Ultrasonic sensor

Abstract

An ultrasonic sensor (101) comprises: a housing (10) having a first surface (51); a transmitting element (31) held by the housing (10) so as to be capable of emitting ultrasonic waves at a first portion of the first surface (51) in a direction away from the first surface (51); and a receiving element (32) held by the housing (10) so as to be capable of detecting the ultrasonic waves that have arrived at a second portion of the first surface (51). The first surface (51) has a half-wavelength shift structure (21) between the first portion and the second portion. The half-wavelength shift structure (21) has a structure in which the phase of a second wave (82), which is a component that advances to the receiving element (32) along the first surface (51) via the half-wavelength shift structure (21) among the ultrasonic waves emitted from the transmitting element (31), is shifted by half a wavelength, as compared with a first wave (81), which is a component that advances to the receiving element (32) along the first surface (51) among the ultrasonic waves emitted from the transmitting element (31).

Description

Ultrasonic Sensor

[0001] The present invention relates to an ultrasonic sensor.

[0002] Japanese Patent Laid-Open Publication No. 11-218572 (Patent Document 1) describes an ultrasonic sensor. In particular, the ultrasonic sensor shown in FIG. 3 of Patent Document 1 includes an integrated housing in which a transmitting horn and a receiving horn are arranged side by side. A transmitting element is disposed behind the transmitting horn, and a receiving element is disposed behind the receiving horn. The transmitting horn and receiving horn are connected by a flat surface of the housing.

[0003] Japanese Patent Application Publication No. 11-218572

[0004] In the ultrasonic sensor described in Patent Document 1, the directivity of the ultrasonic sensor is determined by the directional characteristics of the transmitting element and the acoustic path shape determined by the shape of the housing, so there is a limit to how much the directivity can be increased.

[0005] Furthermore, in the ultrasonic sensor described in Patent Document 1, ultrasonic waves emitted from the transmitting element may not only travel toward the target, but may also propagate along the surface of the housing from the transmitting horn to the receiving horn and be detected by the receiving element. Waves that propagate directly from the transmitting element to the receiving element via the housing are hereinafter referred to as "direct waves." If the signal strength of the direct waves among the ultrasonic waves detected by the receiving element becomes large, accurate detection becomes difficult, especially when attempting to detect a target at a short distance.

[0006] Therefore, an object of the present invention is to provide an ultrasonic sensor that can reduce the influence of direct waves, increase directivity, and more accurately detect an object.

[0007] To achieve the above object, an ultrasonic sensor according to the present invention includes a housing having a first surface, a transmitting element held by the housing so as to be capable of emitting ultrasonic waves at a first portion of the first surface in a direction away from the first surface, and a receiving element held by the housing so as to be capable of detecting the ultrasonic waves arriving at a second portion of the first surface. The first surface has a half-wavelength shift structure between the first portion and the second portion. The half-wavelength shift structure is structured so that a second wave, which is a component of the ultrasonic waves emitted from the transmitting element that passes through the half-wavelength shift structure and then travels along the first surface to the receiving element, has a phase shift of half a wavelength compared to a first wave, which is a component of the ultrasonic waves emitted from the transmitting element that travels along the first surface to the receiving element.

[0008] According to the present invention, the component of the direct wave that reaches the receiving element is canceled by the component that arrives after passing through the half-wavelength shift structure, so the influence of the direct wave can be reduced and the directionality can be increased. Therefore, the ultrasonic sensor in this embodiment can be an ultrasonic sensor that can detect objects more accurately.

