JP2002204496A - Ultrasonic wave transmitter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem of a conventional ultrasonic wave transmitter that cannot have easily set a desired reproduction frequency because a bandwidth of a resonance peak is very narrow. SOLUTION: The ultrasonic wave transmitter of this invention is provided with an ultrasonic wave signal source that outputs a reproduction signal with a reproduction frequency of an ultrasonic wave band, a permanent magnet 8 that generates a magnetic field, a voice coil 5 that undergoes an electromagnetic force through the input of a current in response to the reproduction signal and reaches an operating state, and a dynamic electroacoustic transduction means consisting of a diaphragm 4 that is mechanically vibrated in response to the operation of the voice coil 5 to emit a sound wave, and the reproduction frequency is selected in matching with the primary or secondary natural frequency of the diaphragm 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
The present invention relates to an ultrasonic transmitter that emits ultrasonic waves having a reproduction frequency belonging to an ultrasonic band of z or more.

[0002]

2. Description of the Related Art FIG. 7 is a diagram showing a configuration of a conventional ultrasonic transmitter disclosed in Japanese Patent Application Laid-Open No. 9-327095.
In FIG. 7, reference numerals 21 and 22 denote piezoelectric discs made of a piezoelectric material such as ceramic; 23, a diaphragm made of metal such as stainless steel; 24, a flexible adhesive;
Reference numeral 7 denotes a pin for connecting the piezoelectric disk 21 and the cone vibrator 25, and reference numeral 30 denotes a lead wire.

The ultrasonic transmitter shown in FIG. 7 constitutes a bimorph vibrator (that is, an ultrasonic oscillator) in which piezoelectric disks 21 and 22 are arranged with a vibration plate 23 interposed therebetween. Piezoelectric disk 2
1 upper surface (joining surface of cone vibrator 25) and piezoelectric disc 2
Electrodes are present on the entire lower surface 2 (the bonding surface of the flexible adhesive 24), and each electrode is electrically connected to a terminal pin 29 via a lead wire 30. The composite of the bimorph vibrator and the cone vibrator 25 is configured such that when the bimorph vibrator flexes and vibrates, an annular vibration node 26 is formed on the conical surface of the cone vibrator 25.

Next, the operation will be described. When an electric signal in the ultrasonic band is input from an ultrasonic signal source (not shown) via the terminal pin 29, the bimorph vibrator flexes and vibrates according to the electric signal. Due to the vibration of the bimorph vibrator, the cone vibrator 25 vibrates in the opposite phase with the node 26 of the vibration of the cone vibrator 25 as a boundary. Ultrasonic waves are emitted by the vibration of the cone vibrator 25 and the bimorph vibrator.

FIG. 8 is a diagram showing the output sound pressure frequency characteristics of a conventional ultrasonic transmitter. In FIG. 8, the bimorph vibrator generates a natural frequency f ₁ (natural frequency) depending on the shape and the material, and a higher-order resonance occurs, and a resonance peak of a high output level is obtained near the natural frequency at which this resonance occurs. Can be

[0006]

Since the conventional ultrasonic transmitter is configured as described above, there is a problem that a desired reproduction frequency cannot be easily set because the resonance peak bandwidth is very narrow. Was.

The above problem will be described below. In the conventional ultrasonic transmitter, since the size of the vibration system is small and a very rigid material is used, a very sharp resonance peak characteristic is formed as shown in FIG. For example, the bandwidth in which a level 6 dB lower than the resonance peak level is obtained (the difference between the upper limit value and the lower limit value of the frequency) is generally at most several kHz or less in the ultrasonic band.

On the other hand, since the ultrasonic transmitter for reproducing the ultrasonic band is generally composed of small-sized members, the variation in the natural frequency is large and the production yield is low. Therefore, in the conventional ultrasonic transmitter, design for realizing a desired reproduction frequency is complicated, and frequency adjustment by a circuit is necessary even at the stage of manufacturing.

