JPH07151736A - Focus proximity type composite ae sensor - Google Patents

Abstract

PURPOSE:To provide a focus proximity type composite AE sensor wherein acoustic measurement of a high frequency of a VHF band of 10X10<7> or not much exceeding 10<8> can be conducted, the acoustic measurement in a very small area can be performed highly precisely and which can be applied to minute material to be measured. CONSTITUTION:Supersonic microscope concave spherical surface lenses 2A, 2B, 2C are combined, inclined and disposed for material to be measured 3 and their focuses A', B', C' are converged in the neighborhood of an acoustic measurement part. And water 7 is used as a transmission medium. An acoustic wave produced from an acoustic production point P' is scattered from the focuses A', B', C' and measurement can be performed with transducers 5 of respective concave spherical surface lenses 2A, 2B, 2C. The position of the acoustic production point P' can be found from its measured waveform and characteristics of the material to be measured 3 can be found out.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AE sensor necessary for studying the characteristics of a material under stress, and in particular, it can detect an acoustic signal from a minute object to be measured and can catch a high frequency signal. A focus proximity type AE sensor.

[0002]

2. Description of the Related Art An acoustic signal (AE signal) is emitted when a material is deformed or destroyed. By catching this signal and analyzing the waveform and amplitude, it is possible to know the material characteristics, and it is possible to predict destruction and prevent accidents. Conventionally, an AE sensor (Acostec emission sensor) has been adopted as a detection means for catching a signal. As shown in FIG. 10, solid material (material to be measured)
By attaching a plurality of AE sensors 13 to 12, the position of the sound generation point P'can be specified, and
The material characteristics as described above can be obtained. However, the conventional AE sensor 13 is mainly a piezoelectric type that is directly fixed to the object to be measured, and can pick up only an acoustic signal having a frequency of about 10 × 10 ⁶ Hz.

[0003]

In addition to the solid material, in order to analyze the stress rupture development process of the thin film material formed on the substrate, the frequency is not limited to about 10 × 10 ⁶ Hz, and a higher frequency is used. It is necessary to catch an acoustic signal such as VHF of about 10 × 10 ^{7 to} 10 ⁸ Hz. For that purpose, an ultrasonic microscope concave spherical lens is used as an AE sensor, and is disclosed in the following document, for example. "Non-Contact
Measurement of Acoustic Emission Signals in the 1
00MHz Frequency Range Using an Acoustical Microsco
pe '' (H. Kanai, N.Chubachi, T. Sannomiya Department of E
electrical Engineering, Faculty of Engineering, Tohok
u University, Japan), ACUSTICA Vol.76 (1992), PP.199〜
204. FIG. 9 shows an AE sensor 2 including a concave spherical lens. This AE sensor 2 is composed of a glass-like delay material 4 and a transducer 5 fixed to it, and a concave spherical surface 6 is formed on the lower end side of the delay material. As shown in FIG. 9, the AE signal from the measured material 3 diverges from the acoustic generation point P ′, enters the delay member 4 as a divergent spherical wave, and is received by the transducer 5. In addition, the concave spherical lens AE sensor 2
In this case, water 7 is used as the transmission medium (coupler).

A single AE sensor 2 is sufficient if only the characteristics of the material 3 to be measured are to be known, but in order to specify the sound generation point P'and to know the various characteristics of the material 3 to be measured, a plurality of AE sensors 2 can be used. Simultaneous measurement by the AE sensor 2 is required. Figure 8
Shows an example thereof. In this example, 3 of A, B, C
The AE sensors 2A, 2B, 2C are arranged in parallel, and the respective collection points A ', B', C'are converged on the surface of the measured material 3. Surrounding the sound generation point (P ') not shown, A', B ',
By arranging C ', its position can be obtained. However, in this case, for example, the distance h between the focal points A'and C'has a considerably large value. Normally, the transducer is made of a piezoelectric material having a size of about 0.5 mm or more, and in this case, the distance h is 1.5 mm or more. Since a high frequency acoustic signal is strongly attenuated in the process of propagating in the material to be measured, it is necessary to make the distance between the acoustic generation point and the focal point as small as possible in order to measure at a high SN ratio. . on the other hand,
For example, in order to accurately obtain the position of the sound generation point P ′ of a fine material to be measured having a diameter of only 500 μm, each focus A ′,
B'and C'need to converge within about 200 μm,
This condition cannot be satisfied by the AE sensors 2A, 2B and 2C shown in FIG. An array structure in which concave spherical lenses are connected in series is disclosed in the following document, for example. "ACO
USTIC INK PRINTING '' (B.Hadimioglu, SAElrod, DLSte
inmetz, M.Lim, J, C.Zesch, BTKhuri-Yakub, EGRawson,
and CFQuate), Xerox Palo Alto Reseach Center 3333
Coyote Hill Road Palo Alto, CA.94304,1992 IEEE 199
2 ULTRASONICS SYMPOSIUM pp.929-935.

