JP2021111964A - Ultrasonic sensor - Google Patents

Abstract

To provide an ultrasonic sensor capable of suppressing the scattering of ultrasonic waves at a lid.SOLUTION: An ultrasonic sensor includes a case 50 in which an accommodating recess 51 is formed, a sensor unit 10 that is housed in the accommodating recess 51 of the case 50, and includes a plurality of ultrasonic elements 25 that transmit the exploration waves and receive the reflected waves reflected by an obstacle as the received waves, and a lid 80 that is arranged in the case 50 so as to close the accommodating recess 51 and constitutes the casing 40. The lid 80 is made of a perforated member in which a gap is formed in a structure so as to communicate a space inside the accommodating recess 51 and a space outside, and the scattering cross section defined by the average length of the structure and the average width of the gap is 1×10-5 m2 or less.SELECTED DRAWING: Figure 1

Description

The present invention relates to an ultrasonic sensor having an ultrasonic element housed in a casing having a lid.

Conventionally, an ultrasonic sensor has been proposed in which a sensor portion in which an ultrasonic element capable of transmitting and receiving ultrasonic waves is formed is housed in a casing having a lid portion (see, for example, Patent Document 1). The lid portion is composed of a perforated member in which a plurality of voids for communicating the space inside the casing and the space outside the casing are formed.

Such ultrasonic sensors are used, for example, to construct an object detection device mounted on a vehicle and detecting an object located around the vehicle. Specifically, an ultrasonic sensor transmits a search wave as an ultrasonic wave to the outside through a gap formed in a lid portion, and receives the reflected wave reflected by an obstacle as a received wave. Then, the ultrasonic sensor detects an obstacle based on the received wave received by the ultrasonic element.

Japanese Unexamined Patent Publication No. 2012-21720

By the way, in the above-mentioned ultrasonic sensor, the present inventors are studying the following ultrasonic sensor. That is, when a plurality of ultrasonic elements are formed in the sensor unit, the received wave received by each ultrasonic element has a phase difference depending on the direction of the received wave (that is, the direction of the obstacle). Therefore, the present inventors form an ultrasonic sensor by forming a plurality of ultrasonic elements in the sensor unit, and when the ultrasonic sensor is mounted on a vehicle, the phase difference of the received wave received by each ultrasonic element. We are also considering detecting the direction of obstacles based on.

However, when the ultrasonic wave passes through the gap of the lid portion, the phase information of the ultrasonic wave may be disturbed due to the occurrence of scattering. Therefore, when such an ultrasonic sensor is mounted on a vehicle, the detection accuracy may decrease due to the disorder of the phase information.

In view of the above points, it is an object of the present invention to provide an ultrasonic sensor capable of suppressing scattering of ultrasonic waves at the lid portion.

A first aspect of claim 1 for achieving the above object is an ultrasonic sensor in which a sensor unit (10) in which a plurality of ultrasonic elements (25) are formed in a casing (40) is housed, and is a housing recess (51). ) Is formed, and a plurality of ultrasonic elements are formed, which are housed in the housing recess of the case and transmit the exploration wave, and receive the reflected wave reflected by the obstacle as the received wave. A sensor portion and a lid portion (80) arranged in a case so as to close the accommodating recess to form a casing are provided, and the lid portion is provided in a structure (81) with a space inside the accommodating recess and an external space. It is composed of a porous member in which a void (82) is formed so as to communicate with each other, and the scattering cross section defined by the average length of the structure and the average width of the void is 1 × ^10-5 [m ² ] or less. There is.

According to this, since the scattering cross section is set to 1 × 10 ^-5 [m ² ] or less, it is possible to suppress the occurrence of ultrasonic scattering (that is, phase shift) at the lid portion. Therefore, for example, when the direction of an obstacle is detected based on the phase difference of the received wave received by each ultrasonic element, it is possible to suppress a decrease in detection accuracy.

The reference reference numerals in parentheses attached to each component or the like indicate an example of the correspondence between the component or the like and the specific component or the like described in the embodiment described later.

