US3789234A

US3789234A - Magnetic sensor using a parametrically excited second harmonic oscillator

Info

Publication number: US3789234A
Application number: US00298008A
Authority: US
Inventors: T Watanabe; T Fukui; S Suzuki
Original assignee: Kokusai Denshin Denwa KK
Current assignee: KDDI Corp
Priority date: 1971-10-18
Filing date: 1972-10-16
Publication date: 1974-01-29
Anticipated expiration: 1991-01-29
Also published as: DE2251110A1; DE2251110B2; JPS547205B2; JPS4847812A; DE2251110C3

Abstract

A magnetic sensor using a parametrically excited second harmonic oscillator for detecting a minute magnetic field by utilizing a change in the phase of the second harmonic of the oscillator in accordance with the direction of an external magnetic field. At least three inductance elements each formed with a magnetic wire member and its winding are employed for forming the parametrically excited second harmonic oscillator, one of the three inductance elements being a main element and the others auxiliary elements, the auxiliary elements being disposed about the main element. The windings of the elements being interconnected in series in such a manner that when the same exciting voltage is applied to the magnetic members a magnetic field established by a second harmonic current flowing in the winding of the main element and a magnetic field by the second harmonic current flowing in the winding of each auxiliary element may be opposite in direction to each other, so that a sensitivity characteristic against an external magnetic field is made extremely sharp with respect to a head portion of one end of the main element.

Description

United States Patent 1191 Watanabe et al.

[ Jan. 29, 1974 1 1 MAGNETIC SENSOR USING A PARAMETRICALLY EXCITED SECOND HARMONIC OSCILLATOR [75] Inventors: Teruji Watanabe, Niza; Takasuke Fukui, Tokyo; Shizuo Suzuki, Kawasaki, all of Japan [73] Assignee: Kokusai Denshin Denwa Kabushiki Kaisha, Tokyo, Japan [22] Filed: Oct. 16, 1972 [21] Appl. No.: 298,008

[30] Foreign Application Priority Data Primary Examiner-James W. Moffitt Attorney, Agent, or Firm-Robert E. Burns; Emmanuel J. Lobato [5 7] ABSTRACT A magnetic sensor using a parametrically excited second harmonic oscillator for detecting a minute magnetic field by utilizing a change in the phase of the second harmonic of the oscillator in accordance with the direction of an external magnetic field. At least three inductance elements each formed with a magnetic wire member and its winding are employed for forming the parametrically excited second harmonic oscillator, one of the three inductance elements being a main element and the others auxiliary elements, the auxiliary elements being disposed about the main element. The windings of the elements being interconnected in series in such a manner that when the same exciting voltage is applied to the magnetic members a magnetic field established by a second harmonic current flowing in the winding of the main element and a magnetic field by the second harmonic current flowing in the winding of each auxiliary element may be opposite in direction to each other, so that a sensitivity characteristic against an external magnetic field is made extremely sharp with respect to a head portion of one end of the main element.

5 Claims, 19 Drawing Figures PATENTED JAN 2 9 I974 SHEET 1 BF 4 PRIOR AR 7 PR] OR AR T PATENTEI] JAN 2 91974 SHEET 3 BF 4 Fig. 5F

PATENTED 3, 789,234

sum u 0F 4 MAGNETIC SENSOR USING A PARAMETRICALLY EXCITED SECOND HARMONIC OSCILLATOR This invention relates to a magnetic sensor in which a parametrically excited second harmonic oscillator is formed with a magnetic wire member having a magnetic film disposed on a conductor so that a small magnetic field is detected by a change in the oscillation phase of the second harmonic oscillator.

Conventional magnetic sensors of the type, such as disclosed in Japanese Pat. No. 45-10031, have a defect that a narrow sensing beam characteristic is difficult to obtain because of their construction.

An object of this invention is to provide a magnetic sensor using a parametrically excited second harmonic oscillator, which provides an extremely narrow sensing characteristic.

