JP5609613B2 - Shock and acoustic sensor - Google Patents

Description

  The present invention relates to an impact and acoustic sensor capable of detecting impact and sound pressure, and more particularly to an impact and acoustic sensor using a plurality of piezoelectric plates.

  Conventionally, various acoustic sensors and acceleration sensors using piezoelectric elements have been proposed. The following Patent Document 1 discloses a mechanical vibration canceling piezoelectric ceramic microphone.

  As shown in FIG. 16, in the microphone 1001, piezoelectric elements 1003 and 1004 are disposed to face each other in a housing 1002. The piezoelectric elements 1003 and 1004 are respectively attached to diaphragms 1005 and 1006 partitioning the housing 1002. Thereby, the inside of the housing 1002 is partitioned into spaces A1 to A3. The space A3 is a portion where the diaphragms 1005 and 1006 are opposed to each other. A through hole 1002a is formed in the housing 1002 so as to face the space A3. Further, through holes 1002b and 1002c are formed so as to be continuous with the spaces A1 and A2, respectively.

  The piezoelectric elements 1003 and 1004 are connected in series. That is, the wiring 1007 is connected to one end of the piezoelectric element 1003, and the other electrode of the piezoelectric element 1003 is connected to the wiring 1008. One electrode of the piezoelectric element 1004 is in contact with the wiring 1008 and the other electrode is in contact with the wiring 1009.

  In the microphone 1001, when a sound wave reaches the space A3 from the through hole 1002a, the piezoelectric elements 1003 and 1004 are displaced in opposite phases. That is, the diaphragms 1005 and 1006 are bent so as to protrude toward the spaces A1 and A2, respectively, and accordingly, the piezoelectric elements 1003 and 1004 are also bent so as to protrude toward the spaces A1 and A2. In this case, since the piezoelectric elements 1003 and 1004 are connected in series, based on the signal from the piezoelectric element 1003 and the signal from the piezoelectric element 1004, an output corresponding to the sound pressure input in the output device 1010 can be taken out. it can. That is, it functions as a microphone.

  On the other hand, as shown in FIG. 17, when an impact is applied in the direction indicated by the arrow F, the piezoelectric elements 1003 and 1004 are displaced in phase. However, in the arrow F direction, the polarization direction of the piezoelectric element 1003 and the polarization direction of the piezoelectric element 1004 are opposite to each other. Therefore, the polarity of the signal extracted from the piezoelectric element 1003 and the polarity of the signal extracted from the piezoelectric element 1004 are reversed. Accordingly, no signal is output from the output device 1010.

  Therefore, the microphone 1001 does not output sound when an impact or the like is applied, and only the electric signal based on the sound pressure reaching the housing 1002 from the through hole 1002a is taken out.

JP-T 6-508498

  In the microphone 1001 described in Patent Document 1, an electric signal due to an impact force can be erased as described above. However, such a microphone 1001 can detect a signal due to sound pressure, but cannot detect the impact force itself. That is, when the microphone 1001 is used as an acoustic sensor and it is desired to detect an impact, an impact sensor has to be prepared separately.

  An object of the present invention is to provide an impact and acoustic sensor that is configured using a plurality of piezoelectric elements and that can detect not only sound but also impact.

  The impact and acoustic sensor according to the present invention includes a package and first and second piezoelectric elements housed in the package. In the package, the space on one side of each of the plate-like first and second piezoelectric elements is an acoustically closed space.

  The first and second piezoelectric elements are arranged in the package so as to be deformed in the opposite phase with respect to the acoustic input and to be deformed in the same phase with respect to the vibration input. In the present invention, there is provided a wiring structure for individually taking out the output of the first piezoelectric element and the output of the second piezoelectric element.

In this onset bright, the first and second signal processing circuit connected to the piezoelectric element is further provided. In the signal processing circuit, when the output signal of the first piezoelectric element is x and the output signal of the second piezoelectric element is y, the signal processing circuit outputs ax + by (where a and b are complex numbers) as the acoustic output. And ax-by is output as a signal output. In this case, an ax + by acoustic output and an ax−by impact detection output can be extracted from the signal processing circuit.

  The first and second piezoelectric elements may be bimorph piezoelectric elements or unimorph piezoelectric elements.

  In a further specific aspect of the impact and acoustic sensor according to the present invention, the first piezoelectric element and the second piezoelectric element are arranged to face each other in the package. In this case, the dimension in the direction perpendicular to the opposing direction of the first and second piezoelectric elements can be reduced.

  Further, in still another specific aspect of the shock and acoustic sensor according to the present invention, a space between the first piezoelectric element and the second piezoelectric element is acoustically closed in the package, Sound is guided to the opposite side of the space between the first piezoelectric element and the second piezoelectric element. In this case, since the rear air chamber is common to the acoustic input, the degree of decrease in acoustic detection sensitivity is equal between the first and second piezoelectric elements. Therefore, when vibration is detected, the signal removal performance by sound can be improved, and the S / N can be increased. Furthermore, the volume of the space sandwiched between the first and second piezoelectric elements does not change with respect to the vibration input. Therefore, it is difficult for the acceleration sensitivity to decrease due to air. Accordingly, since the signal removal performance due to vibration is enhanced during sound detection, the S / N during sound detection can be increased.

