JP2004032499A - Ultrasonic sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonic sensor for efficiently transmitting and receiving ultrasonic waves. <P>SOLUTION: The ultrasonic sensor 1 comprises a case 2 having an opening at a part that opposes a sound source; a plate 3 that is arranged at the opening of the case 2 and has a pattern where light is alternately transmitted or is not transmitted in a plurality of annular regions formed by a plurality of concentric circles; and a horn 4 that is arranged inside the case 2 while a reciving surface is made to face the opening and receives ultrasonic waves from the sound source. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an ultrasonic sensor that can use ultrasonic waves in transmission and reception.
[0002]
[Prior art]
Conventionally, ultrasonic waves have been used in various applications. For example, it is used as a signal transmitting means in a fish finder, an anti-collision sensor of a car, a remote controller for cutting or home electric appliances, and the like. Recently, it has been proposed to use ultrasonic waves as power transmission means in, for example, a cardiac pacemaker.
[0003]
Ultrasonic waves as signal transmission means were sufficient to use even weak signals with low sound pressure if the sensor could receive signals with a good S / N ratio, but recently the range of use as signal transmission means has expanded. In addition, it is desired to transmit and receive an ultrasonic signal to and from a farther object. The transmission and reception of the ultrasonic signal to and from the object at a farther distance can be dealt with by increasing the sound pressure of the ultrasonic signal transmitted from the transducer.
[0004]
[Problems to be solved by the invention]
However, in the case of a small ultrasonic sensor used for a remote controller of a home appliance, for example, due to external restrictions such as size, a small power supply must be used as a driving source, and as a result, an ultrasonic wave that can be transmitted is transmitted. Sound pressure is limited. Therefore, an ultrasonic sensor capable of receiving ultrasonic waves more efficiently is desired.
Similarly, also when using ultrasonic waves as power transmission means, it is possible to transmit a large amount of electric power if ultrasonic waves having a high sound pressure can be transmitted and received. In particular, a heart pacemaker or the like is desirably small in nature, and therefore, an ultrasonic sensor capable of efficiently receiving ultrasonic waves is desired.
[0005]
Conventionally, in order to receive ultrasonic waves efficiently, attention has been paid to horns that increase the directivity of ultrasonic waves generated by vibrators, and the sensitivity of ultrasonic sensors is improved by increasing the processing accuracy of the horn. Was. However, when the ultrasonic sensor is small, it is difficult to accurately process a horn made of a metal material in accordance with the frequency of the ultrasonic wave to be received. Further, in order to produce a precise horn, it is necessary to improve the processing accuracy, which increases the production cost. Further, even if a horn manufactured with high accuracy is used, it is difficult to obtain a sufficient sound pressure when the horn is miniaturized, and it is hard to say that the effect is large.
Then, this invention is made in order to solve the above-mentioned subject, and an object of this invention is to provide the ultrasonic sensor which can receive an ultrasonic wave efficiently.
[0006]
[Means for Solving the Problems]
In order to solve the above-described problem, an ultrasonic sensor according to the present invention includes a plate having an opening, and a receiving unit having a receiving surface facing the opening, and the opening includes the receiving unit. It is characterized by being substantially the same shape as the part. According to this ultrasonic sensor, when the size of the opening is large enough to cause diffraction of the ultrasonic wave passing through the opening, the ultrasonic wave incident from the sound source into the case is diffracted when passing through the plate. , And reinforce each other where the phases match. In addition, the substantially same shape means that the opening and the receiving surface have the same shape and the same area, of course, the latter is larger than the former, and the former is included in the latter when the former is projected on the latter. Including.
[0007]
In addition, an ultrasonic sensor according to the present invention includes a plate having an opening, and a receiving unit having a receiving surface facing the opening, and the plate has an annular shape that transmits ultrasonic waves through the opening. It is characterized in that the region and the annular region that does not transmit light have a pattern formed concentrically and alternately. According to this ultrasonic sensor, the ultrasonic wave incident from the sound source into the case causes interference by diffraction when passing through the pattern formed in the opening of the plate.
[0008]
In the above ultrasonic sensor, the receiving surface may be substantially circular in plan view. According to this ultrasonic sensor, it is possible to efficiently receive an ultrasonic wave that has interfered due to diffraction.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
[First Embodiment]
Hereinafter, a first embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a sectional view of the ultrasonic sensor according to the first embodiment, and FIG. 2 is a front view of a plate used in the ultrasonic sensor.