To attain the above object of this invention, a magnetic sensor using a parametrically excited second harmonic oscillator is provided in which at least one inductance element is formed with a magnetic wire member having a magnetic film deposited on a conductor and a winding wound thereon; in which a capacitor is connected in parallel with the winding to constitute a resonance circuit; and in which an AC exciting current is applied to the magnetic wire member to produce a second harmonic of the exciting current in the resonance circuit; whereby a minute magnetic field is detected by utilizing a change in the phase of the second harmonic in accordance with the direction of an external magnetic field.

In accordance with the principle of this invention, at least three inductance elements each formed with a magnetic wire member and its winding are employed, one of the three inductance elements being a main element and the others auxiliary elements; the auxiliary elements being disposed about the main element; and the windings of the elements being interconnected in series in such a manner that when the same exciting voltage is applied to the magnetic members a magnetic field established by a second harmonic current flowing in the winding of the main element and a magnetic field by the second harmonic current flowing in the winding of each auxiliary element may be opposite in direction to each other, whereby a sensitivity characteristic against an external magnetic field is made extremely sharp with respect to a head portion of one end of the main element.

The principle, construction and operations of this invention will be understood from the following detailed discussion taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a diagram showing the construction of a conventional parametric magnetic sensor;

FIG. 2 is a diagram illustrating the construction of a conventional parametric magnetic sensor of differential type designed to avoid the influence of an external uniform magnetic field;

FIGS. 3A, 33, 4A, 4B and 4C are diagrams showing examples of this invention and their magnetic sensitivity distribution curves;

FIGS. 5A to 5G, 6A to 6C and 7 are diagrams illustrating other examples of this invention constructed in the form of modules respectively; and

FIG. 8 is a characteristic diagram showing experimental examples of the magnetic sensitivity distribution curves of the parametric magnetic sensors of this invention and the prior art respectively.

For clearly describing the difference between the conventional arts and this invention, conventional devices are previously described.

A conventional device of this kind is constructed as shown in FIG. 1 or 2. FIG. 1 illustrates a single-type magnetic sensor (refer to Japanese Pat. No. 45-10031). Reference numeral 3 indicates a magnetic wire member having a magnetic film deposited on a conductor in such a manner as to have an easy magnetization direction in its circumferential direction, and 4 an oscillation winding wound on the magnetic member 3.

The magnetic member 3 and the winding 4 make up an inductance element L. Reference numerals 1 and la designate exciting terminals, to which an exciting voltage e, ofa frequencyfis applied, 2 and 2a output terminals, and reference character C identifies a capacitor connected in parallel with the winding 4. The inductance element L and the capacitor C constitute a resonance circuit of a frequency 2f. Accordingly, if the resonance circuit is excited with the exciting voltage e, between the input terminals 1 and la, a second harmonic voltage 2 is produced between the output ter

minals

2 and 2a.

In this case, if the intensity of magnetic field (for example, a magnetic field from a magnetizer M) acting on a head H which is either one of both ends of the magnetic member 3 is in excess of a certain value, the oscillation phase of the voltage e is dependent on the direction of magnetic flux in the magnetic field. The sensitivity distribution curve of the magnetic sensor in this case is dipole-shaped as indicated by a reference numeral 5 in FIG. 1 but only the half circle on the outside of the head H (on the right of the line YYa) is considered for the sake of brevity.

FIG. 2 shows the construction of a differential type magnetic sensor, which employs an inductance element consisting of

magnetic wire members

3 and 3a and a winding 4 as is the case with the example of FIG. I. The sensitivity distribution curve of this magnetic sensor is substantially semi-circular on the right of the line YYa as indicated by

reference numerals

9 and 9a in FIG. 2, as is the case with the example of FIG. 1, but, at a point 10 between the two

magnetic members

3 and 3a, the action on the

magnetic members

3 and 3a is in equilibrium and sensitivity is the infinitesimal.

