JP2014082572

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DESCRIPTION JP2014082572
Abstract: The present invention provides an electro-acoustic transducer in which the connection
between a vibrating member and a piezoelectric member has mechanical strength that does not
break against long-term vibration and does not reduce the effect of acoustic radiation. An electroacoustic transducer includes a rigid frame 7, a support member 5 attached to the frame 7, and a
piezoelectric member (piezoelectric ceramic 3) made of a piezoelectric material supported by the
support member 5. And a metal diaphragm 2 attached to the surface of the piezoelectric
member. Furthermore, the electroacoustic transducer has a vibrating member (cone 1) directly
joined to the metal vibrating plate 2 without any other member, and the vibrating member is a
piezoelectric member via the metallic vibrating plate 2 And the vibration can be transmitted to
each other. [Selected figure] Figure 1
Electro-acoustic transducer
[0001]
The present invention relates to an electroacoustic transducer having a vibrating member.
[0002]
In recent years, the demand for portable electronic devices such as mobile phones, notebook
computers, and PDAs (Personal Digital Assistants) has been expanding.
In such electronic devices, sound functions such as videophone calls, video playback, hands-free
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phones, etc. are frequently used. In order to use these acoustic functions, an electroacoustic
transducer is required to convert the sound wave and the electrical signal emitted by the
electronic device. An electroacoustic transducer to which a piezoelectric effect is applied is used
for an electroacoustic transducer such as a cellular phone. The electro-acoustic transducer to
which the piezoelectric effect is applied generates vibration using the expansion and contraction
motion generated by applying an electric field to a piezoelectric member made of a piezoelectric
material.
[0003]
As shown in FIG. 5, an electro-acoustic transducer having a cone (cone-like diaphragm) 1 having
a bottom having an elliptical shape with the major axis at the node of the first resonant
frequency and the minor axis at the second resonant frequency. A vessel is disclosed in Patent
Document 1. The electro-acoustic transducer includes a cone 1, a piezoelectric ceramic
(piezoelectric element disk) 3 connected to the cone 1, a lead wire (electrode lead wire of the
piezoelectric element) 8 for transmitting an electric signal to the piezoelectric ceramic 3, have.
The electroacoustic transducer further includes a frame 7 supporting the piezoelectric ceramic 3
and an elastic material (cushion material) 6 for preventing the vibration of the piezoelectric
ceramic 3 from being transmitted to the frame 7. The elliptical bottom of the cone 1 is fixed to
the piezoelectric ceramic 3 by means such as an adhesive (adhesive layer 10). By forming the
bottom of the cone 1 in an elliptical shape having a diameter matched to the nodes of the first
and second resonant frequencies, the resonant modes are dispersed, and uniform response can
be obtained over a wider frequency band.
[0004]
An electroacoustic transducer (ultrasonic ceramic microphone) in which a metal diaphragm
formed by bending a part of the side surface of a cone (conical metal resonator) outward is
attached to a piezoelectric ceramic (piezoelectric ceramic plate), It is disclosed in Patent
Document 2. This electroacoustic transducer is comprised from the vibrator ¦ oscillator which
consists of a cone ¦ corn, a metal diaphragm, and piezoelectric ceramics, a lead wire, an elastic
material (elastic adhesive agent), a flame ¦ frame (case), and a terminal board. By integrally
forming the metal diaphragm and the cone bonded to the piezoelectric ceramic, it is not
necessary to use an adhesive between the cone and the metal diaphragm, so the frequency
change with respect to the temperature change is extremely small, the sound pressure As the
level is improved, the stability of production is improved.
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[0005]
Japanese Patent Application Laid-Open No. 60-214200 Japanese Patent Application Laid-Open
No. 1-222599
[0006]
In the invention disclosed in Patent Document 1, the bottom of the cone and the piezoelectric
ceramic are bonded with an adhesive or the like, and when the cone vibrates by sound waves or
when the piezoelectric ceramic vibrates by an electronic signal, the adhesive vibrates. Susceptible
to
Vibration from the cone or the piezoelectric ceramic generates a large stress in the adhesive, and
the mechanical strength of the adhesive may possibly endure long-term vibration without
causing damage. The failure of the adhesive not only hinders accurate transmission of vibration
between the cone and the piezoelectric ceramic, but also causes a problem of causing peeling
between the cone and the piezoelectric ceramic. Furthermore, due to the low mechanical strength
of the adhesive, antiphase vibration is generated between the cone and the piezoelectric ceramic,
resulting in a problem that the efficiency of acoustic radiation of the cone is reduced.
