Piezoelectric sensor and method for manufacturing piezoelectric sensor

Abstract

To improve the efficiency of converting force into electricity in a piezoelectric element without forming a piezoelectric composite by reducing the volume of a piezoelectric body such as piezoelectric ceramics.SOLUTION: In the piezoelectric sensor including the stacked piezoelectric elements and the acoustic matching layer 14, the acoustic matching layer includes the first surface 14a1 relatively close to the piezoelectric elements and the second surface 14a2 located on the side opposite to the first surface in the thickness direction of the acoustic matching layer and relatively far from the piezoelectric elements, and the acoustic impedances of the acoustic matching layer gradually approach the acoustic impedances of the piezoelectric elements from the second surface to the first surface along the thickness direction.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a piezoelectric sensor having a laminated piezoelectric element and an acoustic matching layer, and a method for manufacturing the piezoelectric sensor. [Background technology]

[0002] Generally, piezoelectric elements are used to detect vibrations. Piezoelectric elements can convert the force applied to them into voltage through the piezoelectric effect, so they are used to convert vibrations transmitted to them through a medium into a voltage value (i.e., a numerical value).

[0003] Elastic waves that propagate through media such as air and water are called sound waves, and the ease with which sound waves propagate varies depending on the medium. The ease with which sound waves propagate through a medium is numerically expressed by acoustic impedance.

[0004] In addition, in a situation where two media with different acoustic impedances are placed in contact with each other, if the acoustic impedance of the first medium is Z1 and the acoustic impedance of the second medium is Z2, a part of the sound wave propagating from the first medium to the second medium is reflected at the interface between the first and second media. In this case, the reflectance R is expressed as R = (Z2 - Z1) / (Z2 + Z1).

[0005] The smaller the difference in acoustic impedance (Z2-Z1) between the first and second media, the smaller the reflectance R (i.e., sound waves are more likely to transmit through the interface). Conversely, the larger the difference in acoustic impedance (Z2-Z1), the larger the reflectance R (i.e., sound waves are more likely to be reflected at the interface).

[0006] Generally, a piezoelectric element has a piezoelectric body such as PZT (lead zirconate titanate) and first and second electrodes arranged to sandwich the piezoelectric body. When a sound wave propagating through a medium is received by the piezoelectric element, the difference in acoustic impedance between the medium and the piezoelectric element is relatively large, so the sound wave is likely to be reflected when transmitted from the medium to the piezoelectric element.

[0007] Therefore, in order to reduce the reflectance, an acoustic matching layer having an acoustic impedance lower than that of the piezoelectric element and higher than that of the medium is provided in contact with the piezoelectric element. The piezoelectric element receives sound waves from the medium through the acoustic matching layer, making it easier for the piezoelectric element to receive sound waves than when no acoustic matching layer is used.

[0008] Incidentally, it is known to use a composite (referred to as a piezoelectric composite, piezocomposite, etc.) in which a piezoelectric body and a resin are integrated in order to reduce the difference between the acoustic impedance of a piezoelectric element and the acoustic impedance of a medium (see, for example, Patent Document 1).

[0009] When manufacturing the piezoelectric composite described in Patent Document 1, for example, first, a plurality of cutting grooves are formed in a grid pattern in a plate-shaped piezoelectric body (i.e., piezoelectric ceramic) made of ceramics so as not to completely cut the piezoelectric body, thereby forming a plurality of rectangular pillar portions, and then each cutting groove is filled with resin and solidified.

[0010] After the piezoelectric body and resin are integrated, the base portion of the piezoelectric body that supports each rectangular column portion is removed by polishing, thereby producing a piezoelectric composite (so-called 1-3 composite) in which the regularly arranged rectangular column portions of the piezoelectric body are fixed to each other with resin and integrated.

[0011] By using such a piezoelectric composite, the difference in acoustic impedance between the piezoelectric element and the medium can be reduced, improving the sound wave transmittance T (T=1-R), but the volume of the piezoelectric body is reduced, which reduces the efficiency of converting applied force into electricity. In other words, there is a trade-off between the volume of the piezoelectric body and the efficiency with which the piezoelectric element converts force into electricity. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-309297 Summary of the Invention [Problem to be solved by the invention]

[0013] The present invention has been made in consideration of the above problems, and aims to improve the efficiency of converting force into electricity without reducing the volume of a piezoelectric body such as a piezoelectric ceramic to form a piezoelectric composite. [Means for solving the problem]

[0014] According to one aspect of the present invention, there is provided a piezoelectric sensor having a laminated piezoelectric element and an acoustic matching layer, wherein the acoustic matching layer includes a first surface that is relatively close to the piezoelectric element and a second surface that is located on the opposite side of the thickness direction of the acoustic matching layer from the first surface and is relatively far from the piezoelectric element, and the acoustic impedance of the acoustic matching layer gradually approaches the acoustic impedance of the piezoelectric element as it progresses from the second surface to the first surface along the thickness direction.

