Magnetic reproducing head having a distributed-constant circuit type magnetic field detector

A distributed-constant circuit type magnetic field detector which includes a magnetic member whose permeability varies with changes in a magnetic field applied thereto disposed at a point where a magnetic field is produced in a distributed-constant circuit excited with an electromagnetic wave and a detector for detecting a change in electromagnetic field distribution in the distributed-constant circuit produced by a variation in permeability of the magnetic member upon application thereto of a magnetic field to be detected.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a distributed-constant circuit type 
magnetic field detector for detecting an external magnetic field working 
on a novel principle and suitable for use, for example, in a magnetic 
reproducing head which detects a signal magnetic field from a magnetic 
recording medium such as a magnetic tape, a magnetic disk, and a floppy 
disk. 
2. Description of the Related Art 
In reproducing magnetic record recorded on magnetic recording media, 
ring-shaped inductive magnetic heads utilizing electromagnetic induction 
have long been used. However, with the recent increase in recording 
density and operating frequency, various problems are arising. 
First, the increase in the recording density is lowering the relative speed 
between the magnetic reproducing head and the recording medium. Hence, the 
reproduced output power by the inductive reproducing head is becoming 
extremely lower. 
To cope with this situation, development and practical use of 
magnetoresistive effect (MR) reproducing heads are being advanced. The MR 
head is that of a magnetic flux sensitive type not dependent on its 
relative speed with the magnetic recording medium. Since the reproduced 
output by it is proportional to the current passed through the MR element, 
it is expected theoretically that the voltage will become higher the 
larger the current is. In practice, however, there is an upper limit to it 
because of heat to be produced by the current flow. On the other hand, 
since the reproduced output power is proportional also to the MR ratio of 
the MR element, materials having greater MR ratio are being intensively 
searched for. At present, Permalloy is being used chiefly, but its 
reproducing output power is not sufficient because its MR ratio is not 
higher than 2% or so. Besides, there is a big problem with the MR head 
that it produces Barkhausen noise to deteriorate the S/N ratio. 
As another magnetic reproducing head of a magnetic flux sensitive type, 
there is proposed a magnetic reproducing head utilizing a change in the 
resonance characteristic of a coil by an external magnetic field (for 
example, Preprints for Spring National Conference of the Institute of 
Electronics, Information and Communication Engineers, 1990, pp. 5-35). 
However, this proposed head is not adapted to be a distributed-constant 
circuit and, further, permeability of the magnetic member used therein is 
in the frequency domain under 1 GHz. 
As described above, with the recent rapid increase in the information 
quantity to be recorded, there are strong demands for higher recording 
density and higher-frequency performance in magnetic recording. These 
demands are especially strong in the field of hard disk units as external 
memory for video equipment and computers. Video equipment is required to 
support the high-definition television and digital television coming into 
existence and hard disk units are urged to support the extended scale of 
software and increased quantity of processed data and so on accompanying 
improvement in performance of computers. To meet the demands for higher 
recording density and performance at higher frequency, it is necessary for 
the magnetic reproducing head to be highly sensitive and excellent in 
high-frequency characteristics. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a magnetic field detector 
functioning with high sensitivity and excellent high-frequency 
characteristics. 
According to the present invention, there is provided a 
distributed-constant circuit type magnetic field detector which comprises 
a magnetic member whose permeability varies with changes in a magnetic 
field applied thereto disposed at a point where a magnetic field is 
produced in a distributed-constant circuit excited with an electromagnetic 
wave and means for detecting a change in electromagnetic field 
distribution in the distributed-constant circuit produced by a variation 
in permeability of the magnetic member upon application thereto of a 
magnetic field to be detected, whereby the magnetic field to be detected 
is detected. 
The present invention makes it possible to achieve magnetic reproduction, 
i.e., magnetic detection, with high sensitivity and excellent 
high-frequency characteristics. When applied to a magnetic reproducing 
head, it can effectively meet the demand for magnetic recording of higher 
packing density and at higher frequency.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention is directed to the provision of a 
distributed-constant circuit type magnetic field detector capable of 
detecting external magnetic field, namely, detecting existence or 
nonexistence and intensity of an external magnetic field, and, more 
particularly, detecting with high sensitivity a signal magnetic field 
generated by magnetic record made on a magnetic recording medium and 
forming a magnetic reproducing head meeting the demand for achievement of 
higher packing density and performance at higher frequency. 
The basic structure of the present invention, as shown in the structural 
drawing of FIG. 1A, has a magnetic member 2, of which permeability .mu. 
(the permeability herein refers to complex permeability) varies with 
changes in external magnetic field applied thereto, disposed at a point 
where a magnetic field is generated in the circuit of a distributed 
constant circuit 1 excited with an electromagnetic wave. 
More specifically, the magnetic member 2 is set up at a point where a 
magnetic field is generated when the distributed-constant circuit 1 
incorporating the magnetic member 2 is excited by an oscillator 3. 
A magnetic field to be detected is directly or indirectly applied to the 
magnetic member 2, whereby the permeability of it is varied, and the 
change in the electromagnetic field distribution in the 
distributed-constant circuit 1 due to the variation in the permeability is 
detected, and thus the magnetic field to be detected is detected. 
According to another arrangement of the present invention, the 
distributed-constant circuit 1 including the magnetic member 2 in the 
above described basic structure has its terminal specially arranged to be 
impedance-unmatched so that a standing wave is produced. 
The standing wave voltage dependent on a change in the magnetic field to be 
detected applied to the magnetic member 2 is amplitude-detected at a point 
of the distributed-constant circuit 1, where the standing wave voltage 
exhibits its substantially minimum value (a point of node) under the 
condition of no magnetic field to be detected applied thereto, and 
thereby, the detection of the magnetic field to be detected is achieved. 
According to another arrangement of the present invention, at least a 
portion of the distributed-constant circuit 1 in the above described basic 
structure is provided with a distributed-constant resonator. 
A magnetic member 2 is disposed at a point where a magnetic field is 
generated within the distributed-constant resonator. A change in the 
resonance characteristic of the resonator due to a variation in the 
permeability of the magnetic member 2 dependent on the magnetic field to 
be detected applied to the magnetic member 2 is detected and, thereby, 
detection or measurement of the magnetic field to be detected is achieved. 
According to a further arrangement of the present invention, the circuit in 
the above described basic structure has the magnetic member 2 provided 
with a magnetic yoke conducting the magnetic field to be detected such 
that a magnetic circuit including the magnetic member 2 is formed. 
According to a still further arrangement of the invention, a 
distributed-constant circuit 1 has a magnetic member whose permeability 
varies upon application of an external magnetic field disposed in the 
vicinity of its terminal portion and, in addition, the terminal portion is 
short-circuited. 
According to another arrangement of the present invention, there is 
provided a magnetic member 2 whose permeability is varied upon application 
of the magnetic field to be detected at the terminal portion of a coplanar 
waveguide line or a coplanar line, and the change in the reflection 
coefficient at the terminal portion due to the variation of the 
permeability is detected, and thereby, the detection of the magnetic field 
to be detected is achieved. 
According to another arrangement of the present invention, there is 
disposed a magnetic member 2 whose permeability is varied upon application 
of the magnetic field to be detected at the terminal portion of the above 
coplanar waveguide line or the coplanar line, and it is adapted such that 
the variation in the permeability thereof at a frequency within the range 
from 1 Ghz to 10 GHz is utilized. 
According to another arrangement of the present invention, a coplanar line 
having a portion in which the line width is gradually increased while the 
ratio between conductor width and conductor spacing is kept constant is 
used as the above coplanar waveguide line or coplanar line. 
According to another arrangement of the present invention, the coplanar 
waveguide line or coplanar line has the top surface covered with a 
dielectric member. 
According to another arrangement of the present invention, a D.C. current 
is passed through the above coplanar waveguide line or coplanar line so 
that a bias magnetic field is applied to the magnetic member 2. 
Functioning of the apparatus of the present invention according to the 
basic structure will be described with reference to FIG. 1. 
