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Force measurements using Fe-rich amorphous wire as magnetostrictive delay line
Sensors and Actuators A 91 (2001) 223±225
Force measurements using Fe-rich amorphous wire as magnetostrictive delay line H. Chiriaca, E. Hristoforoub, Maria Neagua,*, Firuta Borzaa a
National Institute of Research and Development for Technical Physics, 47 Mangeron Blvd., 6600 Iasi 3, Romania b National Technical University, 9 Heroon Polytechniou, Zografou, Athens 15780, Greece
Abstract In this paper, we present experimental results concerning the heat treatment in¯uence on the force response of Fe77.5Si7.5B15 amorphous wire used as magnetostrictive delay line (MDL). The amorphous wires, 125 mm diameter, were tested in the as-cast state, after stress-relief (thermally treated) and after magnetic annealing. The response of the delay line (pulsed output voltage) could be ®tted by a linear curve at certain regions for the case of the as-cast amorphous wires and by an exponential curve for the case of treated wires. The sensitivity is equal to 10 mV/N, the minimum measurable change of the signal being 0.01 mV for the annealed wire corresponding to a minimum change of applied force equal to 0.001 N. # 2001 Elsevier Science B.V. All rights reserved. Keywords: Amorphous positive magnetostrictive wires; Magnetoelastic effects; Magnetostrictive delay lines; Force sensors
1. Introduction Ferromagnetic amorphous wires are very attractive for sensor applications [1±5]. A number of applications of these materials are based on the magnetostrictive delay line (MDL) principle [1,3,5]. The good sensitivity of MDL signals make them attractive for sensor applications, like load cells, where other techniques offer lower sensitivity or hysteresis in their response. Using this technique, we conceived and developed sensing elements for force, torsion, displacement, and magnetic ®eld measurements [5±8]. The aim of this paper is to analyze the in¯uence of the heat treatment on the force response of Fe77.5Si7.5B15 amorphous wire used as MDL. The amorphous wires, 125 mm diameter, were tested in the as-cast state, after stress-relief (thermally treated) and after magnetic annealing. 2. Experimental details and results In the experimental set-up, the amorphous wire was vertically positioned and acts as the MDL [5]. Magnetoelastic waves are generated in the wire by a pulsed current in
* Corresponding author. Tel.: 40-32-130680; fax: 40-32-231132. E-mail address: [email protected] (M. Neagu).
an exciting coil set around one end of it. The waves are propagating through the amorphous wire and they are detected at the opposite end by a receiving coil. A signal generator was used to supply rectangular current pulses in the exciting coil. Biasing coils were set around the exciting and receiving coils in order to maximize the delay line response. The pulsed output voltage was ampli®ed by an ac ampli®er, then applied to a peak to peak detector and read on a display. The distance between the centres of the exciting and receiving coils was kept constant (400 mm) during the measurements. Tensile stress was applied along the length of the MDL by putting weights at the free end of it. During the experiments, the amplitude of the pulsed exciting current was 10 A and its width and period were 3 ms and 10 ms, respectively. The value of the bias magnetic ®eld at the exciting and receiving points was 300 A/m. We have studied the dependence of the peak to peak amplitude of the pulsed voltage output on the force applied along the length of the Fe77.5Si7.5B15 amorphous wire. The amorphous wires were tested in the as-cast state, after stressrelief (thermally treated) and after magnetic annealing. The heat treatments were performed from 200 to 3508C for 15 min up to 4 h in the absence of a magnetic ®eld in a non-inductive furnace, in hydrogen atmosphere. For magnetic annealing, a magnetic ®eld of 4.82 kA/m was applied along the length of the amorphous wires during the heat treatments.
0924-4247/01/$ ± see front matter # 2001 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 4 - 4 2 4 7 ( 0 1 ) 0 0 5 0 1 - 5
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H. Chiriac et al. / Sensors and Actuators A 91 (2001) 223±225
3. Discussion and conclusions
Fig. 1. Dependence of the peak to peak amplitude of the pulsed voltage output on the applied force for Fe77.5Si7.5B15 amorphous wires, 125 mm diameter, tested: in the as-cast state; after heat treatment; after magnetic annealing (a Ð for 3 h; b Ð for 2 h; c Ð for 0.5 h).
