Piezoelectric Acoustic Components

Abstract

Provided is a piezoelectric acoustic component with which the sound pressure difference between a first resonant frequency and an intermediate resonant frequency and the sound pressure difference between the intermediate resonant frequency and a third resonant frequency can be reduced, and furthermore with which a sound pressure of at least 80 dB can be obtained and a frequency range can, to a certain degree, be arbitrarily changed. A first and a second protruding part 14 A and 14 B, which protrude in a direction that follows an outer circumferential part of a circular piezoelectric element 15 and is separated from a first virtual line PL1 along a second virtual line PL2, are formed on a pair of long sides 13 Aa and 13 Ab of a non-fixed portion 13 of a piezoelectric acoustic element. In addition, a first and a second recessed part 14 Ca and 14 Cd and a third and a fourth recessed part 14 Cc and 14 Cb, which protrude toward the first virtual line PL1, are formed adjacent to the first and the second protruding parts 14 A, 14 B on the pair of long sides 13 Aa and 13 Ab of the non-fixed portion 13.

Description

[Technical field]

[0001] The present invention relates to a piezoelectric acoustic component in which a piezoelectric sound-generating element is housed in a case having a sound emission hole, and which is capable of obtaining a sound pressure level equal to or higher than a predetermined level within a frequency range covering a plurality of musical scales. [Background technology]

[0002] A piezoelectric acoustic component using a metallic diaphragm with a rectangular non-fixed portion generates less unusable space (dead space) when mounted than a piezoelectric acoustic component using a circular or elliptical diaphragm, so a certain demand is expected for products using piezoelectric acoustic components. However, when a rectangular metallic diaphragm is used, it is difficult to obtain a relatively large sound pressure in a specified frequency range. In order to solve this problem, a piezoelectric acoustic component shown in Patent No. 6516935 (Patent Document 1) was proposed. This conventional piezoelectric acoustic component includes a piezoelectric sound-producing element consisting of a metallic diaphragm and a piezoelectric element provided on at least one side of the diaphragm, and a case in which the outer periphery of the diaphragm of the piezoelectric sound-producing element is fixed all around, forming a first space and a second space on both sides of the piezoelectric sound-producing element, and one or more sound emission holes are formed in a wall portion facing the first space, and a resonator is formed by the volume of the first space and the one or more sound emission 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 facing each other and shorter than the long sides, and has a pair of recesses in the pair of long sides that are convex toward each other. The piezoelectric element is provided on the region between the pair of recesses in the non-fixed portion of the diaphragm, and the contour shapes of the diaphragm and the piezoelectric element are determined to be symmetrical with respect to a first imaginary line that bisects the pair of short sides and symmetrical with respect to a second imaginary line that bisects 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 be in the range of 1.25 to 1.75. The resonator is configured so that the sound pressures of the first resonance frequency, the third resonance frequency, and the intermediate frequency between the first resonance frequency and the third resonance frequency are each 80 dB or more when a rectangular wave signal or a sine wave signal is input as an input signal. This conventional piezoelectric acoustic component can produce sound pressure of 80 dB or more across a frequency range covering multiple musical scales, and the use of a piezoelectric sound-producing element with a rectangular metal diaphragm makes it possible to hear the sound even in noisy environments. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6516935 Summary of the Invention [Problem to be solved by the invention]

[0004] The inventors have found that in order to further improve audibility, it is desirable to reduce the sound pressure difference between the first and intermediate resonance frequencies and between the intermediate and third resonance frequencies, and that it is desirable to obtain a sound pressure of 80 dB or more and to be able to change the frequency range to some degree. However, it is difficult to meet this demand with the conventional structure.

[0005] The object of the present invention is to provide a piezoelectric acoustic component that can reduce the sound pressure difference between the first resonant frequency and the intermediate resonant frequency, and between the intermediate resonant frequency and the third resonant frequency, while obtaining a sound pressure of 80 dB or more and allowing the frequency range to be changed to some degree as desired. [Means for solving the problem]

[0006] The piezoelectric acoustic component that the present inventor is interested in comprises a piezoelectric sound-generating element made of a metallic diaphragm and a piezoelectric element provided on at least one side of the diaphragm, and a case in which the periphery of the diaphragm of the piezoelectric sound-generating element is fixed over the entire circumference, forming a first space and a second space on both sides of the piezoelectric sound-generating element, and one or more sound emission holes are formed in a wall portion facing the first space, so that the volume of the first space and the one or more sound emission holes form a resonator. The non-fixed portion located inside the fixed portion formed on the periphery of the diaphragm has a pair of long sides facing each other and a pair of short sides facing each other and shorter than the long sides. The piezoelectric element is provided on the central region of the non-fixed portion of the diaphragm. Furthermore, the contour shapes of the diaphragm and the piezoelectric element are determined to be symmetrical with respect to a first imaginary line that bisects the pair of short sides and is symmetrical with respect to a second imaginary line that is perpendicular to the first imaginary line and passes through the center of the piezoelectric element. The configuration of the resonator and the shape of the non-fixed portion are determined so that the sound pressures of the first resonance frequency, the third resonance frequency, and the intermediate frequency between the first resonance frequency and the third resonance frequency are each 80 dB or more when a rectangular wave signal is input as an input signal. In particular, in the piezoelectric acoustic component of the present invention, a pair of long sides of the non-fixed portion are formed with first and second convex portions that are convex along the outer periphery of the piezoelectric element and along the second virtual line in a direction away from the first virtual line. In addition, a pair of long sides of the non-fixed portion are formed with first and second concave portions that are adjacent to the first and second convex portions and are located on a third virtual line that passes through the center of the piezoelectric element and extends to form an acute angle with the second virtual line, and that are convex toward the first virtual line to adjust the frequency range of 80 dB or more.