As described above with reference to FIG. 1A, when the distributed-constant 
circuit 1, or, in concrete terms, a distributed-constant circuit 1 of a 
microstrip line, a waveguide, a coaxial cable, or the like, is exited by 
the oscillator 3, a progressive wave is generated if the terminal. i.e., 
the load terminal, is in an impedance-matched state, and a reflected wave 
is produced in addition to the progressive wave if the terminal is in an 
impedance-unmatched state, so that a standing wave is produced by 
superposition of the progressive and reflected waves. The standing-wave 
ratio is maximized when the terminal of the distributed-constant circuit 1 
is open or short-circuited. 
In the present invention, there is provided a distributed-constant circuit 
1 including a magnetic member 2 whose permeability varies with changes in 
a magnetic field applied thereto, and the magnetic member 2 is disposed at 
the point in the circuit where a magnetic field is generated when it is 
put in an oscillating state. Supposing now that there is produced an 
electromagnetic wave having electric field (voltage) distribution as shown 
in FIG. 1B at an instant in the state where no magnetic field to be 
detected is applied to the magnetic member 2, the distribution of the 
electromagnetic field along the distributed-constant circuit 1 changes as 
the permeability of the circuit varies. Accordingly, if an external 
magnetic field H.sub.ex, i.e., a magnetic field to be detected H.sub.ex 
=H, is applied to the magnetic member 2 and thereby the permeability .mu. 
(real part .mu..sub.r and imaginary part .mu..sub.i) is varied, the 
voltage distribution shown in FIG. 1B is also varied. Therefore, the 
magnetic field to be detected can be detected by detecting, for example, 
phase, amplitude, or wavelength at a specific point x.sub.s of the 
distributed-constant circuit 1. 
The curve 4Z in FIG. 2 shows a waveform of a standing wave of which the 
standing-wave amplitude .vertline.V.vertline. exhibits its minimum value 
V.sub.0 at the specific point x.sub.s, under the condition of an external 
magnetic field H.sub.ex being not applied, i.e., H.sub.ex =0, for example, 
and the terminal of the distributed-constant circuit 1 being in an 
unmatched state. Referring to FIG. 2, the ratio between the maximum value 
and the minimum value of the standing-wave amplitude is called the 
standing-wave voltage ratio, .lambda. denotes the standing-wave 
wavelength, and .lambda./2 denotes the interval at which the crests or the 
troughs of the standing wave cycle. The standing-wave ratio is maximized 
when the terminal is open or short-circuited. 
In the above described state, if the electromagnetic field H.sub.ex applied 
to the magnetic member 2 is changed to H.sub.ex =H, i.e., if the magnetic 
field to be detected is applied, the magnetic-field distribution along the 
distributed-constant circuit 1 is changed, and as a result, for example as 
shown by the curve 4.sub.ex in dotted line in FIG. 2, the standing-wave 
ratio, the standing-wave amplitude .lambda., and/or the phase is changed 
and the standing-wave amplitude .vertline.V.vertline. at the point x.sub.s 
is changed to V.sub.ex. Therefore, by rectifying the V.sub.ex upon 
application of the magnetic field to be detected for example at the point 
x.sub.s where the voltage .vertline.V.vertline. exhibits its minimum value 
V.sub.0 under the condition of no magnetic field to be detected being 
applied, a great change in voltage can be obtained and detection with high 
sensitivity can be achieved. However, when the voltage curve 4Z deviates 
from the ideal state and its waveform therefore exhibits a null at the 
point of the minimum value V.sub.0, the point for voltage rectification 
x.sub.s, for example, is changed to another point slightly shifted from 
the point of V.sub.0. 
Further, when a portion of the distributed-constant circuit 1 is formed of 
a distributed-constant resonator and the magnetic member 2 is disposed 
within the resonator to provide another arrangement of the present 
invention, only the electromagnetic wave satisfying the resonance 
condition is excited within the resonator. Therefore, the variation in the 
permeability of the magnetic member 2 gives a great effect on the 
resonance characteristic to change the resonance wavelength and resonance 
amplitude (the value Q), and thereby the state of excitation of the 
electromagnetic wave within the resonator is greatly changed leading to a 
great change in the electromagnetic-wave distribution in the 
distributed-constant circuit 1. Thus, detection of the magnetic field to 
be detected can be achieved with higher sensitivity. 
Further, when it is arranged such that the magnetic member 2 is 
magnetically coupled with a magnetic yoke and the magnetic field to be 
detected is introduced through the magnetic yoke, the magnetic field to be 
detected can be effectively applied to the magnetic member 2. Therefore, 
especially when the arrangement is applied to a reproducing magnetic head 
for reading the record on a magnetic recording medium, a high reproducing 
sensitivity can be obtained. 
The distributed-constant circuit 1 of the present invention, as shown in 
FIG. 1A indicating its basic structure, comprises a distributed-constant 
circuit 1, or in concrete terms, a microstrip line, a coaxial cable, or 
the like, and it is adapted to be excited by an oscillator 3 through a 
microwave transmission line 10 such as a coaxial cable. 
The distributed-constant circuit 1 is arranged to incorporate a magnetic 
member 2 made of a soft magnetic material, such as CoTaZr amorphous, whose 
permeability .mu., the real part .mu..sub.r or imaginary part .mu..sub.i, 
varies with changes in the magnetic field applied thereto. 
The position where the magnetic member 2 is disposed is selected at a point 
where a strong magnetic field is generated when the distributed-constant 
circuit 1 incorporating the same is excited. 
The distributed-constant circuit 1 can have its terminal, or the so-called 
load terminal, in either of a matched state and an unmatched state. When 
the terminal is in the matched state, there is produced a progressing 
wave, and when it is in the unmatched state, there is produced a standing 
wave by generation of the reflected wave as described above. Especially 
when the terminal is in a short-circuited or open state, the standing-wave 
ratio becomes great. 
FIG. 3 is a schematic structural drawing of an example of the present 
invention applied to a magnetic reproducing head for reading a record 
signal on a magnetic recording medium 5. In this case, the magnetic member 
2 made of the above described soft magnetic material whose permeability 
varies with changes in the magnetic field applied thereto is disposed for 
example at the terminal portion of the distributed-constant circuit 1, and 
the same is arranged to be closely confronted with the magnetic recording 
medium 5 and moved relative to the medium 5 so that a leakage signal 
magnetic field from the record magnetization on the medium 5 is applied to 
the magnetic member 2 to thereby cause a variation in its permeability. A 
change in the electromagnetic field distribution due to the variation in 
the permeability caused by the signal magnetic field is measured as, for 
example, a change in voltage, or a change in amplitude or phase, at a 
specific point in the distributed-constant circuit 1 by a detector 6, such 
as a network analyzer, and/or a rectifier plus a voltmeter. 
FIG. 4 is a diagram showing an arrangement in which the reflection 
coefficient S.sub.11 of a distributed-constant circuit 1 is measured by a 
network analyzer 61 and FIG. 5 is a diagram showing an arrangement in 
which the transmission coefficient S.sub.21 is measured. 
When the terminal of the distributed-constant circuit i is short-circuited 
in the arrangement described in FIG. 3 as shown in FIG. 6, the voltage 
distribution of the standing wave produced when the circuit is excited 
becomes as shown by the curve a in FIG. 6, that is, the voltage is 
minimized at the terminal where a node is formed. Therefore, the current 
is maximized at the terminal and the generated magnetic field is maximized 
at the terminal. Accordingly, the distribution of the standing wave is 
most strongly affected by the permeability at the terminal portion. 
That is, by adopting the arrangement with the terminal portion 
short-circuited as shown in FIG. 6 and a magnetic member 2 whose 
permeability is varied by changes in the external magnetic field disposed 
in the vicinity of the terminal portion, the standing wave is most 
strongly affected by the change in the external magnetic field. 
Therefore, when using the detector of FIG. 6 as a magnetic reproducing head 
and the terminal of the distributed-constant circuit 1 is directly held 
close to a magnetic recording medium 5 to detect the signal magnetic field 
from the medium 5, it is preferred to have the magnetic member disposed at 
the terminal. 
Further, when the terminal portion is short-circuited, the electric field 
generated at the terminal portion is decreased as described above. 
