- Email: [email protected]
Application of amorphous magnetic wires to computer peripherals
Materials Science and Engineering, A 185 (1994) 141-146
141
Application of amorphous magnetic wires to computer peripherals* K. M o h r i Department of Electrical Engineering, Nagoya University, Nagoya 464 (Japan)
Abstract The principles and basic properties of a new flux-detection element, called a "magnetoinductive (MI) element", and a data tablet for inputting hand-written characters and figures into personal computers (PCs) using amorphous magnetic wires are presented. The MI element is as small as a magnetoresistive (MR) element and shows a high sensitivity for flux detection, i.e. as high as that of the flux gate sensor, with a resolution of 10-5-10 - 6 0 e . Also, it is applicable in magnetic heads for computer magnetic discs and disc drive encoders. A quick-response MI element module is constructed using an MI element-FET (field effect transistor) multivibrating oscillator at 200 MHz. A transparent, thin, lightweight and reliable data tablet was constructed using a thin amorphous wire matrix for a Pen-PC assembly, which has a resolution of 0.3 mm and a processing speed of 150 dots per second.
1. Introduction Recently, some new sensor elements and devices using amorphous magnetic wires have been developed to improve the performance and operability of personal computers (PCs) and information processing apparatus, such as word processors. However, a new sensitive flux-detection element has been required for high density, small-sized magnetic disks, such as hard discs and floppy discs, owing to the low signal-to-noise ratios of conventional (inductive) heads with a high permeability core and a pick-up coil. Magneto-resistive (MR) elements are now considered to be hopeful elements, as a result of their ability to detect flux instead of a time derivative of the flux. However, the sensitivity of the flux detection of the MR element is still insufficient, because of its small rate of change of electric resistance; for example, 2%-3% and 4%-5% for applied fields of about 20 Oe and 50 Oe respectively. A new flux-detection element was found using a zero-magnetostrictive amorphous wire, through which a high frequency current is applied. A change of about 50% in the amplitude of an induced a.c. voltage was achieved between the ends of a wire 30/~m in diameter and several millimetres length for an applied field of about 10 Oe, when passing an a.c. current of 10 mA at 1 MHz. We named this new flux-detection element a "magnetoinductive element" (MI element) [1], in which an internal inductance changes (decreases for an a.c. current and increases for a biased a.c. current) for an *Paper presented at the 8th International Conference on Rapidly Quenched and Metastable Materials, August 22-27, 1993, Sendai, Japan. 0921-5093/94/$7.00 SSDI 0921-5093(93)05747-D
applied external field. Some high frequency (10-220 MHz) oscillator circuits were constructed using the MI element, combining them with two bipolar switching transistors or with two N-channel field effect transistors (FETs) [2] to produce quick-response field sensors. A new data tablet for inputting hand-written characters and figures into PCs is required for the construction of a "pen-inputting personal computer" (PenPC), removing the keyboard found in conventional computers. Thus, a new tablet was made using the zero-magnetostrictive amorphous wire matrix, which was vertically magnetized with a field of 150 kHz generated from a magnetic pen [3]. The tablet was set on a liquid crystal panel as a transparent pen-inputting panel.
2. Magnetoinductive effect and MI element When an a.c. current iac is passed through a ferromagnetic wire, as illustrated in Fig. 1, an a.c. voltage ew (wire voltage) appears between the ends of the wire as ew= er~+ eL
(1)
eR=Rwiac
(2) (3)
eL = d ~ / d t
where eR is the ohmic voltage resulting from an electric resistance (wire resistance) Rw, and el. is the inductive voltage resulting from a circumferential flux change. When we assume BH characteristics in the circumferential direction as
B=lao H H = iac/Z:rr
(4) © 1994 - Elsevier Sequoia. All rights reserved
142
Hex
coe o
K. Mohri
/
Amorphous magnetic wires in computer peripherals 800
. . . . . . . .
i
. . . . . . . .
i
. . . . . . . .
