JPWO2021193788A5 - - Google Patents

Description

The present invention relates to a piezoelectric acoustic component in which a piezoelectric sound generating element is housed in a case provided with a sound emitting hole, and is capable of obtaining a sound pressure of a predetermined level or higher in a frequency range corresponding to a plurality of musical scales.

Piezoelectric acoustic components that use a metal diaphragm with a rectangular non-fixed part are more susceptible to unusable space (dead space) than piezoelectric acoustic components that use a circular or elliptical diaphragm. ), a certain level of demand is expected for products that use piezoelectric acoustic components. However, when a rectangular metal diaphragm is used, it is difficult to obtain a reasonably large sound pressure in a predetermined frequency range. In order to solve this problem, a piezoelectric acoustic component disclosed in Japanese Patent No. 6,516,935 (Patent Document 1) was proposed. In this conventional piezoelectric acoustic component, a piezoelectric sounding element consisting of a metal diaphragm and a piezoelectric element provided on at least one side of the diaphragm, and an outer periphery of the diaphragm of the piezoelectric sounding element are fixed over the entire circumference. , is configured to form a first space and a second space on both sides of the piezoelectric sounding element, and one or more sound emitting holes are formed in the wall facing the first space to increase the volume of the first space. and a case forming a resonator with one or more sound emitting holes. In this conventional piezoelectric acoustic component, the non-fixed portion located inside the outer periphery of the diaphragm has a pair of long sides facing each other and a pair of short sides shorter than the long sides and facing each other. , has a pair of recesses that are convex toward each other in a pair of long sides. Further, the piezoelectric element is provided on a region between the pair of recesses in the non-fixed part of the diaphragm, and the respective contour shapes of the diaphragm and the piezoelectric element are aligned with a first imaginary line that bisects the pair of short sides. and a second imaginary line bisecting the pair of long sides. Furthermore, the ratio L1/W1 of the length L1 of the long side to the length W1 of the short side is determined to fall within the range of 1.25 to 1.75. When a rectangular wave signal or a sine wave signal is input as an input signal, the sound pressure of the first resonant frequency, the third resonant frequency, and the intermediate frequency between the first resonant frequency and the third resonant frequency are each 80 dB or more. The resonator is configured so that According to this conventional piezoelectric acoustic component, it is possible to obtain a sound pressure of 80 dB or more over a frequency range corresponding to multiple scales, and it is possible to obtain sound pressure of 80 dB or more over a frequency range corresponding to multiple scales. But now I can hear it.

Patent No. 6516935

In order to further improve audibility, it is desirable to reduce the sound pressure difference between the primary resonance frequency and the intermediate resonance frequency, the sound pressure difference between the intermediate resonance frequency and the tertiary resonance frequency, and to obtain a sound pressure of 80 dB or more. The inventor has found that it is preferable to be able to change the frequency range arbitrarily to some extent. However, conventional structures have difficulty meeting this demand.

It is an object of the present invention to reduce the sound pressure difference between the primary resonance frequency and the intermediate resonance frequency, the sound pressure difference between the intermediate resonance frequency and the tertiary resonance frequency, and to obtain a sound pressure of 80 dB or more. The object of the present invention is to provide a piezoelectric acoustic component that can be arbitrarily changed to some extent.

The piezoelectric acoustic component targeted by the present inventor includes a piezoelectric sounding element consisting of a metal diaphragm and a piezoelectric element provided on at least one side of the diaphragm, and a piezoelectric sounding element that is made of a metal diaphragm and a piezoelectric element provided on at least one side of the diaphragm. The structure is configured such that a first space and a second space are formed on both sides of the piezoelectric sound generating element, and one or more sound emitting holes are formed in a wall portion facing the first space. The case includes a resonator having a volume of space and one or more sound emitting holes. The non-fixed portion located inside the fixed portion formed on the outer periphery of the diaphragm includes a pair of long sides facing each other and a pair of short sides shorter than the long sides and facing each other. A piezoelectric element is also provided on the central region of the non-fixed portion of the diaphragm. Furthermore, the respective outline shapes of the diaphragm and the piezoelectric element are symmetrical with respect to a first imaginary line that bisects the pair of short sides, and a second imaginary line that is orthogonal to the first imaginary line and passes through the center of the piezoelectric element. It is determined to be symmetrical about the line. Then, when a rectangular wave signal is input as an input signal, the sound pressure of the first resonant frequency, the third resonant frequency, and the intermediate frequency between the first resonant frequency and the third resonant frequency are each 80 dB or more. The configuration of the resonator and the shape of the non-fixed portion are determined. In particular, in the piezoelectric acoustic component of the present invention, a pair of long sides of the non-fixed portion has a convex groove along the outer periphery of the piezoelectric element and along the second imaginary line in a direction away from the first imaginary line. First and second protrusions are formed. Further, on the pair of long sides of the non-fixed portion, there is a third imaginary line adjacent to the first and second convex portions that extends through the center of the piezoelectric element and forms an acute angle with the second imaginary line. First and second recesses are formed to be located at and convex toward the first virtual line so as to adjust a frequency range of 80 dB or more.

In this way, when a rectangular wave signal or a sine wave signal is input, the sound pressure of the first resonant frequency, the third resonant frequency, and the intermediate frequency between the first resonant frequency and the third resonant frequency will each be 80 dB or more. In addition to increasing the minimum sound pressure in the frequency region between the primary resonance frequency and the intermediate frequency, and also increasing the minimum sound pressure in the frequency region between the intermediate frequency and the tertiary resonance frequency, the primary resonance The sound pressure difference in the entire frequency range between the main frequency and the tertiary resonance frequency can be reduced. Note that the resonator may be configured such that the sound pressure at the intermediate frequency between the primary resonance frequency and the tertiary resonance frequency is greater than or equal to the sound pressure at the primary resonance frequency and the sound pressure at the tertiary resonance frequency. .

