KR101218616B1 - Calibration method of contract transducer for absolute measurement of nonlinearity parameter, apparatus for calibration by using the method, and method and apparatus for absolute measurement of the parameter by using the method - Google Patents

Abstract

The present invention relates to a calibration method that can easily and accurately specify the characteristics of a transmission unit and to accurately specify a nonlinear parameter, a calibration apparatus to which the calibration method is applied, and a nonlinear parameter measurement method and apparatus to which the calibration method is applied. It is about.
The present invention is to obtain the power transfer function and the current-displacement transfer function of the transfer unit by measuring the input current input to the inspection target and the output current output through the transfer unit is reflected by the input current inside the inspection target. The present invention relates to a delivery calibration method and apparatus for measuring non-linear parameters.
The present invention calculates the power transfer function and the current-displacement transfer function of the transfer unit, and after measuring the output current passing through the test object, obtains the absolute displacement amplitude of the harmonic components, thereby measuring the nonlinear parameters. It relates to a non-linear parameter measurement method and apparatus that can be.

Description

CALIBRATION method of contract transducer for absolute measurement of nonlinearity parameter, apparatus for calibration by using the method for calibration of delivery unit for nonlinear parameter measurement, calibration apparatus using the calibration method, and nonlinear parameter measurement method and apparatus using the calibration method , and method and apparatus for absolute measurement of the parameter by using the method}

The present invention relates to a calibration method that can easily and accurately specify the characteristics of a transmission unit and to accurately specify a nonlinear parameter, a calibration apparatus to which the calibration method is applied, and a nonlinear parameter measurement method and apparatus to which the calibration method is applied. It is about.

The present invention is to obtain the power transfer function and the current-displacement transfer function of the transfer unit by measuring the input current input to the inspection target and the output current output through the transfer unit is reflected by the input current inside the inspection target. The present invention relates to a delivery calibration method and apparatus for measuring non-linear parameters.

The present invention calculates the power transfer function and the current-displacement transfer function of the transfer unit, and after measuring the output current passing through the test object, obtains the absolute displacement amplitude of the harmonic components, thereby measuring the nonlinear parameters. It relates to a non-linear parameter measurement method and apparatus that can be.

In general, non-destruction inspection refers to a method of externally inspecting internal defects such as pores, aging / deterioration, cracking, fatigue damage, etc. without destroying industrial products or materials.

As the non-destructive inspection method, a method using radiation or ultrasonic waves, a eddy current test, a magnetic particle inspection method, or the like has been selectively employed depending on the kind and defect of the material.

Here, the ultrasonic method is a technique that can be applied more easily at the actual inspection site than other methods, but there is a problem that it is not easy to measure the nonlinearity parameter required to specify the physical property value of the inspection object. Has come.

Schematically, when a wave having a single frequency is transmitted to an inspection object, harmonic distortion of the wave is generated according to the material properties. The more precise the measurement of the harmonic distortion, the more accurate the nonlinear parameter is.

However, the accurate measurement of harmonic distortion is eventually formed in contact with the inspection object, requiring the characteristic of the transmission unit that performs the function of mediating the wave between the inspection object and the measurement device.

Conventionally, there has been a problem that a calibration operation that specifies the characteristics of this delivery section has not been easy to apply to the inspection site and thus the accuracy is poor.

Therefore, the calibration method for specifying the characteristics of the transmission part is simple and accurate, and the development of a calibration method capable of accurately specifying nonlinear parameters, a calibration apparatus employing the calibration method, and a measurement method and apparatus for measuring the nonlinear parameter applying the calibration method It is a desperate situation.

Hereinafter, the prior art related to the non-destructive inspection using ultrasonic waves will be examined.

First, Korean Patent Laid-Open Publication No. 10-2009-0015596 relates to a structural health monitoring method using guided ultrasonic waves, and characterized in that it detects damage to a structure by analyzing an amplitude change of a signal difference received from a sensor.

This is positive in terms of determining the location of the damage by using the propagation time of the guided ultrasonic wave after detecting the damage using the sensor, but there is no description on how to measure the nonlinear parameter.

Secondly, Korean Patent Laid-Open Publication No. 10-2005-0061976 relates to a non-destructive inspection ultrasonic detection system, which is characterized by a system including five piezoelectric elements, an ultrasonic wave generator, and an ultrasonic wave receiver. No method or the like is described.

Third, the Republic of Korea Patent Publication No. 10-2005-0042542 relates to a non-destructive acoustic sensing method using a nonlinear acoustic response, characterized in that the relative nonlinear coefficient and the defect existence index is calculated for the frequency of the incident ultrasound. .

Here, the relative nonlinear coefficient is the ratio of the amplitude power spectrum of the double oscillation frequency to the amplitude power spectrum of the incident frequency, and the defect existence index is the relative nonlinear coefficient of the reference specimen without defect and the average relative nonlinear coefficient of the test specimen. It is defined as the difference from.

Although it is positive to newly define the relative nonlinear coefficient and the defect existence index and perform the non-destructive test using the same, it is not described in terms of measuring the nonlinear parameter or calibrating the transmission unit for measuring the nonlinear parameter.