It is sectional drawing of the ultrasonic sensor in 1st Embodiment. It is an enlarged view of the vicinity of the sensor part shown in FIG. It is a figure which shows the relationship of the number of ultrasonic elements, a directing angle, and a sound pressure. It is an enlarged view of the lid part shown in FIG. It is a figure which shows the relationship between the scattering cross section, the average length and the average width. It is a figure which shows the relationship between a sound pressure loss, an average length and a porosity. It is sectional drawing of the ultrasonic sensor in 2nd Embodiment. It is sectional drawing of the ultrasonic sensor in 3rd Embodiment. It is sectional drawing of the ultrasonic sensor in 4th Embodiment. It is sectional drawing of the vicinity of the sensor part in 5th Embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In each of the following embodiments, parts that are the same or equal to each other will be described with the same reference numerals.

(First Embodiment)
The first embodiment will be described with reference to the drawings. It should be noted that the ultrasonic sensor of the present embodiment is suitable for being applied to, for example, an object detection device mounted around a bumper of a vehicle and detecting an object located around the vehicle. An example of being attached to the above will be described.

As shown in FIG. 1, the ultrasonic sensor of the present embodiment has a configuration in which a sensor unit 10 is housed in a casing 40. First, the configuration of the sensor unit 10 will be described.

The sensor unit 10 is configured to transmit an ultrasonic wave for exploration along a directional axis. The exploration wave is transmitted from the sensor unit 10 with a predetermined spread (that is, a directivity angle). The directional axis is a virtual straight line extending along the exploration wave transmitted from the sensor unit 10 and serves as a reference for the directional angle. In other words, the directional axis is the axis that passes through the center of the exploration wave. Further, the sensor unit 10 is configured to receive the received wave including the reflected wave reflected by the obstacle existing in the surroundings and output the detection signal based on the reception result. In the present embodiment, the sensor unit 10 includes a transducer unit 20, a support member 30, and the like, as shown in FIG.

In the present embodiment, the transducer unit 20 is a MEMS type configured by using a sensor substrate 24 composed of an SOI substrate in which a support substrate 21, an embedded insulating film 22, and a semiconductor layer 23 are laminated in this order. It is configured to have the ultrasonic element 25 of the above. SOI is an abbreviation for Silicon on Insulator, and MEMS is an abbreviation for Micro Electro Mechanical Systems. In the following, the surface of the semiconductor layer 23 opposite to the embedded insulating film 22 is referred to as one surface 24a of the sensor substrate 24, and the surface of the support substrate 21 opposite to the embedded insulating film 22 is the other side of the sensor substrate 24. This will be described as surface 24b.

A plurality of diaphragm portions 27 are formed on the sensor substrate 24 by forming recesses 26 from the other surface 24b side. In the present embodiment, the sensor substrate 24 is formed with recesses 26 so that the diaphragm portions 27 are arranged two-dimensionally. In the present embodiment, the recess 26 is formed so as to penetrate the embedded insulating film 22 and reach the semiconductor layer 23, and the diaphragm portion 27 is composed of the semiconductor layer 23. However, the recess 26 may be formed so as to leave the embedded insulating film 22 remaining, and the diaphragm portion 27 may be formed by the embedded insulating film 22 and the semiconductor layer 23.

A piezoelectric element 28 is formed on each diaphragm portion 27 by laminating the back surface electrode 28a, the piezoelectric film 28b, and the front surface electrode 28c in this order. In this embodiment, a plurality of ultrasonic elements 25 are formed on the sensor substrate 24 in this way. That is, the ultrasonic element 25 of this embodiment is configured as a PMUT. PMUT is an abbreviation for Piezoelectric Micro-machined Ultrasonic Transducers.

In the present embodiment, the back electrode 28a of each piezoelectric element 28 is integrated so that a common ground potential is applied. The piezoelectric film 28b is a piezoelectric ceramic having no lead such as aluminum nitride (ScAlN) or aluminum nitride (AlN), or a piezoelectric ceramic containing lead such as lead zirconate titanate (PZT) but having high versatility. It is configured. The piezoelectric film 28b is formed on the diaphragm portion 27 so as to have a planar shape equivalent to that of the diaphragm portion 27.