In particular, the inventor found through various tests that a frequency range of 80 dB or more can be adjusted by the combination of the first and second convex portions and the first and second concave portions. The present invention is also based on this knowledge. Such findings are new and could only be discovered through various tests.

On one of the pair of long sides of the non-fixed portion, there is a first imaginary line adjacent to the pair of protrusions and located at a position where a fourth imaginary line passing through which is symmetrical to the third imaginary line with respect to the second imaginary line. A third recess that is convex toward the imaginary line may further be formed. In this way, adjustment can be made to narrow the frequency range of 80 dB or more.

Further, on the pair of long sides of the non-fixed portion, there is a first imaginary line adjacent to the pair of protrusions and located at a position where a fourth imaginary line passing through which is symmetrical to the third imaginary line with respect to the second imaginary line. A third recess and a fourth recess that are convex toward the imaginary line may be further formed. In this way, the frequency range of 80 dB or more can be further narrowed.

Preferably, the distance between the first recess and the third recess is equal to the distance between the second recess and the fourth recess, and the distance is preferably 10 mm to 13 mm. In this range, when the distance is shortened, the resonant frequency becomes high, the sound pressure becomes high, and the bandwidth becomes narrow. When the distance W3 is made large, the resonant frequency becomes low, the sound pressure becomes low, and the bandwidth There is a tendency for the area to become wider.

In the present invention, the ratio L0/W0 of the length L0 of the long side of the non-fixed portion of the diaphragm to the length W0 of the short side is determined to fall within the range of 2.1 to 2.4. preferable. This range exceeds the same size ratio in the piezoelectric acoustic component of Patent Document 1, and it has been confirmed that setting the size ratio within this range further enhances the effect.

Also, the distance L21 from the center of the piezoelectric element to one of the pair of short sides along the first imaginary line, and the distance L22 from the center of the piezoelectric element to the other of the pair of short sides along the first imaginary line. If the ratio L21/L22 is in the range of 10:10 to 12:8, the sound pressure for obtaining the above effects of the present invention can be maintained.

The contour shape of the piezoelectric element may be symmetrical, but may in particular be circular, elliptical or polygonal. The closer the contour shape is to a circle, the narrower the frequency range of 80 dB or more can be.

Preferably, the case includes a sounding element holder that has an opening having the same shape as the contour of the non-fixed portion of the diaphragm and fixes the outer circumferential portion of the diaphragm. When such a sound generating element holder is used, the contour shape of the non-fixed portion of the diaphragm is determined by the shape of the opening. As a result, a rectangular shape can be used as the shape of the diaphragm, and the processing cost of the diaphragm can be reduced.

A piezoelectric element may be provided on the back surface of the diaphragm. In this way, the piezoelectric element will not be damaged or contaminated.

The non-fixed part of the diaphragm is made of an alloy plate made of iron and nickel with a thickness of 10 μm to 150 μm, and the piezoelectric element has multiple laminated parts in which PZT ceramics with a thickness of 30 μm to 100 μm are laminated via intermediate electrodes. It has a structure including a stacked laminate and a pair of outer electrodes placed on both sides of the laminate, and the adhesive used to bond the piezoelectric element to the diaphragm has a Shore D hardness of 75 to 85. Moreover, the thickness is preferably 1 μm to 10 μm.

Of the pair of outer electrodes, at least the outer electrode that is not bonded to the diaphragm may be provided with a pair of recesses RC that are located on the first imaginary line and that are convex toward the center of the outer electrode. Providing such a recess can reduce the stress generated in response to the primary resonance frequency, suppress the stress from increasing locally, and extend the life of the piezoelectric element.

The shape of the pair of recesses is such that the stress generated in response to the primary resonance frequency is close to the stress generated in response to the tertiary resonance frequency. In this way, it is possible to reduce the variation in the magnitude of the stress generated in response to the primary resonance frequency and the stress generated in response to the tertiary resonance frequency, and further reduce the life span of the piezoelectric element. can be suppressed.

If a solder resist layer with a through hole for forming a lead wire soldering part is formed on the outer electrode of the pair of outer electrodes that is not bonded to the diaphragm, the position of the through hole and The size is preferably determined so as to suppress a decrease in sound pressure at the primary resonance frequency, which is lowered due to the presence of the solder resist layer, and also to suppress an increase in stress at the primary resonance frequency. By determining the position of the through hole for forming the lead wire soldering portion in this manner, the influence of stress generated by the presence of the soldering portion on the acoustic characteristics can be reduced. Specifically, when the diameter R of the piezoelectric element is 13 mm to 15 mm and the diameter of the through hole is in the range of 1.5 mm to 3 mm, the distance between the center of the piezoelectric element and the outer periphery of the through hole When r=1.5 mm, X is preferably 2.3 mm or more, and when r=3 mm, X is preferably 3 mm or more.

Further, if the solder resist layer is formed of a resin coat having moisture-proofing properties and insulating properties, the acoustic characteristics can be maintained over a long period of time. If the thickness of this solder resist layer is determined so as to reduce the Q value of the resonance peak of the primary resonance frequency and the tertiary resonance frequency, it becomes possible to improve the acoustic characteristics due to the presence of the solder resist layer.