The present invention enables acoustic detection of a minute area by using an AE sensor having a spherical lens capable of detecting VHF band high frequency of about 10 × 10 ⁸ Hz, which enables acoustic measurement of an extremely small material and high An object of the present invention is to provide a focus proximity type composite AE sensor capable of accurate acoustic analysis.

[0006]

In order to achieve the above object, the present invention is a sensor for detecting an acoustic signal (AE signal) generated by deformation, destruction, etc. of a material to judge the characteristic of the material. A plurality of concave spherical lenses of an ultrasonic microscope are arranged, the spherical lenses are arranged so as to be inclined with respect to each other, and the focal points are located in the vicinity of each other and are not spatially coincident with each other. And a focus proximity type composite AE sensor as described above.

[0007]

The concave spherical lens is arranged so that its focus converges near the acoustic measurement point. By three-dimensionally devising the inclination angle and the arrangement position thereof, it is possible to set each focus extremely close to the acoustic measurement point to the extent that the acoustic signal does not decay and disappear in the process of propagation of the acoustic signal to the material to be measured. The position of the acoustic measurement point can be accurately obtained by detecting the sound wave by the concave spherical lens.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view showing the overall structure of an embodiment of the present invention, FIG. 2 is a diagram showing the measurement results of acoustic waves according to this embodiment, and FIG. 3 is a sound generation point P'and the focal position of each concave spherical lens. FIG. 4 is a plan view showing the X and Y coordinates of A ', B', and C ', FIG. 4 is a schematic front view of another embodiment of the present invention, and FIG. 5 is A shown in FIG.
FIG. 6 is a perspective view of an E sensor, FIG. 6 is a schematic front view of yet another embodiment, and FIG. 7 is a schematic front view of another embodiment of the present invention. The concave spherical lenses shown in FIGS. 4 to 7 are at positions spatially displaced from each other, and a cross section corresponding to the cross section taken along the line D-D of FIG. 5 is shown.

As shown in FIG. 1, a focus proximity type composite AE sensor 1 of this embodiment comprises three concave microscope spherical lens 2 of an ultrasonic microscope. For convenience of description, the three concave microscope spherical lenses 2 of the ultrasonic microscope will be referred to as concave spherical lenses 2A, 2B, and 2C. For example, the object to be measured is vertical x horizontal x 1 mm thick.
Measured material 3 consisting of 500 μm × 50 μm SiO ₂
Is set horizontally, each concave spherical lens 2A, 2B, 2
C is arranged so as to be inclined with respect to the horizontal plane and at a position where it does not interfere with each other. In addition, each concave spherical lens 2A, 2
The focal points A ', B', C'of B, 2C are converged on the surface of the material 3 to be measured at three points. In the figure, the focal point A'is closest to the sound generating point P ', and the focal points B'and C'are further away in this order. Each concave spherical lens 2A, 2B, 2C is composed of a glass-like delay material 4 and a transducer 5, and a concave spherical surface 6 is formed on the lower end side of the delay material 4. The concave spherical lens 2
A, 2B, and 2C may have the same shape, but are not limited thereto. Also, each concave spherical lens 2A, 2B, 2C
Water 7 as a transmission medium of ultrasonic waves is filled between the and the material 3 to be measured. In this embodiment, three concave spherical lenses are used, but four or more lenses may be used. However, the focal points of all concave spherical lenses are not aligned on the same straight line.

