JPH0545346A - Ultrasonic probe - Google Patents

Abstract

PURPOSE:To obtain echoes of high flaw detecting sensitivity and high measuring accuracy by converging waves at a focal point at the side of a transversal wave oscillator separately provided from a longitudinal wave oscillator and, detecting the echoes of the longitudinal wave+transversal wave by two oscillators. CONSTITUTION:Longitudinal ultrasonic beams of a piezoelectric element 2b are brought in and refracted with an angle between the critical angles alpha1 and beta2 of the longitudinal and transversal waves by an acoustic lens 3a, turned to transversal waves in a test specimen 6 and converged at the position of a focal point F. Meanwhile, longitudinal ultrasonic beams from a piezoelectric element 2a enter to be refracted with an angle smaller than the angle alpha1, and converged in the vicinity of the point F inside the test specimen 6 as longitudinal waves, then passing through the test specimen. A focal area F where directional areas 12a, 12b of the ultrasonic beams of the elements 2a, 2b overlap is formed. When a defect exists in the area F, the element 2a detects the longitudinal wave echoes when mainly the longitudinal waves propagate in the test specimen 6. On the other hand, the element 2b detects the transversal wave echoes when the transversal waves propagate in the test specimen 6, as longitudinal wave echoes converted at the surface of the test specimen 6. These two detecting signals are processed to be a defect detecting signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic probe (hereinafter referred to as a probe), and more particularly to a probe capable of obtaining an echo having high flaw detection sensitivity and high measurement accuracy.

[0002]

2. Description of the Related Art An ultrasonic flaw detector is capable of nondestructively inspecting defects (inspection objects) inside an object (object to be inspected) by utilizing ultrasonic waves. Or ultrasonic waves are introduced into the inside of the probe by interposing an ultrasonic transmission medium between the probe and the subject. The ultrasonic waves used include longitudinal waves and transverse waves.

A longitudinal wave generation type probe is also generally used in the case of utilizing a transverse wave ultrasonic wave, and the longitudinal wave and the transverse wave are selected by the angle of incidence on the surface of the subject. That is, when the incident angle at the ultrasonic wave incident point of the probe with respect to the subject becomes large, longitudinal waves are converted into transverse waves when entering the inside of the subject and flaw detection as transverse waves can be performed, and the incident angle with respect to the subject is small. In this case, the ultrasonic wave of the longitudinal wave mainly penetrates into the subject as a longitudinal wave and becomes a flaw detection of the longitudinal wave. However, in reality, it is difficult to generate purely a longitudinal wave or a transverse wave, and the longitudinal wave and the transverse wave are mixed even in the conventional focus type probe as shown in FIG.

[0004]

In FIG. 3, 9 is a probe, 1 is its housing, 2 is a piezoelectric element as an ultrasonic transducer, 3 is an acoustic lens, 4 is a damper material, and 5 is The lead wire 6 is the subject. And, the dotted line shows the focusing line of the ultrasonic beam by the probe 9. Although the dotted line is a straight line, in reality, the surface of the subject is slightly refracted depending on the material of the subject 6.

By the way, longitudinal waves and transverse waves have different propagation speeds of sound waves in the medium. In ultrasonic measurement, it is impossible to distinguish which wave is an echo when these waves interfere with each other because of the calculation of the path length based on the speed of sound. As a result, it is difficult to measure the accurate distance to the defect. This lowers the flaw detection accuracy. This becomes a problem especially when the inside of the subject is multi-layered and has a plurality of boundary surfaces, or when there are some defects in different depth directions in a state of overlapping in a plan view. The reason is that the reflected wave of the longitudinal wave at the back boundary surface (or defect) and the reflected wave at the front boundary surface (or defect) interfere with each other.