[0009] FIG. 1 is a cross-sectional view of an ultrasonic sensor according to a first embodiment of the present invention. FIG. 2 is an explanatory diagram of how ultrasonic waves spread from the ultrasonic sensor according to the first embodiment of the present invention. FIG. 3 is a diagram showing simulation results in a case where there is no slit in simulation 1. FIG. 4 is a diagram showing simulation results in a case where the slit depth D is 1 mm in simulation 1. FIG. 5 is a diagram showing simulation results in a case where the slit depth D is 2 mm in simulation 1. FIG. 6 is a diagram showing simulation results in a case where the slit depth D is 3 mm in simulation 1. FIG. 7 is a diagram showing a method for evaluating the FOV in simulation 1. FIG. 8 is a cross-sectional view of a first modified example of the ultrasonic sensor according to the first embodiment of the present invention. FIG. 9 is a cross-sectional view of a second modified example of the ultrasonic sensor according to the first embodiment of the present invention. FIG. 10 is a cross-sectional view of a third modified example of the ultrasonic sensor according to the first embodiment of the present invention. FIG. 11 is a cross-sectional view of a fourth modified example of the ultrasonic sensor according to the first embodiment of the present invention. FIG. 12 is an explanatory diagram of a slit width W of an ultrasonic sensor according to a second embodiment of the present invention. FIG. 13 is a diagram showing simulation results in a case where the slit width W is 0.1 mm in simulation 2. FIG. 14 is a diagram showing simulation results in a case where the slit width W is 0.5 mm in simulation 2. FIG. 15 is a diagram showing simulation results in a case where the slit width W is 1 mm in simulation 2. FIG. 10 is a diagram showing simulation results when the slit width W is 2 mm in simulation 2. FIG. 11 is a diagram showing simulation results when the slit width W is 3 mm in simulation 2. FIG. 12 is a diagram showing simulation results when the slit width W is 4 mm in simulation 2. FIG. 13 is a diagram showing simulation results when the slit width W is 8 mm in simulation 2. FIG. 14 is a polar chart of the FOV derived from simulation 2. FIG. 15 is a graph showing the results of simulation 2. FIG. 16 is an explanatory diagram of the distance A to the slit of the ultrasonic sensor in embodiment 3 based on the present invention. FIG. 17 is a diagram showing simulation results when the distance A to the slit is 2 mm in simulation 3.1 is a diagram showing simulation results in Simulation 3 when the distance A to the slit is 4 mm. FIG. 2 is a diagram showing simulation results in Simulation 3 when the distance A to the slit is 6 mm. FIG. 3 is a diagram showing simulation results in Simulation 3 when the distance A to the slit is 8 mm. FIG. 4 is a graph showing the results of Simulation 3. FIG. 5 is a cross-sectional view of an ultrasonic sensor in a fourth embodiment according to the present invention. FIG. 6 is an explanatory diagram of dimensions of each part when a part of an acoustic path is horn-shaped. FIG. 7 is a diagram showing simulation results in Simulation 4 when a horn shape is present and a slit is not provided as a half-wavelength shift structure. FIG. 8 is a graph showing simulation results in Simulation 4 when a horn shape is present and a slit is not provided as a half-wavelength shift structure, with the horizontal axis representing angle and the vertical axis representing sound pressure level. FIG. 9 is a diagram showing simulation results in Simulation 4 when a horn shape is present and a slit is provided as a half-wavelength shift structure with a distance A = 2 mm and a width W = 1 mm. FIG. 10 is a graph showing simulation results in Simulation 4 when a horn shape is present and a slit is provided as a half-wavelength shift structure with a distance A = 2 mm and a width W = 1 mm, with the horizontal axis representing angle and the vertical axis representing sound pressure level. 10 is a diagram showing simulation results in a case where a horn shape is provided and slits as a half-wavelength shift structure are provided at a distance A = 4 mm and a width W = 1 mm in Simulation 4. FIG. 11 is a graph showing the simulation results in a case where a horn shape is provided and slits as a half-wavelength shift structure are provided at a distance A = 4 mm and a width W = 1 mm in Simulation 4, with the horizontal axis representing angle and the vertical axis representing sound pressure level. FIG. 12 is a diagram showing the simulation results in a case where a horn shape is provided and slits as a half-wavelength shift structure are provided at a distance A = 4 mm and a width W = 2 mm in Simulation 4. FIG. 13 is a graph showing the simulation results in a case where a horn shape is provided and slits as a half-wavelength shift structure are provided at a distance A = 4 mm and a width W = 2 mm in Simulation 4, with the horizontal axis representing angle and the vertical axis representing sound pressure level. FIG. 14 is a perspective view of a model having an annular slit shown for explanation in a fifth embodiment according to the present invention.FIG. 10 is a perspective view of a model having an arc-shaped slit shown for explanation in embodiment 5 in accordance with the present invention. FIG. 11 is a plan view of a model having an arc-shaped slit shown for explanation in embodiment 5 in accordance with the present invention. FIG. 12 is a diagram showing sound pressure levels in a cross section cut along the XZ plane among the simulation results obtained in simulation 5. FIG. 13 is a diagram showing sound pressure levels in a cross section cut along the YZ plane among the simulation results obtained in simulation 5. FIG. 14 is a graph collectively displaying two simulation results obtained in simulation 5. FIG. 15 is a cross-sectional view of an ultrasonic sensor in embodiment 6 in accordance with the present invention.