[0007]
In order to solve the problem due to the adhesive having a low mechanical strength as described
above, in the invention disclosed in Patent Document 2, a part of the side of the cone is cut out
and bent outward to integrally form a metal with the cone. A diaphragm is formed, and the metal
diaphragm is attached to the piezoelectric ceramic. However, because a part of the side of the
cone is bent outward, the mechanical strength of the cone itself becomes low, and it can not
withstand the long-term vibration, especially at the boundary between the cone and the metal
diaphragm, resulting in breakage. There is a risk of
[0008]
Therefore, an object of the present invention is to solve the above-mentioned problems, and the
connection between the vibrating member and the piezoelectric member has mechanical strength
that does not break against long-term vibration, and further the effect of acoustic radiation
Providing an electroacoustic transducer that does not reduce
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[0009]
In order to achieve the above object, the present invention is an electroacoustic transducer,
comprising: a rigid frame; a support member attached to the frame; and a piezoelectric member
made of a piezoelectric material supported by the support member And a vibrating member that
is directly bonded to the surface of the piezoelectric member, and a vibrating member that is
directly joined to the metallic vibrating plate without any other member, and the vibrating
member is made via the vibrating metal plate. It is characterized in that vibrations can be
transmitted to and from the piezoelectric member.
[0010]
According to the present invention, a metal vibration plate is provided between the vibration
member and the piezoelectric member, and the vibration member and the metal vibration plate
are directly joined without any other member, thereby receiving long-term vibration. It is
possible to construct an electroacoustic transducer which is not damaged.
In addition, since the vibrating member itself is not directly cut out and directly joined to the
metal diaphragm, the mechanical strength of the vibrating member itself is high, and is not
damaged even by long-term vibration, thereby reducing the effect of acoustic radiation. I will not
let you.
[0011]
It is a sectional view showing an electroacoustic transducer of an embodiment of the present
invention.
It is a perspective view which shows the process of pressing in a vibration member and a metal
diaphragm. It is sectional drawing which shows the modification made into the structure except
the metal supporting plate of embodiment of this invention. It is sectional drawing which shows
the modification which made the vibration member of embodiment of this invention the flat
form. FIG. 7 is a cross-sectional view showing a conventional electroacoustic transducer having
an adhesive layer.
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[0012]
Hereinafter, embodiments of the present invention will be described with reference to the
drawings.
[0013]
FIG. 1 is a cross-sectional view showing an electro-acoustic transducer provided with a conicalshaped vibrating member according to an embodiment of the present invention.
[0014]
The electroacoustic transducer comprises a cone 1, a metal diaphragm 2, a piezoelectric ceramic
3, a metal support plate 4, a support member 5, an elastic member 6, a frame 7, a lead wire 8
and an electrode 9. It is configured.
The cone 1 is a vibrating member that vibrates by a sound wave or an electric signal, and is
formed in a continuous and continuous conical shape, and is made of metal.
The metal diaphragm 2 is provided on the top side of the conical cone 1 and formed in a flat
plate shape, and is made of metal. The piezoelectric ceramic 3 which is a piezoelectric member is
provided on the back surface of the surface of the metal diaphragm 2 to which the cone 1 is
connected, and is formed in a flat plate shape. The metal support plate 4 is provided on the back
surface of the surface of the piezoelectric ceramic 3 to which the metal diaphragm 2 is
connected, is formed in a flat plate shape, and is made of metal. The support member 5 is
provided on the back surface of the surface of the metal support plate 4 to which the
piezoelectric ceramic 3 is connected, and is formed in a flat plate shape. The elastic member 6 is
provided at both ends of the support member 5 and is made of an elastomer, an adhesive having
elasticity, or the like. The frame 7 is disposed so as to surround the metal diaphragm 2, the
piezoelectric ceramic 3 and the metal supporting plate 4, has a recess, and supports the
supporting member 5 via the elastic member 6. It is made of a high strength material or the like.
At least two lead wires 8 are provided. One end of one lead wire 8a is connected to one surface of
the piezoelectric ceramic 3 and the other end to the electrode 9a, and the other lead wire 8b is
connected to the other end of the piezoelectric ceramic 3 And the other end are respectively
connected to the electrode 9b. The electrodes 9 are attached to the outer wall of the frame 7.
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[0015]
The cone 1 and the metal diaphragm 2 are directly joined without another member such as a
resin-based or rubber-based adhesive. In the present embodiment, as shown in FIG. 2, a hole for
accommodating the cone 1 is provided at the central portion of the metal diaphragm 2. The cone
1 has a cylindrical portion having a diameter larger than the diameter of the hole of the metal
diaphragm 2 on the apex side of the conical shape of the cone 1. In the present embodiment, the
cylindrical portion of the cone 1 is press-fitted into the hole of the metal diaphragm 2 so that the
cone 1 and the metal diaphragm 2 are mechanically and directly joined. In addition, about the
method to which cone 1 and metal diaphragm 2 are directly joined, you may join integrally using
welding etc. other than press-fitting.