  In still another specific aspect of the impact and acoustic sensor according to the present invention, sound is guided to a space sandwiched between the first piezoelectric element and the second piezoelectric element in the package, and the first The opposite side of the second piezoelectric element from the space is an acoustically closed space. In this case, the sound pressure caused by sound is evenly applied to the first and second piezoelectric elements by being guided to the space between the first and second piezoelectric elements. Therefore, as a function of the impact sensor, a noise signal caused by sound can be removed in a wide frequency band.

  In still another specific aspect of the impact and acoustic sensor according to the present invention, the first plate-like piezoelectric element and the second plate-like piezoelectric element are arranged in parallel in the package so as not to face each other. In each of the first and second piezoelectric elements, a rear air chamber, which is an acoustically closed space, is provided on a surface opposite to the pressure-receiving surface that receives an acoustic signal. The pressure receiving surface and the rear air chamber of the element and the pressure receiving surface and the rear air chamber of the second piezoelectric element are opposite to the first and second piezoelectric elements. In this case, the impact along the thickness direction of the first and second piezoelectric elements and the size of the acoustic sensor can be reduced. That is, a low-profile shock and acoustic sensor can be provided.

In still another specific aspect of the impact and acoustic sensor according to the present invention, the surface density σ of the first and second piezoelectric elements is in the range of 0.01 to 1 kg / m ² . In this case, a small and highly sensitive impact and acoustic sensor can be provided.

  The shock and acoustic sensor according to the present invention is arranged so that the first piezoelectric element and the second piezoelectric element are deformed in the opposite phase with respect to the acoustic input and deformed in the same phase with respect to the vibration input. Since the wiring structure is formed so that the outputs of the first and second piezoelectric elements are individually taken out, it is possible to detect both sound and impact. Therefore, it is possible to detect impact and sound with a single sensor.

(A) And (b) is front sectional drawing of the impact and acoustic sensor which concerns on the 1st Embodiment of this invention, and the connection relation of the 1st, 2nd piezoelectric element of this impact and acoustic sensor, and a signal processing circuit FIG. (A) is a disassembled perspective view for demonstrating the laminated structure of the 1st, 2nd piezoelectric element in 1st Embodiment, (b) and (c) are the 1st, 2nd piezoelectric element. It is each typical top view which shows the electrode shape of the lower surface of this. It is a circuit diagram which shows the 1st, 2nd piezoelectric element and signal processing circuit of the impact and acoustic sensor of 1st Embodiment. (A) And (b) is each model which shows the displacement state of the 1st and 2nd piezoelectric element when a vibration input is added and a sound input is added in the impact and acoustic sensor of 1st Embodiment. FIG. It is a figure which shows the sensitivity characteristic as an acoustic sensor of the impact and acoustic sensor of 1st Embodiment. It is a figure which shows the sensitivity characteristic as an impact sensor of the impact and acoustic sensor of 1st Embodiment. It is a schematic diagram which shows an example with a favorable balance of the sound pressure sensitivity and acceleration sensitivity in an impact and acoustic sensor. It is a schematic diagram which shows the example in which the balance of the sound pressure sensitivity and acceleration sensitivity in an impact and acoustic sensor is not good. It is a block diagram which shows the connection relationship of the impact and acoustic sensor and signal processing circuit in the modification of the impact and acoustic sensor of this invention. It is front sectional drawing of the impact and acoustic sensor of the 2nd Embodiment of this invention. It is front sectional drawing of the impact and acoustic sensor which concerns on the 3rd Embodiment of this invention. It is a disassembled perspective view of the impact and acoustic sensor of the 3rd Embodiment of this invention. It is a typical front sectional view of an impact and acoustic sensor concerning a 4th embodiment of the present invention. It is a perspective view of the impact and acoustic sensor of the 4th Embodiment of this invention. It is a typical front sectional view of an impact and acoustic sensor concerning a 5th embodiment of the present invention. It is typical sectional drawing which shows an example of the conventional microphone. FIG. 17 is a schematic front sectional view for explaining a displacement state of a piezoelectric element when acceleration is applied to the microphone shown in FIG. 16.

  Hereinafter, the present invention will be clarified by describing specific embodiments of the present invention with reference to the drawings.

  Fig.1 (a) is front sectional drawing which shows the impact and acoustic sensor which concerns on the 1st Embodiment of this invention.

  The impact and acoustic sensor 1 has a package 2. The package 2 includes a substrate 3 and a lid member 4 fixed to the upper surface of the substrate 3. The substrate 3 is made of an insulating material. Electrode lands 5 to 7 are formed on the upper surface of the substrate 3. External electrodes 8 and 9 are formed on the lower surface of the substrate 3. A via hole electrode 11 is formed on the substrate 3 so as to electrically connect the electrode land 6 and the external electrode 9. Although not shown in FIG. 1A, the electrode land 5 and the FET 12 are electrically connected, and the electrode land 7 and the external electrode 8 are connected via holes. An FET 12 and an FET 12A (not shown) are mounted on the substrate 3 so as to be electrically connected to the electrode lands 6 and 7.

  The FET 12 and the FET 12A have a function of amplifying the outputs of the first and second piezoelectric elements 16 and 20. The FET 12 and FET 12A constitute a part of a signal processing circuit described later.

