JP2009058378A - Magnetometric sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetometric sensor that can minimize the effect of the noise, is small, has high induced electromotive force E, and has detection accuracy of high sensitivity. <P>SOLUTION: This magnetometric sensor 1 has a piezoelectric ceramic element 2 of a square-bar shape that is made of bismuth layer compound and is polarized in the arrow A direction, and excitation electrodes 3a and 3b are formed near both end surfaces of the piezoelectric ceramic element 2. A plurality of internal electrodes 4 and 5 are embedded in parallel, in the direction orthogonal to the polarization direction A close to both the ends of the piezoelectric ceramic element 2; surface electrodes 7a, 7b, 8a and 8b are formed at the ends of side surfaces 6a and 6b of the piezoelectric ceramic element 2; and the internal electrodes 4 and 5 are electrically connected to the surface electrodes 7a, 7b, 8a and 8b and form detection electrodes 9a and 9b. When the alternating current electric field of resonance frequency is applied to the excitation electrodes 3a and 3b, the magnetometric sensor 1 is driven in the longitudinal direction vibration mode, and the detection electrodes 9a and 9b detect the strength of the magnetic field. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a magnetic sensor, and more particularly to a magnetic sensor for detecting magnetism by applying an alternating electric field to an electrode formed on a piezoelectric ceramic body to vibrate in a magnetic field.

  As is known as Fleming's right-hand rule, an electromotive force is generated when a conductor moves in a magnetic field. A magnetic sensor is known that utilizes this phenomenon to form an excitation electrode on a piezoelectric ceramic body, apply an alternating electric field to the excitation electrode and vibrate it in a magnetic field, thereby detecting magnetism.

For example, Non-Patent Document 1 includes a piezoelectric ceramic body 101 mainly composed of Pb (Zr, Ti) O ₃ (lead zirconate titanate; hereinafter referred to as “PZT”) as shown in FIG. A pair of excitation electrodes 102a and 102b are formed at substantially central portions of both main surfaces of the piezoelectric ceramic body 101, and are electrically insulated from the excitation electrodes 102a and 102b at end portions of the both main surfaces. A magnetic sensor 100 having detection electrodes 103 (103a, 103b) and 104 (104a, 104b) is described.

  In Non-Patent Document 1, the piezoelectric ceramic body 101 is polarized in the direction of arrow y, and when an AC electric field is applied to the excitation electrodes 102a and 102b, the magnetic sensor 100 has a length direction (arrow x Resonant vibration occurs. A voltage proportional to the strength of the magnetic field is generated between the detection electrode 103 and the detection electrode 104 by vibrating the surface of the magnetic sensor 100 at high speed.

  In Patent Document 1, as shown in FIG. 19, a coil 106, a piezoelectric ceramic 108 that receives a signal having a predetermined frequency from an oscillator 107 and vibrates the coil 106, and a voltage generated in the vibrating coil 106. A magnetic sensor provided with a voltmeter 109 for measuring is proposed.

  In Patent Document 1, a sensor unit 110 composed of a coil 106 and a piezoelectric ceramic 108 is installed at a place where the strength of a magnetic field is to be measured, and a signal having a predetermined frequency is input from an oscillator 107 to the piezoelectric ceramic 108. Then, the piezoelectric ceramic 108 is distorted or stressed according to the input signal, and the coil 106 on the piezoelectric ceramic 108 vibrates, and the vibrated coil 106 crosses the magnetic flux to generate a voltage. This voltage is measured by a voltmeter 109, and the strength of the magnetic field is measured based on this voltage value.

  Patent Document 2 proposes a magnetic detection method in which a piezoelectric element is vibrated in a plane in a magnetic field, and electromagnetic induction is generated by the vibration of the piezoelectric element, thereby detecting the strength of magnetism in the magnetic field. Yes.

  In Patent Document 2, a circular coil is formed on a piezoelectric element made of piezoelectric ceramic, quartz, barium titanate, lithium niobate, etc., and the circular coil is vibrated by the vibration of the piezoelectric element to generate electromagnetic induction in the coil. The induced electromotive force is detected, and the magnetic flux across the coil is measured.

  On the other hand, Non-Patent Document 2 describes the large amplitude characteristics of piezoelectric ceramics for power devices.

  In Non-Patent Document 2, the vibration velocity v (= vibration amplitude × frequency) theoretically changes in proportion to the applied electric field E, but when the PZT piezoelectric ceramic material is driven at the resonance frequency, the electric field strength is increased. It is reported that when a certain level is exceeded, the vibration velocity v gradually becomes not proportional to the applied electric field and eventually becomes saturated. This Non-Patent Document 2 also shows the relationship between the vibration speed limit of the PZT piezoelectric ceramic material and the driving electric field. The vibration speed limit varies depending on the material composition, but in the PZT piezoelectric ceramic material, It is reported that the speed does not exceed 1 m / s at the maximum.

  Non-Patent Document 3 describes the relationship between the piezoelectricity evaluation method and the composition of the PZT piezoelectric ceramic and high power characteristics such as vibration level characteristics.

  In this Non-Patent Document 3, when a PZT piezoelectric ceramic is driven at a resonance frequency, if the vibration speed v exceeds a certain value, the resonance frequency fr and the mechanical quality factor Qm decrease as the vibration speed v increases. Has been reported.

JP-A-11-142492 JP-A-9-145807 Keita Dan, Kentaro Nakamura, Sadayuki Ueha, “A Novel Magnetic Field Sensor using Piezoelectric Vibration”, Proc. Symp. Ultrason. Electron., November 15-17, 2006, Vol. 27 (2006), p.217 −218 Sadayuki Takahashi “New Development of Piezoelectric Materials”, TIC Corporation, New Ceramics VOL.11, No.8 (1988), p29-34 Takahashi Sadayuki “Evaluation of High Power Materials”, TIC Co., Ltd., New Ceramics (1995), No.6, p.17-21

  When a piezoelectric element is driven to vibrate a coil formed on the piezoelectric element, an electromotive force is generated by electromagnetic induction. In this case, the induced electromotive force E is expressed by Formula (1) according to Faraday's law of electromagnetic induction.

E = N (ΔΦ / Δt) (1)
Here, N is the number of turns of the coil, Φ is a magnetic flux penetrating the coil, and t is time. ΔΦ / Δt represents a change in magnetic flux passing through the coil per unit time.

  When electromagnetic induction is generated by vibrating a coil, the induction starting force E is expressed by Equation (1). However, instead of the coil, the detection electrodes 103 and 104 in a closed circuit are vibrated as in Non-Patent Document 1. When induced, the induced electromotive force E can be expressed by Equation (2).

E = vBW (2)
Here, v is the vibration velocity of the detection electrodes 103 and 104, B is the magnetic flux density penetrating the detection electrodes 103 and 104, and W is the length of the detection electrodes 103 and 104.

  Therefore, in Non-Patent Document 1, in order to increase the sensitivity as the magnetic sensor, that is, the induced activation force E, as is clear from the equation (2), the vibration speed v and the magnetic flux density B are increased, or the detection electrode It is necessary to increase the length W of 103 and 104.

  However, when a PZT material is used as the piezoelectric ceramic material, even if an attempt is made to increase the vibration speed v, the vibration speed v has a limit of 1 m / s at most, as shown in Non-Patent Document 2. Therefore, with a PZT-based piezoelectric ceramic material, it is difficult to stably obtain a large vibration speed v and increase the induced electromotive force E.