[0015] Preferably, the acoustic matching layer has a first region made of a first material, and a second region made of a second material having an acoustic impedance different from that of the first material.

[0016] Preferably, the main body portion constituting the acoustic matching layer has the first surface and the second surface located on the opposite side of the first surface in the thickness direction, and corresponds to the first region, the main body portion includes a groove having a depth that does not reach from the second surface to the first surface, the second material is embedded in the groove, the groove in which the second material is embedded corresponds to the second region, and the acoustic impedance of the second material is lower than the acoustic impedance of the first material.

[0017] Preferably, the groove includes a first groove having a predetermined depth that does not reach from the second surface to the first surface, and a second groove that does not reach from the second surface to the first surface and is deeper than the first groove.

[0018] Preferably, the first material constituting the first region is single crystal silicon or alumina sintered body, and the second material constituting the second region is epoxy resin.

[0019] Preferably, the piezoelectric sensor further comprises an additional acoustic matching layer made of a third material having an acoustic impedance lower than that of the acoustic matching layer and fixed to the second surface of the acoustic matching layer.

[0020] According to another aspect of the present invention, there is provided a method for manufacturing a piezoelectric sensor having a laminated piezoelectric element and an acoustic matching layer, wherein a main body portion constituting the acoustic matching layer has a first surface and a second surface located on the opposite side of the first surface in the thickness direction of the main body portion and is made of a first material, and the method for manufacturing a piezoelectric sensor includes a groove forming step of forming a groove on the second surface of the main body portion, an embedding step of embedding a second material having an acoustic impedance lower than the acoustic impedance of the first material into the groove of the main body portion, and a fixing step of fixing the piezoelectric element to the first surface of the main body portion.

[0021] Preferably, the groove forming step includes a first groove forming step of forming a first groove having a predetermined depth that does not reach from the second surface to the first surface, and a second groove forming step of forming a second groove that does not reach from the second surface to the first surface and is deeper than the first groove.

[0022] Preferably, the first material is single crystal silicon or alumina sintered body, and in the embedding step, a liquid epoxy resin is embedded in the groove as the second material, and then the epoxy resin is hardened.

[0023] Preferably, the method for manufacturing the piezoelectric sensor further includes an additional fixing step of fixing an additional acoustic matching layer made of a third material having an acoustic impedance lower than the acoustic impedance of the acoustic matching layer to the second surface of the main body portion. [Effects of the Invention]

[0024] A piezoelectric sensor according to one aspect of the present invention includes a laminated piezoelectric element and an acoustic matching layer. The acoustic impedance of the acoustic matching layer gradually approaches that of the piezoelectric element along the thickness direction of the acoustic matching layer, moving from the second surface, which is relatively far from the piezoelectric element, to the first surface, which is relatively close to the piezoelectric element. This improves the transmittance of sound waves to the piezoelectric element without reducing the volume of the piezoelectric body to form a piezoelectric composite, thereby improving the efficiency of converting force into electricity in the piezoelectric element.

[0025] In another aspect of the method for manufacturing a piezoelectric sensor of the present invention, a groove is formed on the second surface of the main body portion of the acoustic matching layer (groove forming process), a second material having an acoustic impedance lower than the acoustic impedance of the first material constituting the main body portion is embedded in this groove (embedding process), and a piezoelectric element is fixed to the first surface of the main body portion (fixing process).

[0026] Therefore, the acoustic impedance of the acoustic matching layer gradually approaches the acoustic impedance of the piezoelectric element along the thickness direction of the acoustic matching layer, moving from the second surface, which is relatively far from the piezoelectric element, to the first surface, which is relatively close to the piezoelectric element. This makes it possible to improve the transmittance of sound waves to the piezoelectric element without reducing the volume of the piezoelectric body to form a piezoelectric composite, thereby improving the efficiency of converting force into electricity in the piezoelectric element. [Brief explanation of the drawings]

[0027] [Figure 1] FIG. 1 is a partial cross-sectional side view showing an overview of an ultrasonic flow meter. [Figure 2] FIG. 2(A) is a perspective view of the piezoelectric sensor, and FIG. 2(B) is a side view of the piezoelectric sensor. [Figure 3] FIG. 2 is a cross-sectional view of a first acoustic matching layer. [Figure 4] FIG. 1 is a flow diagram of a method for manufacturing a piezoelectric sensor. [Figure 5] FIG. 5(A) is a partial cross-sectional side view showing the groove forming step, and FIG. 5(B) is a plan view of the first acoustic matching layer after the groove forming step. [Figure 6]FIG. 10 is a partial cross-sectional side view showing the embedding step. [Figure 7] FIG. 7(A) is a side view showing the fixing step, and FIG. 7(B) is a side view showing an additional fixing step. DETAILED DESCRIPTION OF THE INVENTION

[0028] An embodiment of the present invention will be described with reference to the accompanying drawings. Fig. 1 is a partial cross-sectional side view showing an overview of a transit time type ultrasonic flow meter 2 equipped with piezoelectric sensors 10 (10a, 10b). The ultrasonic flow meter 2 has a pipe portion 4.