  The lid member 4 has an opening that opens downward. The lower opening edge is bonded to the upper surface of the substrate 3. Thereby, a space surrounded by the upper surface of the substrate 3 and the lid member 4 is formed. A through hole 4 a is formed on the upper surface of the lid member 4. The through hole 4a is a sound passage hole for guiding sound to the space in the package 2, as will be described later. In the present embodiment, the lid member 4 is made of metal. As a result, the internal space can be electromagnetically shielded. However, the lid member 4 may be formed of a conductive material other than metal, or a material having a conductive layer on the surface or inside thereof. Furthermore, the lid member 4 may be formed of an insulating material that does not have an electromagnetic shielding function.

  In the space in the package 2, a rectangular frame spacer 14 is bonded via a conductive adhesive layer 13. In the present embodiment, the rectangular frame spacer 14 is made of insulating ceramics. However, other insulating materials may be used.

  A plate-like first piezoelectric element 16 is bonded onto the spacer 14 via an adhesive layer 15. In addition, a rectangular frame-shaped holding member 18 is joined to the first piezoelectric element 16 via an adhesive layer 17. A plate-like second piezoelectric element 20 is bonded onto the rectangular frame-shaped holding member 18 via an adhesive layer 19.

  FIG. 2A is an exploded perspective view of a structure in which the first piezoelectric element 16, the holding member 18, and the second piezoelectric element 20 are stacked. As shown in FIG. 2A, the first piezoelectric element 16 includes a rectangular plate-shaped piezoelectric plate 16a whose main surfaces face each other. The piezoelectric plate 16a is made of two layers of piezoelectric ceramics, and each is polarized in the opposite direction of the thickness direction. A first electrode 16b is formed on the upper surface which is one main surface of the piezoelectric plate 16a. As shown in FIG. 2B, a second electrode 16c is formed on the lower surface which is the other main surface of the piezoelectric plate 16a. The first electrode 16b is drawn to one end of the piezoelectric plate 16a, and the second electrode 16c is drawn to the other end. In this embodiment, lead zirconate titanate ceramics are used as the piezoelectric material, but piezoelectric materials such as lead-free piezoelectric ceramics such as potassium sodium niobate and alkali niobate ceramics may be used as appropriate. it can.

  In the present embodiment, the first and second piezoelectric elements 16 and 20 are bimorph piezoelectric elements in which piezoelectric layers having electrodes formed on the upper surface and the lower surface of the elastic plate are disposed. Then, the upper and lower piezoelectric layers are electrically connected in series. Moreover, in the present invention, the first and second piezoelectric elements may have a bimorph structure and may have a structure in which the upper and lower piezoelectric layers are electrically connected in parallel, or have a unimorph structure. It may be a thing. Further, the number of piezoelectric layers is not particularly limited, and in the case of the bimorph type piezoelectric element, more piezoelectric layers may be laminated. When a unimorph type piezoelectric element is used, a plurality of piezoelectric layers may be laminated to form one piezoelectric body. In addition, you may have an internal electrode inside a piezoelectric material layer.

  Similarly, as shown in FIGS. 2A and 2C, the second piezoelectric element 20 also includes a rectangular plate-shaped piezoelectric plate 20a and first and second electrodes 20b and 20c. The first electrode 20b is drawn to one end of the piezoelectric plate 20a, and the second electrode 20c is drawn to the other end.

  As shown in FIG. 2A, in the laminated structure, first and second side electrodes 21 and 22 are formed on one end side in the length direction. The first side electrode 21 is electrically connected to the first electrode 16 b of the first piezoelectric element 16, and the second side electrode 22 is connected to the first electrode 20 b of the second piezoelectric element 20. It is connected. That is, on the side surface of the multilayer body, the first and second side surface electrodes 21 and 22 are formed at different positions in the width direction of the multilayer structure.

  Similarly, a third side surface electrode 23 is formed on the other end side of the laminated structure, and the third side surface electrode 23 corresponds to the second electrode 16c of the first piezoelectric element 16 and the second piezoelectric element. The second electrode 20c of the element 20 is connected.

  As shown in FIGS. 2A and 2B, the first electrode 16b and the second electrode 16c are partially formed on the upper and lower surfaces of the piezoelectric plate 16a. The first electrode 16b and the second electrode 16c have the same shape except for the lead portion, and are opposed to each other through the piezoelectric plate 16a. In the present embodiment, the shape of the opposing portion excluding the lead portions of the first electrode 16b and the second electrode 16c is rectangular. However, the planar shape of the facing portion is not limited to a rectangle.

Not shown in the above-described FET12 and FIG 1 (b) FETs 12a constitutes a part of the first, second piezoelectric elements 16, 20 electrically connected to the signal processing circuit, respectively. The first side surface electrode 21 is connected to the electrode land 5, the electrode lands 5, although not shown in FIG. 1 (b), is connected to the FET 12. Similarly, the 2nd piezoelectric element 20 is connected to the 2nd side electrode 22, and the 2nd side electrode 22 is connected to FET12A via the electrode land which is not illustrated. On the other hand, the third side surface electrode 23 is connected to the electrode land 6 shown in FIG. 1 (b), are connected through the electrode land 6 in FET 12, FETs 12a. As shown in FIG. 1 (b), first, second piezoelectric elements 16, 20 of the impact and acoustic sensors 1 are connected in series. One end of the first piezoelectric element 16 is connected to the signal processing circuit 26 via the first side electrode 21 described above. One end of the second piezoelectric element 20 is connected to the signal processing circuit 26 via the second side electrode 22. One ends of the first and second piezoelectric elements 16 and 20 connected to each other are commonly connected, and are connected to the signal processing circuit 26 by the third side surface electrode 23. Therefore, the sensor portion including the first and second piezoelectric elements 16 and 20 constitutes a three-terminal type sensor having three output terminals.

