JP3362484B2 - Combined focus AE sensor - Google Patents

Description

Description: 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 more particularly to an AE sensor for detecting an acoustic signal from a minute object to be measured. The present invention relates to a close-focus type composite AE sensor that can detect and catch a high-frequency signal. 2. Description of the Related Art When a material is deformed or broken, an acoustic signal (AE signal) is emitted. By catching this signal and analyzing the waveform and amplitude, it is possible to know the material properties and to predict the destruction and prevent accidents. Conventionally, an AE sensor (acoustic emission sensor) is employed as a detecting means for catching a signal. As shown in FIG. 10, a solid material (a material to be measured)
By attaching a plurality of AE sensors 13 to the position 12, the position of the sound generation point P 'can be specified,
The material characteristics as described above can be obtained. However, the conventional AE sensor 13 is mainly of a piezoelectric type directly fixed to an object to be measured, and can only pick up an acoustic signal having a frequency of about 10 × 10 ⁶ Hz. [0003] Apart from solid materials, in order to analyze the stress rupture development process of a thin film material formed on a substrate, the frequency is limited to about 10 × 10 ⁶ Hz. Further, it is necessary to catch a high frequency acoustic signal such as VHF of about 10 × 10 ^{7 to} 10 ⁸ Hz. For this 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 the AE sensor 2 composed of a concave spherical lens. The AE sensor 2 comprises a glass-like delay member 4 and a transducer 5 fixed thereto, and a concave spherical surface 6 is formed on the lower end side of the delay member. As shown in FIG. 9, the AE signal from the measured material 3 diverges from the sound generation point P ′, enters the delay member 4 as a divergent spherical wave, and is received by the transducer 5. The AE sensor 2 of a concave spherical lens
In this case, water 7 is used as a transmission medium (coupler). A single AE sensor 2 is sufficient if only the characteristics of the material 3 to be measured are known. However, in order to identify the sound generation point P 'and to know various characteristics of the material 3 to be measured, a plurality of AE sensors 2 are required. AE sensor 2 requires simultaneous measurement. FIG.
Shows an example. In this example, three of A, B and C
The AE sensors 2A, 2B, and 2C are arranged side by side, and respective convergence points A ', B', and C 'converge on the surface of the material 3 to be measured. 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 interval h between the focal points A 'and C' has a considerably large value. Usually, the transducer is made of a piezoelectric material 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 through a material to be measured, it is necessary to make the distance between the sound generating 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 determine the position of the sound generation point P 'of a fine material to be measured having a diameter of only 500 μm, the focal points A',
B ′ and C ′ need to converge within about 200 μm,
This condition cannot be satisfied with 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, for example, the following document. "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. According to the present invention, an AE sensor having a spherical lens capable of detecting a high frequency of about 10 × 10 ⁸ Hz in a VHF band can be used to detect sound in a very small area. An object of the present invention is to provide a close-focus type composite AE sensor capable of performing accurate acoustic analysis. SUMMARY OF THE INVENTION In order to achieve the above object, the present invention judges the characteristics of a material by detecting an acoustic signal (AE signal) generated by deformation or destruction of the material. A plurality of concave spherical lenses of an ultrasonic microscope, wherein the spherical lenses are arranged obliquely to each other, and each focal point is located near each other, and spatially. This constitutes a near-focus composite AE sensor that does not match. The concave spherical lens is arranged so as to be inclined such that its focal point converges near the acoustic measurement point. By devising the inclination angle and the arrangement position thereof three-dimensionally, each focal point can be set very close to the acoustic measurement point so as not to be attenuated and lost in the process of transmitting the acoustic signal to the material to be measured. The position of the acoustic measurement point can be accurately determined by the sound wave detection by the concave spherical lens. 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 one embodiment of the present invention, FIG. 2 is a diagram showing measurement results of acoustic waves according to this embodiment, and FIG. 3 is a diagram showing an acoustic generation point P 'and a 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.