Therefore, the change in the admittivity at the terminal portion produces 
little effect on the standing-wave distribution. Accordingly, noise to be 
produced by electrical causes when the terminal is brought closer to the 
magnetic recording medium 5 can be reduced. 
Furthermore, in the detection of the signal magnetic field from the 
magnetic recording medium 5 according to record magnetization on the 
medium 5, that is, in the signal reproduction, even if an electrical 
connection is produced between the distributed-constant circuit 1 and the 
medium 5 when they are brought into contact, current is prevented from 
flowing between the circuit 1 and the medium 5 in case the terminal 
portion is short-circuited and, in addition, the side of the medium 5 is 
grounded. Therefore, noise is prevented from occurring on such occasion. 
The distributed-constant circuit 1 in the present invention can be provided 
by a microstrip type arrangement for example as show in FIG. 7. 
In this case, the circuit (FIGS. 7a and 7b) is structured of a line 
conductor 9 made of Au, Cu, or the like in a strip form disposed on a 
ground conductor 7 made of Au, Cu, or the like through a dielectric member 
8 made of glass, Al.sub.2 O.sub.3, sapphire, or similar material whose 
permittivity is high and high-frequency loss is low and through, at its 
portion on the terminal side, a magnetic member 2 made of an amorphous 
soft magnetic thin film of Co.sub.75 Ta.sub.11 Zr.sub.14, and the line 
conductor 9 and the ground conductor 7 are short-circuited at the 
terminal. 
Also in the distributed-constant circuit 1 provided by the above microstrip 
line type waveguide line, if a standing wave is produced in the state 
where no external magnetic field is applied, i.e., where H.sub.ex =0, the 
excited state changes when an external magnetic field H.sub.ex =H is 
applied. Therefore, by rectifying voltages according to curves 4Z and 
4.sub.ex and measuring the change in voltage at a specific point in the 
strip line, or at a specific point for example on the transmission line 10 
connecting the strip line and the oscillator indicated by dotted line A in 
FIG. 2, detection or measurement of the external magnetic field H.sub.ex 
can be achieved. FIG. 8 shows the relationship between the detected 
voltage and the external magnetic field (magnetic field to be detected), 
from which it is known that a change in magnetic field of 1 (Oe), for 
example, can be detected with such high sensitivity as a voltage change as 
great as approximately 200 mV. In this case, referring to the structure 
shown in FIG. 7, the line conductor was 30 .mu.m wide and 1 .mu.m thick, 
and the magnetic member 2 was 1 mm long, 30 .mu.m wide, and 0.5 .mu.m 
thick. 
Further, the dependency on the external magnetic field of the impedance of 
the distributed-constant circuit 1 of the above described structure was 
measured using a network analyzer (HP8719A made by Hewlett-Packard Corp.) 
within the range of frequencies f from 130 MHz to 8 GHz. The test results 
are shown in FIG. 9. In FIG. 9, the curve 91 corresponds to the case where 
the external magnetic field H.sub.ex =0 and the curve 92 corresponds to 
the case where H.sub.ex =80 A/m. The points of each curve indicated by 
.DELTA.2, .DELTA.4, .DELTA.6, and .DELTA.8 show the values when f=2 GHz, 
f=4 GHz, f=6 GHz, and f=8 GHz, respectively. As apparent from the diagram, 
the input impedance of the waveguide line, hence the electromagnetic-wave 
distribution in the waveguide line, is dependent on the external magnetic 
field H.sub.ex. 
According to the test results by means of the network analyzer, it is known 
that the external magnetic field, i.e., the magnetic field to be detected 
H.sub.ex, can be detected. 
Further, referring to FIG. 10, a case where a microstrip line type 
structure is used will be described below in detail. Parts in FIG. 10 
corresponding to those in FIG. 7 are denoted by like reference numerals. 
Also in this case, the structure has a ground conductor 7 and a line 
conductor 9 with for example a dielectric member 8 and a magnetic member 2 
interposed therebetween. 
In fabricating the device, as shown in FIG. 11, a dielectric member 8 
formed of a substrate of Al.sub.2 O.sub.3, sapphire, or a similar material 
whose permittivity is high and high-frequency loss is low is prepared and 
a thin film 25 of an amorphous soft magnetic material Co.sub.75 Ta.sub.11 
Zr.sub.14 of a thickness of 0.7 .mu.m, for example, is deposited on the 
substrate by sputtering. 
In order that the permeability .mu. of the thin film 25 of the soft 
magnetic material exhibits a sharp magnetic-field dependency, it is 
heat-treated under application of a fixed magnetic field of 1 kOe, for 
example, in a temperature of 300.degree. C. for one hour, whereby it is 
provided with uniaxial anisotropy of an anisotropic magnetic field Hk of 
approximately 0.2 (Oe), for example. 
On the entire surface of the soft magnetic material thin film 25, a good 
conductive layer, not shown, of a material with good conductivity such as 
Au or Cu is deposited to a thickness of 1 .mu.m by sputtering. 
Then, the good conductive layer, together with the underlying soft magnetic 
material thin film 25, is subjected to pattern etching by photolithography 
into a strip form for example with a length of 2 mm and a width of 30 
.mu.m, while having the axis of easy magnetization e.a of the soft 
magnetic material thin film 25 virtually aligned in the lateral direction. 
Thus, a line conductor 9 in a strip form made of a good conductive Cu 
layer is formed and, at the same time, a magnetic member 2, which is 
formed of a portion of the soft magnetic material thin film 25 and 
permeability of which is dependent on the external magnetic field, is 
formed underlying the conductive layer. 
Then, the dielectric member 8 with the magnetic member 2 and the line 
conductor 9 formed thereon is joined to a block with good conductivity 
such as a Cu block constituting the ground conductor 7. 
In this way, a microstrip line whose load terminal 1a being, for example, 
opened is structured. 
In the above described microstrip type distributed-constant circuit 1, an 
oscillator 3, i.e., a high-frequency power source, is connected between 
the line 9 and the ground conductor 7 through a transmission line 10 
formed for example of a coaxial cable. 
The distributed-constant circuit 1 formed of the microwave waveguide line 
is excited by means of the oscillator 3, i.e., the high-frequency power 
source, set to a frequency for example of about 1 GHz and the exciting 
frequency is adjusted so that a node of the standing wave is formed at the 
point x=x.sub.s as indicated in FIG. 2 by the curve 4Z drawn by solid 
line. Then, the standing-wave voltage at the point x=x.sub.s is rectified 
by means of a rectification circuit 62 and the voltage is measured by a 
voltmeter 63. Thus, as described with reference to FIG. 2, the magnetic 
field can be detected as a change between V.sub.0 and V.sub.ex. 
FIG. 12 is a transverse sectional view of the microstrip line forming the 
distributed-constant circuit 1. In the diagram, the thin lines a.sub.1, 
a.sub.2, as, . . . indicate distribution of the magnetic field and the 
thin broken lines b.sub.1, b.sub.2, b.sub.3, . . . indicate distribution 
of the electric field. In this case, the magnetic field is generated in 
the lateral direction of the line conductor 9. Therefore, when the 
magnetic member 2 having its axis of easy magnetization e.a in the lateral 
direction is placed there, the permeability .mu. with respect to the 
lateral magnetic field generated by the microwave can be changed by 
application of the external magnetic field H.sub.ex along the axis of 
difficult magnetization. As a result, the standing-wave ratio and/or the 
standing-wave amplitude .lambda. is changed. 
The detector, i.e., magnetic head, of the above described structure is 
brought into position, as described with reference to FIG. 3, such that 
the load terminal (open terminal) 1a of the microstrip type 
distributed-constant circuit 1 is closely confronted with a magnetic 
recording medium (not shown) so as to detect a leakage magnetic field from 
the record on the magnetic recording medium, i.e., a signal magnetic 
field, as the external magnetic field H.sub.ex. Thus, the magnetic signal 
can be taken out by being converted to an electric signal. 
In this case, the permeability of the magnetic member 2 in the direction of 
its axis of easy magnetization is small when no external magnetic field 
H.sub.ex is applied thereto in the direction perpendicular to its axis of 
easy magnetization, but it gradually increases as the magnetic field in 
the direction perpendicular to the axis of easy magnetization is applied 
thereto and gradually increased. The permeability reaches a maximum at 
around H.sub.ex =Hk, and then it decreases as the magnetic field is 
increased further. 