With the above structure, when a sound wave is emitted from the sound generating point P'of the material 3 to be measured, this sound wave is emitted from the sound generating point P'to the focal points A ', B of the respective concave spherical lenses 2A, 2B, 2C. ′, C ′, each focus A ′, B ′,
The concave spherical lens 2 diverges from C'and becomes a divergent spherical wave.
It is incident on A, 2B, and 2C. This divergent spherical wave is detected by each transducer 4, converted into an electric signal, and a sound wave having a waveform as shown in FIG. 2 is measured.

In FIG. 2, the horizontal axis represents time, and the vertical axis represents the time waveform (acoustic amplitude) of the propagated sound wave.
If a sound wave is generated from the sound generation point P ′ on the surface of the material to be measured at a certain moment (point at time 0 in FIG. 2), the concave spherical lens 2A delays the time by t, for example, according to the positional relationship between the three focal points. The waveform is measured, the waveform is measured by the concave spherical lens 2B after a delay of time a, and the waveform is measured by the concave spherical lens 2C after a delay by time b.

As shown in FIG. 3, each concave spherical lens 2A,
X and Y coordinates of focal points A ', B', and C'of 2B and 2C are X.
a, Ya, Xb, Yb, Xc, Yc, and X, Y coordinates of the sound generation point P ′ are Xp, Yp. In order to simplify the calculation, if the time required for sound wave propagation from the piezoelectric body of each concave spherical lens 2A, 2B, 2C to each focal point is constant and the thickness of the material 3 to be measured is ignored, the sound generation point P ' The coordinates are obtained from the following calculation formula (Equation 1). Where V
Is the speed of sound at which the AE signal propagates through the measured material 3,
M in the equation (1) represents the propagation time of the acoustic wave from the sound generation point P'to the focus A ', and m + a in the equation (2) represents the propagation time of the acoustic wave from the sound generation point P'to the focus B'. Shows,
M + a + b in the equation (3) represents the propagation time of the acoustic wave from the acoustic generation point P'to the focal point C '. Also, from FIG. 2, time a,
b can be obtained, and each focus A ′, B ′,
Since the coordinates Xa, Ya, Xb, Yb, Xc, Yc of C'are known, the coordinates Xp, Yp of the sound generation point P'can be obtained by the equations (4) and (5). Further, it is possible to analyze the characteristics of the material 3 to be measured from the acoustic wave of FIG. Further, when V is known, it is possible to measure the depth of the sound generation point in the thick material 3 to be measured. Known methods may be applied correspondingly to these position measuring methods.

[0013]

[Equation 1]

In the above embodiment, the concave spherical lenses 2A, 2B and 2C which are independent of each other are described as being inclined, but the focus proximity type composite AE sensor 1a shown in FIGS. 4 and 5 has a concave spherical lens 2A. , 2B, 2C are combined to form an integrated structure. In the case of the previous embodiment, since the concave spherical lenses 2A, 2B and 2C are independent, there is no mutual acoustic interference between the transducers 5 and accurate acoustic measurement is possible. On the other hand, in the case of FIGS. 4 and 5, the concave spherical lenses 2A, 2B and 2C are formed because of the integral structure.
This has the advantage that the arrangement can be formed with high precision.
Of course, mutual interference between the transducers 4 can be almost suppressed by devising the shape. According to this embodiment, the distance g between the focal point A'and the focal point C'is set to h in the prior art (FIG. 8).
The value can be made extremely small compared to. The same applies to the focus B '. In this embodiment as well, the position of the sound generation point P'can be accurately obtained from the coordinates of the focal points A ', B', C'and the time of transmission of the acoustic wave to each concave spherical lens, as in the previous embodiment.

FIG. 6 shows each concave spherical lens 2A,
Focus proximity type composite AE in which 2B and 2C are integrally formed
It shows the sensor 1b. In this embodiment, the transducer 5 is fixed to the concave spherical surface 6 side. In this embodiment as well, the characteristics of the material 3 to be measured and the position of the sound generation point P ′ are obtained in the same manner as in the above embodiments.