[0029] The pipe section 4 has a linear inlet section 4a, a measuring section 4b, and an outlet section 4c. The inlet section 4a is arranged at one end of the measuring section 4b in the longitudinal direction 4b. L The outlet 4c is connected to the measurement section 4b at the other end of the measurement section 4b so as to be approximately parallel to the inlet 4a.

[0030] Longitudinal direction 4b of measuring section 4b L A recess 4d is provided at one end of the measuring section 4b, and the piezoelectric sensor 10a is fixed in the recess 4d using adhesive, filler, sealant, etc. L At the other end of the piezoelectric sensor 10, a recess 4e is provided, and a piezoelectric sensor 10b is fixed in the recess 4e in the same manner.

[0031] The piezoelectric sensors 10a and 10b are not exposed inside the pipe 4, but are covered with an appropriate material (not shown). Therefore, the piezoelectric sensors 10a and 10b of this embodiment are not in direct contact with the fluid 6 flowing inside the pipe 4, but may be in direct contact with it.

[0032] A flow of fluid 6, such as water, is formed in the pipe 4, traveling from the inlet 4a to the outlet 4c. The ultrasonic waves traveling from the piezoelectric sensor 10a to the piezoelectric sensor 10b are forward of the flow of the fluid 6, whereas the ultrasonic waves traveling from the piezoelectric sensor 10b to the piezoelectric sensor 10a are reversed.

[0033] Therefore, the time T required for the ultrasonic wave generated by the piezoelectric sensor 10a to be received by the piezoelectric sensor 10b is A is the time T required for the ultrasonic wave generated by the piezoelectric sensor 10b to be received by the piezoelectric sensor 10a. B In the ultrasonic flow meter 2, the time required for ultrasonic wave propagation T A and T B The flow velocity, flow rate, etc. of the fluid 6 are calculated using the above.

[0034] Fig. 2(A) is a perspective view of the piezoelectric sensor 10 in this embodiment, and Fig. 2(B) is a side view of the piezoelectric sensor 10. Since the piezoelectric sensors 10a and 10b have substantially the same structure, hereinafter, each may be referred to as the piezoelectric sensor 10.

[0035] 2(A) and 2(B), the piezoelectric sensor 10 has a piezoelectric element 12, a first acoustic matching layer (acoustic matching layer) 14, and a second acoustic matching layer (additional acoustic matching layer) 16, which are stacked one on top of the other. The piezoelectric element 12, the first acoustic matching layer 14, and the second acoustic matching layer 16 are each disk-shaped and arranged substantially concentrically.

[0036] In the piezoelectric sensor 10, the piezoelectric element 12 has the smallest diameter, and the second acoustic matching layer 16 has the largest diameter. The diameter of the first acoustic matching layer 14 is larger than the diameter of the piezoelectric element 12 and smaller than the diameter of the second acoustic matching layer 16.

[0037] The piezoelectric element 12 has a disk-shaped piezoelectric body, i.e., a piezoelectric material layer 12a, made of a ferroelectric ceramic such as PZT, barium titanate, or lead titanate. However, the piezoelectric material layer 12a is not limited to ferroelectric ceramics and may be made of other materials, and the shape of the piezoelectric material layer 12a is not limited to a disk shape and may be polygonal.

[0038] In this embodiment, the polarization direction of the piezoelectric material layer 12a is the thickness direction 12a of the piezoelectric material layer 12a. T The thickness direction 12a is approximately parallel to the T A first electrode 12b made of metal is provided on a first surface 12a1 of the piezoelectric material layer 12a located at one end of the piezoelectric material layer 12a. T Similarly, a second electrode 12c made of metal is provided on a second surface 12a2 of the piezoelectric material layer 12a located at the other end of the piezoelectric material layer 12a.

[0039] The first electrode 12b is circular in plan view and covers substantially the entire first surface 12a1 of the piezoelectric material layer 12a. A first lead wire (not shown) is connected to the first electrode 12b. Similarly, the second electrode 12c is circular in plan view and covers substantially the entire second surface 12a2 of the piezoelectric material layer 12a. A second lead wire (not shown) is connected to the second electrode 12c.

[0040] In this embodiment, the first electrode 12b and the second electrode 12c are mainly made of silver (Ag) and have a thickness of about 1.0 μm to 3.0 μm. However, the material and thickness of the first electrode 12b and the second electrode 12c are not particularly limited as long as they have an appropriate volume resistance value that allows them to function as electrodes of the piezoelectric element 12.

[0041] The first acoustic matching layer 14 includes a first surface 14a1 that is relatively close to the piezoelectric element 12 and a second surface 14a2 that is relatively far from the piezoelectric element 12. The second surface 14a2 is a surface extending in the thickness direction 14a of the first acoustic matching layer 14. T , it is located on the opposite side to the first surface 14a1.