  Further, if the length W of the detection electrodes 103 and 104 is to be increased, it is necessary to increase the length in the width direction of the piezoelectric ceramic 101 itself, resulting in an increase in size of the magnetic sensor. That is, downsizing of the magnetic sensor is also required due to the demand for downsizing of the electronic device, and increasing the length of the piezoelectric ceramic 101 in the width direction is contrary to the downsizing of the magnetic sensor.

  Further, Non-Patent Document 1 has a problem that noise is likely to be generated for the reason described below, resulting in a decrease in the S / N ratio.

  When the magnetic sensor 100 of Non-Patent Document 1 is driven in the longitudinal vibration mode, the piezoelectric ceramic body 101 is displaced and contracted in the direction of the arrow x ′ as shown by the phantom line in FIG. As indicated by the imaginary line 21, it is displaced and extended in the direction of the arrow x ″.

However, the PZT-based material used in Non-Patent Document 1 has an electromechanical coupling coefficient k ₃₁ (hereinafter referred to as “k ₃₁ value”) of longitudinal vibration and an electromechanical coupling coefficient k ₃₃ (hereinafter referred to as “k ₃₁ value”). Hereinafter, the “k ₃₃ value”) is large, and as shown by a in FIGS. 20 and 21, charges due to the piezoelectric effect are generated on the detection electrodes 103a, 103b, 104a, and 104b. This may affect the induction starting force E, and as a result, the S / N ratio may be lowered.

  That is, when driven in the longitudinal vibration mode, noise in the longitudinal vibration mode is generated, and when driven in the longitudinal vibration mode, noise in the longitudinal vibration mode is generated, and these noises are induced by the inductive activation force E. As a result, the S / N ratio may be lowered.

  As described above, in Non-Patent Document 1, it is difficult to obtain a small magnetic sensor having a large induced activation force E and high sensitivity.

  On the other hand, in Patent Document 1, in order to increase the induction starting force E, it is necessary to increase the number N of turns of the coil 106, as is apparent from Equation (1).

  However, when the number of turns N of the coil 106 is increased, the area for forming the coil 106 must be increased, which leads to an increase in the size of the magnetic sensor and meet the demand for downsizing of the electronic device. It becomes difficult.

  In Patent Document 2, when a single crystal such as quartz, barium titanate, or lithium niobate is used as a piezoelectric element, an internal electrode cannot be formed. It is difficult to dramatically increase the length. Therefore, in order to amplify the induced electromotive force E, the element size must be increased to increase the number of turns of the coil, or the length of the coil must be increased. As in Non-Patent Document 1 and Patent Document 1, Contrary to the demand for smaller electronic devices.

  On the other hand, when a piezoelectric ceramic is used as the piezoelectric element, a laminated structure can be formed, and the induced electromotive force E can be amplified by forming a detection electrode with laminated internal electrodes.

  However, in Patent Document 2, a PZT-based material is used as the piezoelectric ceramic. Therefore, as in Non-Patent Document 1, the vibration speed v has a limit of 1 m / s at most, and S / The N ratio is lowered, and it is difficult to obtain highly sensitive measurement accuracy.

  That is, as is clear from the description of Non-Patent Document 2, when a PZT-based piezoelectric ceramic material is used, there is a limit to the vibration speed v, and a highly sensitive magnetic sensor having a large induced electromotive force E is obtained. Have difficulty.

  In addition, the piezoelectric element needs to be excited by a driving electric field at or near the resonance frequency.

  However, Non-Patent Document 3 reports that the resonance frequency fr and the mechanical quality factor Qm of the PZT-based piezoelectric ceramic material decrease as the vibration speed v increases. It is difficult to keep it constant. In order to keep the vibration speed v constant, it is conceivable to separately provide a circuit that follows the change in the resonance frequency fr or compensates for the decrease in the mechanical quality factor Qm. There is a risk of complicating the device and increasing the cost.

  The present invention has been made in view of such circumstances, and provides a magnetic sensor that can eliminate the influence of noise as much as possible, has a large induced activation force E even with a small size, and has high detection accuracy. For the purpose.

  In order to achieve the above object, a magnetic sensor according to the present invention includes a piezoelectric ceramic body made of a bismuth layered compound, a pair of excitation electrodes formed on both end faces in the polarization direction of the piezoelectric ceramic body, and at least the piezoelectric sensor. A detection electrode formed on a surface other than the both end faces of the ceramic body, and a voltage is applied between the pair of excitation electrodes to drive the vibration in the same direction as the polarization direction. It is detected by the detection electrode.

  In the magnetic sensor of the present invention, the detection electrode is formed on the surface of the piezoelectric ceramic body by electrically connecting the plurality of internal electrodes embedded in the ceramic body. And a surface electrode connected to the substrate.

  The magnetic sensor according to the present invention is preferably characterized in that the detection electrode is formed on the surface of the ceramic body so as to be opposed to the ceramic body. It is also preferable that the electrode is made of a Ni—Fe alloy.

  Furthermore, in the magnetic sensor of the present invention, the bismuth layered compound is characterized in that the c-axis of the crystal axis is oriented in a direction orthogonal to the polarization direction of the piezoelectric ceramic body.

Since the bismuth layered compound has large crystal anisotropy, when the same electric field is applied, the longitudinal vibration mode (vibration direction is the polarization direction) in the longitudinal vibration mode (vibration direction is the same as the polarization direction). In comparison with the vertical direction), the vibration velocity v can be increased and a large induced electromotive force E can be obtained. In addition, the bismuth layered compound has an electromechanical coupling coefficient k ₃₁ (k ₃₁ value) of longitudinal vibration that is very small compared to an electromechanical coupling coefficient k ₃₃ (k ₃₃ value) of longitudinal vibration. The influence of noise caused by the piezoelectric effect can be eliminated as much as possible.

  That is, according to the magnetic sensor, a piezoelectric ceramic body made of a bismuth layered compound, a pair of excitation electrodes formed on both end faces in the polarization direction of the piezoelectric ceramic body, and at least the both ends of the piezoelectric ceramic body A detection electrode formed on a surface other than the surface, a voltage is applied between the pair of excitation electrodes to drive the vibration in the same direction as the polarization direction, and the strength of the magnetic field is detected by the detection electrode. Therefore, the influence of noise due to the piezoelectric effect in the length direction is eliminated as much as possible, and a large induced electromotive force E can be obtained. Moreover, since fluctuations in the resonance frequency fr can be suppressed even when the vibration speed v increases, it is not necessary to separately provide a compensation circuit that keeps the vibration speed v constant. Therefore, a highly sensitive magnetic sensor can be obtained without causing an increase in product cost.

  A plurality of internal electrodes embedded in the ceramic body; and a surface electrode formed on the surface of the piezoelectric ceramic body to electrically connect the plurality of internal electrodes. Therefore, the detection electrodes can be laminated so that the detection signal can be amplified, and a high-accuracy porcelain sensor capable of outputting a large detection signal even if it is small can be obtained.

  Further, the detection electrode is formed of a high magnetic permeability material such as a Ni-Fe alloy on the surface of the ceramic body so as to be opposed to the ceramic body so that the detection electrode is laminated. Even if not, the magnetic flux density can be dramatically increased. This makes it possible to obtain a highly sensitive magnetic sensor having a large induced activation force E.

  In the bismuth layered compound, the c-axis of the crystal axis is oriented in a direction orthogonal to the polarization direction of the piezoelectric ceramic body, so that the vibration speed can be further increased and the length direction can be increased. The influence of noise caused by vibration can be more effectively suppressed. That is, since the bismuth layered compound has a large crystal anisotropy as described above and does not have a spontaneous polarization component in the c-axis direction or is small even if it has, the electric charge due to the piezoelectric effect is almost generated in the c-axis direction. Without affecting the noise, it is possible to more effectively suppress the influence of noise caused by longitudinal vibration.