If the frequency of the high-frequency power source, i.e., the carrier 
frequency f, is set to 1 GHz, for example, and even though the frequency 
of the record signal magnetic field H.sub.ex is set to such a sufficiently 
high frequency as about 100 MHz being one digit lower than the carrier 
frequency, the carrier component can be removed by amplitude-detection by 
means of the rectification circuit 62 and only the change in H.sub.ex can 
be taken out as a voltage change. 
FIG. 13 shows the output voltage V.sub.D of the detector circuit measured 
against changing external magnetic field H.sub.ex under the condition of 
the above described arrangement being applied with no bias magnetic field. 
In this case, in practically detecting the magnetic field from the medium, 
a bias magnetic field application means 11 of an electromagnet or a 
permanent magnet is disposed as shown in FIG. 10 so that the center of 
operation is brought to the point B.sub.1 or B.sub.2 where the 
magnetic-field dependency of V.sub.D is the steepest and good in 
linearity. By providing the bias magnetic field H.sub.B in this way, an 
output with excellent sensitivity and small distortion can be obtained. 
Although the example shown in FIG. 10 was such that the magnetic member 2 
and the line conductor 9 are made in the same pattern, it is not 
necessarily needed to have them made in the same pattern. 
Further, although the magnetic member 2 was of the structure included in 
the waveguide line formed of a microstrip line, the magnetic member 2 can 
be arranged as a portion of, or in place of, the dielectric member 8 when 
the magnetic member 2 has an insulating (dielectric) property, or it can 
be arranged as a portion of, or in place of, the conductor 7 or 9 when it 
has good conductivity. 
Further, although the magnetic member 2 described with reference to FIG. 10 
was made in a strip form and its axis of easy magnetization e.a was set in 
the lateral direction, the orientation of the axis of easy magnetization 
and the intensity of anisotropic magnetic field can be selected according 
to the purpose or manner of its use. 
Further, although the above described examples were of the cases where the 
signal magnetic field from the magnetic recording medium 5 was directly 
applied to the magnetic member 2 of the distributed-constant circuit 1, it 
is also possible to prepare for example a magnetic yoke 12, which is 
formed of a soft magnetic member with high permeability in which a 
magnetic gap g is made as shown in FIG. 14, and dispose the magnetic 
member 2 in the magnetic path of the magnetic yoke 12. 
When the magnetic yoke 12 is arranged as described above and the magnetic 
field to be detected is introduced through the gap g provided therein, the 
degree of freedom in selecting the position, form, and the like of the 
magnetic member 2 is made larger. Hence, the position, form, etc. of the 
magnetic member 2 can be set up so that the electromagnetic field in the 
distributed-constant circuit 1 is most greatly affected by it. Hence, the 
sensitivity can be improved. Further, the efficiency of application of the 
external magnetic field, i.e., the magnetic field to be detected, to the 
magnetic member 2 can be improved, whereby still higher sensitivity can be 
obtained. Especially when the structure is applied to a reproducing 
magnetic head to be arranged opposite to a magnetic recording medium 5, by 
arranging the gap g to be closely confronted with the magnetic recording 
medium 5, the leakage magnetic field from the record magnetization on the 
medium 5, i.e., the record signal magnetic field, can be satisfactorily 
read by it with high resolution and high sensitivity. 
In an example shown in FIG. 15, a magnetic yoke 12 including a magnetic gap 
g is magnetically coupled for example with a distributed-constant circuit 
1 of the microstrip line type waveguide line of the structure described in 
FIG. 10. Parts in FIG. 15 corresponding to those in FIG. 10 and FIG. 14 
are denoted by like reference numerals and explanation of the same will 
therefore be omitted. 
Further, the distributed-constant circuit 1 of the apparatus of the present 
invention can also be structured such that a portion of it is provided by 
a distributed-constant resonator. In such case, as shown in one example in 
FIG. 16, the distributed-constant circuit 1 is constituted of a 
distributed-constant resonator 21 and an external circuit 22. 
The external circuit 22 is formed of a transmission line 10 connecting an 
oscillator 3 with the distributed-constant resonator 21 and a voltmeter 
63, for example, as a detector 6 disposed at a specific point x.sub.1 of 
the transmission line 10. 
Further, a magnetic member 2 whose permeability varies with changes in the 
external magnetic field H.sub.ex, i.e., the magnetic field to be detected, 
is disposed within the distributed-constant resonator 21. 
The magnetic member 2 is disposed for example at such a point where the 
internal magnetic field of the distributed-constant resonator 21 including 
the magnetic member 2 is as strong as possible when it is excited at the 
resonant frequency .omega..sub.0 and where the external magnetic field 
H.sub.ex can be detected most advantageously. 
For example, when a reproducing magnetic head is formed with the above 
described arrangement, the resonator 21 will be disposed on the terminal 
side of the distributed-constant circuit 1 and the magnetic member 2 
within the distributed-constant resonator 21 will be disposed on its 
terminal side and the terminal will be closely confronted with the 
magnetic recording medium 5 so that the signal magnetic field from the 
medium 5 as the magnetic field to be detected, i.e., the external magnetic 
field H.sub.ex, may be applied to the magnetic member 2. 
As a means for structuring the distributed-constant resonator 21, there is 
a method to short-circuit the distributed-constant circuit 1 at the 
boundary between the portion desired to be used as the 
distributed-constant resonator 21 and the portion to be used as the 
external circuit 
The high-frequency permeability .mu. can be divided into a real part 
.mu..sub.r and an imaginary part .mu..sub.i. That is, .mu. can be 
expressed as .mu.=.mu..sub.i +i.mu..sub.r. 
In this case, .mu..sub.r or .mu..sub.i varies with changes in the external 
magnetic field H.sub.ex. 
First, the case where the variation of the real part of permeability 
.mu..sub.r is utilized will be considered. Suppose now that the resonant 
frequency of the distributed-constant resonator 21 is .omega..sub.0 when 
H.sub.ex =0 and the resonator is in a resonant state at the resonant 
frequency .omega..sub.0 provided by the oscillator 3, in which the voltage 
distribution is as indicated by the curve a.sub.0 in FIG. 17A. Then, if 
the external magnetic field is changed and the real part .mu..sub.r of the 
permeability .mu. of the magnetic member 2 is varied under an external 
magnetic field H.sub.ex =H, the resonant frequency will deviate from 
.omega..sub.0 and therefore the resonator 21 will stop resonating, and the 
voltage distribution will be changed and become as indicated by the curve 
a.sub.ex in FIG. 17B. Therefore, if the point x.sub.1 for voltage 
detection, i.e., for voltage rectification, is set up at the position 
where the voltage is at its maximum value in the distribution under the 
condition of H.sub.ex =0 in FIG. 17A, the voltage at the point x.sub.1 
will be lowered upon application of the magnetic field H.sub.ex. Thus, 
detection of H.sub.ex, for example detection of a signal magnetic field 
from record on a magnetic recording medium 5, that is, reproduction, can 
be achieved. 
In the above case, the lower the loss in the distributed-constant circuit 
is and the smaller the electromagnetic coupling between the external 
circuit 22 and the distributed-constant resonator 21 is, the higher 
becomes Q of the distributed-constant resonator 21, and the higher Q of 
the resonator 21 is, the greater becomes the variation in the voltage due 
to the change in H.sub.ex. 
In the above described example, the distributed-constant resonator 21 was 
arranged to be resonant when H.sub.ex =0 and to go out of resonant 
frequency when H.sub.ex =H. It is also possible to arrange such that the 
resonator, conversely, becomes resonant when H.sub.ex =H and goes out of 
resonant frequency when H.sub.ex =0. 
A case where variation of the imaginary part .mu..sub.i of the permeability 
.mu. of the magnetic member 2 with changes in the external magnetic field 
is utilized will be described below. 