[0042] The first electrode 12b of the piezoelectric element 12 is fixed to the first surface 14a1 of the first acoustic matching layer 14 via, for example, an adhesive layer (not shown). However, the method of fixing the piezoelectric element 12 to the first acoustic matching layer 14 is not limited to adhesive, and they may also be fixed by welding, fusion, or the like.

[0043] The first acoustic matching layer 14 of this embodiment has a main body portion (i.e., a first region) 14a made of single crystal silicon (i.e., a first material) (see FIG. 3). That is, the main body portion 14a is a disk-shaped single crystal silicon substrate. However, the material making up the main body portion 14a is not limited to single crystal silicon.

[0044] The material constituting the main body 14a only needs to have an acoustic impedance lower than that of the piezoelectric material layer 12a, and an alumina sintered body may be used instead of single crystal silicon. Here, the first acoustic matching layer 14 will be further described with reference to FIG. 3.

[0045] Fig. 3 is a cross-sectional view of the first acoustic matching layer 14. As shown in Fig. 3, the main body portion 14a has a first surface 14a1 and a second surface 14a2. The main body portion 14a further has a plurality of grooves 14b that extend from the second surface 14a2 to a depth that does not reach the first surface 14a1. The plurality of grooves 14b include first grooves 14b1 and second grooves 14b2.

[0046] The grooves 14b are formed in a lattice pattern when the second surface 14a2 is viewed from above (see FIG. 5B). However, as shown in FIG. 5B, the grooves 14b have a repeating unit of a second groove 14b2, a first first groove 14b1, and a second first groove 14b1 in a first direction 14d1 along the second surface 14a2.

[0047] Similarly, the grooves 14b also have a repeating unit of a second groove 14b2, a first first groove 14b1, and a second first groove 14b1 in a second direction 14d2 perpendicular to the first direction 14d1 on the second surface 14a2.

[0048] 3, the first groove 14b1 is a relatively shallow groove having a predetermined depth (e.g., 100 μm from the second surface 14a2) that does not reach from the second surface 14a2 to the first surface 14a1. In contrast, the second groove 14b2 is a relatively deep groove that does not reach from the second surface 14a2 to the first surface 14a1 and is deeper than the first groove 14b1 (e.g., 200 μm from the second surface 14a2).

[0049] A thermosetting resin (i.e., a second material) such as epoxy resin is filled in each groove 14b (i.e., the first groove 14b1 and the second groove 14b2). As will be described in detail later, for example, a groove filling region (i.e., a second region) 14c is formed by filling each groove 14b with liquid epoxy resin and then curing the liquid epoxy resin.

[0050] The acoustic impedance of the groove filling region 14c is different from the acoustic impedance of the main body portion 14a. In this embodiment, the acoustic impedance of the groove filling region 14c, which is made of cured epoxy resin, is lower than the acoustic impedance of the main body portion 14a, which is made of single crystal silicon.

[0051] The first acoustic matching layer 14 can be considered to have a layered structure of a first layer 14e1, a second layer 14e2, and a third layer 14e3, as shown in Fig. 3. Although dashed lines are shown at the boundaries between the layers in Fig. 3, no lines indicating the boundaries actually exist in the actual first acoustic matching layer 14. The boundaries between the layers are shown in the thickness direction 14a. T is approximately perpendicular to the

[0052] First layer 14e1 has a region of single crystal silicon that is part of main body 14a, a region of epoxy resin filled in first groove 14b1, and a region of epoxy resin filled in second groove 14b2. The volume ratio of single crystal silicon that is part of main body 14a to the entire first layer 14e1 is approximately 25%.

[0053] The second layer 14e2 has a region of single crystal silicon that is part of the main body 14a and a region of epoxy resin filled in the second groove 14b2. The volume ratio of the single crystal silicon that is part of the main body 14a to the entire second layer 14e2 is approximately 69%. In contrast, the third layer 14e3 has only the region of single crystal silicon that is part of the main body 14a.

[0054] In this embodiment, the first acoustic matching layer 14 has a thickness direction 14a. T The volume ratio of single crystal silicon having a relatively high acoustic impedance increases stepwise from the second surface 14a2 to the first surface 14a1 along the thickness direction 14a. T The acoustic impedance gradually increases along the line from the second surface 14a2 to the first surface 14a1.

[0055] That is, in the thickness direction 14a T The acoustic impedance of the first acoustic matching layer 14 can be made gradually closer to the acoustic impedance of the piezoelectric element 12 as it moves from the second surface 14a2 to the first surface 14a1 along the line.

[0056] Therefore, the transmittance of sound waves to the piezoelectric element 12 can be improved without reducing the volume of the piezoelectric material layer 12a to make it a piezoelectric composite, thereby improving the efficiency of converting force into electricity in the piezoelectric element 12.

[0057] 2(B), the first surface 16a1 of the second acoustic matching layer 16 is fixed to the second surface 14a2 of the first acoustic matching layer 14 via an adhesive layer (not shown). However, the first acoustic matching layer 14 and the second acoustic matching layer 16 may be fixed to each other by means of other means such as welding or fusion bonding, without being limited to adhesive.

