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BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
ultrasonic probe used in an ultrasonic flaw detector or the like. 2. Description of the Related Art
An ultrasonic flaw detector is an object to be inspected (a device for nondestructively inspecting
a defect inside a subject, and is generally well known. In such an ultrasonic flaw detector, an
ultrasonic probe is used which outputs ultrasonic waves and converts the reflected waves of the
output ultrasonic waves into electrical signals. The ultrasound probe will be described with
reference to the drawings. FIG. 2 is a cross-sectional view of a conventional ultrasonic probe. In
the figure, l is a housing of the ultrasound probe. Reference numeral 2 denotes a piezoelectric
element housed in the housing 1, which radiates an ultrasonic wave when a pulse voltage is
applied, and inputs its reflected wave and converts it into an electrical signal proportional to the
input. Reference numeral 3 denotes an acoustic lens provided on the front surface 1 of the
piezoelectric element 2 in the drawing, and is a concave lens. The piezoelectric element 2 is
bonded to the acoustic lens 3 with a toner. Reference numeral 4 denotes a backing material
provided on the back surface of the piezoelectric element 2, 5 denotes a lead wire connected to
the piezoelectric element 2, and 6 denotes a subject. When flaw detection is performed, the
subject 6 and the ultrasound probe are placed in a water tank, and the transfer of the ultrasound
writing between the ultrasound probe and the subject 6 is performed via water. When a pulse
voltage is applied to the piezoelectric element 2, the piezoelectric element 2 emits an ultrasonic
wave. The ultrasonic waves are focused by the acoustic lens 3 as shown by the broken line and
are made to enter the subject 6. The ultrasonic waves reflected at various places (surface, bottom,
defect, etc.) of the subject 6 again pass through the acoustic lens 3 and return to the piezoelectric
element 2 to excite it and be proportional to the size of the ultrasonic wave, fc! This signal is
converted into a signal which is output from the lead 5 to an external signal processing circuit
(not shown). The signal processing circuit appropriately processes the signal to analyze the
presence or absence of the internal defect of the subject 6 and the position and the size thereof.
[Problems to be Solved by the Invention] By the way, when the ultrasonic wave output from the
ultrasonic probe is incident on the object 6 (solid), the vibration in the body 6 to be conditioned
is the same as the traveling direction. Waves and transversal waves are generated whose
vibrations are perpendicular to the direction of travel. The propagation velocity at which the
transverse wave propagates in the subject 6 is 0.5 to 0.6 times the propagation velocity of the
longitudinal wave. As described above, since longitudinal waves and configurations having
different speeds are mixed in the subject 6 and the respective reflected waves return to the
ultrasonic wave contactor, for example, the longitudinal waves are employed to perform flaw
detection. In spite of that, there is a problem that the flaw detection accuracy often drops due to
the fact that the transverse wave is often adopted to carry out the flaw detection.
Also, when the object 6 has a multilayer structure, a reflected wave is generated at the interface
between the layers, but since there is a difference in propagation velocity between the
longitudinal wave and the transverse wave as described above, the longitudinal wave at a certain
interface There is also a possibility that interference may occur between the reflected wave of
and the reflected wave of the transverse wave at the other interface, and the desired flaw
detection may become difficult. The object of the present invention is to solve the problems of
the prior art and to provide an ultrasonic probe capable of preventing the mixing of longitudinal
waves and transverse waves, and thus capable of performing flaw detection with high accuracy
and high reliability. It is in. [Means for Solving the Problems] In order to achieve the above
object, the present invention relates to a piezoelectric element for transmitting and receiving
ultrasonic waves and an ultrasonic probe provided with an acoustic lens adjacent to the
piezoelectric element. A% reduction is provided between the lens and the piezoelectric element,
in the ultrasonic wave output from the acoustic lens, a region of high impedance with respect to
the ultrasonic wave output within the longitudinal wave critical angle. [Operation] Of the
ultrasonic waves outputted from the piezoelectric element, the ultrasonic waves outputted from
the piezoelectric element portion in direct contact with the acoustic lens are inputted to the
acoustic lens and radiated from the acoustic lens. This ultrasonic wave is an angle at which the
incident angle with respect to the subject exceeds the critical angle of the longitudinal wave, so
the ultrasonic wave generated in the subject becomes a transverse wave. On the other hand,
although the ultrasonic wave emitted from the piezoelectric element in contact with the high
impedance area is inputted to the area, this area is made of a substance showing high impedance
to the ultrasonic wave like an air layer, for example. Therefore, the inputted ultrasonic waves are
greatly attenuated, and the ultrasonic waves reaching the acoustic lens become extremely small.
