Ultrasonic transceiver

Abstract

To provide an aerial ultrasonic transceiver capable of solving a problem of insufficient sound pressure due to poor vibration efficiency of an inner bottom surface of a bottomed cylindrical case when a resonance frequency and a drive frequency are different from each other in an ultrasonic sensor.SOLUTION: In an aerial ultrasonic transceiver, when a short axis length in a region of a portion vibrated by a driving of a piezoelectric element is A and a long axis length is B, and the short axis length of the piezoelectric element is A'; and the long axis length is B';, A' / A is 0.55 to 0.95 and B' / B is 0.55 to 0.95, it is possible to reduce an inhibition of vibration due to a rigidity of the piezoelectric element and efficiently vibrate a bottom surface of a bottomed cylindrical case even when a resonance frequency and a driving frequency are distant from each other. As a result, even when the resonance frequency and the drive frequency are separated from each other, it is possible to design an ultrasonic sensor in which a sound pressure and a wide band are compatible with each other such that the sound pressure is 100 dB or more and a band is from 4.8 kHz to 13.2 kHz.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an ultrasonic sensor for use in the air, in which a piezoelectric element is attached to a cylindrical case with a bottom. [Background technology]

[0002] 2. Description of the Related Art A safety device that is attached to a vehicle and that warns the driver of the risk of collision when the vehicle approaches an object 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 terminals electrically connected to each electrode of the piezoelectric element are taken out to the outside. The piezoelectric element is covered with a sponge-like or felt-like sound-absorbing material and then sealed with an elastic filler such as silicone rubber. The back of the open side of the bottomed cylindrical case is completely covered with a filler such as silicone rubber, preventing liquid from seeping inside. FIG. 6 shows a cylindrical case (8) with a bottom and a piezoelectric element (6c) in a conventional ultrasonic sensor, and FIG. 7 shows a structural diagram. The ultrasonic sensor is configured such that a piezoelectric element (6c) is adhered to the inner bottom surface of a cylindrical case (8) made of an aluminum alloy, and molded foamed silicone (7) is placed on top of that, and lead wires (9a) and (9b) are electrically connected by soldering to each electrode of the piezoelectric element (6c) and each terminal of the pin terminals (10a) and (10b), and the opening side inside the cylindrical case (8) is sealed by filling it with an elastic body (11) made of non-porous silicone resin. Due to the above-mentioned structure, the electrodes of the piezoelectric element inside the ultrasonic sensor do not short-circuit with each other, so the sensor can be used outdoors where it may be exposed to liquids. Furthermore, a waterproof ultrasonic sensor has a piezoelectric element covered by a metal case, and therefore has a relatively strong structure.

[0005] The drive frequency of ultrasonic sensors mounted on vehicles is generally fixed. When the resonant frequency of an ultrasonic sensor, which is derived from the shape of its housing, matches the drive frequency input from an external source, Although the device is designed to emit sound waves efficiently, if the resonant frequency deviates due to manufacturing variations in the product, the difference with the drive frequency may become large, causing sound waves to be emitted less efficiently and resulting in a decrease in sound pressure. If the resonant frequency of an ultrasonic sensor can be made wider, it will be possible to ensure a constant output regardless of the resonant frequency, and it will also be possible to use it in applications where multiple drive frequencies are used. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent Publication No. 2007-112297 [Patent Document 2] Patent Publication No. 2010-154059 [Patent Document 3] Patent Publication No. 2021-072589 Summary of the Invention [Problem to be solved by the invention]

[0007] Conventional ultrasonic sensors have a resonant frequency due to the shape of the housing, and if there is a difference between this resonant frequency and the drive frequency, the vibration efficiency decreases, preventing the sound waves from reaching farther and making it impossible to detect objects.There are also ultrasonic sensors that operate at a drive frequency that is different from the resonant frequency by suppressing the vibration efficiency of the sensor (for example, Patent Document 3), but this has the problem of not being able to detect distant objects because the sound pressure is low and the sound waves can only reach a short distance. [Means for solving the problem]