(A) is an exploded perspective view of a piezoelectric acoustic component including a piezoelectric sound generating element of the present embodiment, and (B) is an exploded perspective view of the state of FIG. 1(A) viewed from below. (A) and (B) are plan views of different piezoelectric sound generating elements, and (C) is a diagram showing changes in frequency characteristics when the aspect ratio (L0/W0) is changed. FIG. 3 is a diagram showing the frequency characteristics of the piezoelectric acoustic component of this embodiment using the piezoelectric sound generating elements of FIGS. 2(A) and 2(B). (A) shows a piezoelectric sounding element having a combination of first and second protrusions, first and fourth recesses, and a third recess, and (B) shows a combination of first and second protrusions and a third recess. Another piezoelectric sounding element having a combination of first and fourth recesses is shown, and (C) is a diagram showing the sound pressure-frequency characteristics of FIGS. 4(A) and (B). Similar to FIG. 2(A), (A) shows a piezoelectric sounding element with a convex part and a recessed part, (B) shows a piezoelectric sounding element without a convex part and a recessed part, and (C) shows a piezoelectric sounding element with these two piezoelectric sounding elements. FIG. 3 is a diagram showing sound pressure-frequency characteristics when using the element. (A) to (C) are cases where the unfixed part of the piezoelectric sound element has four recesses, and when the dimension between two recesses facing each other in the width direction is changed, the sound pressure-frequency characteristics change. It is a diagram showing three types of piezoelectric sounding elements prepared to confirm how the sound changes, and (D) is a diagram showing the sound pressure-frequency characteristics of these three types of piezoelectric sounding elements. (A) to (G) are cases where the unfixed part of the piezoelectric sound element has four recesses, and the long side of the unfixed part is FIG. 7 is a diagram showing seven types of piezoelectric sound generating elements prepared in order to confirm how the sound pressure-frequency characteristics change when the distance between a pair of recesses is changed. (A) is a diagram showing the sound pressure-frequency characteristics when using the piezoelectric sounding elements of FIGS. 7(A) to (D), and (B) is a diagram showing the sound pressure-frequency characteristics when using the piezoelectric sounding elements of FIGS. 7(E) to (G). FIG. 3 is a diagram showing the sound pressure-frequency characteristics when using. (A) to (G) are cases where the non-fixed part of the piezoelectric sound element has four recesses, and when the longitudinal position of the non-fixed part of the piezoelectric element is changed, the sound pressure-frequency characteristics change. FIG. 7 is a diagram showing seven types of piezoelectric sounding elements prepared to confirm how they change. FIG. 9 is a diagram showing sound pressure-frequency characteristics when the piezoelectric sound generating elements of FIGS. 9(A) to 9(G) are used. (A) to (E) are piezoelectric sounding elements prepared to confirm how the sound pressure-frequency characteristics change when the outline shape of the piezoelectric element is changed to a circular shape or a regular polygonal shape. FIG. FIG. 12 is a diagram showing sound pressure-frequency characteristics when the piezoelectric sound generating elements of FIGS. 11(A) to 11(E) are used. (A) to (C) are diagrams showing piezoelectric sound generating elements prepared in order to confirm how the sound pressure-frequency characteristics change when the contour shape of the piezoelectric element is circular and elliptical. . FIG. 14 is a diagram showing sound pressure-frequency characteristics when the piezoelectric sound generating elements of FIGS. 13(A) to 13(C) are used. (A) to (D) are located on the first imaginary line PL1 and convex toward the center of the outer electrode at least on the outer electrode of the pair of outer electrodes of the piezoelectric element that is not bonded to the diaphragm. 15(a) to (d) are diagrams showing a piezoelectric sounding element prepared to confirm the influence of sound pressure-frequency characteristics when a pair of arc-shaped recesses are provided; FIG. ) to (D) are diagrams showing the sound pressure-frequency characteristics and equivalent stress of the corresponding piezoelectric sounding elements. (A) is a plan view showing a structure in which lead wires are soldered to a piezoelectric element, and (B) is an exploded perspective view of this structure. (A) shows the relationship between sound pressure and frequency (frequency characteristics) under preferred soldering conditions, and (B) shows the relationship between sound pressure and frequency (frequency characteristics) under conditions that adversely affect acoustic characteristics. . (A) is a diagram showing the state of stress during primary resonance and tertiary resonance when measured by applying an acoustic signal without forming a soldered part, and (B) to (D) are diagrams showing the state of stress at the time of the through hole. FIG. 3 is a diagram showing the state of stress during primary resonance and tertiary resonance when measured by changing the position and size of the stress. (A) shows the relationship between sound pressure and frequency (f-dB characteristics) with and without a solder resist layer, and (B) shows with and without a solder resist layer. It shows the relationship between impedance and frequency (impedance curve) when

Embodiments of the piezoelectric acoustic component of the present invention will be described below with reference to the drawings.

FIG. 1(A) shows an exploded perspective view of a piezoelectric acoustic component 1 equipped with a piezoelectric sounding element according to the present embodiment, and FIG. 1(B) is an exploded perspective view taken along line BB in FIG. 1(A). It is. FIG. 2 is a plan view of the piezoelectric sound element. Note that in this embodiment, the thickness dimensions of some parts are exaggerated in order to facilitate understanding. A piezoelectric acoustic component 1 shown in FIGS. 1(A) and 1(B) is a piezoelectric acoustic component used for purposes such as generating an alarm with multiple tones in a noisy environment such as outside a car. . In FIG. 1, the four corners of the outline of the diaphragm 12 described later are rounded, but the outline of the diaphragm 12 from FIG. 2 onwards has a rectangular shape with four right-angled corners.

The piezoelectric acoustic component 1 includes a case including a sounding element holder 9 having an opening 7 between a lower case half 3 and an upper case half 5. The lower case half 3 is integrally molded from an insulating resin such as polypropylene, and includes a rectangular bottom wall 31 and a peripheral wall 32 that stands up from the periphery of the bottom wall 31. The lower case half 3 includes a rectangular bottom wall 31 and a peripheral wall 32 that stands up from the periphery of the bottom wall 31. The upper case half 5 is integrally molded from an insulating resin such as polypropylene, and includes a rectangular upper wall 51 and a peripheral wall 52 that stands up from the periphery of the upper wall 51. The upper case half 5 includes a rectangular upper wall portion 51 and a peripheral wall portion 52 that extends downward from the periphery of the upper wall portion 51. Four sound emitting holes 4 are formed in the upper wall portion 51 near the four corners.