[0007] By doing this, when a square wave signal or a sine wave signal is input, the sound pressure of the first resonance frequency, the third resonance frequency, and the intermediate frequency between the first resonance frequency and the third resonance frequency will each be 80 dB or more. In addition, the minimum sound pressure in the frequency range between the first resonance frequency and the intermediate frequency is increased, and the minimum sound pressure in the frequency range between the intermediate frequency and the third resonance frequency is also increased, primaryThe sound pressure difference in the entire frequency range from the main resonance frequency to the third resonance frequency can be reduced. The resonator may be configured so that the sound pressure of an intermediate frequency between the first resonance frequency and the third resonance frequency is equal to or greater than the sound pressure of the first resonance frequency and the sound pressure of the third resonance frequency.

[0008] In particular, the inventors have found through various tests that the frequency range can be adjusted by 80 dB or more by combining the first and second convex portions and the first and second concave portions. The present invention is also based on this finding. Such finding is novel and could only have been found through various tests.

[0009] A third concave portion may be formed on one of the pair of long sides of the non-fixed portion, adjacent to the pair of convex portions, at a position where a fourth imaginary line that is symmetrical to the third imaginary line with respect to the second imaginary line passes through, and that is convex toward the first imaginary line. In this way, it is possible to adjust the frequency range of 80 dB or more in a narrower direction.

[0010] In addition, a pair of long sides of the non-fixed portion may further include a third recess and a fourth recess that are adjacent to the pair of protrusions and protrude toward the first virtual line at a position where a fourth virtual line that is symmetrical to the third virtual line with respect to the second virtual line passes. In this way, the frequency range of 80 dB or more can be further adjusted in a narrower direction.

[0011] It is preferable that the distance between the first and third recesses and the distance between the second and fourth recesses are equal and are 10 mm to 13 mm. Within this range, when the distance is reduced, the resonant frequency tends to be higher, the sound pressure tends to be higher, and the bandwidth tends to be narrower, and when the distance W3 is increased, the resonant frequency tends to be lower, the sound pressure tends to be lower, and the bandwidth tends to be wider.

[0012] In the present invention, it is preferable that 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 set to be in the range of 2.1 to 2.4. This range exceeds the same dimensional ratio in the piezoelectric acoustic component of Patent Document 1, and it has been confirmed that setting the dimensional ratio in this range enhances the effect.

[0013] Furthermore, if the ratio L21 / L22 of the distance L21 from the center of the piezoelectric element to one of the pair of short sides along the first imaginary line to the distance L22 from the center of the piezoelectric element to the other of the pair of short sides along the first imaginary line is in the range of 10:10 to 12:8, the sound pressure required to obtain the above-mentioned effects of the present invention can be maintained.

[0014] The contour shape of the piezoelectric element may be symmetrical, in particular circular, elliptical or polygonal. The closer the contour shape is to a circle, the narrower the frequency range above 80 dB can be.

[0015] It is preferable that the case has an opening having the same shape as the contour of the non-fixed portion of the diaphragm and a sound-generating element holder for fixing the outer periphery of the diaphragm. When such a sound-generating element holder is used, the contour of the non-fixed portion of the diaphragm is determined by the shape of the opening. As a result, the shape of the diaphragm can be rectangular, and the processing cost of the diaphragm can be reduced.

[0016] A piezoelectric element may be provided on the rear surface of the diaphragm, which prevents the piezoelectric element from being damaged or soiled.

[0017] The non-fixed portion of the diaphragm is made of an alloy plate of iron mixed with nickel having a thickness of 10 μm to 150 μm, and the piezoelectric element has a structure including a laminate having a plurality of laminated parts in which PZT ceramics having a thickness of 30 μm to 100 μm are laminated via intermediate electrodes, and a pair of outer electrodes arranged on both sides of the laminate, and it is preferable that 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.

[0018] Of the pair of outer electrodes, at least the outer electrode not bonded to the diaphragm may have a pair of recesses RC located on the first virtual line and protruding toward the center of the outer electrode. By providing such recesses, it is possible to reduce the stress generated in response to the primary resonance frequency, suppress the stress from becoming large locally, and extend the life of the piezoelectric element.

[0019] The pair of recesses are shaped so that the stress generated in response to the primary resonance frequency is close to the stress generated in response to the tertiary resonance frequency, thereby making it 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 suppress the decrease in the life span of the piezoelectric element.

[0020] The pair of recesses are shaped so that the stress generated in response to the primary resonance frequency is close to the stress generated in response to the tertiary resonance frequency, thereby making it 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 suppress the decrease in the life span of the piezoelectric element. When a solder resist layer having a through hole for forming a lead soldering portion is formed on the outer electrode of the pair of outer electrodes that is not bonded to the diaphragm, the position and size of the through hole are preferably determined so as to suppress the decrease in sound pressure at the primary resonance frequency caused by the presence of the solder resist layer and to suppress the increase in stress at the primary resonance frequency. By determining the position of the through hole for forming the lead soldering portion in this manner, the effect on the acoustic characteristics of the stress generated by the presence of the soldering portion 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 r When r is a value in the range of 1.5 mm to 3 mm, if the distance between the center of the piezoelectric element and the outer periphery of the through hole is X, then 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.

