JPH0772006A - Frequency adjusting method for ultrasonic sensor - Google Patents

Abstract

PURPOSE:To provide a frequency adjusting method for an ultrasonic sensor which enables the adjusting of a frequency easily in a short time in any direction of heightening or lowering a resonance frequency. CONSTITUTION:In this frequency adjusting method of an ultrasonic sensor which has a piezo-electric diaphragm 3 and a conical acoustic impedance adjusting member 7 connected to the piezo-electric diaphragm 3, the acoustic impedance adjusting member 7 is deformed to vary an angle between the side 7a of the acoustic impedance adjusting member 7 and the piezo-electric diaphragm 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of adjusting the frequency of an ultrasonic sensor, and more particularly to a method of adjusting the frequency of an ultrasonic sensor having a structure in which an acoustic impedance adjusting member is joined to a piezoelectric diaphragm.

[0002]

2. Description of the Related Art FIG. 1 is a sectional view showing an example of a conventionally known ultrasonic sensor. The ultrasonic sensor 1 has a case 2. The case 2 is a case body 2 having an opening at the bottom.
a and a base plate 2b attached to the case body 2a so as to close the opening of the case body 2a.

A unimorph type piezoelectric vibrating plate 3 is disposed in the case 2. That is, the base plate 2b
The unimorph type piezoelectric vibrating plate 3 is fixed to the mounting portion 2c exposed on the upper surface of the via the insulating adhesive 4.

The piezoelectric vibrating plate 3 has a structure in which a piezoelectric ceramic plate 3b is attached to the lower surface of a metal plate 3a, and an electrode 3c is formed on the lower surface of the piezoelectric ceramic plate 3b. Electrode 3
The lead wire 5a is electrically connected to c. The lead wire 5a is a through hole 2d provided in the base plate 2b.
From the case 2 to the base plate 2b
At the same time, it is electrically connected to the insert-molded terminal 6. Although not shown in FIG. 1, a lead wire is also joined to the metal plate 3a on the upper surface side of the piezoelectric ceramic plate 3b, and the lead wire is arranged in parallel with the terminal 6 in the paper back direction on the drawing of the terminal 6. Is electrically connected to the other terminal.

A cone-shaped acoustic impedance adjusting member 7 is joined to the upper surface of the piezoelectric vibrating plate 3, and a plurality of openings 2e are formed in the case body 2a in front of the acoustic impedance adjusting member 7.

In the ultrasonic sensor 1, by applying an AC voltage from the above-mentioned pair of terminals, the piezoelectric vibrating plate 3 and the acoustic impedance adjusting member 7 are vibrated and an ultrasonic wave is applied to a target portion. Then, by receiving the reflected ultrasonic waves, the piezoelectric diaphragm 3 and the acoustic impedance adjusting member 7 vibrate, and the voltage generated by the vibration is taken out from the pair of terminals.

By the way, the ultrasonic sensor 1 has a relatively high Q.
Although it exhibits a frequency characteristic having a value, it is often used at a fixed frequency such as 40 kHz depending on the resonance frequency of the drive circuit. That is, the ultrasonic sensor 1 was not used at the peak resonance frequency, but was often used at a certain fixed frequency as described above. Therefore, it is required to reduce the characteristic variation at a certain frequency as described above, but for that purpose, the resonance frequency at the peak needs to be kept constant.

However, since the acoustic impedance adjusting member 7 is joined to the piezoelectric vibrating plate 3, there is a problem that the resonance frequency easily varies depending on the joining state of the acoustic impedance adjusting member 7. Therefore, conventionally, frequency adjustment has been performed by applying an adhesive or the like to the acoustic impedance adjusting member 7 and increasing the mass of the vibrating portion.

[0009]

[Problem to be Solved by the Invention] Conventional ultrasonic sensor 1
Since the frequency adjusting method of (1) was performed by applying an adhesive or the like to increase the mass, it was possible to adjust only in the direction of decreasing the resonance frequency. That is, it was not possible to adjust the resonance frequency. Therefore, even if an attempt is made to increase the resonance frequency of the ultrasonic sensor 1 that has been manufactured once, it has been impossible with the conventional frequency adjustment method.

