JP2010074544A - Protection housing for open type ultrasonic transmitting/receiving unit and ultrasonic sensor - Google Patents

Abstract

In a protective housing and an ultrasonic sensor for an open-type ultrasonic transmission / reception unit, a simple configuration suppresses a change in ultrasonic output or an input signal with respect to a change in environmental temperature and realizes a highly reliable operation. .
An ultrasonic sensor 10 includes a protective housing 1 and an open type ultrasonic transmission / reception unit 2 (ultrasonic unit 2). The protective housing 1 has a cylindrical body 11 that surrounds the case 20 of the ultrasonic unit 2, and an open space 3 that opens forward is formed by a wall surface 12 that extends forward of the cylindrical body 11. The protective housing 1 is in contact with the wall surface 12 and includes a sound absorbing member 4 at a resonance mode node (standing wave node) in the open space 3. The sound absorbing member 4 suppresses the sharpness of resonance in the open space 3 of the protective housing 1, thereby suppressing the degree of change in the ultrasonic output with respect to the change in the environmental temperature, and realizing a highly reliable operation of the ultrasonic sensor 10. .
[Selection] Figure 1

Description

  The present invention relates to a protective housing for an open-type ultrasonic transmission / reception unit, and an ultrasonic sensor including these open-type ultrasonic transmission / reception units and a protective housing.

  2. Description of the Related Art Conventionally, an open-type ultrasonic transmission / reception unit (hereinafter referred to as an ultrasonic unit) that transmits or receives ultrasonic waves is used for distance measurement and obstacle detection. The ultrasonic unit has a structure in which a vibrating body made of a piezoelectric element that vibrates when transmitting or receiving ultrasonic waves, a resonator fixed to the vibrating body, or the like directly touches the outside air. Since such an ultrasonic unit is mounted on a vehicle or the like and used for ensuring safety, for example, stable operation and highly reliable measurement accuracy and detection accuracy are required.

  Therefore, there has been known an ultrasonic unit which has a stable directivity by improving the positioning method and the fixing support method of the vibrating body at the time of manufacture, so that the dispersion of the ultrasonic output, that is, the ultrasonic sound pressure output is small. (For example, refer to Patent Document 1).

In addition, even when the frequency range of the applied voltage applied to the piezoelectric element deviates from the frequency range adjusted to the maximum level of the sound pressure output, the decrease in the sound pressure output is less than before. An ultrasonic unit is known (for example, see Patent Document 2).
JP-A-6-253395 JP-A-5-328498 (Patent No. 3010242)

  Such a conventional ultrasonic unit is often used for a human body detection sensor for an automatic door, a car detection sensor for a parking lot, a security sensor in a vehicle interior, etc., and its assumed use environment temperature is −40 ° C. Therefore, a highly reliable operation is required under a severe and wide-ranging environment such as 80 to 80 ° C.

  In addition, the ultrasonic unit is usually installed in a protective housing having an opening for securing directivity as a sensor, protection from mechanical or chemical damage, ease of handling and mounting, and the like. Such a protective housing inevitably constitutes a resonator (called a Helmholtz resonator) for a specific frequency. The energy efficiency and reception sensitivity of ultrasound transmission / reception is higher at the frequency of the ultrasound when the protective housing is in the resonant mode. Therefore, in many cases, a protective housing is used that is in a resonance mode for a predetermined frequency or an operation mode close thereto.

  However, since the wavelength of the ultrasonic wave changes when the temperature of the environment in which the ultrasonic unit as described above is used, that is, the temperature of the air as the medium fluctuates, the protective housing does not operate as a resonator for a predetermined frequency. Ultrasonic output decreases. This will be described with reference to the relationship between the wavelength of ultrasonic waves in air and the temperature shown in FIG. Assuming that the wavelength λ≈8.5 mm at the air temperature T = 20 ° C. is set as the resonance mode condition of the protective housing, λ = 9.4 mm when T = 80 ° C., and λ = 7. 6 mm. If the temperature change from T = 20 ° C. is ΔT = ± 60 ° C., even if the frequency is constant, the wavelength changes by ± 0.9 mm, so that the protective housing does not operate as a resonator and the ultrasonic output is reduced. When the ultrasonic output is lowered, the detection device using the ultrasonic unit as a sensor is likely to cause erroneous detection or malfunction. The frequency is uniquely determined from the wavelength and temperature.

