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New viscosimeter based on the ac field induced rotation of magnetostrictive amorphous wires
Sensors and Actuators A 91 (2001) 112±115
New viscosimeter based on the ac ®eld induced rotation of magnetostrictive amorphous wires  vaÂria,b, V. Raposoa, A. Hernandoa M. VaÂzqueza,*, F.J. CastanÄoa, T.-A. O a
Instituto de Magnetismo Aplicado UCM-RENFE and Instituto de Ciencia de Materiales de Madrid, CSIC, 28230 Las Rozas, Madrid, Spain b National Institute of Research & Development for Technical Physics, 6600 Iasi, Romania
Abstract The rotation of amorphous wires under the presence of an alternating magnetic axial ®eld of the order of several kHz is a new phenomenon discovered recently. In this work, we present a new viscosimeter based in the variation of the mechanical rotation frequency of these wires into different liquids. The rotation frequency has been found to decrease linearly with viscosity. # 2001 Elsevier Science B.V. All rights reserved. Keywords: Viscosimeter; Magnetostriction; Amorphous wires; Magnetoelastic resonance
1. Introduction Magnetostrictive amorphous wires prepared by in-rotating-water quenching display remarkable magnetic behavior, suitable for sensor applications [1]. Such behavior originates in the unique domain structures formed in these wires due to the magnetoelastic coupling between frozen-in internal stresses induced during rapid quenching from the melt and magnetostriction [2]. This peculiar magnetic behavior gives rise to some very speci®c effects, e.g. large Barkhausen jump, for wires with large positive or negative magnetostriction, and to others, such as giant magneto-impedance, for nearly zero magnetostrictive wires. All these effects determine the large application potential of amorphous wires. A striking new effect has been very recently observed in amorphous wires with large magnetostriction, either positive or negative: a spontaneous mechanical rotation of such a wire with frequencies of 10 Hz, when subjected to an ac magnetic ®eld having a frequency of the order of kHz, applied along the wire axis. The effect appears for a wellde®ned spectrum of frequencies of the ac applied ®eld, that includes fundamentals and harmonics, and a systematic correlation between the frequency and amplitude of the ac ®eld on one hand, and the sample length on the other, has been established [3,4]. The magneto-mechanical rotation of magnetostrictive amorphous wires attracts a considerable attention from both *
Corresponding author. Tel.: 34-1-6-30-17-24; fax: 34-1-6-30-16-25.
scientists interested in explaining its nature, as well as from engineers interested in developing new applications. Latest reports on this topic consider the effect as resulting from several contributions: (1) magnetoelastic resonance due to the magnetostrictive nature of these materials; (2) Lorentz force produced by the ac ®eld on the in-phase coupled radial currents and (3) the lack of perfect symmetry in both wire diameter and position with respect to the applied ®eld. Although the physical origin of this new phenomenon is not yet fully understood, it already offers novel application opportunities. In fact, as has been recently reported, this effect is strongly in¯uenced by a superimposed dc magnetic ®eld, resulting in the possibility of developing a new family of ®eld and current sensors, as well as of more sophisticated ®eld mapping devices, like a ®eld positioning microrotor [5]. Here, we report on a new parameter affecting that rotation: the friction with the medium. A dependence of this rotational behavior is expected with the viscosity. The aim of this paper has been then to propose a new viscosimeter based on this phenomenon. 2. Experimental set-ups Two experimental set-ups have been used. The ®rst one was used for the determination of the rotation spectra of the samples as a function of the frequency and applied magnetic ®eld for choosing the best possible con®guration for the viscosimeter. The second one is a simpli®ed but improved
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 4 8 8 - 5
M. VaÂzquez et al. / Sensors and Actuators A 91 (2001) 112±115
113
Fig. 1. Schematic representation of the experimental set-up used to investigate the rotation of amorphous magnetostrictive wires.