  FIG. 3 is a diagram showing a circuit configuration including the first and second piezoelectric elements 16 and 20 and the signal processing circuit 26 of the impact and acoustic sensor 1. As shown in FIG. 3, the above-described FET 12 and another FET 12 </ b> A are built in the package 2. In FIG. 1A, only the FET 12 is shown. The FET 12 and FET 12A are provided for amplifying the outputs of the first and second piezoelectric elements 16 and 20, respectively. The FET 12 and FET 12A are not necessarily provided.

  The input ends of the signal processing circuit 26 are the first to third side electrodes 21 to 23 described above. The first side electrode 21 is connected to the gate terminal of the FET 12. Similarly, the second side electrode 22 is connected to the gate terminal of the FET 12A. The drain electrodes of the FET 12 and FET 12A are connected to operational amplifiers 27 and 29 via coupling capacitors 31 and 32, respectively. The output terminal of the operational amplifier 27 is connected to one input terminal of the A / D converter 28. The output terminal of the operational amplifier 29 is connected to the other input terminal of the A / D converter 28.

  The source electrodes of the first and second FETs 12 and 12A are connected to the ground potential.

  Further, an adder / subtracter 33 is connected to the subsequent stage of the A / D converter 28, and the adder / subtractor 33 is connected to the first output terminal 34. The first output terminal 34 outputs an output signal based on the detected sound. The second output terminal 35 outputs an output signal based on the detected impact.

  In the present embodiment, the output signal of the first piezoelectric element 16 is given to the first side electrode 21 that is the first input terminal of the signal processing circuit 26. This output signal is amplified by the operational amplifier 27 and converted into a digital signal by the A / D converter 28. Similarly, the output signal of the second piezoelectric element 20 is given to the second side surface electrode 22 which is the third input terminal of the signal processing circuit 26, and the output signal is digitally output by the A / D converter 28. Converted to a signal.

  The signal extracted from the first piezoelectric element 16 is processed as described above, the signal given to the adder / subtractor 33 is x, and the signal extracted from the second piezoelectric element 20 is processed as described above. The signal given to the adder / subtractor 33 is y. The adder / subtractor 33 calculates ax + by or ax−by. Here, a and b are arbitrary complex numbers. Note that a and b may be real numbers.

  ax + by corresponds to an output signal when sound is detected, and is output from the output terminal 34. ax-by is output from the second output terminal 35 as a signal when an impact, that is, vibration is detected.

  That is, in the present embodiment, by processing the outputs of the first and second piezoelectric elements 16 and 20 by the signal processing circuit 26, not only can sound be detected, but also impact and vibration can be detected. It is said that. This principle will be described with reference to FIGS. 4 (a) and 4 (b).

  As shown in FIG. 4A, when acceleration is applied to the portion where the first and second piezoelectric elements 16 and 20 are stacked, as shown by an arrow F1, that is, in the direction shown by the arrow F1, the impact is applied. Is added, the first and second piezoelectric elements 16 and 20 are displaced in phase. For example, as shown in FIG. 4A, the direction in which the main surface of the first piezoelectric element 16 extends and the direction in which the main surface of the second piezoelectric element 20 extend are not orthogonal to each other. Since they are arranged in parallel, when acceleration having a component perpendicular to the main surface is applied from the upper side to the lower side of the main surface, the first piezoelectric element 16 is bent downward and the second piezoelectric element 20 is similarly bent. The first piezoelectric element 16 is bent in a convex downward direction that is the same bending direction.

  Therefore, the impact, that is, the vibration can be detected by calculating ax-by from the output signals x and y of the first and second piezoelectric elements 16 and 20 connected in series.

  On the other hand, in the impact and acoustic sensor 1 shown in FIG. 1A, when sound is guided into the package 2 from the through hole 4a, the first piezoelectric element is shown as indicated by arrows B1 and B2 in FIG. In the element 16 and the second piezoelectric element 20, the sound pressure is applied from the outer surface toward the space where the two faces each other. Therefore, as shown in FIG. 4B, the first piezoelectric element 16 and the second piezoelectric element 20 are displaced in opposite phases by the sound pressure. Therefore, by calculating ax + by from the output signals of the first and second piezoelectric elements 16 and 20 connected in series, an output signal based on the sound can be extracted.

  That is, in the present embodiment, the first and second piezoelectric elements 16 and 20 are displaced in the opposite phase in the package 2 when sound is applied, and are displaced in the same phase when an impact or acceleration is applied. Thus, the first and second piezoelectric elements 16 and 20 are arranged.

  More specifically, in the first embodiment, as described above, the plate-like first and second piezoelectric elements 16 and 20 are opposed to each other across the space A so that their principal surfaces are parallel to each other. ing. This space A is sealed by a rectangular frame-shaped holding member 18 and adhesive layers 17 and 19. Accordingly, the space A is an acoustically closed space and forms a rear air chamber of the piezoelectric elements 16 and 20. The rear air chamber refers to a closed space located on the surface opposite to the side to which sound pressure is applied when the plate-like piezoelectric vibrator vibrates.