[0010] The dimensional ratios shown in the drawings do not necessarily represent the actual ratios, and may be exaggerated for the sake of convenience. In the following description, when the concepts of up and down are mentioned, they do not necessarily mean absolute up and down, but may mean relative up and down in the illustrated position.

[0011] (Embodiment 1) An ultrasonic sensor according to embodiment 1 of the present invention will be described with reference to Figure 1. A cross-sectional view of an ultrasonic sensor 101 according to this embodiment is shown in Figure 1. Below, the transmitting element 31 may be abbreviated as "Tx" and the receiving element 32 may be abbreviated as "Rx".

[0012] The ultrasonic sensor 101 includes a housing 10, a transmitting element 31, and a receiving element 32. The housing 10 has a first surface 51. In the example shown here, the first surface 51 is the top surface of the housing 10. The transmitting element 31 is held by the housing 10 so as to be able to emit ultrasonic waves at a first portion of the first surface 51 in a direction away from the first surface 51, i.e., in the direction indicated by arrow 91. The receiving element 32 is held by the housing 10 so as to be able to detect ultrasonic waves arriving at a second portion of the first surface 51. The first surface 51 has a half-wavelength shift structure 21 between the first portion and the second portion. The half-wavelength shift structure 21 has a structure in which a second wave 82, which is a component of the ultrasonic waves emitted from the transmitting element 31 that passes through the half-wavelength shift structure 21 and then travels along the first surface 51 to the receiving element 32, has a phase shift of half a wavelength compared to a first wave 81, which is a component of the ultrasonic waves emitted from the transmitting element 31 that travels along the first surface 51 to the receiving element 32. Details of the half-wavelength shift structure 21 will be described later.

[0013] The transmitting element 31 is mounted on the substrate 11. The receiving element 32 is mounted on the substrate 12. The housing 10 has two recesses on its underside. As shown in FIG. 1 , the substrate 11 is attached to the bottom surface of one of the two recesses on the underside of the housing 10, and the substrate 12 is attached to the bottom surface of the other recess. The first surface 51 of the housing 10 has two openings. The substrates 11 and 12 also have openings. One opening on the first surface 51 of the housing 10 communicates with an opening on the substrate 11, forming a recess 41. The transmitting element 31 is exposed at the bottom of the recess 41. The other opening on the first surface 51 of the housing 10 communicates with an opening on the substrate 12, forming a recess 42. The receiving element 32 is exposed at the bottom of the recess 42. The transmitting element 31 emits ultrasonic waves from the bottom of the recess 41 in the direction of arrow 91. The receiving element 32 can detect ultrasonic waves arriving at the bottom of the recess 42. The passage formed by communication between the opening in the housing 10 and the opening in the substrate 11 or 12 is called an "acoustic path." The recesses provided on the top surfaces of the transmitting element 31 and the receiving element 32 in FIG. 1 are called "acoustic holes."

[0014] In the example shown in this embodiment, the half-wavelength shift structure 21 is a recess provided in the first surface 51. The half-wavelength shift structure 21 may be a slit-shaped recess. The "slit-shaped recess" here refers to a groove. The half-wavelength shift structure 21 may be a slit-shaped recess that includes a portion extending in a direction intersecting a straight line connecting the first portion and the second portion on the first surface 51. The half-wavelength shift structure 21 may be an annular recess provided so as to surround the first portion and be spaced apart from the first portion.

[0015] In this embodiment, in addition to the first wave 81 that propagates as a direct wave from the transmitting element 31 to the receiving element 32, i.e., from the first location to the second location, there is also a second wave 82 that enters the recess serving as the half-wavelength shift structure 21 from the first location, reflects off the bottom surface of the recess, emerges from the recess, and propagates from there to the second location. Both the first wave 81 and the second wave 82 reach the receiving element 32 in the second location, but at that point in time, the first wave 81 and the second wave 82 are out of phase with each other by a half wavelength, and therefore interfere with each other so as to cancel each other out.

[0016] This phenomenon is shown in a different way in Figure 2. In this figure, the spreading of ultrasonic waves is represented by an arc. Ultrasonic waves 71 are emitted from the transmitting element 31, pass through the acoustic path, and are emitted so as to spread from the first portion. Part of the ultrasonic waves 71 enters the half-wavelength shift structure 21, is reflected, and then emerges from the half-wavelength shift structure 21, spreading as ultrasonic waves 72 starting from the half-wavelength shift structure 21. The ultrasonic waves 71 and 72 interfere with each other with a phase difference of half a wavelength, so they cancel each other out, thereby narrowing the field of view (FOV) of the ultrasonic waves 71.