The sound generating element holder 9 is integrally formed of a hard insulating resin with low thermal expansion, such as an insulating resin made of polybutylene terephthalate to which glass is added. A diaphragm 12 of a piezoelectric sound element 11 having a piezoelectric element 15 provided on a diaphragm 12 is fixed around the opening 7 using an adhesive. The opening 7 has the same contour shape as the non-fixed portion 13 of the diaphragm 12 of the piezoelectric sounding element, which will be described in detail later. In the piezoelectric acoustic component 1 of this embodiment, the non-fixed portion 13 of the diaphragm 12 includes a pair of long sides 13Aa and 13Ab that face each other, and a pair of short sides 13Ba and 13Ba that are shorter than the long sides and face each other. 13Bb, and the contour shape of the non-fixed portion 13 of the diaphragm 12 is symmetrical with respect to a first virtual line PL1 that bisects the pair of short sides 13Ba and 13Bb, and a first line that bisects the pair of long sides 13Aa and 13Ab. It has a shape that is symmetrical with respect to the virtual line PL2 of No. 2.

In this embodiment, a piezoelectric element made of PZT ceramic and provided with a pair of outer electrodes is used as the piezoelectric element 15. At least the outer electrode 16 of the pair of outer electrodes that is not bonded to the diaphragm is formed of a silver electrode. The shape of the outer electrode 16 is similar to the shape of the piezoelectric element 15. In this embodiment, the outlines of the piezoelectric element 15 and the outer electrode 16 are circular. In this embodiment, since the piezoelectric element 15 is arranged on the back surface of the diaphragm 12 as shown in FIG. 1(B), the circular outline 15' of the piezoelectric element 15 is indicated by a broken line in FIG. It is shown. The piezoelectric element 15 is provided on the central region of the diaphragm 12, and the contour shapes of the non-fixed portion 13 of the diaphragm 12 and the piezoelectric element 15 form a first half that bisects the pair of short sides 13Ba and 13Bb. It is determined to be symmetrical with respect to a virtual line PL1 and symmetrical with respect to a second virtual line PL2 that bisects the pair of long sides 13Aa and 13Ab.

In the piezoelectric acoustic component 1 of this embodiment, as shown in FIG. In addition, first and second convex portions 14A and 14B are formed along the second imaginary line PL2 to be convex in the direction away from the first imaginary line PL1. Further, a pair of long sides 13Aa and 13Ab of the non-fixed portion 13 are adjacent to the first and second convex portions 14A and 14B, and have an acute angle between them and a second imaginary line PL2 that passes through the center of the piezoelectric element 15. First and second recesses 14Ca and 14Cd are formed so as to be located on a third imaginary line PL3 extending as shown in FIG. Further, a pair of long sides 13Aa and 13Bb of the non-fixed portion 13 are adjacent to the first and second convex portions 14A and 14B, and form an acute angle with a second virtual line PL2 that passes through the center of the piezoelectric element 15. a third virtual line PL4 extending so as to be convex toward the first virtual line PL1 and located on a fourth virtual line PL4 that is symmetrical to the third virtual line PL3 with respect to the second virtual line; Fourth recesses 14Cc and 14Cb are formed.

The lower case half 3, the sound-producing element holder 9, and the upper case half 5 are hermetically joined to each other by ultrasonic welding with the sound-producing element holder 9 sandwiched between the peripheral wall 32 and the peripheral wall 52. The case is now complete. As a result, with the piezoelectric sounding element 11 fixed to the sounding element holder 9, a first space S1 and a second space S2 are formed inside the case on both sides of the piezoelectric sounding element. The sound emission hole 4 communicates with the first space S1. The first space S1 constitutes the air chamber of the resonator.

As will be described later, the inventor has discovered that a frequency range of 80 dB or more can be adjusted by combining the first and second convex portions 14A and 14B and the first to fourth concave portions 14Ca to 14Cd. The present invention is based on this knowledge. In the embodiment described above, the frequency range of 80 dB or more is adjusted by all combinations of the first and second convex portions 14A and 14B and the first to fourth concave portions 14Ca to 14Cd. However, the basic combination is a combination of the first and second convex portions 14A and 14B and the first and fourth concave portions 14Ca and 14Cb or the second and third concave portions 14Cd and 14Cc. Another combination is a combination of the first and second convex portions 14A and 14B, the first and second concave portions 14Ca and 14Cd, and the fourth or third concave portion 14Cb or 14Cc. In any combination, the sound pressure at the primary resonance frequency, the tertiary resonance frequency, and the intermediate frequency between the primary resonance frequency and the tertiary resonance frequency when a rectangular wave signal or sine wave signal is input is , each not only exceeds 80 dB, but also increases the minimum sound pressure in the frequency region between the primary resonant frequency and the intermediate frequency, and also increases the minimum sound pressure in the frequency region between the intermediate frequency and the 3rd resonant frequency. , It is possible to reduce the sound pressure difference in the entire frequency region between the first-order resonance frequency and the third-order resonance frequency. As the number of concave portions (14Ca to 14Cd) increases, it becomes possible to narrow the frequency range of 80 dB or more.

