JP4131179B2 - Giant magnetostrictive broadband ultrasonic generator - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a giant magnetostrictive broadband ultrasonic generator that uses a magnetostrictive material to generate ultrasound in a wide band.
[0002]
[Prior art]
Most conventional ultrasonic transducers (or vibration transducers) are resonant types using piezoelectric ceramics as vibration elements (see FIG. 6, for example, Non-Patent Document 1). The ultrasonic transducer shown in FIG. 6 performs both conversion of electricity into ultrasonic waves and conversion of ultrasonic waves into electricity (transmission and reception of ultrasonic waves) using a piezoelectric ceramic as a vibration element. The bimorph type ultrasonic transducer shown in FIG. 6A includes two piezoelectric ceramics 61 and 62, a cone 63, a case 64, leads 65 and 66, and a screen 67. The piezoelectric ceramics 61 and 62 are bonded to each other, and a lead 65 and a lead 66 are connected to a surface opposite to the bonded surface, respectively.
[0003]
On the other hand, the unimorph type ultrasonic transducer shown in FIG. 6B includes a single piezoelectric ceramic 71, a case 72, leads 73 and 74, an internal wiring 75, and a glass 76. The piezoelectric ceramic 71 is connected to a lead 73 via an internal wiring 75 and grounded to a case 72.
[0004]
Since the resonance type ultrasonic transducer uses the resonance phenomenon of the piezoelectric ceramic, the transmission and reception characteristics of the ultrasonic wave are good in a relatively narrow frequency band around the resonance frequency. This resonance frequency may change due to manufacturing variations, shift due to the influence of disturbances such as temperature and vibration, or be affected by changes over time such as changes in the performance of the adhesive layer. In such a case, when driving at the same frequency, an influence such as a decrease in output occurs. For this reason, the resonance type ultrasonic transducer may require tuning of the resonance frequency before or during use.
[0005]
On the other hand, an electrostatic ultrasonic transducer that vibrates due to an electrostatic effect has also been realized (FIG. 7). The electrostatic ultrasonic transducer shown in FIG. 7 uses a dielectric 81 (insulator) such as PET (polyethylene terephthalate resin) having a thickness of about 3 to 10 μm as a vibrating body. An upper electrode 82 formed as a metal foil is integrally formed on the upper surface of the dielectric 81 by a process such as vapor deposition, and a lower electrode 83 of brass is provided in contact with the lower surface. . The lower electrode 83 is connected to a lead 84 and is fixed to a base plate 85 made of bakelite or the like. The dielectric 81, the upper electrode 82, and the base plate 85 are caulked by the case 80 together with the metal rings 86, 87, and 88 and the mesh 89.
[0006]
On the surface of the lower electrode 83 on the dielectric 81 side, a plurality of minute grooves of about several tens to several hundreds μm having a non-uniform shape are formed. Since this minute groove becomes a gap between the lower electrode 83 and the dielectric 81, the electrostatic capacity distribution between the upper electrode 82 and the lower electrode 83 changes minutely. The random minute grooves are formed by manually rubbing the surface of the lower electrode 83 with a file. In the electrostatic ultrasonic transducer, the frequency characteristics of the ultrasonic transducer are wide-banded by forming innumerable capacitors having different gap sizes and depths in this way. However, the characteristic individual difference is very large, and the efficiency is low due to manual work.
[0007]
Further, since the intensity of sound pressure due to ultrasonic waves increases in proportion to the frequency and amplitude, it is important to increase one of them. However, ultrasonic waves with a high frequency have a drawback that the attenuation rate is high and the reaching distance is short.
[0008]
[Non-Patent Document 1]
Ryosuke Masuda, “Beginners Book 2, First Sensor Technology” Industrial Research Co., Ltd., November 18, 1998, pp. 131-133
[0009]
[Problems to be solved by the invention]
By the way, there is a demand for ultrasonic transducers to make the sound pressure level constant over a wide frequency range in addition to widening the frequency characteristics. On the other hand, as described above, the resonance type ultrasonic transducer as shown in Non-Patent Document 1 has a problem that the frequency band is narrow, while the electrostatic type ultrasonic transducer has a frequency band comparison. However, there is a problem that manufacturing efficiency is poor.