[0017] According to this embodiment, as described above, the components of the direct waves that reach the receiving elements 32 are canceled out, thereby reducing the influence of the direct waves and increasing the directivity. Therefore, the ultrasonic sensor according to this embodiment can be an ultrasonic sensor that can detect objects more accurately. This effect was also confirmed by the simulation described below.

[0018] (Simulation 1) When a slit-shaped recess (hereinafter referred to as "slit") is provided as a half-wavelength shift structure, a simulation was performed to investigate how the depth D of the slit should be preferably set.

[0019] The condition parameters used in this simulation are as follows: The acoustic path size for both the transmitting element 31 and the receiving element 32 was 1.1 mm in diameter and 1.0 mm in depth. The diameter of the acoustic holes in the transmitting element 31 and the receiving element 32 was 1.1 mm. The distance between the transmitting element 31 and the receiving element 32 was 20 mm. The slit serving as the half-wavelength shift structure 21 was annularly arranged to surround the transmitting element 31. The frequency of the ultrasonic waves used was 42.5 kHz. The wavelength λ of this ultrasonic wave was 8 mm. The distance A between the transmitting element 31 and the end of the slit closest to the transmitting element 31 was 4 mm. The slit width W was 1 mm. The simulation was performed with four slit depths D: 1 mm, 2 mm, 3 mm, and 4 mm. A simulation was also performed without a slit. The simulation results are shown in Figures 3 to 7, respectively. Figure 3 shows the case without a slit. This was obtained by performing a simulation for comparison. In the following, the configuration without a slit may be referred to as "Ref."

[0020] 3 to 7, the transmitting element 31 is placed at the bottom of the recess 41. The receiving element 32 is placed at point 60, which is the center of the bottom surface of the recess 42. In the simulation, the sound pressure at point 60 is calculated. The sound pressure at point 60, i.e., the sound pressure detected by the receiving element 32, is displayed at the bottom of FIGS. 3 to 7. This represents the sound pressure of the direct wave, so a smaller value is preferable.

[0021] The sound pressure values ​​detected by the receiving element 32 are summarized in Table 1. The FOV evaluation in Table 1 was performed assuming a semicircle with a radius of 10 mm from the center of the Tx acoustic hole, as shown in Figure 8. The FOV was evaluated from 0° to 90° along this semicircle.

[0022]

[0023] As is clear from Table 1, the sound pressure at the receiving element 32 is minimum when the slit depth D is 1 / 4 of the wavelength λ, i.e., 2.0 mm. This is the most preferable setting. Therefore, it is preferable that the depth D of the recess is 1 / 4 of the wavelength λ of the ultrasonic wave.

[0024] The recess is preferably provided in an annular shape so as to surround the first portion, so that the first wave 81 and the second wave 82 are out of phase with each other by a half wavelength in all directions, and can be caused to interfere with each other so as to cancel each other out.

[0025] (Modifications) Furthermore, modifications of the half-wavelength shift structure will be described. Instead of the half-wavelength shift structure 21 described in the first embodiment, half-wavelength shift structures as shown in Figures 9 to 12 may be adopted. The ultrasonic sensor 102 shown in Figure 9 has a tapered half-wavelength shift structure 22. The term "tapered" here refers to a shape in which the width increases from the bottom toward the first surface 51 when viewed in a cross-sectional view such as Figure 9.

[0026] The ultrasonic sensor 103 shown in FIG. 10 includes a "reverse tapered" half-wavelength shift structure 23.

[0027] 11 includes a half-wavelength shift structure 25. The half-wavelength shift structure 25 is not simply a recess provided in the housing 10, but includes a structure in which the inside of the recess is filled with a medium other than air.

[0028] The ultrasonic sensor 105 shown in FIG. 12 includes a half-wavelength shift structure 26. The half-wavelength shift structure 26 includes a tunnel through which the ultrasonic wave detours. The second wave that detours through the tunnel and emerges has a phase shift of half a wavelength compared to the first wave that travels directly through the first surface 51. In this way, the half-wavelength shift structure may be some kind of structure other than a simple recess. The half-wavelength shift structure 26 is shown as one example.

[0029] Second Embodiment A second embodiment of the present invention will be described with reference to FIGS.

[0030] In this embodiment, as shown in Fig. 13, attention is focused on the width W of the slit provided as the half-wavelength shift structure 21 in the ultrasonic sensor 101. The ultrasonic sensor 101 itself is the same as the ultrasonic sensor 101 described in embodiment 1, and therefore the basic configuration is similar to that described in embodiment 1. In this embodiment, the following simulation was performed to investigate how the slit width W should be preferably set.