  The present invention solves the above problems, and with a simple configuration, it is possible to suppress a change in ultrasonic output or input signal with respect to a change in environmental temperature, and to protect an ultrasonic unit capable of realizing a highly reliable operation. It is an object to provide a housing and an ultrasonic sensor.

  In order to achieve the above object, the invention of claim 1 is a protective housing for an open-type ultrasonic transmission / reception unit comprising an outer periphery of a vibrating body for transmitting or receiving ultrasonic waves surrounded by a case. The housing forms an open space that opens to the front of the vibrating body by a wall surface that surrounds the case and extends forward, and includes a sound absorbing member at a node portion of the resonance mode in the open space.

  According to a second aspect of the present invention, in the protective housing according to the first aspect, the sound absorbing member has a ring shape, and the sound absorbing member is provided at a recessed step portion at the opening end of the wall surface.

  According to a third aspect of the present invention, in the protective housing according to the first or second aspect, a dust-like mesh member is provided in the open space.

  According to a fourth aspect of the present invention, in the protective housing according to any one of the first to third aspects, the wall surface has a tapered portion that narrows the open space toward the front.

  The invention of claim 5 is an ultrasonic sensor comprising an open-type ultrasonic transmission / reception unit and the protective housing according to any one of claims 1 to 4.

  According to the first aspect of the invention, since the sound absorbing member is provided at the resonance mode node of the protective housing, the sharpness of resonance of the protective housing (so-called Q value) is suppressed. Therefore, an ultrasonic sensor including such a protective housing in the ultrasonic unit has a small output change due to a change in ambient temperature and can realize a stable and reliable operation.

  According to invention of Claim 2, since a level | step-difference part is used, a sound-absorbing member can be provided simply. Further, since the sound absorbing member is ring-shaped, the ultrasonic output is not excessively reduced, and the desired effect can be easily realized with easy handling.

  According to invention of Claim 3, the function as a protective housing can be enriched.

  According to the invention of claim 4, directivity can be imparted to the transmission ultrasonic wave by the protective housing.

  According to the invention of claim 5, the function of the open-type ultrasonic transmission / reception unit can be stably extracted, the output change due to the ambient temperature change is small, and a stable and reliable operation without erroneous detection or malfunction is realized. it can.

(First embodiment)
A protective housing and an ultrasonic sensor for an open-type ultrasonic transmission / reception unit according to a first embodiment of the present invention will be described with reference to FIGS. As shown in FIGS. 1 and 2, the ultrasonic sensor 10 includes a protective housing 1 and an open-type ultrasonic transmission / reception unit 2 (hereinafter referred to as an ultrasonic unit 2). The protective housing 1 has a cylindrical body 11 that surrounds the case 20 of the ultrasonic unit 2, and an open space 3 that opens forward is formed by a wall surface 12 that extends forward of the cylindrical body 11. The protective housing 1 is in contact with the wall surface 12 and includes a sound absorbing member 4 at a resonance mode node (standing wave node) in the open space 3. In the present specification, the front is the direction in which ultrasonic waves are transmitted or the direction in which received ultrasonic waves are propagated, the rear is the reverse direction of the front, and the front rear surface is defined by the front rear.

  Here, first, the ultrasonic unit 2 will be described. The ultrasonic unit 2 includes a vibrating body 21 that vibrates at a frequency of ultrasonic waves to be transmitted or received, and a piezoelectric element 22 that is an electromechanical transducer that vibrates integrally with the vibrating body 21 on the rear surface side of the vibrating body 21. The resonator 23 is on the front side of the vibrating body 21 and resonates with the vibrating body 21, the support 24 that supports these vibrating portions from the rear, and the outer periphery of the vibrating portion including the vibrating body 21. And a cylindrical case 20 fixed to the outer edge of the support base 24. Each of these components has a substantially circular outer shape, and the direction of the center axis of the circle is the front-rear direction. The ultrasonic unit 2 includes two electrode pins 25 erected on the support base 24 and two lead wires 26 that electrically connect each electrode pin 25 and the piezoelectric element 22. The entire sound wave unit 2 is fixed to the substrate 27 by electrode pins 25.