[0021] Furthermore, if the solder resist layer is formed of a resin coating that has moisture resistance and insulation properties, the acoustic characteristics can be maintained for 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 peaks of the first and third resonance frequencies, the presence of the solder resist layer can improve the acoustic characteristics. [Brief description of the drawings]

[0022] [Figure 1] FIG. 1(A) is an exploded perspective view of a piezoelectric acoustic component equipped with a piezoelectric sound-producing element according to the present embodiment, and FIG. 1(B) is an exploded perspective view of the state of FIG. 1(A) seen from below. [Diagram 2] 13(A) and (B) are plan views of different piezoelectric sound-producing elements, and (C) is a diagram showing the change in frequency characteristics when the aspect ratio (L0 / W0) is changed. [Diagram 3] 3 is a diagram showing the frequency characteristics of a piezoelectric acoustic component according to the present embodiment that uses the piezoelectric sound-producing element of FIGS. 2(A) and 2(B). FIG. [Figure 4] (A) shows a piezoelectric sound-producing element having a combination of first and second convex portions, first and fourth concave portions, and a third concave portion, (B) shows another piezoelectric sound-producing element having a combination of first and second convex portions, and first and fourth concave portions, and (C) is a diagram showing the sound pressure-frequency characteristics of Figures 4(A) and (B). [Diagram 5] (A) shows a piezoelectric sound-producing element with convex and concave portions, similar to Figure 2(A), (B) shows a piezoelectric sound-producing element without convex and concave portions, and (C) is a diagram showing the sound pressure-frequency characteristics when these two piezoelectric sound-producing elements are used. [Figure 6] (A) to (C) are figures showing three types of piezoelectric sound-producing elements prepared to confirm how the sound pressure-frequency characteristics change when the non-fixed part of the piezoelectric sound-producing element has four recesses and the dimension between two opposing recesses in the width direction is changed, and (D) is a diagram showing the sound pressure-frequency characteristics of these three types of piezoelectric sound-producing elements. [Figure 7](A) to (G) are figures showing seven types of piezoelectric sound-producing elements prepared to confirm how the sound pressure-frequency characteristics change when the non-fixed part of the piezoelectric sound-producing element has four recesses and the distance between a pair of recesses on the long side of the non-fixed part is changed without changing the dimension between the two recesses facing each other in the width direction. [Figure 8] 7(A) is a graph showing the sound pressure-frequency characteristics when using the piezoelectric sound-producing elements of Figures 7(A) to (D), and (B) is a graph showing the sound pressure-frequency characteristics when using the piezoelectric sound-producing elements of Figures 7(E) to (G). [Figure 9] (A) to (G) are figures showing seven types of piezoelectric sound-producing elements prepared to confirm how the sound pressure-frequency characteristics change when the longitudinal position of the non-fixed part of the piezoelectric sound-producing element, which has four recesses, is changed. [Figure 10] 10 is a diagram showing sound pressure-frequency characteristics when the piezoelectric sound-generating elements of FIGS. 9(A) to (G) are used. FIG. [Figure 11] 1A to 1E are diagrams showing piezoelectric sound-producing elements prepared to confirm how the sound pressure-frequency characteristics change when the contour shape of the piezoelectric element is changed from a circular shape to a regular polygonal shape. [Figure 12] 12 is a diagram showing sound pressure-frequency characteristics when the piezoelectric sound-generating elements of FIGS. 11(A) to 11(E) are used. FIG. [Figure 13] 1A to 1C are diagrams showing piezoelectric sound-producing elements prepared in order to confirm how the sound pressure-frequency characteristics change when the contour shape of the piezoelectric element is made circular or elliptical. [Figure 14] 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. [Figure 15]15(A) to 15(D) are diagrams showing a piezoelectric sound-producing element prepared to confirm the effect of the sound pressure-frequency characteristics when a pair of arc-shaped recesses that are located on the first virtual line PL1 and convex toward the center of the outer electrode are provided on at least one of a pair of outer electrodes of the piezoelectric element, the outer electrode that is not bonded to the diaphragm, and (a) to (d) are diagrams showing the sound pressure-frequency characteristics and equivalent stress of the corresponding piezoelectric sound-producing elements of Figures 15(A) to 15(D). [Figure 16] FIG. 1A is a plan view showing a structure in which lead wires are soldered to a piezoelectric element, and FIG. [Figure 17] (A) shows the relationship between sound pressure and frequency (frequency characteristics) under favorable soldering conditions, and (B) shows the relationship between sound pressure and frequency (frequency characteristics) under conditions that adversely affect the acoustic characteristics. [Figure 18] FIG. 1A shows the stress state at the time of the first resonance and the third resonance when an acoustic signal is applied and measured without forming a soldering portion, and FIG. 1B to FIG. 1D show the stress state at the time of the first resonance and the third resonance when measured by changing the position and size of the through hole. [Figure 19] (A) shows the relationship between sound pressure and frequency (f-dB characteristics) when a solder resist layer is formed and when it is not formed, and (B) shows the relationship between impedance and frequency (impedance curve) when a solder resist layer is formed and when it is not formed. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the piezoelectric acoustic component of the present invention will be described with reference to the drawings.

[0024] FIG. 1(A) shows an exploded perspective view of a piezoelectric acoustic component 1 having a piezoelectric sound-producing element according to the present embodiment, and FIG. 1(B) is an exploded perspective view taken along line BB in FIG. 1(A). FIG. 2 is a plan view of the piezoelectric sound-producing element. In this embodiment, the thickness dimensions of some of the components are exaggerated for ease of understanding. The piezoelectric acoustic component 1 shown in FIGS. 1(A) and (B) is a piezoelectric acoustic component used for applications such as generating an alarm with a multi-tone sound in a noisy environment such as outside a car. In FIG. 1, the four corners of the outline of the diaphragm 12, which will be described later, are rounded, but the outline of the diaphragm 12 in FIG. 2 and subsequent figures has a rectangular shape with right-angled corners.