For example, if the region 9 is a region in which the oscillation phase reverses from 0" to 1r, the region 9a is that in which the phase reverses from 'n'" to 0". The single type oscillation element of FIG. 1 is subject to the influence of an external uniform magnetic field, whereas the differential type oscillating element of FIG. 2 is adapted to avoid the influence of the external uniform magnetic field. However, either oscillating element has a defect that a narrow sensing beam characteristic is difficult to obtain.

FIG. 3A shows one example of this invention, which employs three inductance elements (hereinafter referred to as elements): the central one is a main element and the others are auxiliary elements and in which the elements are disposed in a two-dimensional plane with the auxiliary elements spaced a suitable distance (D) apart from the main element 9 and one end of the main element is used as a head H. In this case, the winding wound on the main element 9 is positioned as close to the head H as possible and those on the

auxiliary elements

10 and 11 are a suitable distance (d) apart from the head H of the main element 9. The windings of these elements are interconnected in series so that a magnetic field generated by a current flowing in the main element 9 and those in the

auxiliary elements

10 and 11 may be opposite to each other, and a capacitor C is connected in parallel with the seriesconnected windings to constitute an oscillator circuit. Further, no limitation is set on the direction of the exciting current but it is effective for narrowing the beam width if the magnetic wire members of the respective elements are interconnected in series in such a manner that the exciting current flowing in the magnetic wire member of the main element 9 and those flowing in the magnetic wire members of the auxiliary elements 10 and II may be opposite in direction to each other. It is preferred to select the numbers of turns of the winding of each element so that the sum of the number of turns of the windings of the auxiliary elements may be equal to that of the main element.

Various constructions are considered for applying the exciting voltage e, to the magnetic wire members forming the respective elements. For example, it is possible to apply the voltage to the magnetic wire members interconnected in parallel as depicted in FIG. 3B.

In the magnetic sensor thus constructed, if the exciting voltage e,is applied between the

terminals

1 and 1a, the second harmonic voltage e is produced between the

output terminals

2 and 2a in the same manner as that in the prior magnetic sensors described previously. Under such conditions, a second harmonic field by the second harmonic voltage e and an internal DC magnetic field by the second harmonic magnetic field are established in each element but the internal DC magnetic field in the main element 9 and those in the auxiliary elements 10 and l] are reverse in direction from each other. Then, when the magnetizer M is placed in the neighborhood of the head H, if a magnetic field being established by the magnetizer M is large and opposite in direction to the internalDC magnetic field in the main element 9, the oscillation phase of the aforementioned second harmonic voltage reverses from O to 1r or vice versa and the internal DC magnetic field also reverses correspondingly.

Further, in response to the reversal of the oscillation phase of the second harmonic voltage and the internal DC magnetic field in the main element 9, those in the

auxiliary elements

10 and 11 also reverse. It is desirable that the oscillation phase of the second harmonic voltage in each element is restored to its original one when the magnetizer M is moved away from the head H.

Means for restoring the oscillation phase may be, for example, of such a construction that a small magnet is attached to the opposite end of the main element 9 from the head H or that another winding is wound on the main element 9 and supplied with a minute DC cur rent.

If the magnetizer M is moved away from the head H toward the auxiliary element 10, the magnetic fields established by the magnetizer M in the main element 9 and the auxiliary element 10 are in the same direction but the intensity of the field in the element 9 is low, while that in the element 10 is high. In this case, since the internal DC magnetic field and the magnetic field by the magnetizer M in the element 10 are opposite in direction from each other, if the magnetic field by the magnetizer M is appropriately larger than the internal one by the second harmonic voltage, the oscillation phase can be reversed. Thus, the magnetic effect of the magnetizer M acts on the main element 9 and the

auxiliary ones

10 and 11 in reverse directions, so that there exists a point intermediate between the

elements

9 and 10 or 9 and 111 where the magnetic force of the magnetizer M applied to the main element 9 to contribute to the reversal of the oscillation phase is in equilibrium with that applied to the

auxiliary element

10 or 11 to contribute to holding of the oscillation phase. Since this point is independent of the magnitude of the magnetic force of the magnetizer M, the directivity characteristic of the sensitivity distribution curve can be narrowed by decreasing the distances (D) between the main element 9 and the

auxiliary elements

10 and 11. For example, by selecting the diameter of the magnetic wire member of the main element 9 to be 0.5mm and reducing the distances (D) between the main element 9 and the auxiliary elements 10 and I] as short as possible, the sensitivity distribution curve can be made extremely narrow.