  The vibrating body 21 is made of a disk-shaped metal member. The piezoelectric element 22 has a disk shape smaller than the vibrating body 21 and is bonded and fixed to the rear surface side of the vibrating body 21 so as to be electrically connected. The piezoelectric element 22 is fixed to the support base 24 by an elastic member 24a such as silicon rubber disposed so as to locally support several points on the outer edge portion thereof. The elastic member 24 a blocks the vibration so that the vibration of the vibration portion including the piezoelectric element 22 is not transmitted to the support base 24. In addition, a lead wire 26 is directly electrically connected to the rear surface of the piezoelectric element 22, and a lead wire 26 is connected to the front surface via a metallic vibrating body 21. The resonator 23 has an inverted triangular pyramid shape with the bottom surface facing forward, and its apex portion is fixed to the substantially central portion on the front side of the vibrating body 21 with an adhesive 23 a.

  When the ultrasonic unit 2 configured as described above transmits ultrasonic waves, a voltage is applied to both surfaces of the piezoelectric element 22 via each electrode pin 25, and high-frequency (tone burst wave) power that is a drive signal for generating ultrasonic waves is generated. Supplied. Due to the power supply, the piezoelectric element 22 vibrates the vibrating body 21 and the resonator 23, and ultrasonic waves are transmitted into the air from the front surface of the resonator 23 that moves back and forth. When receiving an ultrasonic wave, the ultrasonic wave propagating to the front surface of the resonator 23 vibrates the resonator 23, and hence the vibrating body 21 and the piezoelectric element 22, and the vibration of the piezoelectric element 22 becomes an electric vibration. Output from pin 25.

  Next, the protective housing 1 will be described. The protective housing 1 has a leg portion 11b that holds the cylindrical body 11, and the leg portion 11b is arranged and configured to surround the entire substrate 27 from above. The protective housing 1 can be formed by resin molding. The open space 3 becomes a resonance space for ultrasonic waves having a specific frequency. That is, the cylindrical body 11 constitutes a resonator (Helmholtz resonator) with respect to a specific frequency, and the opening end portion 11a or the vicinity thereof serves as a resonance mode node. The nodes are distributed in a planar shape so as to cross the open space 3.

  The change in the sound pressure in the open space 3 when the open space 3 is in the resonance mode is, for example, as shown in FIG. 3A, the sound pressure low position PL and the sound pressure high along the coordinate axis x in the forward direction. The positions PH are alternately generated, and the position of the opening end portion 11a becomes the low sound pressure position PL. In this resonance mode, the particle velocity of air as a medium corresponds to the change in sound pressure, and as shown in FIG. 3B, the particle velocity high position VH and the particle velocity low along the coordinate axis x. The positions VL are alternately generated, and the position of the opening end portion 11a becomes the particle velocity high position VH. The sound pressure low position PL is a resonance mode node, and in this example, there are two nodes. In general, the nodes of the resonance mode are generated at a plurality of locations along the coordinate axis x depending on the structure of the open space 3 and the frequency of the ultrasonic waves.

  The sound absorbing member 4 of the protective housing 1 suppresses the sharpness of resonance (so-called Q value) in the open space 3 in the resonance mode to a low level, and the degree of change in ultrasonic output with respect to change in environmental temperature (temperature of air as a medium). Suppress. Such a sound absorbing member 4 is made of a porous material such as a foamed material such as urethane or a sintered metal, or a material such as a viscoelastic material such as rubber. The material of the sound absorbing member 4 is not limited to these, and any material that can absorb sound in an ultrasonic frequency range transmitted or received by the ultrasonic unit 2, for example, a frequency band of several tens of kHz, is preferably used. .

  Here, it will be described that the open space 3 is set to the resonance mode. When the ultrasonic unit 2 is used as an ultrasonic sensor, the protective housing 1 is ultrasonic in order to ensure the directivity of the ultrasonic sensor, protect it from mechanical or chemical damage, and facilitate handling and installation. It arrange | positions so that the unit 2 may be surrounded. Such a protective housing 1 consequently constitutes a resonator for the desired specific frequency from the viewpoint of energy efficiency. This is because the energy efficiency at the time of ultrasonic transmission or the reception sensitivity at the time of reception becomes high at the ultrasonic frequency when the protective housing 1 is in the resonance mode. Therefore, the cylindrical body 11 is configured to form the open space 3 that is in a resonance mode with respect to the frequency of the ultrasonic wave to be used.