Further, when ultrasonic flaw detection is performed using a focus type probe, if the focus is focused and the flaw detection accuracy is increased, the echo level is lowered and the flaw detection sensitivity is lowered. Conversely, the focus is increased to increase the flaw detection sensitivity. If it is taken large, the flaw detection accuracy is lowered, and there is a drawback that sufficient flaw detection cannot be performed depending on the subject. An object of the present invention is to solve the above-mentioned problems of the prior art, and to provide a probe having high flaw detection sensitivity and capable of obtaining an echo with high measurement accuracy.

[0007]

A probe according to the present invention which achieves the above object has a disk-shaped first oscillator in the center and a ring-shaped second oscillator provided concentrically with the first oscillator.
And an acoustic lens that causes the ultrasonic waves from the second ring-shaped oscillator to enter the subject in a range larger than the critical angle of the longitudinal wave and smaller than the critical angle of the transverse wave and focused at a predetermined position. And to obtain an echo from the subject by driving the first and second oscillators.

[0008]

As described above, in addition to the oscillator mainly composed of the longitudinal wave, the oscillator for generating the transverse wave is separately provided inside the object, and the focus is performed on the side of the oscillator for generating the transverse wave. If the two transducers receive the echoes of the longitudinal wave and the transverse wave at the focus focusing position by driving, the defect of the subject near the focus is highly sensitive and highly accurate echo can be obtained. it can.

[0009]

1 is a longitudinal sectional view and a lateral sectional view of an embodiment of a probe to which the present invention is applied, and FIG. 2 is an explanatory view of its ultrasonic peak focusing state. In addition,
The same components as those in FIG. 3 are designated by the same reference numerals. Figure 1 (a)
As shown in the longitudinal sectional view of FIG. 1 and the transverse sectional view along the surface of the piezoelectric element, the probe 10 is a piezoelectric element housed in the housing 1 and has its center aligned with the center line position of the cylinder of the housing 1. It is composed of a small disk-shaped piezoelectric element 2a provided and a ring-shaped piezoelectric element 2b whose center coincides with the center of the piezoelectric element 2a and is provided outside thereof. These piezoelectric elements generate longitudinal waves,
The acoustic lens 3a makes the longitudinal ultrasonic beam generated by the ring-shaped piezoelectric element 2b incident at an angle between the critical angle α _{1 of the} longitudinal wave and the critical angle α _{2 of the} transverse wave and refracts it. Then, it acts to make a transverse wave inside the subject 6 and focus it at the focal position F. Further, an ultrasonic wave of a longitudinal wave generated by the disk-shaped piezoelectric element 2a is made incident at an angle smaller than the critical angle α ₁ and refracted to be a longitudinal wave inside the subject 6 and is focused near the focal point F. It acts to pass through here. In addition, 7 is a lead of the piezoelectric element 2a, and 8
Is a lead wire of the piezoelectric element 2b.

As a result, as shown in FIG. 2, when these two piezoelectric elements 2a and 2b are driven, the directivity region 12a of the ultrasonic beam by the piezoelectric element 2a and the ultrasonic beam by the piezoelectric element 2b are generated. A focus area F that overlaps the directional area 12b is formed. Therefore, when a longitudinal wave (longitudinal wave + transverse wave) mainly due to the ultrasonic beam of the piezoelectric element 2a propagates inside the subject 6 and there is a defect in the previous focal region, the echo of the longitudinal wave is received by the piezoelectric element 2a. It is detected. Separately from this, when the transverse wave generated by the ultrasonic beam of the piezoelectric element 2b propagates inside the subject 6 and there is a defect in the previous focal region, the echo of the transverse wave is converted into a longitudinal wave echo on the surface of the subject 6. The piezoelectric element 2b receives and detects a longitudinal wave echo. By processing the two echo reception signals detected here as a defect detection signal, a large echo level can be obtained, so that the sensitivity is high, and the focus is high on the side of the transverse wave. Accurate defects can be detected.