FIG. 4A shows another example in which the twodimensional construction of FIG. 3A or 3B is rendered into a three-dimensional one. The operation of this example is the same as that in the case of FIG. 3A or 3B and its detected distribution curve can be expressed in a cubic form such as depicted in FIG. 48. FIG. 4C illustrates the arrangement of the respective elements viewed from a direction Z, that is, from the direction of the head of the main element. FIG. 4A shows an example in which four auxiliary elements are symmetrically arranged about the main element 9 but the num ber of the auxiliary elements is not limited specifically to four but may be two as depicted in FIG. 3A or 3B or more than two. It is sufficient for the purpose to dispose the auxiliary elements along the peripheral surface of a cylinder drawn about the main element and connect their magnetic wire members and windings as described previously in connection with FIGS. 3A, 38, 4A, 4B and 4C.

In order to provide for a further enhanced sharp directivity of the magnetic sensor of FIG. 3A or 33, a magnetic member 20 such as ferrite is provided on the opposite side from the head H as shown to short only the magnetic paths of the respective elements to insulate them as exciting current paths between the elements, by which magnetic flux entering from the head H of the main element 9 is caused to pass through the short-circuit path 20 and return to the head H through a plurality of the

auxiliary elements

10, 11 without leakage from the opposite end of the main element from the head, thereby to improve the directivity characteristic of the magnetic sensor.

FIGS. 5A to 5G illustrate another example, in which the magnetic sensor of three-dimensional construction in FIG. 4A is constructed in the form of a module. For example, as shown in FIG. 5A,

elements

23 and 24 are attached on the upper side of a substrate 30 to copper foils 25 provided at the marginal portion of the substrate on the underside of which the element 11 is similarly mounted.

While, as depicted in FIG. 5D, the

elements

10 and 9 are attached to copper foils 25 on both sides of a substrate 31 respectively. Then, the substrate are assembled together with spacers 26 therebetween into a unitary structure as shown in FIG. 5G. FIGS. SE, SE, and

FIGS. 5C, 5F (both shown in section) illustrate examples of the similar construction as FIGS. 5A, 5D, which is different in the arrangement on each substrate from the above example but exactly identical therewith in the final construction.

FIGS. 6A, 6B and 6C shows another example in which the magnetic sensor of FIG. 4A is constructed by using module substrate as in FIGS. 5A to 5G. After the elements are attached to one side of each of the

substrate

30 and 31 such as depicted in FIG. 6A and 68 as described above in connection with FIG. 5A to 5G, the both substrate are assembled together with their cuts 28 engaged with each other as illustrated in FIG. 6C.

FIG. 7 illustrates another example in which a mag netic sensor similar to that of FIGS. 6A, 6B and 6C is constructed by using a hollow square substrate 29 and in which the auxiliary inductance elements and the main element are held on the outside and inside of the substrate respectively.

With such a module construction, the magnetic sensor can also be readily constructed in a cubic form.

As has been described above, in the narrow beam type magnetic sensor of this invention, its magnetism detecting distribution curve can be made extremely sharp to provide high resolution by appropriate selection of the distance D between the main element serving as a head for detecting magnetic information and each of the auxiliary elements and the distance d between the winding end of the main element and those of the auxiliary elements. Therefore, the magnetic sensor of this invention is capable of discriminating magnetic signals of high density, small in size and high in reliability, and hence is extremely effective for inclustrial purposes.