  Next, the evaluation result of the ultrasonic sensor 10 will be described. As shown in FIG. 4, the ultrasonic sensor 10 is evaluated by the frequency dependence of the output level S of sound pressure for convenience. That is, instead of evaluating how the sound pressure output level S changes with respect to the temperature change of the medium, the wavelength change due to the temperature change is replaced with the frequency change under a constant temperature. In this embodiment, the resonance frequency of the open space 3 at room temperature of 20 ° C. is about 40 kHz, and the output level S at this frequency is 0 dB. As a comparative example, a curve c shows the frequency dependence of the output level S in front of the ultrasonic sensor 10 when the sound absorbing member 4 is not provided, and a curve d is the case of the present embodiment having the sound absorbing member 4. The frequency dependence of is shown.

  As shown in FIG. 4, when the frequency is shifted from the resonance frequency by +5 kHz, the output level S is decreased by 7 dB in the comparative example (curve c), whereas in the present embodiment (curve d), the output level is only 1 dB. It falls within the decline. In this case, +5 kHz corresponds to a case where the air temperature of the medium fluctuates by -60 ° C from 20 ° C to -40 ° C. In this way, the amount of drop in the output level S of the sound pressure in front of the ultrasonic sensor 10 is reduced with respect to temperature fluctuations by the action of the sound absorbing member 4, and stable output characteristics can be obtained as a sensor. I understand.

  As described above, according to the protective housing 1 of the present embodiment, the sound absorption member 4 is provided at the node of the resonance mode so that the resonance sharpness of the protective housing 1 is kept low. Or the degree of change in sensitivity when receiving ultrasonic waves. In addition, the ultrasonic sensor 10 including such a protective housing 1 in the ultrasonic unit 2 has less change in output due to a change in ambient environment temperature than the conventional one, and can realize a stable and reliable operation.

  Here, the arrangement of the sound absorbing member 4 and the degree of sound absorption will be described. As described above, the sound absorbing member 4 constitutes the ultrasonic sensor 10 that is not sensitively influenced by changes in the environmental temperature or the like by reducing the sharpness of resonance while maintaining the function of the open space 3 as a resonator. Is. Therefore, since the sound absorbing member 4 only needs to realize such a configuration, in the case of a material having a high sound absorption efficiency, it is sufficient to provide a small area on the wall surface 12 in the vicinity of the opening end portion 11a, and the material having a low sound absorption efficiency. In this case, a large area may be provided. In the present embodiment, the sound absorbing member 4 is provided on the wall surface 12 in the vicinity of the opening end portion 11a. However, the sound pressure is not limited to the opening end portion 11a, but another sound pressure on the side close to the ultrasonic unit 2. The sound absorbing member 4 may be provided at the low position PL. The reason why the sound absorbing member 4 is arranged at the low sound pressure position PL, that is, the position of the node is that the sound absorbing effect is high at this position, and the sound absorbing member 4 may be arranged at a position other than the node. . The sound absorbing member 4 can be attached to the wall surface 12 by, for example, bonding, applying, or fitting.

  The above-described ultrasonic unit 2 is an example of an ultrasonic transmission / reception unit generally called an open type, and has a structure in which a vibrating body 21 or the like that vibrates when transmitting or receiving ultrasonic waves directly touches the outside air. It has become. The ultrasonic unit 2 is protected by the protective housing 1 to be an ultrasonic sensor 10 that can stably exhibit its function. For example, the ultrasonic unit 2 can be mounted on a vehicle or the like and used for distance measurement or obstacle measurement. The ultrasonic sensor 10 can be used alone for both transmitting and receiving, and a plurality of dedicated sensors for transmission and reception can be used in combination.