[0058] The second acoustic matching layer 16 includes a first surface 16a1 that is relatively close to the first acoustic matching layer 14 and a second surface 16a2 that is relatively far from the first acoustic matching layer 14. The second surface 16a2 is a surface extending in a thickness direction 16a of the second acoustic matching layer 16. T, it is located on the opposite side to the first surface 16a1.

[0059] The second acoustic matching layer 16 is made of a third material having an acoustic impedance lower than that of the first acoustic matching layer 14. The second acoustic matching layer 16 of this embodiment is made of polyvinyl chloride (i.e., PVC), and the density of the second acoustic matching layer 16 is 1 / 2 mm in the radial direction and the thickness direction 16a. T is approximately uniform in

[0060] 1, the piezoelectric element 12 is located at the deepest position of the recesses 4d, 4e among the layers constituting the piezoelectric sensor 10, and the second acoustic matching layer 16 is located at the shallowest position of the recesses 4d, 4e among the layers constituting the piezoelectric sensor 10. In other words, the second acoustic matching layer 16 is located closest to the fluid 6 among the layers constituting the piezoelectric sensor 10.

[0061] By using the second acoustic matching layer 16 in the piezoelectric sensor 10, it is possible to further reduce the reflectance R of the sound wave at the interface between the piezoelectric sensor 10 and a gas such as air or a liquid such as water (i.e., the medium that is the fluid 6) compared to when the second acoustic matching layer 16 is not used in the piezoelectric sensor 10. In other words, it is possible to increase the transmittance T of the sound wave at the interface.

[0062] In the piezoelectric sensor 10, by setting the piezoelectric element 12 to the smallest diameter, the second acoustic matching layer 16 to the largest diameter, and the diameter of the first acoustic matching layer 14 to be greater than the diameter of the piezoelectric element 12 and less than the diameter of the second acoustic matching layer 16, the acoustic matching effect can be reliably obtained even if the radial center positions of the piezoelectric element 12, the first acoustic matching layer 14, and the second acoustic matching layer 16 do not completely coincide in a planar view.

[0063] Next, a method for manufacturing the piezoelectric sensor 10 will be described with reference to Fig. 4 to Fig. 7(B). Fig. 4 is a flow diagram of the method for manufacturing the piezoelectric sensor 10. In this embodiment, a groove forming step S10 (including a first groove forming step S12 and a second groove forming step S14), an embedding step S20, a fixing step S30, and an additional fixing step S40 are performed in this order.

[0064] However, there is no particular limitation on the order of the fixing step S30 for fixing the piezoelectric element 12 to the first surface 14a1 of the first acoustic matching layer 14. The fixing step S30 may be performed before the embedding step S20 or before the groove forming step S10.

[0065] 5(A) is a partial cross-sectional side view showing the groove forming step S10. A cutting device is used in the groove forming step S10. The cutting device has a disk-shaped chuck table (not shown) and a cutting unit 20 arranged above the chuck table.

[0066] The chuck table has a substantially flat holding surface and applies negative pressure to suction and hold the main body 14a so that the second surface 14a2 of the main body 14a is exposed upward. Note that, in order to reduce damage to the main body 14a during cutting, a resin protective tape (not shown) may be attached to the first surface 14a1.

[0067] Furthermore, although the main body portion 14a of this embodiment is made of single crystal silicon as described above, the main body portion 14a may alternatively be made of a plate-shaped alumina sintered body such as a disk.

[0068] The cutting unit 20 has a cylindrical spindle 22. A portion of the spindle 22 is accommodated in a spindle housing (not shown) in a manner that allows it to rotate by a hydrostatic air bearing. The spindle 22 can be rotated at high speed by a motor provided in the spindle housing.

[0069] A mount 24 is fixed to the tip of the spindle 22 using a bolt (not shown). A hub-shaped cutting blade 26 is fixed to the mount 24 using a fixing nut 28.

[0070] The cutting blade 26 includes an annular base 26a made of metal and an annular cutting edge 26b fixed to one surface of the base 26a. The cutting edge 26b of the cutting blade 26 has a thickness of, for example, 25 μm.

[0071] The cutting blade 26 is not limited to the hub type, but may be a hubless type (that is, a washer type) that does not have a base 26a and is formed only by the cutting edge 26b.

[0072] In the groove forming step S10, first, the spindle 22 is rotated at high speed, and the lower end of the spindle 22 is positioned at a depth corresponding to the second groove 14b2. Then, the chuck table is processed and fed in a predetermined direction (a direction parallel to the X-axis direction in FIG. 5(A)), thereby moving the lower end of the cutting blade 26 from one end to the other end of the main body 14a in the predetermined direction.

[0073] In this embodiment, one second groove 14b2 is formed in the main body portion 14a by multiple processing feeds, so after the first processing feed, the cutting unit 20 is raised so as not to come into contact with the main body portion 14a. Then, the chuck table is moved in the direction opposite to the processing feed direction to return to its original position.