Fig. 1a±c presents the dependence of the peak to peak amplitude of the pulsed voltage output on the applied force for the Fe77.5Si7.5B15 amorphous wires, 125 mm diameter, in the as-cast state, after heat treatment at 250, 280 and 3008C for 3, 2 and 0.5 h, respectively, and after magnetic annealing under a magnetic ®eld of 4.82 kA/m for the same temperatures and duration of annealing. The measurements have been performed by increasing and decreasing the magnitude of the force applied along the length of the amorphous wire, the hysteresis of the MDL response being negligible.
The experimental results show a monotonic dependence of the pulsed voltage output amplitude with the force applied along the length of the amorphous wire. The amplitude of the elastic waves generated in the delay line, under ®xed conditions of pulsed exciting current and bias magnetic ®eld at the exciting and receiving points depends on the state of the wire (as-cast or treated). The response could be ®tted by a linear curve at certain regions of the response for the case of the as-cast amorphous wires and by an exponential curve for the case of treated wires. The response curves' shape is a consequence of the complex anisotropies related to the internal stresses and those induced by the applied force. The obtained results can be explained taking into consideration the speci®c magnetic domain structure in Fe-based amorphous wires. For these materials, the magnetoelastic coupling between the high positive magnetostriction and internal stresses leads, in a ®rst approximation, to a domain structure consisting of an inner core axially magnetized and an outer shell radially magnetized [1±3]. The force applied along the length of the amorphous wire determines the reorientation of the magnetic moments. In this condition, the inner core axially magnetized is practically magnetomechanically inactive, while in the outer shell, the magnetic domains are forced to orient along the axis of the amorphous wire. The initial orientation of the magnetic domains in the outer shell make an angle a with respect to the wire axis. The output voltage in the receiving coil has a maximum amplitude Vomax for a 90, which becomes V o a < V omax for a < 90 . A force applied along the length of the amorphous wire determines a rotation of the magnetic moments in the outer shell at an angle a0 , smaller than a, so that the output voltage becomes V o a0 < V o a < V omax . The elastic strain becomes 0 for a 0, at a tensile stress Smax, which, according to our experimental work, has been found to be 200 MPa for the as-cast wire and smaller for the annealed ones. For the tensile stress Smax, the voltage output becomes V o 0 0. For tensile stresses S > Smax , the angle a remains 0 up to the Hook's point of the wire. If the tensile stress S is within the limits of the unhysteretic mechanical behavior of the amorphous wire, the decrease of stress results in a unhysteretic return to the angle a. Thus, if the applied force is within the limits of the elastic region of the amorphous wire, the result is a unhysteretic pulsed output voltage response. The thermal treatment reduces the as-cast residual stresses leading to improvements in the magnetostrictive response of the delay line. It can be observed that the maximum detectable force is strongly dependent on the treatment. The sensitivity is equal to 10 mV/N, the minimum measurable change of the signal being 0.01 mV for annealed wires, corresponding to a minimum change of applied force equal to 0.001 N.
H. Chiriac et al. / Sensors and Actuators A 91 (2001) 223±225
The obtained results suggest the possibility to use amorphous wires as force sensor elements working on the delay line principle.
References [1] P.T. Squire, D. Atkinson, M.R.J. Gibbs, S. Atalay, Amorphous wires and their applications, J. Magn. Magn. Mater. 132 (1994) 10±21. [2] P.T. Squire, D. Atkinson, S. Atalay, Magnetostrictive and magnetoelastic properties of rapidly quenched wire, IEEE Trans. Magn. 31 (1995) 1239±1248.
225
[3] M. Vazquez, A. Hernando, A soft magnetic wire for sensor applications, J. Phys. D: Appl. Phys. 29 (1996) 939±949. [4] F.B. Humphrey, Applications of amorphous wire, Mater. Sci. Eng. A179/A180 (1994) 66±71. [5] E. Hristoforou, Magnetostrictive delay line and their applications, Sens. Actuators A: Phys. 59 (1997) 183±191. [6] H. Chiriac, E. Hristoforou, M. Neagu, I. Darie, T.A. Ovari, Amorphous wire delay lines used for magnetic field measurements, IEEE Trans. Magn. 33 (1997) 4041±4043. [7] H. Chiriac, E. Hristoforou, M. Neagu, I. Darie, V. Nagacevschi, Pulse effect on the response of FeSiB wires delay lines, Mater. Sci. Eng. A226 (1997) 1093±1097. [8] E. Hristoforou, H. Chiriac, M. Neagu, I. Darie, A. Ovari, Torsion and stress in amorphous positive magnetostrictive wires, IEEE Trans. Magn. 32 (5) (1996) 4953±4955.
