KR102106940B1 - Ultrasonic nondestructive inspection device using overtone vibrator - Google Patents

Abstract

The inspection apparatus of the present invention includes an irradiation unit that applies first and second ultrasonic waves to an object to be inspected; A receiver configured to receive a signal that has passed through the subject; It includes; a processing unit for analyzing the signal received from the receiving unit to analyze the defect or property of the subject, the first ultrasound has a fundamental frequency, the second ultrasound has an odd multiple of the fundamental frequency You can.

Description

Ultrasonic non-destructive testing device using a harmonic oscillator {ULTRASONIC NONDESTRUCTIVE INSPECTION DEVICE USING OVERTONE VIBRATOR}

The present invention relates to an ultrasonic non-destructive inspection device for inspecting defects of an object using ultrasonic waves.

Among the non-destructive inspection techniques, ultrasonic inspection is a representative technique for detecting defects in industrial equipment and evaluating reliability. In ultrasonic testing, nonlinear defects such as cracks are the most difficult to inspect. For micro-crack, it is a common method to perform defect inspection by identifying the diffraction wave at the tip of the crack or the reflected wave at the crack surface.

However, in the case of a closed crack or a partially closed crack, it is very difficult to detect a defect because the diffraction signal at the tip of the crack is very weak or the reflection signal of the crack surface does not appear.

A phased array ultrasonic inspection that focuses a beam on a defect and strengthens a detection signal accordingly has been developed, but it is difficult to expect an improvement effect to detect a crack which is a nonlinear defect.

In addition, a method of emitting a strong incident wave and detecting a nonlinear component generated when the crack surface is opened and closed by the incident wave can be considered, but in the case of a closed crack, the nonlinearity due to the opening and closing of the crack surface despite the strong incident wave The component output is so weak that it is difficult to perform a successful inspection.

Korean Registered Patent Publication No. 1414520 discloses a technique for determining whether a structure is small by vibrating a structure by applying signals of different frequencies.

Korean Registered Patent Publication No. 1414520

The present invention is to provide an ultrasonic non-destructive testing device capable of normally performing non-destructive testing regardless of the type of the object to be tested.

The inspection apparatus of the present invention includes an irradiation unit that applies first and second ultrasonic waves to an object to be inspected; A receiver configured to receive a reflected signal that has passed through the subject; And a processing unit configured to analyze the reflected signal to analyze defects or properties of the inspected object. The first ultrasound may have a fundamental frequency, and the second ultrasound may have a natural frequency that is an odd multiple of the fundamental frequency.

According to the present invention, the size (amplitude) of the second harmonic can be increased by using a harmonic oscillator and nonlinear wave synthesis. Therefore, a nonlinear ultrasonic non-destructive test of various test subjects can be accurately performed regardless of a test subject having a thin thickness and a high attenuation high scattering property.

1 is a schematic view showing an ultrasonic inspection apparatus of the present invention.
2 is a schematic view showing an ultrasound diagnostic means of a comparative example.
3 is a graph showing a received wave spectrum of a comparative example.
4 is a block diagram showing the inspection apparatus of the present invention.
5 is a schematic view showing another irradiation unit of the present invention.
6 is a schematic view illustrating an ultrasonic beam focusing process by time reversal processing of the present invention.
7 is a schematic view showing an ultrasound diagnostic method of the present invention.

Hereinafter, embodiments according to the present invention will be described in detail with reference to the accompanying drawings. In this process, the size or shape of the components shown in the drawings may be exaggerated for clarity and convenience of description. In addition, terms specifically defined in consideration of the configuration and operation of the present invention may vary depending on the intention or custom of the user or operator. Definitions of these terms should be made based on the contents throughout this specification.

1 is a schematic view showing an ultrasonic inspection apparatus of the present invention, and FIG. 2 is a schematic view showing an ultrasonic diagnostic means of a comparative example. 3 is a graph showing a received wave spectrum of a comparative example.

When single-frequency ultrasonic waves of strong intensity propagate inside the subject 10, harmonics due to nonlinearity of the subject material or damage to the subject are additionally generated. A non-destructive inspection method that detects and inspects material properties or damage by observing the additional harmonic changes is called a nonlinear ultrasound method.