An ultrasonic sensor generally denoted by reference numeral 1 has a case 2 having a cylindrical shape with an open bottom surface, a plate 3 disposed in an opening of the case 2, and a substantially central portion of another bottom surface in the case 2. And a sensor section 4 disposed in the first section. The sensor portion 4 has a piezoelectric plate 6 supported on a base (not shown) via a metal plate 5, and a conical shape with an open bottom surface. A horn 7 whose open bottom surface functions as a receiving unit facing the plate 3, one end is connected to the piezoelectric plate 6, and the other end is connected to an input / output terminal 8 led out of the case 2 to the outside of the case 2. And a cable 11 having one end connected to the metal plate 5 and the other end connected to an input / output terminal 10 extending from the inside of the case 2 to the outside of the case 2.
[0010]
The plate 3 is made of, for example, aluminum, titanium, or the like. As shown in FIG. 2, a concentric pattern including an annular region that transmits ultrasonic waves and an annular region that does not transmit ultrasonic waves is formed, and the case 3 is formed by support rods 12a and 12b. 2 is provided in the opening. In the ultrasonic sensor 1 having such a plate 3, when an ultrasonic wave is incident on the plate 3 from a sound source, the ultrasonic wave is caused to interfere by the plate 3, and the portions having the same phase strengthen each other, and as a result, Increase the sound pressure of the incident ultrasonic waves. The ultrasonic wave whose sound pressure has been increased reaches the receiving surface of the horn 7 and causes the horn 7 to resonate. The horn 7 is formed in advance in correspondence with the frequency of the ultrasonic wave to be received, and thereby efficiently converts acoustic energy (ultrasonic energy) into vibration. The vibration of the horn 7 causes a mechanical effect on the piezoelectric plate 6 to cause a piezoelectric effect. As a result, a potential difference is generated between the piezoelectric plate 6 and the metal plate 5, and electric energy is generated. This electric energy is led out of the ultrasonic sensor 1 by the cables 9 and 11 and the input / output terminals 8 and 10 and used according to the application.
The receiving surface of the horn 7 refers to the surface of the horn 7 that faces the plate 3 (the inner surface of the cone).
In the present embodiment, the shape of the case 2 described as a cylinder is not limited to a cylinder as long as the case 2 supports the plate 3, and further, the side wall does not necessarily have to be closed. .
[0011]
Pattern plate 3, k arbitrary natural number, lambda and when the wavelength of the ultrasonic wave, the inner diameter or outer diameter R _N of the radius that is, each pattern of each concentric can be set by the equation (1).
R _N = {λ × n / (2 × k)} ^1/2 (1)
The radius of the concentric circles forming the pattern of the plate 3 is m (0, 1, 2,...) From the center of the concentric circles (the center of the concentric circles is 0). ) To (4). In other words, when a concentric pattern in which the central portion is a pattern remaining portion as shown in FIG. 2 is formed, the inner diameter of the pattern remaining portion is obtained by substituting n calculated by Expression (2) into Expression (1). , The outer diameter is obtained by substituting n calculated by equation (3) into equation (1). Also, the inner diameter of the pattern-extracted portion is obtained by substituting n calculated by equation (3) into equation (1), and the outer diameter is obtained by substituting n calculated by equation (4) into equation (1). Ask.
n = 2 × m (2)
n = 2 × m + 1 (3)
n = 2 × m + 2 (4)
[0012]
Further, as shown in FIG. 3, the pattern of the plate 3 may be the same as that of FIG. In this case, the inner diameter of the pattern-extracted portion is obtained by substituting n calculated by equation (2) into equation (1), and the outer diameter is obtained by substituting n calculated by equation (3) into equation (1). Ask by The inner diameter of the remaining portion of the pattern is obtained by substituting n calculated by equation (3) into equation (1), and the outer diameter is obtained by substituting n calculated by equation (4) into equation (1). Can be.
Even in this manner, a concentric pattern of the plate 3 is formed.
[0013]
In the present embodiment, the reason why the pattern of the plate 3 is set as in the equations (1) to (4) will be described below.
Generally, the radius R _N of the Fresnel zone plate is represented by the formula (5) shown below.
