JP7105116B2 - ultrasonic sensor - Google Patents

Description

The present invention relates to ultrasonic sensors.

As an ultrasonic sensor of this type, there is one disclosed in Patent Document 1. The ultrasonic sensor of Patent Literature 1 includes a case with a groove on the bottom and a piezoelectric element attached to the bottom of the case. The ultrasonic sensor of Patent Literature 1 can be driven at a plurality of resonance frequencies due to grooves provided in the bottom of the case.

Japanese Patent No. 5111977

In general, in order to detect an obstacle at a short distance with an ultrasonic sensor, it is necessary to stop the reverberation in a short period of time. That is, an ultrasonic sensor for detecting short-range obstacles must have a Q value as low as possible. In addition, there is a demand for an ultrasonic sensor having a wide usable band due to the ease of adjustment of the drive circuit of the ultrasonic sensor.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide an ultrasonic sensor that has a low Q value and broadband transmission characteristics.

The present invention, as a first ultrasonic sensor,
An ultrasonic sensor comprising a case, a support structure, and a transducer having a piezoelectric element,
the case has a bottom and a side, and
The side portion extends upward in the vertical direction from the bottom portion,
the bottom and the sides define a housing;
the support structure is fixed on the bottom within the housing, and
the vibrator is supported by the support structure and positioned within the housing,
In a horizontal plane orthogonal to the vertical direction, the vibrator is larger than the support structure,
The Young's modulus of the support structure is less than the Young's modulus of the transducer to provide the ultrasonic sensor.

Further, the present invention provides a first ultrasonic sensor as a second ultrasonic sensor,
The Young's modulus of the support structure is less than the Young's modulus of the case to provide the ultrasonic sensor.

The present invention also provides a third ultrasonic sensor, which is the first or second ultrasonic sensor,
The vibrator further comprises a substrate,
The substrate has elasticity,
The piezoelectric element is provided on the substrate,
The ultrasonic sensor is provided in which the substrate and the piezoelectric element have the same size in the horizontal plane.

Further, according to the present invention, as a fourth ultrasonic sensor, any one of the first to third ultrasonic sensors,
The natural resonant frequency of the transducer provides an ultrasonic sensor that is higher than the natural resonant frequency of the case.

In the ultrasonic sensor of the present invention, the Young's modulus of the support structure is smaller than the Young's modulus of the transducer. As a result, the ultrasonic sensor of the present invention has a low Q value and broadband transmission characteristics.

1 is a perspective view showing an ultrasonic sensor according to an embodiment of the invention; FIG. 2 is a partially cutaway perspective view showing the ultrasonic sensor of FIG. 1; FIG. In the figure, a part of the support structure is shown enlarged. 2 is a graph showing frequency response analysis results by the finite element method (FEM) of the ultrasonic sensor of FIG. 1; 2 is a graph showing the relationship between the Young's modulus of the support structure and the resonance frequency in the ultrasonic sensor of FIG. 1; 2 is a graph showing the results of actual measurement of the frequency characteristics of the ultrasonic sensor of FIG. 1;

As shown in FIGS. 1 and 2, an ultrasonic sensor 100 according to an embodiment of the present invention includes a case 200, a support structure 300, and a vibrator 400 having a piezoelectric element 410. FIG.

As shown in FIGS. 1 and 2, the case 200 of this embodiment has a bottom portion 210, side portions 220, and a housing portion 250. As shown in FIGS. Case 200 of the present embodiment has a bottomed cylindrical shape with an open upper end. In this embodiment, the vertical direction is the Z direction. Also, the upward direction is the +Z direction and the downward direction is the -Z direction. Note that the present invention is not limited to this, and the case 200 may have a shape other than a cylindrical shape with a bottom. The Young's modulus of the case 200 of this embodiment is approximately 70 GPa.

