JP2019216310A - Piezoelectric electro-acoustic transducer and manufacturing method thereof - Google Patents

Abstract

To provide a piezoelectric electro-acoustic transducer capable of obtaining excellent sound pressure characteristics when lead-free piezoelectric ceramic is used as a material of a piezoelectric body, and a manufacturing method thereof.SOLUTION: In a piezoelectric electro-acoustic transducer 1, a piezoelectric body 19 of a piezoelectric diaphragm 5 comprises a lead-free piezoelectric ceramic composition. When, at 25°C, a first frequency at which the piezoelectric diaphragm 5 has the maximum vibration amount is denoted as f_XL, a first vibration amount that is the maximum vibration amount is denoted as XL, a second frequency at which the piezoelectric diaphragm 5 has the second maximum vibration amount is denoted as f_XS, a second vibration amount that is the second maximum vibration amount is denoted as XS, and a ratio between the first vibration amount and the second vibration amount is denoted as XS/XL, the characteristic of f_XL<f_XS and 1.0>XS/XL>0.5 is satisfied.SELECTED DRAWING: Figure 4

Description

  The present disclosure relates to a piezoelectric electroacoustic transducer capable of converting an electric signal into sound, and a method for manufacturing the piezoelectric electroacoustic transducer.

  Conventionally, as a technique related to a piezoelectric electroacoustic transducer, in order to obtain stable oscillation, a resonance angular frequency Wa of a case and a resonance angular frequency Wb of a piezoelectric diaphragm (that is, a piezoelectric diaphragm having a piezoelectric body in the diaphragm) are used. Is known so that the ratio Wb / Wa is between 0.7 and 1.0 (see Patent Document 1).

Further, as a temperature compensation method of the sound pressure characteristic of the piezoelectric electroacoustic transducer, a method of setting the resonance frequency of the case lower than the resonance frequency of the piezoelectric diaphragm is known (see Patent Documents 2 and 3).
In the above-described piezoelectric electroacoustic transducer, a leaded piezoelectric ceramic containing lead and a lead-free piezoelectric ceramic containing no lead are known as a material of the piezoelectric body.

  As the leaded piezoelectric ceramic, a lead zirconate titanate (PZT) -based ceramic is widely used. Further, as a lead-free piezoelectric ceramic, for example, a lead-free piezoelectric ceramic composition containing an alkali niobate-based perovskite oxide as a main phase and a potassium sodium niobate (KNN) -based ceramic are disclosed (see Patent Documents 4 to 6). .

Japanese Patent No. 3068221 JP-A-6-6899 JP-A-11-52958 JP-A-5647120 JP-A-5723959 JP-A-5715309

  By the way, in piezoelectric electroacoustic transducers, lead-free piezoelectric ceramics have not been widely used as piezoelectric ceramics, because they have lower piezoelectric characteristics than leaded piezoelectric ceramics.

  However, in recent years, as described in Patent Documents 4 to 6, the characteristics of lead-free piezoelectric ceramics (for example, KNN-based ceramics) have been improved, so that there is a possibility that lead-free piezoelectric ceramics can be applied to a piezoelectric electroacoustic transducer. Have been.

  However, lead-free piezoelectric ceramics such as KNN-based ceramics usually have different temperature characteristics (see FIG. 1) from PZT-based ceramics, which are leaded piezoelectric ceramics. Therefore, when a lead-free piezoelectric ceramic such as a KNN-based ceramic is used as the piezoelectric ceramic when designing a piezoelectric electroacoustic transducer, if the same design as a leaded piezoelectric ceramic such as a PZT-based ceramic is performed, There has been a problem that the sound pressure characteristic at a low temperature is remarkably deteriorated.

Specifically, as shown in FIG. 1, the piezoelectric constant d ₃₁ normalized at 25 ° C. (that is, the value normalized at 25 ° C. as 100%) is obtained when a PZT ceramic is used as the piezoelectric ceramic. , when the temperature is increased, the piezoelectric constant d ₃₁ is gradually increased at a constant rate of increase, the degree of increase is slight. Thus, the PZT-based ceramic, even if the temperature changes, the change in sound pressure corresponding to the piezoelectric constant d ₃₁ is small.

In contrast, in the case of using the KNN-based ceramic, the temperature changes, the piezoelectric constant d ₃₁ was a peak of about 20 ° C., varies greatly. Specifically, when the temperature is lower than about 20 ° C., the piezoelectric constant d ₃₁ rapidly increases as the temperature increases, and the degree of the increase is such that when the temperature changes by 40 ° C., the change in the piezoelectric constant d ₃₁ is 40%. And big. In addition, when the temperature exceeds 20 ° C., the piezoelectric constant d ₃₁ decreases as the temperature increases, contrary to the PZT ceramic.

