocity from some other quantity. The frequency response of such pitot probes is poor, and both instruments cause some blockage of the flow by their physical presence.
b Fig.3 a - block diagram of the experiment; in the present experiments
b - transducer
used
J. Parchini and his staff at Watertown Wire Products Company, Watertown, Massachusetts is also appreciated. References 1
2 3 4
Bradfield, G. National Physical Laboratory (UK) memorandum, PHYS/U8-1952 (Elasticity symposium, 20 March 1952) Brockelsby, C. F., Palfreeman, J. S., Gibson, R. W. Ultrasonic delay lines, chapter 6 (Butterworths, London 1963) Lynnworth, L. C. et al. Ultrasound propagation measurements and applications, Ini JNdt (to be published) Papadakis, E. P. Ultrasound and polymerization, Panametrics Inc tech memo no 7 UR-93 (January 1971) 1 Lynnworth, L. C. et al. Proceedings of the 1970 ultrasonics symposium, IEEE Cat No 7OC69SU (1971) 83
ULTRASONICS.
The rate of volume flow is a fundamental quantity of all ducted aerodynamic systems. Unfortunately it is a very difficult quantity to measure, even in steady (ie, not timedependent) conditions. When the flow is time-dependent, the difficulties are compounded to such an extent that little reliance can be placed upon existing methods of measurement.
SEPTEMBER
1972
At the National Physical Laboratory an instrument is being developed to overcome many of these problems. The principle of operation is that a narrow ultrasonic beam projected across the duct is convected downstream by a distance which is proportional to the flow rate. The constant of proportionality is the speed of sound in the duct, so that no calibration is necessary if that speed is known. Furthermore, it is not necessary to insert any part of the instrument into the flow, so that no significant disturbance is caused to the quantity being measured. The theory of operation is quite simple. A reciprocating piston will radiate sound as a narrow beam, provided that the frequency is high enough for the wavelength to be small by comparison with the piston diameter. Such a beam directed across an air duct will cause highly localized acoustic pressure at its point of impingement on the opposite wall. But, as shown in Fig.4, the beam is convected downstream and the point of impingement is moved by a distance D, given by 1 u(x) D= / -& where u(x) = local velocity of the fluid 1 = diameter of the duct = velocity of sound and a
197