As understood from FIGS. 1 and 2, the bottom portion 210 of the present embodiment has a flat plate shape perpendicular to the vertical direction. More specifically, the bottom portion 210 has a disc shape perpendicular to the vertical direction. The bottom portion 210 defines the lower end of the case 200 in the vertical direction. The bottom portion 210 has an upper surface 212 facing upward in the vertical direction. The bottom portion 210 does not have a vertically penetrating groove.

As understood from FIGS. 1 and 2, the side portion 220 of this embodiment has a tubular shape extending in the vertical direction. More specifically, side portion 220 has a cylindrical shape extending in the vertical direction. The side portion 220 is positioned above the bottom portion 210 in the vertical direction. That is, the side portion 220 extends upward in the vertical direction from the bottom portion 210 . More specifically, the side portion 220 extends upward from the outer end of the bottom portion 210 in the orthogonal direction perpendicular to the vertical direction.

As shown in FIG. 2, the accommodating portion 250 of the present embodiment is a space extending vertically. Bottom 210 and side 220 define a housing 250 . More specifically, the bottom portion 210 defines the lower end of the housing portion 250, and the side portion 220 defines the outer end of the housing portion 250 in the orthogonal direction. The upper end of the housing portion 250 is open. However, in order to shorten the reverberation time, the upper end of the accommodating portion 250 may be closed by inserting a urethane-based or silicone-based resin damping material, a foamed sound absorbing material, or the like. Further, in order to give directivity to the ultrasonic sensor 100, the thickness of the side portion 220 in the orthogonal direction may be partially changed so that the cross-sectional shape of the accommodating portion 250 orthogonal to the vertical direction may be elliptical.

Referring to FIG. 2, support structure 300 of the present embodiment is made of resin. More specifically, the support structure 300 is preferably made of engineering plastics or super engineering plastics. The support structure 300 has a columnar shape extending in the vertical direction. More specifically, the support structure 300 has a columnar shape extending vertically. Note that the present invention is not limited to this, and the support structure 300 may have a shape other than a cylindrical shape.

As shown in FIG. 2 , the support structure 300 of this embodiment is fixed on the bottom portion 210 within the housing portion 250 . More specifically, the support structure 300 is fixed to the upper surface 212 of the bottom portion 210 of the case 200 within the housing portion 250 . That is, the support structure 300 extends upward from the upper surface 212 of the bottom portion 210 of the case 200 within the housing portion 250 .

As shown in FIG. 2, the support structure 300 of this embodiment has a beam 310 and two adhesive layers 320 . The beam 310 is sandwiched between two adhesive layers 320 in the vertical direction. The adhesive layers 320 are positioned at both ends of the beam 310 in the vertical direction. That is, the lower end of the adhesive layer 320 located on the upper side is connected to the upper end of the beam 310 , and the upper end of the adhesive layer 320 located on the lower side is connected to the lower end of the beam 310 . The bottom 210 of the case 200 and the beams 310 of the support structure 300 are connected via a lower adhesive layer 320 . That is, the upper surface 212 of the bottom part 210 of the case 200 is connected to the lower end of the adhesive layer 320 under the support structure 300 . Also, the vibrator 400 and the beam 310 of the support structure 300 are connected via the adhesive layer 320 on the upper side. That is, the lower end of the vibrator 400 is connected to the upper end of the adhesive layer 320 on the upper side of the support structure 300 .

Referring to FIG. 2, bottom 210 of case 200 and beams 310 of support structure 300 are adhered with a silicone adhesive. Also, the vibrator 400 and the beam 310 of the support structure 300 are adhered with a silicone-based adhesive. That is, the adhesive layer 320 of the support structure 300 of the present embodiment is solidified silicone adhesive. Note that the present invention is not limited to this, and the adhesive layer 320 may be made of, for example, a urethane-based resin other than a silicone-based resin.

The Young's modulus of the support structure 300 of this embodiment is smaller than the Young's modulus of the case 200 . Specifically, the Young's modulus of the support structure 300 of this embodiment is 10 to 1000 MPa.