  Therefore, in the case of KNN ceramics, the sound pressure at low temperatures is low, and as the temperature increases, the sound pressure sharply increases and then decreases. That is, in a lead-free piezoelectric ceramic such as a KNN-based ceramic, a change in sound pressure with respect to a change in temperature is large.

  The present disclosure has been made in order to solve the above-described problems, and provides a piezoelectric electro-acoustic transducer that can obtain excellent sound pressure characteristics when a lead-free piezoelectric ceramic is used as a material of a piezoelectric body, and a method for manufacturing the same. The purpose is to provide.

  (1) A first aspect of the present disclosure includes a configuration in which a piezoelectric vibrating plate having a piezoelectric body is housed in a case, the case has a resonance space that resonates with vibration of the piezoelectric vibrating plate, and the case has a resonance space. The present invention relates to a piezoelectric-type electro-acoustic transducer having a sound emission hole that communicates with the external space.

  In this piezoelectric electroacoustic transducer, the piezoelectric body of the piezoelectric diaphragm is made of a lead-free piezoelectric ceramic composition. Further, at 25 ° C., f_XL is the first frequency at which the vibration amount of the piezoelectric vibrating plate is the maximum, XL is the first vibration amount which is the maximum vibrating amount, and the second is the second vibration amount at which the vibration amount of the piezoelectric vibrating plate has the second magnitude. When the frequency is f_XS, the second vibration amount as the second vibration amount is XS, and the ratio of the first vibration amount to the second vibration amount is XS / XL, f_XL <f_XS and 1.0> XS /XL>0.5.

In the first aspect, since the lead-free piezoelectric ceramic composition is used as the piezoelectric body of the piezoelectric diaphragm, it is not necessary to use lead, and therefore, the adverse effect of lead on the environment can be suppressed.
In the first aspect, the first frequency f_XL and the second frequency f_XS satisfy the relationship of f_XL <f_XS, and the ratio XS / XL between the first vibration amount XL and the second vibration amount XS is 1 .0> XS / XL> 0.5.

  Therefore, as will be clear from an experimental example described later, even if the temperature changes from a low temperature (for example, −30 ° C.) to a high temperature (for example, + 85 ° C.), a high sound pressure can be obtained on average. That is, it has excellent sound pressure characteristics with respect to temperature (that is, even when the temperature changes).

Here, the principle of the present disclosure will be described.
It is considered that the first frequency f_XL is derived from the resonance frequency of the piezoelectric diaphragm, and the second frequency f_XS is derived from the resonance frequency of the resonance space in the case. Accordingly, hereinafter, the description will be made assuming that the resonance frequency of the piezoelectric diaphragm is f_XL and the resonance frequency of the resonance space in the case is f_XS.

The resonance frequency f_XS of the resonance space in the case shifts to the low frequency side when the temperature is low and shifts to the high frequency side when the temperature is high because of the fluctuation of the sound speed of air (see FIG. 2).
In addition, since the sound pressure increases when the resonance frequency f_XL of the piezoelectric diaphragm and the resonance frequency f_XS of the resonance space in the case are closer, if f_XL <f_XS, the resonance frequency f_XS of the resonance space in the case at a low temperature is low. A higher sound pressure can be obtained by approaching the resonance frequency f_XL of the piezoelectric diaphragm.

Therefore, by setting f_XL <f_XS, it is possible to supplement, for example, the characteristics of a KNN-based ceramic (see FIG. 1) whose characteristics are lower than that of a PZT-based ceramic at a low temperature.
On the other hand, when the temperature is high, the resonance frequency f_XS of the resonance space in the case is shifted to the high frequency side. Therefore, if f_XL <f_XS, at high temperature, the resonance frequency f_XL of the piezoelectric diaphragm and the resonance frequency f_XS of the resonance space in the case are separated from each other, so that the sound pressure is reduced.

Further, as shown in FIG. 1, for example, the material properties of a KNN-based ceramic are not as low as at a low temperature, but lower at a high temperature as compared with, for example, a PZT-based ceramic.
Because of these two factors, a decrease in sound pressure occurs at high temperatures. Therefore, in order to obtain a high average sound pressure from low to high temperatures, even when f_XL <f_XS, the resonance frequencies f_XL and f_XS are very different. It cannot be a frequency.

  In this regard, according to the study of the present inventor, the sensitivity (that is, the sensitivity (that is, the oscillation amount ratio XS / XL) is not defined by the resonance frequency ratio but defined by the vibration amount ratio XS / XL, as described in Patent Document 1. The evaluation accuracy for sound pressure) was high. That is, when the first frequency f_XL and the second frequency f_XS are f_XL <f_XS, and the ratio XS / XL of the vibration amount is in the range of 1.0> XS / XL> 0.5. It has been found that a high sound pressure can be obtained on average from a low temperature (for example, −30 ° C.) to a high temperature (for example, + 85 ° C.).