In addition, the characteristics were not stable until the applied adhesive was cured. Therefore, the properties could not be measured until the adhesive was cured. Moreover, when the adhesive was applied and the characteristics were measured, if it was necessary to further apply the adhesive, it was necessary to apply the adhesive again, wait for the adhesive to cure, and measure again. . Therefore, there is a problem that it takes a very long time to adjust the frequency.

An object of the present invention is to provide a method capable of easily adjusting the frequency in any of the upper and lower directions in an ultrasonic sensor having an acoustic impedance adjusting member in a short time.

[0012]

The present invention is a method for adjusting the frequency of an ultrasonic sensor, comprising a piezoelectric diaphragm and an acoustic impedance adjusting member joined to one surface of the piezoelectric diaphragm. A frequency adjusting method for an ultrasonic sensor, wherein the frequency is adjusted by deforming the acoustic impedance adjusting member while the adjusting member is bonded to the piezoelectric plate.

As the acoustic impedance adjusting member, those having various structures are used. When a general cone-shaped acoustic impedance adjusting member is used, the cone-shaped member according to claim 2 is used. The acoustic impedance adjusting member is deformed so that the angle θ formed by the side surface of the piezoelectric vibrating plate changes.

[0014]

In view of the fact that it takes a very long time to adjust the frequency by applying the adhesive, the inventor of the present application can change the shape of the acoustic impedance adjusting member to adjust the piezoelectric diaphragm and the acoustic impedance. The present invention has been accomplished on the assumption that the resonance frequency of the ultrasonic sensor determined by the member may be changed.

That is, as shown in FIG. 2, the resonance frequency of the flat piezoelectric vibrating plate is constant (broken line A). Also,
When the inclination angle θ (see FIG. 1) of the side surface of the cone-shaped acoustic impedance adjusting member is changed, the resonance frequency of only the acoustic impedance adjusting member changes with the angle θ (see broken line B).

However, the ultrasonic sensor 1 in which both are joined
Then, since the vibrations of the above two modes are coupled, the resonance frequency changes as the angle θ changes, as shown by solid lines C and D. Therefore, the sound pressure and sensitivity of the ultrasonic sensor are improved in the vicinity of the degeneracy of the resonance of the piezoelectric diaphragm and the resonance of the acoustic impedance adjusting member (the portion from θ = X to θ = Y in FIG. 2). It has been found that the angle θ may be deformed so that the range becomes such a range.

That is, according to the frequency adjusting method of the ultrasonic sensor of the present invention, the frequency of the ultrasonic sensor 1 is adjusted by deforming the shape of the acoustic impedance adjusting member in a state where the acoustic impedance adjusting member is bonded to the piezoelectric vibrating plate. Therefore, the resonance frequency can be adjusted in either a lowering direction or a higher direction.

In addition, since it is not necessary to wait for the curing time of the adhesive as in the conventional method, it is possible to adjust the resonance frequency in a very short time and with high accuracy.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be clarified by describing embodiments with reference to the drawings.

In the resonance frequency adjusting method shown in FIGS. 3 to 6 below, only the piezoelectric vibrating plate portion and the acoustic impedance adjusting member portion of the ultrasonic sensor are shown. Like the ultrasonic sensor 1, other members such as the case 2 and the terminal 6 are combined to form the same as the conventional ultrasonic sensor 1.

FIG. 3 is a sectional view for explaining a frequency adjusting method for an ultrasonic sensor according to an embodiment of the present invention.
The acoustic impedance adjusting member 7 is bonded onto the piezoelectric vibrating plate 3. This acoustic impedance joining member 7
It is configured as a cone-shaped member, and in this embodiment,
The adjustment rod 11 having the conical end surface 11a is brought into contact with the lower end of the acoustic impedance adjusting member 7 from above, whereby the acoustic impedance adjusting member 7 is deformed.

In this method, the frequency adjusting rod 11 is contacted from above to reduce the angle θ formed between the side surface 7a of the acoustic impedance adjusting member 7 and the piezoelectric vibrating plate 3, thereby lowering the resonance frequency. To be done.