  Note that the acoustically closed space refers to a space that does not substantially transmit sound waves between the inside and outside of the space. Such a space is not necessarily limited to a sealed space, but also includes a space in which a small through hole for reducing the pressure difference between the inside and the outside is provided in a portion separating the inside of the outside space from the outside of the space.

  In the present embodiment, as described above, the output signals of the first and second piezoelectric elements 16 and 20 are converted into digital signals by the A / D converter 28, but they are processed as analog signals. Also good. Furthermore, after performing some modulation processing such as frequency modulation, an arithmetic processing equivalent to the above addition and subtraction may be performed. Further, in the present embodiment, the FET is built in the sensor package and the other signal processing circuits are outside the package, but the entire signal processing circuit or other partial configuration may be built in the sensor package. Of course, it is not always necessary to use an FET as the amplifier circuit, and a part or all of the signal processing circuit may be integrated in the IC.

  When the piezoelectric element is deformed, a volume change occurs in the rear air chamber. Along with this, the piezoelectric element receives a pressure acting as a reaction force, so that the sensitivity of the piezoelectric element decreases. The amount of decrease in sensitivity generally depends on the amount of deformation of the piezoelectric element and the volume of the rear air chamber. In the present embodiment, the rear air chamber is common to the first and second piezoelectric elements 16 and 20. Accordingly, a decrease in sound detection sensitivity occurs equally in the first and second piezoelectric elements 16 and 20. Therefore, S / N when an impact is detected as an impact sensor can be increased.

  On the other hand, when detecting an impact, that is, vibration, the first and second piezoelectric elements 16 and 20 are deformed in phase, so that the volume of the space A between the two piezoelectric elements hardly changes. Therefore, the vibration detection sensitivity is hardly lowered, and the sensitivity difference between the first and second piezoelectric elements 16 and 20 is hardly caused. Therefore, in the case of detecting sound, since the vibration signal removal performance is excellent, the S / N of the sound detection signal can be increased.

  Note that the sound detected in the present embodiment is not limited to a sound having an audible frequency, but includes a high frequency signal from a low frequency signal of several Hz or less to an ultrasonic region.

  From the viewpoint of the noise removal effect, it is preferable to perform fine adjustment in the addition and subtraction processes. The sensitivity of the first and second piezoelectric elements depends on the material variation of the piezoelectric element, the variation in the processing process, and the pressure and acoustic resistance that are received as reaction force due to the volume change of the rear air chamber when the piezoelectric element is deformed. Differences can occur. When a sensitivity difference occurs, a simple addition / subtraction such as x + y and xy reduces the noise removal effect. Similarly, the gain variation at the time of amplification by the signal processing circuit also causes a reduction in the noise removal effect. On the other hand, by performing fine adjustment in the addition / subtraction process so as to correct the sensitivity difference and the gain difference, the effect of canceling the signal based on vibration can be enhanced when detecting sound. Similarly, when detecting vibration, the effect of canceling the output signal by the acoustic signal can be enhanced. Such fine adjustment includes a method of adjusting the complex numbers a and b at the time of addition and subtraction. In normal adjustment, a and b are real numbers out of complex numbers, and a sufficient effect can be obtained. About the setting of said a and b, after producing the impact and acoustic sensor 1, what is necessary is just to adjust according to the output signal from a signal processing circuit. For sound, a phase difference occurs in the sound pressure applied to the first and second piezoelectric elements at a frequency of approximately 10 kHz or more. In the high frequency section, a and b are complex numbers, phase correction is performed, and addition / subtraction is performed, so that the effect of removing an acoustic signal can be enhanced when functioning as an impact sensor.

  FIG. 5 shows sensitivity frequency characteristics for detecting sound pressure in the impact and acoustic sensor of the above embodiment. The solid line shows the sound pressure sensitivity, and the broken line shows the sensitivity of the acceleration that is shock or noise. It can be seen that sound pressure can be measured with high sensitivity over a wide frequency range from 100 Hz to 20000 Hz, while the sensitivity of acceleration that becomes noise is lower by 33 dB or more.

  That is, in this embodiment, as described above, the rear air chamber is sandwiched between the first and second piezoelectric elements 16 and 20. Therefore, even if the vibration input changes, the piezoelectric element deforms in phase and the volume of the rear air chamber does not change. Therefore, deformation of the first and second piezoelectric elements 16 and 20 is difficult to be prevented. Therefore, the acceleration sensitivity is hardly lowered, and at the same time, the sensitivity difference is hardly caused. Therefore, as shown in FIG. 5, the acceleration sensitivity that becomes noise can be sufficiently lowered. That is, S / N can be effectively increased.

  FIG. 6 is a diagram showing characteristics of acceleration sensitivity and sound pressure sensitivity as noise when an impact, that is, acceleration is detected in the impact and acoustic sensor of the above embodiment.

  As can be seen from FIG. 6, even when detecting acceleration, the acceleration can be detected with high sensitivity over a wide frequency range. On the other hand, it can be seen that the sound pressure sensitivity that is noise in that case is lower by 40 dB or more over a wide frequency range.