[0031] (Simulation 2) The condition parameters in this simulation were basically the same as those described in Simulation 1. The slit depth was 2 mm. The slit width W was set to 1 / 80, 1 / 16, 1 / 8, 1 / 4, 3 / 8, 1 / 2, and 1 times the wavelength, and simulations were performed for each case. 1 / 80, 1 / 16, 1 / 8, 1 / 4, 3 / 8, 1 / 2, and 1 times the wavelength correspond to 0.1 mm, 0.5 mm, 1 mm, 2 mm, 3 mm, 4 mm, and 8 mm, respectively. Simulation results for each value of width W are shown in Figures 14 to 20. A polar chart of the FOV is shown in Figure 21. A graph with the horizontal axis representing angle and the vertical axis representing sound pressure level is shown in Figure 22. Figures 21 and 22 collectively display values ​​extracted from the simulation results shown in Figures 16 to 22.

[0032] Table 2 shows a summary of the sound pressure values ​​detected by the receiving element 32. The values ​​corresponding to "without slit" in Table 2 are a direct reprint of the simulation results for "without slit" in Simulation 1.

[0033]

[0034] As is clear from Table 2, the sound pressure at the receiving element 32 is small when the slit width W is equal to or greater than 1 / 16 of the wavelength λ, i.e., 0.5 mm, and less than 1 / 2 of the wavelength λ, i.e., 4.0 mm. In other words, it is preferable for the slit width W to be within this range. Therefore, it is preferable that the width W of the recess measured along the direction connecting the first portion and the second portion is equal to or greater than 1 / 16 and less than 1 / 2 of the wavelength λ of the ultrasonic wave.

[0035] Looking more precisely at Table 2, the sound pressure at the receiving element 32 is small when the slit width is 1 / 8 of the wavelength λ, i.e., 1.0 mm or more, and 3 / 8 of the wavelength λ, i.e., 3.0 mm or less. In other words, it is particularly preferable when the slit width W is within this range. Therefore, it is preferable that the width of the recess measured along the direction connecting the first portion and the second portion is 1 / 8 to 3 / 8 of the wavelength λ of the ultrasonic wave.

[0036] Third Embodiment A third embodiment of the present invention will be described with reference to FIGS.

[0037] In this embodiment, attention is focused on the distance A between the transmitting element 31 and the slit, as shown in Fig. 23. The distance A is the length from the center of the transmitting element 31 to the end of the slit that is closer to the transmitting element 31. In this embodiment, the following simulation was performed to investigate how to preferably set the distance A to the slit provided as a half-wavelength shift structure.

[0038] (Simulation 3) The condition parameters in this simulation were basically the same as those explained in Simulation 1. The slit depth D was 2 mm, and the slit width W was 1 mm. The distance A to the slit was set to four values: 2 mm, 4 mm, 6 mm, and 8 mm, and a simulation was performed for each case. The simulation results for each value of distance A are shown in Figures 24 to 27. Figure 28 is a graph in which the horizontal axis represents angle and the vertical axis represents sound pressure level. Figure 28 shows values ​​extracted from the simulation results shown in Figures 24 to 27.

[0039] Table 3 shows a summary of the sound pressure values ​​detected by the receiving element 32. The values ​​corresponding to "without slit" in Table 3 are a direct reprint of the simulation results for "without slit" in Simulation 1.

[0040]

[0041] As is clear from Table 3, when the distance A is 4.0 mm or less, i.e., ½ of the wavelength λ or less, direct waves are reduced, the FOV is narrowed, and side lobes are suppressed. Therefore, when viewed from a direction perpendicular to the first surface, it is preferable that the length A from the center of the transmitting element to the end of the recess closest to the center is ½ of the wavelength λ of the ultrasonic wave or less.

[0042] Fourth Embodiment A fourth embodiment of the present invention will be described with reference to FIGS.

[0043] In this embodiment, as shown in Fig. 29 , a portion of the acoustic path corresponding to the transmitting element 31 and the receiving element 32 is horn-shaped. Here, the opening provided in the housing 10 is horn-shaped. As shown in the enlarged view in Fig. 30 , the diameter of the opening in the housing 10 at the first surface 51 is D1, and the diameter at the opposite surface, that is, the second surface 52, is D2. In this embodiment, the following simulation was performed to confirm whether or not the configuration in which a slit is provided as a half-wavelength shift structure is effective even when such a configuration is adopted.