In this case, a change of the value Q of the resonator 21 on account of the 
change in the loss component of the resonator 21 due to the variation in 
.mu..sub.i is utilized. Supposing, for example, that the value Q is at its 
high level when H.sub.ex =0 as shown by the curve 181 in FIG. 18, if the 
frequency from the oscillator 3 is changed to .omega..sub.1 deviated from 
its resonant frequency .omega..sub.0, a non-resonant state as shown in 
FIG. 19A is brought about. However, if the value Q is lowered, for 
example, as shown by the curve 182 in FIG. 18 due to a variation in 
.mu..sub.i when H.sub.ex becomes H.sub.ex =H, then, resonance as shown in 
FIG. 19B occurs even at the exciting frequency .omega..sub.1. Therefore, 
it becomes possible to detect the external magnetic field H.sub.ex by 
detecting for example the change in voltage at the specific point x.sub.1. 
Although changes of the real part .mu..sub.r and the imaginary part 
.mu..sub.i of the permeability .mu. of the magnetic member 2 were 
independently treated in the foregoing, it is also possible to arrange 
such that both the changes are produced at the same time and a synergistic 
voltage change is produced for example at a specific point x.sub.1 to 
thereby improve the sensitivity further. 
In the examples described above with reference to FIG. 16 etc., the 
magnetic member 2 can also be arranged to have the structure coupled with 
a magnetic yoke 12 as described for example in FIG. 14. 
While, as described above, the distributed-constant circuit type magnetic 
field detector according to the present invention can be formed into a 
reproducing magnetic head for reading a record signal on a magnetic 
recording medium 5, such as a magnetic tape, a magnetic sheet, and a 
magnetic disk, the same can further be formed into a recording and 
reproducing magnetic head by adding it a recording head function of an 
electromagnetic inductive type. 
An example of adding a function of an electromagnetic inductive recording 
head to a reproducing head of a microstrip line type, for example, will be 
described with reference to a side view of FIG. 20A and a plan view of 
FIG. 20B. In this example, the above described magnetic member 2 of a soft 
magnetic material whose permeability varies with changes in the applied 
magnetic field is disposed on a ground conductor 7 made of Cu. Then, a 
magnetic yoke 12 for example of magnetic ferrite coupled with the magnetic 
member 2 or that using the magnetic member 2 as its constituent, or that 
as a whole structured of the magnetic member 2 is provided. 
The magnetic yoke 12 forms a magnetic yoke 12 (magnetic core) of a C-shaped 
or U-shaped thin film with a magnetic gap g provided at its end portion. 
On the magnetic yoke 12, there is disposed a line conductor 9 of a layer 
of Au, Cu, or the like shaped in a linear form as shown in the plan view 
of FIG. 20B or arranged in conformity with the pattern of the magnetic 
yoke 12 as shown in FIG. 21, such that a microstrip line is formed of the 
conductors 9 and 7. In this case, it is preferred that the microstrip line 
is short-circuited at the portion close to the gap where the magnetic 
field from the medium is at its maximum intensity. Further, the magnetic 
yoke 12 is provided with a head winding 24, i.e., an electromagnetic 
induction winding. 
When the magnetic yoke 12 is conductive in the above described arrangement, 
an insulating layer 23 of SiO.sub.2 or the like is interposed between the 
yoke 12 and each of the conductors 7 and 9. 
In this arrangement, in making magnetic record on a magnetic recording 
medium 5, a current corresponding to a record signal from a recording 
signal source 25 is supplied to the head winding 24, under the condition 
of no high-frequency current being supplied from the oscillator 3, so that 
magnetic flux is generated in the magnetic yoke and the record magnetic 
field is produced from the magnetic gap g, and thereby, the magnetic 
recording is made on the magnetic recording medium 5 arranged before the 
same in contact or confrontation with it. 
In reading the record, the waveguide line is excited by means of the 
oscillator 3. Under this condition, the leakage magnetic flux of record 
magnetization from the magnetic recording medium 5 is given to the 
magnetic member 2 constituting the magnetic yoke 12 or a part of it 
through the gap g. Then, since the state of oscillation in the waveguide 
line is changed by a variation in permeability of the magnetic member 2, 
detection of the magnetic field, hence, reading of the record on the 
magnetic recording medium, i.e., reproduction, can be achieved by 
performing for example voltage rectification or phase detection at a 
specific point of the waveguide line or transmission line using a 
detecting or measuring device 6 as described above. 
Also in this case, the sensitivity can be improved by forming a portion of 
the microstrip line into a distributed-constant resonator or the like as 
described above. 
Another example of the present invention applied to a recording and 
reproducing head will be described below. In this example, the apparatus 
is formed with a ring resonator as shown in a plan view and a side view of 
FIGS. 22A and 22B, wherein a portion of a dielectric member 85 in an 
ordinary ring resonator is arranged by a ring-shaped magnetic yoke 12. 
In this case, a microstrip line 30 is formed of a ground conductor 7 with a 
large area with a line conductor 9 in a strip form provided on a portion 
thereof with a dielectric member 85 interposed therebetween. At another 
portion of the ground conductor 7, there is provided a ring-shaped 
thin-film magnetic yoke 12 (magnetic core) at least a portion of which is 
formed of a magnetic member 2 whose permeability varies with changes in 
the applied magnetic field and which is provided with a gap g, and, 
further, a line conductor 29 in a ring shape is formed thereon along the 
ring of the magnetic yoke 12, and thereby a ring resonator 31 is formed. 
If, in this case, the magnetic yoke 12 is conductive, an insulating layer 
23 is interposed between the magnetic yoke 12 and each of the conductors 7 
and 29. Although the conductors 9 and 29 are patterns separated from each 
other, they are, so to say, in capacitive coupling with each other. 
The magnetic yoke 12 is provided with a head winding 24 round it. 
Also in the magnetic head of the above described arrangement, in recording, 
a record signal current is supplied to the head winding 24 from a record 
signal source 25, with the microstrip line 30 and the ring-shaped 
resonator 31 not excited, so that magnetic flux is passed through the 
magnetic yoke 12 and a magnetic recording medium 5 is magnetized for 
making record by the magnetic field from the gap g closely confronted with 
the magnetic recording medium 5. 
In reproduction, the ring resonator 31 is excited by the oscillator 3 
through the microstrip line 30 and the permeability of the magnetic member 
2 is varied according to signal magnetic flux from the record on the 
magnetic recording medium 5 introduced therein through the magnetic gap g, 
whereby the resonant characteristics of the resonator are changed. Then, 
for example a change in the voltage distribution depending on the change 
in the resonant frequency or change in Q, for example, is detected at a 
specific point, for example of the microstrip line or transmission line 8 
as described with reference to FIG. 16 to FIG. 19. 
The size of the ring resonator 31 is determined depending on whether the 
variation in the real part .mu..sub.r or that in the imaginary part 
.mu..sub.i of the permeability .mu. of the magnetic member 2 is utilized. 
More specifically, when the variation in the real part .mu..sub.r is 
utilized, since the resonant wavelength itself is changed by the signal 
magnetic flux, in order that the resonator resonates under the condition 
of no magnetic flux applied thereto, the circumferential length L is set 
to L=.lambda.g/2, where the resonant wavelength is .lambda.g. 
When the variation in the imaginary part .mu..sub.i is utilized, the value 
Q of the resonator is changed upon application of the signal magnetic 
flux. Hence, in the case where Q is lowered upon application of the 
magnetic flux, in order that no resonance takes place in the state where 
the value Q is high when no signal magnetic flux is applied but a 
resonance takes place when the value Q is lowered with a magnetic flux 
applied, as described with reference to FIG. 18, the circumferential 
length L is set to be slightly deviated from the resonant wavelength 
.lambda.g, i.e., L=(.lambda.g/2)+.DELTA.L. In this case, instead of 
changing the length L, a method to set the frequency slightly shifted from 
the resonant frequency may be used. 
In the apparatus of the present invention, a coaxial cable arrangement can 
also be employed. An example of such arrangement similarly applied to a 
recording and reproducing magnetic head is shown in FIG. 23. FIG. 23 is a 
schematic perspective view of the example. 
In this case, a distributed-constant circuit 1 of a coaxial cable type 
comprises a center conductor 32, and a dielectric member 38 and a ground 
conductor 33 provided around the center conductor coaxially therewith. The 
terminal portion of the distributed-constant circuit 1 is for example 
short-circuited. 