As a result, a piezoelectric electroacoustic transducer having excellent sound pressure characteristics as in the first aspect can be obtained.
The lead-free piezoelectric ceramic composition is a material of a piezoelectric ceramic that does not contain lead.

(2) In the second aspect of the present disclosure, the lead-free piezoelectric ceramic composition may be a composition containing an alkali niobate-based perovskite oxide as a main phase.
The second aspect exemplifies a lead-free piezoelectric ceramic composition that is preferable as a material for a piezoelectric body. That is, by using a composition containing a main phase of an alkali niobate-based perovskite oxide as a lead-free piezoelectric ceramic composition, it has excellent sound pressure characteristics with respect to temperature.

Here, the lead-free piezoelectric ceramic composition containing an alkali niobate-based perovskite oxide as the main phase is defined as a composition formula (KaNa _b Li _c C _d ) _e (D _f E _g ) O _h (element C is Ca, Ba). At least one element, element D is at least one element containing at least Nb among Nb, Ti, and Zr; element E is at least one element of Fe, Co, and Zn; a + b + c + d = 1; a + b + c is not zero; 80 <e <1.10, f + g = 1, and h is an arbitrary value constituting perovskite).

Examples of the alkali niobate-based perovskite oxide include the substances described in the above-mentioned References 4 to 6.
(3) In the third aspect of the present disclosure, the crystal phase transition temperature of the lead-free piezoelectric ceramic composition may be in a range of −30 ° C. to + 85 ° C.

  The crystal phase transition temperature of the lead-free piezoelectric ceramic composition is usually in the range of −30 ° C. to + 85 ° C. When the crystal phase transition temperature is in the range of −30 ° C. to + 85 ° C., the piezoelectric characteristics (accordingly, sound pressure characteristics) are separated by a peak at a certain temperature as illustrated in FIG. Change greatly.

  When such a lead-free piezoelectric ceramic composition is used for a piezoelectric material such as a conventional PZT ceramic, excellent sound pressure characteristics (that is, characteristics in which sound pressure changes little even when temperature changes) cannot be obtained. There is.

  However, as described above, by setting f_XL <f_XS and 1.0> XS / XL> 0.5, excellent sound pressure characteristics can be obtained. It can be adopted as a material of the piezoelectric body.

(4) A fourth aspect of the present disclosure relates to a method for manufacturing the piezoelectric electroacoustic transducer according to any one of the first to third aspects.
In this method of manufacturing a piezoelectric electroacoustic transducer, in the first step, the piezoelectric vibrating plate and the case are designed so as to have a characteristic of f_XL <f_XS. In the second step, the piezoelectric diaphragm is attached to the case. In the third step, the first frequency f_XL and the first vibration amount XL and the second frequency f_XS and the second vibration amount XS are obtained by vibrating the piezoelectric diaphragm attached to the case. In the fourth step, the first frequency f_XL and the second frequency f_XS have a relationship of f_XL <f_XS, and the ratio XS / XL between the first vibration amount XL and the second vibration amount XS is 1.0. > XS / XL> 0.5 is determined.

  Then, when the first frequency f_XL and the second frequency f_XS are not in the magnitude relationship (that is, f_XL <f_XS), or when the ratio XS / XL between the first vibration amount XL and the second vibration amount XS falls within the range ( That is, if 1.0> XS / XL> 0.5), the first frequency f_XL and / or the second frequency f_XS are changed so that the first frequency f_XL and the second frequency f_XS satisfy the magnitude relationship. The steps from the first step to the fourth step are repeated so that the ratio XS / XL between the first vibration amount XL and the second vibration amount XS falls within the range.

  In this manner, a piezoelectric electroacoustic transducer having desired characteristics (ie, excellent sound pressure characteristics) can be manufactured.

5 is a graph showing the relationship between temperature and piezoelectric characteristics for PZT-based ceramics and KNN-based ceramics. It is a graph which shows the resonance frequency f_XL of the piezoelectric diaphragm, the resonance frequency f_XS of the resonance space in a case, and the relationship between a vibration amount. It is a perspective view showing a piezoelectric type electroacoustic transducer of an embodiment. It is sectional drawing which shows the cross section which fractured | ruptured along the axial center of the piezoelectric electroacoustic transducer of embodiment. It is a bottom view showing the piezoelectric diaphragm of a piezoelectric type electroacoustic transducer of an embodiment. It is explanatory drawing which shows the manufacturing method of the piezoelectric electroacoustic transducer of embodiment. 6 is a graph showing the experimental result of Experimental Example 1, that is, the relationship between the frequency of an AC voltage applied to the piezoelectric diaphragm and the amount of vibration of the piezoelectric diaphragm. 9 is a graph showing another experimental result of Experimental Example 1, that is, a relationship between temperature and sound pressure. 9 is a graph showing an experimental result of Experimental Example 2, that is, a relationship between temperature and sound pressure.

