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BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
electro-acoustic transducer for converting an electrical signal into sound, and more particularly
to an electro-acoustic transducer constructed by bonding a piezoelectric body and a diaphragm.
An electro-acoustic transducer using a piezoelectric material has been widely used
conventionally, and is used as, for example, an ultrasonic wave generator or a piezoelectric
buzzer. The piezoelectric buzzer is made of metal 9 such as permalloy (Fe 58%) in order to
lengthen the wavelength of the generated sound. A piezoelectric body attached to a diaphragm
such as Ni 42%) is used. The resonance frequency ω at the mth order resonance of this
piezoelectric buzzer is expressed by equation (1). Here, a: diaphragm radius h: thickness Y:
Young's modulus :: specific gravity σ: Poisson's ratio α: reference constant at the mth order
resonance, which differs depending on the supporting method (see Table 1). In the case of this
piezoelectric buzzer, with the miniaturization of electronic devices, further miniaturization is
required, and attempts have been made to make the diaphragm as thin as possible. Furthermore,
a material with a small Young's modulus is also required. It is being explored. [Problems to be
Solved by the Invention] The electro-acoustic transducer using a conventional piezoelectric body
is typically PZT as a piezoelectric body and brass as a diaphragm. Permalloy (Fe5B%, Ni 42%) is
used, but its thickness is limited to 70μ because it is weak in 9 elasticity, so it is necessary to
make the diameter a dog to lower the resonance frequency and make it a soft tone There was a
problem that the demand for miniaturization could not be sufficiently answered. The present
invention has been made to solve the above problems, and an object thereof is to provide an
electroacoustic transducer which can be miniaturized and has a sufficiently low resonant
frequency. [Means for Solving the Problems] In order to solve the above-mentioned problems, in
the present invention, in the electro-acoustic transducer in which the piezoelectric body and the
diaphragm are attached, the diaphragm is made of amorphous metal. It is characterized by Since
the amorphous metal is strong enough to obtain sufficient strength even if it is made thin, the
thickness of the diaphragm can be made thin, and the resonance frequency can be lowered.
described in detail with reference to FIG. In FIG. 1, (a) is a plan view of an electroacoustic
transducer according to the present invention, and (b) is a cross-sectional view. In the figure, 10
indicates an electroacoustic transducer as a whole, 1 is a diaphragm, 4 is a piezoelectric body
having electrodes 2 and 3. The piezoelectric body 4 is. The electrode 2 is a main electrode that
covers most of the main surface of the piezoelectric body 4, the reference numeral 3 is a
feedback electrode formed in a natural shape as shown, and the reference numeral 5 is a large
back surface. It is a back electrode which covers a part.
The feedback electrode 3 does not necessarily have to be in the form of a feedback, but it is
sufficient if at least a signal capable of sustaining oscillation when the self-oscillation circuit is
configured can be taken out. The diaphragm 1 is usually made larger than the piezoelectric body
4, and peripheral support, vibration node point support, etc. are performed according to the
purpose of use. In the present invention, in such an electroacoustic transducer, the diaphragm 1
is made of amorphous metal. As the amorphous metal, various materials are used depending on
the type of the piezoelectric body and the like, and those having a thermal expansion coefficient
close to that of the piezoelectric body are selected. For example, when PZT is used as a
piezoelectric material, an iron alloy-based amorphous alloy having a thermal expansion
coefficient close to that is selected. Examples of this include Fe5oP1s + Fe5o & o, FegoZrto +
Fe5oP1s (Jy * FeysB + oS11zrFe62Mo □ oC, sIFeoCrI2MOsCu + Fea @ Cr, 6MO2 ° CIH, etc.).
The amorphous metal is produced by a metal quenching method using a roll, etc., but according
to this production method, a thin one having a thickness of 50 μm or less, or in some cases 20
to 30 μm, can be easily obtained. Moreover, even if it is an amorphous metal having a thickness
of 20 to 30 μ, its strength is sufficient. A drive circuit when such an electroacoustic transducer
10 is used for a sound generator such as a buzzer is shown in FIG. Main electrodes of the
electroacoustic transducer 10 The back electrode 5 is connected between the emitter and the
collector of the transistor TR, and the feedback electrode 3 is connected to the base. Selfoscillation is performed by this. As a result of experiment, the characteristics of the
electroacoustic transducer manufactured with 0 diaphragm thickness 28μ diameter 16 da
(composition Fe7aBloS i, 2) 0 piezoelectric element thickness 85μ diameter 130 has a resonance
impedance of 120 Ω and a good value When using the obtained 0% Ni 42% permalloy, the
thickness of the O diaphragm is 70 μm, the diameter is 1600 μm, and the thickness 85 μm is
130, so that the primary resonance frequency of 5020 Hz is obtained as a result of the
experiment. By the way, if it is assumed that the former diaphragm is composed of a 28μN
142% diaphragm from the latter experimental results. The next resonance frequency is 3650 H 2
(in accordance with the formula), and the effect of the amorphous is as follows in terms of the
next resonance frequency. 3.1 (%) out of 3650-3537 This also shows the advantage of using
amorphous. Needless to say, the electro-acoustic transducer 10 can be used not only for an
acoustic generator but also for a piezoelectric microphone or the like that converts sound into an
electrical signal.
[Effects] As described above, according to the present invention, since the diaphragm is made of
an amorphous metal of sufficient strength even if it is thin, the resonant frequency of the vibrator
can be lowered. This is the same resonant frequency. 0 means that the electroacoustic transducer
can be further miniaturized 0 Furthermore, since an amorphous metal has a Young's modulus Y
20 to 40% smaller than a metal of the same composition. As understood from the equation (1),
according to this, the resonance frequency can be further lowered.
Brief description of the drawings
FIG. 1 is a view showing an embodiment of the present invention, and FIG. 2 is a view showing an
example of a sound generator using the electro-acoustic transducer according to the present
1 ・ ・ ・ diaphragm. 2: Main electrode. 3 ... feedback electrode. 4 ... Piezoelectric porcelain. 5 · · ·
back electrode. Patent Applicant TDK Corporation Attorney Attorney Atsushi Yamatani Atsushi
Yamaya (α) (b) Fig. 1 Fig. 2 Fig. 2
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