In this embodiment, as shown in FIGS. 2(A) and 2(C), the aspect ratio L0/W0 of the length L0 of the long side and the length W0 of the short side of the non-fixed portion 13 of the diaphragm 12 is as follows. It is set to fall within the range of 2.1 to 2.4. This range exceeds the same size ratio in the piezoelectric acoustic component of Patent Document 1, and as can be seen from the comparison data shown in FIG. 2(C), by using this size ratio range, the frequency range of 80 dB or more It has been confirmed that it enhances the adjustment effect of

In addition, a resonator provided with one or more sound emission holes 4 has a sound pressure at an intermediate frequency between the primary resonance frequency and the tertiary resonance frequency when a rectangular wave signal or a sine wave signal is input as an input signal. The sound pressure is set to be equal to or higher than the sound pressure at the primary resonance frequency and the sound pressure at the tertiary resonance frequency. This point is the same as the piezoelectric acoustic component shown in Patent Document 1. Further, the number of sound emitting holes 4 is arbitrary.

[Frequency characteristics of the first embodiment]
FIG. 3 shows the frequency characteristics of the piezoelectric acoustic component of this embodiment using the piezoelectric sound generating elements of FIGS. 2(A) and 2(B). The piezoelectric sounding element of FIG. 2(B) has the same aspect ratio as the piezoelectric sounding element of FIG. 2(A), but the lengths of the recesses 14Cb and 14Cc are slightly longer. However, as shown in FIG. 3, it can be seen that this difference has almost no effect on the sound pressure-frequency characteristics.

FIG. 4(A) shows a piezoelectric sound element having a combination of a first convex portion 14A, a second convex portion 14B, first and second concave portions 14Ca and 14Cd, and a third concave portion 14Cc. 4(B) shows a piezoelectric sounding element having a combination of a first convex portion 14A, a second convex portion 14B, and first and fourth concave portions 14Ca and 14Cd. FIG. 4(C) shows the sound pressure-frequency characteristics of FIGS. 4(A) and 4(B). As can be seen from the comparison between Figures 4(C) and 3, as the number of recesses increases, it becomes possible to narrow the frequency range of 80 dB or more, and to improve the flatness of the sound pressure. .

Further, FIG. 5(A) shows a piezoelectric sound element having a first convex portion 14A, a second convex portion 14B, and first to fourth concave portions 14Ca and 14Cd, similar to FIG. 2(A). 5(B) shows a piezoelectric sounding element without these convex portions and concave portions. FIG. 5(C) shows the sound pressure-frequency characteristics when these two piezoelectric sound generating elements are used. As can be seen from FIG. 5(C), the piezoelectric sounding element of FIG. 5(B) without convex portions and concave portions cannot narrow the frequency range of 80 dB or more.

6(A) to 6(C) show a case where the non-fixed portion 13 of the piezoelectric sounding element is provided with four recesses 14Ca to 14Cd, which are opposite to each other in the width direction, as in the embodiment of FIG. 2(A). Three types of piezoelectric sound generating elements prepared in order to confirm how the sound pressure-frequency characteristics change when the dimension W3 between the two recesses is changed are shown. The non-fixed portion 13 of the diaphragm 12 of the piezoelectric sounding element is preferably made of a plate made of an alloy of iron and nickel and having a thickness of 10 μm to 150 μm. Furthermore, the piezoelectric element has a structure comprising a laminate in which a plurality of laminated parts of PZT ceramics having a thickness of 30 μm to 100 μm are laminated with intermediate electrodes interposed therebetween, and a pair of outer electrodes arranged on both sides of the laminate. It is preferable to have one. Furthermore, it is preferable that the acrylic adhesive for bonding the piezoelectric element to the diaphragm has a Shore D hardness of 75 to 85 and a thickness of 1 μm to 10 μm. Further, a piezoelectric element may be provided on the surface of the diaphragm 12.

In the example of FIG. 6, the diameter of the piezoelectric element 15 was 15 mm, the thickness was 60 μm, the thickness of the metal diaphragm was 75 μm, and W3 was 10.5 mm, 11.6 mm, and 12.6 mm. From the sound pressure-frequency characteristics in Figure 6(D), the smaller the dimension of W3, the higher the resonant frequency and sound pressure, and the narrower the band, and the larger the dimension of W3, the lower the resonant frequency and sound pressure. It can be seen that the band becomes wider.

7(A) to 7(G) show a case where the non-fixed portion 13 of the piezoelectric sounding element is provided with four recesses 14Ca to 14Cd, which are opposite to each other in the width direction, as in the embodiment of FIG. 2(A). When the distance L3 between the pair of recesses 14Ca and 14Cb (or 14Cc and 14Cd) of the long sides 13Aa and 13Ab of the non-fixed portion 13 is changed without changing the dimension W3 between the two recesses (14Ca, 14Cc). 7 shows seven types of piezoelectric sound generating elements prepared to confirm how the sound pressure-frequency characteristics change. Note that the piezoelectric sounding element in FIG. 7(G) is a case in which the pair of recesses 14Ca and 14Cb (or 14Cc and 14Cd) is maximized. In this case, the length L2 of the diaphragm 12 is increased to make the sound pressure-frequency characteristics similar to those of other piezoelectric sound generating elements. FIG. 8(A) shows the sound pressure-frequency characteristics when using the piezoelectric sound generating elements shown in FIGS. 7(A) to (D), and FIG. It shows the sound pressure-frequency characteristics when using a piezoelectric sounding element. In the piezoelectric sound generating elements shown in FIGS. 7A to 7F, the piezoelectric element 15 made of PZT ceramic has a diameter of 14 mm and a thickness of 60 μm, a metal diaphragm has a thickness of 75 μm, and W3 is 12.2 mm to 12 mm. .7 mm (variable), L2 was 35.6 mm, and L3 was 9 mm, 10 mm, 11 mm, 14 mm, 16 mm, and 18 mm. In the piezoelectric sounding element shown in FIG. 7(G), L2 was 39 mm and L3 was 37 mm. From the sound pressure-frequency characteristics in FIGS. 8(A) and 8(B), if the dimension of L3 is decreased, the variable range of the dimension of W3 becomes narrower, and there is a limit to the adjustment to increase the primary resonance frequency. As a result, a phenomenon occurs in which the band widens and the sound pressure decreases. Conversely, if the L3 dimension is increased, the L2 dimension must be increased in order to maintain the same bandwidth, and the external dimensions will become larger. Note that even when the L3 dimension is set to a maximum of 37 mm as shown in FIG. 7(G), the sound pressure-frequency characteristics are not inferior.