As shown in FIG. 2, the vibrator 400 of this embodiment is supported by the support structure 300 and positioned within the housing portion 250 . The vibrator 400 is larger than the support structure 300 in a horizontal plane perpendicular to the vertical direction. Support structure 300 supports the center of transducer 400 . Note that the present invention is not limited to this, and the support structure 300 may support portions other than the center of the vibrator 400 . For example, the support structure 300 may support both ends of the vibrator 400 in the orthogonal direction, or may support the vibrator 400 at multiple locations. The Young's modulus of the transducer 400 is greater than the Young's modulus of the support structure 300 . That is, the Young's modulus of the support structure 300 is smaller than the Young's modulus of the vibrator 400 . The natural resonance frequency of vibrator 400 is higher than the natural resonance frequency of case 200 . More specifically, the resonance frequency of the primary bending mode of the vibrator 400 is higher than the resonance frequency of the secondary bending mode of the case 200 .

As can be understood from FIG. 2, the vibrator 400 of this embodiment has a flat plate shape perpendicular to the vertical direction. More specifically, the vibrator 400 has a disc shape perpendicular to the vertical direction. Note that the present invention is not limited to this, and the vibrator 400 may have a shape other than the disk shape, such as a rectangular shape.

As shown in FIG. 2, the vibrator 400 of this embodiment further includes a substrate 420 . That is, vibrator 400 of the present embodiment includes piezoelectric element 410 and substrate 420 . The vibrator 400 of this embodiment is a unimorph type vibrator. However, the present invention is not limited to this, and the vibrator 400 of the present invention may be a bimorph type vibrator or the like.

As shown in FIG. 2, the piezoelectric element 410 of this embodiment is a piezoelectric ceramic that expands and contracts when a voltage is applied in the vertical direction. Note that lead wires and terminals for applying voltage to the piezoelectric element 410 are not shown in FIG. The piezoelectric element 410 has a flat plate shape perpendicular to the vertical direction. More specifically, the piezoelectric element 410 has a disc shape perpendicular to the vertical direction. The Young's modulus of the piezoelectric element 410 of this embodiment is approximately 65 GPa.

Referring to FIG. 2, substrate 420 of the present embodiment is made of metal and has elasticity. The present invention is not limited to this, and the substrate 420 may be made of a resin other than metal, such as fiber-reinforced plastic. Piezoelectric element 410 is provided on substrate 420 . More specifically, the piezoelectric element 410 is attached to the top surface of the substrate 420 . The substrate 420 has a flat plate shape perpendicular to the vertical direction. More specifically, the substrate 420 has a disc shape perpendicular to the vertical direction. In a horizontal plane perpendicular to the vertical direction, the substrate 420 and the piezoelectric element 410 have the same size. The present invention is not limited to this, and the substrate 420 and the piezoelectric element 410 may have different sizes. The Young's modulus of the substrate 420 of this embodiment is approximately 100 GPa. Considering that the Young's modulus of the case 200 is about 70 GPa, the Young's modulus of the piezoelectric element 410 is about 65 GPa, and the Young's modulus of the support structure 300 is 10-1000 MPa, as described above, the Young's modulus of the support structure 300 is The ratio is smaller than both case 200 and vibrator 400 .

Referring to FIG. 2, a portion of substrate 420 of vibrator 400 and beam 310 of support structure 300 are adhered with a silicone adhesive. That is, a portion of the substrate 420 of the vibrator 400 and the beam 310 of the support structure 300 are connected via the adhesive layer 320 on the upper side. More specifically, the lower end of a portion of the substrate 420 of the vibrator 400 is connected to the upper end of the adhesive layer 320 on the upper side of the support structure 300 . The beam 310 of the support structure 300 supports the center of the substrate 420 of the vibrator 400 via the adhesive layer 320 on the upper side.

A frequency response analysis by the finite element method (FEM) was performed for the ultrasonic sensor 100 having the support structure 300 with different Young's modulus. The analysis results are shown in FIG.