FeCoSiB 30 ~tm dia.
. . . . . . .
g
l=5mm /. oa = 2 kg/mmz Hex = 0./'~/' Iw=15mA ~ , f
600
a-wire
J
E 4OO eac
o
Fig. 1. A.c. excitation of a magnetic wire. 200
--~
0
~
. . . . . . . .
101
where r is the wire radius, the internal inductance of the wire is expressed as
....... -"' Hex = 800 A/m
I
. . . . . . . .
102
(a)
I
. . . . . . . .
103 f (KHz)
I
. . . . . .
104
lO s
Li = l~olw/2 (eL = L i dia¢/dt)
(5)
where P0 is the differential permeability (dB/dH) in the circumferential direction, and depends on the amplitude I m and the frequency f of i,c, respectively, and an external field Hex, as I~o(Im, f, flex). Also, lw is the wire length. It should be noted that L i is apparently independent of r in eqn. (5). A marked change in the amplitude [ew] of ew for Hex was obtained, as shown in Figs. 2(a) and 2(b), by using a slightly negative magnetostrictive amorphous wire ((Fe0.06Co0.94)72.5Si12.5B15;B~ = 0.7 Wb m-2; 2s = _ 10-7 m; made by Unitika Ltd.). This wire was cold drawn from 124/~m to 30/~m in diameter, and then annealed under a tension of 2 kg mm -2 at 475 °C, heating for 1 min. A decrease of 50% in l ew[ for H~ of 400 A m - l (5 Oe) was obtained for iac with I m of 5-14 mA and f = 1 MHz. Here, rew[ is more than 150 mV at I m = / 5 mA. The increasing curve of lew[ for Hex= 10 Oe with increasing fresults from the skin effect in the wire. Figure 3 represents measured results of lew I vs. Hex characteristics at 1 MHz with I m values of 7.5 mA and 15 mA. Such a large change in ew for Hex is obtained only in the tension-annealed amorphous wires. The sensitivity of flux detection is about 100 times more than that of the MR elements. Figure 4(a) shows a change in the B H hysteresis loops in the circumferential direction with Hc~, and Fig. 4(b) illustrates a possible domain pattern of the slightly negative magnetostrictive amorphous wires. The coercive force H c and/~o decrease with increasing Hex, as a result of the decrease in the domain wall energy density and increase in the magnetization rotation respectively [4]. Therefore, L~ decreases with increasing Hex- We call this sensitive electromagnetic phenomena the "magnetoinductive effect" or "magnetoimpedance effect" (MI effect). In the low frequency range (less than 200 kHz), the detection of eL from ew is difficult because leLI ~ leRI. However, l eLI Can be detected using a simple eR cancellation circuit (a kind of bridge circuit), as illustrated
800
. . . .
I
. . . .
I
. . . .
FeCoSiB 30 ~.m dia. 1= 5 m m oa = 2 kg/mm 2 f=lMHz J
600
[
. . . .
I
. . . .
I
. . . .
Hex - 0 "~ - ~ , , ' j
.o
f
~.--"..... -.-"
400 o
...-""~"-"~ Hex = 800 A/m 200
O
,
0
,
,
I
. . . .
10
I
20
. . . .
I
. . . .
I
30 40 Iw (mA)
. . . .
P
,
50
,
.
60
(b) Fig. 2. (a) [ ew[ vs. fcharacteristics with lw = 15 m A and (b) l ew I vs. lw characteristics with f = 1 MHz: FeCoSiB; diameter, 30 pm; 1= 5.5 mm; Oa=2 kg mm -2.