  Next, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a perspective view showing an embodiment (first embodiment) of a magnetic sensor according to the present invention, and FIG. 2 is a longitudinal sectional view thereof.

  1 and 2, the magnetic sensor 1 includes a square bar-shaped piezoelectric ceramic body 2 made of a bismuth layered compound and polarized in the direction of arrow A, and is displaced in the direction of arrow X in the same direction as the polarization direction A. It is configured to drive in the longitudinal vibration mode.

  Specifically, in the magnetic sensor 1, excitation electrodes 3 a and 3 b are formed on both end faces of the piezoelectric ceramic body 2. Further, in the vicinity of both ends of the piezoelectric ceramic body 2, a plurality of internal electrodes 4, 5 are embedded side by side in the width direction (direction orthogonal to the polarization direction A), and the side surface of the piezoelectric ceramic body 2. Surface electrodes 7a, 7b, 8a and 8b are formed at the ends of 6a and 6b. That is, the internal electrodes 4, 5 and the surface electrodes 7a, 7b, 8a, 8b are electrically connected, and the internal electrodes 4, 5 and the surface electrodes 7a, 7b, 8a, 8b constitute a pair of detection electrodes. 9a and 9b are formed.

  The magnetic sensor 1 resonates and displaces in the direction of the arrow X when an AC electric field at or near the resonance frequency is applied to the excitation electrodes 3a and 3b. This makes it possible to obtain a large induced electromotive force E corresponding to the vibration velocity v of the detection electrodes 9a, 9b, and to detect the strength of the magnetic field with high sensitivity.

  Here, the reason why the piezoelectric ceramic body 2 is formed of a bismuth layered compound instead of a conventional PZT material is as follows.

Since the PZT-based material has a perovskite crystal structure (general formula ABO ₃ ), the crystal anisotropy is smaller than that of the bismuth layered compound. As a result, it is considered that the resonance frequency fr and the mechanical quality factor Qm are lowered as the vibration speed v is increased.

  On the other hand, in the bismuth layered compound, the bismuth layer is periodically formed in the direction perpendicular to the c-axis of the crystal axis, and the crystal anisotropy is large, so that the non-180 ° domain rotation hardly occurs. Therefore, it is possible to increase the vibration speed v, and even if the vibration speed v increases, it is considered that the decrease in the resonance frequency fr and the mechanical quality factor Qm can be suppressed.

  When the vibration velocity v increases, the induced electromotive force E also increases (see the above formula (2)). Therefore, when the piezoelectric ceramic body 2 is formed of a bismuth layered compound, the piezoelectric ceramic body is made of a PZT material. Compared with the case where 2 is formed, the induced electromotive force E can be remarkably increased. Moreover, even if the vibration speed v increases, the decrease in the resonance frequency fr and the mechanical quality factor Qm can be suppressed. Therefore, it is not necessary to separately provide a compensation circuit for keeping the vibration speed v constant.

In addition, as described in the section “Problems to be Solved by the Invention”, PZT-based materials have both large k ₃₁ and k ₃₃ values (for example, the k ₃₁ value is about 29% and the k ₃₃ value is 67%), electric charges due to the piezoelectric effect are generated on the detection electrode, which becomes noise and affects the induced activation force E, and as a result, the S / N ratio may be lowered.

  That is, when driven in the longitudinal vibration mode, noise in the longitudinal vibration mode is generated. On the other hand, when driven in the longitudinal vibration mode, noise in the longitudinal vibration mode is generated, and these noises are inductively activated. The force E is affected, and as a result, the S / N ratio may be lowered.

On the other hand, the bismuth layered compound has a large anisotropy as described above, and the k ₃₁ value is much smaller than the k ₃₃ value. Incidentally, in the case of a bismuth layered compound, the k ₃₁ value is 3 to 6% and the k ₃₃ value is about 14 to 32%. Therefore, by making the displacement direction (vibration direction) X and the polarization direction A the same direction and vibrating in the longitudinal vibration mode, the influence of noise due to the piezoelectric effect in the length direction can be reduced.

  In addition, the vibration speed can be increased by driving in the longitudinal vibration mode.

  That is, since the bismuth layered compound has a large crystal anisotropy as described above, when the same electric field is applied, the vibration velocity v is larger in the longitudinal vibration mode than in the longitudinal vibration mode. And a larger induced electromotive force E can be obtained.

  Thus, by forming the piezoelectric ceramic body with a bismuth layered compound and vibrating in the longitudinal vibration mode, the induced electromotive force E is large, and the influence of noise caused by the piezoelectric vibration in the length direction is eliminated as much as possible. A highly sensitive magnetic sensor can be obtained.

Such a bismuth layered compound is not particularly limited. For example, Bi ₂ SrNb ₂ O ₉ , BiWO ₆ , CaBiNb ₂ O ₉ , BaBiNb ₂ O ₉ , PbBi ₂ Nb ₂ O ₉ , Bi _{3 TiNbO 9, Bi 3 TiTaO 9,} Bi 4 Ti 3 O 12, SrBi 3 Ti 2 NbO 12, BaBi 3 Ti 2 NbO 12, PbBi 3 Ti 2 NbO 12, CaBi 4 Ti 4 O 15, SrBi 4 Ti 4 O 15, _{BaBi 4 Ti 4 O 15, PbBi} 4 Ti 4 O 15, Na 0.5 Bi 4.5 Ti 4 O 15, K 0.5 Bi 4 Ti 4 O 15, Ca 2 Bi 4 Ti 5 O 18, Sr 2 Bi 4 Ti 5 O 18, the _{Ba 2 Bi 4 Ti 5 O 18} , Bi 6 Ti 3 Wo 18, Bi 7 Ti 4 NbO 21, Bi 10 Ti 3 W 3 O 30 and the like It is possible to use.

  Further, in the magnetic sensor 1 of the first embodiment, the internal electrodes 4 and 5 constituting the detection electrodes 9a and 9b have a laminated structure, and therefore the value of the current output from the detection electrodes 9a and 9b. Can be increased.

  Furthermore, the bismuth layered compound is preferably oriented with the c-axis of the crystal axis in a direction perpendicular to the polarization direction A of the ceramic body 2 (direction indicated by arrow C in FIG. 1).

  That is, the bismuth layered compound has a large crystal anisotropy as described above, and has no or even no spontaneous polarization in the c-axis direction due to the crystal anisotropy. Therefore, it is considered that charges due to the piezoelectric effect are not substantially generated in the c-axis direction.

  Therefore, by orienting the c-axis of the crystal axis in a direction orthogonal to the polarization direction A of the ceramic body 2, it is possible to more effectively eliminate the influence of noise caused by longitudinal vibration.

  The c-axis oriented bismuth layered compound can be easily produced by a TGG (Templated Grain Growth) method or the like, as will be described in detail later. That is, for example, after a ceramic molded body containing a c-axis oriented plate-like ceramic powder and a non-oriented calcined powder is manufactured, the ceramic molded body can be easily manufactured by heat treatment.

  Next, a second embodiment of the magnetic sensor according to the present invention will be described in detail.

  FIG. 3 is a perspective view showing a second embodiment of the magnetic sensor, and FIG. 4 is a longitudinal sectional view thereof.

  3 and 4, the magnetic sensor 11 includes a piezoceramic body 12 having a square bar shape that is polarized in the direction of arrow A and is made of a bismuth layered compound, as in the first embodiment. It is configured to be displaced in the direction of the arrow X in the same direction and to be driven in the longitudinal vibration mode.

