JP2002214008A - Ultrasonic sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an ultrasonic sensor which is good in sensitivity and adhesion of a piezoelectric element or an acoustic matching layer and superior in hermetic waterproof and cheaply manufacturable. SOLUTION: The ultrasonic sensor 10 comprises a case 12 composed of a cylinder 14 and a base 16, and a separator 18 formed on the base 16 to cover the opening of the cylinder 14 of the case 12. The separator 18 has holes 20. A piezoelectric element 22 and an acoustic matching layer 34 are adhered to both sides of a portion of the separator 18 where the holes 20 are formed and filled with adhesives through which the piezoelectric element 22 is adhered directly to the matching layer 34.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an ultrasonic sensor, and more particularly to an ultrasonic sensor used for a gas flow meter, for example.

[0002]

2. Description of the Related Art FIG. 6 is an illustrative view showing one example of a conventional ultrasonic sensor. The ultrasonic sensor 1 includes a case 2 having a cylindrical shape. Inside the case 2, the piezoelectric element 4 is bonded to the top 3. Further, outside the case 2, the acoustic matching layer 5 is bonded to the top 3. In such an ultrasonic sensor 1, when a signal is input to the piezoelectric element 4, the piezoelectric element 4 vibrates, and an ultrasonic wave is emitted via the acoustic matching layer 5. In addition, a signal is output from the piezoelectric element 4 by the ultrasonic wave received via the acoustic matching layer 5. The acoustic matching layer 5 is formed to match acoustic impedance with a medium through which ultrasonic waves propagate outside the ultrasonic sensor.

When a gas flow rate or the like is measured using such an ultrasonic sensor 1, two ultrasonic sensors are attached to a gas pipe 6 so as to be oblique to a gas flow path as shown in FIG. 1 are mounted facing each other. Then, ultrasonic waves are emitted from one ultrasonic sensor 1 and received by the other ultrasonic sensor 1. Conversely, ultrasonic waves are emitted from the other ultrasonic sensor 1 and received by the one ultrasonic sensor 1. The gas flow rate is measured from the difference between the times required for transmitting and receiving the ultrasonic waves in these two directions.

In an ultrasonic sensor having a plate-shaped isolation wall, since a loss of vibration energy between the piezoelectric element 4 and the acoustic matching layer 5 is large, the ultrasonic sensor is formed of a thin film as shown in FIG. An ultrasonic sensor 1 has also been proposed in which a piezoelectric element 4 and an acoustic matching layer 5 are opposed to each other via an isolation wall 7 to suppress loss of vibration energy.

[0005]

However, in an ultrasonic sensor in which a thin film having airtightness and waterproofness is formed as an isolation wall, it is difficult to bond the film to the piezoelectric element or to bond the film to the acoustic matching layer. It is. In addition, when a temperature change occurs, stress concentrates on a separating wall interposed between the piezoelectric element and the acoustic matching layer due to a difference in thermal expansion coefficient between the piezoelectric element and the acoustic matching layer, and the bonded portion is deteriorated. In such an ultrasonic sensor, a water-repellent material such as a fluororesin or a surface-treated metal film is often used in order to improve airtightness and waterproofness. When these materials are used, In
Further, there is a problem that the adhesiveness is reduced.

If the adhesion between the piezoelectric element or the acoustic matching layer and the separator is weak, when the ultrasonic sensor is placed in a humid atmosphere,
Moisture enters the bonding interface. If the temperature of the atmosphere is lowered while the moisture remains, the freezing causes a sudden adhesion failure. Further, in order to obtain a more complete airtight and waterproof structure, it is necessary to increase the thickness of the separator. However, in this case, attenuation of vibration energy from the piezoelectric element to the acoustic matching layer increases, leading to a decrease in sensitivity. Further, in order to improve the adhesive strength, a special joining technique such as welding or the use of a special adhesive or member having low thermal expansion property is inevitable, which leads to an increase in cost.

[0007] Therefore, a main object of the present invention is to provide an ultrasonic sensor which has good adhesiveness of a piezoelectric element and an acoustic matching layer, has excellent airtight and waterproof properties, has good sensitivity, and can be manufactured at low cost. It is to be.

[0008]

SUMMARY OF THE INVENTION The present invention provides an airtight and waterproof isolation wall, a piezoelectric element adhered to one surface of the isolation wall, and the other surface of the isolation wall facing the piezoelectric element. And an acoustic matching layer adhered to the piezoelectric element, wherein a hole is formed in the isolation wall at a portion sandwiched between the piezoelectric element and the acoustic matching layer. In such an ultrasonic sensor, the piezoelectric element and the acoustic matching layer are joined with an adhesive through a hole formed in the partition wall.

By forming a hole in the isolation wall, the piezoelectric element and the acoustic matching layer are directly bonded through the hole, and a strong adhesive force can be obtained. At this time, the holes formed in the isolation wall are sealed with the piezoelectric element, the acoustic matching layer, and the adhesive, so that airtightness and waterproofness can be ensured. Further, since the formation of the hole apparently reduces the rigidity of the isolation wall, a thicker isolation wall can be used with the same sensitivity as compared with the case where the isolation wall having no hole is used. .

The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description of embodiments of the present invention with reference to the accompanying drawings.

[0011]

FIG. 1 is a plan view showing an example of an ultrasonic sensor according to the present invention, and FIG. 2 is an illustrative view thereof. The ultrasonic sensor 10 includes a case 12. Case 12
For example, a substrate portion 16 including a cylindrical tubular portion 14 and extending from one end of the tubular portion 14 to the periphery is formed. Substrate part 16
On the upper side, an isolation wall 18 is formed so as to cover the opening of the cylindrical portion 14. The isolation wall 18 is formed of, for example, an airtight and waterproof film. A plurality of holes 20 are formed in the center of the isolation wall 18.

