JP2004274597A - Giant magnetostrictive broadband ultrasonic generator - Google Patents

Abstract

The present invention provides a giant magnetostrictive broadband ultrasonic generator capable of generating a constant level of sound pressure over a wide band.
A giant magnetostrictive element, which is a vibrating body having giant magnetostrictive characteristics, a magnetic field coil for applying a fluctuating magnetic field to the giant magnetostrictive element, a preload disc spring for applying a preload to the giant magnetostrictive element, a giant magnetostriction A giant magnetostrictive broadband ultrasonic generator 100 including a bias permanent magnet 12 for applying a bias magnetic field to the element 10.
[Selection diagram] Fig. 1

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a giant magnetostrictive broadband ultrasonic generator that generates ultrasonic waves in a wide band using a giant magnetostrictive material.
[0002]
[Prior art]
Most conventional ultrasonic transducers (or vibration transducers) are of the resonance type using piezoelectric ceramics as vibration elements (see FIG. 6, for example, Non-Patent Document 1). The ultrasonic transducer shown in FIG. 6 performs both the conversion of electricity into ultrasonic waves and the conversion of ultrasonic waves into electricity (transmission and reception of ultrasonic waves) using piezoelectric ceramics as the 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 leads 65 and 66 are connected to the surface opposite to the bonding surface.
[0003]
On the other hand, the unimorph type ultrasonic transducer shown in FIG. 6B includes one piezoelectric ceramic 71, a case 72, leads 73 and 74, internal wiring 75, and glass 76. The piezoelectric ceramic 71 is connected to a lead 73 via an internal wiring 75 and is grounded to a case 72.
[0004]
Since the resonance type ultrasonic transducer utilizes the resonance phenomenon of the piezoelectric ceramic, the transmission and reception characteristics of the ultrasonic wave are improved in a relatively narrow frequency band around the resonance frequency. The resonance frequency may change due to manufacturing variations, shift due to the influence of disturbance such as temperature and vibration, or change over time such as a change in the performance of the adhesive layer. In such a case, when driving at the same frequency, an effect such as a decrease in output occurs. Therefore, the resonance type ultrasonic transducer sometimes needs to tune the resonance frequency before or during use.
[0005]
On the other hand, a wideband type 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 vibrator. 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 so as to contact the lower surface. . The lower electrode 83 is connected to a lead 84 and 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 a case 80 together with metal rings 86, 87, and 88, and a mesh 89.
[0006]
On the surface of the lower electrode 83 on the side of the dielectric 81, a plurality of microscopic grooves having a non-uniform shape of about several tens to several hundreds μm are formed. Since the minute groove becomes a gap between the lower electrode 83 and the dielectric 81, the distribution of the capacitance between the upper electrode 82 and the lower electrode 83 changes minutely. The random minute grooves are formed by manually roughing the surface of the lower electrode 83 with a file. In the case of an electrostatic ultrasonic transducer, the frequency characteristics of the ultrasonic transducer are broadened by forming an infinite number of capacitors having different sizes and depths of air gaps. However, there is a great difference between individual characteristics, and it is a manual operation, which is inefficient.
[0007]
Further, since the intensity of the sound pressure by the ultrasonic wave increases in proportion to the frequency and the amplitude, it is important to increase either of them. However, an ultrasonic wave having a high frequency has a disadvantage that the attenuation rate is high and the reach is short.
[0008]
[Non-Patent Document 1] Ryosuke Masuda, "Beginners Book 2, First Sensor Technology," Industrial Research Committee, November 18, 1998, pp. 131-133
[0009]
[Problems to be solved by the invention]
By the way, there is a demand for an ultrasonic transducer to make the sound pressure level constant over a wide frequency range, in addition to broadening the frequency characteristics. On the other hand, as described above, on the other hand, 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 comparatively narrow frequency band. There is a problem that the production efficiency is poor, although the target can be widened.
[0010]
In order to obtain a constant sound pressure level in a wide frequency band, it is necessary to control the amplitude of the ultrasonic wave to a predetermined value over a wide frequency band. The magnitude of the amplitude can be managed by the displacement of a vibrating element or a vibrating body that is a source of ultrasonic waves. In a resonance type ultrasonic transducer using the above-described piezoelectric material or an electrostatic type ultrasonic transducer in a wide frequency band, the amount of displacement of a vibrating element or a vibrating body is small. Therefore, in order to manage the displacement amount with high accuracy, it is necessary to further improve the manufacturing quality and perform the output control with higher accuracy.
[0011]
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a giant magnetostrictive broadband ultrasonic generator capable of generating a constant 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 in which the displacement of a vibrating body with respect to a change in a magnetic field is large and the displacement can be easily managed.
[0012]
[Means for Solving the Problems]
In order to solve the above problems, the present invention provides a vibrating body having giant magnetostriction characteristics, a fluctuating magnetic field generating means for applying a fluctuating magnetic field to the vibrating body, a preload generating means for applying a preload to the vibrating body, And a bias magnetic field generating means. According to this configuration, since the vibrating body having the giant magnetostriction characteristics is used, the displacement amount of the vibrating body can be increased as compared with the vibrating body using a piezoelectric material or the like. Further, since the preload is applied to the vibrating body by the preload generating means, the magnetostriction gradient (magnetostriction 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 displacement can be improved. it can.
[0013]
Further, in the invention, it is preferable that a vibrating means including a plurality of vibrators vibrated by the vibrating body is provided at a tip end of the vibrating body. According to this configuration, since the plurality of transducers vibrate simultaneously at high frequency, it is possible to generate ultrasonic waves over a wide band.
[0014]
Further, the invention is characterized in that the vibrator is a needle-like projection extending in a vibration direction of the vibrator. According to this configuration, more vibrators can be provided at the tip of the vibrator, and ultrasonic waves can be generated over a wider frequency band.
[0015]