FIG. 6 is a schematic front view of still another embodiment of the E sensor, and FIG. 7 is a schematic front view of another embodiment of the present invention. Each of the concave spherical lenses shown in FIGS. 4 to 7 is spatially shifted from each other, and shows a cross section corresponding to a cross section taken along line DD of FIG. As shown in FIG. 1, a near-focus type composite AE sensor 1 of the present embodiment comprises three concave spherical lenses 2 of an ultrasonic microscope. The three ultrasonic microscope concave spherical lenses 2 are referred to as concave spherical lenses 2A, 2B, and 2C for convenience of description. For example, as an object to be measured, length × width × thickness is 1 mm ×
Material 3 to be measured composed of 500 μm × 50 μm SiO ₂
Is set horizontally, each concave spherical lens 2A, 2B, 2
C is arranged at an angle 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', and C 'of B and 2C are converged at three points on the surface of the material 3 to be measured. In the figure, the focal point A 'is closest to the sound generating point P', and the focal points B 'and C' move away in this order. Each of the concave spherical lenses 2A, 2B, and 2C includes a glass-like delay member 4 and a transducer 5, and a concave spherical surface 6 is formed on the lower end side of the delay member 4. The concave spherical lens 2
A, 2B, and 2C may have the same shape, but are not limited thereto. Further, each concave spherical lens 2A, 2B, 2C
The space 7 and the material 3 to be measured are filled with water 7 as a medium for transmitting ultrasonic waves. 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 generation point P 'of the material 3 to be measured, the sound wave is transmitted from the sound generation point P' to the focal points A ', B of the concave spherical lenses 2A, 2B, 2C. , C ', and focuses A', B ',
C ′ diverges from C ′ to form a divergent spherical wave, concave spherical lens 2
A, 2B, and 2C. This diverging spherical wave is detected by each transducer 4 and converted into an electric signal, and a sound wave having a waveform as shown in FIG. 2 is measured. FIG. 2 shows time on the horizontal axis and the time waveform (acoustic amplitude) of the propagated sound wave on the vertical axis.
Assuming that 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 0 in FIG. 2), the concave spherical lens 2A delays by, for example, time t according to the positional relationship between the three focal points. The waveform is measured, the waveform is measured by the concave spherical lens 2B with a delay of time a, and the waveform is measured by the concave spherical lens 2C with a delay of time b. As shown in FIG. 3, each concave spherical lens 2A,
X and Y coordinates of focal points A ′, B ′, C ′ of 2B and 2C are represented by X
a, Ya, Xb, Yb, Xc, Yc, and the X, Y coordinates of the sound generation point P 'are Xp, Yp. In order to simplify the calculation, the time required for sound wave propagation from the piezoelectric body of each concave spherical lens 2A, 2B, 2C to each focal point is fixed, and the thickness of the sound generation point P 'is ignored if the thickness of the material 3 to be measured is ignored. The coordinates are obtained from the following formula (Equation 1). Where V
Is the sound speed at which the AE signal propagates in the material 3 to be measured,
M in equation (1) indicates the transmission time of the acoustic wave from the sound generation point P 'to the focal point A', and m + a in equation (2) indicates the transmission time of the acoustic wave from the sound generation point P 'to the focal point B'. Show,
M + a + b in the equation (3) indicates the transmission time of the acoustic wave from the sound generation point P ′ to the focal point C ′. Also, from FIG.
b can be obtained, and the focal points A ', B',
Since the coordinates Xa, Ya, Xb, Yb, Xc, and Yc of C 'are known, the coordinates Xp and 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 to be measured 3 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. In addition, what is necessary is just to apply a well-known method mutatis mutandis to these position measuring methods. ## EQU1 ## In the above embodiment, the independent concave spherical lenses 2A, 2B and 2C have been described as being inclined. However, the close-focus type composite AE sensor 1a shown in FIGS. 4 and 5 is different from the concave spherical lens 2A. , 2B, and 2C are integrated into an integrated structure. In the case of the above embodiment, since the concave spherical lenses 2A, 2B, and 2C are independent, accurate acoustic measurement can be performed without any acoustic mutual interference of the transducers 5. On the other hand, in the case of FIGS. 4 and 5, each concave spherical lens 2A, 2B, 2C has an integral structure.
Has the advantage that the arrangement can be formed with high precision.
