JP2009047463A - Magnetism detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetism detector excellent in a magnetic sensitivity characteristic, simplifying a constitution, utilizing a proportional characteristic region of a MI element, and detecting a magnetism. <P>SOLUTION: The magnetism detector 1 of the invention includes: a plurality of magneto-impedance elements 13, 13 connected in series and disposed in parallel; a coil 5 wound around a plurality of the magneto-impedance elements 13, 13; an output detecting section 7 for detecting an electrical output from the coil 5; a current carrying section 9 for carrying a current in the coil 5; and a switch means 11 for switching a connection of the coil 5 between the current carrying section 9 and the output detecting section 7. After a current is carried from the current carrying section 9 to the coil 5 and a magnetic field is temporarily applied to the magneto-impedance elements 13, 13, the connection of the coil 5 is switched to the output detecting section 7 by the switch means 11, and the magnetism is measured by measuring the electrical output from the coil 5. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a magnetic detection device that detects weak magnetism such as geomagnetism.

  Patent Document 1 discloses measuring magnetism acting on an amorphous wire by measuring an electrical output of a detection coil wound around the amorphous wire (magnetic sensor). The technique of Patent Document 1 is configured to detect a damped oscillation voltage induced by a current change at the start-up due to interruption of a current flowing through an amorphous wire by a sample hold circuit.

  On the other hand, a detection coil is wound around the magneto-impedance (MI element), and a bias coil for applying a high magnetic field is provided around the magneto-impedance element to measure the voltage of the detection coil that changes according to the magnetic strength. It is known (Known technique 1). In the known technique 1, as indicated by a symbol a in FIG. 2, the MI element has a proportional characteristic in a predetermined region (3 to 5 G (Gauss)), so that the output of the detection coil is in this proportional property region a. Is to be detected.

Japanese Patent No. 3801194

  However, the technique of Patent Document 1 has a problem that the amorphous wire has low sensitivity characteristics and requires a sample-and-hold circuit, which complicates the magnetic detection circuit.

  Although the above-described known technique 1 uses an MI element and has excellent controllability such as magnetic sensitivity characteristics and direction of magnetic field, as shown in FIG. 2, a magnetic field is set so as to be in a proportional characteristic region a (near 4G). There is a problem that a coil for imparting strength (hereinafter referred to as “magnetic field coil”) is required.

  The present invention has been made by paying attention to the above circumstances, and provides a magnetic detection device that can detect magnetism using the proportional characteristic region of the MI element with a simple configuration and excellent magnetic sensitivity characteristics.

  The invention described in claim 1 detects a plurality of magneto-impedance elements connected in series and arranged in parallel to each other, a coil wound around the whole of the plurality of magneto-impedance elements, and an electrical output of the coil. An output detection unit, an energization unit for energizing the coil, and switch means for switching the connection of the coil between the energization unit and the output detection unit are energized from the energization unit to the coil to temporarily apply a magnetic field to the magneto-impedance element. After that, the magnetism is measured by switching the connection of the coil to the output detector by the switch means and measuring the electrical output of the coil.

  In the magneto-impedance elements connected in series and arranged in parallel, the inventors of the present invention have a curve A indicating a resistance value with respect to the magnetic field strength as shown in FIG. It has been found that a hysteresis is generated that results in a curve B that translates.

  Accordingly, as shown in FIG. 2, in the relationship between the magnetic field strength and the resistance value in the magneto-impedance element, the region a showing the proportional characteristic is, for example, in the range of 4G (Gauss) ± 0.3G, but the hysteresis is reduced. As a result, the curve A of the relationship between the magnetic field strength and the resistance value moved in parallel, and the region a showing the proportional characteristic could be made a region lower than 4G (0 ± 0.3G).

  Furthermore, it has been found that such a phenomenon occurs when a plurality of magneto-impedance elements connected in series are arranged in parallel, instead of simply applying a temporary magnetic field to the magneto-impedance elements.

  Therefore, according to the first aspect of the present invention, the proportional characteristic region can be obtained in the relationship between the magnetic field strength and the resistance value of the magneto-impedance element even in the low magnetic field strength region without providing the bias coil as in the known technique 1. Can be used to measure the magnetic strength.

