JP2003284190A - Ultrasonic wave sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonic wave sensor with high sensitivity that can simplify the manufacturing processes, is excellent in the moistureproof, and easy for the dimension design without dispersion. <P>SOLUTION: In the ultrasonic wave sensor of this invention, the case is made of foamed aluminum and is characterized in that an impedance matching layer is integrally formed to the case made of foamed aluminum. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic sensor using a piezoelectric element which can be used as a gas sensor, for example.

[0002]

2. Description of the Related Art Conventionally, various ultrasonic sensors of this type have been proposed in which a metal case is used to magnetically shield an internal piezoelectric element in order to solve the problem of noise caused by electromagnetic waves from the outside. Has been done.

An example of an ultrasonic sensor using such a metal case is shown in FIG. 4 of the accompanying drawings. In the ultrasonic sensor shown in FIG. 4, a piezoelectric element 4 provided with electrodes 2 and 3 on the inner bottom surface of a metal case 1 made of SUS and on the upper and lower surfaces respectively
Are fixed by the adhesive layer 5. A metal base plate 6 is hermetically welded to the opening peripheral edge portion 1 a of the metal case 1. Input / output terminals 7 and 8 are erected on the metal base plate 6 via an insulator 9. The input / output terminals 7 and 8 are connected to the electrodes 2 and 3 formed on the upper and lower surfaces of the piezoelectric element 4 by the lead wire 1
They are connected via 0 and 11.

On the outside of the inner bottom surface of the metal case 1 to which the piezoelectric element 4 is attached, an impedance matching layer 12 made of a plastic material such as epoxy resin is provided to match the impedance between the metal case 1 and air. Are fixed by an adhesive. This impedance matching layer 1
The impedance matching between the metal case 1 and the air is achieved by the element 2, the electroacoustic conversion efficiency is improved, and a large output voltage is obtained.

FIG. 5 shows another example of a conventional ultrasonic sensor using a metal case. In this example, the metal case 1 is made of a thin plate material of SUS and has a cap shape. The other parts are configured substantially the same as those shown in FIG. 4, and each part is denoted by the same reference numeral as in FIG.

[0006]

By the way, in the ultrasonic sensor using such a metal case, an impedance made of a plastic material such as epoxy resin is used in order to match the impedance between the metal case and air as described above. It is necessary to provide a matching layer, and such an impedance matching layer is usually fixed to the outside of the metal case via an adhesive layer. However, there is a problem in that the adhesive layer between the metal case and the impedance matching layer causes variations in sensor sensitivity or causes a decrease in sensitivity.

Further, since such an ultrasonic sensor is used in a rather harsh environment, there is a problem in weather resistance and moisture resistance of the plastic material forming the impedance matching layer.

Further, in the manufacture of this type of ultrasonic sensor, it is necessary to prepare a metal case and an impedance matching layer separately and bond them with an adhesive, which is time-consuming to manufacture. Furthermore, the sensor tends to be heavy due to the weight of the metal case as described above.

Therefore, the present invention solves the above problems of the conventional structure, simplifies the manufacturing process, is excellent in moisture resistance, is easy in dimension design, and is a highly sensitive ultrasonic sensor without variation. Is intended to provide.

[0010]

In order to achieve the above object, according to the present invention, a piezoelectric element having a pair of electrodes is attached to the inner bottom surface of a case, and the electrodes of the piezoelectric element are attached to the peripheral edge of the opening of the case. An ultrasonic sensor connected to a connection terminal attached to a base member hermetically fixed to the portion is characterized in that the case is made of foam aluminum and an impedance matching layer is integrally formed in the foam aluminum case.

The aluminum foam forming the case may preferably be closed cell.

In the thus constructed ultrasonic sensor according to the present invention, since the case is made of foamed aluminum, the internal piezoelectric element is magnetically shielded to prevent noise due to electromagnetic waves from the outside which affects the sensitivity of the sensor. A sensor that can be removed and has excellent moisture resistance can be provided.

Further, since the case and the impedance matching layer are integrally formed, in terms of manufacturing the sensor, directivity and dimensional design for removing unnecessary vibration are facilitated, and moreover, the case and the impedance matching layer are combined. Since there is no joining step, the assembly is simplified and the moisture resistance can be further improved.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to FIGS. 1 to 3 of the accompanying drawings. FIG. 1 shows an ultrasonic sensor according to an embodiment of the present invention. The illustrated sensor is made of foamed aluminum and has a truncated cone-shaped case 20 and a circular base member 2 made of a metal material.
1 and a disk-shaped piezoelectric element 22. Case 20
The foamed aluminum material constituting the above is preferably an aluminum foamed body composed of a thin film cell structure of closed cells, and has a very low specific gravity, thermal, mechanical and electromagnetic characteristics (high temperature resistance). , Corrosion resistance and electromagnetic wave shielding)). Foamed aluminum material is usually formed by melting an aluminum material, adding a thickener such as calcium to the molten aluminum material and stirring, and then adding a hydride as a foaming agent to the thickened aluminum material and stirring. To be done.

The foamed aluminum case 20 has a circular impedance matching layer 20a integrally formed on the top thereof for achieving impedance matching between the case 20 and air. Also, as shown in the drawing, a circular base member 2 is provided at the lower open end 20b of the aluminum foam case 20.
The outer peripheral edge portion 21a of 1 is sealed and welded.