  Specifically, in the magnetic sensor 11, excitation electrodes 13a and 13b are formed on both end faces of the piezoelectric ceramic element body 12, and a Ni-Fe alloy or the like is formed in the vicinity of both ends of both main faces 14a and 14b. Detection electrodes 15 (15a, 15b) and 16 (16a, 16b) made of a magnetic permeability material are formed in the width direction (direction perpendicular to the polarization direction A).

  In this magnetic sensor 11, when an alternating electric field at or near the resonance frequency is applied to the excitation electrodes 13a and 13b, the magnetic sensor 11 resonates and is displaced in the arrow X direction. As a result, it is possible to obtain an induced electromotive force E corresponding to the vibration velocity v of the detection electrodes 15 and 16, and the strength of the magnetic field can be detected with high sensitivity.

  That is, also in the second embodiment, as in the first embodiment, the piezoelectric ceramic body 12 is formed of a bismuth layered compound and is driven in the longitudinal vibration mode. It is possible to increase the noise and to eliminate as much as possible the influence of noise caused by longitudinal vibration.

  In addition, in the second embodiment, since the detection electrodes 15 and 16 are formed of a high magnetic permeability material such as a Ni—Fe alloy, a large induction starting force E can be obtained.

  That is, the magnetic flux density B is represented by the product of the magnetic permeability μ and the magnetic field strength H, as shown by the formula (3).

B = μ × H (3)
For example, a Ni—Fe alloy, particularly a Ni—Fe alloy having a Ni content of 78%, which is called permalloy, has a very high relative permeability of about 1.0 × 10 ⁵ . Therefore, by forming the detection electrodes 15 and 16 with a high permeability material such as a Ni—Fe alloy, the magnetic flux density B can be drastically improved, and a desired large induced activation force E can be obtained.

  Needless to say, the present invention is not limited to the above embodiment, and various modifications can be made without departing from the scope of the invention.

  Next, examples of the present invention will be specifically described.

[Sample No. 1]
Using a non-oriented SrBi ₂ Nb ₂ O _9- based material (hereinafter referred to as “non-oriented SBN-based material”) as a bismuth layered compound, a magnetic sensor operating in a longitudinal vibration mode as shown in FIG. 1 was produced. .

  FIG. 5 is a manufacturing process diagram showing the manufacturing procedure of this magnetic sensor.

First, SrCO ₃ , Bi ₂ O ₃ , Nd ₂ O ₃ , Nb ₂ O ₅ , and MnCO ₃ were prepared as ceramic raw materials. Then, the ceramic raw material is weighed so that the final composition is the composition formula {Sr _0.9 Nd _0.1 Bi ₂ Nb ₂ O ₉ + 0.01MnO}, and this weighed product is used as PSZ (Partially Stabilized Zirconia) balls and The mixture was put into a ball mill together with pure water and pulverized and mixed in the ball mill for about 20 hours to obtain a mixture.

  Subsequently, the obtained mixture was dried and then calcined at a temperature of 800 ° C. for 2 hours to synthesize it, thereby obtaining a calcined powder.

  After that, calcined powder, appropriate amount of organic binder, dispersing agent, antifoaming agent and surfactant are added, put into the ball mill again with PSZ balls and pure water, and wet mixed in the ball mill for about 16 hours. A ceramic slurry was prepared. Then, using this ceramic slurry, a ceramic green sheet 21 having a thickness of about 200 μm was produced by a doctor blade method as shown in FIG.

  Next, a Pt paste containing Pt as a conductive material was prepared. Then, the Pt paste was screen-printed in a predetermined direction near both ends of the ceramic green sheet 21 in the width direction and dried to form internal electrodes 22a and 22b as shown in FIG. 5B.

  Next, the ceramic green sheets 21 on which the internal electrodes 22a and 22b are formed are stacked, and further sandwiched between the ceramic green sheets 21 on which the internal electrodes are not formed, and a pressure of 200 MPa is applied so that the thickness becomes about 6 mm. Pressure was applied for 1 minute and pressure bonded to produce a ceramic molded body. And after performing a binder removal process at 500 degreeC for this ceramic molded object, it baked at the temperature of 1200 degreeC for 2 hours, and produced a sintered compact block, thickness T: 10 mm, width W: 10 mm, length L: Cut out to 5 mm, as shown in FIG. 5C, a piezoelectric ceramic body 23 was obtained in which internal electrodes 22a and 22b were embedded side by side.

  Then, excitation electrodes 24a and 24b are formed on both end faces in the length direction (vibration direction) by sputtering using Ag as a target, and an electric field of 8 kV / mm is applied in 200 ° C. silicone oil for 10 minutes to polarize the electrodes. Processed. Next, the piezoelectric ceramic body 23 was cut with a dicing saw so that the thickness T was 2 mm, the width W was 2 mm, and the length L was 5 mm. Thereafter, in order to connect the internal electrodes 22a and 22b exposed on the side surfaces of the piezoelectric ceramic body 23 in parallel, Ag paste containing Ag is applied to the side surfaces to form the surface electrodes 25a and 25b. Sample No. 1 as shown in FIG. In the figure, an arrow D indicates the polarization direction.

  A silver wire having a diameter of 0.2 mm was connected to the excitation electrodes 24a and 24b for applying an electric field, and a silver wire having a diameter of 0.2 mm was connected to the surface electrodes 25a and 25b for detecting an output signal.

[Sample No. 2]
A magnetic sensor that uses a PbZrO ₃ —PbTiO ₃ —Pb (Mn, Nb) O ₃ -based material (hereinafter referred to as “PZT-based material”) as a piezoelectric ceramic material and operates in a longitudinal vibration mode as in the case of sample number 1. Was made.

That is, first, Pb ₃ O ₄ , MnCO ₃ , Nb ₂ O ₅ , ZrO ₂ , and TiO ₂ were prepared as ceramic raw materials. The final composition was weighed so that the composition formula _{{0.9Pb (Zr 0.49 Ti 0.51)} O 3 -0.1Pb (Mn 1/3 Nb 2/3) O 3}, were weighed the ceramic raw materials.

  Thereafter, a ceramic green sheet having a thickness of about 200 μm was produced by the same method and procedure as Sample No. 1.

  Next, using an Ag—Pd paste containing Ag—Pd as a conductive material, an internal electrode was formed on the ceramic green sheet by the same method and procedure as Sample No. 1, and then a ceramic molded body was produced.

  And after performing a binder removal process at 500 degreeC for this ceramic molded object, it baked at the temperature of 1150 degreeC for 2 hours, and produced a sintered compact block, thickness T: 10 mm, width W: 10 mm, length L : Cut out to 5 mm to obtain a piezoelectric ceramic body in which internal electrodes were embedded side by side.

  After that, excitation electrodes are formed on both end surfaces in the length direction (vibration direction) by sputtering using Ag as a target, and an electric field of 5 kV / mm is applied for 30 minutes in 100 ° C. silicone oil to perform polarization treatment. It was. Next, the piezoelectric ceramic body was cut with a dicing saw so that the thickness T was 2 mm, the width W was 2 mm, and the length L was 5 mm. Thereafter, in order to connect in parallel the internal electrodes exposed on the side surfaces of the piezoelectric ceramic body, Ag paste containing Ag is applied to the side surfaces to form surface electrodes, whereby the sample number is driven in the longitudinal vibration mode. Two samples were prepared.

  As in sample No. 1, a silver wire having a diameter of 0.2 mm was connected to the excitation electrode for applying an electric field, and a silver wire having a diameter of 0.2 mm was connected to the surface electrode for detecting an output signal.