In addition, since the conventional ultrasonic transmitter is used near the natural frequency, the amplitude of the vibration becomes excessive when the input level is increased, and the ceramic disk, the metal vibration plate, and the supporting and fixing portion are increased. There is a problem that a difference in relative displacement occurs at the joining portion, which causes peeling or breakage, thereby limiting the input resistance.

Furthermore, since the conventional ultrasonic transmitter has a configuration electrically equivalent to a capacitor having a capacitance, the current of the leakage resistance cannot be ignored as the input level is increased, and the small structure However, since the heat capacity is small, there is a problem that damage such as dissolution of the adhesive occurs due to Joule heat.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and maintains the output sound pressure level high and widens the resonance peak bandwidth to increase the reproduction frequency of the ultrasonic band. An object is to configure an ultrasonic transmitter that can be easily set.

Another object of the present invention is to provide an ultrasonic transmitter in which peeling or breakage at a joint between components is less likely to occur.

It is a further object of the present invention to provide an ultrasonic transmitter which is less likely to be damaged such as dissolution of an adhesive due to Joule heat.

[0014]

SUMMARY OF THE INVENTION An ultrasonic transmitter according to the present invention includes an ultrasonic signal source for outputting a reproduction signal having a reproduction frequency in an ultrasonic band, a permanent magnet for generating a magnetic field, and a permanent magnet. A voice coil that is installed in a magnetic field that vibrates and vibrates due to electromagnetic induction when a current proportional to the reproduction signal flows, and a vibration that adheres to the voice coil and emits ultrasonic waves belonging to the ultrasonic band due to the vibration of the voice coil And electrokinetic electroacoustic conversion means having a plate.

In the ultrasonic transmitter according to the present invention, the primary or secondary natural frequency at which the resonance peak of the output sound pressure frequency characteristic of the ultrasonic wave radiated by the diaphragm occurs is defined as the reproduction frequency of the ultrasonic signal source. It is something to do.

In the ultrasonic transmitter according to the present invention, the sound pressure level of the resonance peak at the natural frequency is set to be higher than the average output sound pressure level at the lower frequency than the natural frequency by 10 dB or more. It was done.

An ultrasonic transmitter according to the present invention includes a horn acoustically coupled to a diaphragm provided in an electroacoustic conversion means, and radiates ultrasonic waves emitted from the diaphragm via the horn. is there.

In the ultrasonic transmitter according to the present invention, the electroacoustic conversion means includes a magnetic fluid for immersing the voice coil and dissipating Joule heat generated from the voice coil.

An ultrasonic transmitter according to the present invention, wherein the electroacoustic conversion means includes a damping material for suppressing vibration of the diaphragm and controlling the output sound pressure frequency characteristic of the ultrasonic wave radiated by the diaphragm. It is.

In the ultrasonic transmitter according to the present invention, the electroacoustic conversion means includes a sound absorbing material for absorbing the ultrasonic waves emitted from the diaphragm.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below. Embodiment 1 FIG. FIG. 1 is a diagram showing a configuration of an ultrasonic transmitter according to Embodiment 1 of the present invention. FIG. 1 shows a cross section of a rotating body of the ultrasonic transmitter with the line AA ′ as a rotation axis. In FIG. 1, 1 is a vibration system, 2 is a magnetic circuit,
3 is a horn. The vibration system 1 and the magnetic circuit 2 constitute electrokinetic electro-acoustic conversion means, and the electro-acoustic conversion means and an unillustrated ultrasonic signal source constitute an ultrasonic transmitter according to the first embodiment. I have.

In the vibration system 1, reference numeral 4 denotes a diaphragm having a circular flat plate shape, 5 denotes a voice coil fixed concentrically with the diaphragm 4,
Reference numeral 6 denotes an edge forming an outer peripheral portion integrally with the diaphragm 4, and reference numeral 7 denotes a spacer for supporting and fixing the edge 6. In the magnetic circuit 2, 8 is a ring-shaped permanent magnet, 9 is a pole piece, 1
0 is a plate, and 11 is a gap between the pole piece 9 and the plate 10. The horn 3 has an inner wall shape whose cross-sectional area gradually increases from the entire surface of the vibration system 1, and is fixed to the magnetic circuit 2. The electro-acoustic conversion means of the ultrasonic transmitter of FIG. 1 has the same configuration as a general dynamic speaker (electrodynamic type), but is different from the driving method of the vibration system 1 and the use of the horn 3 related thereto. It is characterized by having the property.