Further, the present invention is characterized in that the vibrating body has a columnar shape in which a plurality of grooves are formed or a thin plate-shaped 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 includes a coil wound in a cylindrical shape around the vibrating body, and the preload generating means includes a vibrating body. The bias magnetic field generating means is a cylindrical permanent magnet provided around the fluctuating magnetic field generating means, and the bias magnetic field generating means is formed of an elastic body contracted in a vibration direction, and the bias magnetic field generating means is surrounded by a cylindrical yoke. Features. According to this configuration, the components can be efficiently combined, and the size and efficiency of the device can be reduced.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of a giant magnetostrictive broadband ultrasonic wave generator according to the present invention will be described with reference to the drawings.
[0018]
FIG. 1 is a sectional view showing a configuration example of an embodiment of a giant magnetostrictive broadband ultrasonic wave generator according to the present invention. The 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, It includes a flange portion 18, a vibration pin 19, and a power supply terminal 20.
[0019]
The giant magnetostrictive element 10 is a columnar vibrator having giant magnetostrictive characteristics, and is formed of a giant magnetostrictive material such as a Tb-Dy-Fe alloy (an alloy of terbium-dysprosium-iron). A giant magnetostrictive element made of a Tb-Dy-Fe alloy has a displacement of about 2000 ppm, far exceeding that of a piezoelectric material made of PZT or the like. For example, when the thickness of the element (direction A) is 10 mm, the change amount is 20 μm.
[0020]
The magnetic field coil 11 serves as a fluctuating magnetic field generating means for applying a fluctuating magnetic field to the giant magnetostrictive element 10, and is a coil wound in a cylindrical shape around the giant magnetostrictive element 10. When an alternating current is applied to the magnetic field coil 11, a magnetic field varying 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 its 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 preload generating means for applying a preload to the giant magnetostrictive element 10. The preloading 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 (the 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 a magnetic flux generated by the magnetic field coil 11 and the bias permanent magnet 12 passes. Further, the yokes 14, 16, and 17 form 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 is formed in the center of the yoke 16 so that a flange portion 18 can move in the direction of arrow A. Is provided.
[0023]
The flange portion 18 is made of a non-magnetic material such as a metal such as stainless steel or brass or a plastic so as to have a two-stage cylindrical shape. The bottom surface of the flange portion 18 is fixed to the tip of the giant magnetostrictive element 10, and the opposite surface constitutes a contact portion of the preload disc spring 13 and a support portion of the vibrating pin 19 at the tip. ing.
[0024]
The vibrating pin 19 is a vibrator for generating ultrasonic waves fixed to the distal end of the flange portion 18, and is a needle-like protrusion extending in the vibration direction of the giant magnetostrictive element 10 (direction of arrow A). . The vibrating pins 19 are made of an iron-based, plastic-based, or silicon-based material, each have a diameter of about 100 μm, and a total of several hundred to several thousand pins are provided at the tip of the flange portion 18. As shown in FIG. 2, the vibration pins 19 are fixed by fitting the vibration pins 19, 19,... Into a plurality of recesses 18a, 18a,. . By using the vibrating pins 19 as needle-like protrusions extending in the vibration direction of the giant magnetostrictive element 10, more vibrating pins 19 can be densely provided at the tip of the giant magnetostrictive element 10. Thereby, an ultrasonic wave 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 supply 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 the magnetic field coil 11 generates a fluctuating magnetic field. The giant magnetostrictive element 10 vibrates in the direction of arrow A due to the fluctuating magnetic field. The vibration of the giant magnetostrictive element 10 results in the vibration of the flange portion 18 and the vibration pin 19 vibrates. That is, the plurality of vibrating pins 19 vibrate at a high frequency at the same time, and ultrasonic waves are generated using the vibrating pins 19 as a main vibration source.
[0027]
The frequency characteristics of the giant magnetostrictive broadband ultrasonic generator 100 when generating ultrasonic waves are broadband, for example, as shown in FIG. In the conventional device 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, in the giant magnetostrictive broadband ultrasonic generator 100 of the present embodiment, as shown by the solid line, a good (relatively large and constant) sound pressure level can be obtained in a wide frequency band. I have. 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 constantly applied to the giant magnetostrictive element 10 by the bias permanent magnet 12. Thereby, the giant magnetostrictive element 10 is displaced more linearly in response to a change in the current supplied to the magnetic field coil 11. That is, as shown in FIG. 4, for example, as compared with the case where there is no bias magnetic field (dashed line), when the bias magnetic field is present (solid line), the displacement is made to be more linear and larger with respect to the change of the current. Has become.
[0029]
A preload is applied to the giant magnetostrictive element 10 by a preload disc spring 13. Thereby, the magnetostriction efficiency (magnetostriction gradient) is increased. That is, as shown in FIG. 5, for example, by applying a preload, a larger magnetostriction can be obtained for the same magnetic field than when no preload is applied.
[0030]
The giant magnetostrictive element 10 may have a columnar shape in which a plurality of grooves are formed, or may have a thin plate-like member laminated in the vibration direction. In this case, the high frequency characteristics of the magnetostrictive element 10 as a magnetostrictive material can be further improved. Further, the preloading disc spring 13 is not limited to a disc spring, but may be a coil spring, a spiral spring, a leaf spring, or the like, or may be a preloading unit using hydraulic pressure or air pressure. Further, the bias permanent magnet 12 can be replaced with an electromagnet or the like.
[0031]
According to the present embodiment, the amount of displacement of the vibrating body can be large, so that the degree of influence of manufacturing variations can be reduced, and the amount of displacement can be controlled more accurately. The displacement can be easily managed. Therefore, it is possible to more easily generate a certain level of sound pressure over a wide band.
[0032]
As applied products of the present invention, a distance measuring sensor, a shape recognition sensor by three-dimensional scanning, a target material analysis sensor by a change in sound pressure, and the like are conceivable.
[Brief description of the drawings]
FIG. 1 is a sectional view showing an embodiment of a giant magnetostrictive broadband ultrasonic wave generator according to the present invention.
FIG. 2 is a plan view showing a shape of a tip (part) of a flange portion 18.
FIG. 3 is a frequency sound pressure characteristic diagram of the giant magnetostrictive broadband ultrasonic generator 100 of FIG.
FIG. 4 is a diagram showing a change in a current-displacement characteristic depending on presence / absence of 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 resonance ultrasonic transducer.
FIG. 7 is a configuration diagram of a conventional electrostatic broadband ultrasonic transducer.
[Description of References] 10 giant magnetostrictive element, 11 magnetic field coil, 12 bias permanent magnet, 13 disc spring for preload, 14 to 17 yoke, 18 flange, 19 vibrating pin, 20 power supply terminal, 100 giant magnetostrictive broadband ultrasonic wave generation apparatus