R _N = {λ × n × r ₁ × r ₂ / (r ₁ + r ₂ )} ^1/2 (5)
The wavelength of the equation radius R _N of the Fresnel zone plate of formula (5), the sound that has been diffracted gap constructively interfere, i.e. converge to a point (reach) when sound in phase And the distance from the sound source to one point. At this time, r ₁ and r ₂ represent distances from the sound source. In equation (5), it is assumed that two sound sources pass through the slit. However, in the case of the present embodiment, since it is considered that the sound source is a single sound source, r ₁ = r ₂ = r. Therefore, equation (5) becomes as shown in equation (6).
R _N = (λ × n × r / 2) ^1/2 (6)
Here, since the distance between the sound source and the ultrasonic sensor depends on the use environment, the positional relationship between the sound source and the ultrasonic sensor, the outer shape of the case 2, and the like, r cannot be uniquely determined. Therefore, in the present embodiment, the adjustment parameter k is used, and 1 / k is substituted for r. Substituting r = 1 / k into equation (6) yields equation (1).
[0014]
Here, the adjustment parameter k is set in consideration of the outer shape of the case 2, the area of the opening of the plate 3, the number of concentric circles of the pattern formed on the plate 3, and the like. At this time, the number of concentric patterns formed on the plate 3 is determined in consideration of the balance between the opening area of the plate 3, the area of the pattern-extracted portion of the plate 3, and the interval at which ultrasonic waves are diffracted. 2 is set so that it can sufficiently enter the inside.
[0015]
When concentric patterns having different radii R as shown in FIG. 2 or FIG. 3 are placed on the front surface of the sensor section 4, ultrasonic waves passing through a plurality of concentric slits cause interference by diffraction, and the horn 7 may receive the ultrasonic waves. The available sound pressure increases. This is shown in FIG. FIG. 4 is a diagram showing a sound pressure distribution in the horn 7 when Fresnel diffraction occurs. In FIG. 4, the dotted line is the average sound pressure without the plate 3. When the plate 3 is disposed in the opening of the case 2, when the distance between the plate 3 and the horn 7 is short, the ultrasonic wave passing through the plate 3 causes interference by Fresnel diffraction, and the edge of the pattern of the plate 3 in the horn 7. The sound pressure received by the part facing the part increases.
[0016]
It goes without saying that the interval between the plate 3 and the horn 7 when the interference due to Fresnel diffraction occurs can be calculated from the distance from the sound source to the ultrasonic sensor 1 and the frequency of the ultrasonic wave by the Fresnel diffraction equation. . For example, when the distance from the sound source to the ultrasonic sensor 1 is 1 m and the frequency of the ultrasonic wave is 25 kHz, the distance between the plate 3 and the horn 7 is 7.4 mm.
[0017]
As described above, the ultrasonic sensor 1 converts ultrasonic energy into electrical energy by causing the horn 7 to resonate with ultrasonic waves. Therefore, what is important for the ultrasonic sensor 1 to efficiently receive ultrasonic waves is not the average sound pressure of the ultrasonic waves to be received but the maximum value of the ultrasonic waves to be received. Therefore, in the ultrasonic sensor 1 according to the present embodiment, by disposing the plate 3, the sound pressure received by the horn 7 at the portion facing the edge portion of the pattern of the plate 3 is increased, so that the ultrasonic sensor 1 can be efficiently supersonic. Sound waves can be received.
Note that the pattern shown in FIG. 2 and the pattern shown in FIG. 3 can obtain the same effect.
[0018]
The opening of the plate 3 (the outer periphery of the outermost portion without the pattern) has substantially the same outer diameter as the opening on the bottom surface of the horn 7. With such a configuration, the ultrasonic sensor 1 according to the present embodiment can efficiently receive an ultrasonic wave whose sound pressure has increased due to interference.
[0019]
In the present embodiment, the type of diffraction caused by the plate 3 is not limited to Fresnel diffraction. For example, if the ultrasonic wave passing through the plate 3 causes interference due to diffraction, such as the diffraction of a Fraunhofer, and the sound pressure received by the horn 7 increases, the ultrasonic sensor 1 according to the present embodiment includes various types of ultrasonic sensors. It can respond to diffraction.
[0020]
In addition, the material of the plate 3 can be appropriately changed as long as it does not transmit ultrasonic waves. Further, the shape of the plate 3 is not limited to a plate shape, but may be a film shape.
[0021]
[Second embodiment]
Next, a second embodiment of the present invention will be described in detail with reference to the drawings. FIG. 5 is a sectional view of the ultrasonic sensor according to the second embodiment. In the ultrasonic sensor 20 according to the second embodiment, a plate 21 having a substantially circular opening is provided instead of the plate 3 at the opening of the case 2 of the ultrasonic sensor 1 shown as the first embodiment. It is a thing. Therefore, the same components and components as those of the first embodiment are denoted by the same names and reference numerals, and the description will be appropriately omitted.