Next, the operation will be described. A reproduction signal in the ultrasonic band output from an ultrasonic signal source (not shown) is provided to the voice coil 5 via an amplifier (not shown). The permanent magnet 8 generates a strong magnetic field. When a current corresponding to the reproduction signal flows through the voice coil 5, the voice coil 5 inserted into the gap 11 of the magnetic circuit 2 receives an electromagnetic force according to Fleming's law. Vibrates in the vertical direction of FIG. 1 (parallel to the line AA ′). Since the diaphragm 4 supported by the edge 6 is fixed to the voice coil 5, it vibrates integrally with the voice coil 5 to generate ultrasonic waves. The generated ultrasonic waves
The sound is amplified acoustically by the horn 3 to a high level, and is radiated upward in FIG.

The output sound pressure frequency characteristic of the vibration system 1 has the characteristic shown in FIG. 2 at a point in the space on the line AA 'without the horn 3, similarly to a normal speaker.
FIG. 2 is a diagram showing output sound pressure frequency characteristics of a general speaker. The horizontal axis represents the frequency, and the vertical axis represents the output sound pressure level. From the low band to the middle band, a flat frequency characteristic is shown, and the high band has a fluctuation characteristic in which a resonance peak or a dip exists. The origin of the frequency characteristics in the high frequency range is because the frequency characteristics fall within the divided vibration band. That is, while the diaphragm 4 vibrates with a uniform amplitude over the entire surface of the diaphragm 4 in a low frequency range, a mechanical natural resonance phenomenon of the diaphragm 4 occurs in a high frequency range. The lowest-order resonance occurs at the natural frequency f ₁ in FIG. 2, and a large number of resonances occur at the natural frequency f ₁ and higher-order frequencies.

The output sound pressure frequency characteristic exhibits a resonance peak near a natural frequency at which these resonances occur. Considering the speaker from the material point of view, this resonance peak
The higher the rigidity of the diaphragm 4, the higher the frequency. The lower the internal loss of the diaphragm 4, the higher the level. Also, the smaller the size, the higher the frequency.

In a general loudspeaker, the high-frequency resonance peak and the fluctuation characteristics associated with the high-frequency resonance cause deterioration of sound quality. In addition, measures are taken to suppress the fluctuation characteristics and flatten the frequency characteristics. That is, the general design policy of the speaker diaphragm is to control the natural frequency to be high and the resonance peak to be low.

On the other hand, in the first embodiment, the main purpose is to positively use the resonance peak whose level increases, and the vibration is adjusted so that a high output sound pressure level can be obtained at the reproduction frequency of the reproduction signal. The primary or secondary natural frequencies f ₁ and f _{2 of the} plate 4 are made to match the reproduction frequency of the reproduction signal. According to this idea, to reduce the size and weight in order to increase efficiency, and at the same time, to maximize the resonance peak level while maintaining the bandwidth,
The diaphragm 4 having high rigidity and small internal loss is used. As the diaphragm 4, for example, a metal diaphragm such as aluminum or titanium can be used.

At this time, considering that the reproduction frequency is the same as that of the conventional ultrasonic transmitter, the outer diameter and the outer diameter of the diaphragm 4 are compared with the external dimensions of the piezoelectric ceramic vibrator in the conventional ultrasonic transmitter. The diameter of the driving voice coil 5 is large, and the material is also low in rigidity and small in internal loss. Therefore, as compared with the conventional ultrasonic transmitter, the output sound pressure level is equal to or less than that of the conventional ultrasonic transmitter, but the sharpness of the resonance peak is reduced, and the bandwidth of the resonance peak is widened and the frequency of several kHz to several tens kHz is increased. Characteristics can be obtained. This is shown in FIG.