Since the diaphragm portion 27 is two-dimensionally formed in each ultrasonic element 25 as described above, each ultrasonic element 25 is in a two-dimensionally arranged state. Then, each ultrasonic element 25 is connected to a control unit or the like (not shown) via a bonding wire 35, a connection terminal 36, or the like, which will be described later. When an ultrasonic sensor is mounted on a vehicle, the control unit is composed of, for example, an in-vehicle ECU (abbreviation of Electronic Control Unit).

Further, in each ultrasonic element 25, assuming that the distance between the centers of the adjacent ultrasonic elements 25 is the distance d, each distance d is the wavelength of the exploration wave so that the orientation is not binarized with respect to a certain phase difference. It is preferably less than half. That is, assuming that the wavelength of the exploration wave is λ, the interval d is preferably d <λ / 2. In other words, the distance between the centers of the adjacent ultrasonic elements 25 is the distance between the centers of the adjacent diaphragm portions 27.

A pad portion 29 that is electrically connected to the back surface electrode 28a and the front surface electrode 28c is formed on one surface 24a of the sensor substrate 24.

In such an ultrasonic element 25, when a driving voltage which is an AC voltage is applied to the piezoelectric element 28, the diaphragm portion 27 ultrasonically vibrates and transmits a search wave. For example, in the present embodiment, the phase of each piezoelectric element 28 is such that the directional axis of the exploration wave coincides with the normal direction with respect to one surface 24a of the sensor substrate 24 (hereinafter, also simply referred to as the normal direction of the sensor substrate 24). The same drive voltage is applied. In this case, as shown in FIG. 3, it is confirmed that the directivity angle can be easily changed by changing the number of the ultrasonic elements 25. Specifically, the sensor unit 10 can narrow the directional angle as the number of ultrasonic elements 25 increases, and can widen the directional angle as the number of ultrasonic elements 25 decreases. Further, the sensor unit 10 can increase the sound pressure as the number of the ultrasonic elements 25 increases, and can detect even a distant obstacle.

Therefore, it is preferable that the number of ultrasonic elements 25 formed in the sensor unit 10 is appropriately changed based on the height when mounted on the vehicle, the detection range, and the like. In this case, the directional angle of the exploration wave may be adjusted by forming a large number of ultrasonic elements 25 and controlling the number of the ultrasonic elements 25 to be energized. It is preferable that the sensor unit 10 transmits an exploration wave of about 40 to 80 kHz so that the influence of air attenuation is unlikely to be large and does not cause discomfort to the human body.

Then, when the ultrasonic element 25 receives the received wave, the diaphragm portion 27 vibrates, and an electric charge is generated in the piezoelectric element 28 based on the vibration. Therefore, when the ultrasonic element 25 receives the received wave, it outputs a detection signal corresponding to the received wave. In this case, when the plurality of ultrasonic elements 25 receive the received wave from the direction inclined with respect to the normal direction, the received wave received by each ultrasonic element 25 has a phase difference according to the inclination. ing. Therefore, the control unit (not shown) connected to the sensor unit 10 detects the direction of the received wave (that is, the direction in which the obstacle exists) from the phase difference.

The support member 30 is a member that fixes and supports the transducer unit 20. In the present embodiment, the support member 30 is composed of a multilayer board, a printed circuit board, or the like. And although not particularly shown, various circuit components for signal processing may be mounted.

Further, the support member 30 of the present embodiment has a shape having a concave portion 31 and a convex portion 32 formed so as to surround the concave portion 31. The sensor substrate 24 is mounted on the recess 31 via a joining member 33 so that the other surface 24b of the sensor substrate 24 faces the bottom surface of the recess 31. A silicone-based adhesive or the like is used for the joining member 33.

A pad portion 34 is formed on the convex portion 32 of the support member 30. The pad portion 34 is electrically connected to the pad portion 29 formed on the sensor substrate 24 via a bonding wire 35.

Further, the support member 30 is provided with a metal connection terminal 36 so as to penetrate the convex portion 32 and the pad portion 34. Then, the connection terminal 36 is mechanically connected to the support member 30 and electrically connected to the pad portion 34 by forming a joining member 37 such as solder. As a result, each ultrasonic element 25 is connected to the connection terminal 36 via the pad portions 29 and 34. Further, on the pad portion 34, a solder resist 38 is arranged between a portion connected to the bonding wire 35 and a portion connected to the bonding member 37.