Claims (5)

A vibrating body having giant magnetostriction characteristics;
Fluctuating magnetic field generating means for applying a fluctuating magnetic field to the vibrating body;
A preload generating means for applying a preload to the vibrating body;
A giant magnetostrictive broadband ultrasonic generator, comprising: a bias magnetic field generating means for applying a bias magnetic field to a vibrating body. 2. The giant magnetostrictive broadband ultrasonic generator according to claim 1, wherein a vibrating means including a plurality of vibrators vibrated by the vibrating body is provided at a tip end of the vibrating body. 3. The giant magnetostrictive broadband ultrasonic generator according to claim 2, wherein the vibrator is a needle-like projection extending in a vibration direction of the vibrator. The super vibrator according to any one of claims 1 to 3, wherein the vibrator has a columnar shape in which a plurality of grooves are formed, or is formed by laminating thin plate-shaped members in a vibration direction. Magnetostrictive broadband ultrasonic generator. The vibrator has a cylindrical shape,
The fluctuating magnetic field generating means comprises a coil wound in a cylindrical shape around a vibrator,
The preload generating means is made of an elastic body contracted in a vibration direction of the vibrating body,
5. The bias magnetic field generating means is a cylindrical permanent magnet provided around the fluctuating magnetic field generating means, and comprises a magnet surrounded by a cylindrical yoke. 2. The giant magnetostrictive broadband ultrasonic generator according to claim 1.

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