FIG. 3 is a diagram showing the sound pressure frequency characteristics of the output of the ultrasonic transmitter of FIG. The horizontal axis represents the frequency, and the vertical axis represents the output sound pressure level. The sound pressure frequency characteristics of the ultrasonic transmitter according to the first embodiment are indicated by solid lines, and the sound pressure frequency characteristics (dashed line) of the conventional ultrasonic transmitter are also shown. Comparing the bandwidth at the resonance peak, the ultrasonic transmitter according to the first embodiment is wider than the conventional ultrasonic transmitter, so that the reproduction frequency can be easily set, Variations in manufacturing can be absorbed and frequency adjustment by a circuit can be made unnecessary.

By setting the difference between the resonance peak level and the average level of the flat portion in the middle band to 10 dB or more, a practical output sound pressure frequency characteristic can be obtained. By using the horn 3, the level can be increased. Become. Horn 3, it is designed to effectively amplify the sound wave of the frequency f ₁ of the resonance peaks formed by the vibrating plate 4.
If for example use a exponential horn to the horn 3, optimally so that the frequency f ₁ is set larger than the cutoff frequency of the exponential horn, the length and opening diameter of the horn 3, the cross-sectional shape amplification is maximized I will make it.

In the ultrasonic transmitter according to the first embodiment, since the amplitude of the movable portion of the diaphragm 4 supported by the edge 6 and the movable portion of the voice coil 5 is ensured, the sound pressure at the reproduction frequency is maintained. Not only can the level be improved, but also the structure is less susceptible to breakage as compared with a conventional ultrasonic transmitter using a member having small dimensions and high rigidity.

Further, the configuration is such that measures can be easily taken against the temperature rise at the time of continuous energization or large input. That is,
The heat resistance of the voice coil 5 itself through which the driving current flows is improved, or a heat radiation member is arranged near the voice coil 5 to take measures against the temperature rise. For example, as shown in FIG. 4, the magnetic fluid 12 is injected into the gap 11 of the magnetic circuit 2 to immerse the voice coil 5, and the heat generated from the voice coil 5 can be easily dissipated.

As described above, according to the first embodiment,
An ultrasonic signal source that outputs a reproduction signal having a reproduction frequency in the ultrasonic band, a permanent magnet 8 that generates a magnetic field, and is installed in the magnetic field and operates by receiving an electromagnetic force by input of a current corresponding to the reproduction signal. Voice coil 5 and diaphragm 4 that emits sound waves by mechanically vibrating according to the operation of voice coil 5
And an electro-acoustic electroacoustic conversion means composed of:
Since the reproduction frequency is made to match the primary or secondary natural frequency of the diaphragm 4, the resonance peak level at the desired natural frequency can be maintained and the resonance peak bandwidth can be widened. The effect that the output sound pressure level is maintained high, the reproduction frequency can be easily set, and an ultrasonic transmitter that is less likely to peel or break as compared with the conventional ultrasonic transmitter can be obtained.

According to the first embodiment, the output sound pressure frequency characteristics of the sound wave radiated by the ultrasonic transmitter
Since the difference between the output sound pressure level at the resonance peak of the natural frequency and the average output sound pressure level in the band equal to or lower than the natural frequency is secured to 10 dB or more, an ultrasonic transmitter having practical output sound pressure frequency characteristics Can be obtained.

Further, according to the first embodiment, the horn 3 for acoustically amplifying the sound wave emitted from the diaphragm 4 is provided, so that the sound pressure level of the emitted sound wave can be further increased. The effect that it can be obtained is obtained.

Further, according to the first embodiment, since the magnetic fluid 12 for dispersing the Joule heat generated by immersing the voice coil 5 is provided, breakage such as dissolution of the adhesive due to the Joule heat hardly occurs. The effect that an ultrasonic transmitter can be constituted is obtained.