The above is the configuration of the sensor unit 10 in this embodiment.

As shown in FIG. 1, the casing 40 has a case 50 in which the accommodating recess 51 is formed, and a lid portion 80 arranged so as to close the accommodating recess 51.

In the present embodiment, the case 50 has a mounting member 60 and a side wall member 70 made of metal or the like. As shown in FIG. 2, the mounting member 60 is formed with a plurality of through holes 61 corresponding to the number of connection terminals 36 provided in the support member 30. The support member 30 is arranged on the mounting member 60 via the joining member 62 so that the connection terminal 36 penetrates the through hole 61. The through hole 61 is filled with an insulating member (not shown) for insulating the connection terminal 36 and the mounting member 60. Further, a silicone-based adhesive or the like is used for the joining member 62, and an epoxy resin, a sealing glass or the like is used as the insulating member.

As shown in FIG. 1, the side wall member 70 is a tubular member having one end and the other end, and a step portion 71 is formed on the inner peripheral surface on the other end side. One end of the side wall member 70 is fixed to the mounting member 60 so as to accommodate the sensor portion 10 inside. That is, the accommodating recess 51 of the case 50 is configured such that one end of the tubular side wall member 70 is fixed to the mounting member 60. Although not particularly limited, the side wall member 70 is fixed to the mounting member 60, for example, by caulking or fixing with an adhesive or the like.

As shown in FIG. 4, the lid portion 80 is composed of a perforated member in which a gap 82 is formed in the structure 81. Such a lid 80 includes, for example, Gore-Tex (registered trademark) made of resin, punch metal having a plurality of through holes formed in a metal plate, a metal non-woven fabric made by knitting fine metal wires, and the like. Used. Note that FIG. 4 is a schematic view of the case where the lid portion 80 is made of resin, and the length of the structure 81 is shown as the length a and the width of the gap 82 is shown as the width b. However, the length a of the structure 81 here is the length of the portion of the structure 81 sandwiched between the gaps 82, and the width b of the gaps is the distance between the adjacent structures 81. be.

Then, as shown in FIG. 1, the lid portion 80 has an outer edge end portion joined to the stepped portion 71 formed on the side wall member 70 via a joining member such as an adhesive (not shown). The gap 82 of the lid portion 80 is formed so that the space inside the accommodating recess 51 in the case 50 and the external space outside the case 50 communicate with each other.

The above is the basic configuration of an ultrasonic sensor in this embodiment. Further, in the present embodiment, the lid portion 80 is further configured as follows.

First, when sound waves pass through a porous member, documents such as "Krodel et al, Acoustic properties of porous microlattice from effective medium to scattering dominated regimes, The journal of the Acoustical Society of America 144, 319, 2018" If the scattering cross section defined by using the width of the void and the length of the structure is 1.0 × ^10-5 m ² or less, it is possible to make it difficult for sound wave scattering (that is, phase shift) to occur. Is reported.

Therefore, in the present embodiment, assuming that the average value of the length a of the structure 81 is the average length A [m] and the average value of the width b of the void 82 is the average width B [m], the average length A And the average width B is adjusted so that the scattering cross section is 1.0 × ^10-5 m ^{2 or less.} The average length A and the average width B here include an error caused by a slight variation such as a manufacturing error, and allow a deviation of, for example, about ± 5%.

Specifically, the present inventors diligently examined the relationship between the scattering cross section, the average length A of the structure 81, and the average width B of the voids 82, and obtained the results shown in FIG. As shown in FIG. 5, it is confirmed that the scattering cross section increases as the average length A of the structure and the average width B of the voids increase. The scattering cross section is represented by the following _{mathematical formula 1 based on FIG. 5, assuming} that the scattering cross section is σ s, the predetermined first constant is γ, and the predetermined second constant is ε.

[Equation 1] σ _s = γ × log ₁₀ (A) + log ₁₀ (ε × B)
Therefore, in the present embodiment, the average length A and the average width B are defined so that _{γ × log 10} (A) + log ₁₀ (ε × B) is 1.0 × ^10-5 m ^{2 or less.} ..