[0025] The piezoelectric acoustic component 1 includes a case having a sound-emitting 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 standing from the peripheral edge of the bottom wall 31. The lower case half 3 includes a rectangular bottom wall 31 and a peripheral wall 32 standing from the peripheral edge of the bottom wall 31. The upper case half 5 is integrally molded from an insulating resin such as polypropylene, and includes a rectangular top wall 51 and a peripheral wall 52 standing from the peripheral edge of the top wall 51. The upper case half 5 includes a rectangular top wall 51 and a peripheral wall 52 standing down from the peripheral edge of the top wall 51. The top wall 51 has four sound emission holes 4 formed near the four corners.

[0026] The sound-producing element holder 9 is integrally molded from a hard insulating resin with low thermal expansion, such as an insulating resin obtained by adding glass to polybutylene terephthalate. The diaphragm 12 of the piezoelectric sound-producing element 11, which has a piezoelectric element 15 provided thereon, 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 sound-producing 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 has a pair of long sides 13Aa and 13Ab facing each other and a pair of short sides 13Ba and 13Bb facing each other and shorter than the long sides, and the contour shape of the non-fixed portion 13 of the diaphragm 12 has a shape that is symmetrical with respect to a first imaginary line PL1 that bisects the pair of short sides 13Ba and 13Bb and is symmetrical with respect to a second imaginary line PL2 that bisects the pair of long sides 13Aa and 13Ab.

[0027] In this embodiment, a piezoelectric element made of PZT ceramic having a pair of outer electrodes is used as the piezoelectric element 15. At least the outer electrode 16, which 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 contour shapes of the piezoelectric element 15 and the outer electrode 16 are circular. In this embodiment, the piezoelectric element 15 is disposed on the back surface of the diaphragm 12 as shown in FIG. 1(B), so that the circular contour 15' of the piezoelectric element 15 is shown by a broken line in FIG. 1(A). 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 are determined to be symmetrical with respect to a first imaginary line PL1 that bisects the pair of short sides 13Ba and 13Bb and to be symmetrical with respect to a second imaginary line PL2 that bisects the pair of long sides 13Aa and 13Ab.

[0028] 1(A), in the piezoelectric acoustic component 1 of this embodiment, first and second convex portions 14A and 14B are formed on a pair of long sides 13Aa and 13Ab of the non-fixed portion 13, which are convex in a direction away from the first virtual line PL1 along the second virtual line PL2 and along the outer periphery of the contour 15' of the circular piezoelectric element 15. In addition, first and second concave portions 14Ca and 14Cd are formed on the pair of long sides 13Aa and 13Ab of the non-fixed portion 13, which are adjacent to the first and second convex portions 14A and 14B and are located on a third virtual line PL3 that passes through the center of the piezoelectric element 15 and extends to form an acute angle with the second virtual line PL2, and are convex toward the first virtual line PL1. Furthermore, a pair of long sides 13Aa and 13Bb of the non-fixed portion 13 are formed with third and fourth recesses 14Cc and 14Cb, which are adjacent to the first and second protrusions 14A and 14B, extend through the center of the piezoelectric element 15 to form an acute angle with the second virtual line PL2, and are located on a fourth virtual line PL4 that is symmetrical to the third virtual line PL3 with respect to the second virtual line, and are convex toward the first virtual line PL1.

[0029] The lower case half 3, the sound-producing element holder 9, and the upper case half 5 are hermetically joined together by ultrasonic welding with the sound-producing element holder 9 sandwiched between the peripheral wall 32 and the peripheral wall 52 to complete the case. With the piezoelectric sound-producing element 11 fixed to the sound-producing element holder 9, a first space S1 and a second space S2 are formed inside the case on either side of the piezoelectric sound-producing element. The sound emission hole 4 communicates with the first space S1. The first space S1 forms the air chamber of the resonator.

[0030] The inventors have found that the frequency range of 80 dB or more can be adjusted by combining the first and second convex parts 14A and 14B with the first to fourth concave parts 14Ca to 14Cd, as described below. The present invention is based on this finding. In the above embodiment, the frequency range of 80 dB or more is adjusted by all combinations of the first and second convex parts 14A and 14B with the first to fourth concave parts 14Ca to 14Cd. However, the basic combination is the combination of the first and second convex parts 14A and 14B with the first and fourth concave parts 14Ca and 14Cb or the second and third concave parts 14Cd and 14Cc. And another combination is the combination of the first and second convex parts 14A and 14B with the first and second concave parts 14Ca and 14Cd with the fourth or third concave parts 14Cb or 14Cc. Regardless of the combination, when a square wave signal or a sine wave signal is input, the sound pressure of the first resonance frequency, the third resonance frequency, and the intermediate frequency between the first resonance frequency and the third resonance frequency are each 80 dB or more. In addition, the minimum sound pressure in the frequency range between the first resonance frequency and the intermediate frequency is increased, and the minimum sound pressure in the frequency range between the intermediate frequency and the third resonance frequency is also increased, primary It is possible to reduce the sound pressure difference in the entire frequency range from the resonant frequency to the third resonant frequency. As the number of recesses (14Ca to 14Cd) increases, it becomes possible to narrow the frequency range of 80 dB or more.