[0074] Next, the lower end of the spindle 22 is repositioned at a depth corresponding to the second groove 14b2, and the cutting unit 20 is moved a small amount along the indexing feed direction (the Y-axis direction in Figure 5(A)) perpendicular to the processing feed direction so that the cutting groove formed just before and the cutting blade 26 partially overlap in the processing feed direction (i.e., indexing feed is performed).

[0075] In this state, the chuck table is again subjected to processing feed. By repeating such processing feed and minute indexing feed multiple times, one second groove 14b2 having a width of, for example, 200 μm (i.e., the length in the Y-axis direction in FIG. 5(A)) is formed in the main body portion 14a (second groove forming step S14).

[0076] Then, the cutting unit 20 is indexed by a predetermined indexing feed amount (for example, 200 μm) along the indexing feed direction. After that, two first grooves 14b1 are formed in sequence.

[0077] First, the lower end of the spindle 22 is positioned at a depth corresponding to the first groove 14b1, and then the chuck table is fed for processing. At this time, similar to the second groove forming step S14, the first first groove 14b1 having a width of 200 μm is formed in the main body portion 14a by performing the processing feed and the minute indexing feed multiple times (first first groove forming step S12).

[0078] Next, the cutting unit 20 is indexed by a predetermined index feed amount (e.g., 200 μm), and similarly, processing feed and minute index feed are performed multiple times to form a second first groove 14b1 having a width of 200 μm in the main body portion 14a (second first groove forming process S12).

[0079] In this way, by repeating the second groove forming step S14, the first first groove forming step S12, and the second first groove forming step S12 in the first direction 14d1 of the second surface 14a2, multiple second grooves 14b2 and multiple first grooves 14b1 are formed on the second surface 14a2.

[0080] Next, the chuck table is rotated 90 degrees around a predetermined rotation axis parallel to the Z-axis direction. Then, similarly, the second groove forming step S14, the first first groove forming step S12, and the second first groove forming step S12 are repeated in the second direction 14d2 to form a plurality of second grooves 14b2 and a plurality of first grooves 14b1 on the second surface 14a2.

[0081] 5(B) is a plan view of the first acoustic matching layer 14 after the groove forming step S10. As described above, the first grooves 14b1 have a predetermined depth that does not reach from the second surface 14a2 to the first surface 14a1, and the second grooves 14b2 do not reach from the second surface 14a2 to the first surface 14a1 and are deeper than the first grooves 14b1.

[0082] In the example shown in FIG. 5(B), the first grooves 14b in the first direction 14d1 and the second direction 14d2 are designated as second grooves 14b2, but they may be designated as the first first groove 14b1 or the second first groove 14b1.

[0083] Alternatively, the first groove 14b in the first direction 14d1 may be the first or second first groove 14b1, and the first groove 14b in the second direction 14d2 may be the second groove 14b2. Alternatively, the first groove 14b in the first direction 14d1 may be the second groove 14b2, and the first groove 14b in the second direction 14d2 may be the first or second first groove 14b1.

[0084] After the groove forming step S10, a thermosetting resin (i.e., a second material) such as epoxy resin is filled into each groove 14b (i.e., the first groove 14b1 and the second groove 14b2) (filling step S20). In the filling step S20, for example, a two-component liquid constant volume discharge device (a so-called dispenser) is used.

[0085] The liquid constant amount dispensing device has a first tank (not shown) containing a base agent for epoxy resin, a second tank (not shown) containing a hardener for epoxy resin, a pump (not shown) for discharging the base agent and hardener at a predetermined mixing ratio, a nozzle 30 (see Figure 6) for discharging the mixed base agent and hardener, and a controller (not shown) for controlling the amount and timing of dispensing.

[0086] The nozzle 30 is configured to be movable along a predetermined direction (the Y-axis direction in FIG. 6). A chuck table (not shown) that suction-holds the first acoustic matching layer 14 is provided below the nozzle 30. The chuck table is movable along the X-axis direction.

[0087] 6 is a partial cross-sectional side view showing the embedding step S20. In the embedding step S20, first, the first acoustic matching layer 14 is suction-held on the holding surface of a chuck table so that the second surface 14a2 is exposed upward.

[0088] Next, the lower end of the nozzle 30 is positioned directly above one end of the groove 14b, and the liquid epoxy resin is discharged from the nozzle 30 while the chuck table is moved along the X-axis direction.

[0089] The controller appropriately adjusts the volume of the liquid epoxy resin discharged from the nozzle 30 and the moving speed of the chuck table according to the depth and length of the grooves 14b. The liquid epoxy resin is filled into each groove 14b and then cured, thereby forming a groove filling region (i.e., second region) 14c (see FIG. 3).

[0090] Since the first acoustic matching layer 14 has the groove-filled region 14c, the acoustic impedance of the first acoustic matching layer 14 is T , and gradually approaches the acoustic impedance of the piezoelectric element 12 as it moves from the second surface 14a2 to the first surface 14a1.