[0044] (Simulation 4) The condition parameters for this simulation were as follows: The housing 10 was assumed to be a 40 mm x 40 mm square plate with a thickness of 5 mm. The lower half of the acoustic path was assumed to be a cylindrical hole with a diameter of 1.1 mm and a depth of 1.0 mm. The upper half of the acoustic path was assumed to be a conical opening with a diameter D1 = 3.8 mm, a diameter D2 = 1.1 mm, and a height of 1.0 mm.

[0045] Two distances L were assumed between the transmitting element 31 and the receiving element 32: 4 mm and 10 mm. Distance L is the center-to-center distance. The frequency and wavelength of the ultrasonic waves used were the same as those described in Simulation 1. Two distances A to the slit were assumed: 2 mm and 4 mm. Two widths W of the slit were assumed: 1 mm and 2 mm. The depth D of the slit was 2 mm. The FOV was assumed to be an arc with a radius of 15 cm centered on the center of the acoustic hole, and was evaluated by the sound pressure level of the ultrasonic waves reaching each point on this arc.

[0046] First, simulation results for a case with a horn shape but without a slit as a half-wavelength shift structure are shown in Figures 31 and 32. Figure 32 is a graph of the simulation results shown in Figure 31, with the horizontal axis representing angle and the vertical axis representing sound pressure level, and directivity can be read from this graph. The display format of this graph also applies to Figures 34, 36, and 38, which will be described later. As shown at the bottom of Figure 31, the sound pressure of the ultrasonic waves received when the distance L was 4 mm was 62.5 dB. The sound pressure of the ultrasonic waves received when the distance L was 10 mm was 54.2 dB.

[0047] Next, the simulation results for the case where there is a horn shape, there is a slit as a half-wavelength shift structure, the distance to the slit A=2 mm, and the slit width W=1 mm are shown in FIGS.

[0048] Furthermore, the simulation results for the case where there is a horn shape, there is a slit as a half-wavelength shift structure, the distance to the slit A=4 mm, and the slit width W=1 mm are shown in FIGS.

[0049] Furthermore, simulation results for the case where there is a horn shape, there is a slit as a half-wavelength shift structure, the distance to the slit A=4 mm, and the slit width W=2 mm are shown in FIGS.

[0050] Table 4 shows a summary of the sound pressure values ​​detected by the receiving element 32. From these results, it can be said that even when part of the acoustic path is horn-shaped, by employing slits as a half-wavelength shift structure, it is possible to obtain the same effects as those shown in Simulations 1 to 3. In other words, it is possible to reduce direct waves, narrow the FOV, and suppress side lobes.

[0051]

[0052] Fifth Embodiment A fifth embodiment of the present invention will be described with reference to FIGS.

[0053] The slit assumed in the first to fourth embodiments is the annular slit shown in FIG. 39 . FIG. 39 does not show the ultrasonic sensor itself, but shows a model assumed for simulation. Therefore, the acoustic hole of the transmitting element is located in the center, while the receiving element is not. By examining the sound pressure level at which ultrasonic waves emitted from the transmitting element reach each location in such a model, it is possible to determine the sound pressure of the ultrasonic waves that would be received when the receiving element is located at that location. In this embodiment, the slit, i.e., the recess, is provided so as to correspond to a portion of the ring surrounding the first location, as shown in FIG. 40 . In other words, an arc-shaped slit is provided. While FIG. 40 shows a perspective view, a plan view of this would be as shown in FIG. 41 .

[0054] The following simulation was performed to investigate how the spread of ultrasonic waves differs when an annular slit is provided as shown in Figure 39 and when an arc-shaped slit is provided as shown in Figures 40 and 41.

[0055] (Simulation 5) The X, Y, and Z directions are defined as shown in Figure 40. Focus on the cross section cut on the XZ plane indicated by arrow 95 and the cross section cut on the YZ plane indicated by arrow 96. The size of the acoustic path was 1.1 mm in diameter and 1.0 mm in depth. The acoustic hole provided in the transmitting element 31 had a diameter of 1.1 mm. The ultrasonic frequency used was the same as that described above. The distance A was 4 mm. The slit width W was 1 mm. The slit depth D was 2 mm. In Figure 40, the ranges in which the arc-shaped slits were formed are, expressed in azimuth angles, from -45° to +45° and from +135° to +225°.