[0008] The resonant frequency of an ultrasonic sensor is generally determined by the shape of the housing, because the shape of the housing determines the distance between vibration nodes, which in turn determines a single wavelength and resonant frequency. When the resonant frequency and the drive frequency are close and vibration is efficient, the vibration mode of the vibration surface has a mountain-shaped profile.In contrast, when the resonant frequency and the drive frequency are far apart, the force that deforms the vibration surface is weak, and the rigidity of the piezoelectric element causes the vibration mode profile around the element to become nearly flat, and the amplitude is smaller than when the resonant frequency and the drive frequency are the same, so it does not function satisfactorily as an ultrasonic sensor. In this invention, if the minor axis length of the bottomed cylindrical case in the area where it vibrates when driven by the piezoelectric element is A and the major axis length is B, and the minor axis length of the piezoelectric element is A' and the major axis length is B', by adjusting the shape of the housing and the piezoelectric element so that A' / A is 0.55 to 0.95 and B' / B is 0.55 to 0.95, it is possible to reduce the inhibition of vibration due to the rigidity of the piezoelectric element even when the resonant frequency and the drive frequency are far apart, thereby enabling efficient vibration by approaching the vibration mode in the area where resonance is most likely to occur.This results in an ultrasonic sensor that can vibrate efficiently over a wide frequency range. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram showing a bottomed cylindrical case and a piezoelectric element in an embodiment of an ultrasonic sensor according to claim 1 of the present invention. [Figure 2] 1 is a cross-sectional view of an ultrasonic sensor according to an embodiment of the ultrasonic sensor of claim 1 of the present invention. [Figure 3] Graph of sound pressure versus difference between resonance frequency and drive frequency for the product of the present invention and a conventional product (normalized by maximum sound pressure) [Figure 4] Vibration mode seen in the longitudinal cross section of a cylindrical case with a bottom when the resonance frequency and driving frequency are the same [Figure 5] Vibration mode seen in the longitudinal cross section of a cylindrical case with a bottom when the resonant frequency and driving frequency do not match [Figure 6] A diagram showing a conventional ultrasonic sensor with a closed-end cylindrical case and a piezoelectric element. [Figure 7] Cross-section of a conventional ultrasonic sensor [Figure 8] FIG. 1 is a diagram showing the relationship between A' / A and B' / B and the sound pressure band in an ultrasonic sensor according to an embodiment of the present invention. [Figure 9] FIG. 1 is a diagram showing the relationship between A' / A and B' / B and sound pressure in an ultrasonic sensor according to an embodiment of the present invention. [Figure 10] FIG. 10 is a diagram showing a bottomed cylindrical case and a piezoelectric element in another embodiment of the ultrasonic sensor according to claim 1 of the present invention. [Figure 11] FIG. 1 is a diagram showing the relationship between A' / A, B' / B and sound pressure in another embodiment of the ultrasonic sensor according to claim 1 of the present invention. [Figure 12] FIG. 1 is a diagram showing the relationship between A' / A, B' / B, and the band in another embodiment of the ultrasonic sensor according to claim 1 of the present invention. DETAILED DESCRIPTION OF THE INVENTION Embodiments relating to claim 1 of the present invention