  That is, in the present embodiment, as described above, the first and second piezoelectric elements 16 and 20 are common. Accordingly, a decrease in sound detection sensitivity occurs equally in the first and second piezoelectric elements 16 and 20. Therefore, it is possible to sufficiently reduce the sound pressure sensitivity that becomes noise. Further, as described above, since the volume of the rear air chamber hardly changes with respect to vibration, the acceleration sensitivity is hardly lowered. Therefore, as shown in FIG. 6, it is possible to effectively increase the sensitivity to acceleration and sufficiently reduce the sound pressure sensitivity that becomes noise. That is, the S / N when an impact is detected as an impact sensor can be increased.

Preferably, the surface density σ of the first and second piezoelectric elements 16 and ^{20 is in} the range of 0.01 to 1 kg / m ² . This will be described below.

The force received by the piezoelectric elements 16 and 20 per unit area due to the sound input of the sound pressure p (Pa) is fs, and the force received per unit area from the vibration input of the acceleration c (m / sec ² ) is fa. When the surface density σ [kg / m ² ] which is the mass per unit area of the piezoelectric elements 16 and ²⁰ is used, fs [N] = p [Pa] · 1 [m ² ], and fa [N] = σ It is expressed as [kg / m ² ] · 1 [m ² ] · c [m / s ² ].

The output voltage at the time of sound input is proportional to fs, and the output voltage for vibration input is proportional to fa. The sound pressure sensitivity is represented by an output voltage with respect to sound pressure p = 1 [Pa], and the acceleration sensitivity is represented by an output voltage with respect to c = 1G = 9.8 [m / sec ² ]. Therefore, the ratio of acceleration sensitivity / sound pressure sensitivity is fa / fs = 1 / (9.8 × σ). That is, the balance between acceleration sensitivity and sound pressure sensitivity depends on the surface density σ.

  Here, when fs = fa, that is, σ = p / c, the output voltages of the acoustic sensor and the vibration sensor are equal, as schematically shown in FIG. Assuming that p and c are standard signal levels of sound pressure and acceleration to be detected, the isolation between the signal and the noise is most enhanced under the condition of σ = p / c.

  On the other hand, FIG. 8 shows an example in the case of σ> p / c. In this case, it can be seen that noise due to vibration is likely to be generated during acoustic detection.

  As described above, the balance between the acoustic detection sensitivity and the acceleration detection sensitivity can be adjusted by the surface density σ. Therefore, it is desirable to adjust the sensitivity balance with the surface density σ so that the acoustic and impact sensor signal voltages output when the standard values of the sound pressure and acceleration desired to be detected are input. Thereby, the isolation between the sound pressure signal or acceleration signal and the acceleration signal or sound pressure signal that becomes noise can be enhanced.

For example, for a sound of 1 pa often used as a reference level and an acceleration of 1 G (9.8 m / sec ² ), when σ = 1 / 9.8, that is, σ is about 0.1 kg / m ² , The isolation is the best. When the density of the piezoelectric elements 16 and 20 is 8 × 10 ⁻³ kg / m ³ , it can be seen that the thickness of the piezoelectric elements 16 and 20 is preferably 13 μm.

As described above, in view of general applications, it is understood that the surface density σ may be in the range of 0.01 to 1 kg / m ² .

  In the above-described embodiment, the three-terminal type impact and acoustic sensor is configured. However, as shown in FIG. 9, the four-terminal type impact and acoustic signals for individually extracting the signals of the first and second piezoelectric elements 16 and 20 are provided. An acoustic sensor may be used.

  FIG. 10 is a front sectional view of an impact and acoustic sensor according to the second embodiment of the present invention. The impact and acoustic sensor 41 of the present embodiment is configured in substantially the same manner as the impact and acoustic sensor 1 shown in FIG. The difference is that the through hole 4 a is not formed in the lid member 4, and instead, the through hole 3 a is formed in the substrate 3. That is, a portion for guiding sound into the package 2 is provided not on the package 2 but on the substrate 3. Since it is the same about other points, the description of the first embodiment will be incorporated by giving the same reference numerals to the same parts.

  In the present embodiment, it is not necessary to provide a clearance above the lid member 4 when the impact and acoustic sensor 41 is built in the device. Accordingly, it is possible to reduce the height of a product in which the impact and acoustic sensor 41 is incorporated. Moreover, in this embodiment, since the other structure is the same as that of 1st Embodiment, the effect similar to 1st Embodiment can be acquired.

  FIG. 11 is a front sectional view of an impact and acoustic sensor according to a third embodiment of the present invention, and FIG. 12 is an exploded perspective view thereof.

  In the present embodiment, a spacer substrate 63 is laminated on the substrate 3 via an adhesive layer 62. A first piezoelectric element 65 is laminated on the spacer substrate 63 via an adhesive layer 64 having a substantially circular opening. Although schematically shown in FIG. 11, as shown in FIG. 12, the first piezoelectric element 65 is composed of a piezoelectric plate, and a circular first electrode 65a and a first electrode are formed on the upper surface of the piezoelectric plate. And a ring-shaped second electrode 65b provided so as to surround 65a.