[0056] The simulation results are shown in Figures 42 and 43. Figure 42 shows the sound pressure level in a cross section cut along the XZ plane (hereinafter referred to as the "XZ plane FOV"), and Figure 43 shows the sound pressure level in a cross section cut along the YZ plane (hereinafter referred to as the "YZ plane FOV"). Figure 44 shows the two simulation results together on a single graph, with the horizontal axis representing the direction and the vertical axis representing the sound pressure level.

[0057] While the cross section cut in the YZ plane, i.e., arrow 96, does not intersect with the slit, the cross section cut in the XZ plane, i.e., arrow 95, does intersect with the slit, so the slit has an effect in this direction. As is clear from Figure 44, the FOV remains wide in the direction where there is no slit, but narrows in the direction where there is a slit. Specifically, the YZ plane FOV has a spread of ±80°, and the XZ plane FOV has a spread of ±40°.

[0058] In this way, by forming the slits partially, it is possible to impart the effect of FOV control by the slits only in the direction in which the slits are formed. Here, FOV control mainly means narrowing the FOV. Therefore, by forming or not forming the slits or by designing the slit shape, it is possible to intentionally control the directivity in any plane. For example, it is also possible to narrow the FOV in only one of the horizontal and vertical directions as desired.

[0059] The transmitting element 31 is preferably a micromachined ultrasonic transducer (MUT) or a micro electro mechanical systems (MEMS) speaker. By adopting this configuration, an ultrasonic sensor with wide directivity can be realized.

[0060] Preferably, a hole having a diameter of 2 mm or less is provided in the first surface 51 in the first portion, and the transmitting element is disposed so that the ultrasonic waves are emitted from the hole. By adopting this configuration, the ultrasonic waves are emitted as if from a point sound source, making it easy to control the directivity.

[0061] Sixth Embodiment An ultrasonic sensor according to a sixth embodiment of the present invention will be described with reference to Fig. 45. Fig. 45 shows a cross-sectional view of an ultrasonic sensor 106 according to this embodiment.

[0062] The ultrasonic sensor 106 has a basic configuration in common with the ultrasonic sensor 101 shown in the first embodiment. However, the ultrasonic sensor 106 has a structure other than a recess as a half-wavelength shift structure. Specifically, the ultrasonic sensor 106 has a half-wavelength shift structure 27 as shown in FIG. 45 . The half-wavelength shift structure 27 includes a convex portion that protrudes from the first surface of the housing 10. The position and shape of the convex portion shown here are merely an example and are shown schematically. The position and shape of the half-wavelength shift structure 27 are not limited to those shown here. However, the position of the side surface of the convex portion as the half-wavelength shift structure 27 that is closer to the recess 41 is set so that when ultrasonic waves are reflected by this side surface, the phase is shifted by half a wavelength.

[0063] In this embodiment, in addition to the first wave 81 that propagates as a direct wave from the transmitting element 31 to the receiving element 32, i.e., from the first location to the second location, there is also a second wave 82 that propagates from the first location to the second location after being reflected by the side surface of the convex portion serving as the half-wavelength shift structure 27. Both the first wave 81 and the second wave 82 reach the receiving element 32 in the second location, but at that point in time, the first wave 81 and the second wave 82 are out of phase with each other by a half wavelength, and therefore interfere with each other to cancel each other out.

[0064] In this embodiment, the same effects as those described in the first embodiment can be obtained.

[0065] It should be noted that a plurality of the above-described embodiments may be appropriately combined and employed. The above-described embodiments disclosed herein are illustrative in all respects and are not limiting. The scope of the present invention is defined by the claims, and includes all modifications within the meaning and scope of the claims.

[0066] (Supplementary Note 1) An ultrasonic sensor comprising: a housing having a first surface; a transmitting element held by the housing so as to be able to emit ultrasonic waves at a first portion of the first surface in a direction away from the first surface; and a receiving element held by the housing so as to be able to detect ultrasonic waves that have arrived at a second portion of the first surface, wherein the first surface has a half-wavelength shift structure between the first portion and the second portion, and the half-wavelength shift structure has a structure such that a second wave, which is a component of the ultrasonic waves emitted from the transmitting element that passes through the half-wavelength shift structure and then travels along the first surface to the receiving element, has a phase shift of half a wavelength compared to a first wave, which is a component of the ultrasonic waves emitted from the transmitting element that travels along the first surface to the receiving element.

[0067] (Supplementary Note 2) The ultrasonic sensor according to Supplementary Note 1, wherein the half-wavelength shift structure is a recess provided on the first surface.

[0068] (Supplementary Note 3) The ultrasonic sensor according to Supplementary Note 2, wherein the depth of the recess is ¼ of the wavelength of the ultrasonic wave.