In the conventional nonlinear ultrasound method, as shown in FIG. 2, a vibrator 90 is used that injects ultrasonic waves of a single frequency ω1 of strong intensity into a damaged material having a plastic deformation, fatigue, creep, or the like (hereinafter, an object 10). Nonlinear ultrasound examination, which observes the second harmonic 2ω1 that occurs when a single frequency ω1 ultrasonic wave is incident on the subject, is known as an effective method for early detection of damage. As shown in FIG. 3, the second harmonic is most frequently observed among a large number of harmonics, but the second harmonic is also very small in size (amplitude), so it is not easy to measure. In particular, non-linear diagnosis of a test subject having a high attenuation and high scattering material is almost impossible.

Referring to FIG. 3, in the case of the comparative example in which ultrasonic waves of a single frequency ω1 were applied to a subject, the magnitude of the second harmonic component (Spectrum of 2nd harmonics) is almost 0 based on the fundamental component (Spectrum of fundamental frequency). It can have a value that converges to. Therefore, it is practically impossible to calculate a nonlinear parameter value targeting the defect 20 inside the inspected object 10 in an actual field where noise is present.

Therefore, there is a need for a method that can easily apply the nonlinear ultrasonic inspection method by increasing the generation of the second harmonic component.

The inspection apparatus of the present invention can increase the size of the second harmonic by using the principle of harmonic oscillator and nonlinear wave synthesis. The inspection apparatus of the present invention can accurately inspect the properties and damages of various objects under test by using the second harmonic whose size is increased.

The inspection apparatus of the present invention may include an irradiation unit 110, a reception unit 130, and a processing unit 150.

The irradiation unit 110 may include an overtone frequency vibrator that simultaneously generates the first ultrasonic wave ① and the second ultrasonic wave ② and simultaneously applies them to the subject 10. The irradiation unit may simultaneously apply the first ultrasound and the second ultrasound to the same point of the subject, or may apply a composite signal (synthetic waveform) of the first ultrasound and the second ultrasound to a point of the subject.

The first ultrasound may have a basic frequency ω1.

The second ultrasound may have an odd multiple natural frequency 3ω1 that is dominant to the basic frequency ω1.

A finite amplitude tone burst waveform may be applied to the subject 10 by an irradiation unit that applies the first ultrasound and the second ultrasound. When the tone burst waveform propagates inside the subject, the differential frequency component 3ω1-ω1 = 2ω1 by nonlinear wave synthesis may overlap the second harmonic 2ω1 of the fundamental frequency ω1. As a result, the second harmonic component increases as the received wave spectrum shown in FIG.

The receiver may receive the reflected signal that has passed through the subject. The processing unit may analyze the reflected signal to analyze the defect or property of the subject. For example, the second harmonic component increased by the first ultrasound and the second ultrasound may be received by the receiving unit 130 and may have a size that can be analyzed by the processing unit 150.

To improve the size of the second harmonic component, the initial setting of the harmonic oscillator is very important.

The inspection apparatus of the present invention may be provided with a setting unit related to the initial setting of the harmonic oscillator.

It is required to select a piezoelectric material suitable for harmonic vibration and to produce an optimal harmonic oscillator, and also a setting technique for setting an irradiating part such as a harmonic oscillator.

The setting unit may include a measuring unit, an applying unit, and a processing unit 150.

The measurement unit may measure the natural frequency of the irradiation unit.

The applicator may calculate the relative magnitude ratios of the amplitudes of the first ultrasound and the second ultrasound for increasing the size of the second harmonic according to the natural vibration characteristics of the irradiation unit 110 identified by the measurement unit.

The first ultrasound and the second ultrasound having a size (amplitude) calculated by the applying unit are synthesized, and may be applied to the inspected object by the irradiation unit 110.

The processing unit 150 may analyze a sound field of a nonlinear wave generated by various excitations of the irradiation unit 110 and received by the reception unit 130. In addition, the processing unit may be in charge of signal processing of the received wave received through the receiving unit and extraction and analysis of various frequency components.