When the coaxial cable type distributed-constant circuit 1 is excited by an 
oscillator 3, there are produced an electric field in the radial direction 
as indicated by arrows in dotted line in FIG. 24 and a magnetic field in a 
circular direction as indicated by arrows in solid line. As the 
permeability in the circular direction is varied, the electromagnetic 
field distribution within the coaxial cable type distributed-constant 
circuit 1 changes. 
Meanwhile, as the coaxial cable type distributed-constant circuit 1 with 
its terminal short-circuited as described above is excited by the 
oscillator 3, a standing wave is produced as shown in the electromagnetic 
field distribution along the axis in FIG. 25. The solid line in FIG. 25 
indicates the electric field distribution and the dotted line indicates 
the magnetic field distribution. A magnetic member 2 whose permeability 
varies with changes in magnetic field is disposed in the position where 
the electric field distribution has its minimum value (namely, the 
position of node), i.e., the position where the magnetic field 
distribution has its maximum value (namely, the position of loop) as shown 
in FIG. 25 as well as in FIG. 23 and a transverse sectional view of the 
distributed-constant circuit 1 of FIG. 26. 
The magnetic member 2 is made in a ring-shaped plate form disposed between 
the center conductor 32 and the ground conductor 33 surrounding it, with 
its planar direction cutting the center conductor 32 at right angle and 
provided with a magnetic gap g cut at a portion of it in the radial 
direction. 
The magnetic gap g faces outward through a window made at a portion of the 
ground conductor 33 and is adapted to be closely confronted with a 
magnetic recording medium 5. 
The magnetic member 2 can be formed of a ring-shaped CoTaZr plate as 
described above or provided by depositing a CoTaZr thin film on an 
insulating substrate. 
When the magnetic member 2 has conductivity, an insulating layer 23 is 
interposed between the magnetic member 2 and each of the conductors 32 and 
33 as shown in FIG. 26. 
While the peripheral ground conductor 33 is provided a window 34 made 
therein, the size of the window 34 can be made small enough as compared 
with the wavelength of the electromagnetic field exciting the 
distributed-constant circuit 1, and therefore, the effect of the window 34 
on the excitation condition is negligible. 
Recording and reproducing operations of the magnetic head of the above 
described structure on a magnetic recording medium will now be described. 
In the recording, a current corresponding to the record signal at a 
frequency on the order for example of 10 MHz from a record signal source 
25 is passed for example between the center conductor 32 and the ground 
conductor 33, with the distributed-constant circuit 1 not excited, so that 
magnetic flux is generated in the ring-shaped magnetic member 2 and a 
record magnetic field is generated from its magnetic gap g, and the record 
is made, through the window 34, on the magnetic recording medium 5 closely 
confronted with the gap. 
In the reproduction, the recording signal source 25 is cut off from the 
distributed-constant circuit 1, the distributed-constant circuit 1 is 
excited by the oscillator 3 as described in FIG. 25, and the magnetic gap 
g is brought to be closely confronted with the magnetic recording medium 
5. Then, a magnetic field according to magnetization of the record signal 
on the magnetic medium 5 is applied from the magnetic gap g to the 
magnetic member 2, causing its permeability to vary. Thereby, the circular 
electromagnetic field in the distributed-constant circuit 1 is affected 
and the standing wave ratio, amplitude, etc. are changed. Then, by 
rectifying the voltage, for example, at a specific point of the 
transmission line 10, as shown in FIG. 23, or of the distributed-constant 
circuit 1, to thereby detect or measure a change in voltage, reading of 
the record signal on the magnetic recording medium 5, i.e., reproduction, 
can be achieved. 
FIG. 27 is a perspective view of another example of the 
distributed-constant circuit type magnetic field detector of the present 
invention applied to a magnetic reproducing head. In this case, a coplanar 
waveguide line is used as the microwave waveguide line. The apparatus in 
the present example comprises a coplanar waveguide line 70 being 
short-circuited at its terminal and having a thin film magnetic member 2 
whose permeability varies with signal magnetic flux penetrating thereto, a 
microwave source, i.e., an oscillator 3, a rectification diode 71, and a 
voltmeter 63. 
The rectification diode 71 is covered with an insulating material and 
enclosed by a grounded shielding conductor. 
The coplanar waveguide line 70 is a type of microwave waveguide line and 
formed, as shown in FIG. 27, with a dielectric member 8 having good 
conductive layers of Au, Cu, or the like deposited thereon by patterning 
such that one layer serves as a line conductor 9 and the other layers on 
both sides thereof serve as ground conductors 7. 
FIG. 28A is a top view of the coplanar waveguide line 70 shown in FIG. 27, 
and FIG. 28B and FIG. 28C are sectional views taken along broken lines b 
and c in FIG. 27. 
In front of the terminal portion of the waveguide line 70 where the 
magnetic member 2 is provided, there is arranged a magnetic recording 
medium 5, from which a record signal is to be read out, so as to move in 
the direction indicated by the arrow d in sliding contact with or slightly 
separated from the terminal portion. 
When a microwave is injected into the coplanar waveguide line 70 from the 
oscillator 3, the microwave is reflected by the short-circuited terminal 
portion and, as a result, a standing wave as shown in FIG. 29 is produced 
through interference between the progressive wave and the reflected wave. 
At that time, denoting the lateral direction of the conductor 9 by W1 and 
the longitudinal direction by L1, a magnetic field of the microwave is 
generated in the direction W1 around the line conductor 9, and therefore, 
the reflection coefficient at the terminal portion is determined dependent 
on the permeability of the thin film magnetic member 2 in the direction 
W1. When the magnetic member 2 is provided with such magnetic anisotropy 
that the axis of easy magnetization is aligned with the direction W1, the 
magnetization changes its orientation from the direction W1 to the 
direction L1 as the signal magnetic flux is injected into the same. As a 
result the permeability in the direction W1 varies, and thus, the 
permeability can be greatly varied by a slight change in magnetic flux. 
FIG. 30 is a diagram showing results of measurement of the input impedance 
of the coplanar waveguide type magnetic reproducing head shown in FIG. 27 
obtained by connecting the head to a network analyzer (HP8719A made by 
Hewlett-Packard Corp.). The range of frequencies at which the measurement 
was made was from 130 MHZ to 5 GHz. The broken line indicates the results 
when no external magnetic field is applied and the solid line indicates 
when an external magnetic field of 80 A/m is applied. Considerable changes 
in the input impedance (reflection coefficient) upon application of the 
external magnetic field are observed at the frequencies from 2.5 GHz to 
4.5 GHz. It is generally considered that the permeability of magnetic 
materials sharply decreases in the high-frequency range and shows a very 
small value in the frequency range of several GHz. But, the results of 
measurement shown in FIG. 30 indicate that there is a frequency range 
within a high-frequency domain over 1 GHz where the permeability greatly 
varies under the application of external magnetic field. Hence, by 
utilizing the variation in the permeability in such frequency region, the 
operating frequencies can be set to 1-10 GHz. 
As a result of a change in the reflection coefficient at the terminal 
portion of the coplanar waveguide line 70, there are produced a change in 
the phase of the standing wave as shown in FIG. 31A and/or a change in the 
standing wave ratio as shown in FIG. 31B. By performing 
amplitude-detection of voltage by means of the diode 71 disposed in the 
vicinity of a node of the standing wave where the voltage amplitude of the 
standing wave in the coplanar waveguide line 70 shows its greatest change 
as shown in FIG. 27, the change in the signal flux can be detected as the 
greatest voltage change and the record signal can thereby be reproduced. 
In the above described arrangement, by providing a coil 92 around the 
terminal portion of the coplanar waveguide line as shown in FIG. 41 and 
passing a current therethrough, it is achieved to apply a bias magnetic 
field to the magnetic member 2 shown, for example, in FIG. 28a in the 
direction L1, and thereby, a performance excellent in sensitivity and 
linearity as described earlier can be obtained. 