Further, as the average width B of the gap 82 in the lid portion 80 approaches a value of (1/2) × n times (where n is a natural number) the wavelength of the exploration wave, ultrasonic waves are more likely to be scattered. Therefore, in the present embodiment, the average width B of the voids 82 is formed to be less than λ / 2. However, the average width B of the void 82 is preferably a value away from λ / 2, because ultrasonic waves are more likely to be scattered as the value approaches 1/2 the wavelength. Therefore, in the present embodiment, the average length A of the structure 81 and the average width B of the voids 82 are ^{set to values such that the scattering cross section is 1.0 × 10-5} m ² or less, and for example, the exploration wave. It is 1/10 or less of the wavelength.

Further, in an ultrasonic sensor having a lid portion 80, an energy loss occurs when an ultrasonic wave passes through the lid portion 80, so that a sound pressure loss may occur. Therefore, the present inventors have taken the ratio of the void 82 to the structure 81 as the porosity, and diligently examined the relationship between the sound pressure loss and the porosity, and obtained the result shown in FIG. At present, if the sound pressure loss is 10 dB or less, it is within the permissible range, and it is desired that the sound pressure loss be 10 dB or less.

As shown in FIG. 6, the sound pressure loss depends on the porosity and the mean width B of the voids. Specifically, the sound pressure loss increases as the mean width B decreases. This is because the smaller the average width B, the larger the surface area inside the lid 80, and the larger the energy loss generated when ultrasonic waves pass. Further, the sound pressure loss becomes larger as the porosity becomes smaller because it becomes more difficult for ultrasonic waves to pass through.

Then, when the average width B is 0.00005 to 0.0004 mm, it is confirmed that the sound pressure loss is 10 dB or less when the porosity is 80% or more. When the average width B is 0.005 to 0.15 mm, it is confirmed that the sound pressure loss is 10 dB or less when the porosity is 70% or more. When the average width B is 0.2 to 2 mm, it is confirmed that the sound pressure loss is 10 dB or less when the porosity is 30% or more. Therefore, in the lid portion 80 of the present embodiment, the average width B and the porosity are adjusted so that the sound pressure loss is 10 dB or less.

When the lid portion 80 has an average width B of 0.00005 to 0.0004 mm, the lid portion 80 is made of a resin member. In this case, the average width B of 0.00005 to 0.0004 mm is a value derived based on the processing limit in manufacturing, processing difficulty, and the like.

When the lid portion 80 has an average width B of 0.005 to 0.15 mm, the lid portion 80 is made of, for example, a metal non-woven fabric or the like. In this case, the average width B of 0.005 to 0.15 mm is a value derived based on the processing limit in manufacturing, processing difficulty, and the like.

When the lid portion 80 has an average width B of 0.2 to 2 mm, the lid portion 80 is made of, for example, punch metal. In this case, 0.2 mm, which is the lower limit of the average width B, is a value derived based on the processing limit in manufacturing, processing difficulty, and the like. The upper limit of the average width B, 2 mm, is a value derived based on a value at which ultrasonic waves are less likely to be scattered. That is, in the present embodiment, the wavelength of the exploration wave transmitted from the sensor unit 10 is 40 to 80 kHz, and when the average width B is 2 mm or more, it overlaps with the value of (1/2) × n times the wavelength of the exploration wave. Or, if it becomes too close to (1/2) × n times, ultrasonic scattering is likely to occur. Therefore, in the present embodiment, the average width B is set to 2 mm or less.

Assuming that the sound pressure loss is Lt, the porosity is X, the predetermined third constant is α, and the predetermined fourth constant is β, the relationship between the sound pressure loss and the porosity is as follows based on FIG. It is shown by Equation 2.

[Equation 2] Lt = α × (X) ^−β
Therefore, when the lid portion 80 has an average width B different from the average width B shown in FIG. 6, the porosity X is adjusted so that the sound pressure loss Lt is 10 dB or less based on the above formula 2. do it.