According to the inspection apparatus of the present invention, the application unit may apply a finite amplitude toneburst waveform having a frequency of ω1 or ω1 & 3ω1 to a single ultrasonic oscillator (overtone oscillator) having a basic frequency ω1 and an odd multiple natural frequency 3ω1. When the corresponding tone bust wave propagates inside the subject, the second harmonic component 2ω1 of the second frequency component 3ω1-ω1 = 2ω1 and ω1 by nonlinear wave synthesis may overlap each other. As a result, it is possible to generate a second harmonic having an amplitude that can be detected by the receiver and analyzed by the processor. Therefore, the generation of the second harmonic is basically suppressed, such as a material having a thin thickness, a high attenuation, or a high scattering material, or a nonlinear ultrasonic method may be applied to a test subject of a material having high energy loss. In addition, the damage degree of various materials can be detected with high sensitivity and high precision, and the reliability of nonlinear ultrasonic non-destructive testing can be significantly improved.

The irradiation unit of the present invention may use a composite wave of the first ultrasound and the second ultrasound from the incident stage of the inspection signal to the subject. In the propagation process inside the subject, various frequency components are generated by wave joint, and in particular, a second harmonic component is additionally generated. Therefore, the receiver can receive the second harmonic of a large amplitude.

The irradiation unit may excite ultrasonic waves in a contact or non-contact method to the subject.

In order to perform a diagnosis, such as determining the location of damage to a test object in an actual field, it is required to measure absolute nonlinear parameter values through calibration of a receiving unit that receives a signal passing through the test object. The calibration operation of the receiver is performed using the second harmonic component included in the signal. However, in the case of a known nonlinear ultrasound method, the measured second harmonic component has a fatal limit of almost zero. Therefore, the conventional nonlinear ultrasonic inspection method is not used in the actual field where various noises that make it difficult to detect the second harmonic are scattered, and is applied only in a laboratory capable of excluding noise.

4 is a block diagram showing the inspection apparatus of the present invention. 5 is a schematic view showing another irradiation unit of the present invention. 6 is a schematic view illustrating an ultrasonic beam focusing process by time reversal processing of the present invention. 7 is a schematic view showing an ultrasound diagnostic method of the present invention.

In order to generate second harmonics that are robust against noise, that is, have a strong intensity, the inspection apparatus of the present invention may include an irradiation unit 110, a reception unit 130, and a processing unit 150.

The irradiation unit 110 may generate ultrasound waves propagated from the first surface 11 of the object 10 to the second surface (bottom surface) 12. The first surface 11 and the second surface 12 may be different surfaces, for example, the first surface 11 is the upper surface of the object 10, and the second surface 12 is the object 10 It can be the underside of.

The receiving unit 130 is mounted on the first surface 11 of the subject 10 and can receive the first reflected signal and the second reflected signal.

A plurality of receiving units may be provided, and at least one of the receiving units may be integrally formed with the irradiation unit.

As another example, as shown in FIG. 5, the irradiator 110 may include a laser irradiator that irradiates a laser toward the first surface 11 at a position spaced apart from the subject 10. The first and second ultrasonic waves passing through the subject 10 may be generated by excitation of the laser irradiated onto the first surface 11, or a composite waveform of the first ultrasonic wave and the second ultrasonic wave may be generated. have.

The first reflected signal may be a signal in which ultrasonic waves propagated from the first surface 11 to the second surface (bottom surface) 12 of the subject 10 are reflected.

The second reflection signal may be a signal in which the time inversion signal propagated from the first surface 11 to the second surface 12 is reflected. In this case, the time inversion signal may be generated using the first reflection signal.

The irradiated portion contacting or spaced from the first surface may generate ultrasonic waves and radiate toward the second surface 12. In order to improve the spatial resolution, the plurality of receivers 130 may be arranged at points symmetrically with respect to the point of the subject to which ultrasonic waves are input.

The plurality of receivers 130 disposed on the first surface 11 may receive the first reflected signal from which ultrasonic waves are reflected from the second surface 12.

The plurality of receivers 130 may re-emit the time inversion signal. The time inversion signal propagates from the first surface 11 toward the second surface 12, and the second reflected signal may be received by the plurality of receivers.

When the first reflected signal is reflected from the specific position P on the second surface 12, the time reversal signal emitted from the plurality of receivers 130 may be focused on the specific position P. Since a plurality of beams emitted from the plurality of receivers 130 are focused at a specific location P, the resolution of the second reflected signal corresponding to the beam reflected at the specific location P can be improved.