[0022]
The plate 21 is made of the same material as that of the plate 3 shown in the first embodiment, has a disk shape, and has an opening having a size large enough to cause diffraction of ultrasonic waves passing through the central portion thereof. And is disposed in the opening of the case 2. In the ultrasonic sensor 20 having such a configuration, when an ultrasonic wave from a sound source enters the opening of the plate 21, the ultrasonic waves diffracted by the opening of the plate 21 interfere with each other, and a portion having the same phase is formed. Reinforce each other and, as a result, increase the sound pressure of the incident ultrasonic waves. FIG. 6 is a diagram illustrating a sound pressure distribution in the horn 7 according to the second embodiment when Fresnel diffraction occurs. If the distance between the horn 7 and the plate 21 disposed in the opening of the case 2 of the ultrasonic sensor 1 is short, the ultrasonic waves incident on the ultrasonic sensor 1 cause interference by Fresnel diffraction, and the horn 7 The sound pressure received by the portion facing the edge of the opening of the case 2 increases. As described above, since the ultrasonic sensor 20 according to the present embodiment receives the ultrasonic waves having a higher sound pressure by the horn 7 by disposing the plate 21, it is possible to efficiently receive the ultrasonic waves. It becomes.
[0023]
It goes without saying that the interval between the plate 21 and the horn 7 when the interference due to Fresnel diffraction occurs can be calculated from the distance from the sound source to the ultrasonic sensor 1 and the frequency of the ultrasonic wave by the Fresnel diffraction equation. . For example, when the distance from the sound source to the ultrasonic sensor 1 is 1 m and the frequency of the ultrasonic wave is 40 kHz, the distance between the plate 3 and the horn 7 is 1.2 cm.
[0024]
Also in the present embodiment, the type of diffraction caused by plate 21 is not limited to Fresnel diffraction. For example, if ultrasonic waves passing through the opening of the case 2 cause interference due to diffraction, such as diffraction of Fraunhofer, and the sound pressure received by the horn 7 increases, the ultrasonic sensor 20 according to the present embodiment will be described. Can respond to various diffractions.
[0025]
Further, in the present embodiment, the shape of the plate 21 can be freely deformed and changed as appropriate as long as the outer diameter of the opening is large enough to cause diffraction of the ultrasonic wave passing through the opening. it can.
Further, the shape of the opening is not limited to a circle, but may be another shape such as an ellipse or a rectangle.
[0026]
Further, in the present embodiment shown in FIG. 5, the outer diameter of the case 2 is formed smaller than the opening of the plate 21, but it is possible to cause diffraction of the ultrasonic wave passing through the opening of the plate 21, If the increase in sound pressure due to the interference is on the horn 7, the sound pressure can be set freely. This modification is shown in FIG.
[0027]
FIG. 7 is a sectional view of a modified example of the ultrasonic sensor according to the second embodiment. The ultrasonic sensor 30 shown in FIG. 7 has a configuration in which a plate 31 is provided in the case 2 so as to cover the opening of the case 2 instead of the plate 21 of the ultrasonic sensor 20 shown in FIG. Therefore, the same components and components as those of the first embodiment and the ultrasonic sensor 20 shown in FIG. 5 are denoted by the same names and reference numerals, and the description thereof will not be repeated.
[0028]
The plate 31 is made of the same material as the plate 3 described in the first embodiment, has a plate-like shape having an opening at the center, and is disposed on the case 2 so as to cover the opening of the case 2. Is established. The opening of the plate 31 has such a size that the ultrasonic waves passing through the opening cause diffraction. In the ultrasonic sensor 30 having such a configuration, when an ultrasonic wave from a sound source enters the opening of the plate 31, the ultrasonic waves diffracted by the opening of the plate 31 interfere with each other, and a portion having the same phase is formed. Strengthen each other and, as a result, increase the sound pressure of the incident ultrasonic waves. Thus, the ultrasonic sensor 30 shown in FIG. 7 can receive ultrasonic waves efficiently regardless of the outer diameter of the case 2 by disposing the plate 31.
[0029]
In the modification shown in FIG. 7, the shape of the plate 31 is freely deformed and changed as appropriate as long as the outer diameter of the opening is large enough to cause diffraction of ultrasonic waves passing through the opening. be able to.