in Fig. 5. This circuit shows a more sensitive MI effect, as [eLI/[eL(H=O)[ is 50% and 80% for Hex values of 2 Oe and 5 0 e respectively. The pulse-like waveform of eL was observed without Hex, in tension-annealed wires which had rectangular B H hysteresis loops in the circumferential direction. The main advantage of the MI element is that the sensitivity of flux detection is almost independent of the element length, from 1 mm to 100 mm or more, compared with the flux gate sensor, in which the sensitivity of flux detection decreases with decreasing head length as a result of the demagnetizing effect. Figure 6 represents an application of an MI element to a rotary encoder with a ring magnet 30 mm in diameter and with 120 magnetic poles. A clear waveform of Hex was detected using a tension-annealed amorphous wire 30 p m in diameter and 2 mm length magnetized with iac = 2 mA and 100 kHz as a head. Hex is detected through a detection circuit (a
K. Mohri 400 30O > E
i
i
/
Amorphous magnetic wires in computer peripherals
etot
i
FeCoSiB 30 ~tm¢~ ,~ l=5mm ~ oa = 2 kg/mm z ~ \ f = 1MHz /" ~k
200
•
,
100
o ........
.
.
.
i
.
- 1000
iac
"=. Iw = 7.5 mA ="°"---o
.
-500
.
.
.
@
o
o -'--I=
0
a-wire
,
.o" .t~
i
.
.
.
.
0 Hex (A/m)
........
i
.
500
.
.
eac
o
.
(a)
1000
FeCoSiB -5 30 ~tm dia. oa = 2 kg/mm z // 1= 5 m m [ l w = 15mA ]
Fig. 3. [G[ vs. H¢x characteristics with the parameter l,d FeCoSiB; diameter, 30 pm; / = 5 . 5 mm; G = 2 kg mm-2; f = 1 MHz.
B0 (T) 0.41
143
J~x 1__ C?(A/,n) I
i
i
-1000
I
i
-500
i
.
.
L_ .
.
.
.
0 Hex (A/m)
i
.
500
.
.
.
i
1000
Fig. 5. Detection of e L and MI effect: FeCoSiB; diameter, 30/~m; tension annealed; l = 2 mm; 1~ = 3 m A ; f = 100 kHz).
(b) Fig. 4. (a) BH hysteresis loop with H~ as parameter. (b) Domain model for slightly negative magnetostrictive amorphous wires: (i) as-cast wire; (ii) cold-drawn and then tension-annealed wire.
L
(b)
------=~------ -~0.4 [lit (A/m) (a)
L
"0,
'~96'
¢,"
....
(a)
FUrl
demodulator (DM) circuit) with a diode and a capacitor from e L (an amplitude modulated wave). An inverse MI effect is obtained by applying a fully biased iac (lm( 1 + sin (ot)), in which l eLI increases from almost zero with increasing Hex, owing to magnetization rotation processes.
(b)
vet2
Fig. 6. Application to a rotary encoder head for a 120-pole ring magnet 30 mm in diameter.
3. MI-transistor oscillator modules for field sensors Field sensors were made using a pair of MI elements with inverse d.c. bias fields, as illustrated in Fig. 7. Thus, field detection becomes more sensitive and more linear than in each individual MI element. The MI elements can work with a d.c. voltage source using a multivibrating oscillator, for example, combining MI elements with transistors (bipolar or FET ).
Figure 8 shows a MI-bipolar switching transistor multivibrator circuit. The inverse MI effect occurs in each MI element, through which a half-sinusoidal current flows, as a result of the switching of each transistor. The output voltage changes with Hex = 0.5 Oe when a d.c. bias field of 0.25 Oe is applied inversely to each MI element using a coil. The oscillation frequency fosc is 1/{~(LiCb) 1/2}and is about 1 MHz at
K. Mohri
144
J -Hb
Hb
/ Amorphous magnetic wires in computer peripherals
Hex
f
Fig. 9. MI-FET resonant oscillator(200 MHz) for a field sensor.