The receiver 130 may receive a second reflected signal in which the time inverted signal of the first reflected signal is reflected on the second surface 12.

The processing unit 150 may calculate a nonlinear parameter value of the subject 10 using the second reflected signal.

Ultrasound may be reflected at the P position on the second surface 12 of the subject 10. Since the second surface 12 is a portion that borders with other media such as air and a support plate, the first reflection signal or the second reflection signal reflected on the second surface 12 is subject to minute cracks in the subject 10. A second harmonic component having a very large magnitude compared to the reflected signal may be included. Since the second harmonic component included in the signal reflected on the second surface 12 can be distinguished from noise, it can be easily grasped even in an actual site where noise is mixed.

The plurality of receivers 130 disposed on the first surface 11 of the subject 10 to generate a second harmonic component more robust to noise may generate a focused beam focused at the P position.

For reliable beam focusing, three or more arrayed receivers 130 may be in close contact with the first surface 11 of the subject 10, and a time reversal method may be applied for beam focusing. The time reversal signal to which the time reversal method is applied can be accurately focused on the P position of the second surface 12.

Since the signal emitted from each receiving unit 130 to the subject 10 is time-reversed, the ultrasonic beam can be accurately focused at the P position where the nonlinear defect exists even without knowing the prior information including the characteristics of the subject 10. .

The receiving unit 130 or the processing unit 150 is of particular interest in the non-linear component signal caused by multiple modes of the interface, the Lamb wave, or the non-linear component signal caused by reflected waves of various modes in the flat-shaped object 10 The signal of the mode is extracted and it is time-reversed.

Although the drawing shows a time reversal method for an array transducer in which N receivers 130 are arranged, the embodiment of the present invention is not limited to the array transducer, but is also limited by the receiver 130 installed individually. Can be implemented.

Referring to the first picture of FIG. 6, one of N receivers 130 provided in the array transducer is excited. The excited incident wave propagates to the subject 10.

Referring to the second picture of FIG. 6, the scattering signal (first reflection signal) reflected at the P position of the second surface 12 corresponding to the boundary surface of the subject 10 is received by each receiving unit 130. The characteristics of the medium of the subject 10, the surface geometry of the subject 10, and the distance difference from each receiving part 130 disposed on the first surface 11 to the second surface 12 are different for each receiving part 130 It is represented by a physical amount, such as a difference in the time delay amount of the echo signal or a waveform difference of each receiver 130.

According to the time reversal method of the present invention, only data regarding a time delay amount difference or a waveform difference is required, and knowledge of prior information is not required at all.

Since the distance to the P position is divided by the speed of the ultrasound, the time delay amount or waveform difference for each receiver 130 is different from the surface geometry of the subject 10 or the distance from each receiver 130 to the P position. Preliminary information such as differences is already included. Accordingly, if the time delay amount is calculated from the signal emitted and received by the receiving unit 130 and time reversal processing is used, detection of the P position is possible without knowing prior information such as surface geometry or media characteristics.

Although the prior information about the array transducer or the subject 10 is not known at all, the signal returned by propagating the inside of the subject 10 is used to return the prior information regarding the geometry and physical properties of the subject 10 It is reflected as it is. In the time reversal method, the propagation time of ultrasonic waves is based on the invariant characteristics of the array transducer or the subject 10 even if no prior information about the array transducer or the subject 10 is input. Moreover, according to the present invention, the size of the second harmonic can be significantly increased due to the first ultrasonic wave and the second ultrasonic wave.

Referring to the third picture of FIG. 6, without relying on obtaining prior information, time reversal is performed based on the difference in the time delay amount of each receiving unit 130 by the waveforms (first reflected signals) received by the N receiving units 130. Process. Each receiving unit 130 injects a new waveform (time reversal signal) subjected to time reversal into the subject 10. The time-reversed ultrasound beam (time-reversing signal) is accurately focused on the P position.

It is possible to use the original signal received in the time reversal processing of the received signal as it is, or to selectively extract the nonlinear signal of a specific mode of interest, time-reverse processing it, and to accurately analyze the P position.