  A holding member 67 is laminated on the first piezoelectric element 65 via an adhesive layer 66 having a circular opening member. The holding member 67 has a circular opening similarly to the adhesive layer 66. A second piezoelectric element 69 is laminated on the holding member 67 via an adhesive layer 68 having a circular opening. The second piezoelectric element 69 is configured similarly to the first piezoelectric element 65.

  A lid substrate 71 is laminated on the second piezoelectric element 69 via an adhesive layer 70 having a circular opening. A through hole 71 a is formed in the lid substrate 71. The through hole 71 a is a part that guides sound into the package 2.

  That is, in the third embodiment, the internal space is formed by laminating the first and second piezoelectric elements 65 and 69 and the lid substrate 71 without using the lid member 4. Here, in order to guide the sound pressure to the lower surface of the first piezoelectric element 65 below, the sound passage hole 72 shown in FIG. 11 is formed. The sound passage hole 72 is formed so as to penetrate the second piezoelectric element 69, the adhesive layer 68, the holding member 67, the adhesive layer 66, and the first piezoelectric element 65.

  Therefore, as indicated by an arrow D in FIG. 11, the sound pressure guided to the inside is also guided to the space on the lower surface side of the first piezoelectric element 65.

  As described above, in the present invention, the cover substrate 71 is used instead of the cover material 4 opened downward, and the piezoelectric element and the adhesive layer are laminated to eliminate the through-hole for introducing the sound into the inside. A closed internal space may be formed. According to this embodiment, the impact and acoustic sensor 61 can be obtained simply by stacking a plurality of sheet-like members. Therefore, the manufacturing process can be simplified. Further, the impact and acoustic sensor 61 can be easily reduced in size and height.

  Also in the present embodiment, as in the first embodiment, since the portion where the first and second piezoelectric elements are opposed is a closed space, as in the first embodiment, the impact and Sound can be detected reliably and with high accuracy.

  FIG. 13 is a front sectional view of an impact and acoustic sensor according to the fourth embodiment of the present invention, and FIG. 14 is a perspective view thereof. In the impact and acoustic sensor 81 of the present embodiment, a package is configured by stacking a plurality of sheet-like members, as in the third embodiment. That is, the spacer substrate 82 is laminated on the substrate 3. A support portion 82 a protruding upward is formed on the outer peripheral edge of the spacer substrate 82. A first piezoelectric element 83 is stacked on the support portion 82a. The first piezoelectric element 83 is laminated with the second piezoelectric element 85 via the spacer 84. The first and second piezoelectric elements 83 and 85 are configured in the same manner as in the first embodiment. Here, a through hole 84 a communicating with the outside is formed on the side of the spacer 84. The through hole 84a functions as a sound passage hole.

  A lid substrate 86 is bonded to the upper surface of the second piezoelectric element 85. The lid substrate 86 has a frame-shaped support portion 86a on the outer periphery of the lower surface. A frame-shaped support portion 86 a is joined to the upper surface of the second piezoelectric element 85. In FIG. 13, it is pointed out that illustration of an adhesive layer and the like for joining the members is omitted. A conductive film 87 is formed so as to cover the outer surface of the laminated structure on the substrate 3.

  Like this embodiment, you may provide the through-hole 84a used as a sound passage hole in the side surface of a package. In the present embodiment, the through hole 84a that is a sound passage hole communicates with the space between the first and second piezoelectric elements 83 and 85. Therefore, the sound pressure of the sound guided from the through hole 84 a is received by the upper surface of the first piezoelectric element 83 and the lower surface of the second piezoelectric element 85. Thus, the sound pressure may be guided between the first and second piezoelectric elements facing each other.

  Also in the present embodiment, when the sound pressure is detected, the first and second piezoelectric elements 83 and 85 are displaced in opposite phases, and when an impact is applied, the first and second piezoelectric elements 83 and 85 are Displace in phase. Therefore, as in the first embodiment, sound and impact can be detected with high accuracy. In addition, since sound pressure due to sound is equally applied to the first and second piezoelectric elements, a noise signal caused by sound can be removed in a wide frequency band as a function of the impact sensor. In a structure in which the space between the diaphragms is acoustically closed, if the frequency increases to about 10 kHz or more, a phase difference occurs in the sound that reaches the outer position of the two diaphragms, and the sound signal is generated when functioning as an impact sensor. The removal effect decreases. On the other hand, in the present embodiment, in which sound is guided to the space between the diaphragms, the sound pressure applied to the two diaphragms is in phase, so that such a problem does not occur and a high noise removal effect is obtained in a wide frequency band. It is done.

  FIG. 15 is a front sectional view of an impact and acoustic sensor according to the fifth embodiment of the present invention. In the impact and acoustic sensor 91 of this embodiment, a spacer 93 having openings 93 a and 93 b is laminated on a substrate 92. A first piezoelectric element 94 is stacked on the substrate 92 so as to close the opening 93a. Similarly, the second piezoelectric element 95 is stacked so as to close the opening 93b.

  A lid substrate 96 is laminated on the upper surfaces of the first and second piezoelectric elements 94 and 95. The lid substrate 96 has recesses 96a and 96b on the lower surface. The recess 96 a is formed to face the opening 93 a of the spacer 93. Similarly, the recess 96b is formed to face the opening 93b. Therefore, in the impact and acoustic sensor 91, a package is constituted by the substrate 92, the spacer 93, the portion of the first and second piezoelectric elements 94 and 95 supported by the spacer 93 and the lid substrate 96, and the lid substrate 96. Yes.