Fig. 7. Principle of M I field sensor.
in diameter) using a field generation pen, a double frequency voltage e(2f) is generated at both ends of the wire. The amplitude of e(2f) is almost constant when the pen is slid along the wire, while it decreases sharply when the pen is moved horizontally away from the wire. A small d.c. current (5 mA) is applied through a wire while detecting e(2f), in order to set an original flux state in the circumferential direction. The pen point position is estimated by comparing e(2f) in each of three wires in X and Y coordinates with data logged into the CPU. A pen-point detection resolution of 0.3 mm and an inputting speed of 150 dots per second were obtained. A transparent tablet plane was realized using wire 30 /~m in diameter wire, which could be set on a liquid crystal panel for coincidence of the inputting and outputting operations of computers. The pen-inputting computer can be used not only as an indoor information processing tool but also as a portable outdoor information terminal, owing to its keyboardless construction.
JMI
Cl _-
It2 l
Fig. 8. MI element-bipolar transistor multivibratoras a sensitive field sensor. MI element is 30/zm in diameter and 5 mm long. Hex = 0, using MI elements 30/~m in diameter and 5 mm long. A marked frequency modulation (FM) was obtained in the circuit when foscwas changed from 900 kHz to 2.7 MHz for Hex = 5 Oe. Some quick-response and stable telemeter-type field sensors are expected to be possible using the FM circuit. Figure 9 represents an M I - F E T (N-channel, depletion-type) multivibrating resonant oscillator with an oscillation frequency of about 220 MHz [5]. The oscillation frequency is determined from fosc = 1/2ar(LiCds) 1/2 where Cds is the FET capacitance between the drain a n d t h e source. Oscillation at such a high frequency was achieved for the first time ever using amorphous wires, because their energy losses have been predicted to be too high at frequencies over 10 MHz. A high sensitivity of field detection similar to that of a flux gate sensor was obtained, despite a very high frequency oscillation state. Field signals with frequencies from 0 to about 10 MHz were detected using the amplitude modulation (AM) principle.
4. Data tablet for pen-inputting computer A transparent-type data tablet was constructed using a zero-magnetostrictive amorphous wire matrix [6], utilizing the outstanding mechanical strength (about 400 kg mm-z) and high circumferential permeability of the amorphous wire. Figure 10 schematically illustrates the total system of the tablet. When an a.c. field (150 kHz) is applied vertically to an amorphous wire (50/~m
5. Conclusions New high performance elements and devices for computer peripherals utilizing amorphous magnetic wire were presented. Unique and outstanding effects, such as the large Barkhausen, Matteucci and MI effects, in amorphous magnetic wires have been found, since developed in 1981 by Unitika Ltd. Various high performance sensors and devices have been developed by combining the ultrahigh mechanical strength with the unique effects. One of the most important roles of the amorphous wire in the field of device construction is matching it with semiconductors, as a result of its high frequency operation and small size. Various new high performance sensors and devices are expected in the near future with combined amorphous wire-semiconductor technology.
Acknowledgment The author would like to express his gratitude to Dr. T. Uchiyama and Dr. L. V. Panina of Nagoya Univer-
K. Mohri
/
Amorphous magnetic wires in computer peripherals
145
AMORPHOUS WIRE MATRIX
inimmlm
1||
mmmmmmm mmmmmmm mmmmmm immmmmm mlmmmmmm |~mmmmmm inmmmnm mmmmmmm
I I
L
u
l llll X-DECOOER
IN I I l l I L
Fig. 10. Data tablet for pen-inputting computers using amorphous wire matrix. sity, and Mr. K. Bushida of Unitika Ltd. R & D (working in N a g o y a University) for their help with the manuscript. References
1 K. Mohri, K. Kawashima, T. Kohzawa and H. Yoshida, IEEE Trans. Magn., 29 (2)(1993) 1245.
2 Y. Yoshida, K. Mohri and T. Uchiyama, IEEE Trans. Magn., 29(5)(1993)3177. 3 K. Kimura, M. Kanoh, K. Kawashima, K. Mohri, M. Takagi and L. V. Panina, IEEE Trans. Magn., 27 (6) ( 1991 ) 4861. 4 L. V. Panina, K. Kawashima and K. Mohri, Abstracts of 16th Ann. Conf. on Magnetics in Japan, 1992, p. 366.