Inside the case 12, a piezoelectric element 22 is bonded to the center of the isolation wall 18. At this time, the hole 20 formed in the isolation wall 18 is covered with the piezoelectric element 22. The piezoelectric element 22 includes, for example, a disk-shaped piezoelectric substrate 24.
, And electrodes 26 and 28 are formed on both surfaces thereof.
Then, one electrode 26 is bonded to the isolation wall 18. For example, a lead wire 30 is connected to these electrodes 26 and 28, and the lead wire 30 is led out through a lid member 32 formed at the other opening of the cylindrical portion 14.

Further, an acoustic matching layer 34 is bonded to the outside of the isolation wall 18 so as to face the piezoelectric element 22.
The acoustic matching layer 34 is formed by, for example, mixing and molding a glass balloon and an epoxy resin. Then, the acoustic matching layer 34 is provided with the holes 2 formed in the isolation wall 18.
0 is disposed. This acoustic matching layer 3
Reference numeral 4 is used for matching acoustic impedance with the outside when the piezoelectric element 22 vibrates and emits an ultrasonic wave to the outside.

In the ultrasonic sensor 10, since the hole 20 is formed in the isolation wall 18, the hole 20 is filled with the adhesive 36 as shown in FIG. Therefore, the piezoelectric element 22 and the acoustic matching layer 34 are bonded to the isolation wall 18 by the adhesive 36 and the holes 2
0 are directly bonded to each other. The hole 20 does not need to be completely filled with the adhesive 36 alone, and a frit 38 may be formed in the hole 20 as shown in FIG.

As described above, in this ultrasonic sensor 10,
Since the piezoelectric element 22 and the acoustic matching layer 34 are directly bonded via the holes 20, a strong adhesive force can be obtained in this portion. Therefore, the piezoelectric element 22 and the acoustic matching layer 3
Insufficient adhesive force between the piezoelectric element 4 and the isolation wall 18 and a difference in thermal expansion coefficient between the piezoelectric element 22 and the acoustic matching layer 34 can prevent poor adhesion due to stress applied to the isolation wall 18 and the like.

Further, by forming the hole 20 in the isolation wall 18, the apparent rigidity of the isolation wall 18 is reduced.
With the same sensitivity, it is possible to form a thicker film than when a film having no holes is used, and it is possible to improve the adhesiveness of the isolation wall 18 itself and the airtight and waterproof properties. Further, a strong adhesive force can be obtained by using the same epoxy-based adhesive as the acoustic matching layer 34 as the adhesive 36. Further, since a strong adhesive force can be obtained, a special bonding technique such as welding is not required, and the ultrasonic sensor can be manufactured at low cost. At this time,
Since the hole 20 is sealed with the piezoelectric element 22, the acoustic matching layer 34, and the adhesive 36, airtightness and waterproofness can be ensured.

The separating wall 18 is not limited to a membrane.
It may be plate-shaped. In this case, as shown in FIG. 5, the top part of the case 12 having a canopy shape can be used as the partition wall 18, and a hole 20 is formed in this top part. Then, the piezoelectric element 22 and the acoustic matching layer 34 are bonded to both sides of the hole 20 forming portion. Also in the ultrasonic sensor 10 having such a structure, since the piezoelectric element 22 and the acoustic matching layer 34 can be directly bonded through the holes 20, a strong adhesive force can be obtained, and the airtight waterproof property can be improved. Can be secured.

[0018]

According to the present invention, the adhesion between the piezoelectric element and the acoustic matching layer adhered to the isolation wall is large, so that the piezoelectric element and the acoustic matching layer are not affected by the stress due to the ambient temperature and the adhesiveness of the isolation wall. It is possible to obtain an ultrasonic sensor in which the layer is not easily separated. In addition, by forming a hole in the isolation wall, apparently the rigidity of the isolation wall is reduced, so that, with the same sensitivity, the isolation wall can be made thicker than the isolation wall without the hole, and the adhesiveness and airtight waterproofness Performance can be improved. Furthermore, since the hole formed in the isolation wall is sealed with the piezoelectric element, the acoustic matching layer, and the adhesive, airtight waterproofness can be ensured.

[Brief description of the drawings]

FIG. 1 is a plan view showing an example of an ultrasonic sensor according to the present invention.

FIG. 2 is an illustrative view of the ultrasonic sensor shown in FIG. 1;

FIG. 3 is an illustrative view showing one example of a relationship among a partition wall, a piezoelectric element, and an acoustic matching layer;

FIG. 4 is an illustrative view showing another example of the relationship among the isolation wall, the piezoelectric element, and the acoustic matching layer;

FIG. 5 is an illustrative view showing another example of the ultrasonic sensor according to the present invention;

FIG. 6 is an illustrative view showing one example of a conventional ultrasonic sensor;

FIG. 7 is an illustrative view showing an example in which an ultrasonic sensor is used as a gas flow meter;

FIG. 8 is an illustrative view showing another example of the conventional ultrasonic sensor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Ultrasonic sensor 12 Case 18 Isolation wall 20 Hole 22 Piezoelectric element 34 Acoustic matching layer 36 Adhesive

Claims (2)

[Claims] 1. An isolation wall having airtightness and waterproofness, a piezoelectric element adhered to one surface of the isolation wall, and an acoustic matching adhered to the other surface of the isolation wall so as to face the piezoelectric element. An ultrasonic sensor including a layer, wherein a hole is formed in the isolation wall at a portion sandwiched between the piezoelectric element and the acoustic matching layer. 2. The ultrasonic sensor according to claim 1, wherein the piezoelectric element and the acoustic matching layer are joined with an adhesive through the hole formed in the partition wall.