version of the previous one used for the measurement of the viscosity properly. Both are based in the measurement of the frequency of a laser beam, which reaches a photodiode. Fig. 1 shows the experimental set-up used for the characterization of the rotation of amorphous wires with different parameters as the magnitude of both ac and dc magnetic ®elds, tube diameter, excitation frequency and others. Fig. 2 shows the schematic diagram of the experimental set-up used to measure the viscosity of liquids. The principle of the proposed viscosimeter is the change of the wire rotation frequency when it is put into different liquids, while other parameters Ð frequency and amplitude of the applied ac ®eld, glass tube diameter Ð are kept constant. In both set-ups, the alternating ®eld (Hac) was provided by a magnetizing coil fed with a current supplied by a HAMEG HM 8030 function generator. In the ®rst set-up, this signal
was ampli®ed by a KEPCO ampli®er. The frequency of this alternating ®eld was varied from a few kHz to 200 kHz. The amplitude of the current ¯owing through the ac coil was obtained measuring, with a digital oscilloscope, the voltage drop through a resistance. A set of Helmholtz coils were used to provide a directionally controlled axial dc magnetic ®eld. In order to accurately determine the wire rotation frequencies, a 4 mm long Cu wire was glued, forming 908 with the wire axis, to one end of the wires. The presence of such Cu wire did not modify the regions where rotation occurred, with respect to those obtained for the wire by itself. On the other hand, a He±Ne laser beam was both aimed to the edge of a photodiode and aligned so that the attached Cu wire intercepted the beam when rotation occurred. The He±Ne laser, ac coil and photodiode were mounted on an optical
Fig. 2. Schematic diagram of the experimental set-up used for viscosity measurements based on the magneto-mechanical rotation of a magnetostrictive amorphous wire: 1, laser; 2, detector; 3, function generator; 4, Cu wire; 5, glass tube; 6, amorphous wire.
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M. VaÂzquez et al. / Sensors and Actuators A 91 (2001) 112±115
bench to obtain an stable alignment. In this way, when rotation occurred the Cu wire intercepted the laser beam, introducing sharp peaks in the photodiode output which allows an accurate determination of the wire rotation frequency. We were also able to measure the wire rotation frequency without the above mentioned Cu ¯ap, although the peaks introduced in the photodiode signal were much wider and thus the determination of the wire rotation frequencies less accurate. 3. Results Holding for the optimum condition of rotation to be applied to the viscosimeter, we will ®rstly summarize the phenomenological characterization of the rotation of amorphous wires in order to ®nd the best con®guration for using these materials in a viscosimeter. The rotation frequency of both positive and negative magnetostrictive amorphous wires has been previously investigated. The experimental set-up for these measurements and the details of the amorphous wires used for the experiments is described in [3,4]. The spectrum obtained on plotting the ®eld exciting frequency versus wire rotation frequency corresponding to a FeSiB wire, sited within an ac coil with f 1 mm, is shown in Fig. 3(a). For a ®xed exciting frequency, there is always an ac ®eld threshold, below which no rotation was observed. The wire rotation frequency increases on increas-
Fig. 3. (a) Exciting frequency vs. wire rotation frequency and (b) exciting frequency vs. ac field for a FeSiB wire. Solid and dashed lines are shown as a guide to the eye.