[0010]
In order to obtain a constant sound pressure level in a wide frequency band, it is necessary to manage the amplitude of the ultrasonic wave to a predetermined magnitude over a wide frequency band. The magnitude of the amplitude can be managed by the amount of displacement of the vibrating element or vibrating body that is the source of ultrasonic waves. The resonance type ultrasonic transducer using the piezoelectric material as described above and the electrostatic ultrasonic transducer having a wide frequency band have a small displacement amount of the vibration element and the vibration body. Therefore, if the displacement amount is to be managed with high accuracy, it is necessary to further improve the manufacturing quality or perform output control with higher accuracy.
[0011]
The present invention has been made in view of the above circumstances, and an object thereof is to provide a giant magnetostrictive broadband ultrasonic generator capable of generating a certain level of sound pressure over a wide band. More specifically, it is an object of the present invention to provide a giant magnetostrictive broadband ultrasonic generator that has a large amount of displacement of a vibrating body with respect to a change in a magnetic field and that can easily manage the amount of displacement.
[0012]
[Means for Solving the Problems]
In order to solve the above problems, the present invention provides a vibrating body having a giant magnetostrictive characteristic, a varying magnetic field generating means for applying a varying magnetic field to the vibrating body, a preload generating means for applying a preload to the vibrating body, and a bias magnetic field applied to the vibrating body. And a bias magnetic field generating means for applying. According to this configuration, since the vibrating body having the giant magnetostrictive characteristic is used, the displacement amount of the vibrating body can be increased as compared with the case where a piezoelectric material or the like is used for the vibrating body. Further, since the preload is applied to the vibrating body by the preload generating means, the magnetostrictive gradient (magnetostrictive gradient) is increased, and the bias magnetic field is applied to the vibrating body by the bias magnetic field generating means, so that the linearity of the displacement can be improved. it can.
[0013]
Further, the present invention is characterized in that a vibrating means comprising a plurality of vibrators vibrated by the vibrating body is provided at the tip of the vibrating body. According to this configuration, since a plurality of vibrators vibrate at a high frequency simultaneously, it is possible to generate ultrasonic waves over a wide band.
[0014]
In the invention, it is preferable that the vibrator is a needle-like protrusion that extends in the vibration direction of the vibrator. According to this configuration, more vibrators can be provided at the tip of the vibrating body, and ultrasonic waves can be generated over a wider frequency band.
[0015]
In addition, the present invention is characterized in that the vibrating body is a cylinder having a plurality of grooves or a thin plate member laminated in the vibration direction. According to this configuration, the high frequency characteristics of the vibrator can be improved.
[0016]
Further, according to the present invention, the vibrating body has a columnar shape, the fluctuating magnetic field generating means comprises a coil wound around in a cylindrical shape around the vibrating body, and the preload generating means is a vibrating body. The bias magnetic field generating means is a cylindrical permanent magnet provided around the variable magnetic field generating means and surrounded by a cylindrical yoke. Features. According to this configuration, the components can be combined efficiently, and the apparatus can be reduced in size and efficiency.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of a giant magnetostrictive broadband ultrasonic generator according to the present invention will be described with reference to the drawings.
[0018]
FIG. 1 is a cross-sectional view showing a configuration example of an embodiment of a giant magnetostrictive broadband ultrasonic generator according to the present invention. A giant magnetostrictive broadband ultrasonic generator 100 shown in FIG. 1 includes a giant magnetostrictive element 10, a magnetic field coil 11, a bias permanent magnet 12, a preload disc spring 13, yokes 14, 15, 16, and 17, A flange portion 18, a vibration pin 19, and a power supply terminal 20 are provided.
[0019]
The giant magnetostrictive element 10 is a cylindrical vibration body having giant magnetostrictive characteristics, and is made of a giant magnetostrictive material such as a Tb-Dy-Fe alloy (terbium-dysprosium-iron alloy). A giant magnetostrictive element made of a Tb—Dy—Fe alloy has a displacement amount of about 2000 ppm, far exceeding that of a piezoelectric material made of PZT or the like. For example, when the element thickness (direction A) is 10 mm, the amount of change is 20 μm.