Hereinafter, embodiments of a piezoelectric electroacoustic transducer to which the present disclosure is applied and a method for manufacturing the same will be described with reference to the drawings.
[1. Embodiment]
[1-1. overall structure]
First, the overall configuration of the piezoelectric electroacoustic transducer according to the embodiment will be described with reference to FIGS.

  As shown in FIGS. 3 and 4, a piezoelectric electro-acoustic transducer 1 (hereinafter sometimes simply referred to as an electro-acoustic transducer) 1 of the present embodiment is a so-called piezoelectric sounder capable of converting an electric signal into sound. It is.

The electroacoustic transducer 1 is a substantially disk-shaped device having a predetermined thickness in appearance, and includes a case 3 and a piezoelectric vibration plate 5 built in the case 3.
The case 3 is a substantially disk-shaped member having an axial center O extending in the vertical direction in FIG. 4 and having an open rear end (the lower part in FIG. 4), and is made of, for example, plastic made of PA (polyamide resin). is there. The case 3 includes a cylindrical support ring 7, and a circular top plate 11 arranged so as to close the opening 9 on the distal end side (upper side in FIG. 4) of the support ring 7. The ring 7 and the top plate 11 are integrally formed.

  Specifically, the top plate 11 is a plate material having a circular shape in plan view as viewed from above and below in FIG. 4, and the top plate 11 and the support ring 7 are coaxially arranged. Note that the top plate 11 is arranged perpendicular to the axis center O.

  Further, a circular sound emission hole 13 is provided at the center of the top plate 11 so as to penetrate the top plate 11 in the thickness direction (the vertical direction in FIG. 4). That is, the sound emission hole 13 is circular in plan view, and is provided coaxially with the axis center O.

  On the other hand, the piezoelectric vibrating plate 5 is a plate material having a circular shape in plan view, is arranged so as to close the opening 15 on the rear end side of the support ring 7, and is joined to the inner peripheral surface 7 a of the support ring 7. . That is, the piezoelectric vibrating plate 5 is fitted into the support ring 7 and the outer edge 5a of the piezoelectric vibrating plate 5 and the inner peripheral surface 7a of the support ring 7 are arranged in close contact with each other, and an adhesive (see FIG. (Not shown).

  Further, inside the case 3, a resonance space (that is, a resonance chamber) 27 that is a cylindrical internal space (that is, a cavity) is formed between the top plate 11 and the piezoelectric vibration plate 5. Since the piezoelectric vibration plate 5 is disposed perpendicular to the axis O, the piezoelectric vibration plate 5 and the top plate 11 are parallel.

  As shown in FIG. 5, the piezoelectric vibration plate 5 includes a metal plate (that is, a conductive vibration plate) 17 having a circular shape in plan view and a plate-shaped piezoelectric body 19 made of lead-free piezoelectric ceramic having a circular shape in plan view. , Is provided. As a material of the diaphragm 17, for example, an iron-nickel alloy (for example, 42 alloy) or brass (Brass) can be adopted.

  A thin-film electrode (inner electrode) 20 made of, for example, Ag is formed on one surface of the piezoelectric body 19 in the thickness direction (upper inner surface in FIG. 4), and the other surface in the thickness direction of the piezoelectric body 19 is formed. An electrode (outer electrode) 21 of a thin film made of, for example, Ag is formed on the lower outer surface of FIG. 4. Note that the piezoelectric body 19 provided with both electrodes 20 and 21 is referred to as a piezoelectric element 22.

  The piezoelectric body 19 has a smaller diameter than the diaphragm 17, and the electrodes 20 and 21 have a smaller diameter than the piezoelectric body 19. The piezoelectric body 19 and the electrodes 20 and 21 are arranged coaxially with the diaphragm 17.

Since the diaphragm 17 has a larger diameter than the piezoelectric body 19, the outer edge 17 a of the diaphragm 17 is the outer edge 5 a of the piezoelectric diaphragm 5 and is joined to the inner peripheral surface 7 a of the supporting ring 7. .
Further, the vibration plate 17 and the piezoelectric element 22 (more specifically, the inner electrode 20) are joined by, for example, a conductive adhesive, and the vibration plate 17 and the outer electrode 21 of the piezoelectric element 22 are connected to the lead terminals 23, respectively. 25 are connected.