ing the amplitude of the ac ®eld. The maximum ®eld amplitude for a certain exciting frequency was limited by the experimental set-up. Fig. 3(b) shows the ac ®eld regions in which rotation occurred for each rotation peak. The data presented in Fig. 3(a) corresponds to the maximum amplitude of the ac ®eld (dotted line in Fig. 3(b)). As it can be observed, for a given sample length, the effect appears for certain frequencies (noted as A±E in Fig. 3(a)) and reappears around multiples and linear combinations of these frequencies. Nonetheless, if f is increased, some of these rotation regions have disappeared and the wire rotation frequencies are signi®cantly reduced. As a general comment, it must be stated that the number of regions where rotation occurred increases on decreasing the diameter of the inner tube of the ac coil. Due to the lack of perfect straightness of the wire, it touches its surrounding glass tube what introduces rotational friction. Fig. 4 illustrates the wire rotation frequency versus ac ®eld amplitude in FeSiB and CoSiB wires with positive and negative magnetostriction, respectively, for given values of the frequency of the ac exciting ®eld. As observed, a minimum amplitude of the exciting ®eld is required to detect rotation for both types of wires. In the case of the CoSiB wire, the rotation frequency increases very sharply with the ac ®eld frequency and then reaches saturation, while for the FeSiB wire, the rotation frequency increases almost linearly with the frequency of the exciting ®eld. From these results, we can conclude that the better wire to be used as sensing element in the viscosimeter is the FeSiB one, and that the ac ®eld should be of the order of 6000 A/m to reach the maximum wire rotation frequency. On the other hand, maintaining constant the amplitude of the ac ®eld, the effect of a directionally controlled axial dc ®eld is to reduce smoothly the wire rotation frequency until it reaches a threshold above which no rotation was observed. Fig. 5 shows typical examples of the trend followed by the wire rotation frequency on applying a directionally controlled dc ®eld. This data corresponds to the FeSiB (full circles) and the CoSiB (open circles) wires, both within an
Fig. 4. Wire rotation frequency versus ac field amplitude for a FeSiB wire and a CoSiB wire. Solid lines are shown as a guide to the eye.
M. VaÂzquez et al. / Sensors and Actuators A 91 (2001) 112±115
Fig. 5. Effect of a dc field on the wire rotation frequency for both FeSiB (full circles) and CoSiB (open circles) wires. The ac field amplitude was maintained constant to 2176 A/m.
ac coil with f 1 mm and submitted to a 2176 A/m constant alternating ®eld at frequencies of 23.8 and 32.1 kHz, respectively. Although this dependence suggests the use of this effect for magnetic ®eld sensor, in its use as a viscosimeter, any external dc ®eld should be avoided since it always reduces the rotation frequency, and so the sensitivity of the sensor. With these results in mind, we can choose an appropriate frequency of excitation for the coil in which a large enough frequency of rotation occurs. In our case, we have chosen the FeSiB wire because of its higher rotation frequency (see Fig. 4). The frequency of the ac ®eld should be around 14 kHz, which gives the best rotation for this wire, and the amplitude was chosen to be 6000 A/m. No dc ®eld was applied. Fig. 6 shows the relationship between the wire rotation frequency and the viscosity of several liquids for an ac ®eld amplitude of 6000 A/m and an exciting frequency of 14.7 kHz for a 5.5 cm long wire. One observes that there is a linear dependence of the wire frequency on the viscosity of the investigated liquids, this principle being very appropriate for such application. The same principle, i.e. the dependence of the rotation frequency with friction can be employed in other cases where the rotation of wire is damped.
115
Fig. 6. Relationship between the wire rotation frequency and the viscosity of several liquids for an ac field amplitude of 6000 A/m and an exciting frequency of 14.7 kHz for a 5.5 cm long wire.
4. Conclusions The spontaneous rotation of magnetostrictive amorphous wires with ac exciting magnetic ®elds has been used for the development of a new viscosimeter. The device has been tested for several liquids showing a convenient linear dependence between the rotation frequency and the viscosity. Acknowledgements V.R. would like to thank the Comunidad de Madrid for his grant under project CAM 07N/0033/98. References [1] P.T. Squire, D. Atkinson, M.R.J. Gibbs, S. Atalay, J. Magn. Magn. Mater. 132 (1994) 10. [2] M. VaÂzquez, D.-X. Chen, IEEE Trans. Magn. 32 (1995) 1229. Â vaÂri, IEEE Trans. Magn. 33 (1997) [3] H. Chiriac, C.S. Marinescu, T.-A. O 3349. [4] F.J. CastanÄo, M. VaÂzquez, D.-X. Chen, M. Tena, C. Prados, E. Pina, A. Hernando, G. Rivero, Appl. Phys. Lett. 75 (1999) 2117. Â vaÂri, D.-X. Chen, A. Hernando, [5] F.J. CastanÄo, M. VaÂzquez, T.-A. O IEEE Trans. Magn. (2000), in press.