[0091] In other words, the first acoustic matching layer 14 has an inherent property resulting from the material that constitutes it and its structure, such that the acoustic impedance gradually increases as it moves from the second surface 14a2 to the first surface 14a1, approaching the acoustic impedance of the piezoelectric element 12.

[0092] In this way, by devising the structure and material of the first acoustic matching layer 14, it is possible to improve the transmittance of sound waves to the piezoelectric element 12 without reducing the volume of the piezoelectric material layer 12a to make it a piezoelectric composite, thereby improving the efficiency of converting force into electricity in the piezoelectric element 12.

[0093] 7A is a side view showing the fixing step S30. In this embodiment, after the embedding step S20, the fixing step S30 is performed to fix the piezoelectric element 12 to the first surface 14a1 of the main body portion 14a using, for example, an adhesive. The fixing step S30 may be performed before the embedding step S20 or before the groove forming step S10.

[0094] 7(B) is a side view showing the additional fixing step S40. The additional fixing step S40 may be performed after the embedding step S20, or may be performed before the fixing step S30. In the additional fixing step S40, the second acoustic matching layer 16 made of polyvinyl chloride is fixed to the first surface 14a1 of the main body portion 14a using an adhesive.

[0095] (Example) Table 1 below shows an estimate of the transmittance of acoustic waves from the second surface 16a2 of the second acoustic matching layer 16 in contact with the medium to the piezoelectric material layer 12a in a piezoelectric sensor 10 (see FIGS. 2(A) and 2(B)) including the first acoustic matching layer 14 having the layered structure shown in Fig. 3. The transmittance and total transmittance are calculated based on the acoustic impedance of each layer.

[0096] The total number of first grooves 14b1 and second grooves 14b2 in the first direction 14d1 was about 40, and the total number of first grooves 14b1 and second grooves 14b2 in the second direction 14d2 was also about 40.

[0097] The depth of the first grooves 14b1 from the second surface 14a2 was 100 μm, and the depth of the second grooves 14b2 from the second surface 14a2 was 200 μm. The interval between adjacent grooves 14b in the first direction 14d1 was 200 μm, and the interval between adjacent grooves 14b in the second direction 14d2 was also 200 μm.

[0098] Note that the influence on transmittance of the adhesive that secures the piezoelectric element 12 and the first acoustic matching layer 14, and the adhesive that secures the first acoustic matching layer 14 and the second acoustic matching layer 16, is not taken into consideration, and the second electrode 12c that constitutes the piezoelectric element 12 is also not taken into consideration. The transmittance and total transmittance percentages in Table 1 are rounded down to the nearest whole number. The same applies to Table 2, which will be described later.

[0099] [Table 1]

[0100] (Comparative Example) Table 2 below shows an estimate of the transmittance of sound waves from the second surface 16a2 of the second acoustic matching layer 16 to the piezoelectric material layer 12a when the first acoustic matching layer 14 in the above-mentioned embodiment does not have the groove filling region 14c and is a single-plate single-crystal silicon substrate.

[0101] [Table 2]

[0102] The underlined total transmittances shown in the lower right corner of Tables 1 and 2 correspond to the transmittance of sound waves from the second surface 16a2 of the second acoustic matching layer 16, which is in contact with the medium, to the piezoelectric material layer 12a. As is clear from a comparison of Tables 1 and 2, by providing the groove filling region 14c in the first acoustic matching layer 14, the transmission efficiency of sound waves to the piezoelectric element 12 improves from approximately 25% to approximately 30%.

[0103] (Modification) In the above-described embodiment, a disk-shaped single-crystal silicon substrate was used as the main body portion 14a of the first acoustic matching layer 14. However, the main body portion 14a may also be made of a thermosetting resin hardened into a disk shape. In this case, in the groove forming step S10, a plurality of grooves 14b are provided in the main body portion 14a in a lattice pattern, as in the above-described embodiment.

[0104] In the subsequent embedding step S20, a thin plate made of single crystal silicon or sintered alumina is inserted to form the groove filling region 14c with single crystal silicon or sintered alumina. The fixing step S30 and the additional fixing step S40 are the same as those in the above-described embodiment.

[0105] In this modification, the acoustic impedance of the groove-filled region 14c is also higher than the acoustic impedance of the main body portion 14a. That is, the acoustic impedances of the main body portion 14a and the groove-filled region 14c are different from each other. The acoustic impedance of the first acoustic matching layer 14 gradually approaches the acoustic impedance of the piezoelectric element 12 from the second surface 14a2 to the first surface 14a1.

[0106] Therefore, the thickness direction 14a of the first acoustic matching layer 14 T The acoustic impedance of the first acoustic matching layer 14 can be adjusted so that it gradually approaches the acoustic impedance of the piezoelectric element 12 as it moves from the second surface 14a2 to the first surface 14a1.