9A to 9G show the case where the non-fixed portion 13 of the piezoelectric sound element is provided with four recesses 14Ca to 14Cd as in the embodiment of FIG. 2, and the non-fixed portion of the piezoelectric element 15 is Seven types of piezoelectric sound generating elements prepared in order to confirm how the sound pressure-frequency characteristics change when the longitudinal position of 13 (longitudinal arrangement ratio L21:L22) are changed are shown. . In these piezoelectric sounding elements, the piezoelectric element 15 made of PZT ceramic had a diameter of 14 mm and a thickness of 60 μm, the metal diaphragm had a thickness of 75 μm, W3 was 12.2 mm, and L3 was 14 mm. The ratios of L21:L22 in the sound pressure power generation elements in FIGS. 9(A) to (G) are 15:5, 14:6, 13:7, 12:8, 11:9, 10.5:9.5, It was 10:10. From the sound pressure-frequency characteristics in FIG. 10, it can be seen that the larger the ratio L21:L22, the lower the primary and tertiary resonance frequencies and the lower the sound pressure, and the wider the band. The second and third resonance frequencies and sound pressure become higher, and the band becomes narrower. Practically, the ratio of L21:L22 is preferably in the range of 12:8 to 10:10.

[Shape of piezoelectric element]
11(A) to (E) were prepared to confirm how the sound pressure-frequency characteristics change when the outline shape of the piezoelectric element 15 is changed to a circular shape and a regular polygonal shape. A piezoelectric sounding element is shown. FIG. 12 shows the sound pressure-frequency characteristics when these piezoelectric sound generating elements are used.

13(A) to (C) show piezoelectric sound generating elements prepared in order to confirm how the sound pressure-frequency characteristics change when the contour shape of the piezoelectric element 15 is circular and oval. It shows. FIG. 14 shows the sound pressure-frequency characteristics when these piezoelectric sound generating elements are used. If the piezoelectric element has a symmetrical shape with respect to the first and second virtual lines (PL1, PL2), there will be almost no difference in the sound pressure-frequency characteristics due to the difference in the contour shape of the piezoelectric element, but it will be easier to manufacture. In terms of cost and cost, a circular piezoelectric element is suitable. Note that the closer the contour shape is to a circle, the narrower the frequency range of 80 dB or more can be.

[Electrode shape]
15(A) to (D) show that among the pair of outer electrodes of the piezoelectric element 15, at least the outer electrode 16 that is not bonded to the diaphragm is located on the first imaginary line PL1 and This is a piezoelectric sounding element prepared in order to confirm the influence of sound pressure-frequency characteristics when a pair of arc-shaped recesses 16A that are convex toward the center is provided, and FIGS. 15(a) to 15(d) show , which shows the sound pressure-frequency characteristics and equivalent stress of the corresponding piezoelectric sounding elements of FIGS. 15(A) to 15(D). The radii of curvature r of the pair of arcuate recesses 16A shown in FIGS. 15(B) to 15(D) were 2 mm, 4 mm, and 6 mm. Providing such a recess 16A can reduce the stress generated in response to the primary resonance frequency, suppress the stress from increasing locally, and extend the life of the piezoelectric element.

Note that the shape of the recessed portion 16A is not limited to the semicircular arc shape as in the above embodiment, but may be any shape such as a rectangular shape or a triangular shape. It is preferable that the shape of the recess 16A is such that the stress generated in response to the primary resonance frequency has a value close to the stress generated in response to the tertiary resonance frequency. In this way, it is possible to reduce the variation in the magnitude of the stress generated in response to the primary resonance frequency and the stress generated in response to the tertiary resonance frequency, and further reduce the life span of the piezoelectric element. can be suppressed.

If the piezoelectric element has a single layer structure with outer electrodes on both sides, it is sufficient to provide at least the outer electrode on the non-adhesive side. Furthermore, in the case where the piezoelectric element has a multilayer structure having electrodes inside as well, a recess 16A may be formed in the internal electrode.

[Resonator (sound emission hole in the case)]
If the total opening area of the sound emission holes provided in the case is within an appropriate range, the value of the intermediate frequency will not change significantly, and furthermore, the sound pressure of the intermediate frequency will not vary greatly. In addition, even if the number of sound emission holes is changed without changing the total opening area of the sound emission holes much, the difference between the sound pressure at the primary resonance frequency and the sound pressure at the tertiary resonance frequency does not become large, and the sound pressure at high sound pressure frequencies characteristics are obtained. As long as the total aperture area remains unchanged, the number of sound emitting holes has no effect on the frequency characteristics. Therefore, the number of sound emitting holes may be one or more.

[Shape of non-fixed part of diaphragm]
In the embodiments described above, a rectangular metal plate is used as the diaphragm 12, and the four corners of the non-fixed portion 13 are shown in a right-angled shape. However, practically, it is preferable to round or taper the four corners of the non-fixed portion 13 as in the embodiment shown in FIG.

[Lead wire soldering structure]
FIG. 16(A) is a plan view showing a structure in which the lead wire 18 is soldered to the piezoelectric element 15, and FIG. 16(B) is an exploded perspective view of this structure. First, on the outer electrode 16 made of a silver electrode which is not bonded to the diaphragm 12 among the pair of outer electrodes, a solder resist is provided with a through hole 17A for forming a soldering part for soldering the lead wire 18. A layer 17 is formed. The solder resist layer 17 is formed by screen printing using a resin coat such as acrylate having moisture-proofing and insulating properties. The thickness of the solder resist layer 17 is 5 to 50 μm. Since the solder resist layer 17 has substantially the same shape and size as the outer electrode 16, it also has the function of covering the outer electrode 16 made of a silver electrode and preventing migration from occurring and corrosion of the silver electrode. He is showing his full potential.