Force measurements using Fe-rich amorphous wire as magnetostrictive delay line H. Chiriaca, E. Hristoforoub, Maria Neagua,*, Firuta Borzaa a
National Institute of Research and Development for Technical Physics, 47 Mangeron Blvd., 6600 Iasi 3, Romania b National Technical University, 9 Heroon Polytechniou, Zografou, Athens 15780, Greece
Abstract In this paper, we present experimental results concerning the heat treatment in¯uence on the force response of Fe77.5Si7.5B15 amorphous wire used as magnetostrictive delay line (MDL). The amorphous wires, 125 mm diameter, were tested in the as-cast state, after stress-relief (thermally treated) and after magnetic annealing. The response of the delay line (pulsed output voltage) could be ®tted by a linear curve at certain regions for the case of the as-cast amorphous wires and by an exponential curve for the case of treated wires. The sensitivity is equal to 10 mV/N, the minimum measurable change of the signal being 0.01 mV for the annealed wire corresponding to a minimum change of applied force equal to 0.001 N. # 2001 Elsevier Science B.V. All rights reserved. Keywords: Amorphous positive magnetostrictive wires; Magnetoelastic effects; Magnetostrictive delay lines; Force sensors
1. Introduction Ferromagnetic amorphous wires are very attractive for sensor applications [1±5]. A number of applications of these materials are based on the magnetostrictive delay line (MDL) principle [1,3,5]. The good sensitivity of MDL signals make them attractive for sensor applications, like load cells, where other techniques offer lower sensitivity or hysteresis in their response. Using this technique, we conceived and developed sensing elements for force, torsion, displacement, and magnetic ®eld measurements [5±8]. The aim of this paper is to analyze the in¯uence of the heat treatment on the force response of Fe77.5Si7.5B15 amorphous wire used as MDL. The amorphous wires, 125 mm diameter, were tested in the as-cast state, after stress-relief (thermally treated) and after magnetic annealing. 2. Experimental details and results In the experimental set-up, the amorphous wire was vertically positioned and acts as the MDL [5]. Magnetoelastic waves are generated in the wire by a pulsed current in
* Corresponding author. Tel.: 40-32-130680; fax: 40-32-231132. E-mail address: [email protected] (M. Neagu).
an exciting coil set around one end of it. The waves are propagating through the amorphous wire and they are detected at the opposite end by a receiving coil. A signal generator was used to supply rectangular current pulses in the exciting coil. Biasing coils were set around the exciting and receiving coils in order to maximize the delay line response. The pulsed output voltage was ampli®ed by an ac ampli®er, then applied to a peak to peak detector and read on a display. The distance between the centres of the exciting and receiving coils was kept constant (400 mm) during the measurements. Tensile stress was applied along the length of the MDL by putting weights at the free end of it. During the experiments, the amplitude of the pulsed exciting current was 10 A and its width and period were 3 ms and 10 ms, respectively. The value of the bias magnetic ®eld at the exciting and receiving points was 300 A/m. We have studied the dependence of the peak to peak amplitude of the pulsed voltage output on the force applied along the length of the Fe77.5Si7.5B15 amorphous wire. The amorphous wires were tested in the as-cast state, after stressrelief (thermally treated) and after magnetic annealing. The heat treatments were performed from 200 to 3508C for 15 min up to 4 h in the absence of a magnetic ®eld in a non-inductive furnace, in hydrogen atmosphere. For magnetic annealing, a magnetic ®eld of 4.82 kA/m was applied along the length of the amorphous wires during the heat treatments.
0924-4247/01/$ ± see front matter # 2001 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 4 - 4 2 4 7 ( 0 1 ) 0 0 5 0 1 - 5
224
H. Chiriac et al. / Sensors and Actuators A 91 (2001) 223±225
3. Discussion and conclusions
Fig. 1. Dependence of the peak to peak amplitude of the pulsed voltage output on the applied force for Fe77.5Si7.5B15 amorphous wires, 125 mm diameter, tested: in the as-cast state; after heat treatment; after magnetic annealing (a Ð for 3 h; b Ð for 2 h; c Ð for 0.5 h).