New viscosimeter based on the ac ®eld induced rotation of magnetostrictive amorphous wires  vaÂria,b, V. Raposoa, A. Hernandoa M. VaÂzqueza,*, F.J. CastanÄoa, T.-A. O a
Instituto de Magnetismo Aplicado UCM-RENFE and Instituto de Ciencia de Materiales de Madrid, CSIC, 28230 Las Rozas, Madrid, Spain b National Institute of Research & Development for Technical Physics, 6600 Iasi, Romania
Abstract The rotation of amorphous wires under the presence of an alternating magnetic axial ®eld of the order of several kHz is a new phenomenon discovered recently. In this work, we present a new viscosimeter based in the variation of the mechanical rotation frequency of these wires into different liquids. The rotation frequency has been found to decrease linearly with viscosity. # 2001 Elsevier Science B.V. All rights reserved. Keywords: Viscosimeter; Magnetostriction; Amorphous wires; Magnetoelastic resonance
1. Introduction Magnetostrictive amorphous wires prepared by in-rotating-water quenching display remarkable magnetic behavior, suitable for sensor applications [1]. Such behavior originates in the unique domain structures formed in these wires due to the magnetoelastic coupling between frozen-in internal stresses induced during rapid quenching from the melt and magnetostriction [2]. This peculiar magnetic behavior gives rise to some very speci®c effects, e.g. large Barkhausen jump, for wires with large positive or negative magnetostriction, and to others, such as giant magneto-impedance, for nearly zero magnetostrictive wires. All these effects determine the large application potential of amorphous wires. A striking new effect has been very recently observed in amorphous wires with large magnetostriction, either positive or negative: a spontaneous mechanical rotation of such a wire with frequencies of 10 Hz, when subjected to an ac magnetic ®eld having a frequency of the order of kHz, applied along the wire axis. The effect appears for a wellde®ned spectrum of frequencies of the ac applied ®eld, that includes fundamentals and harmonics, and a systematic correlation between the frequency and amplitude of the ac ®eld on one hand, and the sample length on the other, has been established [3,4]. The magneto-mechanical rotation of magnetostrictive amorphous wires attracts a considerable attention from both *
Corresponding author. Tel.: 34-1-6-30-17-24; fax: 34-1-6-30-16-25.
scientists interested in explaining its nature, as well as from engineers interested in developing new applications. Latest reports on this topic consider the effect as resulting from several contributions: (1) magnetoelastic resonance due to the magnetostrictive nature of these materials; (2) Lorentz force produced by the ac ®eld on the in-phase coupled radial currents and (3) the lack of perfect symmetry in both wire diameter and position with respect to the applied ®eld. Although the physical origin of this new phenomenon is not yet fully understood, it already offers novel application opportunities. In fact, as has been recently reported, this effect is strongly in¯uenced by a superimposed dc magnetic ®eld, resulting in the possibility of developing a new family of ®eld and current sensors, as well as of more sophisticated ®eld mapping devices, like a ®eld positioning microrotor [5]. Here, we report on a new parameter affecting that rotation: the friction with the medium. A dependence of this rotational behavior is expected with the viscosity. The aim of this paper has been then to propose a new viscosimeter based on this phenomenon. 2. Experimental set-ups Two experimental set-ups have been used. The ®rst one was used for the determination of the rotation spectra of the samples as a function of the frequency and applied magnetic ®eld for choosing the best possible con®guration for the viscosimeter. The second one is a simpli®ed but improved
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 4 8 8 - 5
M. VaÂzquez et al. / Sensors and Actuators A 91 (2001) 112±115
113
Fig. 1. Schematic representation of the experimental set-up used to investigate the rotation of amorphous magnetostrictive wires.