Further, when the magnetic member 2 is provided with magnetic anisotropy 
having the axis of easy magnetization oriented in the direction L1, a 
required D.C. bias current may be applied between the line conductor 9 and 
the ground conductor 7. Then, by the current flow in the direction L1 
through the line conductor 9 where the magnetic member 2 is disposed, a 
bias magnetic field perpendicular to it is applied to the magnetic member 
2 in its lateral direction W1. Also by this means, a performance excellent 
in sensitivity and linearity can be obtained. 
However, in the case where a coplanar waveguide line 70 is used for the 
microwave waveguide line as described above, the line of the 
short-circuited portion of the line conductor 9 and the ground conductor 7 
at the terminal of the coplanar waveguide line 70 where the magnetic 
member 2 receives the strongest signal magnetic flux from the medium is 
divided into two directions. Hence, the magnetic field component of the 
microwave at this portion comes to deviate from its state uniformly 
aligned in the lateral direction of the line conductor 9. As a result, the 
change in the characteristic impedance of the waveguide line 70 exhibited 
when the permeability of the thin film magnetic member 2 is varied by the 
penetration of the signal flux becomes smaller. As the record wavelength 
from the medium 5 is decreased, the distance in the direction of the 
magnetic member 2 reachable by the signal magnetic flux becomes shorter, 
and when the reachable distance becomes virtually equal to the width of 
the short-circuiting line, the sensitivity sharply drops. Accordingly, the 
width of the short-circuiting line must be set below the record 
wavelength, but when it is made extremely narrow, electric resistance 
increases, lost increases, and sensitivity lowers. 
Such problem can be overcome by arranging the magnetic member 2 at the 
short-circuiting line portion 79 of the coplanar waveguide line 70 as 
shown in FIG. 32. In this case, around the short-circuiting line 79 in 
FIG. 32, the magnetic field is generated in the lateral direction of the 
short-circuiting line 79, i.e., in the direction L1, and therefore, the 
reflection coefficient depends on the permeability in the lateral 
direction of the magnetic member 2. When the permeability of the magnetic 
thin film in the above described arrangement is varied by penetration of 
the signal magnetic flux from the medium, the reflection coefficient at 
the terminal portion changes. At this time, if the magnetic member 2 is 
provided with such magnetic anisotropy that its axis of easy magnetization 
is in the direction W1, the magnetization changes its orientation from the 
direction W1 to the direction L1 upon penetration of the signal magnetic 
flux, whereby the permeability in the direction L1 is effectively varied. 
Further, in this case, by passing a D.C. bias current between the ground 
conductors 7 having the line conductor 9 in between, i.e., through the 
short-circuiting line 79, to thereby apply a required bias magnetic field 
to the magnetic member 2 in its lateral direction (the direction 
perpendicular to the direction W1), the condition for obtaining excellent 
sensitivity and linearity as described above can be set up. 
When the magnetic member 2 is disposed at the short-circuiting line portion 
79 as described above, a coplanar line 90 with its terminal portion 
short-circuited as shown in FIG. 33 can be used as the microwave waveguide 
line. FIG. 33A is a plan view of the coplanar line 90, and FIG. 33B and 
FIG. 33C are sectional views taken along line B--B and line C--C in FIG. 
33A. In this case, as shown in FIG. 33, there are provided, by patterning 
of good conductor, two line conductors spaced a predetermined distance 
apart, of which one line is serving as a ground conductor 7. Since the 
magnetic field is generated in the lateral direction (direction L2) of the 
short-circuiting line 79, the reflection coefficient depends on the 
permeability of the magnetic member 2 in the direction L2. If the magnetic 
anisotropy is provided for the magnetic member 2 such that its axis of 
easy magnetization is in the direction W2, the magnetization changes its 
orientation from the direction W2 to the direction L2 upon penetration of 
the signal magnetic flux, whereby the permeability in the direction L2 is 
varied. Further, by passing a required D.C. bias current between the line 
conductor 9 and the ground conductor 7, hence through the short-circuiting 
line 79, the magnetic member 2 can be provided with a bias magnetic field 
in the direction L2. 
In actual fabrication of a coplanar microwave waveguide type magnetic 
reproducing head as shown for example in FIG. 27, the coplanar waveguide 
line 70 is fabricated by dividing it, for example, into a 
magneto-sensitive portion 701 and a rectification portion 702 as shown in 
FIG. 34. 
The magneto-sensitive portion 701 was fabricated in the following way. In 
this case, a glass substrate was used as the dielectric member 8 shown in 
FIG. 27. On the substrate, an amorphous magnetic thin film of Co.sub.75 
Ta.sub.11 Zr.sub.14 was deposited to a thickness of D1=0.5 .mu.m by 
sputtering and then the substrate was heat treated under a temperature of 
300.degree. C. and a magnetic field of 80.times.10.sup.3 A/m, whereby the 
magnetic thin film was provided with magnetic anisotropy around H.sub.K 
=160 A/m. Then, the same was subjected to patterning by a photo process, 
i.e., photolithography, into a form 30 .mu.m wide and 100 .mu.m long 
having the axis of easy magnetization aligned with the lateral direction. 
Then, to form a coplanar waveguide line 70 thereon, Cr was sputtered to 
the entire surface to a thickness of around 50 nm and then, over the same, 
Au was sputtered to a thickness of 1 .mu.m. The Cr film is formed to 
obtain a good bond between the glass substrate as the dielectric member 
and Au. Then, over the same, a line conductor 9 and ground conductors 7 
were formed by a photo process such that the magnetic member 2 underlies 
the terminal portion of the line conductor 9, as shown in an enlarged plan 
view of FIG. 34, and the line conductor 9 is 30 .mu.m wide, the line 
conductor 9 and the ground conductor 7 are spaced a distance of 10 .mu.m 
apart, the ground conductor 7 is 5 mm wide, the short-circuiting line 9 is 
30 .mu.m wide, and the waveguide line is 15 mm long. Further, a cover 
glass 8' (dielectric member) was bonded onto the same. At this time the 
input terminal portion of the coplanar waveguide line 70, which is 
necessary for wire bonding, was left uncovered with the cover glass 8'. 
The product is cut along the waveguide line pattern using a diamond 
cutter. Then, the glass at the terminal portion, as shown in a further 
enlarged view of the terminal portion of FIG. 35, was ground with a 
grinding film so that the front end of the magnetic thin film may smoothly 
contact with a magnetic recording medium when the portion is brought into 
contact with the magnetic recording medium in magnetic reproduction, and 
thus the magneto-sensitive portion 701 was fabricated. 
Then, in fabricating the rectification portion 702, Cr was deposited onto a 
glass substrate 8 to a thickness of 50 nm by sputtering, and over the 
same, Au was deposited to a thickness of 1 .mu.m, and thereafter, as show 
in FIG. 34, a line conductor 9 with a width of 1 mm was formed, a ground 
conductor 7 was formed a distance of 0.33 mm apart from the line conductor 
9, and the waveguide line length was set to 2.0 mm by a photo process. At 
this time, the ratio between the width of the line conductor 9 and the 
distance between the line conductor 9 and the ground conductor 7 was made 
equal to that in the magneto-sensitive portion 701 to obtain equal 
characteristic impedance. Then, the glass substrate 8 of the waveguide 
line was cut along the waveguide line pattern using a diamond cutter. 
Then, as shown in FIG. 36, one terminal of a schottky diode 71 for 
rectification was attached to the ground conductor 7 by conductive paste, 
solder, or the like. At that time, the schottky diode 71 was sheathed with 
a shielding conductor 72, as shown in FIG, 36, formed of an insulating 
layer 80 of an insulating film or the like surrounding the diode and a 
conductive film wound around the same, and the shielding conductor 72 was 
grounded. Thus, penetration of electromagnetic wave into the diode 71 is 
shut off and occurrence of noise is prevented. 
The point at which the diode 71 is connected to the line conductor 9 
depends on the frequency of the introduced microwave and selected to be in 
the vicinity of a node of the standing wave produced. 
Further, as shown in FIG. 34, coaxial connectors 81 and 82 were attached to 
the product. The outer ground conductor of the coaxial connector 82 was 
connected with the ground conductor 7 of the coplanar waveguide line 70 
and the center conductor was connected with the other terminal of the 
diode 71. Thus, the rectification portion 702 was fabricated. 