Further, the shape of the opening is not limited to a circle, but may be another shape such as an ellipse or a rectangle.
Further, when utilizing the Fresnel diffraction phenomenon, the shape of the opening of the plate 31 and the bottom of the horn 7 may be substantially the same, or the latter may be formed slightly larger than the former.
[0030]
Next, another modified example of the present embodiment is shown in FIG. FIG. 8 shows an example in which an ultrasonic sensor is incorporated in the device. The ultrasonic sensor 1 is provided inside a case 41 of the device 40. The case 41 has an opening 42 having a substantially circular shape equivalent to the opening of the ultrasonic sensor 1 and having a small area at a portion facing the opening of the ultrasonic sensor 1. The outer diameter of the opening 42 is large enough to cause diffraction of the passing ultrasonic waves. In the modification shown in FIG. 8, the case 41 realizes the same function as the plate 21 shown in FIG. 5 or the plate 31 shown in FIG. 7, and when the ultrasonic wave enters the opening 42 from the sound source, The opening 42 causes the ultrasonic waves to cause interference by diffraction, and the portions having the same phase reinforce each other, and as a result, the sound pressure of the ultrasonic waves is increased. As described above, the device 40 can increase the sound pressure of the ultrasonic wave incident on the ultrasonic sensor 1 from the sound source by providing the opening portion 42 in the case 41, and thus efficiently receive the ultrasonic wave. It becomes possible.
[0031]
In the modification shown in FIG. 8, the shape of the case 41 is freely deformed and changed as appropriate as long as the outer diameter of the opening 42 is large enough to cause diffraction of the ultrasonic wave passing through the opening. can do.
The shape of the opening 42 is not limited to a circle, but may be another shape such as an ellipse or a rectangle.
[0032]
【The invention's effect】
As described above, according to the present invention, an opening having substantially the same shape as a receiving portion provided on a plate causes interference by diffraction of ultrasonic waves incident from the opening, and portions having the same phase reinforce each other. Accordingly, the sound pressure of the ultrasonic wave received by the receiving unit can be increased, so that the ultrasonic wave can be received efficiently.
Further, according to the present invention, by providing a pattern in which an annular region that transmits ultrasonic waves and an annular region that does not transmit ultrasonic waves are alternately formed concentrically in the opening of the plate, ultrasonic waves incident from the opening can be prevented. Since interference due to diffraction is caused by the pattern and the sound pressure of the ultrasonic wave received by the receiving unit can be increased, it is possible to efficiently receive the ultrasonic wave.
Further, according to the present invention, since the receiving surface has substantially the same shape as the opening, the receiving surface can efficiently receive ultrasonic waves.
[Brief description of the drawings]
FIG. 1 is a sectional view of an ultrasonic sensor according to a first embodiment.
FIG. 2 is a front view of a plate.
FIG. 3 is a front view of a plate.
FIG. 4 is a diagram showing a sound pressure distribution in a horn 7;
FIG. 5 is a sectional view of an ultrasonic sensor according to a second embodiment.
FIG. 6 is a diagram showing a sound pressure distribution in a horn 7 according to the second embodiment.
FIG. 7 is a sectional view of a modification of the second embodiment.
FIG. 8 is an example in which an ultrasonic sensor is incorporated in an apparatus.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Ultrasonic sensor, 2 ... Case, 3 ... Plate, 4 ... Sensor part, 5 ... Metal plate, 6 ... Piezoelectric plate, 7 ... Horn, 8 ... Input / output terminal, 9 ... Cable, 10 ... Input / output terminal 11: Cable, 12a, 12b: Support rod, 20: Ultrasonic sensor, 21: Plate, 30: Ultrasonic sensor, 31: Plate, 40: Device, 41: Case, 42: Opening.

Claims (3)

A plate having an opening;
A receiving unit having a receiving surface facing the opening,
The ultrasonic sensor according to claim 1, wherein the opening has substantially the same shape as the receiving unit. A plate having an opening;
A receiving unit having a receiving surface facing the opening,
The ultrasonic sensor, wherein the plate has a pattern in which annular regions that transmit ultrasonic waves and annular regions that do not transmit ultrasonic waves are alternately formed concentrically in the opening. The ultrasonic sensor according to claim 2,
An ultrasonic sensor, wherein the receiving surface is substantially circular in a plan view.

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