In this example, the through hole 17A for forming the soldering part is formed at a position where the second virtual line PL2 intersects the through hole 17A, but the position and size of the through hole 17A are limited to the example. It is not something that will be done. The position and size of the through hole 17A are determined so as to suppress the decrease in sound pressure at the primary resonance frequency, which is lowered by the presence of the solder resist layer 17, and to suppress the increase in stress at the primary resonance frequency. good. Specifically, when the diameter R of the piezoelectric element 15 having a circular outline is 13 mm to 15 mm, the diameter of the through hole 17A is preferably 1.5 mm to 3 mm. If the distance between the center of the piezoelectric element 15 and the outer periphery of the through hole 17A is X, then when r=1.5 mm, X is 2.3 mm or more, and when r=3 mm, X is 3 mm or more. It is preferable to determine the diameter and position of the through hole 17A so that The diameter of the soldered portion 19 of the core wire of the lead wire 18 is substantially the same as that of the through hole 17A.

FIG. 17A shows the relationship between sound pressure and frequency (frequency characteristics) when the position of the through hole 17A is set to X=5 mm and r=2 mm as preferred soldering conditions. Furthermore, FIG. 17(B) shows the relationship between sound pressure and frequency (frequency characteristics) when the position of the through hole 17A is set to X = 2.5 mm and R = 2 mm as conditions that adversely affect the acoustic characteristics. . In FIG. 17(A), the sound pressure at the primary resonance frequency has decreased slightly, and the peak value of stress has also decreased. On the other hand, in FIG. 17(B), the sound pressure at the primary resonance frequency has decreased slightly and the peak stress value has increased. This increase in stress caused the PZT ceramic of the piezoelectric element 15 to break. From FIGS. 17A and 17B, the position (X) and size (radius r) of the through hole 17A are such that the position (X) and size (radius r) of the through hole 17A suppress the decrease in the sound pressure of the primary resonance frequency, which is lowered due to the presence of the solder resist layer 17. Moreover, it can be seen that it is determined so as to suppress the increase in stress at the primary resonance frequency.

FIG. 18(A) is a diagram showing stress states during primary resonance and tertiary resonance when measured by applying an acoustic signal without forming a soldered portion. FIG. 18(B) shows the state of stress during primary resonance and tertiary resonance when the soldered part 19 is formed with the position of the through hole 17A set at X = 4 mm and r = 2 mm, and measured by applying an acoustic signal. FIG. FIG. 18(C) shows the stress during primary resonance and tertiary resonance when the soldered portion 19 is formed with the position of the through hole 17A set at X = 1.5 mm and r = 2 mm, and is measured by applying an acoustic signal. FIG. FIG. 18(D) shows the primary resonance and the tertiary resonance when the through hole 17A is positioned at X=2.25 mm and r=3.5 mm, the soldered part 19 is formed, and an acoustic signal is applied. It is a figure showing the state of stress at the time. In the case of FIGS. 18C and 18D, it was confirmed that the stress around the through hole 17A increased and the PZT ceramic of the piezoelectric element was damaged from the vicinity of the soldered portion 19.

Further, FIG. 19(A) shows the relationship between sound pressure and frequency (f-dB characteristics) when the solder resist layer 17 made of a resin coat with a thickness of 20 μm is formed and when it is not formed. B) shows the relationship between impedance and frequency (impedance curve) when the solder resist layer 17 made of a resin coat is formed and when it is not formed. From these results, it can be seen that by providing the solder resist layer 17 made of a resin coat, the Q value of the resonance peak can be reduced and the f-dB characteristic becomes flat. It has been confirmed that the following effects can be obtained by providing the solder resist layer 17 with a predetermined thickness.

(1) It was confirmed that the sound pressure of the primary resonance can be lowered while maintaining the lowest sound pressure within the acoustic band (2 to 2.9 KHz), and that the sound pressure can be flattened by 2 dB.

(2) It was confirmed that the hysteresis region that causes a jump phenomenon (a phenomenon in which the sound pressure decreases vertically) near the third-order resonance can be reduced.

(3) Since the resonance peak of the impedance curve was reduced, it was confirmed that the Q value was reduced.

From the above, if the thickness of the solder resist layer 17 is determined to reduce the Q value of the resonance peak of the primary resonance frequency and the tertiary resonance frequency, it is possible to improve the acoustic characteristics due to the presence of the solder resist layer 17. It was confirmed that

According to the present invention, it is possible to reduce the sound pressure difference between the primary resonant frequency and the intermediate resonant frequency, and the sound pressure difference between the intermediate resonant frequency and the tertiary resonant frequency, and moreover, it is possible to obtain a sound pressure of 80 dB or more. It is possible to provide a piezoelectric acoustic component that can be arbitrarily changed to some extent.