[0031] In this embodiment, as shown in Figures 2(A) and (C), the aspect ratio L0 / W0 of the long side length L0 and the short side length W0 of the non-fixed portion 13 of the diaphragm 12 is set to be in the range of 2.1 to 2.4. This range exceeds the same dimensional ratio in the piezoelectric acoustic component of Patent Document 1, and as can be seen from the comparative data shown in Figure 2(C), it has been confirmed that by setting the dimensional ratio in this range, the adjustment effect in the frequency range of 80 dB or more is improved.

[0032] Furthermore, a resonator provided with one or more sound emitting holes 4 is designed so that the sound pressure of an intermediate frequency between the primary resonance frequency and the tertiary resonance frequency when a square wave signal or a sine wave signal is input as an input signal is equal to or greater than the sound pressure of the primary resonance frequency and the sound pressure of the tertiary resonance frequency. This is the same as the piezoelectric acoustic component shown in Patent Document 1. Furthermore, the number of sound emitting holes 4 is arbitrary.

[0033] [Frequency characteristics of the first embodiment] Fig. 3 shows the frequency characteristics of a piezoelectric acoustic component of this embodiment using the piezoelectric sound-producing elements of Fig. 2(A) and (B). The piezoelectric sound-producing element of Fig. 2(B) has the same aspect ratio as the piezoelectric sound-producing element of Fig. 2(A), but the lengths of the recesses 14Cb and 14Cc are slightly longer. However, as shown in Fig. 3, this difference has almost no effect on the sound pressure-frequency characteristics.

[0034] Fig. 4(A) shows a piezoelectric sound-producing element having a combination of the first convex portion 14A and the second convex portion 14B, the first and second recesses 14Ca and 14Cd, and the third recess 14Cc, and Fig. 4(B) shows a piezoelectric sound-producing element having a combination of the first convex portion 14A and the second convex portion 14B, the first and fourth recesses 14Ca and 14Cd. Fig. 4(C) shows the sound pressure-frequency characteristics of Fig. 4(A) and (B). As can be seen from a comparison of Fig. 4(C) and Fig. 3, when the number of recesses is increased, it becomes possible to adjust the frequency range above 80 dB in a narrower direction, and the flatness of the sound pressure can be improved.

[0035] Also, Fig. 5(A) shows a piezoelectric sound-producing element having a first convex portion 14A and a second convex portion 14B and a first to fourth concave portions 14Ca and 14Cd, similar to Fig. 2(A), while Fig. 5(B) shows a piezoelectric sound-producing element without these convex portions and concave portions. Fig. 5(C) shows the sound pressure-frequency characteristics when these two piezoelectric sound-producing elements are used. As can be seen from Fig. 5(C), the piezoelectric sound-producing element of Fig. 5(B) without convex portions and concave portions cannot narrow the frequency range above 80 dB.

[0036] 6(A) to 6(C) show three types of piezoelectric sound-producing elements prepared to confirm how the sound pressure-frequency characteristics change when the dimension W3 between two opposing recesses in the width direction is changed in the case where the non-fixed portion 13 of the piezoelectric sound-producing element has four recesses 14Ca to 14Cd as in the embodiment of FIG. 2(A). The non-fixed portion 13 of the diaphragm 12 of the piezoelectric sound-producing element is preferably made of an alloy plate made of iron and nickel with a thickness of 10 μm to 150 μm. The piezoelectric element preferably has a structure including a laminate in which a plurality of laminated portions are laminated with PZT ceramics with a thickness of 30 μm to 100 μm through intermediate electrodes, and a pair of outer electrodes arranged on both sides of the laminate. 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. The piezoelectric element may be provided on the surface of the diaphragm 12.

[0037] In the example of Fig. 6, the diameter of the piezoelectric element 15 is 15 mm, the thickness is 60 μm, the thickness of the metal diaphragm is 75 μm, and W3 is 10.5 mm, 11.6 mm, and 12.6 mm. From the sound pressure-frequency characteristics in Fig. 6(D), it can be seen that the smaller the dimension of W3, the higher the resonant frequency and sound pressure become, and the narrower the band becomes, and the larger the dimension of W3, the lower the resonant frequency and sound pressure become, and the wider the band becomes.

[0038] 7(A) to (G) show seven types of piezoelectric sound-producing elements prepared to confirm how the sound pressure-frequency characteristics change when the non-fixed part 13 of the piezoelectric sound-producing element has four recesses 14Ca to 14Cd as in the embodiment of FIG. 2(A), and the distance L3 between the pair of recesses 14Ca and 14Cb (or 14Cc and 14Cd) on the long side sides 13Aa and 13Ab of the non-fixed part 13 is changed without changing the dimension W3 between the two recesses (14Ca, 14Cc) facing each other in the width direction. The piezoelectric sound-producing element in FIG. 7(G) is a case where 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 closer to those of other piezoelectric sound-producing elements. Fig. 8(A) shows the sound pressure-frequency characteristics when the piezoelectric sound-producing elements of Fig. 7(A) to (D) are used, and Fig. 8(B) shows the sound pressure-frequency characteristics when the piezoelectric sound-producing elements of Fig. 7(E) to (G) are used. In the piezoelectric sound-producing elements of Fig. 7(A) to (F), the diameter of the piezoelectric element 15 made of PZT ceramic is 14 mm and the thickness is 60 μm, the thickness of the metal diaphragm is 75 μm, W3 is 12.2 mm to 12.7 mm (variable), L2 is 35.6 mm, and L3 is 9 mm, 10 mm, 11 mm, 14 mm, 16 mm, and 18 mm. In the piezoelectric sound-producing element of Fig. 7(G), L2 is 39 mm and L3 is 37 mm. From the sound pressure-frequency characteristics of Fig. 8(A) and (B), if the dimension of L3 is reduced, the variable range of the dimension of W3 becomes narrow, and there is a limit to the adjustment to increase the primary resonance frequency. As a result, the frequency band widens and the sound pressure drops. Conversely, if the L3 dimension is increased, the L2 dimension must be increased to maintain the same bandwidth, and the external dimensions become larger. Note that even if the L3 dimension is set to a maximum of 37 mm as shown in Figure 7(G), the sound pressure-frequency characteristics are not inferior.