[0016]
The metal diaphragm 2 and the piezoelectric ceramic 3 are bonded in a state in which the lead
wire 8 a is connected to the surface of the piezoelectric ceramic 3 and in a state of being
laminated by an epoxy adhesive or the like. Similarly, the piezoelectric ceramic 3 and the metal
supporting plate 4 are bonded in a state in which the lead wire 8 b is connected to the surface of
the piezoelectric ceramic 3 and laminated with an epoxy adhesive or the like. The thickness of
the metal diaphragm 2 and the metal support plate 4 at this time is configured in accordance
with a desired resonance frequency. The piezoelectric ceramic 3 is thicker than the metal
diaphragm 2 and the metal supporting plate 4 and, for example, a large one such as 200 μm
thick is used.
[0017]
The metal support plate 4 and the support member 5 are adhered in a state of being laminated
by an epoxy adhesive or the like. In addition, without providing the metal supporting plate 4
between the piezoelectric ceramic 3 and the supporting member 5, as shown in FIG. 3, the
piezoelectric ceramic 3 and the supporting member 5 may be bonded. The support member 5 is
held by an elastic member 6 at its end. The elastic member 6 is bonded to the inner wall of the
frame 7. Thereby, the metal diaphragm 2, the piezoelectric ceramic 3, the metal support plate 4
and the support member 5 which are stacked and bonded are accommodated in the recess of the
frame 7. The cone 1 is arranged to protrude from the recess of the frame 7. The support member
5 may not be bonded to the frame 7 via the elastic member 6, and the support member 5 may be
bonded to the frame 7.
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[0018]
The lead wires 8 connected to the respective surfaces of the piezoelectric ceramic 3 are drawn
out from the inside of the recess of the frame 7 and bonded to the electrodes 9 attached to the
outer wall of the frame 7. The electrode 9 is connected to a CPU (Central Processing Unit) (not
shown) or the like mounted on a portable electronic device, and transmits an electric signal
converted from a sound wave to the CPU, or an electric signal from the CPU It is transmitted to
the ceramics 3.
[0019]
Further, as shown in FIG. 4, in the present embodiment, the shape of the vibration member which
is the cone 1 may not be conical but may be flat. The flat vibrating member has a cylindrical
portion which protrudes from the center of the flat shape and which has a diameter larger than
the diameter of the hole of the continuous metal diaphragm 2 without break. By pressing the flat
plate-shaped cylindrical portion into the hole of the metal diaphragm 2, the flat plate and the
metal diaphragm 2 are mechanically and directly joined. In addition, about the method to which a
flat plate shape and the metal diaphragm 2 are directly joined, you may join integrally using
welding etc. other than press injection. By making the vibrating member into a flat plate shape,
the processing cost when creating the vibrating member itself can be suppressed, and the
manufacturing cost of the entire electroacoustic transducer can be reduced.
[0020]
The method of mutually converting a sound wave and an electric signal by the electroacoustic
transducer of the structure demonstrated above is demonstrated.
[0021]
The behavior of each component when sound is generated from the portable electronic device in
a frequency band of 40 kHz or more will be described.
[0022]
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A CPU (not shown) mounted on the portable electronic device transmits an electrical signal to the
electrode 9.
Each of the electrodes 9a and 9b that receives the electrical signal transmits the electrical signal
to the piezoelectric ceramic 3 inside the frame 7 through the lead wires 8a and 8b connected to
the respective electrodes 9a and 9b.
Since the piezoelectric ceramic 3 is a piezoelectric material, the shape of the piezoelectric
ceramic 3 is deformed by the piezoelectric effect when an electrical signal is received. The
displacement due to the deformation of the shape of the piezoelectric ceramic 3 is transmitted to
the metal diaphragm 2 and the metal supporting plate 4.
[0023]
The displacement transmitted to the metal diaphragm 2 allows the metal diaphragm 2 to expand
or contract by an amount according to the magnitude of the displacement. The expansion or
contraction of the metal diaphragm 2 is transmitted to the cone 1 pressed into the hole of the
metal diaphragm 2. In response to this, the entire cone 1 vibrates to generate a sound wave.
Since the electric signal input from the CPU (not shown) to the piezoelectric ceramic 3 is
intermittent, the piezoelectric ceramic 3 is intermittently expanded or contracted, so that the
displacement becomes vibration, and this vibration is transmitted through the metal diaphragm
2. Transmit to cone 1 The portable electronic device emits a sound to the outside by the sound
wave generated by the vibration of the cone 1.
[0024]
The metal support plate 4 can expand or reduce the amount according to the magnitude of the
displacement by the displacement transmitted to the metal support plate 4. When the metal
support plate 4 expands or contracts, the elastic member 6 holding the metal support plate 4 is
deformed, but the elastic member 6 absorbs the transferred displacement by the elastic force.