[0020]
The magnetic field coil 11 is a variable magnetic field generating means for applying a variable magnetic field to the giant magnetostrictive element 10, and is a coil wound around the giant magnetostrictive element 10 in a cylindrical shape. When an alternating current is passed through the magnetic field coil 11, a magnetic field that fluctuates in the direction of arrow A is generated.
[0021]
The bias permanent magnet 12 serves as bias magnetic field generating means for applying a bias magnetic field to the giant magnetostrictive element 10, and the magnetization direction is the direction of arrow A. The bias permanent magnet 12 is a cylindrical permanent magnet provided around the magnetic field coil 11, and is surrounded by a cylindrical yoke 14. The preload disc spring 13 serves as a preload generating means for applying a preload to the giant magnetostrictive element 10. The preload disc spring 13 is an elastic body that is sandwiched between the flange portion 18 and the yoke 17 and contracted in the vibration direction of the giant magnetostrictive element 10 (direction of arrow A).
[0022]
The yokes 14, 15, 16, and 17 are made of a ferromagnetic magnetic material, and form a magnetic circuit through which the magnetic flux generated by the magnetic field coil 11 and the bias permanent magnet 12 passes. Further, the yokes 14, 16, and 17 serve as an outer frame of the giant magnetostrictive broadband ultrasonic generator 100, and the yokes 14, 15, and 16 have a function of supporting the giant magnetostrictive element 10, the magnetic field coil 11, and the bias permanent magnet 12. Have. The yokes 14 and 15 have a cylindrical shape (or an annular shape), the yokes 16 and 17 have a disk shape, and a through-hole for allowing the flange portion 18 to move in the direction of arrow A at the center of the yoke 16. Is provided.
[0023]
The flange portion 18 is composed of a metal such as stainless steel or brass, or a nonmagnetic material such as plastic so as to have a two-stage cylindrical shape. The bottom surface of the flange portion 18 is fixed to the tip portion of the giant magnetostrictive element 10, and the opposite surface constitutes the contact portion of the preload disc spring 13 and the support portion of the vibration pin 19 at the tip portion. ing.
[0024]
The vibration pin 19 is an ultrasonic wave generating vibrator fixed to the tip of the flange portion 18, and is a needle-like protrusion that extends in the vibration direction of the giant magnetostrictive element 10 (direction of arrow A). . The vibration pins 19 are made of an iron-based, plastic-based, or silicon-based material, each having a diameter of about 100 μm, and a total of hundreds to thousands are provided at the tip of the flange portion 18. As shown in FIG. 2, the vibration pin 19 is fixed by fitting the vibration pins 19, 19,... Into a plurality of recesses 18a, 18a,. . Thus, by making the vibration pins 19 into needle-like protrusions extending in the vibration direction of the giant magnetostrictive element 10, more vibration pins 19 can be densely provided at the tip of the giant magnetostrictive element 10. As a result, ultrasonic waves can be generated over a wider frequency band.
[0025]
The power supply terminal 20 is a connector fixed to the yoke 16 and includes a contact and an insulating member. The power terminal 20 is provided with two contacts connected to both ends of the magnetic field coil 11.
[0026]
With the above configuration, when an AC voltage having a frequency of 20 kHz or more is applied from the power supply terminal 20 to both ends of the magnetic field coil 11, an alternating current flows through the magnetic field coil 11 and a magnetic field is generated by the magnetic field coil 11. The giant magnetostrictive element 10 vibrates in the direction of arrow A due to this fluctuating magnetic field. The vibration of the giant magnetostrictive element 10 becomes the vibration of the flange portion 18 and the vibration pin 19 vibrates. That is, the plurality of vibration pins 19 simultaneously vibrate at a high frequency, and ultrasonic waves are generated using the vibration pins 19 as a main vibration source.
[0027]
The frequency characteristics when ultrasonic waves are generated by the giant magnetostrictive broadband ultrasonic generator 100 are, for example, wideband as shown in FIG. In the conventional element as shown in FIG. 6, a good sound pressure level can be obtained only for an input in a frequency band near the resonance frequency, as indicated by a broken line. In contrast, the giant magnetostrictive broadband ultrasonic generator 100 of the present embodiment can obtain a good (relatively large and constant) sound pressure level in a wide frequency band, as shown by the solid line. Yes. In FIG. 3, the horizontal axis represents the frequency of the applied AC voltage, and the vertical axis represents the sound pressure level.