[0039] 9(A) to (G) show seven types of piezoelectric sound-generating elements prepared to confirm how the sound pressure-frequency characteristics change when the longitudinal position (longitudinal arrangement ratio L21:L22) of the non-fixed part 13 of the piezoelectric sound-generating element is changed when the non-fixed part 13 of the piezoelectric element 15 has four recesses 14Ca to 14Cd as in the embodiment of FIG. 2. These piezoelectric sound-generating elements had a diameter of 14 mm and a thickness of 60 μm of the piezoelectric element 15 made of PZT ceramic, a thickness of 75 μm of the metal diaphragm, W3 was 12.2 mm, and L3 was 14 mm. The ratios of L21:L22 in the sound pressure generating elements of FIG. 9(A) to (G) were 15:5, 14:6, 13:7, 12:8, 11:9, 10.5:9.5, and 10:10. From the sound pressure-frequency characteristics in Fig. 10, the larger the ratio L21:L22, the lower the first and third resonance frequencies and sound pressure, and the wider the band, and the smaller the ratio L21:L22, the higher the first and third resonance frequencies and sound pressure, and the narrower the band. For practical purposes, the ratio L21:L22 is preferably in the range of 12:8 to 10:10.

[0040] [Piezoelectric element shape] Figures 11(A) to (E) show piezoelectric sound-producing elements prepared to confirm how the sound pressure-frequency characteristics change when the contour shape of the piezoelectric element 15 is changed from a circular shape to a regular polygonal shape. Figure 12 shows the sound pressure-frequency characteristics when these piezoelectric sound-producing elements are used.

[0041] Figures 13(A) to (C) show piezoelectric sound-producing elements prepared to confirm how the sound pressure-frequency characteristics change when the contour shape of the piezoelectric element 15 is circular and when it is elliptical. Figure 14 shows the sound pressure-frequency characteristics when these piezoelectric sound-producing elements are used. If the piezoelectric element is symmetrical with respect to the first and second imaginary lines (PL1, PL2), there is almost no difference in the sound pressure-frequency characteristics due to differences in the contour shape of the piezoelectric element, but from the standpoint of ease of manufacture and cost, a circular piezoelectric element is suitable. Note that the closer the contour shape is to a circle, the narrower the frequency range above 80 dB can be made.

[0042] [Electrode shape] Figures 15(A) to (D) show piezoelectric sound-generating elements prepared to confirm the effect of sound pressure-frequency characteristics when a pair of arc-shaped recesses 16A located on the first virtual line PL1 and convex toward the center of the outer electrode 16 are provided on at least the outer electrode 16 of the pair of outer electrodes of the piezoelectric element 15 that is not bonded to the diaphragm, and Figures 15(a) to (d) show the sound pressure-frequency characteristics and equivalent stress of the corresponding piezoelectric sound-generating elements of Figures 15(A) to (D). The pair of arc-shaped recesses 16A shown in Figures 15(B) to (D) have curvature radii r of 2 mm, 4 mm, and 6 mm. By providing such recesses 16A, the stress generated corresponding to the primary resonance frequency can be reduced, and the stress can be prevented from increasing locally, thereby extending the life of the piezoelectric element.

[0043] The shape of the recess 16A is not limited to a semicircular arc as in the above embodiment, and may be any shape such as a rectangle or a triangle. The shape of the recess 16A is preferably 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, 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 can be reduced, and the reduction in the life of the piezoelectric element can be suppressed.

[0044] In the case where the piezoelectric element has a single-layer structure with outer electrodes on both sides, the recess 16A may be provided at least on the outer electrode on the non-adhesive side. In the case where the piezoelectric element has a multi-layer structure with electrodes also inside, the recess 16A may be formed in the inner electrode.

[0045] [Resonator (sound emission hole in the case)] If the total opening area of ​​the sound emission holes in the case is within an appropriate range, the intermediate frequency value will not change significantly, and there will be no significant difference in the sound pressure of the intermediate frequencies. Furthermore, even if the number of sound emission holes is changed without changing the total opening area of ​​the sound emission holes too much, the difference in sound pressure between the first resonance frequency and the third resonance frequency will not increase, and a high sound pressure frequency characteristic will be obtained. If the total opening area does not change, the number of sound emission holes does not affect the frequency characteristic. Therefore, the number of sound emission holes needs to be one or more.

[0046] [Shape of the non-fixed part of the diaphragm] In the above-mentioned embodiment, in the embodiment shown in Fig. 2 onwards, a rectangular metal plate is used as the diaphragm 12, and the four corners of the non-fixed portion 13 are shown as right-angled. However, in practice, it is preferable to make the four corners of the non-fixed portion 13 rounded or tapered, as in the embodiment shown in Fig. 1.