141
Application of amorphous magnetic wires to computer peripherals* K. M o h r i Department of Electrical Engineering, Nagoya University, Nagoya 464 (Japan)
Abstract The principles and basic properties of a new flux-detection element, called a "magnetoinductive (MI) element", and a data tablet for inputting hand-written characters and figures into personal computers (PCs) using amorphous magnetic wires are presented. The MI element is as small as a magnetoresistive (MR) element and shows a high sensitivity for flux detection, i.e. as high as that of the flux gate sensor, with a resolution of 10-5-10 - 6 0 e . Also, it is applicable in magnetic heads for computer magnetic discs and disc drive encoders. A quick-response MI element module is constructed using an MI element-FET (field effect transistor) multivibrating oscillator at 200 MHz. A transparent, thin, lightweight and reliable data tablet was constructed using a thin amorphous wire matrix for a Pen-PC assembly, which has a resolution of 0.3 mm and a processing speed of 150 dots per second.
1. Introduction Recently, some new sensor elements and devices using amorphous magnetic wires have been developed to improve the performance and operability of personal computers (PCs) and information processing apparatus, such as word processors. However, a new sensitive flux-detection element has been required for high density, small-sized magnetic disks, such as hard discs and floppy discs, owing to the low signal-to-noise ratios of conventional (inductive) heads with a high permeability core and a pick-up coil. Magneto-resistive (MR) elements are now considered to be hopeful elements, as a result of their ability to detect flux instead of a time derivative of the flux. However, the sensitivity of the flux detection of the MR element is still insufficient, because of its small rate of change of electric resistance; for example, 2%-3% and 4%-5% for applied fields of about 20 Oe and 50 Oe respectively. A new flux-detection element was found using a zero-magnetostrictive amorphous wire, through which a high frequency current is applied. A change of about 50% in the amplitude of an induced a.c. voltage was achieved between the ends of a wire 30/~m in diameter and several millimetres length for an applied field of about 10 Oe, when passing an a.c. current of 10 mA at 1 MHz. We named this new flux-detection element a "magnetoinductive element" (MI element) [1], in which an internal inductance changes (decreases for an a.c. current and increases for a biased a.c. current) for an *Paper presented at the 8th International Conference on Rapidly Quenched and Metastable Materials, August 22-27, 1993, Sendai, Japan. 0921-5093/94/$7.00 SSDI 0921-5093(93)05747-D
applied external field. Some high frequency (10-220 MHz) oscillator circuits were constructed using the MI element, combining them with two bipolar switching transistors or with two N-channel field effect transistors (FETs) [2] to produce quick-response field sensors. A new data tablet for inputting hand-written characters and figures into PCs is required for the construction of a "pen-inputting personal computer" (PenPC), removing the keyboard found in conventional computers. Thus, a new tablet was made using the zero-magnetostrictive amorphous wire matrix, which was vertically magnetized with a field of 150 kHz generated from a magnetic pen [3]. The tablet was set on a liquid crystal panel as a transparent pen-inputting panel.
2. Magnetoinductive effect and MI element When an a.c. current iac is passed through a ferromagnetic wire, as illustrated in Fig. 1, an a.c. voltage ew (wire voltage) appears between the ends of the wire as ew= er~+ eL
(1)
eR=Rwiac
(2) (3)
eL = d ~ / d t
where eR is the ohmic voltage resulting from an electric resistance (wire resistance) Rw, and el. is the inductive voltage resulting from a circumferential flux change. When we assume BH characteristics in the circumferential direction as
B=lao H H = iac/Z:rr
(4) © 1994 - Elsevier Sequoia. All rights reserved
142
Hex
coe o
K. Mohri
/
Amorphous magnetic wires in computer peripherals 800
. . . . . . . .
i
. . . . . . . .
i
. . . . . . . .
FeCoSiB 30 ~tm dia.