  As in this embodiment, the first and second piezoelectric elements 94 and 95 may be arranged in parallel so that the piezoelectric elements do not face each other. Here, a through-hole 96 c is formed in the lid substrate 96 so as to face the first piezoelectric element 94 in the recess 96 a closed by the first piezoelectric element 94. This through hole 96c functions as a sound passage hole. Therefore, the opening 93a, which is a closed space, constitutes the rear air chamber.

  On the other hand, on the second piezoelectric element 95 side, a through hole 92 a is formed in the substrate 92 so as to face the second piezoelectric element 95. The through hole 92a functions as a sound passage hole. Therefore, the space where the recess 96 b is closed by the second piezoelectric element 95 constitutes the rear air chamber of the second piezoelectric element 95.

  Also in this embodiment, the first and second piezoelectric elements 94 and 95 are displaced in the opposite phase when a sound pressure is applied, and are displaced in the same phase when an impact is applied. Therefore, the same effect as the first embodiment can be obtained. In addition, since the first and second piezoelectric elements 94 and 95 are arranged side by side as described above, it is possible to reduce the height.

DESCRIPTION OF SYMBOLS 1 ... Impact and acoustic sensor 2 ... Package 3 ... Board | substrate 3a ... Through-hole 4 ... Cover material 4a ... Through-hole 5-7 ... Electrode land 8, 9 ... External electrode 11 ... Via-hole electrode 12 ... FET
12A ... FET
DESCRIPTION OF SYMBOLS 13 ... Conductive adhesive layer 14 ... Spacer 15 ... Adhesive layer 16 ... 1st piezoelectric element 16a ... Piezoelectric plate 16b ... 1st electrode 16c ... 2nd electrode 17, 19 ... Adhesive layer 18 ... Holding member 20 ... second piezoelectric element 20a ... piezoelectric plate 20b ... first electrode 20c ... second electrode 21 ... first side electrode 22 ... second side electrode 23 ... third side electrode 24 ... fourth side electrode DESCRIPTION OF SYMBOLS 25 ... External electrode 26 ... Signal processing circuit 27, 29 ... Operational amplifier 28 ... A / D converter 31, 32 ... Capacitor 33 ... Adder / subtractor 34 ... First output terminal 35 ... Second output terminal 36 ... External electrode 41 ... Shock and acoustic sensor 61 ... Shock and acoustic sensor 62 ... Adhesive layer 63 ... Spacer substrate 64 ... Adhesive layer 65 ... First piezoelectric element 65a ... First electrode 65b ... Second electrode 66 ... Adhesive layer 67 …Retention Material 68 ... Adhesive layer 69 ... Second piezoelectric element 70 ... Adhesive layer 71 ... Cover substrate 71a ... Through hole 72 ... Sound passage hole 72 ... Cover substrate 81 ... Acoustic sensor 82 ... Spacer substrate 82a ... Support part 83 ... First 1 piezoelectric element 84 ... spacer 84 a ... through hole 85 ... second piezoelectric element 86 ... lid substrate 86a ... support part 87 ... conductive film 91 ... acoustic sensor 92 ... substrate 92a ... through hole 93 ... spacer 93a, 93b ... opening 94 ... first piezoelectric element 95 ... second piezoelectric element 96 ... lid substrate 96a, 96b ... concave portion 96c ... through hole

Claims (6)

Package and
First and second piezoelectric elements housed in the package;
The first piezoelectric element and the second piezoelectric element are arranged so as to be deformed in an opposite phase with respect to the acoustic input and to be deformed in the same phase with respect to the vibration input, And a wiring structure for individually taking out the output of the second piezoelectric element,
A signal processing circuit connected to the first and second piezoelectric elements,
When the output signal of the first piezoelectric element is x and the output signal of the second piezoelectric element is y, the signal processing circuit outputs ax + by (where a and b are complex numbers) as the acoustic output, and the vibration output and it is configured to output the ax-by as, shock and acoustic sensors.   The impact and acoustic sensor according to claim 1, wherein the first piezoelectric element and the second piezoelectric element are disposed so as to face each other in the package.   The impact according to claim 2, wherein a space between the first piezoelectric element and the second piezoelectric element is acoustically closed in the package, and sound is guided to a side opposite to the space. And acoustic sensors.   Within the package, sound is guided to a space between the first piezoelectric element and the second piezoelectric element, and the opposite side of the first and second piezoelectric elements from the space is acoustically The shock and acoustic sensor according to claim 2, which is a closed space.   The first plate-like piezoelectric element and the second plate-like piezoelectric element are provided in the package, and the first and second piezoelectric elements are opposite to the pressure-receiving surface that receives an acoustic signal. A rear air chamber that is an acoustically closed space is provided on the surface, and the pressure receiving surface and the rear air chamber of the first piezoelectric element, and the pressure receiving surface and the rear air chamber of the second piezoelectric element are the first. The impact and acoustic sensor according to claim 1, wherein the shock and acoustic sensor is opposite to the second piezoelectric element. The impact and acoustic sensor according to any one of claims 1 to 5, wherein a surface density σ of the first and second piezoelectric elements is in a range of 0.01 to 1 kg / m ² .

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