[0047] [Lead wire soldering structure] FIG. 16(A) is a plan view showing a structure in which a lead wire 18 is soldered to a piezoelectric element 15, and FIG. 16(B) is an exploded perspective view of this structure. First, a solder resist layer 17 having a through hole 17A for forming a soldering portion for soldering the lead wire 18 is formed on the outer electrode 16 made of a silver electrode, which is one of the pair of outer electrodes and is not bonded to the diaphragm 12. The solder resist layer 17 is formed by screen printing using a resin coat such as acrylate having moisture resistance and insulating properties. The thickness of the solder resist layer 17 is 5 to 50 μm. The solder resist layer 17 has substantially the same shape and size as the outer electrode 16, and therefore also functions to cover the outer electrode 16 made of a silver electrode and prevent the occurrence of migration and corrosion of the silver electrode.

[0048] In this embodiment, the through hole 17A for forming the soldering portion is formed at a position where the second virtual line PL2 intersects with the through hole 17A, but the position and size of the through hole 17A are not limited to those in the embodiment. The position and size of the through hole 17A are determined so as to suppress the reduction in the sound pressure of the primary resonance frequency caused by the presence of the solder resist layer 17, and primaryIt is sufficient that the stress at the resonant frequency is suppressed. 15 When the diameter R is 13 mm to 15 mm, the straightness of the through hole 17A is The diameter is The thickness is preferably 1.5 mm to 3 mm. 15 It is preferable to determine the diameter and position of through hole 17A so that, if r=1.5 mm, then X is 2.3 mm or more, and if r=3 mm, then X is 3 mm or more. The diameter of soldered portion 19 of the core of lead wire 18 is substantially the same as that of through hole 17A.

[0049] FIG. 17(A) shows the relationship between sound pressure and frequency (frequency characteristics) when the position of through hole 17A is set to X=5 mm and r=2 mm, which are preferable soldering conditions. FIG. 17(B) shows the relationship between sound pressure and frequency (frequency characteristics) when the position of through hole 17A is set to X=2.5 mm and R=2 mm, which are conditions that adversely affect the acoustic characteristics. In FIG. 17(A), the sound pressure at the first resonance frequency is slightly lowered and the peak value of the stress is also lower. In contrast, in FIG. 17(B), the sound pressure at the first resonance frequency is slightly lowered and the peak value of the stress is higher. This increase in stress damages the PZT ceramic of piezoelectric element 15. From FIGS. 17(A) and (B), it can be seen that the position (X) and size (radius r) of through hole 17A are suitable for suppressing the decrease in sound pressure at the first resonance frequency that is lowered due to the presence of solder resist layer 17, and also for preventing the decrease in sound pressure at the first resonance frequency that is lowered due to the presence of solder resist layer 17. primary It can be seen that this is determined so as to suppress the rise in stress at the resonant frequency.

[0050] FIG. 18(A) is a diagram showing the state of stress at the time of the first resonance and the third resonance when an acoustic signal is applied and measured without forming a soldered portion. FIG. 18(B) is a diagram showing the state of stress at the time of the first resonance and the third resonance when an acoustic signal is applied and measured with a soldered portion 19 formed with a position of the through hole 17A of X=4 mm and r=2 mm. FIG. 18(C) is a diagram showing the state of stress at the time of the first resonance and the third resonance when an acoustic signal is applied and measured with a soldered portion 19 formed with a position of the through hole 17A of X=1.5 mm and r=2 mm. FIG. 18(D) is a diagram showing the state of stress at the time of the first resonance and the third resonance when an acoustic signal is applied and measured with a soldered portion 19 formed with a position of the through hole 17A of X=2.25 mm and r=3.5 mm. In the cases of FIGS. 18(C) and (D), it was confirmed that the stress around the through hole 17A becomes large, and damage to the PZT ceramic of the piezoelectric element occurs from the vicinity of the soldered portion 19.

[0051] Fig. 19(A) shows the relationship between sound pressure and frequency (f-dB characteristics) when a solder resist layer 17 made of a resin coat with a thickness of 20 μm is formed and when it is not formed, and Fig. 19(B) shows the relationship between impedance and frequency (impedance curve) when a solder resist layer 17 made of a resin coat is formed and when it is not formed. From these results, it is found that providing a solder resist layer 17 made of a resin coat can reduce the Q value of the resonance peak and flatten the f-dB characteristics. It was also confirmed that providing a solder resist layer 17 of a specified thickness provides the following effects.

[0052] (1) It was confirmed that the sound pressure of the first resonance could be lowered while maintaining the minimum sound pressure within the acoustic band (2 to 2.9 KHz), and that the sound pressure could be flattened by 2 dB.

[0053] (2) It was confirmed that the hysteresis region that causes a jump phenomenon (a vertical drop in sound pressure) near the third resonance can be reduced.

[0054] (3) It was confirmed that the Q value was reduced because the resonance peak of the impedance curve was reduced.

[0055] From the above, it has been confirmed that if the thickness of the solder resist layer 17 is determined so as to reduce the Q value of the resonance peaks of the first and third resonance frequencies, the presence of the solder resist layer 17 makes it possible to improve the acoustic characteristics. [Industrial Applicability]

[0056] According to the present invention, it is possible to provide a piezoelectric acoustic component that can reduce the sound pressure difference between the first resonant frequency and the intermediate resonant frequency, and between the intermediate resonant frequency and the third resonant frequency, while also being able to obtain a sound pressure of 80 dB or more and allowing the frequency range to be changed to some degree as desired. [Explanation of symbols]

[0057] 1 Piezoelectric acoustic components 3 Lower case half 4 sound hole 5 Upper case half 7 Openings 9 Sound element holder 11 Piezoelectric sound element 12 Diaphragm 13 Non-fixed part 13Aa, 13Ab long side 13Ba, 13Bb short side 14A, 14B Convex part 14Ca~14Cd Concave 15 Piezoelectric element 16 outer electrode 16A Recess PL1 First virtual line PL2 Second virtual line PL3 Third virtual line PL4 4th virtual line S1 First Space S2 The Second Space