. . . . . . .
g
l=5mm /. oa = 2 kg/mmz Hex = 0./'~/' Iw=15mA ~ , f
600
a-wire
J
E 4OO eac
o
Fig. 1. A.c. excitation of a magnetic wire. 200
--~
0
~
. . . . . . . .
101
where r is the wire radius, the internal inductance of the wire is expressed as
....... -"' Hex = 800 A/m
I
. . . . . . . .
102
(a)
I
. . . . . . . .
103 f (KHz)
I
. . . . . .
104
lO s
Li = l~olw/2 (eL = L i dia¢/dt)
(5)
where P0 is the differential permeability (dB/dH) in the circumferential direction, and depends on the amplitude I m and the frequency f of i,c, respectively, and an external field Hex, as I~o(Im, f, flex). Also, lw is the wire length. It should be noted that L i is apparently independent of r in eqn. (5). A marked change in the amplitude [ew] of ew for Hex was obtained, as shown in Figs. 2(a) and 2(b), by using a slightly negative magnetostrictive amorphous wire ((Fe0.06Co0.94)72.5Si12.5B15;B~ = 0.7 Wb m-2; 2s = _ 10-7 m; made by Unitika Ltd.). This wire was cold drawn from 124/~m to 30/~m in diameter, and then annealed under a tension of 2 kg mm -2 at 475 °C, heating for 1 min. A decrease of 50% in l ew[ for H~ of 400 A m - l (5 Oe) was obtained for iac with I m of 5-14 mA and f = 1 MHz. Here, rew[ is more than 150 mV at I m = / 5 mA. The increasing curve of lew[ for Hex= 10 Oe with increasing fresults from the skin effect in the wire. Figure 3 represents measured results of lew I vs. Hex characteristics at 1 MHz with I m values of 7.5 mA and 15 mA. Such a large change in ew for Hex is obtained only in the tension-annealed amorphous wires. The sensitivity of flux detection is about 100 times more than that of the MR elements. Figure 4(a) shows a change in the B H hysteresis loops in the circumferential direction with Hc~, and Fig. 4(b) illustrates a possible domain pattern of the slightly negative magnetostrictive amorphous wires. The coercive force H c and/~o decrease with increasing Hex, as a result of the decrease in the domain wall energy density and increase in the magnetization rotation respectively [4]. Therefore, L~ decreases with increasing Hex- We call this sensitive electromagnetic phenomena the "magnetoinductive effect" or "magnetoimpedance effect" (MI effect). In the low frequency range (less than 200 kHz), the detection of eL from ew is difficult because leLI ~ leRI. However, l eLI Can be detected using a simple eR cancellation circuit (a kind of bridge circuit), as illustrated
800
. . . .
I
. . . .
I
. . . .
FeCoSiB 30 ~.m dia. 1= 5 m m oa = 2 kg/mm 2 f=lMHz J
600
[
. . . .
I
. . . .
I
. . . .
Hex - 0 "~ - ~ , , ' j
.o
f
~.--"..... -.-"
400 o
...-""~"-"~ Hex = 800 A/m 200
O
,
0
,
,
I
. . . .
10
I
20
. . . .
I
. . . .
I
30 40 Iw (mA)
. . . .
P
,
50
,
.
60
(b) Fig. 2. (a) [ ew[ vs. fcharacteristics with lw = 15 m A and (b) l ew I vs. lw characteristics with f = 1 MHz: FeCoSiB; diameter, 30 pm; 1= 5.5 mm; Oa=2 kg mm -2.