The focus proximity type composite AE sensor 1c shown in FIG. 7 is formed as follows. It is based on an AE sensor which first forms a concave spherical surface 8 indicated by the chain double-dashed line and has an unseparated monolithic transducer as shown. Next, the concave spherical surface 8 is reprocessed into three concave spherical surfaces 9, 10, 11 having different curvatures. At the same time, the transducer having the integral structure is divided into three, and the transducer 5
It is formed as A, 5B, 5C. The concave spherical surface 9 corresponds to the transducer 5A, the concave spherical surface 10 corresponds to the transducer 5B, and the concave spherical surface 11 corresponds to the transducer 5C. With the above structure, the focal points A ', B', and
C'can be directed. According to the present embodiment, it is possible to obtain almost the same effect as the above embodiment.

As described above, the focus proximity type composite AE sensors 1, 1a, 1b, 1c having various shapes have been described, but the present invention is not limited to them, and the acoustic measurement site of the material 3 to be measured is described. A arranged so that the focus can be converged in the vicinity
Any E sensor may be used. Of course, as described above, the concave spherical lenses do not have to have the same structure.

[0018]

According to the present invention, the following remarkable effects are obtained. 1) By adopting the structure in which a plurality of ultrasonic microscope concave spherical lenses are arranged to be inclined with respect to each other, the focal point can be arranged in the vicinity of the acoustic measurement point of the material. Therefore, it is possible to prevent signal loss due to attenuation when the acoustic signal propagates in the material to be measured, and it is possible to perform acoustic measurement in a minute area, and it is possible to perform acoustic measurement of an extremely small material. 2) Since the focal position of each concave spherical lens can be accurately positioned with respect to the acoustic measurement point, highly accurate acoustic measurement can be performed and the position of the acoustic generation point can be accurately detected. 3) 1 by adopting concave microscope spherical lens
Acoustic measurement of VHF band high frequency of about 0 × 10 ^{7 to} 10 ⁸ Hz is possible. This makes it possible to catch the AE signal generated when the thin film material is destroyed, for example.

[Brief description of drawings]

FIG. 1 is a perspective view showing the overall structure of an embodiment of the present invention.

FIG. 2 is a waveform diagram showing an example of a time waveform of a sound wave measured according to this embodiment.

FIG. 3 is a plan view showing the X and Y coordinates of the focal points A, B and C of each concave spherical lens and the sound generation point P ′ on the surface of the measured material.

FIG. 4 is a front view of another embodiment of the present invention.

5 is a perspective view of the embodiment of FIG.

FIG. 6 is a front view of another embodiment of the present invention.

FIG. 7 is a front view of yet another embodiment of the present invention.

FIG. 8 is a sectional view of a conventional composite AE sensor.

FIG. 9 is a sectional view of a conventional stand-alone AE sensor.

FIG. 10 is a schematic perspective view showing a sound measurement method using a conventional AE sensor.

[Explanation of symbols]

 1 Focal Proximity Type Composite AE Sensor 1a Focal Proximity Type Composite AE Sensor 1b Focal Proximity Type Composite AE Sensor 1c Focal Proximity Type Composite AE Sensor 2 AE Sensor 2A Concave Spherical Lens 2B Concave Spherical Lens 2C Concave Spherical Lens 3 Measured Material 4 Delay Material 5 Transducer 6 Concave spherical surface 7 Water 8 Concave spherical surface 9 Concave spherical surface 10 Concave spherical surface 11 Concave spherical surface 12 Measured material 13 AE sensor

Claims (1)

[Claims] 1. A sensor for detecting an acoustic signal (AE signal) generated by deformation, destruction, etc. of a material to judge the characteristic of the material, wherein a plurality of concave spherical lenses of an ultrasonic microscope are provided. A focus proximity composite AE sensor, characterized in that each of the concave spherical lenses is arranged to be inclined with respect to each other, and the respective focal points are located in the vicinity of each other and are not spatially coincident with each other.