Ultrasonic transceiver

Abstract

To provide an ultrasonic sensor for suppressing the radiation of an unintended beam called a side lobe while maintaining a beam pattern in a vertical direction narrow.SOLUTION: The ultrasonic wave transmitter-receiver is structured such that a thick part with a projection 12 and a thin part are provided to a center of a bottom face of a bottomed cylindrical case and a slit 11 whose width is 80-90% of a distance between the thick parts is provided to the thin part of the bottomed cylindrical case. Thus, the rigidity of the node of the vibration is increased, the vibration of the reverse phase near the node of the vibration can be reduced, and the generation of the side lobe is suppressed.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to an ultrasonic sensor for air (hereinafter, an airborne ultrasonic transducer will be referred to as an ultrasonic sensor) in which a piezoelectric element (2) is attached to a cylindrical case (1) with a bottom. [Background technology]

[0002] 2. Description of the Related Art A safety device in which a distance meter unit using an ultrasonic sensor is attached to a vehicle and which warns the driver of the risk of a collision when an object approaches the vehicle is widely used. In particular, a safety device that uses a distance meter unit to detect an object behind the vehicle when the vehicle is backing up and notifies the driver of the approaching object is often used (for example, Patent Document 1).

[0003] Specifically, safety devices have been invented that alert the driver with a buzzer when an object is approaching, and brake-linked safety devices that activate the brakes to prevent the vehicle from moving when there is an obstacle in front of the vehicle.

[0004] In the range finder unit using an ultrasonic sensor used here, a waterproof ultrasonic sensor is mainly used. A waterproof ultrasonic sensor is introduced in, for example, Patent Document 2. (In the document, the waterproof ultrasonic sensor is called a waterproof ultrasonic transmitter / receiver.) A waterproof ultrasonic sensor has a piezoelectric element with electrodes on both sides attached to the bottom of a cylindrical case with a bottom and an opening on the side, and terminals electrically connected to each electrode of the piezoelectric element are taken out to the outside. The top of the piezoelectric element is covered with a sponge-like or felt-like sound-absorbing material, which is then sealed with an elastic filler such as silicone rubber. There are also structures in which a foam material is used on the top of the element instead of a sponge-like or felt-like sound-absorbing material (for example, Patent Document 3). In addition, the openings on the side of the cylindrical case and the back of the opening side of the cylindrical case are completely covered with a filler such as silicone rubber, preventing liquid from seeping inside. Because of this structure, the electrodes of the piezoelectric element inside the ultrasonic sensor do not short-circuit, so it can be used outdoors where it may be exposed to liquid. Furthermore, a waterproof ultrasonic sensor has a piezoelectric element covered by a metal case, and therefore has a relatively strong structure.

[0005] The beam pattern of an ultrasonic sensor mounted on a vehicle is generally designed to be wide in the horizontal direction and narrow in the vertical direction so as not to detect the road surface. It is easy to narrow the vertical beam pattern, but narrowing it also results in unintended beams called side lobes being emitted in directions other than the radiation direction. These side lobes can lead to abnormal detection, so it is desirable to reduce them. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent Publication No. 2007-112297 [Patent Document 2] Patent Publication No. 2009-112248 [Patent Document 3] Patent Publication No. 2021-072589 Summary of the Invention [Problem to be solved by the invention]

[0007] In conventional ultrasonic sensors, when an attempt is made to narrow the beam pattern in the vertical direction, a trade-off occurs, which is the generation of side lobes in directions other than the radiation direction. This side lobe tends to become larger when the vertical beam pattern is narrowed, In order to design a system that suppresses side lobes, the vertical beam pattern could not be narrowed beyond a certain point. [Means for solving the problem]