Fig. 1a±c presents the dependence of the peak to peak amplitude of the pulsed voltage output on the applied force for the Fe77.5Si7.5B15 amorphous wires, 125 mm diameter, in the as-cast state, after heat treatment at 250, 280 and 3008C for 3, 2 and 0.5 h, respectively, and after magnetic annealing under a magnetic ®eld of 4.82 kA/m for the same temperatures and duration of annealing. The measurements have been performed by increasing and decreasing the magnitude of the force applied along the length of the amorphous wire, the hysteresis of the MDL response being negligible.
The experimental results show a monotonic dependence of the pulsed voltage output amplitude with the force applied along the length of the amorphous wire. The amplitude of the elastic waves generated in the delay line, under ®xed conditions of pulsed exciting current and bias magnetic ®eld at the exciting and receiving points depends on the state of the wire (as-cast or treated). The response could be ®tted by a linear curve at certain regions of the response for the case of the as-cast amorphous wires and by an exponential curve for the case of treated wires. The response curves' shape is a consequence of the complex anisotropies related to the internal stresses and those induced by the applied force. The obtained results can be explained taking into consideration the speci®c magnetic domain structure in Fe-based amorphous wires. For these materials, the magnetoelastic coupling between the high positive magnetostriction and internal stresses leads, in a ®rst approximation, to a domain structure consisting of an inner core axially magnetized and an outer shell radially magnetized [1±3]. The force applied along the length of the amorphous wire determines the reorientation of the magnetic moments. In this condition, the inner core axially magnetized is practically magnetomechanically inactive, while in the outer shell, the magnetic domains are forced to orient along the axis of the amorphous wire. The initial orientation of the magnetic domains in the outer shell make an angle a with respect to the wire axis. The output voltage in the receiving coil has a maximum amplitude Vomax for a 90, which becomes V o a < V omax for a < 90 . A force applied along the length of the amorphous wire determines a rotation of the magnetic moments in the outer shell at an angle a0 , smaller than a, so that the output voltage becomes V o a0 < V o a < V omax . The elastic strain becomes 0 for a 0, at a tensile stress Smax, which, according to our experimental work, has been found to be 200 MPa for the as-cast wire and smaller for the annealed ones. For the tensile stress Smax, the voltage output becomes V o 0 0. For tensile stresses S > Smax , the angle a remains 0 up to the Hook's point of the wire. If the tensile stress S is within the limits of the unhysteretic mechanical behavior of the amorphous wire, the decrease of stress results in a unhysteretic return to the angle a. Thus, if the applied force is within the limits of the elastic region of the amorphous wire, the result is a unhysteretic pulsed output voltage response. The thermal treatment reduces the as-cast residual stresses leading to improvements in the magnetostrictive response of the delay line. It can be observed that the maximum detectable force is strongly dependent on the treatment. The sensitivity is equal to 10 mV/N, the minimum measurable change of the signal being 0.01 mV for annealed wires, corresponding to a minimum change of applied force equal to 0.001 N.
H. Chiriac et al. / Sensors and Actuators A 91 (2001) 223±225
The obtained results suggest the possibility to use amorphous wires as force sensor elements working on the delay line principle.
References [1] P.T. Squire, D. Atkinson, M.R.J. Gibbs, S. Atalay, Amorphous wires and their applications, J. Magn. Magn. Mater. 132 (1994) 10±21. [2] P.T. Squire, D. Atkinson, S. Atalay, Magnetostrictive and magnetoelastic properties of rapidly quenched wire, IEEE Trans. Magn. 31 (1995) 1239±1248.
225
[3] M. Vazquez, A. Hernando, A soft magnetic wire for sensor applications, J. Phys. D: Appl. Phys. 29 (1996) 939±949. [4] F.B. Humphrey, Applications of amorphous wire, Mater. Sci. Eng. A179/A180 (1994) 66±71. [5] E. Hristoforou, Magnetostrictive delay line and their applications, Sens. Actuators A: Phys. 59 (1997) 183±191. [6] H. Chiriac, E. Hristoforou, M. Neagu, I. Darie, T.A. Ovari, Amorphous wire delay lines used for magnetic field measurements, IEEE Trans. Magn. 33 (1997) 4041±4043. [7] H. Chiriac, E. Hristoforou, M. Neagu, I. Darie, V. Nagacevschi, Pulse effect on the response of FeSiB wires delay lines, Mater. Sci. Eng. A226 (1997) 1093±1097. [8] E. Hristoforou, H. Chiriac, M. Neagu, I. Darie, A. Ovari, Torsion and stress in amorphous positive magnetostrictive wires, IEEE Trans. Magn. 32 (5) (1996) 4953±4955.