(Second Embodiment)
5A and 5B show the protective housing 1 and the ultrasonic sensor 10 according to the second embodiment. In the present embodiment, the structure of the sound absorbing member 4 and its installation structure are different from those of the first embodiment. That is, as shown in FIG. 5A, the sound absorbing member 4 has a ring shape, and is inserted and disposed in the recessed step portion 13 formed at the opening end portion of the wall surface 12 of the cylindrical body 11. The sound absorbing member 4 is formed of, for example, a rubber-based material that is a viscoelastic body, and is press-fitted into the stepped portion 13 or bonded and fixed. The thickness (length in the front-rear direction) of the sound absorbing member 4 is, for example, 2.3 mm or more when the frequency of ultrasonic waves to be transmitted / received is 40 kHz. This is a length of ¼ or more of the assumed wavelength (9.4 mm at 80 ° C., 7.6 mm at −40 ° C.).

  According to the present embodiment, since the step portion 13 is used, the sound absorbing member 4 can be provided easily, and since the sound absorbing member 4 is ring-shaped, it is easy to handle, and by changing the ring size, the sound absorbing member 4 can be provided. The degree can be finely adjusted, and a desired effect can be easily realized.

(Third embodiment)
FIG. 6 shows a protective housing 1 and an ultrasonic sensor 10 according to the third embodiment. In the present embodiment, the structure of the sound absorbing member 4 and its installation structure are different from those of the second embodiment. That is, the sound absorbing member 4 has a flat plate shape having a large number of openings, and is fixed by being press-fitted or bonded to a depressed step portion 13 formed at the opening end of the wall surface 12 of the cylindrical body 11. The opening size of the opening in the sound absorbing member 4 is, for example, 0.76 mm or less when the frequency of ultrasonic waves to be transmitted / received is 40 kHz, that is, an assumed wavelength (9.4 mm at 80 ° C., 7.6 mm at −40 ° C.). 1/10 or less. The thickness of the sound absorbing member 4 is 2.3 mm or more. This is a length of 1/4 or more of the assumed wavelength. The lower limit of the spread size of the opening and the upper limit of the thickness of the sound absorbing member 4 are determined by the allowable attenuation amount of the output level S.

  The sound absorbing member 4 is composed of a wire mesh satisfying predetermined opening and thickness conditions, a sintered metal porous body, a foamed resin body, and the like. The sound absorbing member 4 is not limited to a single structure, and a plurality of sound absorbing members may be stacked to have a predetermined thickness. As in the first and second embodiments, the sound absorbing member 4 in the present embodiment can ensure the stability of the ultrasonic sensor 10 with respect to environmental temperature changes, and can prevent foreign matter from entering the ultrasonic unit 2. Intrusion can be prevented.

(Fourth embodiment)
7 and 8 show a protective housing 1 and an ultrasonic sensor 10 according to the fourth embodiment. In the present embodiment, the structure of the open space 3 is different from that of the first embodiment. That is, the open space 3 in the protective housing 1 of the present embodiment includes a cylindrical wall surface 12a on the side close to the ultrasonic unit 2, a wall surface 12b that forms a tapered portion that narrows the open space 3 forward, and an open end. It is formed of a wall surface 12 in which a cylindrical wall surface 12c on the side of the section is successively connected. Similarly to the first embodiment, the sound absorbing member 4 is provided on the opening end side of the wall surface 12c, that is, on the node portion of the resonance mode.

  In the open space 3 as shown in FIGS. 7 and 8, a sound absorbing action is generated due to a change in the cross-section of the tapered portion that narrows toward the opening. Therefore, the arrangement area of the sound absorbing member 4 is smaller than that in the first embodiment. Can be reduced. In addition, since the entrance of the open space 3 is narrowed, entry of foreign matter from the outside into the ultrasonic unit 2 can be reduced. Further, the protective housing 1 can give stronger directivity to the transmitted ultrasonic waves.

(Fifth embodiment)
FIG. 9 shows a protective housing 1 and an ultrasonic sensor 10 according to the fifth embodiment. In the present embodiment, as in the second embodiment relative to the first embodiment, the structure of the sound absorbing member 4 and its installation structure are different from those in the fourth embodiment. That is, the sound absorbing member 4 has a ring shape, and is disposed in the depressed step portion 13 formed at the opening end portion of the wall surface 12c. The material and dimensions of the sound absorbing member 4, the fixing structure, and the effects thereof are the same as in the second embodiment.