[0008] A conventional ultrasonic sensor is composed of a cylindrical case with a bottom, a piezoelectric element, a sound absorbing material, a terminal, and a sealing material. The ultrasonic sensor of the present invention has the same basic structure as conventional ultrasonic sensors, but the shape of the bottomed cylindrical case is different from that of conventional sensors, with a slit opening on the vibrating surface side of the thin-walled section, and the width of this slit is arranged to be 80% or more but less than 90% of the distance A between the thick-walled sections, and a convex section is provided in the center of the thick-walled section of the bottomed cylindrical case. Generally, ultrasonic sensors have a part that vibrates directly due to an element called the vibration surface, a part that does not vibrate such as a side wall, and a joint part (10) that connects the vibrating part and the non-vibrating part. If the joint part (10) has high rigidity, only the vibration surface vibrates, and no side lobes are generated, but if the joint part (10) has low rigidity, the vibration surface and the joint part (10) vibrate together, generating small anti-phase vibrations near the fulcrum, which become side lobes. If the width of the slit portion of the bottomed cylindrical case is widened, the rigidity of the joint portion (10) around the slit portion decreases, making it more likely for side lobes to occur. In this invention, in order to narrow the beam pattern in the vertical direction while suppressing the occurrence of side lobes, the width of the slit portion is limited to 80% or more and less than 90% of the distance A between the thick portions, and at the same time, by providing a highly rigid convex portion in the center of the thick portion, the areas with high vibrations within the entire vibrating surface are concentrated in the center, suppressing vibrations in the joint portion (10) around the slit portion. As a result, it has become possible to manufacture a microphone with a narrow vertical beam pattern and suppressed side lobe occurrence. [Effects of the Invention]

[0009] The present invention makes it possible to fabricate an ultrasonic sensor that maintains a narrow beam pattern in the vertical direction while suppressing the emission of unintended beams known as side lobes. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a cross-sectional view of an ultrasonic sensor according to an embodiment of the present invention; [Figure 2] Cross-section of a conventional ultrasonic sensor [Figure 3] 1 is a top view of a cylindrical case with a bottom according to an embodiment of the present invention; [Figure 4] 1 is a diagram showing a bottomed cylindrical case according to an embodiment of the present invention, viewed from an oblique direction; [Figure 5] A graph of the vertical beam pattern when the slit width (13) is 85% in an embodiment of the present invention. [Figure 6] Vertical beam pattern graph when slit width (13) is 70% [Figure 7] Vertical beam pattern graph when slit width (13) is 95% [Figure 8] Vibration contours calculated by simulation in the case where a convex portion is present and the slit width (13) is 85% in the embodiment of the present invention. [Figure 9] Vibration contours calculated by simulation when there is no protrusion and the slit width (13) is 85% [Figure 10] Side lobe level when changing the slit width (13) [Figure 11] Vertical angle when changing slit width (13) [Figure 12] A cross-sectional view of the vibration surface when there is a convex portion and the slit width (13) is 85% in an embodiment of the present invention. [Figure 13] Cross section of the vibration surface when there is no protrusion and the slit width (13) is 85% Embodiments relating to claim 1 of the present invention