[0010] Fig. 1 is a diagram showing a bottomed cylindrical case and a piezoelectric element in an embodiment of an ultrasonic sensor according to claim 1 of the present invention. Fig. 2 is a structural diagram of the embodiment of the ultrasonic sensor according to claim 1 of the present invention. The ultrasonic sensor is configured such that a piezoelectric element (6a) is bonded to the inner bottom surface of a bottomed cylindrical case (8) made of an aluminum alloy, and molded foamed silicone (7) is placed on top of that. Lead wires (9a) and (9b) are electrically connected by soldering to the electrodes of the piezoelectric element (6) and the terminals of pin terminals (10a) and (10b), and the opening inside the bottomed cylindrical case (8) is sealed by filling it with an elastic body (11) made of non-porous silicone resin. FIG. 3 is a graph showing the sound pressure versus the difference between the resonance frequency and the drive frequency of an ultrasonic sensor according to an embodiment of the present invention. FIG. 8 shows the relationship between the bandwidth and A' / A and B' / B in an embodiment related to claim 1 of the present invention, where the minor axis length of the area of ​​the bottomed cylindrical case of the ultrasonic sensor that vibrates when driven by the piezoelectric element is A and the major axis length is B, and the minor axis length of the piezoelectric element is A' and the major axis length is B'. At this time, the vibration mode of the bottom of the cylindrical case and the piezoelectric element are similar, and when A' / A is 0.92 and B' / B is 0.92, the maximum sound pressure is 105.6dB and the bandwidth at half the maximum sound pressure (-6dB) is 8.4kHz, achieving the widest bandwidth while maintaining the same level of sound pressure as conventional products. In Figure 3, the case where the resonance frequency and drive frequency are the same is set to 0, and the drive frequency is changed in 2kHz increments, and the sound pressure is shown when the frequency is separated by 6kHz on both the positive and negative sides. This shows that when the resonance frequency and drive frequency are the same, the sound pressure is about the same as that of the conventional product. Also, when looking at the half-value maximum sound pressure of -6 dB, the sound pressure of the conventional product is about 1 kHz, while that of the product of the present invention is about 8.4 kHz as shown above, which means the band is more than eight times wider. FIG. 4 shows vibration modes based on simulation results when the resonance frequency and the drive frequency of the ultrasonic sensor according to the embodiment of the present invention and a conventional ultrasonic sensor are the same. FIG. 5 shows vibration modes based on simulation results when the resonance frequency and the drive frequency are 6 kHz apart in the ultrasonic sensor according to the embodiment related to claim 1 of the present invention and in a conventional ultrasonic sensor. In both Figures 4 and 5, the vertical axis represents the normalized maximum amplitude when the resonance frequency and drive frequency are the same, and the horizontal axis represents the position of the vibration plane with the center of the long axis of the bottom of the cylindrical case as 0. As shown in Figure 4, when the resonance frequency and drive frequency are the same, the conventional product and the product of the invention show similar vibration profiles, but when the resonance frequency and drive frequency are 6 kHz apart as shown in Figure 5, in the conventional product, the force that deforms the vibration surface is weak and the vibration mode profile around the element is nearly flat due to the rigidity of the piezoelectric element, whereas in the ultrasonic sensor related to the embodiment of the present invention, by optimizing A' / A and B' / B, the force that vibrates the vibration surface is stronger relative to the rigidity of the piezoelectric element, and as a result the amplitude of the vibration surface increases and approaches a mountain-shaped vibration mode as shown in Figure 4, thereby improving vibration efficiency. Further, in relation to the above content, Figure 8 shows the relationship between A' / A and B' / B, sound pressure, and bandwidth in the ultrasonic sensor of the embodiment related to claim 1. From this result, it can be seen that there is a bandwidth of at least 4 kHz and at most 13 kHz. These results show that the bandwidth is at least 4 kHz and at most 13 kHz, which is a significant improvement over the 1 kHz bandwidth of the previous model mentioned above. 9 shows the relationship between A' / A and B' / B and sound pressure in an ultrasonic sensor according to an embodiment of the present invention related to claim 1. Considering that an ultrasonic sensor needs about 100 dB to detect an object within 1 m, when A' / A is between 0.55 and 0.95 and B' / B is between 0.55 and 0.95, the sound pressure will be 100 dB or more and the bandwidth will be 4.8 kHz to 13.2 kHz, making it possible to design an ultrasonic sensor that achieves both high sound pressure and a wide bandwidth. FIG. 10 is a diagram showing a bottomed cylindrical case and a piezoelectric element (6b) in another embodiment of the ultrasonic sensor according to claim 1 of the present invention. Fig. 11 shows the relationship between the band and A' / A and B' / B in another embodiment related to claim 1 of the present invention. Fig. 12 shows the relationship between the sound pressure and A' / A and B' / B in another embodiment related to claim 1 of the present invention. As shown in Figures 11 and 12, even if the shape of the piezoelectric element (6b) attached to the inner bottom surface of the bottomed cylindrical case is polygonal, by optimizing A' / A and B' / B, it is possible to design an ultrasonic sensor that vibrates efficiently and emits sound waves over a wide frequency range as described above. In this example, when the shape of the piezoelectric element (6b) is rectangular, A' / A is 0.72, and B' / B is 0.76, the maximum sound pressure is 104.5 dB and the bandwidth at half the maximum sound pressure of -6 dB is 8.5 kHz. [Industrial Applicability]

[0011] 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]

[0012] 1 Case minor axis length 2 Case major axis length 3. Piezoelectric element minor axis width 4. Piezoelectric element major axis width 5 Inside the bottom of the cylindrical case 6a Piezoelectric element in an embodiment of an ultrasonic sensor according to claim 1 of the present invention 6b Piezoelectric element in another embodiment of the ultrasonic sensor according to claim 1 of the present invention 6c Piezoelectric element in an embodiment of a conventional ultrasonic sensor 7. Silicone foam 8. Cylindrical case with bottom 9a lead wire 9b lead wire 10a pin terminal 10b pin terminal 11 Elastic body made of non-porous silicone resin

Claims

[Claim 1] In an ultrasonic transmitter / receiver for airborne use, a unimorph vibrator having a piezoelectric element bonded to the inner bottom surface of a cylindrical case with a bottom is provided, and ultrasonic waves are transmitted and received by the vibration of the unimorph vibrator, wherein, as shown in Figure 1, the minor axis length of the area vibrating when driven by the piezoelectric element is A, the major axis length is B, and the minor axis length of the piezoelectric element is A', the major axis length is B', and the A' / A is 0.55 to 0.95 and B' / B is 0.55 to 0.95.

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