1 Piezoelectric acoustic component 3 Lower case half 4 Sound emission hole 5 Upper case half 7 Opening 9 Sound element holder 11 Piezoelectric sound element 12 Vibration plate 13 Non-fixed part 13Aa, 13Ab Long side 13Ba, 13Bb Short side 14A, 14B Convex portion 14Ca to 14Cd Concave portion 15 Piezoelectric element 16 Outside electrode 16A Concave portion PL1 First virtual line PL2 Second virtual line PL3 Third virtual line PL4 Fourth virtual line S1 First space S2 Second space

Claims (16)

a piezoelectric sounding element comprising a metal diaphragm and a piezoelectric element provided on at least one side of the diaphragm;
The outer periphery of the diaphragm of the piezoelectric sounding element is fixed over the entire circumference, and a first space and a second space are formed on both sides of the piezoelectric sounding element, and the first space and the second space are formed on both sides of the piezoelectric sounding element. a case in which one or more sound emitting holes are formed in opposing wall parts, and a resonator is configured by the volume of the first space and the one or more sound emitting holes;
The non-fixed portion located inside the fixed portion formed on the outer peripheral portion of the diaphragm includes a pair of long sides facing each other and a pair of short sides shorter than the long sides and facing each other. Ori,
the piezoelectric element is provided on a central region of the non-fixed portion of the diaphragm,
The contour shape of the piezoelectric element is symmetrical with respect to a first imaginary line that bisects the pair of short sides, and is perpendicular to the first imaginary line and passes through the center of the piezoelectric element. It is determined to be symmetrical to
When a rectangular wave signal or a sine wave signal is input as an input signal, the sound pressure of the primary resonant frequency, the tertiary resonant frequency, and the intermediate frequency between the primary resonant frequency and the tertiary resonant frequency are each 80 dB or more. The configuration of the resonator and the shape of the non-fixed portion are determined so that
The pair of long sides of the non-fixed portion are provided with first and second grooves that are convex in a direction away from the first imaginary line along the outer periphery of the piezoelectric element and along the second imaginary line. A convex portion is formed, and
The pair of long sides of the non-fixed portion are adjacent to the first and second convex portions and extend through the center of the piezoelectric element to form an acute angle with the second imaginary line. Piezoelectric acoustics characterized in that first and second recesses are formed that are located on a third imaginary line and protrude toward the first imaginary line so as to adjust a frequency range of 80 dB or more. parts. A fourth imaginary line adjacent to the pair of convex portions and symmetrical to the third imaginary line with respect to the second imaginary line is provided on one of the pair of long sides of the non-fixed portion. 2. The piezoelectric acoustic component according to claim 1, further comprising a third recess that is convex toward the first imaginary line and is formed at a position through which the piezoelectric acoustic component passes. A fourth virtual line that is adjacent to the pair of convex portions and that is symmetrical to the third virtual line with respect to the second virtual line passes through the pair of long sides of the non-fixed portion. The piezoelectric acoustic component according to claim 1, further comprising a third recess and a fourth recess that are convex toward the first imaginary line. The distance between the first recess and the third recess is equal to the distance between the second recess 14 and the fourth recess 14,
The piezoelectric acoustic component according to claim 3, wherein the distance is 10 mm to 13 mm. A ratio L0/W0 of the length L0 of the long side and the length W0 of the short side of the non-fixed portion of the diaphragm is determined to fall within a range of 2.1 to 2.4. 1. The piezoelectric acoustic component according to 1. a distance L21 from the center of the piezoelectric element to one of the pair of short sides measured along the first imaginary line; and a distance L21 from the center of the piezoelectric element to one of the pair of short sides measured along the first imaginary line. The piezoelectric acoustic component according to any one of claims 1 to 5, wherein the ratio L1/L2 of the distance L22 to the other short side is in the range of 10:10 to 12:8. The piezoelectric acoustic component according to any one of claims 1 to 6, wherein the contour shape of the piezoelectric element is circular, elliptical, or polygonal. Any one of claims 1 to 7, wherein the case includes a sounding element holder that fixes an outer peripheral portion of the diaphragm by having an opening that has the same shape as the contour of the non-fixed portion of the diaphragm. The piezoelectric acoustic component according to item 1. The piezoelectric acoustic component according to claim 1, wherein the piezoelectric element is provided on the back surface of the diaphragm. The non-fixed part of the diaphragm is made of an alloy plate made of iron mixed with nickel and has a thickness of 10 μm to 150 μm,
The piezoelectric element has a structure including a laminate in which a plurality of laminated parts are laminated with PZT ceramics having a thickness of 30 μm to 100 μm interposed via intermediate electrodes, and a pair of outer electrodes disposed on both sides of the laminate. has,
The piezoelectric acoustic component according to claim 1, wherein the adhesive for bonding the piezoelectric element to the diaphragm has a Shore D hardness of 75 to 85 and a thickness of 1 μm to 10 μm. Of the pair of outer electrodes, at least the outer electrode that is not bonded to the diaphragm is provided with a pair of recesses located on the first imaginary line and convex toward the center of the outer electrode. The piezoelectric acoustic component according to claim 10. 12. The piezoelectric acoustic component according to claim 11, wherein the shape of the recess is such that the stress generated in response to the first resonance frequency is close to the stress generated in response to the third resonance frequency. . A solder resist layer having a through hole for forming a lead wire soldering portion is formed on the one of the pair of outer electrodes that is not bonded to the diaphragm,
The position and size of the through hole are determined so as to suppress a decrease in sound pressure at the primary resonance frequency due to the presence of the solder resist layer, and to suppress an increase in stress at the primary resonance frequency. The piezoelectric acoustic component according to claim 10. When the diameter R of the piezoelectric element is 13 mm to 15 mm and the diameter of the through hole is in the range of 1.5 mm to 3 mm, the distance between the center of the piezoelectric element and the outer periphery of the through hole is 14. The piezoelectric acoustic component according to claim 13, wherein X is 2.3 mm or more when r=1.5 mm, and X is 3 mm or more when r=3 mm. 14. The piezoelectric acoustic component according to claim 13, wherein the solder resist layer is formed of a resin coat having moisture-proofing and insulating properties. 16. The piezoelectric acoustic component according to claim 15, wherein the thickness of the solder resist layer is determined to reduce the Q value of the resonance peak of the first-order resonance frequency and the third-order resonance frequency.