[0011] 1 is an example of a structural diagram of an ultrasonic sensor according to an embodiment of the present invention. The ultrasonic sensor is configured such that a piezoelectric element (2) including a PZT ceramic and a folded electrode is bonded to the inner bottom surface of a cylindrical case (4) with a bottom made of an aluminum alloy. A molded sponge or foamed silicone (5) is placed on top of the piezoelectric element (2), and lead wires (6a) and (6b) are electrically connected by soldering to the electrodes of the piezoelectric element (2) and the pin terminals (7a) and (7b). The opening inside the cylindrical case with a bottom is sealed by filling it with an elastic body (8) made of silicone resin. The cylindrical case with a bottom has the structure shown in Figs. 3 and 4, with a slit (11) formed by opening a part of the thin wall, and a protrusion (12) provided in the center of the thick wall. The shape of the protrusion (12) is not particularly limited, but in the embodiment relating to claim 1, it is semicircular. The slit width of the bottomed cylindrical case is 85% of the thickness-to-wall distance A so as to be 80% or more and less than 90%. Figure 2 shows the structure of a conventional ultrasonic sensor. The conventional structure is the same as the conventional one except that it does not have the convex portion (12) and the slit portion (11). FIG. 10 shows a graph showing the relationship between the side lobe level and the slit width (13). The side lobe level on the vertical axis is the difference between the sound pressure value at the angle of 90°, which is the center of the graph shown in FIG. 5, and the value at the maximum point of the side lobe. It has been confirmed that when the slit width (13) is large, the side lobes tend to expand, and when there is a convex portion (12), the overall side lobe level is lowered. FIG. 11 shows a graph showing the relationship between the vertical angle and the slit width (13). The vertical angle on the vertical axis is the range of angles at which the sound pressure is -6 dB relative to the central angle at which the sound pressure is at its maximum in Figure 5, and the vertical angle tends to narrow as the slit width (13) increases. FIG. 5 compares an embodiment according to claim 1 of the present invention in which the slit width (13) is 85% and there is a convex portion in the center of the thick portion with an embodiment in which the slit width (13) is 85% and there is no convex portion (12) in the center of the thick portion. It is confirmed that the presence of the convex portion (12) narrows the entire vertical angle in the range of angles from 50° to 130°. FIG. 6 shows a comparison between the case where the slit width (13) is 70% and there is a convex part in the center of the thick part and the case where there is no convex part. Similarly, it is confirmed that when the convex portion (12) is present, the entire vertical angle is narrowed in the angle range of 50° to 130°. FIG. 7 shows a comparison between the case where the slit width (13) is 95% and there is a convex part in the center of the thick part and the case where there is no convex part. Similarly, it is confirmed that when the convex portion (12) is present, the entire vertical angle is narrowed in the angle range of 70° to 110°. Figure 8 shows the amplitude contours calculated by computer simulation when the slit width (13) of an embodiment related to claim 1 of the present invention is 85% and there is a convex portion in the center of the thick portion. The black dot in the center is the point of maximum amplitude. Figure 9 shows the amplitude contours calculated by computer simulation when the slit width (13) is 85% and there is no convex portion in the center of the thick portion. Comparing Figures 8 and 9, it can be seen that Figure 9 vibrates in an elliptical shape. The slit section (16) in Figure 9 is an open section and can vibrate freely, but the straight section (14) and the R-corner (15) on the side wall have high rigidity, creating vibration nodes. As a result, the vibrations occur in an elliptical shape along the straight section (14) and the R-corner (15). The slit section (16) in Figure 8 is also an open section and can vibrate freely, but the straight section (14), the R-corner (15), and the convex section (17) on the side wall have high rigidity, creating vibration nodes. In this case, the straight section (14) is located further back than the R-corner (15) and the convex section (17), so the amplitude of this section is smaller than the locations near the R-corner (15) and the convex section (17). Therefore, the actual vibration nodes vibrate on a plane along the straight line connecting the R-corner (15) and the convex section (17). The results of the computer simulations in Figures 8 and 9 show that the presence or absence of the convex portion (17) significantly changes the shape of the vibration contour line, and is therefore effective. Figures 12 and 13 are cross-sectional views of Figures 8 and 9. Figure 12 is a cross-sectional view of the vibration plane when the slit width (13) is 85% and there is a convex portion in the center of the thick portion. It can be seen from the figure that the vibration plane vibrates in parallel. Figure 13 is a cross-sectional view of the vibration plane when the slit width (13) is 85% and there is no convex portion in the center of the thick portion. In this case, the vibration plane is not parallel, and the vibration plane becomes V-shaped. At this time, an anti-phase generation point (18) that forms an inverted V also occurs, and a side lobe is emitted from this point. In the case of Figure 12, it can be seen that the inverted V-shaped portion is small and the side lobe emission is also small. [Industrial Applicability]

[0012] The present invention can be applied not only to back sensors and corner sensors for vehicles and automatic parking systems, but also to various fields in which ultrasonic sensors are used. [Explanation of symbols]

[0013] 1 Inside the bottom of the cylindrical case 2 Piezoelectric element 4 Side wall of bottomed cylindrical case 5 Elastic Body 6 lead wires 7 terminals 8. Encapsulating material 9 Inside the bottom of the cylindrical case 10. Relief Section 11 Slit section 12. A protrusion disposed on the thick portion of the bottomed cylindrical case 13 Slit width 14 Straight section of side wall 15 Side wall corner R 16 Slit section 17 Convex part in the center of the thick part 18 Location of out-of-phase

Claims

[Claim 1] An ultrasonic transmitter / receiver for air, which has a piezoelectric element attached to the inside of the bottom surface of a cylindrical case with a bottom, to form a unimorph vibrator, and which transmits and receives ultrasonic waves by the vibration of the unimorph vibrator, characterized in that the bottom surface of the cylindrical case is provided with a thick-walled portion that is linear and has a convex portion in the center, and an arc-shaped thin-walled portion, and also has a slit portion that opens to the bottom side of the thin-walled portion of the cylindrical case with a length that is 80% or more and less than 90% of the distance A between the thick-walled portions.

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