Of course, by devising the shape, the mutual interference between the transducers 4 can be almost suppressed. According to the present embodiment, the distance g between the focal point A 'and the focal point C' is set to h of the prior art (FIG.
Can be set to an extremely small value. The same applies to the focal point B '. Also in this embodiment, the position of the sound generation point P 'can be accurately obtained from the coordinates of the focal points A', B ', and C' and the transmission time of the acoustic wave to each concave spherical lens, as in the previous embodiment. FIG. 6 shows each concave spherical lens 2A,
Proximity focal point composite AE in which 2B and 2C are formed in an integrated structure
It shows the sensor 1b. In this embodiment, the transducer 5 is fixed to the concave spherical surface 6 side. Also in this embodiment, the characteristics of the material to be measured 3 and the position of the sound generation point P 'are obtained in the same manner as in the above embodiment. The close-focus type composite AE sensor 1c of FIG. 7 is formed as follows. It is based on an AE sensor which first forms a concave spherical surface 8 shown by a two-dot chain line and has an integral transducer which is not separated as shown. Next, the concave spherical surface 8 is reworked into three concave spherical surfaces 9, 10, and 11 having different curvatures. At the same time, the transducer of integral structure is divided into three parts and the transducer 5
A, 5B, and 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 oriented. According to this embodiment, substantially the same effects as those of the above embodiment can be obtained. As described above, the near-focus composite AE sensors 1, 1 a, 1 b, and 1 c having various shapes have been described. However, the present invention is not limited to these. A that is arranged so that the focal point can be converged in the vicinity
An E sensor is sufficient. Of course, as described above, the respective concave spherical lenses need not have the same structure. According to the present invention, the following remarkable effects are obtained. 1) By adopting a structure in which a plurality of concave spherical lenses of the ultrasonic microscope are arranged obliquely with respect to each other, the focal point can be arranged very close to the acoustic measurement point of the material. Therefore, signal loss due to attenuation when the acoustic signal propagates in the material to be measured can be prevented, and acoustic measurement can be performed in a very small area, so that acoustic measurement of an extremely small material can be performed. 2) Since the focal position of each concave spherical lens can be accurately positioned with respect to the sound measurement point, high-accuracy sound measurement can be performed, and the position of the sound generation point can be accurately detected. 3) The adoption of an ultrasonic microscope concave spherical lens enables 1
Acoustic measurement of high frequency of VHF band of about 0 × 10 ^{7 to} 10 ⁸ Hz is possible. Thus, for example, an AE signal generated when the thin film material is destroyed can be caught.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing the overall structure of an embodiment of the present invention. FIG. 2 is a waveform chart showing an example of a time waveform of a sound wave measured according to the present embodiment. FIG. 3 is a plan view showing X, 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 material to be measured. FIG. 4 is a front view of another embodiment of the present invention. FIG. 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 still another embodiment of the present invention. FIG. 8 is a cross-sectional view of a conventional composite AE sensor. FIG. 9 is a sectional view of a conventional single type AE sensor. FIG. 10 is a schematic perspective view showing a conventional acoustic measurement method using an AE sensor. [Description of Signs] 1 Near-focus composite AE sensor 1a Near-focus composite AE sensor 1b Near-focus composite AE sensor 1c Near-focus composite AE sensor 2 AE sensor 2A Concave spherical lens 2B Concave spherical lens 2C Concave spherical lens 3 Cover Measurement material 4 Delay material 5 Transducer 6 Concave sphere 7 Water 8 Concave sphere 9 Concave sphere 10 Concave sphere 11 Concave sphere 12 Material to be measured 13 AE sensor

Continuation of front page (56) References B. Kanai et. al. , 'Non-Contact Measurement of Acoustic Emission Signals in the 100 MHz Frequency Range. . . ', ACUSTI CA, Germany, May 1992, Vol. 76, no. 4, p. 199-204 (58) Field surveyed (Int. Cl. ⁷ , DB name) G01N 29/00-29/28 JICST file (JOIS)

Claims (1)

(57) [Claim 1] A sensor for detecting an acoustic signal (AE signal) generated by deformation or destruction of a material to judge the characteristics of the material. A near-focus type, comprising a plurality of spherical lenses, wherein each of the concave spherical lenses is arranged to be inclined with respect to each other, and the respective focal points are located close to each other and do not spatially coincide with each other. Composite AE sensor.