As can be seen from FIG. 3, there are resonance modes at 8 kHz and 55 kHz in the ultrasonic sensor 100 having the support structure 300 with a Young's modulus of 4 GPa. Here, the resonance mode at 8 kHz was estimated to be the bending primary mode of case 200 and the resonance mode at 55 kHz was estimated to be the bending secondary mode of case 200 .

Further, as understood from FIG. 3, the ultrasonic sensor 100 having the support structure 300 with a Young's modulus of 500 MPa has resonance modes at 8 kHz and 54 kHz. Here, the resonance mode at 8 kHz was estimated to be the bending primary mode of case 200 and the resonance mode at 54 kHz was estimated to be the bending secondary mode of case 200 .

Furthermore, as understood from FIG. 3, the ultrasonic sensor 100 having the support structure 300 with a Young's modulus of 100 MPa has resonance modes at 7 kHz, 50 kHz and 66 kHz. Here, it was estimated that the 7 kHz resonance mode is the first bending mode of the case 200, the 50 kHz resonance mode is the second bending mode of the case 200, and the 66 kHz resonance mode is the first bending mode of the vibrator 400, respectively.

In addition, as can be seen from FIG. 3, there are resonance modes at 4 kHz, 37 kHz and 61 kHz in the ultrasonic sensor 100 having the support structure 300 with a Young's modulus of 10 MPa. Here, it was estimated that the 4 kHz resonance mode is the first bending mode of the case 200, the 37 kHz resonance mode is the second bending mode of the case 200, and the 61 kHz resonance mode is the first bending mode of the vibrator 400, respectively.

From these frequency response analysis results, by adjusting the Young's modulus of the support structure 300, the resonance frequency of the primary bending mode of the vibrator 400 and the resonance frequency of the secondary bending mode of the case 200 can be kept within a narrow frequency range. It is understood that

FIG. 4 shows an example of the relationship between the Young's modulus of the support structure 300 and the resonance frequency in the primary bending mode of the vibrator 400 and the secondary bending mode of the case 200 .

As understood from FIG. 4, when the Young's modulus of the support structure 300 is 10 to 1000 MPa, the difference (Δf) between the natural resonance frequency of the vibrator 400 and the case 200 should be set to 29 kHz or less. can be done. That is, from FIG. 4, when the Young's modulus of the support structure 300 is 10 to 1000 MPa, the difference (Δf) between the resonant frequency of the primary bending mode of the vibrator 400 and the resonant frequency of the secondary bending mode of the case 200 is 29 kHz. It is understood that the following can be set.

Further, as understood from FIG. 4, when the Young's modulus of the support structure 300 is 10 to 500 MPa, the difference (Δf) between the natural resonance frequency of the vibrator 400 and the natural resonance frequency of the case 200 is set to 26 kHz or less. can do. That is, from FIG. 4, when the Young's modulus of the support structure 300 is 10 to 500 MPa, the difference (Δf) between the resonant frequency of the primary bending mode of the vibrator 400 and the resonant frequency of the secondary bending mode of the case 200 is 26 kHz. It is understood that the following can be set.

Furthermore, as understood from FIG. 4, when the Young's modulus of the support structure 300 is 100 MPa, the difference (Δf) between the natural resonance frequency of the vibrator 400 and the case 200 should be set to 17 kHz or less. can be done. That is, from FIG. 4, when the Young's modulus of the support structure 300 is 100 MPa, the difference (Δf) between the resonance frequency of the primary bending mode of the vibrator 400 and the resonance frequency of the secondary bending mode of the case 200 should be 17 kHz or less. It is understood that it can be set.