  In FIG. 4, d is the radius of the resonance space 27, h is the height (thickness) of the resonance space 27, t is the thickness of the top plate 11, a is the radius of the sound output hole 13, and k1 is the thickness of the diaphragm 17. , K2 is the thickness of the piezoelectric body 19, and r is the radius r of the piezoelectric body 19. The thickness of each of the electrodes 20 and 21 is, for example, about 1/10 of the thickness of the piezoelectric body 19.

  In particular, in the present embodiment, a lead-free piezoelectric ceramic, for example, a KNN-based ceramic is used as the piezoelectric ceramic constituting the piezoelectric body 19. This lead-free piezoelectric ceramic is a lead-free piezoelectric magnetic composition containing an alkali niobate-based oxide as a main phase.

  As the lead-free piezoelectric ceramic, for example, a lead-free piezoelectric ceramic composition described in Patent Document 6 can be employed. The crystal phase transition temperature of the lead-free piezoelectric ceramic composition used in the experimental examples described later is about 20 ° C.

[1-2. Manufacturing method of electroacoustic transducer]
Next, a method for manufacturing the electroacoustic transducer 1 will be described with reference to FIG.
(1) First Step First, the piezoelectric vibrating plate 5 and the case 3 are designed so as to have a characteristic of f_XL <f_XS.

For example, the resonance frequency (ie, the first frequency) f_XL of the piezoelectric diaphragm 5 can be obtained by eigenvalue (eigenfrequency) analysis using the finite element method (FEM).
Specifically, the resonance frequency f_XL of the piezoelectric vibration plate 5 can be obtained by defining parameters such as the shape, dimensions, and material of the vibration plate 17 and the piezoelectric body 19 constituting the piezoelectric vibration plate 5.

  For example, using a well-known computer program (that is, finite element analysis software), parameters such as the thickness, the dimension in the plane direction (for example, the diameter in the case of a circular shape), and the material are defined for the diaphragm 17 and the piezoelectric body 19. The resonance frequency f_XL of the piezoelectric diaphragm 5 can be obtained by simulation.

  The resonance frequency (ie, the second frequency) f_XS of the resonance space 27 in the case 3 can be calculated using the following equation (1).

つまり、式（１）を用い、ケース３の形状、寸法等のパラメータを規定することにより、ケース３内の共鳴空間２７の共振周波数（即ち第２周波数）ｆ_ＸＳを求めることができる。

That is, the resonance frequency f_XS of the resonance space 27 in the case 3 (that is, the second frequency) f_XS can be obtained by defining parameters such as the shape and the size of the case 3 using the equation (1).

  Therefore, for example, a case 3 of a known shape (for example, the shape shown in FIGS. 3 to 5) conventionally used for the electroacoustic transducer 1 is adopted as a basic model, that is, the resonance space 27 in a certain case 3 is used. By keeping the resonance frequency f_XS constant and adjusting a parameter (for example, the thickness of the vibration plate 17) for obtaining the resonance frequency f_XL of the piezoelectric diaphragm 5, the condition of f_XL <f_XS can be satisfied.

  At this time, the resonance frequency f_XS of the resonance space 27 in the case 3 may be changed. Alternatively, contrary to the above method, the resonance frequency f_XL of the resonance space 27 in the case 3 may be changed while the resonance frequency f_XL of the piezoelectric diaphragm 5 is fixed. In order to change the resonance frequency f_XS of the resonance space 27 in the case 3, for example, there is a method of adjusting the size of the sound output hole 13 of the case 3.

  Thus, the piezoelectric vibration plate 5 and the case 3 can be designed to have the characteristic of f_XL <f_XS. That is, the shapes, dimensions, and materials of the piezoelectric diaphragm 5 and the case 3 can be defined.

(2) Second Step Next, the piezoelectric vibration plate 5 and the case 3 designed as described above are actually manufactured, and the piezoelectric vibration plate 5 is fixed to the case 3 with an adhesive.

(3) Third Step Next, the piezoelectric vibration plate 5 attached to the case 3 is vibrated, and the first frequency f_XL, the first vibration amount XL, and the second frequency are measured using a laser Doppler displacement meter (not shown). The frequency f_XS and the second vibration amount XS are obtained.

  Specifically, an AC voltage of, for example, 1500 Hz to 2500 Hz is sequentially applied between the two lead wires 21 and 23 (for example, the AC voltage is applied so as to be gradually increased), and the piezoelectric vibration plate 5 is vibrated. Then, in a state where the piezoelectric vibrating plate 5 is vibrated, a laser is irradiated from the laser Doppler displacement meter to the piezoelectric vibrating plate 5 through the sound emission hole 13 and the reflected light is measured and analyzed. Thereby, the first frequency f_XL and the first vibration amount XL and the second frequency f_XS and the second vibration amount XS can be obtained.