[Sample No. 3]
As the piezoelectric ceramic material, a PZT-based material similar to Sample No. 2 was used, and a magnetic sensor operating in the longitudinal vibration mode was produced.

  FIG. 6 is a manufacturing process diagram showing a manufacturing procedure of the magnetic sensor of sample number 3.

That is, first, Pb ₃ O ₄ , MnCO ₃ , Nb ₂ O ₅ , ZrO ₂ , and TiO ₂ were prepared as ceramic raw materials. Then, using these ceramic raw materials as starting materials, a ceramic green sheet 26 as shown in FIG.

  Next, without forming the internal electrode, the ceramic green sheets 26 were laminated and pressure-bonded to produce a ceramic molded body. Next, the ceramic molded body was subjected to a binder removal treatment at 500 ° C. and then fired at a temperature of 1150 ° C. for 2 hours to produce a sintered body block. Then, as shown in FIG. 6 (b), a length L: 25 mm, a width W: 4 mm, and a thickness T: 1 mm were cut with a dicing saw to obtain a piezoelectric ceramic body 27.

  Next, silver electrodes were formed over the entire area of both main surfaces by sputtering. And the electric field of 5 kV / mm was applied for 30 minutes in 100 degreeC silicone oil, and the polarization process was performed in the thickness direction.

  Next, a part of the silver electrode is removed by etching, and as shown in FIG. 6C, the excitation electrodes 28a and 28b and the detection electrodes 29a, 29b, 30a electrically insulated from the excitation electrodes 28a and 28b, 30b was formed, thereby preparing a sample of sample number 3 that was driven in the longitudinal vibration mode. In the figure, an arrow E indicates the polarization direction.

  A silver wire having a diameter of 0.2 mm is connected to the excitation electrodes 28a and 28b for applying an electric field, and the detection electrodes 29 and 30 have a diameter of 0.2 mm so that the detection electrodes 29 and 30 are connected in series. An output signal detection silver wire was connected.

[Characteristic evaluation of each sample]
For each sample of the sample No. 1-3, using an impedance analyzer (manufactured by Agilent Technologies HP4294A), resonant - k ₃₃ value at the anti-resonance method, and to determine the k ₃₁ value.

As a result, Sample No. 1, k ₃₃ value is 14%, k ₃₁ value was 5%. Further, Sample No. 2 and 3 k ₃₃ value is 67%, k ₃₁ value was 29%.

Sample numbers 2 and 3 in which the piezoelectric ceramic body is formed of a PZT material have a large k ₃₁ value and k ₃₃ value. Therefore, when driven in the longitudinal vibration mode, noise is generated on the detection electrode due to the piezoelectric effect due to the k ₃₁ value, whereas when driven in the longitudinal vibration mode, the k ₃₃ value is generated. It is considered that noise is generated on the detection electrode due to the piezoelectric effect caused by the phenomenon, and in any case, the measurement accuracy is lowered.

In contrast, sample No. 1 in which the piezoelectric ceramic body is formed of a non-oriented SBN material has a k ₃₁ value as small as 5% when driven in the longitudinal vibration mode, and the influence of noise due to the k ₃₁ value is minimized. It can be excluded.

  Next, the relationship between the applied magnetic field and the output current of each sample Nos. 1 to 3 was measured using the measuring apparatus of FIG.

  That is, this measuring apparatus has a first electromagnet 31a and a second electromagnet 31b, and a sample (magnetic sensor) 33 supported by a holder 32 is used for the first electromagnet 31a and the second electromagnet 31a. It is arranged between. A frequency synthesizer 35 is connected to the excitation electrode of the sample 33 via an amplifier 34, and a lock-in amplifier 36 is connected to the detection electrode of the sample 33.

  In the measurement apparatus, a magnetic field in the direction of arrow B is applied to the sample 33 via the first electromagnet 31a and the second electromagnet 31b. When an electric field having a resonance frequency is applied to the sample 33 from the frequency synthesizer 35, the sample 33 resonates and an output signal from the detection electrode is input to the lock-in amplifier 36, whereby an output current or an output current corresponding to the strength of the magnetic field or The output voltage is detected.

  Further, the laser beam from the laser irradiation device 38 is irradiated on the substantially central portion of the end surface of the sample 33, and the vibration speed v corresponding to the applied electric field is measured by the laser Doppler vibrometer 37.

  In this embodiment, an excitation electric field having the same frequency as the resonance frequency is applied to the sample number 1, and the vibration velocity v at this time is measured with a laser Doppler vibrometer so that the vibration velocity is 2 m / s. The applied electric field was adjusted. The output current when the applied magnetic field was changed was measured.

  For sample numbers 2 and 3, the applied electric field was adjusted so that the vibration speed was 0.5 m / s in order to obtain stable vibration, and the output when the applied magnetic field was changed as in sample number 1. The current was measured.

  FIG. 8 shows the measurement results. The mark ◆ indicates the sample number 1, the mark × indicates the sample number 2, and the mark ○ indicates the sample number 3. The horizontal axis represents the applied magnetic field [G], and the vertical axis represents the output current [nA].

  Sample No. 1 is made of a non-oriented SBN material made of a piezoelectric ceramic body and driven in the longitudinal vibration mode, so that stable driving is possible even when the vibration speed is increased to 2 m / s. As the applied magnetic field increased, the output current increased substantially in proportion to the applied magnetic field, and it was found that a high output current of 45 nA or more was obtained when the applied magnetic field was 450G.

  On the other hand, Sample No. 2 is detected because the piezoelectric ceramic body is made of a PZT material and is driven with a vibration speed reduced to 0.5 m / s, and therefore the vibration speed v is low. The output current is low, and only about 10 nA can be obtained even when a 450 G magnetic field is applied.

Sample No. 3 was found to be able to hardly detect the output current when the applied magnetic field is in the range of 0 to 450 G because the piezoelectric ceramic body is made of a PZT material and is driven by longitudinal vibration. . This is thought to be because the vibration speed v is low and the PZT material has a very large k ₃₃ value of 67% and is affected by noise due to the k ₃₃ value.

[Sample No. 4]
Using a non-oriented SBN material as the bismuth layered compound, a magnetic sensor operating in a longitudinal vibration mode as shown in FIG. 3 was produced.

  FIG. 9 is a manufacturing process diagram showing the manufacturing procedure of this magnetic sensor.

First, SrCO ₃ , Bi ₂ O ₃ , Nd ₂ O ₃ , Nb ₂ O ₅ , and MnCO ₃ are prepared as ceramic raw materials, as shown in FIG. A ceramic green sheet 38 having a thickness of about 200 μm was produced.

  Next, without forming an internal electrode, these ceramic green sheets 38 were laminated, and a pressure of 200 MPa was applied for 1 minute so as to have a thickness of about 6 mm, thereby producing a ceramic molded body. And after performing the binder removal process at 500 degreeC for this ceramic molded object, it baked at the temperature of 1200 degreeC for 2 hours, and produced the sintered compact block. And this sintered compact block was cut out to thickness T: 10mm, width W: 10mm, and length L: 5mm, and as shown in FIG.9 (b), the piezoelectric ceramic element | base_body 39 which does not have an internal electrode was obtained. After this, excitation electrodes are formed on both end faces in the length direction (vibration direction) by sputtering using Ag as a target, and an electric field of 8 kV / mm is applied for 10 minutes in 200 ° C. silicone oil to perform polarization treatment. It was. Next, the piezoelectric ceramic body 39 was cut with a dicing saw so that the thickness T was 2 mm, the width W was 2 mm, and the length L was 5 mm.