in Fig. 5. This circuit shows a more sensitive MI effect, as [eLI/[eL(H=O)[ is 50% and 80% for Hex values of 2 Oe and 5 0 e respectively. The pulse-like waveform of eL was observed without Hex, in tension-annealed wires which had rectangular B H hysteresis loops in the circumferential direction. The main advantage of the MI element is that the sensitivity of flux detection is almost independent of the element length, from 1 mm to 100 mm or more, compared with the flux gate sensor, in which the sensitivity of flux detection decreases with decreasing head length as a result of the demagnetizing effect. Figure 6 represents an application of an MI element to a rotary encoder with a ring magnet 30 mm in diameter and with 120 magnetic poles. A clear waveform of Hex was detected using a tension-annealed amorphous wire 30 p m in diameter and 2 mm length magnetized with iac = 2 mA and 100 kHz as a head. Hex is detected through a detection circuit (a
K. Mohri 400 30O > E
i
i
/
Amorphous magnetic wires in computer peripherals
etot
i
FeCoSiB 30 ~tm¢~ ,~ l=5mm ~ oa = 2 kg/mm z ~ \ f = 1MHz /" ~k
200
•
,
100
o ........
.
.
.
i
.
- 1000
iac
"=. Iw = 7.5 mA ="°"---o
.
-500
.
.
.
@
o
o -'--I=
0
a-wire
,
.o" .t~
i
.
.
.
.
0 Hex (A/m)
........
i
.
500
.
.
eac
o
.
(a)
1000
FeCoSiB -5 30 ~tm dia. oa = 2 kg/mm z // 1= 5 m m [ l w = 15mA ]
Fig. 3. [G[ vs. H¢x characteristics with the parameter l,d FeCoSiB; diameter, 30 pm; / = 5 . 5 mm; G = 2 kg mm-2; f = 1 MHz.
B0 (T) 0.41
143
J~x 1__ C?(A/,n) I
i
i
-1000
I
i
-500
i
.
.
L_ .
.
.
.
0 Hex (A/m)
i
.
500
.
.
.
i
1000
Fig. 5. Detection of e L and MI effect: FeCoSiB; diameter, 30/~m; tension annealed; l = 2 mm; 1~ = 3 m A ; f = 100 kHz).
(b) Fig. 4. (a) BH hysteresis loop with H~ as parameter. (b) Domain model for slightly negative magnetostrictive amorphous wires: (i) as-cast wire; (ii) cold-drawn and then tension-annealed wire.
L
(b)
------=~------ -~0.4 [lit (A/m) (a)
L
"0,
'~96'
¢,"
....
(a)
FUrl
demodulator (DM) circuit) with a diode and a capacitor from e L (an amplitude modulated wave). An inverse MI effect is obtained by applying a fully biased iac (lm( 1 + sin (ot)), in which l eLI increases from almost zero with increasing Hex, owing to magnetization rotation processes.
(b)
vet2
Fig. 6. Application to a rotary encoder head for a 120-pole ring magnet 30 mm in diameter.
3. MI-transistor oscillator modules for field sensors Field sensors were made using a pair of MI elements with inverse d.c. bias fields, as illustrated in Fig. 7. Thus, field detection becomes more sensitive and more linear than in each individual MI element. The MI elements can work with a d.c. voltage source using a multivibrating oscillator, for example, combining MI elements with transistors (bipolar or FET ).
Figure 8 shows a MI-bipolar switching transistor multivibrator circuit. The inverse MI effect occurs in each MI element, through which a half-sinusoidal current flows, as a result of the switching of each transistor. The output voltage changes with Hex = 0.5 Oe when a d.c. bias field of 0.25 Oe is applied inversely to each MI element using a coil. The oscillation frequency fosc is 1/{~(LiCb) 1/2}and is about 1 MHz at
K. Mohri
144
J -Hb
Hb
/ Amorphous magnetic wires in computer peripherals
Hex
f
Fig. 9. MI-FET resonant oscillator(200 MHz) for a field sensor.