As described above, in the present embodiment, the average length A of the structure 81 and the average width B of the voids of the lid 80 are defined so that the scattering cross section is 1.0 × ^{10-5 or less.} ing. Specifically, the average length A and the average width B are defined so that γ × log ₁₀ (A) + log ₁₀ (ε × B) is 1.0 × ^10-5 m ^{2 or less.} Therefore, it is possible to suppress the occurrence of ultrasonic scattering at the lid portion 80. Therefore, when the direction of the obstacle is detected based on the phase difference of the received wave received by each ultrasonic element 25, it is possible to suppress the deterioration of the detection accuracy.

Further, the lid portion 80 is configured so that the average width B of the gap 82 is less than λ / 2. Therefore, it is possible to further suppress the scattering of ultrasonic waves.

The porosity of the lid 80 is defined based on the average width B so that the sound pressure loss is 10 dB or less. Therefore, the sound pressure loss can be sufficiently reduced, and the deterioration of the detection accuracy can be suppressed.

Further, in the sensor unit 10, the distance d between the adjacent ultrasonic elements 25 is set to less than λ / 2. Therefore, it is possible to suppress the binarization of the orientation with respect to a certain phase difference, and it is possible to suppress the decrease in the detection range.

Further, the sensor unit 10 is a MEMS type configured by using the sensor substrate 24. Therefore, mass production can be facilitated.

Then, the sensor unit 10 adjusts the number of the ultrasonic elements 25 or the number of the ultrasonic elements 25 to which the driving voltage is applied so as to have a predetermined directional angle. Therefore, the sensor unit 10 can achieve a desired pointing angle.

Further, when a lead-free piezoelectric ceramic such as scandium aluminum nitride or aluminum nitride is used as the piezoelectric film 28b of the sensor unit 10, the sensor unit 10 with reduced impact on the environment can be realized.

(Second Embodiment)
The second embodiment will be described. In this embodiment, the distance between the sensor unit 10 and the lid unit 80 is defined with respect to the first embodiment. Others are the same as those in the first embodiment, and thus the description thereof will be omitted here.

In the present embodiment, as shown in FIG. 7, when the distance between the sensor unit 10 and the lid portion 80 is the distance d1, the distance d1 is λ / 4. The distance d1 between the sensor unit 10 and the lid portion 80 is, in detail, the distance between the surface electrode 28c of the sensor portion 10 and the lid portion 80.

In the present embodiment described above, since the interval d1 is λ / 4, the lid 80 is less likely to vibrate due to the exploration wave, and the exploration wave is less likely to be reflected by the lid 80. Therefore, the detection accuracy can be improved.

(Third Embodiment)
The third embodiment will be described. This embodiment defines the shape of the sensor unit 10 and the height of the side wall member 70 with respect to the first embodiment. Others are the same as those in the first embodiment, and thus the description thereof will be omitted here.

In the present embodiment, as shown in FIG. 8, the distance between the center of the ultrasonic element 25 arranged on the outermost edge side of the sensor unit 10 and the side wall member 70 is defined as the distance s. That is, the shortest distance between the center of each ultrasonic element 25 and the side wall member 70 is defined as the distance s. The center of the ultrasonic element 25 is the center of the piezoelectric element 28 in the present embodiment. Further, in the side wall member 70, the distance between the surface electrode 28c of the ultrasonic element 25 and the other end is defined as the distance h. That is, the distance between the ultrasonic element 25 and the open end of the case 50 is defined as the distance h.

Further, the angle formed by the normal direction (that is, the directional axis) of the sensor substrate 24 in the sensor unit 10 and the spread range of the exploration wave transmitted from the sensor unit 10 is defined as the directional angle θ.

Then, in the present embodiment, the sensor unit 10 and the side wall member 70 are configured and arranged so as to satisfy tan (90-θ) ≧ h / s.

In the present embodiment described above, the sensor unit 10 and the side wall member 70 are configured and arranged so as to satisfy tan (90-θ) ≧ h / s. Therefore, the spread of the exploration wave transmitted from the sensor unit 10 is less likely to be obstructed by the side wall member 70, and it is possible to suppress a decrease in detection accuracy.

(Fourth Embodiment)
A fourth embodiment will be described. In this embodiment, the configuration of the lid portion 80 is changed from that of the first embodiment. Others are the same as those in the first embodiment, and thus the description thereof will be omitted here.