By the way, the critical angle α ₁ of the longitudinal wave is an angle at which the ultrasonic wave cannot penetrate into the inside of the subject 6 as a longitudinal wave when the angle is larger than this (on the basis of the normal line).
Therefore, longitudinal waves and transverse waves coexist at angles smaller than the critical angle α ₁ . When this critical angle α ₁ or more, the subject 6
The longitudinal wave is converted into the transverse wave at the incident point of, and when it becomes an angle larger than the critical angle α ₂ of the transverse wave, the transverse wave cannot penetrate into the inside of the subject 6 and the ultrasonic wave is totally reflected on the surface of the subject 6. The critical angles α ₁ and α ₂ are different depending on the object 6 or the propagation medium interposed between the probe 10 and the object 6. Therefore, the acoustic lens 3a of the probe 10
The radii of the piezoelectric elements 2a and 2b and the like are determined according to the material of the subject 6 to be inspected and the ultrasonic propagation medium (usually water). For example, when the subject 6 is a copper material, the critical angle α ₁ between water and copper is about 14 ° at 25 ° C.,
The critical angle α ₂ is around 28 °. Therefore, according to this, the radius of the piezoelectric elements 2a and 2b and the curvature of the acoustic lens 3a are determined in relation to the focal length.

Since the longitudinal and transverse waves have different propagation velocities, when the focus position is set deep in the subject 6, the echo detected by the piezoelectric element 2a and the echo detected by the piezoelectric element 2b are detected. It is necessary to adjust the time lag with the echo. As a simple method for this adjustment, for example, the delay time corresponding to the difference in the path length between the longitudinal wave and the transverse wave to the focal point F is calculated, and the piezoelectric element 2b is pulse-driven first,
The piezoelectric element 2a may be pulse-driven after the previously calculated predetermined time delay. However, when the focus position is shallow, adjustment of the transverse wave and the longitudinal wave is almost unnecessary, and as can be understood from the focus focusing state of FIG.
It is possible to detect a defect at a focus position determined by a transverse wave with high sensitivity and high accuracy.

As described above, in the embodiment, one ring-shaped piezoelectric element is provided for the disk-shaped piezoelectric element provided at the center.
Although individual pieces are provided, a large number of ring-shaped piezoelectric elements having different radii may be provided concentrically with respect to the central disk-shaped piezoelectric element so that they can be used corresponding to various types of subjects.

[0014]

As can be understood from the above description, according to the present invention, in addition to a vibrator mainly composed of longitudinal waves, a vibrator for generating transverse waves is separately provided inside the subject to generate transverse waves. Focusing is performed on the transducer side, and by driving each of them, longitudinal wave + transverse wave echo is generated at the focus focusing position.
Since the two transducers are used for reception, it is possible to obtain highly accurate echoes with high sensitivity for defects of the subject near the focal point. As a result, it is possible to provide a highly sensitive and highly accurate probe by using each transducer. Furthermore, if only the ring-shaped transducer is driven, only transverse waves can be selectively generated for flaw detection. It is possible, and accurate measurement can be performed without the interference of two waves.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view and a lateral sectional view of an embodiment of a probe to which the present invention is applied.

FIG. 2 is an explanatory diagram of the ultrasonic peak focusing state.

FIG. 3 is a vertical cross-sectional view of a conventional fixed focus probe.

[Explanation of symbols]

1 ... Housing, 2, 2a, 2b ... Piezoelectric element, 3, 3a
... Acoustic lens, 4 ... Damper material, 5, 7, 8 ... Lead wire, 6 ... Subject, 9, 10 ... Probe, 12a, 12b
… Directional area of ultrasonic beam.

Claims (1)

[Claims] 1. A disk-shaped first vibrator in the center, a ring-shaped second vibrator provided concentrically with the disk-shaped first vibrator, and an ultrasonic wave from the second ring-shaped vibrator. An acoustic lens that causes a sound wave to be incident on a subject in a range larger than a critical angle of a longitudinal wave and smaller than a critical angle of a transverse wave to focus the acoustic wave at a predetermined position; An ultrasonic probe characterized by obtaining an echo from a specimen.