Embodiment 2 In the ultrasonic transmitter according to the first embodiment, the shape of diaphragm 4 is circular and flat, but the shape of diaphragm 4 is not limited to this, and may be, for example, elliptical or rectangular. . Further, the cross-sectional shape may be a cone shape or a dome shape like a normal speaker. With these shapes, the same effects as in the first embodiment can be obtained.

In the first embodiment, the edge 6 is also a flat plate. However, the edge 6 may be formed into a roll shape or a corrugated shape. The advantage is that the linearity of the displacement with respect to can be maintained. Further, the edge 6 and the diaphragm 4
And may be formed integrally or separately.

Embodiment 3 In the first and second embodiments, the diaphragm 4 and the edge 6 having a large area are used.
Can be pasted on. Damping material 1 on diaphragm 4
FIG. 5 shows an example where 3 and 14 are attached. By doing so, an effect is obtained that the bandwidth near the resonance peak can be easily controlled.

Embodiment 4 FIG. A damping material may be arranged in the space surrounding structure of the vibration system 1, and a sound absorbing material may be arranged on the front and rear surfaces of the diaphragm 4 and the inner surface of the horn 3. FIG. 6 shows a sound absorbing material 15 at the entrance of the horn 3 facing the diaphragm 4,
The sound absorbing material 1 is provided on the upper surface of the pole piece 9 in the vacant space on the rear side of the diaphragm 4.
6 shows an example in which 6 is attached. By doing so, an effect is obtained that the bandwidth near the resonance peak can be easily controlled.

Embodiment 5 FIG. In the first to fourth embodiments, the configuration using the horn 3 has been described. However, the mounting of the horn 3 may be determined according to the specifications such as the sound pressure level of the resonance peak of the vibration system 1 and the bandwidth. Embodiment 1
The same effect can be obtained in the configuration 4 without the horn 3.

[0042]

As described above, according to the present invention, an ultrasonic signal source that outputs a reproduction signal having a reproduction frequency in the ultrasonic band, a permanent magnet that generates a magnetic field, and a magnetic field generated by the permanent magnet It has a voice coil that is installed and vibrates due to electromagnetic induction when a current proportional to the reproduction signal flows, and a diaphragm that adheres to the voice coil and emits ultrasonic waves belonging to the ultrasonic band by the vibration of the voice coil. Since an electro-acoustic transducer is provided, it is possible to obtain an effect that an ultrasonic transmitter in which peeling or breakage of a joint portion is less likely to occur as compared with a conventional ultrasonic transmitter.

According to the present invention, the primary or secondary natural frequency at which the resonance peak of the output sound pressure frequency characteristic of the ultrasonic wave radiated by the diaphragm occurs is set as the reproduction frequency of the ultrasonic signal source. Therefore, it is possible to secure the sound pressure level of the resonance peak and widen the bandwidth of the resonance peak, configure an ultrasonic transmitter that has a high output sound pressure level of the ultrasonic wave and easily sets the reproduction frequency. The effect that it can be obtained is obtained.

According to the present invention, since the sound pressure level of the resonance peak at the natural frequency is set to be 10 dB or more higher than the average output sound pressure level in the lower frequency range than the natural frequency, the electroacoustic conversion means can be used practically. The advantage is that an ultrasonic transmitter having a characteristic can be configured.

According to the present invention, the horn that acoustically couples with the diaphragm is provided in the electroacoustic conversion means, and the ultrasonic waves emitted by the diaphragm are radiated via the horn. The effect that the output sound pressure level of a sound wave can be increased is obtained.

According to the present invention, the voice coil is dipped,
Since the electro-acoustic conversion means is provided with the magnetic fluid for dissipating Joule heat generated from the voice coil, an effect is obtained that an ultrasonic transmitter that is less likely to be damaged such as dissolution of an adhesive due to Joule heat can be configured.

According to the present invention, the electroacoustic conversion means is provided with the damping material for suppressing the vibration of the diaphragm and controlling the output sound pressure frequency characteristics of the ultrasonic waves emitted from the diaphragm. The effect is obtained that the bandwidth can be easily controlled.