(4) Fourth Step Next, the first frequency f_XL and the second frequency f_XS have a relationship of f_XL <f_XS, and the ratio XS / XL between the first vibration amount XL and the second vibration amount XS is It is determined whether 1.0> XS / XL> 0.5.

  If the magnitude relationship of f_XL <f_XS is satisfied and the ratio XS / XL is within the range of 1.0> XS / XL> 0.5, the desired value of the ratio XS / XL is obtained. It will be.

  On the other hand, when f_XL <f_XS is not satisfied, or when the ratio XS / XL is not within the range of 1.0> XS / XL> 0.5, the target first frequency f_XL and target second frequency f_XS, or , Ratio XS / XL is not obtained.

  Therefore, in this case, the above-described design of the resonance frequency f_XL of the piezoelectric diaphragm 5 and the resonance frequency f_XS of the resonance space 27 in the case 3 is redone, that is, the first frequency f_XL and / or the second frequency f_XS are changed. In other words, the first frequency f_XL and the second frequency f_XS satisfy the magnitude relationship (that is, f_XL <f_XS), and the ratio XS / XL between the first vibration amount XL and the second vibration amount XS is in the range ( That is, the first to fourth steps are repeated so as to satisfy 1.0> XS / XL> 0.5).

  As described above, the resonance frequency f_XL of the piezoelectric vibrating plate 5 and the resonance frequency f_XS of the resonance space 27 in the case 3 can be changed by changing each parameter of the piezoelectric vibrating plate 5 or changing each parameter of the equation (1). And the first frequency f_XL and the first vibration amount XL and the second frequency f_XS and the second vibration amount XS can be changed accordingly, so that the relationship between the first frequency f_XL and the second frequency f_XS can be changed. , And the ratio XS / XL can be adjusted.

  For example, by gradually changing each parameter when obtaining the resonance frequency f_XL of the piezoelectric vibration plate 5 and the resonance frequency f_XS of the resonance space 27 in the case 3, the change between the first vibration amount XL and the second vibration amount XS is obtained. , The ratio XS / XL can be adjusted to a target value.

Thus, the electro-acoustic transducer 1 having desired characteristics (that is, excellent sound pressure characteristics) can be manufactured.
[1-3. effect]
(1) In the electro-acoustic transducer 1 of the present embodiment, since the lead-free piezoelectric ceramic composition is used as the piezoelectric body 19 of the piezoelectric vibrating plate 5, it is not necessary to use lead. Can be suppressed.

  (2) In the present embodiment, the first frequency f_XL and the second frequency f_XS satisfy the relationship of f_XL <f_XS, and the ratio XS / XL between the first vibration amount XL and the second vibration amount XS is 1 .0> XS / XL> 0.5.

  Therefore, as will be clear from an experimental example described later, even if the temperature changes from a low temperature (for example, −30 ° C.) to a high temperature (for example, + 85 ° C.), a high sound pressure can be obtained on average. That is, it has excellent sound pressure characteristics with respect to temperature.

(3) In the present embodiment, the lead-free piezoelectric ceramic composition is a composition having an alkali niobate-based perovskite oxide as a main phase.
As described above, by using a composition having a main phase of an alkali niobate-based perovskite oxide as a lead-free piezoelectric ceramic composition, the electroacoustic transducer 1 has excellent sound pressure characteristics with respect to temperature.

(4) In this embodiment, the crystal phase transition temperature of the lead-free piezoelectric ceramic composition is in the range of −30 ° C. to + 85 ° C.
When the crystal phase transition temperature of the lead-free piezoelectric ceramic composition exists within the operating temperature range of the electroacoustic transducer 1, if the electroacoustic transducer 1 is designed as in the related art, excellent sound pressure characteristics with respect to temperature cannot be obtained. Sometimes.

  However, as described above, by setting f_XL <f_XS and 1.0> XS / XL> 0.5, excellent sound pressure characteristics can be obtained. It can be adopted as a material of the piezoelectric body 19.

  (5) In the method of manufacturing the electroacoustic transducer 1 of the present embodiment, the piezoelectric vibrating plate 5 and the case 3 are designed in the first step so as to have a characteristic of f_XL <f_XS. In the second step, the piezoelectric vibration plate 5 is attached to the case 3. In the third step, the first frequency f_XL and the first vibration amount XL and the second frequency f_XS and the second vibration amount XS are obtained by vibrating the piezoelectric vibration plate 5 attached to the case 3. In the fourth step, the first frequency f_XL and the second frequency f_XS satisfy the magnitude relationship of f_XL <f_XS, and the ratio XS / XL between the first vibration amount XL and the second vibration amount XS is 1. It is determined whether 0> XS / XL> 0.5.