The disc-shaped laminated piezoelectric element 22 is made of a piezoelectric ceramic material such as lead zirconate titanate, and external conductors 23a and 23b are provided on the opposite side surfaces of the piezoelectric element 22, respectively. , Constitute the electrodes. The piezoelectric element 22 has a foamed aluminum case 2 on its upper surface.
The adhesive layer 24 is attached to the central portion of the inner bottom surface of 0.

The circular base member 21 has a connection terminal 25.
A and 25b are hermetically mounted via an insulator 26.
Further, a ground terminal (not shown) is directly attached to the base member 21. The ground terminal is connected to the foamed aluminum case 20 via the base member 21 to prevent the piezoelectric element 22 from being affected by noise caused by electromagnetic waves from the outside. Connection terminal 25a,
The inner ends of 25b are connected to the outer conductors 23a and 23b of the piezoelectric element 22 via lead wires 27a and 27b, respectively.

FIG. 2 shows an ultrasonic sensor according to an embodiment of the present invention. In this case, a case 30 made of foam aluminum has a cylindrical shape and is made of the same foam aluminum material as in the case of FIG. There is. The foamed aluminum case 30 has a circular impedance matching layer 30a integrally formed on the top thereof for matching the impedance between the case 30 and air. Further, as shown in the drawing, an outer peripheral edge portion 31a of a circular base member 31 is hermetically welded to an open end portion 30b below the foamed aluminum case 30.

A circular piezoelectric element 32 made of a piezoelectric ceramic material such as lead zirconate titanate is provided with outer conductors 33a and 33b on opposite side surfaces, and these outer conductors 33a and 33b form electrodes. is doing. The piezoelectric element 32 is attached to the center of the inner bottom surface of the foam aluminum case 30 with an adhesive layer 34.

The circular base member 31 has a connection terminal 35.
a and 35b are hermetically mounted via an insulator 36.
Further, in the base member 31, as in the embodiment of FIG. 1,
The ground terminal is directly attached. Connection terminals 35a, 3
The inner end of 5b is connected to the outer conductors 33a and 33b of the piezoelectric element 32 via lead wires 37a and 37b, respectively.

FIG. 3 shows a modification of the ultrasonic sensor shown in FIG. 2, in which case a case 4 made of foam aluminum is used.
0 is a cylindrical shape, and the impedance matching layer 40a is defined by forming the top wall of the case 40 thick.
The other structure is substantially the same as that of FIG. 2, that is, the lower open end portion 40 of the foamed aluminum case 40.
An outer peripheral edge portion 41a of a circular base member 41 is hermetically welded to b as shown in the figure. A circular piezoelectric element 42 made of a piezoelectric ceramic material is provided with outer conductors 43a and 43b on opposite side surfaces, and these outer conductors 43a and 43b form electrodes. In addition, the piezoelectric element 4
2 is attached to the center of the inner bottom surface of the foamed aluminum case 40 with an adhesive layer 44. The connection terminals 45a and 45b are hermetically mounted on the circular base member 41 via an insulator 46. Further, the base member 41 has a structure shown in FIG.
The ground terminal is directly attached, as in the above embodiment. The inner ends of the connection terminals 45a and 45b are connected to the outer conductor 43 of the piezoelectric element 42 via lead wires 47a and 47b, respectively.
a, 43b.

[0022]

As described above, in the ultrasonic sensor according to the present invention, since the case is made of foam aluminum and the impedance matching layer is integrally formed in the case made of foam aluminum, the internal piezoelectric element is formed. Can be shielded magnetically to remove noise from electromagnetic waves from the outside that affects the sensitivity of the sensor, has excellent moisture resistance, and can be used stably in a harsh environment for a long period of time. The dimensional design for removal can be facilitated and the assembling can be simplified.

[Brief description of drawings]

FIG. 1 is a schematic vertical sectional view showing an ultrasonic sensor according to an embodiment of the present invention.

FIG. 2 is a schematic vertical sectional view showing an ultrasonic sensor according to another embodiment of the present invention.

FIG. 3 is a schematic vertical cross-sectional view showing a modified example of the ultrasonic sensor shown in FIG.

FIG. 4 is a schematic vertical sectional view showing an example of a conventional ultrasonic sensor.

FIG. 5 is a schematic vertical sectional view showing another example of a conventional ultrasonic sensor.

[Explanation of symbols]

20: Aluminum foam case 20a: impedance matching layer 20b: open end 21: Base member 22: Piezoelectric element 23a: External conductor (electrode) 23b: external conductor (electrode) 24: Adhesive layer 25a: connection terminal 25b: Connection terminal 26: Insulator 27a: Lead wire 27b: Lead wire

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 5D019 BB02 BB10 BB11 BB25 BB28                       GG01                 5D107 AA09 AA10 AA16 BB09 CC02                       FF07 FF09

Claims (2)

[Claims] 1. An ultrasonic wave in which a piezoelectric element having a pair of electrodes is attached to an inner bottom surface of a case, and an electrode of the piezoelectric element is connected to a connection terminal attached to a base member which is hermetically fixed to an opening peripheral edge of the case. In the sensor, an ultrasonic sensor characterized in that a case is made of foam aluminum and an impedance matching layer is integrally formed in the foam aluminum case. 2. The ultrasonic sensor according to claim 1, wherein the aluminum foam forming the case is a closed cell.