[0028]
In the configuration shown in FIG. 1, a bias magnetic field is always applied to the giant magnetostrictive element 10 by the bias permanent magnet 12. As a result, the giant magnetostrictive element 10 is displaced more linearly with respect to a change in the current applied to the magnetic field coil 11. That is, for example, as shown in FIG. 4, when there is a bias magnetic field (solid line) as compared to the case without a bias magnetic field (broken line), the current is changed more linearly and more greatly. It has become.
[0029]
Further, a preload is applied to the giant magnetostrictive element 10 by a preload disc spring 13. Thereby, the magnetostriction efficiency (magnetostrictive gradient) is enhanced. That is, for example, as shown in FIG. 5, by applying a preload, it is possible to obtain a larger magnetostriction with respect to the same magnetic field as compared with the case where there is no preload.
[0030]
The giant magnetostrictive element 10 can have a cylindrical shape in which a plurality of grooves are formed, or can be a laminate of thin plate members in the vibration direction. In this case, the high frequency characteristic as the magnetostrictive material of the giant magnetostrictive element 10 can be further improved. The preload disc spring 13 is not limited to a disc spring, and may be a coil spring, a spiral spring, a leaf spring, or the like, or a preload means using hydraulic pressure or air pressure. Further, the bias permanent magnet 12 can be replaced with an electromagnet or the like.
[0031]
According to this embodiment, since the amount of displacement of the vibrating body can be increased, it is possible to reduce the degree of influence of manufacturing variation or to control the amount of displacement more accurately. It becomes easier to manage the amount of displacement. Therefore, a certain level of sound pressure can be easily generated over a wide band.
[0032]
In addition, as a product applied to the present invention, a distance measuring sensor, a shape recognition sensor based on three-dimensional scanning, an object material analysis sensor based on a change in sound pressure, and the like can be considered.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an embodiment of a giant magnetostrictive broadband ultrasonic generator according to the present invention.
FIG. 2 is a plan view showing the shape of a tip portion (a part) of a flange portion 18;
3 is a frequency sound pressure characteristic diagram of the giant magnetostrictive broadband ultrasonic generator 100 of FIG. 1; FIG.
FIG. 4 is a diagram showing a change in current-displacement characteristics with and without a bias magnetic field.
FIG. 5 is a diagram showing a change in magnetic field-magnetostriction characteristics due to preload.
FIG. 6 is a configuration diagram of a conventional piezoelectric ultrasonic transducer.
FIG. 7 is a configuration diagram of a conventional electrostatic broadband ultrasonic transducer.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Giant magnetostrictive element, 11 Magnetic field coil, 12 Bias permanent magnet, 13 Preload disk spring, 14-17 Yoke, 18 Flange part, 19 Vibration pin, 20 Power supply terminal, 100 Giant magnetostrictive type broadband ultrasonic generator

Claims (4)

A vibrator having super magnetostrictive characteristics;
A varying magnetic field generating means for applying a varying magnetic field to the vibrating body;
Preload generating means for applying a preload to the vibrating body;
Bias magnetic field generating means for applying a bias magnetic field to the vibrating body,
A giant-magnetostrictive broadband ultrasonic wave generating device characterized in that a vibrating means comprising a plurality of vibrators vibrated by the vibrating body is provided at the tip of the vibrating body.   2. The giant magnetostrictive broadband ultrasonic generator according to claim 1, wherein the vibrator is a needle-like protrusion extending in a vibration direction of the vibrator.   The super vibrator according to any one of claims 1 to 2, wherein the vibrator has a cylindrical shape in which a plurality of grooves are formed, or a thin plate-like member laminated in a vibration direction. Magnetostrictive broadband ultrasonic generator. The vibrator has a cylindrical shape;
The fluctuating magnetic field generating means is a coil wound around in a cylindrical shape around the vibrating body;
The preload generating means is an elastic body contracted in a vibration direction of the vibrating body;
The bias magnetic field generation means is a cylindrical permanent magnet provided around the fluctuation magnetic field generation means, and is surrounded by a cylindrical yoke. A giant magnetostrictive broadband ultrasonic generator according to claim 1.

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