Referring to the fourth picture of FIG. 6, the ultrasound beam (time reversal signal) focused at the P position is received again (second reflected signal) at each receiver 130. The obtained waveform is a waveform with improved signal-to-noise ratio, and contains accurate information (including coordinates and size) about the P position.

That is, when each receiving unit 130 is excited in a time-reversed state by reflecting the amount of time delay calculated by the time-reversing method, the excited ultrasound waves are focused to the P position. When the ultrasound is focused at the P position, the signal-to-noise ratio is improved, so a clean defect image can be obtained.

In order to improve inspection accuracy of nonlinear defects, it is preferable that a signal reception time of the reception unit 130 is longer than a signal transmission time. As the reception time of the first reflected signal increases, the peak amplitude of the harmonic component increases, so that pure harmonic component can be extracted without noise.

The first reflected signal may be input to the processing unit 150. When the frequency spectrum is obtained by Fourier transforming the first reflected signal in the received time domain, the processor 150 may extract the harmonic spectrum using a window function in the frequency domain. The processor 150 may generate a time inversion signal by converting the extracted harmonic spectrum into a time domain after time inversion processing. The processing unit 150 may amplify the time inversion signal and then provide it to the receiving unit 130.

The receiving unit 130 may re-emit the time inversion signal provided from the processing unit 150 toward the subject 10.

The first reflected signal contains information about a nonlinear defect such as an interface. Therefore, the time-reversing signal obtained by time-reversing the first reflected signal can be accurately focused at the P position having a non-linear characteristic according to the time-reversing processing without knowing any prior information. The time reversal signal propagated to the P position may be reflected from the P position again and be received by each receiver 130.

The processing unit 150 may process the first reflected signal or the second reflected signal received by each receiving unit 130. The processor 150 may analyze the second reflected signal to extract the fundamental frequency component and the second harmonic component, and calculate the nonlinear parameter value using the second harmonic component. At this time, the second harmonic component may be in a state in which the size is significantly increased by the first ultrasound and the second ultrasound provided by the irradiation unit in the initial stage.

The processor 150 may convert the fundamental frequency component or the second harmonic component to the absolute displacement by multiplying the transfer function of the receiver 130. The processing unit 150 may calculate a nonlinear parameter value by synthesizing the second reflected signal by applying a time delay to the reception unit 130. The processor 150 may calculate a nonlinear parameter value by correcting rotation or attenuation of the second reflected signal.

The processing unit 150 includes an oscilloscope 151, a processing module 153, a multi-channel function generator 155, a multi-channel amplifier 157, and an impedance matcher 159 (impedance) matching) can be provided.

The oscilloscope 151 may monitor the first reflected signal or the second reflected signal received from the receiving unit 130 and provide them to the processing module 153.

The processing module 153 may process the first reflected signal and provide it to a multi-channel function generator, or calculate a nonlinear parameter value of the subject 10 using the second reflected signal.

The processing module 153 may be provided with a receiving unit calibration module, a time inversion signal processing module, a receiving signal processing module, an absolute displacement calculation module, a nonlinear parameter value calculation module, and a diffraction and attenuation correction module.

The receiver calibration module may calibrate the reception frequency of the receiver 130 to grasp the absolute displacement of the second harmonic component.

The time inversion signal processing module may apply a time inversion method to the first reflected signal received by each receiving unit 130.

The received signal processing module may process the first reflected signal or the second reflected signal. For example, the received signal processing module may be synthesized after applying a time delay to the plurality of second reflected signals obtained from the plurality of receiving units 130.

The absolute displacement calculation module may calculate an absolute displacement of the second harmonic component or the like by multiplying the fundamental frequency component or the second harmonic component by the transfer function of the receiver 130.

The nonlinear parameter value calculation module may calculate the nonlinear parameter value β as in Equation 1 using the calculated absolute displacement.

The diffraction and attenuation correction module may correct the diffraction element and attenuation element included in the second reflected signal or the like.

The detailed operation and mathematical models of the receiver calibration module, the received signal processing module, the absolute displacement calculation module, the nonlinear parameter value calculation module, the diffraction and attenuation correction module are described in the paper 'Review of Second Harmonic Generation Measurement Techniques for Material State Determination in Metals' (J Nondestruct Eval DOI 10.1007 / s10921-014-0273-5).