  Then, the first frequency f_XL and the second frequency f_XS are not in a relationship of f_XL <f_XS, or the ratio XS / XL between the first vibration amount XL and the second vibration amount XS is within the above range (that is, 1.0). > XS / XL> 0.5), the first frequency f_XL and / or the second frequency f_XS are changed so that the first frequency f_XL and the second frequency f_XS satisfy the magnitude relationship of f_XL <f_XLS, The steps from the first step to the fourth step are repeated so that the ratio XS / XL between the first vibration amount XL and the second vibration amount XS falls within the above range.

Thus, the electro-acoustic transducer 1 having desired characteristics (that is, excellent sound pressure characteristics) can be manufactured.
[1-4. Correspondence of wording]
The piezoelectric electro-acoustic transducer 1, the case 3, the piezoelectric diaphragm 5, the sound emission hole 13, the piezoelectric body 19, and the resonance space 27 of the first embodiment are respectively the piezoelectric electro-acoustic transducer and the case of the present disclosure. , A piezoelectric vibrating plate, a sound emitting hole, a piezoelectric body, and a resonance space.

[2. Experimental example]
Next, an experimental example of the present disclosure will be described.
<Experimental example 1>
In Experimental Example 1, various samples (Nos. 1 to 7) of electroacoustic transducers were produced by the manufacturing method of the above-described embodiment, as shown in Table 1 below.

  In addition, among the samples, No. 1 to No. 5 are samples of Examples within the range of the present disclosure, that is, KNN-based ceramic is used as the material of the piezoelectric body, and f_XL <f_XS and 1.0> XS / XL The sample satisfies the condition of the characteristic of> 0.5. On the other hand, Nos. 6 and 7 are samples of comparative examples outside the scope of the present disclosure, that is, samples using KNN-based ceramics, but not satisfying the above-described characteristics.

In the first experimental example, an AC voltage having a different frequency was applied to the piezoelectric diaphragm to each sample, and the amount of vibration of the piezoelectric diaphragm generated at that time was measured.
Then, of the vibration amounts, the first vibration amount XL at which the vibration amount becomes the maximum, that is, the vibration amount corresponding to the resonance frequency f_XL of the piezoelectric diaphragm (that is, the vibration peak having the largest vibration amount) and the second vibration amount , The vibration amount corresponding to the resonance frequency f_XS of the resonance space in the case (that is, the vibration amount is the second vibration peak small).

  Further, a ratio XS / XL between the first vibration amount XL and the second vibration amount XS was obtained. Further, the ratio f_XL / f_XS between the resonance frequency f_XL of the piezoelectric diaphragm and the resonance frequency f_XS of the resonance space in the case was also obtained.

  The results are shown in FIG. The horizontal axis of FIG. 7 (similarly in FIG. 2) indicates the frequency of the applied AC voltage, and the vertical axis indicates the amount of vibration of the piezoelectric diaphragm. Note that the unit [μmp-p] of the vibration amount means the distance between vibration peaks.

  In addition, each sample was set to the temperature shown in Table 1 below, and an AC voltage of 2 kHz was applied to the piezoelectric vibrating plate of each sample. At that time, the sound pressure of the sound output from the electroacoustic transducer was changed to It was measured by a sound level meter. The sound pressure is shown in FIG. 8 and Table 1 below.

  Furthermore, the average of the sound pressure at each temperature was obtained, and the difference in sound pressure obtained by subtracting the sound pressure at -30 ° C from the sound pressure at 85 ° C was obtained. The average of the sound pressures and the difference between the sound pressures are shown in Table 1 below.

この表１から明らかなように、実施例のNo.１〜５の試料では、温度が低温（−３０℃）から高温（＋８５℃）に変化した場合でも、音圧が全体的に大きい（従って音圧の平均が大きい）ので好適である。

As is clear from Table 1, the samples of Nos. 1 to 5 of the examples have a large sound pressure as a whole even when the temperature changes from a low temperature (−30 ° C.) to a high temperature (+ 85 ° C.). The average of the sound pressure is large).

  On the other hand, in the samples of Nos. 6 and 7 of the comparative example, when the temperature changes from low to high, the average of the sound pressure is small, and the sound pressure sharply decreases at high temperature (+85 in FIG. 8). ° C), which is not preferred.

<Experimental example 2>
In Experimental Example 2, various samples (Nos. 8 to 15) of the electroacoustic transducer were produced by the manufacturing method of the above-described embodiment, as shown in Table 2 below.