version of the previous one used for the measurement of the viscosity properly. Both are based in the measurement of the frequency of a laser beam, which reaches a photodiode. Fig. 1 shows the experimental set-up used for the characterization of the rotation of amorphous wires with different parameters as the magnitude of both ac and dc magnetic ®elds, tube diameter, excitation frequency and others. Fig. 2 shows the schematic diagram of the experimental set-up used to measure the viscosity of liquids. The principle of the proposed viscosimeter is the change of the wire rotation frequency when it is put into different liquids, while other parameters Ð frequency and amplitude of the applied ac ®eld, glass tube diameter Ð are kept constant. In both set-ups, the alternating ®eld (Hac) was provided by a magnetizing coil fed with a current supplied by a HAMEG HM 8030 function generator. In the ®rst set-up, this signal
was ampli®ed by a KEPCO ampli®er. The frequency of this alternating ®eld was varied from a few kHz to 200 kHz. The amplitude of the current ¯owing through the ac coil was obtained measuring, with a digital oscilloscope, the voltage drop through a resistance. A set of Helmholtz coils were used to provide a directionally controlled axial dc magnetic ®eld. In order to accurately determine the wire rotation frequencies, a 4 mm long Cu wire was glued, forming 908 with the wire axis, to one end of the wires. The presence of such Cu wire did not modify the regions where rotation occurred, with respect to those obtained for the wire by itself. On the other hand, a He±Ne laser beam was both aimed to the edge of a photodiode and aligned so that the attached Cu wire intercepted the beam when rotation occurred. The He±Ne laser, ac coil and photodiode were mounted on an optical
Fig. 2. Schematic diagram of the experimental set-up used for viscosity measurements based on the magneto-mechanical rotation of a magnetostrictive amorphous wire: 1, laser; 2, detector; 3, function generator; 4, Cu wire; 5, glass tube; 6, amorphous wire.
114
M. VaÂzquez et al. / Sensors and Actuators A 91 (2001) 112±115
bench to obtain an stable alignment. In this way, when rotation occurred the Cu wire intercepted the laser beam, introducing sharp peaks in the photodiode output which allows an accurate determination of the wire rotation frequency. We were also able to measure the wire rotation frequency without the above mentioned Cu ¯ap, although the peaks introduced in the photodiode signal were much wider and thus the determination of the wire rotation frequencies less accurate. 3. Results Holding for the optimum condition of rotation to be applied to the viscosimeter, we will ®rstly summarize the phenomenological characterization of the rotation of amorphous wires in order to ®nd the best con®guration for using these materials in a viscosimeter. The rotation frequency of both positive and negative magnetostrictive amorphous wires has been previously investigated. The experimental set-up for these measurements and the details of the amorphous wires used for the experiments is described in [3,4]. The spectrum obtained on plotting the ®eld exciting frequency versus wire rotation frequency corresponding to a FeSiB wire, sited within an ac coil with f 1 mm, is shown in Fig. 3(a). For a ®xed exciting frequency, there is always an ac ®eld threshold, below which no rotation was observed. The wire rotation frequency increases on increas-
Fig. 3. (a) Exciting frequency vs. wire rotation frequency and (b) exciting frequency vs. ac field for a FeSiB wire. Solid and dashed lines are shown as a guide to the eye.