Next, a Ni—Fe alloy paste (permeability: about 1.0 × 10 ⁵ ) prepared with a Ni: Fe content ratio of wt% and Ni: Fe = 78: 22 was prepared. Then, Ni—Fe alloy paste is applied and baked in the width direction near the ends of both main surfaces of the piezoelectric ceramic body 39, and as shown in FIG. 9C, the detection electrodes 41a, 41b, 42a, 42b Thus, a sample of sample number 4 was produced. In the figure, the arrow F indicates the polarization direction.

  A silver wire having a diameter of 0.2 mm was connected to the excitation electrodes 40a and 40b for applying an electric field, and a silver wire having a diameter of 0.2 mm was connected to the detection electrodes 41a, 41b, 42a and 42b for detecting an output signal. .

[Sample No. 5]
A PZT material was used as the piezoelectric ceramic material, and a magnetic sensor that operates in the longitudinal vibration mode was fabricated as in Sample No. 4.

That is, first, Pb ₃ O ₄ , MnCO ₃ , Nb ₂ O ₅ , ZrO ₂ , and TiO ₂ were prepared as ceramic raw materials. A ceramic green sheet having a thickness of about 200 μm was prepared by the same method and procedure as Sample No. 2, and a ceramic molded body was manufactured by laminating and pressing, and a sintered body block was manufactured through binder removal processing and sintering processing.

  Then, after performing polarization treatment, a piezoelectric ceramic body having a thickness T: 2 mm, a width W: 2 mm, and a length L: 5 mm was obtained.

  Next, using the same Ni—Fe alloy paste as [Sample No. 4], detection electrodes were formed in the width direction in the vicinity of the ends of both main surfaces of the piezoelectric ceramic body, and a sample No. 5 was produced.

  A silver wire having a diameter of 0.2 mm was connected to the excitation electrode for applying an electric field, and a silver wire having a diameter of 0.2 mm was connected to the detection electrode for detecting an output signal.

[Sample No. 6]
As in the case of Sample No. 5, as in the case of Sample No. 5, except that a PZT-based material is used and a Ni—Fe alloy paste is used for the detection electrode, a magnet that operates in the longitudinal vibration mode is used. I got a sensor.

[Characteristic evaluation of each sample]
For each sample of the sample No. 4-6, similarly to Example 1, was measured k ₃₃ value and k ₃₁ value, Sample No. 4 is similar to Sample No. 1, k ₃₃ value is 14%, k ₃₁ The value was 5%. Sample numbers 5 and 6 had a k ₃₃ value of 67% and a k ₃₁ value of 29%, similar to sample numbers 2 and 3.

  Next, using the measurement apparatus of FIG. 7 described above, the output voltage was measured when the applied magnetic field was changed by driving at the resonance frequency.

  FIG. 10 shows the measurement results. The symbol ◆ indicates the sample number 4, the symbol X indicates the sample number 5, and the symbol O indicates the sample number 6. FIG. The horizontal axis represents the applied magnetic field [G], and the vertical axis represents the output voltage [mV].

  Sample No. 4 is formed of a non-oriented SBN material and is driven in the longitudinal vibration mode, so that stable driving is possible even when the vibration speed is increased to 2 m / s. As the applied magnetic field increased, the output voltage increased substantially in proportion to the applied magnetic field, and it was found that a high output voltage of 2000 mV or higher was obtained when the applied magnetic field was 450 G. That is, since the detection electrode is formed of a Ni—Fe alloy having a high magnetic permeability, a high output voltage can be obtained.

  On the other hand, Sample Nos. 5 and 6 are detected because the piezoelectric ceramic body is made of a PZT material and is driven at a vibration speed reduced to 0.5 m / s, and the vibration speed v is low. The output voltage was low, and it was about 500 mV even when a high magnetic field of 450 G was applied.

[Sample No. 7]
Using a SrBi ₂ Nb ₂ O _9- based material (hereinafter referred to as “oriented SBN-based material”) oriented in the c-axis as a bismuth layered compound, a magnetic sensor that operates in a longitudinal vibration mode as shown in FIG. 1 is manufactured. did.

First, as in sample number 1, each ceramic raw material is weighed so that the final composition satisfies the composition formula {100 (Sr _0.9 Nd _0.1 Bi ₂ Nb ₂ O ₉ ) + MnO}, and wet-mixed in a ball mill for about 20 hours. After the mixture was dried, the mixture was calcined at a temperature of 800 ° C. for 2 hours to obtain a non-oriented calcined powder.

  Next, a part of the calcined powder is taken out, mixed so that the calcined powder and KCl are in a weight ratio of 1: 1, heat treated at a temperature of 1200 ° C. for 5 hours, and then washed with water to remove KCl. Removal gave a ceramic powder.

  Here, when the ceramic powder was observed using a scanning electron microscope, the shape had anisotropy and was oriented in the c-axis, and the ratio of the maximum diameter φ to the height H φ / H (aspect It was confirmed that the ratio was about 5 plate-like.

  Next, the oriented plate-like ceramic powder and the non-oriented calcined powder are mixed at a weight ratio of 1: 1, and further, an appropriate amount of an organic binder, a dispersant, an antifoaming agent, and a surfactant are added. The mixture was added to a ball mill together with PSZ balls and pure water, and wet mixed in the ball mill for about 16 hours to prepare a ceramic slurry. Thereafter, an oriented ceramic sheet having a thickness of about 200 μm was produced by the doctor blade method using this ceramic slurry.

  Thereafter, a Pt paste was screen-printed on a predetermined portion of the oriented ceramic sheet and dried to form internal electrodes.

  Next, a predetermined number of oriented ceramic sheets on which internal electrodes are formed are laminated, and are further sandwiched between oriented ceramic sheets on which no internal electrodes are formed, and a pressure of 200 MPa is applied for 1 minute so that the thickness becomes 6 mm. And pressed to produce a ceramic molded body. And after performing the binder removal process at 500 degreeC for this ceramic molded object, it baked at the temperature of 1200 degreeC for 2 hours, and produced the sintered compact block. By performing such a firing treatment, the plate-like ceramic particles are homoepitaxially grown while taking in non-oriented calcined powder as a seed crystal (template), thereby obtaining an oriented sintered body block (TGG method). . A ceramic sintered body having a thickness T: 10 mm, a width W: 10 mm, and a length L: 5 mm is obtained from the sintered body block, and the c-axis of the crystal axis is perpendicular to the surface having a thickness: 10 mm and a width: 10 mm. It cut out so that it might face, ie, an ab surface might face the length direction.

  Here, when a surface having a thickness of 10 mm and a width of 10 mm was analyzed using an X-ray diffraction method, and the c-axis orientation degree F was determined by the Lotgering method, the orientation degree F was 90%.

  Next, sputtering is performed using Ag as a target, and excitation electrodes are formed on both end faces of the ceramic sintered body. Then, an electric field of 8 kV / mm is applied for 10 minutes in oil at a bath temperature of 200 ° C. in the length direction. Polarization treatment was performed. Then, the sample subjected to the polarization treatment was cut with a dicing saw into the dimensions of thickness T: 2 mm, width W: 2 mm, and length L: 5 mm, as in sample number 1, to obtain a piezoelectric ceramic body on which excitation electrodes were formed. It was. Next, in order to connect the internal electrodes exposed on the side surface of the piezoelectric ceramic body in parallel, Ag paste containing Ag was applied to the side surface to form a surface electrode, and a sample No. 7 was prepared.