Claims

1. a piezoelectric sound-generating element including a metallic diaphragm and a piezoelectric element provided on at least one surface of the diaphragm; a case in which an outer periphery of the vibration plate of the piezoelectric sound-producing element is fixed around the entire periphery, and a first space and a second space are formed on both sides of the piezoelectric sound-producing element, and one or more sound emission holes are formed in a wall portion facing the first space, so that a resonator is formed by the volume of the first space and the one or more sound emission holes, a 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 facing each other and shorter than the long sides; the piezoelectric element is provided on a central region of the non-fixed portion of the diaphragm; a contour shape of the piezoelectric element is determined to be symmetrical with respect to a first imaginary line that bisects the pair of short sides and is symmetrical with respect to a second imaginary line that is perpendicular to the first imaginary line and passes through a center of the piezoelectric element; a configuration of the resonator and a shape of a non-fixed portion are determined so that a sound pressure of a primary resonance frequency, a tertiary resonance frequency, and an intermediate frequency between the primary resonance frequency and the tertiary resonance frequency is 80 dB or more when a rectangular wave signal or a sine wave signal is input as an input signal, A first and a second protrusion are formed on the pair of long sides of the non-fixed portion, the first and second protrusions being protruding along the outer periphery of the piezoelectric element and along the second imaginary line in a direction away from the first imaginary line, and a piezoelectric acoustic component characterized in that a pair of long sides of the non-fixed portion are formed with first and second concave portions adjacent to the first and second convex portions, located on a third imaginary line that passes through the center of the piezoelectric element and extends so as to form an acute angle with the second imaginary line, and that are convex toward the first imaginary line so as to adjust a frequency range of 80 dB or more.

2. 2. The piezoelectric acoustic component according to claim 1, further comprising a third recess formed on one of the pair of long sides of the non-fixed portion, the third recess being adjacent to the pair of protrusions and protruding toward the first imaginary line at a position where a fourth imaginary line that is symmetrical to the third imaginary line with respect to the second imaginary line passes.

3. 2. The piezoelectric acoustic component according to claim 1, further comprising a third recess and a fourth recess formed on the pair of long sides of the non-fixed portion, the third recess and the fourth recess being adjacent to the pair of protrusions and convex toward the first imaginary line at a position where a fourth imaginary line that is symmetrical to the third imaginary line with respect to the second imaginary line passes through.

4. a distance between the first recess and the third recess and a distance between the second recess and the fourth recess are equal; The piezoelectric acoustic component according to claim 3, wherein the distance is 10 mm to 13 mm.

5. 2. A piezoelectric acoustic component according to claim 1, wherein a 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 set to be within a range of 2.1 to 2.

4.

6. A piezoelectric acoustic component as described in any one of claims 1 to 5, wherein the ratio L1 / L2 of the distance L21 from the center of the piezoelectric element to one of the pair of short sides measured along the first virtual line to the distance L22 from the center of the piezoelectric element to the other of the pair of short sides measured along the first virtual line is in the range of 10:10 to 12:

8.

7. 7. The piezoelectric acoustic component according to claim 1, wherein the contour shape of the piezoelectric element is a circle, an ellipse or a polygon.

8. 8. A piezoelectric acoustic component as claimed in any one of claims 1 to 7, wherein the case has an opening having the same shape as the contour of the non-fixed portion of the vibration plate and a sound-producing element holder for fixing the outer periphery of the vibration plate.

9. 2. The piezoelectric acoustic component according to claim 1, wherein the piezoelectric element is provided on a rear surface of the diaphragm.

10. The non-fixed portion of the diaphragm is made of an alloy plate of iron containing nickel and having 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 via intermediate electrodes, and a pair of outer electrodes arranged on both sides of the laminate, 2. 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.

11. 11. A piezoelectric acoustic component as described in claim 10, wherein at least one of the pair of outer electrodes, which is not bonded to the vibration plate, has a pair of recesses located on the first imaginary line and convex toward the center of the outer electrode.

12. 12. The piezoelectric acoustic component according to claim 11, wherein the recess has a shape such that the stress generated in response to a primary resonance frequency is close to the stress generated in response to a tertiary resonance frequency.

13. a solder resist layer having a through hole for forming a lead wire soldering portion is formed on the outer electrode of the pair of outer electrodes that is not bonded to the diaphragm; The piezoelectric acoustic component described in claim 10, characterized in that the position and size of the through hole are determined so as to suppress the decrease in sound pressure at the primary resonant frequency caused by the presence of the solder resist layer, and to suppress the increase in stress at the primary resonant frequency.

14. 14. The piezoelectric acoustic component according to claim 13, wherein when a diameter R of the piezoelectric element is in the range of 13 mm to 15 mm and a diameter r of the through hole is in the range of 1.5 mm to 3 mm, and when a distance X between a center of the piezoelectric element and an outer periphery of the through hole is X, when r = 1.5 mm, X is 2.3 mm or more, and when r = 3 mm, X is 3 mm or more.

15. 14. The piezoelectric acoustic component according to claim 13, wherein the solder resist layer is formed of a resin coat having moisture-proof and insulating properties.

16. 16. The piezoelectric acoustic component according to claim 15, wherein the thickness of the solder resist layer is determined so as to reduce the Q value of the resonance peaks of the first resonance frequency and the third resonance frequency.

Images