In the present embodiment, as shown in FIG. 9, the lid portion 80 has a configuration including a first lid portion 80a and a second lid portion 80b. The first lid portion 80a and the second lid portion 80b have the same configuration, and are configured to satisfy the above conditions, respectively.

The side wall member 70 is formed with a first step portion 71a and a second step portion 71b in order from the mounting member 60 side as the step portion 71.

The first lid portion 80a is arranged on the first step portion 71a via an adhesive or the like (not shown). The second lid portion 80b is arranged on the second step portion 71b via an adhesive (not shown), and is arranged apart from the first lid portion 80a. In this case, in the present embodiment, assuming that the distance between the first lid portion 80a and the second lid portion 80b is the interval d2, the interval d2 is less than λ / 2.

As described above, even if the lid portion 80 is configured to have the first lid portion 80a and the second lid portion 80b, the same effect as that of the first embodiment can be obtained. In the present embodiment, since the distance d2 between the first lid portion 80a and the second lid portion 80b is less than λ / 2, ultrasonic waves are generated between the first lid portion 80a and the second lid portion 80b. Scattering can be suppressed, and deterioration of detection accuracy can be suppressed.

(Fifth Embodiment)
A fifth embodiment will be described. This embodiment is a modification of the configuration of the sensor unit 10 with respect to the first embodiment. Others are the same as those in the first embodiment, and thus the description thereof will be omitted here.

In the present embodiment, as shown in FIG. 10, the ultrasonic element 25 is configured by two-dimensionally arranging a plurality of piezoelectric elements 28 on the recess 31 formed in the support member 30. .. Specifically, in the present embodiment, the back surface electrode 28a is directly formed on the recess 31 of the support member 30, and the sensor substrate 24 is not provided. The piezoelectric element 28 has a bulk shape in which the piezoelectric film 28b is sufficiently thicker than that of the first embodiment. In the present embodiment, the ultrasonic element 25 is configured by such a piezoelectric element 28, and the transducer unit 20 is configured by providing a plurality of the ultrasonic elements 25.

Then, in each ultrasonic element 25, the back surface electrode 28a and the front surface electrode 28c are electrically connected to the pad portion 34 formed on the support member 30 via the bonding wire 35.

In such a sensor unit 10, when a driving voltage which is an AC voltage is applied to each piezoelectric element 28, the piezoelectric element 28 ultrasonically vibrates and transmits an exploration wave. Further, when the ultrasonic element 25 receives the received wave, the piezoelectric element 28 vibrates and an electric charge is generated in the piezoelectric element 28. Therefore, when the ultrasonic element 25 receives the received wave, it outputs a detection signal corresponding to the received wave.

As described above, even if the ultrasonic element 25 is composed of the bulk piezoelectric element 28, the same effect as that of the first embodiment can be obtained.

(Other embodiments)
The present invention is not limited to the above-described embodiment, and can be appropriately modified within the scope of the claims.

For example, in each of the above embodiments, the ultrasonic element 25 may have an interval d between adjacent ultrasonic elements 25 of λ / 2 or more.

Further, in each of the above embodiments, the average width B of the voids 82 may be λ / 2 or more.

Further, in each of the above embodiments, an example in which the phases of the drive voltage (that is, the AC voltage) applied to each ultrasonic element 25 are made equal so that the directional axis of the exploration wave coincides with the normal direction of the sensor substrate 24. Was explained. However, the phase of the drive voltage applied to each ultrasonic element 25 may be controlled so that the directional axis of the exploration wave is in a predetermined direction inclined with respect to the normal direction of the sensor substrate 24. According to this, the detection sensitivity in a desired direction can be increased.

Then, each of the above embodiments may be combined as appropriate. For example, the second embodiment may be appropriately applied to each embodiment so that the interval d1 is λ / 4. When the second embodiment is combined with the fourth embodiment, the distance between the sensor unit 10 and the first lid portion 80a may be set to the interval d2. Further, the third embodiment may be appropriately applied to each embodiment so that the sensor unit 10 and the side wall member 70 are configured and arranged so as to satisfy tan (90-θ) ≧ h / s. Then, the fourth embodiment is appropriately applied to each embodiment so that the lid portion 80 has the first lid portion 80a and the second lid portion 80b, and the interval d2 is less than λ / 2. May be good. Further, the fifth embodiment may be appropriately applied to each of the above embodiments so that the ultrasonic element 25 in the sensor unit 10 is composed of the bulk piezoelectric element 28.