[0107] In addition, the structures, methods, etc. according to the above-described embodiments can be appropriately modified and implemented as long as they do not depart from the scope of the object of the present invention. The piezoelectric sensors 10a and 10b can also be mounted on the ultrasonic flowmeter 2 that uses a method other than the propagation time difference method.

[0108] In the above-described embodiment, the first groove 14b1 and the second groove 14b2 are provided in a lattice pattern. However, as long as the functions of the first layer 14e1 to the third layer 14e3 described above can be realized, the first groove 14b1 and the second groove 14b2 may be provided in a circular and substantially concentric shape, or may have other shapes and arrangements.

Explanation of Reference Numerals

[0109] 2: Ultrasonic flowmeter 4: Pipe portion, 4a: Inlet portion, 4b: Measurement portion, 4b L : Longitudinal direction 4c: Outlet portion, 4d, 4e: Recesses 6: Fluid 10, 10a, 10b: Piezoelectric sensors 12: Piezoelectric element 12a: Piezoelectric material layer, 12a1: First surface, 12a2: Second surface, 12a T : Thickness direction 12b: First electrode, 12c: Second electrode 14: First acoustic matching layer (acoustic matching layer) 14a: Body portion (first region), 14a1: First surface, 14a2: Second surface, 14a T : Thickness direction 14b: Groove, 14b1: First groove, 14b2: Second groove, 14c: Groove filling region (second region) 14d1: First direction, 14d2: Second direction 14e1: First layer, 14e2: Second layer, 14e3: Third layer 16: Second acoustic matching layer (additional acoustic matching layer) 16a1: First surface, 16a2: Second surface, 16a T : Thickness direction 20: Cutting unit, 22: Spindle, 24: Mount 26: Cutting blade, 26a: Base, 26b: Cutting edge, 28: Fixing nut 30: Nozzle S10: Groove formation process, S12: First groove formation process, S14: Second groove formation process S20: Embedding process, S30: Fixation process, S40: Additional fixation process

Claims

1. A piezoelectric sensor having a laminated piezoelectric element and an acoustic matching layer, the acoustic matching layer includes a first surface that is relatively close to the piezoelectric element, and a second surface that is located on the opposite side to the first surface in a thickness direction of the acoustic matching layer and is relatively far from the piezoelectric element, The piezoelectric sensor is characterized in that the acoustic impedance of the acoustic matching layer gradually approaches the acoustic impedance of the piezoelectric element as it moves from the second surface to the first surface along the thickness direction.

2. The acoustic matching layer is a first region made of a first material; a second region made of a second material having an acoustic impedance different from that of the first material; 2. The piezoelectric sensor according to claim 1, further comprising:

3. a main body portion constituting the acoustic matching layer has the first surface and the second surface located on the opposite side to the first surface in the thickness direction, and corresponds to the first region; the main body portion includes a groove having a depth that does not reach from the second surface to the first surface; The groove is filled with the second material, and the groove filled with the second material corresponds to the second region; 3. The piezoelectric sensor of claim 2, wherein the second material has a lower acoustic impedance than the first material.

4. The groove is a first groove having a predetermined depth extending from the second surface but not reaching the first surface; 4. The piezoelectric sensor according to claim 3, further comprising: a second groove extending from the second surface but not reaching the first surface and deeper than the first groove.

5. the first material constituting the first region is single crystal silicon or alumina sintered body, 5. The piezoelectric sensor according to claim 3, wherein the second material constituting the second region is an epoxy resin.

6. 5. The piezoelectric sensor according to claim 1, further comprising an additional acoustic matching layer made of a third material having an acoustic impedance lower than the acoustic impedance of the acoustic matching layer and fixed to the second surface of the acoustic matching layer.

7. A method for manufacturing a piezoelectric sensor having a laminated piezoelectric element and an acoustic matching layer, comprising: a main body constituting the acoustic matching layer has a first surface and a second surface located on the opposite side to the first surface in a thickness direction of the main body, and is made of a first material; The manufacturing method of the piezoelectric sensor is as follows: a groove forming step of forming a groove on the second surface of the main body portion; an embedding step of embedding a second material having an acoustic impedance lower than that of the first material in the groove of the body portion; a fixing step of fixing the piezoelectric element to the first surface of the main body portion; A method for manufacturing a piezoelectric sensor, comprising:

8. The groove forming step includes: a first groove forming step of forming a first groove having a predetermined depth that does not reach the first surface from the second surface; 8. The method for manufacturing a piezoelectric sensor according to claim 7, further comprising: forming a second groove from the second surface so as not to reach the first surface and so as to be deeper than the first groove.

9. the first material is single crystal silicon or alumina sintered body; 9. The method for manufacturing a piezoelectric sensor according to claim 7, wherein in the embedding step, a liquid epoxy resin is embedded in the groove as the second material, and then the epoxy resin is hardened.

10. 9. The method for manufacturing a piezoelectric sensor according to claim 7, further comprising an additional fixing step of fixing an additional acoustic matching layer made of a third material having an acoustic impedance lower than that of the acoustic matching layer to the second surface of the main body portion.

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