FIG. 8 is a graph showing the magnetism detecting distribution curve II of the prior single type magnetic sensor depicted in FIG. 1 and that I of the magnetic sensor of this invention in FIG. 3A or 3B which were measured in the case of D=l mm and d=l.5 mm, and it will be understood from the graph that the narrow beam type construction is remarked by excellent. With the narrow beam type construction shown in FIG. 3A or 3B the detecting resolution is high in the direction of the line Y-Ya but no so much high in the direction of the axis X-Xa (refer to FIGS. 4A, 4B and 4C) perpendicular to that Y-Ya. Then, the use of the construction such as depicted in a construction shown in FIG. 4A makes the detecting distribution curve in the direction of the axis X-Xa sharp and provides a magnetic sensor having a sharp detecting distribution curve in a three-dimensional manner.

The magnetic sensor of this invention serves as a highly excellent magnetism detecting head of high resolution when employed for reading-out of magnetic records.

What we claim is:

l. A magnetic sensor using a parametrically excited second harmonic oscillator, in which at least one inductance element is formed with a magnetic wire member having a magnetic film deposited on a conductor and a winding wound thereon; in which a capacitor is connected in parallel with the winding to constitute a resonance circuit; an AC exciting current is applied to the magnetic wire member to produce a second harmonic of the exciting current in the resonance circuit; whereby a minute magnetic field is detected by utilizing a change in the phase of the second harmonic in accordance with the direction of an external magnetic field; the improvement of the magnetic sensor, characterized in that at least three inductance elements each formed with a magnetic wire member and its winding are employed, one of them being a main element and the others auxiliary elements; the auxiliary elements being disposed about the main element; and the windings of the elements being interconnected in series in such a manner that when the same exciting voltage is applied to the magnetic members a magnetic field established by a second harmonic current flowing in the winding of the main element and a magnetic field by the second harmonic current flowing in the winding of each auxiliary element may be opposite in direction to each other whereby a sensitivity characteristic against an external magnetic field is made extremely sharp with respect to a head portion of one end of the main element.

2. A magnetic sensor according to claim 1, in which three inductance elements are employed, the magnetic wire members of the three inductance elements are arranged in parallel in equal spaces and connected in series to one another so that a center one of the inductance elements is the main element.

3. A magnetic sensor according to claim 1, in which three inductance elements are employed, the magnetic wire members of three inductance elements are arranged in parallel in equal spaces and connected in parallel to one another so that a center one of the inductance elements is the main element.

4. A magnetic sensor according to claim 1, in which in that five inductance elements are employed, the magnetic wire members of four of the five inductance elements are arranged in parallel along edge lines of a regular rectangular solid while the magnetic wire member of one of the five inductance elements are arranged along the center axis of the regular rectangular solid.

5. A magnetic sensor according to claim 1, in which the magnetic wire members are disposed on at least one substrate of micromodule.

Claims

1. A magnetic sensor using a parametrically excited second harmonic oscillator, in which at least one inductance element is formed with a magnetic wire member having a magnetic film deposited on a conductor and a winding wound thereon; in which a capacitor is connected in parallel with the winding to constitute a resonance circuit; an AC exciting current is applied to the magnetic wire member to produce a second harmonic of the exciting current in the resonance circuit; whereby a minute magnetic field is detected by utilizing a change in the phase of the second harmonic in accordance with the direction of an external magnetic field; the improvement of the magnetic sensor, characterized in that at least three inductance elements each formed with a magnetic wire member and its winding are employed, one of them being a main element and the others auxiliary elements; the auxiliary elements being disposed about the main element; and the windings of the elements being interconnected in series in such a manner that when the same exciting voltage is applied to the magnetic members a magnetic field established by a second harmonic current flowing in the winding of the main element and a magnetic field by the second harmonic current flowing in the winding of each auxiliary element may be opposite in direction to each other whereby a sensitivity characteristic against an external magnetic field is made exTremely sharp with respect to a head portion of one end of the main element.