From these analyses, by configuring the support structure 300 so that the Young's modulus of the support structure 300 is smaller than the Young's modulus of the vibrator 400 and the Young's modulus of the case 200 , the natural resonance frequency of the vibrator 400 and the natural resonance frequency of the case 200 It was found that the difference (Δf) from the resonance frequency can be adjusted. Further, by adjusting the Young's modulus of the support structure 300 to bring the resonance frequency of the primary bending mode of the vibrator 400 closer to the resonance frequency of the secondary bending mode of the case 200, the resonance frequency of the primary bending mode of the vibrator 400 and the resonance frequency of the bending secondary mode of the case 200 can be moderated, and a broad frequency characteristic can be obtained even in the sound pressure level converted from the amplitude.

Based on the above analysis, the frequency characteristics of the ultrasonic sensor 100 with the Young's modulus of the support structure 300 adjusted to around 100 MPa were actually measured. The measurement results are shown in FIG. Note that the measurement results are converted into sound pressure values when the microphone distance is 40 cm and the input voltage is 150 Vpp.

As shown in FIG. 5, the ultrasonic sensor 100 in which the Young's modulus of the support structure 300 is adjusted to around 100 MPa changes from the resonance frequency (45 kHz) of the second bending mode of the case 200 to the resonance frequency of the first bending mode of the transducer 400. It can be seen that it has a broad frequency characteristic up to a frequency (55 kHz), that is, it has a wideband transmission characteristic.

Q values at resonance frequencies of 45 kHz and 55 kHz were calculated from the results of the actual measurement of the frequency characteristics. Further, as a comparative example, an ultrasonic sensor in which the transducer 400 is directly attached to the upper surface 212 of the bottom portion 210 of the case 200 without the support structure 300 was actually measured for the frequency characteristics, and the Q value at the resonance frequency was calculated. . Accordingly, in the ultrasonic sensor 100 of the present embodiment in which the Young's modulus of the support structure 300 is adjusted to around 100 MPa, the Q value is 17 at the resonance frequency of 45 kHz and the Q value is 8 at the resonance frequency of 55 kHz. We understood each other. Further, it was found that the ultrasonic sensor of the comparative example had only a single resonance mode, and the Q value in this resonance mode was 58. From these, it is understood that the ultrasonic sensor 100 of the present embodiment has a lower Q value and wider band transmission characteristics than the comparative example.

Although the present invention has been specifically described above with reference to the embodiments, the present invention is not limited to these, and various modifications and changes are possible.

The support structure 300 of the present embodiment is made of resin, but the present invention is not limited to this, and may be made of other materials as long as the entire support structure 300 has a desired Young's modulus.

REFERENCE SIGNS LIST 100 ultrasonic sensor 200 case 210 bottom 212 upper surface 220 side 250 housing 300 support structure 310 beam 320 adhesive layer 400 vibrator 410 piezoelectric element 420 substrate

Claims (4)

An ultrasonic sensor comprising a case, a support structure, and a transducer having a piezoelectric element,
the case has a bottom and a side, and
The side portion extends upward in the vertical direction from the bottom portion,
the bottom and the sides define a housing;
the support structure is fixed on the bottom within the housing, and
the vibrator is supported by the support structure and positioned within the housing,
In a horizontal plane orthogonal to the vertical direction, the vibrator is larger than the support structure,
A Young's modulus of the support structure is less than a Young's modulus of the transducer. nine,
the support structure comprises a beam and two adhesive layers;
The beam is sandwiched between the two adhesive layers in the vertical direction.
ultrasonic sensor. The ultrasonic sensor according to claim 1,
The ultrasonic sensor, wherein the Young's modulus of the support structure is less than the Young's modulus of the case. The ultrasonic sensor according to claim 1 or claim 2,
The vibrator further comprises a substrate,
The substrate has elasticity,
The piezoelectric element is provided on the substrate,
The ultrasonic sensor according to claim 1, wherein the substrate and the piezoelectric element have the same size in the horizontal plane. The ultrasonic sensor according to any one of claims 1 to 3,
The ultrasonic sensor, wherein the natural resonance frequency of the transducer is higher than the natural resonance frequency of the case.

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