In addition, all the samples of the comparative examples outside the scope of the present disclosure, that is, KNN-based ceramics are used as the material of the piezoelectric body. However, unlike the present disclosure, the samples have characteristics of f_XL> f_XS. Note that, among the samples, the samples of Nos. 14 and 15 are conventional examples using PZT-based ceramics as the material of the piezoelectric body.
An experiment was performed on each sample in the same manner as in Experimental Example 1 to obtain experimental results. The results are shown in FIG. 9 and Table 2 below.

この表２から明らかなように、比較例のNo.８〜１３の試料では、温度が低温（−３０℃）から高温（＋８５℃）に変化した場合には、音圧の平均が小さいので、好ましくない。特に、温度が低温になるにつれて、音圧が急激に低下するので（図９の−３０℃参照）、好ましくない。

As is clear from Table 2, in the samples of Nos. 8 to 13 of the comparative example, when the temperature changes from low temperature (−30 ° C.) to high temperature (+ 85 ° C.), the average of the sound pressure is small. Not preferred. In particular, as the temperature becomes lower, the sound pressure sharply drops (refer to −30 ° C. in FIG. 9), which is not preferable.

Although the average of the sound pressures of the samples of Nos. 14 and 15 of the comparative example is large, it is not preferable because lead is used as the material of the piezoelectric body.
[3. Other Embodiments]
It should be noted that the present disclosure is not limited to the above-described embodiments and the like, and it goes without saying that various forms can be adopted as long as they belong to the technical scope of the present disclosure.

  (1) As the lead-free piezoelectric ceramic composition, various lead-free piezoelectric ceramics described in Patent Literatures 4 to 6 can be used. In addition, other characteristics shown in FIG. 1 (for example, characteristics similar to those of a KNN-based ceramic) can be used. ) Can be used.

  (2) The function of one component in each of the above embodiments may be assigned to a plurality of components, or the function of a plurality of components may be exerted by one component. Further, a part of the configuration of each of the above embodiments may be omitted. Further, at least a part of the configuration of each of the above embodiments may be added to or replaced with the configuration of another embodiment. In addition, all the aspects included in the technical thought specified from the wording described in the claims are embodiments of the present disclosure.

DESCRIPTION OF SYMBOLS 1 ... Piezoelectric electroacoustic transducer 3 ... Case 5 ... Piezoelectric diaphragm 13 ... Sound emission hole 19 ... Piezoelectric body 27 ... Resonance space

Claims (4)

A piezoelectric vibrating plate having a piezoelectric body is housed in a case, the case has a resonance space in the case that resonates with the vibration of the piezoelectric vibrating plate, and the case communicates the resonance space with an external space. In a piezoelectric electroacoustic transducer having a sound emission hole,
The piezoelectric body of the piezoelectric diaphragm is made of a lead-free piezoelectric ceramic composition,
At 25 ° C., the first frequency at which the amount of vibration of the piezoelectric diaphragm is the maximum is f_XL, the first amount of vibration that is the maximum amount of vibration is XL, and the first amount of vibration of the piezoelectric diaphragm is the second magnitude. When the two frequencies are f_XS, the second vibration amount that is the second vibration amount is XS, and the ratio of the first vibration amount to the second vibration amount is XS / XL,
having the characteristics of f_XL <f_XS and 1.0> XS / XL> 0.5,
Piezoelectric acoustic transducer. The lead-free piezoelectric ceramic composition is a composition having an alkali niobate-based perovskite oxide as a main phase,
The piezoelectric electroacoustic transducer according to claim 1. The crystal phase transition temperature of the lead-free piezoelectric ceramic composition is in a range of −30 ° C. to + 85 ° C.
The piezoelectric electroacoustic transducer according to claim 1. It is a manufacturing method of the piezoelectric electroacoustic transducer according to any one of claims 1 to 3,
A first step of designing the piezoelectric vibrating plate and the case so as to have a characteristic of f_XL <f_XS;
A second step of attaching the piezoelectric diaphragm to the case;
Vibrating the piezoelectric vibration plate attached to the case to obtain the first frequency f_XL and the first vibration amount XL and the second frequency f_XS and the second vibration amount XS;
The first frequency f_XL and the second frequency f_XS have a relationship of f_XL <f_XS, and a ratio XS / XL between the first vibration amount XL and the second vibration amount XS is 1.0> XS / XL> a fourth step of determining whether or not the range is 0.5;
Have
When the first frequency f_XL and the second frequency f_XLS are not in the magnitude relationship, or when the ratio XS / XL between the first vibration amount XL and the second vibration amount XS is not within the range, By changing the first frequency f_XL and / or the second frequency f_XS, the first frequency f_XL and the second frequency f_XS satisfy the magnitude relationship, and the first vibration amount XL and the second vibration The steps from the first step to the fourth step are repeated so that the ratio XS / XL with the amount XS falls within the range.
A method for manufacturing a piezoelectric electroacoustic transducer.

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