Therefore, ultrasonic waves within the critical longitudinal wave angle that cause longitudinal
waves when entering into the subject become substantially zero. As a result of the above, the
ultrasonic waves in the subject become two of transverse waves. The present invention will be
described below based on the illustrated embodiments. FIG. 1 is a cross-sectional view of an
ultrasonic probe according to an embodiment of the present invention. In the figure, the same
parts as the parts shown in FIG. An acoustic lens 8 corresponds to the acoustic lens shown in FIG.
2 and an air layer 9 is shown. The acoustic lens 8 is different from the acoustic lens 3 shown in
FIG. 2 in that the acoustic lens 8 has a recess that constitutes the air layer 9, and the other points
are the same. By the formation of the air layer 9, the piezoelectric element 2 in this portion is
disconnected from the acoustic lens 8. The air layer 9 is formed to have a predetermined size,
which will be described later. Next, the operation of this embodiment will be described. When a
pulse voltage is applied to the piezoelectric element 2, an ultrasonic wave is emitted from the
pressure Kg element 2, and an ultrasonic wave emitted from a portion in contact with the
acoustic lens 8 enters the acoustic lens 8 in its case. Like the ones, it is focused as shown by the
outer dashed line in FIG.
On the other hand, the super-ti emitted from the portion facing the air layer 9 enters the air layer
9 and is significantly attenuated, and the intensity of the ultrasonic wave that has left the air
layer 9 and reached the acoustic lens 8 Is very small. And this ultrasonic wave is by acoustic lens
8! When it is focused to reach the object, it is attenuated further and its intensity is substantially
zero, that is, it can be considered that the ultrasonic wave does not exist. By the way, the angle at
which the ultrasonic wave enters the object 6 and generates a longitudinal wave is limited, and
no longitudinal wave is generated when it is incident at an angle exceeding a certain angle
(critical angle). This critical angle is indicated by v, the angle α in FIG. Similarly, there is also a
critical angle for the transverse waves, which is shown in FIG. 1 by the angle α. Angle α1. The
relationship of α, is (α1 × α,). When the ultrasonic wave is incident on the subject at an angle
α, the ultrasonic wave is totally reflected and is not input into the subject. Therefore, if the air
layer 9 is formed so that the ultrasonic wave passing through the air layer 9 is an ultrasonic
wave focused within the critical angle α1, ultrasonic waves emitted from the acoustic lens 8 are
generated. Those within the angle α1 are substantially not included, and as a result, the
ultrasonic waves generated in the body 6 are only transverse waves. As described above, in the
present embodiment, since the air layer for attenuating the ultrasonic wave within the critical
angle of the longitudinal wave is formed on the piezoelectric element side of the acoustic lens,
only the transverse wave is generated in the object and only the transverse wave is generated.
The flaw detection is carried out, so that data of other waves are erroneously collected or
interference of two waves does not occur when the object has a multilayer structure, so that high
accuracy and high reliability can be obtained. It is possible to do flaw detection. Also, since the
air layer is formed simply by providing a recess on the upper surface of the acoustic lens 8, the
structure is simple and can be easily configured. Although the example in which the air J- is
provided has been described in the above embodiment, the present invention is not limited to
this, and any method can be applied as long as it can attenuate ultrasonic waves. [Effects of the
Invention] As described above, according to the present invention, the high impedance region for
the ultrasonic wave is provided between the element and the acoustic lens so that the ultrasonic
wave is not generated within the critical angle of the longitudinal wave. Only the transverse wave
can be stopped in the subject, thereby erroneously collecting the data of the other wave and fc,
the interference of the two waves does not occur fc, and the high accuracy and high reliability
The flaw detection of
Brief description of the drawings
FIG. 1 is a cross-sectional view of an ultrasound probe according to an embodiment of the
present invention, and FIG. 2 is a cross-sectional view of a conventional ultrasound probe.
2 · · · Piezoelectric element, 6 · · · Open subject, 8 · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · ·
air layer Figure 1 Figure 2 Figure 2 · l + 6: intense body 8: Acoustic lens. 9: The air layer
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