  A silver wire having a diameter of 0.2 mm was connected to the excitation electrode for applying an electric field, and a silver wire having a diameter of 0.2 mm was connected to the surface electrode for detecting an output signal.

[Characteristic evaluation of sample]
For the sample of Sample No. 7, the k ₃₃ value and the k ₃₁ value were measured in the same manner as in Example 1. The k ₃₃ value was 30%, and the k ₃₁ value was 3%. That is, in the oriented SBN material, the k ₃₁ value was sufficiently smaller than the k ₃₃ value, and it was confirmed that the influence of noise caused by the k ₃₁ value can be suppressed when driven in the longitudinal vibration mode.

  Next, using the measuring apparatus shown in FIG. 7, the applied electric field was adjusted so that the vibration speed was 2 m / s, and the output current when the applied magnetic field was changed by vibrating at the resonance frequency was measured.

  FIG. 11 shows the measurement results. As a comparative example, the measurement results of sample numbers 2 and 3 are shown again. In the figure, the horizontal axis represents the applied magnetic field [G], and the vertical axis represents the output current [nA].

  As is clear from FIG. 11, Sample No. 7 is stable even if the vibration speed is increased to 2 m / s because the piezoelectric ceramic body is formed of an oriented SBN material and is driven in the longitudinal vibration mode. Can be driven. As the applied magnetic field rises, the output current rises approximately in proportion to the applied magnetic field, and, similar to Sample No. 1, a high output current of 45 nA or more can be obtained when the applied magnetic field is 450 G. It was found that the sample numbers 2 and 3 using the material were remarkably superior.

  Next, for the sample numbers 2, 3, and 7, the change rate of the resonance frequency when the vibration speed was changed was obtained by using the measurement apparatus of FIG. 7 described above.

  FIG. 12 is a diagram showing the vibration speed dependency of the resonance frequency, where the horizontal axis indicates the vibration speed v [m / s], the vertical axis indicates the resonance frequency change rate Δfr [%], and the ♦ mark indicates the sample number 7. , X is sample number 2, and ▲ is sample number 3.

  As is apparent from FIG. 12, in Sample Nos. 2 and 3 using the PZT piezoelectric ceramic material, when the vibration speed v is increased, the resonance frequency change rate Δfr increases, and the decrease in the resonance frequency fr becomes remarkable. It turns out that it cannot drive.

  On the other hand, it was confirmed that Sample No. 7 using the oriented SBN material did not change substantially even when the vibration speed v increased, and could be driven stably at the resonance frequency.

[Sample No. 8]
Using a non-oriented CaBi ₄ Ti ₄ O _15- based material (hereinafter referred to as “non-oriented CBT-based material”) as a bismuth layered compound, a magnetic sensor operating in a longitudinal vibration mode as shown in FIG. 1 was produced. .

First, CaCO ₃ , Bi ₂ O ₃ , TiO ₂ , and MnCO ₃ were prepared as ceramic raw materials. Then, the ceramic raw material is weighed so that the final composition becomes the composition formula {Ca _0.8 Bi _4.2 Ti ₄ O ₁₅ + 0.01MnO}, and this weighed material is put into a ball mill together with PSZ balls and pure water. The mixture was obtained by wet mixing for about 20 hours.

  Then, a sample No. 8 was prepared by the same method and procedure as [Sample No. 1].

[Characteristic evaluation of sample]
For the sample of Sample No. 8, the k ₃₃ value and the k ₃₁ value were measured in the same manner as in Example 1. The k ₃₃ value was 18% and the k ₃₁ value was 6%. That is, in the non-oriented CBT material, the k ₃₁ value is sufficiently smaller than the k ₃₃ value, and it was confirmed that the influence of noise caused by the k ₃₁ value can be suppressed when driven in the longitudinal vibration mode.

  Next, using the measuring apparatus shown in FIG. 7, the applied electric field was adjusted so that the vibration speed was 2 m / s, and the output current when the applied magnetic field was changed by vibrating at the resonance frequency was measured.

  FIG. 13 shows the measurement results. As a comparative example, the measurement results of sample numbers 2 and 3 are shown again. In the figure, the horizontal axis represents the applied magnetic field [G], and the vertical axis represents the output current [nA].

  As can be seen from FIG. 13, sample No. 8 is made of a non-oriented CBT material made of a piezoelectric ceramic body and vibrates in the longitudinal vibration mode. Therefore, even if the vibration speed is increased to 2 m / s. Stable driving is possible. As the applied magnetic field rises, the output current rises approximately in proportion to the applied magnetic field, and, similar to Sample No. 1, a high output current of 45 nA or more can be obtained when the applied magnetic field is 450 G. It was found that the sample numbers 2 and 3 using the material were remarkably superior.

[Sample No. 9]
A magnetic sensor that operates in a longitudinal vibration mode as shown in FIG. 1 using a CaBi ₄ Ti ₄ O _15- based material (hereinafter referred to as “oriented CBT-based material”) oriented in the c-axis as a bismuth layer compound. did.

First, as in [Sample No. 8], CaCO ₃ , Bi ₂ O ₃ , TiO ₂ , and MnCO ₃ were prepared as ceramic raw materials. Then, the ceramic raw material is weighed so that the final composition becomes the composition formula {Ca _0.8 Bi _4.2 Ti ₄ O ₁₅ + 0.01MnO}, and this weighed material is put into a ball mill together with PSZ balls and pure water. The mixture was obtained by wet mixing for about 20 hours.

  Then, a sample No. 9 was prepared by the same method and procedure as [Sample No. 7]. The ceramic powder had an aspect ratio of about 5 and an orientation degree F of 90%.

[Characteristic evaluation of sample]
With respect to the sample of sample number 9, when the k ₃₃ value and the k ₃₁ value were measured in the same manner as in [Example 1], the k ₃₃ value was 32% and the k ₃₁ value was 4%. That is, in the non-oriented CBT material, the k ₃₁ value was sufficiently smaller than the k ₃₃ value, and it was confirmed that the influence of noise caused by the k ₃₁ value can be suppressed when it is vibrated in the longitudinal vibration mode.

  Next, using the measurement apparatus of FIG. 7 described above, the applied electric field was adjusted so that the vibration speed was 2 m / s, and the output current when the applied magnetic field was changed by driving at the resonance frequency was measured.

  FIG. 14 shows the measurement results. As a comparative example, the measurement results of sample numbers 2 and 3 are shown again. In the figure, the horizontal axis represents the applied magnetic field [G], and the vertical axis represents the output current [nA].

  As can be seen from FIG. 14, sample No. 9 is stable even if the vibration speed is increased to 2 m / s because the piezoelectric ceramic body is formed of an oriented CBT material and is vibrated in the longitudinal vibration mode. Can be driven. As the applied magnetic field rises, the output current rises approximately in proportion to the applied magnetic field, and, similar to Sample No. 1, a high output current of 45 nA or more can be obtained when the applied magnetic field is 450 G. It was found that the sample numbers 2 and 3 using the material were remarkably superior.

  Next, with respect to the sample number 9, the change rate of the resonance frequency when the vibration speed was changed was obtained using the measurement apparatus of FIG. 7 described above.

  FIG. 15 is a diagram showing the vibration speed dependence of the resonance frequency, and sample numbers 2 and 3 are shown again as a comparative example. In the figure, the horizontal axis represents the vibration velocity v (m / s), and the vertical axis represents the resonance frequency change rate Δfr (%).

  As apparent from FIG. 15, sample numbers 2 and 3 using the PZT piezoelectric ceramic material use the oriented CBT material while the resonance frequency change rate Δfr increases as the vibration speed v increases. In Sample No. 9, it was confirmed that the resonance frequency fr hardly changed even when the vibration velocity v increased.