[0069] (Supplementary Note 4) The ultrasonic sensor according to Supplementary Note 2 or 3, wherein a width of the recess measured along a direction connecting the first portion and the second portion is equal to or greater than 1 / 16 and less than 1 / 2 of a wavelength of the ultrasonic wave.

[0070] (Supplementary Note 5) The ultrasonic sensor according to Supplementary Note 4, wherein a width of the recess measured along a direction connecting the first portion and the second portion is equal to or greater than ⅛ and equal to or less than ⅜ of a wavelength of the ultrasonic wave.

[0071] (Supplementary Note 6) The ultrasonic sensor according to Supplementary Note 2 or 3, wherein when viewed from a direction perpendicular to the first surface, the length from the center of the transmitting element to the end of the recess closest to the center is equal to or less than ½ of the wavelength of the ultrasonic wave.

[0072] (Supplementary Note 7) The ultrasonic sensor according to any one of Supplementary Notes 2 to 6, wherein the recess is provided in an annular shape so as to surround the first portion.

[0073] (Supplementary Note 8) The ultrasonic sensor according to any one of Supplementary Notes 2 to 6, wherein the recess is provided to correspond to a part of a ring that surrounds the first portion.

[0074] (Supplementary Note 9) The ultrasonic sensor according to any one of Supplementary Notes 1 to 8, wherein the transmitting element is an MUT or a MEMS speaker.

[0075] (Supplementary Note 10) The ultrasonic sensor according to Supplementary Note 7 or 8, wherein a hole having a diameter of 2 mm or less is provided in the first surface in the first portion, and the transmitting element is positioned so that the ultrasonic wave is emitted from the hole.

[0076] 10 Housing, 11, 12 Substrate, 21, 22, 23, 26, 27 Half-wavelength shift structure, 25 Medium, 31 Transmitting element, 32 Receiving element, 41, 42 Recess, 51 First surface, 52 Second surface, 60, 61, 62 Points, 71, 72 Ultrasonic wave, 81 First wave, 82 Second wave, 91 Arrow (indicating the direction in which ultrasonic waves are emitted), 95, 96 Direction, 101, 102, 103, 104, 105, 106 Ultrasonic sensor.

Claims

1. An ultrasonic sensor comprising: a housing having a first surface; a transmitting element held by the housing so as to be able to emit ultrasonic waves at a first portion of the first surface in a direction away from the first surface; and a receiving element held by the housing so as to be able to detect the ultrasonic waves that have arrived at a second portion of the first surface, wherein the first surface has a half-wavelength shift structure between the first portion and the second portion, and the half-wavelength shift structure has a structure such that the phase of a second wave, which is a component of the ultrasonic waves emitted from the transmitting element that passes through the half-wavelength shift structure and travels along the first surface to the receiving element, is shifted by half a wavelength compared to a first wave, which is a component of the ultrasonic waves emitted from the transmitting element that travels along the first surface to the receiving element.

2. The ultrasonic sensor according to claim 1, wherein the half-wavelength shift structure is a recess provided on the first surface.

3. The ultrasonic sensor according to claim 2, wherein the depth of the recess is 1 / 4 of the wavelength of the ultrasonic wave.

4. An ultrasonic sensor as described in claim 2 or 3, wherein the width of the recess measured along the direction connecting the first portion and the second portion is greater than or equal to 1 / 16 and less than 1 / 2 of the wavelength of the ultrasonic wave.

5. An ultrasonic sensor as described in claim 4, wherein the width of the recess measured along the direction connecting the first portion and the second portion is greater than or equal to 1 / 8 and less than or equal to 3 / 8 of the wavelength of the ultrasonic wave.

6. An ultrasonic sensor as described in claim 2 or 3, wherein when viewed from a direction perpendicular to the first surface, the length from the center of the transmitting element to the end of the recess closest to the center is less than half the wavelength of the ultrasonic wave.

7. The ultrasonic sensor according to any one of claims 2 to 6, wherein the recess is provided in an annular shape so as to surround the first portion.

8. The ultrasonic sensor according to any one of claims 2 to 6, wherein the recess is provided to correspond to a part of a ring surrounding the first portion.

9. The ultrasonic sensor according to any one of claims 1 to 8, wherein the transmitting element is an MUT or MEMS speaker.

10. An ultrasonic sensor as described in claim 7 or 8, wherein a hole having a diameter of 2 mm or less is provided in the first surface at the first portion, and the transmitting element is positioned so that the ultrasonic wave is emitted from the hole.

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