(Sixth embodiment)
FIG. 10 shows the protective housing 1 and the ultrasonic sensor 10 according to the sixth embodiment. In the present embodiment, as in the third embodiment relative to the second embodiment, a flat plate-like sound absorbing member 4 having a large number of openings is different from the fifth embodiment. That is, the sound absorbing member 4 has a flat plate shape, and is disposed in the depressed step portion 13 formed at the opening end of the wall surface 12c. The material and dimensions of the sound absorbing member 4, the fixing structure, and the effects thereof are the same as in the third embodiment.

(Seventh embodiment)
FIG. 11 shows the protective housing 1 and the ultrasonic sensor 10 according to the seventh embodiment. In this embodiment, it can be considered that the length of the wall surface 12c of the protective housing 1 in the fourth embodiment is zero. That is, the open space 3 in the protective housing 1 of the present embodiment includes a cylindrical wall surface 12a on the side close to the ultrasonic unit 2 and a wall surface 12b constituting a tapered portion that narrows the open space 3 toward the front in order. It is formed by the wall surface 12 made to do. The sound absorbing member 4 is provided on the tapered wall surface 12b, that is, the node of the resonance mode. The protective housing 1 and the ultrasonic sensor 10 of this embodiment have the same effects as those of the fourth embodiment.

(Eighth embodiment)
12 to 14 show the protective housing 1 and the ultrasonic sensor 10 according to the eighth embodiment. In the present embodiment, the arrangement and structure of the sound absorbing member 4 are different from those of the fourth embodiment. That is, in the present embodiment, the flat plate-like sound absorbing member 4 having a large number of openings is disposed not at the opening end side of the protective housing 1 but at the resonance mode node on the inner side of the open space 3. As shown in FIGS. 12 and 13, the sound absorbing member 4 is supported by a support member 4 a and is installed so as to be localized around the central axis of the protective housing 1. The material, opening configuration, thickness dimension, and the like of the sound absorbing member 4 can be the same as those of the sound absorbing member 4 in the third embodiment. The support member 4a is configured by a wire mesh having an opening that does not attenuate ultrasonic waves, a combination of a beam and a support bar, or the like.

  The evaluation result of the ultrasonic sensor 10 of this embodiment will be described with reference to FIG. As in the case of FIG. 4, the premise in FIG. 14 is that the resonant frequency of the open space 3 at room temperature of 20 ° C. is about 40 kHz, and the output level S at this frequency is 0 dB. A curve e indicates a comparative example, and a curve f indicates the present embodiment including the sound absorbing member 4. When the frequency deviates by +5 kHz from the resonance frequency, the output level S is reduced by 5 dB in the comparative example (curve e), whereas in the present embodiment (curve f), the output level is only slightly lower than 1 dB. In this case, +5 kHz corresponds to a case where the air temperature of the medium fluctuates by -60 ° C from 20 ° C to -40 ° C. Thus, it can be seen that due to the action of the sound absorbing member 4, the amount of drop in the output level S with respect to temperature fluctuation is reduced, and a stable output characteristic as a sensor can be obtained.

(Ninth embodiment)
FIGS. 15A and 15B show the protective housing 1 and the ultrasonic sensor 10 according to the ninth embodiment. In the present embodiment, a mesh member 5 for dust prevention provided in the open space 3 is different from the fourth embodiment. The mesh member 5 is a member having a shape that does not hinder the propagation of ultrasonic waves transmitted and received by the ultrasonic unit 2 as much as possible, and for example, a wire net is used. The mesh-like member 5 is arranged in a planar shape so as to close the opening of the open space 3 for dust prevention. As shown in FIG. 15A, the arrangement position is preferably on the opening end side for dust prevention. However, unlike the sound absorbing member 4, the arrangement position is not limited to the node portion of the resonance mode. As shown to b), it can be set as arbitrary arrangement positions. According to the present embodiment, the function as the protective housing 1 can be further enhanced by the dustproof effect of the mesh member 5 in addition to the effect of the sound absorbing member 4.

  Although the first to ninth embodiments have been described above, the present invention is not limited to the above-described configuration, and various modifications can be made. For example, the mesh member 5 of the ninth embodiment can be applied to other embodiments. In the first to seventh embodiments, the sound absorbing member 4 arranged at the resonance mode node at the opening end can be arranged at the node close to the ultrasonic unit 2. Further, the length in the front-rear direction of the wall surface 12 of the protective housing 1 and the cylindrical body 11 forming the wall surfaces 12a, 12b, and 12c is an arbitrary length in which the open space 3 is in the resonance mode with respect to a predetermined frequency (use frequency). The sound absorbing member 4 is not limited to one location but can be arranged at a plurality of locations at any node. Further, the open space 3 of the protective housing 1 is not limited to an axially symmetric shape, and the cross section can be an arbitrary shape such as a polygon or an ellipse.