FIG. 4 is a sectional view for explaining a resonance frequency adjusting method according to another embodiment of the present invention. In the present embodiment, the frequency adjusting rod 12 having the inclined surface 12a at the lower end deforms only part of the side surface 7a of the acoustic impedance adjusting member 7 so as to move to the piezoelectric vibrating plate 3 side. In this way, only a part of the acoustic impedance adjusting member 7 may be deformed, whereby the frequency can be adjusted as in the case of the first method.

Further, in the method shown in FIGS. 3 and 4, the adjustment was performed in the direction of lowering the resonance frequency. However, as shown in FIG. 5, the acoustic impedance is adjusted upward by opening the upper end face. Frequency adjusting member 1 having an annular upper end surface 13a inclined at an angle substantially equal to the side surface 7a of the member 7.
3 from the lower side of the acoustic impedance adjusting member 7 to the side surface 7a
The angle θ formed between the side surface 7a and the piezoelectric vibrating plate 3 may be adjusted to be large. In this case,
Since the angle θ becomes large, the frequency adjustment is performed in the direction in which the resonance frequency is increased.

Similarly, as shown in FIG. 6, from the lower surface side of the side surface 7a of the acoustic impedance adjusting member 7, the frequency adjusting rod 14a having the inclined surface 14a at the tip is provided in the direction of the arrow shown in the figure, that is, the acoustic impedance adjusting member 7 The acoustic impedance adjusting member 7 may be deformed so as to make the angle θ between the side surface 7a and the piezoelectric vibrating plate 3 larger by bringing them into contact with each other toward the center side. Even in this case, since the angle θ becomes large, the frequency adjustment is performed in the direction in which the resonance frequency is increased.

The method for deforming the acoustic impedance adjusting member 7 described with reference to FIGS. 3 to 6 is merely an example, and in the present invention, as long as the acoustic impedance adjusting member 7 can be physically deformed. The frequency can be adjusted by any method.

In the above embodiment, the angle θ between the side surface 7a of the acoustic impedance adjusting member 7 and the piezoelectric diaphragm 3 is θ.
Although the acoustic impedance adjusting member 7 is deformed so as to change the above, when the member other than the cone-shaped member is used as the acoustic impedance adjusting member, the angle θ
Instead, by adopting an appropriate method capable of physically deforming the acoustic impedance adjusting member, the resonance frequency can be similarly adjusted.

[Brief description of drawings]

FIG. 1 is a cross-sectional view illustrating an example of an ultrasonic sensor.

FIG. 2 is a diagram for explaining the principle of the present invention.

FIG. 3 is a partial cutaway sectional view for explaining a first method of adjusting the resonance frequency of the ultrasonic sensor in the example.

FIG. 4 is a partial cutaway sectional view for explaining a second method of adjusting the resonance frequency of the ultrasonic sensor in the example.

FIG. 5 is a sectional view for explaining a third method of adjusting the resonance frequency of the ultrasonic sensor in the example.

FIG. 6 is a sectional view for explaining a fourth method of adjusting the resonance frequency of the ultrasonic sensor in the example.

[Explanation of Codes] 1 ... Ultrasonic sensor 3 ... Piezoelectric vibrating plate 3a ... Metal plate 3b ... Piezoelectric ceramic plate 3c ... Electrode 7 ... Acoustic impedance adjusting member 7a ... Side surface

Claims (2)

[Claims] 1. A frequency adjusting method for an ultrasonic sensor, comprising: a piezoelectric diaphragm; and an acoustic impedance adjusting member joined to one surface of the piezoelectric diaphragm, wherein the acoustic impedance adjusting member is joined to the piezoelectric plate. In the state, the frequency is adjusted by deforming the acoustic impedance adjusting member, and the frequency adjusting method for the ultrasonic sensor. 2. The acoustic impedance adjusting member is a cone-shaped member, and the cone member is deformed so that an angle θ formed between a side surface of the cone-shaped member and the piezoelectric vibrating plate changes. Frequency adjustment method for ultrasonic sensors.