KR20170064608A - Lamb wave generator - Google Patents

Abstract

The present invention relates to a plate wave generator using a plurality of wedge bridges and a single piezoelectric element, wherein a plate wave generator according to an embodiment of the present invention includes an ultrasonic probe for generating ultrasonic waves by having a single piezoelectric element, And a plurality of wedge bridges each having a body of a predetermined length and protruding from the body, wherein each of the plurality of wedge bridges is disposed in accordance with an interval based on the wavelength of the plate wave Wedges.

Description

{LAMB WAVE GENERATOR}

BACKGROUND OF THE INVENTION 1. Field of the Invention [0002] The present invention relates to a plate wave generator for generating a plate wave, which is one mode of guided ultrasonic modes.

Recently, a lamb wave or plate wave, which is one of the guided ultrasonic modes used in the ultrasonic nondestructive technique for detecting defects such as cracks in a large structure, is generated and used for non-destructive inspection have. .

In order to generate such a plate wave, in order to generate guided ultrasonic waves by using a plurality of ultrasonic transmitting / receiving piezoelectric elements, a plurality of piezoelectric elements are used. Therefore, a shielding structure for preventing sound waves and electrical interference between the elements should be included. And additional technical elements for securing structural stability such as alignment.

Therefore, the fabrication of array guided ultrasonic transducers, including these problems, requires considerable time and cost, which leads to higher selling prices.

Further, when guided ultrasonic inspection using various plate wave modes and frequencies is required, an array ultrasonic probe manufactured custom-made according to the plate wave mode and the center frequency is required, which increases the manufacturing cost.

Korean Patent Publication No. 2008-0057510

According to one embodiment of the present invention, a film wave generator using a plurality of wedge bridges and a single piezoelectric element is provided.

According to another aspect of the present invention, there is provided a plate wave generator comprising: an ultrasonic probe for generating ultrasonic waves having a single piezoelectric element; and a controller for generating a plate wave by receiving the ultrasonic waves, A plurality of wedge bridges each having a body and protruding from the body, each of the plurality of wedge bridges may include a wedge disposed along an interval based on the wavelength of the film wave.

According to an embodiment of the present invention, it is possible to simplify the structural complexity and reduce the manufacturing cost, thereby generating a desired low-priced and simultaneously desired wave-guided ultrasonic wave.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic view showing a wedge for a plate wave of a plate wave generator according to an embodiment of the present invention; Fig.
2 is a conceptual diagram for generating a plate wave using a plate wave generator according to an embodiment of the present invention.
3 is a view for explaining a governing equation showing the behavior of a sound wave in a solid for a plate-like structure.
4A is a dispersion diagram of phase velocity, and FIG. 4B is a group velocity dispersion diagram.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings, in order that those skilled in the art can easily carry out the present invention.

FIG. 1 is a schematic view showing a wedge for a plate wave of a plate wave generator according to an embodiment of the present invention, and FIG. 2 is a conceptual diagram for generating plate wave using a plate wave generator according to an embodiment of the present invention.

1 and 2, the plate wave generator 100 according to an embodiment of the present invention may include an ultrasonic probe 110 and a wedge 120.

The ultrasonic probe 110 can examine the subject A by sending ultrasonic waves and receiving a signal reflected from the discontinuous portion.

The single piezoelectric element 111 can transmit and receive the ultrasonic waves.

The wedge 120 generates a plate wave in accordance with the ultrasonic wave from the ultrasonic probe 110 and can transmit it to the subject A. [

The wedge 120 includes a body 121 having a predetermined length and a plurality of wedge bridges 122 protruding from the body 121 to generate a plate wave in contact with the object A, And a wedge attaching portion 123 for attaching the bridge 122 to the ultrasonic probe 110. [

The plurality of wedge bridges 122 can generate a plate wave in contact with the object (A) in accordance with ultrasonic waves from the ultrasonic probe 110.

Each of the wedge bridges of the plurality of wedge bridges 122 may be disposed at regular intervals from each other, and the distance D between the wedge bridges may be based on the wavelength of the plate wave and may be the same as the wavelength of the plate wave.

3 is a view for explaining a governing equation showing the behavior of a sound wave in a solid for a plate-like structure.

Referring to FIG. 3, the Navier governing equation (wave motion equation), which is a governing equation representing the behavior of a sound wave in a solid, is expressed as Equation 1 below.