Therefore, the displacement generated by the piezoelectric ceramic 3 is not transmitted to the
frame 7 bonded to the elastic member 6. Even if the elastic force of the elastic member 6 is
insufficient and the displacement is transmitted to the frame 7 or the elastic member 6 is not
provided as described above, the frame 7 has sufficient mechanical strength. Therefore,
distortion of the frame 7 due to the transmission of displacement does not occur.
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[0025]
As shown in FIG. 5, in the prior art, the cone 1 and the piezoelectric ceramic 3 are connected
without the metal diaphragm 2. Since the connection between the cone 1 and the piezoelectric
ceramic 3 is performed by a resin-based or rubber-based adhesive, an adhesive layer 10 is
formed between the cone 1 and the piezoelectric ceramic 3. In this case, when the piezoelectric
ceramic 3 is intermittently deformed by the input electric signal to generate a vibration, the
vibration is transmitted to the cone 1 through the adhesive layer 10. Since the adhesive layer 10
is an adhesive, it has an extremely low mechanical strength as compared to metal and the like,
which may cause the adhesive layer 10 to be damaged without being able to withstand stress
generated by vibration.
[0026]
When the mass of the cone 1 is mc, the mass of the metal diaphragm 2 is mb, the acceleration
applied to each in the ultrasonic region is ac, ab, and the bonding strength f between the cone 1
and the metal diaphragm 2 is broken The relational expression which shows that it does not do is
represented by the following formula.
[0027]
f> mcac + mbab At this time, since the acceleration ac of the cone 1 and the acceleration ab of
the metal diaphragm 2 are respectively proportional to the square of the angular frequency ω of
the ultrasonic frequency, the respective angular velocities become very large.
The velocity of the ultrasonic wave is v, the wavelength is λ, and the radius is r.
[0028]
ω = 2πV / λ a = V <2> / r a = 1 / r × (λ / 2π) 2 × ω <2> ac, ab ∝ω <2> As can be seen
from the above relational expression, cone 1 and Since the connection between the metal
diaphragm 2 and the metal diaphragm 2 is very stressed, its bonding strength f must be very
high. The adhesive strength 10 can not be achieved with the conventional adhesive layer 10, and
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can not be achieved with the structure disclosed in Patent Document 2 in which the rigidity of
the cone 1 itself is deteriorated.
[0029]
On the other hand, in the present embodiment, since the adhesive layer 10 is not provided, there
is no possibility that the connection between the cone 1 and the metal diaphragm 2 will be
damaged even if the vibration is transmitted. That is, if it is the structure which press-fits a part
of cone ¦ corn 1 in the metal diaphragm 2 like this embodiment, the adhering strength f can be
achieved. Therefore, it is possible to suppress breakage of the connection portion between the
cone 1 and the metal diaphragm 2 due to the vibration generated in the piezoelectric ceramic 3.
Furthermore, it can suppress that the effect of the acoustic radiation by cone 1 falls. In addition,
about the connection method of the cone ¦ corn 1 and the metal diaphragm 2, you may use
welding etc. as structures other than the press injection which achieves the adhering strength f.
[0030]
Next, in a frequency band of 40 kHz or more, the behavior of each configuration in the case
where a sound is received from the outside of the portable electronic device and the sound is
converted into an electric signal and transmitted to the CPU will be described.
[0031]
The cone 1 receives an external sound wave, and the cone 1 itself vibrates in accordance with the
sound wave.
The vibration of the cone 1 is transmitted to the metal diaphragm 2 via the connection portion
between the cone 1 and the metal diaphragm 2. Also in this case, since a very large stress is
concentrated on the connection between the cone 1 and the metal diaphragm 2, high mechanical
strength is required for the connection. When the metal diaphragm 2 is deformed by vibration,
the piezoelectric ceramic 3 bonded to the metal diaphragm 2 is also deformed. Since the
piezoelectric ceramic 3 is a piezoelectric body, when deformed, an electric field is generated by
the piezoelectric effect. The lead 8 transmits this electric field as an electric signal to the
electrode 9. The CPU of a portable electronic device (not shown) processes the electric signal
transmitted to the electrode 9.
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[0032]
As described above, in the electroacoustic transducer that converts the sound wave and the
electric signal to each other, the cone 1 and the metal diaphragm 2 are directly joined by a
method such as press-fitting, whereby the cone 1 and the metal diaphragm 2 are The mechanical
strength of the connection is increased. Therefore, even if stress is generated in the connecting
portion due to vibration of the cone 1 due to the sound wave or vibration of the piezoelectric
ceramic 3 due to the electric signal, the connecting portion is not broken and the effect of
acoustic radiation by the cone 1 is not reduced.
[0033]
Reference Signs List 1 cone 2 metal diaphragm 3 piezoelectric ceramic 4 metal support plate 5
support member 6 elastic member 7 frame 8 lead wire 9 electrode 10 adhesive layer
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