  In addition, by switching the connection of the coil between the energization unit and the output detection unit by the switch means, the magnetic output can be temporarily applied to the magneto-impedance element to measure the electrical output, so that a simple configuration (circuit) can be obtained. .

  Embodiments of the present invention will be described below with reference to FIGS. 1 to 3 of the accompanying drawings. FIG. 1 is a circuit diagram illustrating a configuration of a magnetic detection device according to an embodiment of the present invention, and FIG. 2 is a graph illustrating hysteresis when a magnetic field is temporarily applied to a magneto-impedance element according to the present embodiment. FIG. 3 is a graph showing the degree of hysteresis (magnetic field strength at the center of the magnetic axis in the proportional characteristic region) when the width W of the magneto-impedance element is changed while the interval S between adjacent magneto-impedance elements is constant. is there.

  The magnetic detection device 1 according to the present embodiment is used as an azimuth meter mounted on a mobile phone, and measures the azimuth by detecting the intensity of geomagnetism.

  The magnetic detection device 1 includes a magneto-impedance element unit 3, a coil 5 wound around the magneto-impedance element unit 3, an output detection unit 7 that detects an electrical output of the coil, and an energization unit 9 that energizes the coil 5. And a switch means 11 for switching the connection of the coil 5 between the energization unit 9 and the output detection unit 7. Each of these components is formed on-chip on an IC chip.

  In the present embodiment, the magneto-impedance element section 3 has two magneto-impedance elements 13 arranged in parallel and connected to each other in series by a coupling section 14, and has a substantially U shape as a whole. . The width W of the magneto-impedance element 13 is about 40 μm, and the distance S between the two magneto-impedance elements 13 and 13 is about 20 μ.

  The magneto-impedance element 13 changes its impedance greatly when it receives an external magnetic field when a high-frequency current or pulse wave is applied. In this embodiment, one end is connected to a current circuit 12 that supplies a high-frequency current. Yes.

  The relationship between the width W of the magneto-impedance element 13 and the interval S between the magneto-impedance elements 13 and 13 will be described later.

  The coil 5 is wound around the magneto-impedance element portion 3, one end portion 5 a is connected to the ground electrode, and the other end portion 5 b is provided with switch means 11. 9 is energized or connected to the output detector 7 to measure the electrical output (voltage) of the coil.

  The switch unit 11 is connected to the switch control unit 15. For example, when a drive signal for driving the magnetic detection device is received, the switch unit 11 is temporarily connected to the energization unit 9 and then to the output detection unit 7. It comes to connect.

  The output detection unit 7 includes a capacitor 17 and a voltage amplifier 19, and the induced voltage of the coil 15 is applied to the capacitor 17, and the voltage amplifier 19 converts the voltage detected by the coil into a DC voltage, thereby A voltage corresponding to the magnitude of the external magnetic field received by the impedance element unit 3 is output. Thereby, the resistance change of the magneto-impedance element 13 due to the external magnetism can be measured as a change in the induced voltage generated in the coil 15.

  Next, a method of using the magnetic detection device 1 according to the present embodiment and its operation and effects will be described. In the magnetic detection device 1 according to the present embodiment, when detecting geomagnetism, a high-frequency current is supplied from the current circuit 12 to the magneto-impedance element unit 3.

  When the magneto-impedance element 13 receives geomagnetism, the resistance changes in accordance with the magnetic strength, so that the voltage of the coil 5 wound around the magneto-impedance element unit 3 changes accordingly.

  On the other hand, in the switch control unit 15, before the voltage of the coil 5 is detected by the output detection unit 7, the switch means 11 is once connected to the energization unit 9, and the coil 5 is energized temporarily to magnetize the impedance element unit 3. For example, after applying a magnetic field having a strength of 10 G, the switch means 11 is connected to the output detection unit 7 to detect the voltage of the coil 5.