(Equation 1)

Where μ and λ are Lame constants, u is displacement, r is density, and f is force.

To the central axis (x ₁₎ of If for the plate-shaped structure having a thickness 2h as shown in Figure 3 of the above governing equations loosen using the boundary condition that the stress state is zero in the thickness direction (x ₃₎ in the upper and lower surface plates (2) and (3), which represent the symmetric and asymmetric modes, respectively, can be obtained.

(Equation 2)

(Equation 3)

^{Here, p 2 = (ω / C} L) 2 -k 2 ^{a, q 2 = (ω / C} T) and ^{-k 2, ω: circular frequency,} k: wave number, C L: longitudinal velocity, C _T: Transverse wave velocity, and C _P : phase velocity.

(S mode) and asymmetric mode (A) with respect to the frequency (f, MHz) x plate thickness (d, mm) by obtaining the solutions according to the respective frequencies through the numerical analysis of the above- The dispersion curves representing the phase and the group velocity can be obtained.

4A is a dispersion diagram of phase velocity, and FIG. 4B is a group velocity dispersion diagram.

Referring to FIGS. 4A and 4B, a product (fd value) of a frequency and a plate thickness of each mode of a plate wave which can be generated in a plate material structure in a general carbon steel is shown. As shown, S ₀ and A ₀ modes, which are the lowest modes of symmetry and asymmetry at the low fd value, occur first, and as the fd value increases, higher modes are also generated so that a plurality of modes occur simultaneously at a specific fd value Can be seen. It can be seen that the phase velocity and the group velocity of each mode vary depending on the fd value.

Based on the above-mentioned phase velocity and group velocity dispersion diagram, the plate mode and the center frequency are determined according to the application purpose, and the structure of the array guided ultrasonic probe is designed and manufactured. The important design factor here is the center frequency of the ultrasonic transducer and the distance between the elements. The center frequency of the piezoelectric element is determined by the material and the size, and the interval between the piezoelectric elements is expressed by the following equation (4), which is determined by the frequency and the phase velocity of the plate wave mode to be generated.

(Equation 4)

Where λ is the wavelength, and D is the piezoelectric element spacing.

That is, in order to generate the desired plate wave mode most efficiently by using the array guided ultrasonic probe, the piezoelectric element should be arranged at the same interval as the wavelength of the plate wave mode to be generated. Since the wavelength of a generally used plate wave is several millimeters and the size or thickness of the piezoelectric element is several millimeters, precise placement, alignment and stable fixing of the piezoelectric element are indispensable for ensuring the performance of the guided ultrasonic wave. Therefore, precise and complicated processes are required for manufacturing an array type ultrasonic probe using a plurality of piezoelectric elements, which leads directly to an increase in manufacturing cost of the probe.

In order to solve such a problem, a plate wave can be generated by using a wedge that can generate the same effect as an ultrasonic probe using a single piezoelectric element and an arrayed probe, as shown in Figs. 1 and 2.

The wedge 120 of the present invention can be made of the same or similar material as a wedge widely used in a general ultrasonic nondestructive inspection technique, and thus can be easily processed and manufactured at a relatively low cost. Also, Can be replaced and used. It is easy to replace when worn or damaged due to long use.

As described above, according to the present invention, the film wave generator can simplify the structural complexity and lower the fabrication cost, and can generate desired plate waveguide ultrasound at low cost and at the same time.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not intended to limit the invention to the particular forms disclosed. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

100: plate wave generator
110: Ultrasonic probe
111: Single piezoelectric element
120: Wedge
121: Body
122: Wedge bridge
123: Wedge attachment portion

Claims (4)

An ultrasonic probe having a single piezoelectric element to generate ultrasonic waves; And
And a plurality of wedge bridges protruding from the body, each of the plurality of wedge bridges having a body having a predetermined length, the wedge bridges each generating a plate wave based on the wavelength of the plate wave, The wedge
(2).
The method according to claim 1,
Wherein each of the plurality of wedge bridges contacts a surface of an object to be inspected to generate a plate wave.
The method according to claim 1,
Wherein the wedge further comprises a wedge attaching portion and is attached to the ultrasonic probe.
The method according to claim 1,
And the interval is equal to the wavelength of the plate wave.

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