10 Sensor part 25 Ultrasonic element 40 Casing 50 Case 51 Containment recess 80 Lid part 81 Structure 82 Void

Claims (14)

An ultrasonic sensor in which a sensor unit (10) in which a plurality of ultrasonic elements (25) are formed in a casing (40) is housed.
A case (50) in which a storage recess (51) is formed, and a case (50).
The sensor unit formed with the plurality of ultrasonic elements housed in the housing recess of the case, transmit the exploration wave, and receive the reflected wave reflected by the obstacle as the reception wave.
A lid portion (80) arranged in the case so as to close the accommodating recess and constituting the casing is provided.
The lid is composed of a perforated member in which a gap (82) is formed in the structure (81) to communicate the space inside the housing recess with the space outside, and the average length of the structure and the average of the gaps are averaged. An ultrasonic sensor having a scattering cross section defined by the width of 1 × ^10-5 [m ² ] or less. Assuming that the average length of the structure of the lid is A [m], the average width of the voids is B [m], the predetermined first constant is γ, and the predetermined second constant is ε. The ultrasonic sensor according to claim 1, wherein the structure and the void _{satisfy γ × log 10} (A) + log ₁₀ (ε × B) <1 × ^10-5 [m ^2]. Claim 1 in which the average width of the voids and the porosity of the lid are adjusted so that the sound pressure loss is 10 [dB] or less, where the ratio of the voids to the structure is taken as the porosity. Or the ultrasonic sensor according to 2. The lid portion has an average width of the voids of 0.00005 to 0.0004 [mm].
The ultrasonic sensor according to claim 3, wherein the porosity is 80 [%] or more. The lid has an average width of 0.2 to 2 [mm].
The ultrasonic sensor according to claim 3, wherein the porosity is 30 [%] or more. The ultrasonic sensor according to any one of claims 1 to 5, wherein the lid portion has an average width of less than λ / 2, assuming that the wavelength of the exploration wave is λ. The ultrasonic sensor according to any one of claims 1 to 6, wherein the distance (d1) between the sensor unit and the lid portion is λ / 4, where λ is the wavelength of the exploration wave. The distance between the ultrasonic element and the open end of the accommodating recess in the case is h [mm], and the shortest distance between the case and the plurality of ultrasonic elements is s [mm]. The ultrasonic sensor according to any one of claims 1 to 7, wherein the directional angle of the exploration wave transmitted from the sensor unit is θ, and tan (90-θ) ≥ h / s. .. The lid portion has a first lid portion (80a) and a second lid portion (80b), and is arranged in this order from the sensor portion side to the first lid portion and the second lid portion, and the first lid portion. The 1st lid portion and the 2nd lid portion are arranged apart from each other.
The distance (d2) between the first lid portion and the second lid portion is set to less than λ / 2, assuming that the wavelength of the exploration wave is λ, according to any one of claims 1 to 8. Ultrasonic sensor. The ultrasonic sensor according to any one of claims 1 to 9, wherein the distance (d) between the centers of the adjacent ultrasonic elements is less than λ / 2, where λ is the wavelength of the probe wave. The sensor unit
By arranging a plurality of piezoelectric elements (28) having a piezoelectric film (28b), the plurality of ultrasonic elements are formed.
The ultrasonic sensor according to any one of claims 1 to 10, wherein a driving voltage applied to the piezoelectric element in the plurality of ultrasonic elements is controlled to transmit the exploration wave. The ultrasonic sensor according to claim 11, wherein the sensor unit adjusts the number of the plurality of ultrasonic elements or the number of the ultrasonic elements to which the driving voltage is applied so as to have a predetermined pointing angle. .. The ultrasonic sensor according to claim 11, wherein the sensor unit adjusts the phases of drive voltages applied to the plurality of ultrasonic elements so as to have a directional axis along a predetermined direction. The ultrasonic sensor according to any one of claims 11 to 13, wherein the piezoelectric film is made of scandium aluminum nitride or aluminum nitride.

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