ing the amplitude of the ac ®eld. The maximum ®eld amplitude for a certain exciting frequency was limited by the experimental set-up. Fig. 3(b) shows the ac ®eld regions in which rotation occurred for each rotation peak. The data presented in Fig. 3(a) corresponds to the maximum amplitude of the ac ®eld (dotted line in Fig. 3(b)). As it can be observed, for a given sample length, the effect appears for certain frequencies (noted as A±E in Fig. 3(a)) and reappears around multiples and linear combinations of these frequencies. Nonetheless, if f is increased, some of these rotation regions have disappeared and the wire rotation frequencies are signi®cantly reduced. As a general comment, it must be stated that the number of regions where rotation occurred increases on decreasing the diameter of the inner tube of the ac coil. Due to the lack of perfect straightness of the wire, it touches its surrounding glass tube what introduces rotational friction. Fig. 4 illustrates the wire rotation frequency versus ac ®eld amplitude in FeSiB and CoSiB wires with positive and negative magnetostriction, respectively, for given values of the frequency of the ac exciting ®eld. As observed, a minimum amplitude of the exciting ®eld is required to detect rotation for both types of wires. In the case of the CoSiB wire, the rotation frequency increases very sharply with the ac ®eld frequency and then reaches saturation, while for the FeSiB wire, the rotation frequency increases almost linearly with the frequency of the exciting ®eld. From these results, we can conclude that the better wire to be used as sensing element in the viscosimeter is the FeSiB one, and that the ac ®eld should be of the order of 6000 A/m to reach the maximum wire rotation frequency. On the other hand, maintaining constant the amplitude of the ac ®eld, the effect of a directionally controlled axial dc ®eld is to reduce smoothly the wire rotation frequency until it reaches a threshold above which no rotation was observed. Fig. 5 shows typical examples of the trend followed by the wire rotation frequency on applying a directionally controlled dc ®eld. This data corresponds to the FeSiB (full circles) and the CoSiB (open circles) wires, both within an
Fig. 4. Wire rotation frequency versus ac field amplitude for a FeSiB wire and a CoSiB wire. Solid lines are shown as a guide to the eye.
M. VaÂzquez et al. / Sensors and Actuators A 91 (2001) 112±115
Fig. 5. Effect of a dc field on the wire rotation frequency for both FeSiB (full circles) and CoSiB (open circles) wires. The ac field amplitude was maintained constant to 2176 A/m.
ac coil with f 1 mm and submitted to a 2176 A/m constant alternating ®eld at frequencies of 23.8 and 32.1 kHz, respectively. Although this dependence suggests the use of this effect for magnetic ®eld sensor, in its use as a viscosimeter, any external dc ®eld should be avoided since it always reduces the rotation frequency, and so the sensitivity of the sensor. With these results in mind, we can choose an appropriate frequency of excitation for the coil in which a large enough frequency of rotation occurs. In our case, we have chosen the FeSiB wire because of its higher rotation frequency (see Fig. 4). The frequency of the ac ®eld should be around 14 kHz, which gives the best rotation for this wire, and the amplitude was chosen to be 6000 A/m. No dc ®eld was applied. Fig. 6 shows the relationship between the wire rotation frequency and the viscosity of several liquids for an ac ®eld amplitude of 6000 A/m and an exciting frequency of 14.7 kHz for a 5.5 cm long wire. One observes that there is a linear dependence of the wire frequency on the viscosity of the investigated liquids, this principle being very appropriate for such application. The same principle, i.e. the dependence of the rotation frequency with friction can be employed in other cases where the rotation of wire is damped.
115
Fig. 6. Relationship between the wire rotation frequency and the viscosity of several liquids for an ac field amplitude of 6000 A/m and an exciting frequency of 14.7 kHz for a 5.5 cm long wire.
4. Conclusions The spontaneous rotation of magnetostrictive amorphous wires with ac exciting magnetic ®elds has been used for the development of a new viscosimeter. The device has been tested for several liquids showing a convenient linear dependence between the rotation frequency and the viscosity. Acknowledgements V.R. would like to thank the Comunidad de Madrid for his grant under project CAM 07N/0033/98. References [1] P.T. Squire, D. Atkinson, M.R.J. Gibbs, S. Atalay, J. Magn. Magn. Mater. 132 (1994) 10. [2] M. VaÂzquez, D.-X. Chen, IEEE Trans. Magn. 32 (1995) 1229. Â vaÂri, IEEE Trans. Magn. 33 (1997) [3] H. Chiriac, C.S. Marinescu, T.-A. O 3349. [4] F.J. CastanÄo, M. VaÂzquez, D.-X. Chen, M. Tena, C. Prados, E. Pina, A. Hernando, G. Rivero, Appl. Phys. Lett. 75 (1999) 2117. Â vaÂri, D.-X. Chen, A. Hernando, [5] F.J. CastanÄo, M. VaÂzquez, T.-A. O IEEE Trans. Magn. (2000), in press.