The magneto-sensitive portion 701 and the rectification portion 702 
fabricated as described above were fixed in a suitable jig and, as shown 
in FIG. 34, the line conductors 9 in the center of both the portions were 
connected by wire bonding 83 and ground conductors 7 of them on both sides 
were connected by a conductive material 84 such as conductive paste or 
solder. 
Instead of connecting the magneto-sensitive portion 701 and the 
rectification portion 702 by wire bonding as described above, a so-called 
taper line as shown in FIG. 37 can be used as the coplanar waveguide line 
70 of the magneto-sensitive portion 701, in which taper line, the width of 
the line conductor 9 and the distance between the line conductor 9 and the 
ground conductor 7 are made to become gradually larger until they become 
equal to those of the rectification portion 702, while keeping the ratio 
between the width of the line conductor 9 and the distance between the 
line conductor 9 and the ground conductor 7 constant so that the 
characteristic impedance is kept unchanged. By using the taper line, the 
loss caused by the wire bonding can be prevented. 
The above fabricating method of the coplanar waveguide line is equally 
applicable to the coplanar line 90 of FIG. 38. When a taper line is used, 
the ratios between the widths of the line conductor 9 and the ground 
conductor 7 and the distance therebetween are maintained constant. 
FIG. 30 described earlier is that showing the results of measurement of the 
input impedance obtained by connecting the coaxial connector 82 of the 
coplanar waveguide line 70 shown in FIG. 34 and FIG. 35 to the network 
analyzer (HP8719A made by Hewlett-Packard Corp.). Since the frequency at 
which the reflection coefficient, i.e., the permeability of the magnetic 
member 2, changes upon application of an external magnetic field H.sub.ex 
differs with the magnetic characteristic and magnetic material of the 
magnetic member 2, the frequency of the microwave used must be selected 
according to such factors. 
FIG. 39 shows dependency on magnetic field of the output voltage at the 
connector 82 rectified by the rectification diode 71 in the state where an 
oscillator 3 of a microwave source is connected to the coaxial connector 
81 of FIG. 34 and FIG. 35 through a coaxial cable and a microwave at 
around a frequency of 3.6 GHz is input to the waveguide line. A change in 
the output voltage around 30 mV was observed upon application of a 
magnetic field around 100 A/m. 
Further, reproduction of a signal recorded on a magnetic tape, i.e., a 
magnetic recording medium 5, was performed according to a method shown in 
FIG. 40. First, a sine wave signal of 0.1 MHz was recorded on a magnetic 
recording medium 5 (magnetic tape) for VTR using an ordinary ring-shaped 
inductive magnetic head. The same as in the measurement in FIG. 39, a 
microwave at the frequency 3.6 GHz from an oscillator 3 is input to the 
waveguide line. At this time, a magnetic field (.apprxeq.30 A/m), which 
corresponds to the point where the rate of change in the output voltage to 
the change in the magnetic field, dV/dH, is at its maximum in FIG. 39, is 
applied to the thin film magnetic member 2 at the terminal portion as a 
bias magnetic field. The application of the bias magnetic field is 
achieved by providing a coil 92 as shown in the enlarged view of the 
terminal portion of the reproducing head in FIG. 41 and passing a current 
from a bias power source 93 or by arranging a permanent magnet in the 
vicinity of the terminal portion. In the case where a coplanar waveguide 
line is used and a magnetic member is arranged as described in FIG. 32, or 
where a coplanar line as shown in FIG. 33 is used, the bias magnetic field 
can be supplied by passing D.C. current to the coplanar waveguide line or 
the coplanar line. In the above described state, the magnetic member 2 at 
the terminal of the head was arranged to be in contact with the magnetic 
tape for VTR and the voltage rectified by the diode 71 was detected by an 
oscilloscope 94. The results are shown in FIG. 42. As apparent from it, an 
output of 20 mV p--p, two digits or so larger than obtained by an ordinary 
inductive head or an MR head, was obtained. Referring to FIG. 40, 
reference numeral 95 denotes a guide drum of a magnetic recording medium 
5, i.e., of a magnetic tape in the present example, and 96 denotes its 
rotational driving motor. 
The magnetic field detector according to the present invention is not 
limited to the above illustrated examples but various changes and 
modifications can be made according to the purposes of use and manners of 
use. For example, the above described resonator type arrangement can be 
modified to a filter type arrangement which performs magnetic field 
detection by measuring the transmission coefficient of a microwave. 
Further, the present invention can be applied not only to reproducing 
magnetic heads but also to so-called magnetic sensors for various 
purposes. 
According to the apparatus of the present invention, a magnetic member 2 is 
disposed in various types of distributed-constant circuits 1 and voltage, 
phase, or the like is arranged to be detected at a specific point in the 
transmission line, distributed-constant circuit, etc. by utilizing a 
change in standing wave, progressive wave, or the like due to a variation 
in the permeability .mu. of the magnetic member 2 caused by a magnetic 
field to be detected. Therefore, detection with high sensitivity can be 
achieved. 
The apparatus of the present invention, when applied to a reproducing 
magnetic head for reading a signal magnetic field from a magnetic 
recording medium according to recorded information, can achieve 
reproduction regardless of the relative speed between the head and the 
magnetic recording medium, the same as done by an MR magnetic head, and 
with higher sensitivity than that of the MR magnetic head. 
Since the apparatus is arranged in a distributed-constant circuit type, 
i.e., in a microwave waveguide type, the carrier frequency can be 
increased to several hundred MHz or even to the order of GHz. Therefore, a 
high frequency can be used as the recording frequency on the magnetic 
recording medium. Because of this and that the performance is independent 
of the relative speed between the head and the magnetic recording medium, 
recording with higher packing density than before can be achieved. 
More specifically, since the magnetic reproducing head of the present 
invention is of a type sensitive to magnetic-flux, its performance is not 
dependent on the relative speed between the head and the magnetic 
recording medium, and therefore, even if the recording density is 
increased, the decrease in reproduced output power is less than that with 
the inductive magnetic head. Further, as compared with the MR head which 
is also of a magnetic-flux sensitive type, since there is no need to pass 
a current through the magnetic member 2 directly in the head of the 
present invention, it is possible to input larger power thereto and, 
therefore, to obtain larger reproduced output power therefrom than from 
the MR head. Further, since high frequency magnetic field is applied to 
the magnetic member 2 at all times in the present invention, it can be 
expected that magnetic domains in the thin film are smoothly moved by the 
signal flux and, hence, Barkhausen noise hardly occurs and S/N ratio is 
improved. 
Further, when compared with a magnetic reproducing head of the type making 
use of a change in the resonance characteristic of a coil by application 
of an external magnetic field, because the arrangement of the present 
invention utilizes the variation in the permeability of the magnetic 
member 2 in a still higher frequency domain (a domain of several GHz) and 
is adapted to be a distributed-constant circuit, it has advantages as 
described below: 
(1) In a distributed-constant circuit, spatial distribution of the 
electromagnetic wave (microwave) exited therein is greatly changed with a 
small variation in the permeability, and hence a great voltage change can 
be obtained. 
(2) Quantitatively accurate design with high frequency becomes possible, 
and it can be achieved to reduce losses such as a radiation loss and to 
effectively convert a variation in the permeability by a change in signal 
flux into a voltage change. 
(3) By adopting the method to detect a change of a standing wave, not only 
a change in the amplitude of a microwave but also a change in the phase 
can be simultaneously detected as change in voltage and, hence, the 
sensitivity can be greatly improved. 
(4) When frequency is high, wavelength becomes smaller in inverse 
proportion to the frequency, and hence, the phase of a microwave is 
greatly affected by a variation in the permeability and, accordingly, high 
sensitivity can be obtained. 
(5) Since the carrier frequency can be increased and the signal magnetic 
flux from the medium is of the modulating signal of the carrier, a signal 
of higher frequency can be reproduced. 
Thus, the present invention makes it possible to perform magnetic 
reproduction, i.e., magnetic field detection, with high sensitivity and 
excellent high-frequency characteristics, and when applied to a magnetic 
reproducing head, it can effectively meet the demand for higher packing 
density of magnetic record and higher frequency magnetic recording.