  The vibration frequency dependence of the resonance frequency was compared between the oriented SBT material and the non-oriented SBT material. In addition, the relationship between the applied electric field and the vibration speed was examined for the oriented SBT material.

[Sample No. 10]
A ceramic green sheet is prepared by the same method and procedure as sample No. 1, and then a predetermined number of these ceramic green sheets are laminated, pressure-bonded, and fired. Thickness T: 10 mm, width W: 10 mm, length L: 5 mm A piezoelectric ceramic body was obtained.

  Next, sputtering is performed using Ag as a target to form excitation electrodes on both end faces, and then an electric field of 10.0 kV / mm is applied for 30 minutes in oil at a bath temperature of 200 ° C., and polarization treatment is performed in the length direction. went. The sample subjected to the polarization treatment was cut out using a dicing saw with a thickness T: 2 mm, a width W: 2 mm, and a length L: 5 mm, a silver wire having a diameter of 2 mm was connected to the excitation electrode, and non-oriented A sample No. 10 using an SBN material was produced.

  Note that this sample number 10 was prepared simply for measuring the vibration velocity dependence of the resonance frequency, and therefore no detection electrode was formed.

[Sample No. 11]
An oriented ceramic sheet was produced by the same method and procedure as Sample No. 7. Then, a predetermined number of these oriented ceramic sheets are laminated, pressure-bonded, fired, excitation electrodes are formed on both end faces, and a polarization treatment is applied in the length direction. Thickness T: 2 mm, width W: 2 mm, length L : A 5 mm piezoelectric ceramic body was obtained. In addition, it formed so that the ab surface of a crystal axis may face a length direction.

  In addition, since this sample number 11 is a sample for measuring the vibration speed dependency of the resonance frequency like the sample number 10, no detection electrode was formed.

[Characteristic evaluation of each sample]
Using the measuring device of FIG. 7, the dependence of the resonance frequency on the vibration velocity was examined.

  FIG. 16 is a diagram showing the vibration speed dependence of the resonance frequency. The horizontal axis indicates the vibration speed v, the vertical axis indicates the resonance frequency change rate Δfr, the ■ mark indicates the sample number 10, and the □ mark indicates the sample number 11. is there.

  As apparent from FIG. 16, sample number 11 using the non-oriented SBN material has a tendency that the resonance frequency Δfr tends to decrease as the vibration speed v increases, whereas sample number 10 using the oriented SBN material. It was found that the resonance frequency fr hardly changed even when the vibration speed v increased. That is, it was found that by using the oriented SBN material, a magnetic sensor having a stable vibration speed in which fluctuations in the resonance frequency are suppressed can be obtained. This is presumably because the bismuth layered compound has a large crystal anisotropy, so that when it is vibrated in the longitudinal vibration mode, the noise caused by the vibration in the longitudinal direction can be more effectively suppressed.

  Next, various AC electric fields are applied to Sample No. 10 using the oriented SBN material, and laser light from the laser irradiation device 38 is applied to the substantially central portion of the end surface, and the vibration velocity v for each applied electric field is set. Measurement was performed with a laser Doppler vibrometer 37.

  FIG. 17 is a diagram showing the relationship between the applied electric field and the vibration velocity v, where the horizontal axis represents the applied electric field (V / mm) and the vertical axis represents the vibration velocity v (m / s).

  As is apparent from FIG. 17, the vibration speed v fluctuates substantially in proportion to the applied electric field, and it was found that the vibration speed increased to nearly 4 m / s when the applied electric field reached about 14 V / mm.

  That is, when a conventional PZT material is used, the vibration speed is saturated at about 1 m / s (Non-Patent Document 2), but when an oriented SBN material is used, the vibration speed fluctuates substantially in proportion to the applied electric field. This confirmed the usefulness of the oriented SBN material in the magnetic sensor.

  In addition, although illustration is omitted, it was confirmed that for Sample No. 11 using the non-oriented SBN material, when the applied electric field was increased, the vibration speed increased approximately in proportion to the applied electric field up to about 3 m / s. .

It is the perspective view which showed typically one Embodiment (1st Embodiment) of the magnetic sensor which concerns on this invention. It is a longitudinal cross-sectional view of FIG. It is the perspective view which showed typically 2nd Embodiment of the magnetic sensor which concerns on this invention. It is a longitudinal cross-sectional view of FIG. It is a manufacturing process figure which shows the preparation procedures of the sample (this invention sample) of the sample number 1. FIG. It is a manufacturing process figure which shows the preparation procedures of the sample of a sample number 3 (comparative example sample). It is a schematic block block diagram of the measuring apparatus used by the Example of this invention. It is a characteristic view which shows the relationship between the applied magnetic field and output current in each sample of [Example 1]. It is a manufacturing process figure which shows the preparation procedures of the sample (this invention sample) of the sample number 4. FIG. It is a figure which shows the relationship between the applied magnetic field and output voltage in each sample of [Example 2]. It is the figure which showed the relationship between the applied magnetic field of sample number 7, and output current with sample number 2 and 3 (comparative sample). It is the figure which showed the vibration speed dependence of the resonant frequency of the sample number 7 with the sample numbers 2 and 3 (comparative sample). It is the figure which showed the relationship between the applied magnetic field of sample number 8, and output current with sample number 2 and 3 (comparative sample). It is the figure which showed the relationship between the applied magnetic field of sample number 9, and an output current with sample numbers 2 and 3 (comparative sample). It is the figure which showed the vibration speed dependence of the resonant frequency of the sample number 9 with the sample numbers 2 and 3 (comparative sample). It is the figure which showed the vibration speed dependence of the resonant frequency of sample numbers 10 and 11. It is a figure which shows the relationship between the applied electric field of sample number 10, and a vibration speed. It is the perspective view which showed typically the magnetic sensor driven in the length direction vibration mode described in the nonpatent literature 1. It is a schematic block diagram of the magnetic sensor described in patent document 1. . It is a figure which shows the contraction state of the magnetic sensor of a nonpatent literature 1. It is a figure which shows the expansion | extension state of the magnetic sensor of a nonpatent literature 1.

Explanation of symbols

2 Piezoelectric ceramic body 3a, 3b Excitation electrode 9a, 9b Detection electrode 4 Internal electrode 5 Internal electrode 7a, 7b Surface electrode 8a, 8b Surface electrode 12 Piezoelectric ceramic body 13a, 13b Excitation electrode 15 Detection electrode 16 Detection electrode

Claims (5)

A piezoelectric ceramic body made of a bismuth layered compound, a pair of excitation electrodes formed on both end faces in the polarization direction of the piezoelectric ceramic body, and a detection formed on at least a surface other than the both end faces of the piezoelectric ceramic body With electrodes,
A magnetic sensor, wherein an electric field is applied between the pair of excitation electrodes to be driven to vibrate in the same direction as the polarization direction, and the strength of the magnetic field is detected by the detection electrodes.   The detection electrode includes a plurality of internal electrodes embedded in the ceramic body, and a surface electrode formed on the surface of the piezoelectric ceramic body to electrically connect the plurality of internal electrodes. The magnetic sensor according to claim 1.   The magnetic sensor according to claim 1, wherein the detection electrode is formed on the surface of the ceramic body so as to be opposed to the ceramic body.   The magnetic sensor according to claim 3, wherein the detection electrode is made of a Ni—Fe alloy.   5. The magnetic sensor according to claim 1, wherein the bismuth layered compound has a crystal axis c-axis oriented in a direction orthogonal to the polarization direction of the piezoelectric ceramic body.

Images