According to the present invention, the sound-absorbing material for absorbing the ultrasonic waves emitted from the diaphragm is provided in the electroacoustic conversion means, so that the effect of easily controlling the bandwidth of the resonance peak can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an ultrasonic transmitter according to Embodiment 1 of the present invention.

FIG. 2 is a diagram illustrating output sound pressure frequency characteristics of a general speaker.

FIG. 3 is a diagram illustrating a sound pressure frequency characteristic of an output of the ultrasonic transmitter in FIG. 1;

FIG. 4 is a diagram showing a magnetic fluid injected into a gap of a magnetic circuit.

FIG. 5 is a diagram showing an example in which a damping material is attached to a diaphragm.

FIG. 6 is a diagram illustrating an example in which a sound absorbing material is attached to an upper surface of a pole piece in an inlet of a horn facing a diaphragm and a rear side empty space of the diaphragm.

FIG. 7 is a diagram showing a configuration of a conventional ultrasonic transmitter disclosed in Japanese Patent Application Laid-Open No. 9-327095.

FIG. 8 is a diagram showing output sound pressure frequency characteristics of a conventional ultrasonic transmitter.

[Explanation of symbols]

1 vibration system, 2 magnetic circuit, 3 horn, 4 diaphragm,
5 voice coil, 6 edge, 7 spacer, 8 permanent magnet, 9 pole piece, 10 plate, 11 gap, 12 magnetic fluid, 13, 14 damping material, 1
5,16 Sound absorbing material.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Noboru Okino 2-6-1, Otemachi, Chiyoda-ku, Tokyo Within Mitsubishi Electric Engineering Co., Ltd. No. 1-4 Tokai Passenger Railway Co., Ltd. (72) Inventor Kazuhiro Matsuo 1-4-1 Meieki Station, Nakamura-ku, Nagoya-shi, Aichi F-term within Tokai Passenger Railway Co., Ltd. 5D019 AA08 AA09 AA17 AA20 DD02 GG05 GG07 5J083 AC29 CA15 CB30

Claims (7)

[Claims] 1. An ultrasonic signal source for outputting a reproduction signal having a reproduction frequency in an ultrasonic band, a permanent magnet for generating a magnetic field, and a permanent magnet installed in the magnetic field generated by the permanent magnet. An electrodynamic type of electricity having a voice coil that vibrates by an electromagnetic induction action when a proportional current flows, and a diaphragm that is fixed to the voice coil and emits ultrasonic waves belonging to the ultrasonic band by the vibration of the voice coil. An ultrasonic transmitter, comprising: an acoustic conversion unit. 2. The ultrasonic signal source according to claim 1, wherein a primary or secondary natural frequency at which a resonance peak of an output sound pressure frequency characteristic of the ultrasonic wave radiated by the diaphragm occurs is set as a reproduction frequency. Item 7. The ultrasonic transmitter according to Item 1. 3. The electroacoustic conversion means sets the sound pressure level of the resonance peak at the natural frequency higher by 10 dB or more than the average output sound pressure level in the lower frequency range than the natural frequency. An ultrasonic transmitter as described. 4. The electroacoustic conversion means includes a horn acoustically coupled to the diaphragm, and radiates ultrasonic waves emitted by the diaphragm via the horn. Item 3. The ultrasonic transmitter according to Item 2. 5. The electro-acoustic conversion means includes a magnetic fluid for immersing a voice coil and dissipating Joule heat generated from the voice coil. An ultrasonic transmitter as described. 6. The electroacoustic conversion means includes a damping material for suppressing vibration of the diaphragm and controlling output sound pressure frequency characteristics of ultrasonic waves radiated by the diaphragm. Item 6. The ultrasonic transmitter according to any one of Items 5 to 7. 7. The ultrasonic transmission according to claim 2, wherein the electroacoustic conversion unit includes a sound absorbing material that absorbs an ultrasonic wave emitted from the diaphragm. vessel.