Fig. 7. Principle of M I field sensor.
in diameter) using a field generation pen, a double frequency voltage e(2f) is generated at both ends of the wire. The amplitude of e(2f) is almost constant when the pen is slid along the wire, while it decreases sharply when the pen is moved horizontally away from the wire. A small d.c. current (5 mA) is applied through a wire while detecting e(2f), in order to set an original flux state in the circumferential direction. The pen point position is estimated by comparing e(2f) in each of three wires in X and Y coordinates with data logged into the CPU. A pen-point detection resolution of 0.3 mm and an inputting speed of 150 dots per second were obtained. A transparent tablet plane was realized using wire 30 /~m in diameter wire, which could be set on a liquid crystal panel for coincidence of the inputting and outputting operations of computers. The pen-inputting computer can be used not only as an indoor information processing tool but also as a portable outdoor information terminal, owing to its keyboardless construction.
JMI
Cl _-
It2 l
Fig. 8. MI element-bipolar transistor multivibratoras a sensitive field sensor. MI element is 30/zm in diameter and 5 mm long. Hex = 0, using MI elements 30/~m in diameter and 5 mm long. A marked frequency modulation (FM) was obtained in the circuit when foscwas changed from 900 kHz to 2.7 MHz for Hex = 5 Oe. Some quick-response and stable telemeter-type field sensors are expected to be possible using the FM circuit. Figure 9 represents an M I - F E T (N-channel, depletion-type) multivibrating resonant oscillator with an oscillation frequency of about 220 MHz [5]. The oscillation frequency is determined from fosc = 1/2ar(LiCds) 1/2 where Cds is the FET capacitance between the drain a n d t h e source. Oscillation at such a high frequency was achieved for the first time ever using amorphous wires, because their energy losses have been predicted to be too high at frequencies over 10 MHz. A high sensitivity of field detection similar to that of a flux gate sensor was obtained, despite a very high frequency oscillation state. Field signals with frequencies from 0 to about 10 MHz were detected using the amplitude modulation (AM) principle.
4. Data tablet for pen-inputting computer A transparent-type data tablet was constructed using a zero-magnetostrictive amorphous wire matrix [6], utilizing the outstanding mechanical strength (about 400 kg mm-z) and high circumferential permeability of the amorphous wire. Figure 10 schematically illustrates the total system of the tablet. When an a.c. field (150 kHz) is applied vertically to an amorphous wire (50/~m
5. Conclusions New high performance elements and devices for computer peripherals utilizing amorphous magnetic wire were presented. Unique and outstanding effects, such as the large Barkhausen, Matteucci and MI effects, in amorphous magnetic wires have been found, since developed in 1981 by Unitika Ltd. Various high performance sensors and devices have been developed by combining the ultrahigh mechanical strength with the unique effects. One of the most important roles of the amorphous wire in the field of device construction is matching it with semiconductors, as a result of its high frequency operation and small size. Various new high performance sensors and devices are expected in the near future with combined amorphous wire-semiconductor technology.
Acknowledgment The author would like to express his gratitude to Dr. T. Uchiyama and Dr. L. V. Panina of Nagoya Univer-
K. Mohri
/
Amorphous magnetic wires in computer peripherals
145
AMORPHOUS WIRE MATRIX
inimmlm
1||
mmmmmmm mmmmmmm mmmmmm immmmmm mlmmmmmm |~mmmmmm inmmmnm mmmmmmm
I I
L
u
l llll X-DECOOER
IN I I l l I L
Fig. 10. Data tablet for pen-inputting computers using amorphous wire matrix. sity, and Mr. K. Bushida of Unitika Ltd. R & D (working in N a g o y a University) for their help with the manuscript. References
1 K. Mohri, K. Kawashima, T. Kohzawa and H. Yoshida, IEEE Trans. Magn., 29 (2)(1993) 1245.
2 Y. Yoshida, K. Mohri and T. Uchiyama, IEEE Trans. Magn., 29(5)(1993)3177. 3 K. Kimura, M. Kanoh, K. Kawashima, K. Mohri, M. Takagi and L. V. Panina, IEEE Trans. Magn., 27 (6) ( 1991 ) 4861. 4 L. V. Panina, K. Kawashima and K. Mohri, Abstracts of 16th Ann. Conf. on Magnetics in Japan, 1992, p. 366.