The multi-channel function generator may generate each time inversion signal allocated to the plurality of receivers 130 installed on the first surface 11 using the result of processing the first reflected signal.

The multi-channel amplifier may amplify the time inversion signal allocated to each receiver 130.

The impedance matcher prevents the time inversion signal from being reflected from the first surface 11 and returning to the processing unit 150.

The ultrasound diagnosis method of the present invention is as follows.

First, ultrasonic waves may be radiated to the first surface 11 of the object 10 by the excitation of the irradiation unit 110. At this time, the first ultrasound and the second ultrasound may be synthesized.

Ultrasound passing through the inside of the subject 10 may be reflected by the second surface 12 (first reflection signal) and received by the plurality of receivers 130 disposed on the first surface 11. The probe receiving the first reflected signal may also include a probe generating ultrasonic waves.

When the first reflected signal received by each receiver 130 is time-reversed and retransmitted, a beam (time-reverse signal) may be focused on the reflection position P of the second surface 12.

After receiving the second reflection signal at which the time inversion signal is reflected at the position P at each receiving unit 130, and processing the signal, a fundamental frequency component and a second harmonic component may be obtained.

The receiving function may be synthesized by multiplying the transfer function of each receiving unit 130 to convert to an absolute displacement, and applying a time delay to the receiving unit 130.

Nonlinear parameter values before diffraction / attenuation correction can be obtained, and final nonlinear parameter values can be obtained by correcting diffraction and attenuation.

The ultrasonic diagnostic apparatus of the present invention uses first ultrasonic waves and second ultrasonic waves, and uses only one surface of the object 10 through the application of a non-contact excitation and reflection method, and thus has high field applicability. Since the signal returned by propagating the inside of the subject 10 is used for beam focusing, it is not necessary to know in advance the specifications of the array receiving unit 130 or the geometric shape and physical properties of the subject 10. Through the calibration of the receiver 130, absolute nonlinear parameter values of the subject 10 are measured, and diffraction and attenuation correction can be applied to provide more accurate nonlinear parameter values. Since a nonlinear ultrasound diagnosis apparatus is configured using at least three channels of the array receiving unit 130, there is an advantage of high productivity.

Although the embodiments according to the present invention have been described above, they are merely exemplary, and those skilled in the art will understand that various modifications and equivalent ranges of the embodiments are possible therefrom. Therefore, the true technical protection scope of the present invention should be defined by the following claims.

10 ... Subject 11 ... Page 1
12 ... second side 20 ... defect
110 ... Investigation department 130 ... Receiver
150 ... Processing unit 151 ... Oscilloscope
153 ... Processing module 155 ... Multi-channel function generator
157 ... multi-channel amplifier 159 ... impedance matcher

Claims (5)

An irradiation unit for applying the first ultrasound and the second ultrasound to the subject;
A receiver configured to receive a reflected signal that has passed through the subject;
A processing unit analyzing the reflection signal to analyze defects or properties of the subject;
Including,
The first ultrasound has a basic frequency,
The second ultrasound has a natural frequency that is an odd multiple of the basic frequency,
The irradiation unit includes a harmonic vibrator having the fundamental frequency and the odd multiple natural frequency,
A setting unit related to the initial setting of the harmonic oscillator is provided,
The setting unit includes a measuring unit and an applying unit,
The measurement unit measures the natural frequency of the irradiation unit,
The applying unit calculates the relative magnitude ratios of the amplitudes of the first ultrasonic wave and the second ultrasonic wave for increasing the size of the second harmonic according to the natural vibration characteristics of the irradiation portion determined by the measuring unit, and the magnitude calculated by the applying portion The first ultrasonic wave and the second ultrasonic wave having are synthesized, and are applied to the subject by the irradiation unit,
A tone burst waveform of a finite amplitude having the fundamental frequency and the odd multiple natural frequency is applied to the irradiation unit,
When the tone burst waveform propagates inside the subject, the differential frequency component and the second harmonic component by nonlinear wave synthesis overlap each other,
The receiving unit is an inspection device for receiving the second harmonic component whose amplitude is increased due to the overlap.
According to claim 1,
The irradiation unit is a test device for applying a composite waveform of the first ultrasound and the second ultrasound to a point of the subject.
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