  The piezoelectric element 22 may be a monomorph type, a bimorph type, a laminated type, or the like. The protective housing 1 can be applied to the open-type ultrasonic unit 2 having an arbitrary configuration based on the configuration of the arbitrary piezoelectric element 22, and the ultrasonic sensor 10 can be configured. The open-type ultrasonic unit 2 that constitutes the ultrasonic sensor 10 by applying the protective housing 1 includes a cylindrical case 20 that is necessarily disposed so as to surround the outer periphery of the vibrating portion including the vibrating body 21. There is no need to be. That is, the ultrasonic sensor 10 may have a configuration in which the case 20 and the protective housing 1 are combined.

1 is a cross-sectional view of an ultrasonic sensor including a protective housing for an open-type ultrasonic transmission / reception unit according to a first embodiment of the present invention. The perspective view containing the partial cross section of an ultrasonic sensor same as the above. (A) is a sound pressure distribution diagram in the resonance mode state in the open space of the protective housing of the ultrasonic sensor, and (b) is a particle velocity distribution diagram in the resonance mode state. The graph of the frequency dependence of each output level of an ultrasonic sensor same as the above and the ultrasonic sensor of a comparative example. (A) is a disassembled sectional view of the opening end part of the protective housing which concerns on 2nd Embodiment, (b) is sectional drawing of the ultrasonic sensor provided with the protective housing. Sectional drawing of the ultrasonic sensor provided with the protective housing which concerns on 3rd Embodiment. Sectional drawing of the ultrasonic sensor provided with the protective housing which concerns on 4th Embodiment. The perspective view containing the partial cross section of an ultrasonic sensor same as the above. Sectional drawing of the ultrasonic sensor provided with the protective housing which concerns on 5th Embodiment. Sectional drawing of the ultrasonic sensor provided with the protective housing which concerns on 6th Embodiment. Sectional drawing of the ultrasonic sensor provided with the protective housing which concerns on 7th Embodiment. Sectional drawing of the ultrasonic sensor provided with the protective housing which concerns on 8th Embodiment. The perspective view which shows arrangement | positioning of the sound absorption member in a protection housing same as the above. The graph of the frequency dependence of each output level of an ultrasonic sensor same as the above and the ultrasonic sensor of a comparative example. (A) is sectional drawing of the ultrasonic sensor provided with the protective housing which concerns on 9th Embodiment, (b) is sectional drawing which shows the modification of the ultrasonic sensor. The graph which shows the relationship between the wavelength and frequency of the ultrasonic wave in air, and the relationship between a wavelength and temperature.

Explanation of symbols

1 Protective Housing 2 Open Type Ultrasonic Transceiver Unit (Ultrasonic Unit)
DESCRIPTION OF SYMBOLS 3 Open space 4 Sound absorbing member 5 Mesh-like member 10 Ultrasonic sensor 11a Open end 12, 12a, 12b, 12c Wall surface 13 Step part 20 Case 21 Vibrating body

Claims (5)

A protective housing for an open-type ultrasonic transmission / reception unit comprising a case surrounding the outer periphery of a vibrating body for transmitting or receiving ultrasonic waves,
The protective housing is characterized in that an open space that opens to the front of the vibrating body is formed by a wall surface that surrounds the case and extends forward, and a sound absorbing member is provided at a node of a resonance mode in the open space. housing.   2. The protective housing according to claim 1, wherein the sound absorbing member has a ring shape, and the sound absorbing member is provided in a recessed stepped portion at an opening end of the wall surface.   The protective housing according to claim 1 or 2, wherein a dust-proof mesh member is provided in the open space.   The protective housing according to any one of claims 1 to 3, wherein the wall surface includes a tapered portion that narrows the open space toward the front.   An ultrasonic sensor comprising: an open-type ultrasonic transmission / reception unit; and the protective housing according to any one of claims 1 to 4.

Images