  Before the voltage of the coil 5 is detected by the output detection unit 7, when the coil 5 is temporarily energized and a strong magnetic field is temporarily applied to the magneto-impedance element unit 3, as shown in FIG. In part 3, the characteristic curve A indicating the resistance value R with respect to the magnetic field strength G causes a hysteresis that becomes a curve B that translates in parallel to a lower magnetic field strength G (a higher sensitivity to the magnetic field strength). In the example shown in FIG. 2, the coil 5 is energized so that the magnetic field strength of the impedance element unit 3 is 10G.

  Accordingly, in the relationship between the magnetic field strength G and the resistance value R in the magneto-impedance element 13, the region a showing the proportional characteristic on the curve A is at a position where the magnetic field strength is low on the curve B due to hysteresis. Will be shown. In other words, according to the present invention, the magnetic sensitivity of the magneto-impedance element 13 can be increased.

  Further, in order to detect in the proportional characteristic region a of the characteristic curve A indicating the resistance value R with respect to the magnetic field strength G as in the conventional known technique 1, the magnetic field (4G) is applied to the magneto-impedance element 13 during the measurement. Therefore, the configuration is simple.

  Here, the relationship between the width W of the magneto-impedance element 13 and the space | interval S in the hysteresis of the magneto-impedance element part 3 shown in FIG. 2 is demonstrated.

  When a magnetic field is applied to the magneto-impedance element section 3, the characteristic curve A indicating the relationship between the magnetic field strength and the resistance is translated with hysteresis, but the amount of translation varies depending on the width W and the spacing S of the magneto-impedance elements. I understood that.

  Similarly to the above-described embodiment, an experiment was conducted to investigate the magnetic detection characteristics of the magneto-impedance element 13 after passing a current through the coil 5 and applying 10 G to the magneto-impedance element 13. In this experiment, the interval S was fixed at 20 μm, the width W of the magneto-impedance element 13 was variously changed, and the point at which the magnetic center point E (4G) of the proportional characteristic region a became 0 was measured. As a result, as shown in FIG. 3, the magnetic center point E of the proportional characteristic region a was 0 when W was about 40 μm. As is clear from FIG. 3, the magnetic center point E of the proportional characteristic region a approaches 0 as W increases from 20 μm, so that at least if W / S> 1, It is clear that the magnetic detection accuracy of the magneto-impedance element is increased, and preferably W / S ≧ 2.

  Further, although depending on the magnitude of the bias magnetic field applied to the magneto-impedance element unit 3, the magnetic field temporarily applied by the coil 5 is preferably 5 G or more, and if it is 10 G, the magnetic center point E of the proportional characteristic region a is Since it was 0, it was sufficient to detect weak magnetism such as geomagnetism.

  The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the invention.

  For example, the magnetic detection device according to the present invention is not limited to detecting geomagnetism, but may be used as a position detection device that detects the position of the magnetic pole moving.

  The magneto-impedance element portion is not limited to being formed in a substantially U shape by two magneto-impedance elements, but may be three or four arranged in parallel and connected in series.

It is a circuit diagram which shows the structure of the magnetic detection apparatus which concerns on embodiment of this invention. It is the graph explaining the hysteresis at the time of applying a magnetic field temporarily to the magneto impedance element in this embodiment. 6 is a rough diagram showing the magnetic field intensity at the center of the magnetic axis in the proportional characteristic region when the width W of the magneto-impedance element is changed while the interval S between adjacent magneto-impedance elements is constant.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Magnetic detection apparatus 3 Magneto impedance element part 5 Coil 7 Output detection part 9 Current supply part 11 Switch means 13 Magneto impedance element W The width of a magneto impedance element S The space | interval between magneto impedance elements

Claims (1)

  A plurality of magneto-impedance elements connected in series and arranged in parallel to each other, a coil wound around the whole of the plurality of magneto-impedance elements, an output detection unit for detecting the electrical output of the coil, and energization for energizing the coil And a switch means for switching the coil connection between the energization section and the output detection section. After the energization section energizes the coil and temporarily applies a magnetic field to the magneto-impedance element, the switch means connects the coil. A magnetism detection device that measures magnetism by switching to an output detection unit and measuring the electrical output of a coil.

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