SUMMARY OF THE INVENTION An object of the present invention is to provide a calibration method capable of specifying a nonlinear parameter accurately, in which calibration for specifying the characteristics of the transmission unit is simple and accurate, and a calibration apparatus to which the calibration method is applied, and a measurement apparatus for nonlinear parameters to which the calibration method is applied. In providing.

The present invention is to obtain the power transfer function and the current-displacement transfer function of the transfer unit by measuring the input current input to the inspection target and the output current output through the transfer unit is reflected by the input current inside the inspection target. It is an object of the present invention to provide a method and apparatus for calibrating a transmission unit for nonlinear parameter measurement.

The present invention calculates the power transfer function and the current-displacement transfer function of the transfer unit, and after measuring the output current passing through the test object, obtains the absolute displacement amplitude of the harmonic components, thereby measuring the nonlinear parameters. By providing a non-linear parameter measuring method and apparatus, it is intended to solve the technical problem.

The present invention has the remarkable effect that the calibration for specifying the characteristics of the delivery section is simple and accurate, so that the nonlinear parameters can be accurately specified.

The present invention has a remarkable effect of newly defining the electro-acoustic relationship of the delivery unit to calibrate the delivery unit only by measuring the current, and thereby accurately measuring nonlinear parameters.

The present invention has a remarkable effect of specifying a non-linear parameter in an absolute sense irrespective of an inspection object and an inspection condition by simply and accurately defining a calibration method so that it can be easily applied at an actual inspection site.

1 is a view schematically illustrating a process in which harmonics are generated and propagated in an inspection object.
2 is a schematic diagram illustrating a power transfer function in a transfer unit.
3 and 4 are diagrams schematically illustrating a principle of obtaining a transfer function using a calibration operation of the transfer unit.
5 is a diagram schematically illustrating an example of measuring an input current in a calibration device for a calibration operation of a transfer unit.
6 is a view schematically showing an example of measuring the output current in the calibration device for the calibration operation of the transfer unit.
7 is a diagram schematically illustrating an example of measuring an output current in a nonlinear parameter measuring apparatus.
FIG. 8A is a graph of recording the time domain output current measured in FIG. 7.
FIG. 8B is a graph showing the frequency spectrum of harmonics using the output current measured in FIG.
FIG. 9A is a graph showing time-domain displacements of fundamental harmonic components in the frequency spectrum of FIG. 8B.
FIG. 9B is a graph showing the time-domain displacement of the second harmonic component in the frequency spectrum of FIG. 8B.

The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may properly define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention.

Therefore, the embodiments described in the present specification and the configurations shown in the drawings are merely the most preferred embodiments of the present invention and are not intended to represent all of the technical ideas of the present invention. Therefore, various equivalents It should be understood that water and variations may be present.

Before describing the present invention with reference to the accompanying drawings, it should be noted that the present invention is not described or specifically described with respect to a known configuration that can be easily added by a person skilled in the art, Let the sound be revealed.

First, the present invention will be described with reference to nonlinear parameters in detail.

Nonlinear parameters are properties that can be measured by inducing nonlinearity within the inspection object and are important factors for identifying the deformation, microstructure, and damage of materials.

That is, the harmonic distortion phenomenon is generated by transmitting a wave having a single frequency inside the inspection object, and the characteristics of the inspection object are identified by measuring the nonlinear parameter using the wave.

Therefore, it is necessary to measure the nonlinear parameter value in the absolute sense that can represent the characteristics of the inspection object.

는 다음과 같이 정의된다.Non-linear parameters where the planar longitudinal wave propagates inside the nonlinear medium, causing harmonic distortion

Is defined as

는 비선형 파라미터, A₁ 은 기본 고조파 성분의 절대 변위 진폭(absolute displacement amplitude, peak strain amplitude), A₂ 는 2차 고조파 성분의 절대 변위 진폭으로서, 파동이 검사 대상을 통과한 후에 측정된 값을 의미한다. From here,

Is the nonlinear parameter, A ₁ is the absolute displacement amplitude of the fundamental harmonic component, and A ₂ is the absolute displacement amplitude of the second harmonic component, and it is measured after the wave passes the test object. do.

은 기본 주파수이다.
K is the wave number, x is the thickness of the inspection object (wave propagation distance), v is the velocity within the inspection object of the longitudinal wave,

Is the fundamental frequency.

In other words, in order to obtain the nonlinear parameters, the absolute displacement amplitudes of the fundamental harmonic components and the second harmonic components due to the harmonic distortions inside the inspection object must be measured.

1 is a view schematically illustrating a process in which harmonics are generated and propagated in an inspection object.

는 기본 주파수와 동일한 단일 주파수를 갖는 입력 전력이며, 이 입력 전력은 검사 대상에 접촉되어 형성된 전송부를 통해 검사 대상으로 입력된다.

Is input power having a single frequency equal to the fundamental frequency, and the input power is input to the inspection object through a transmission unit formed in contact with the inspection object.

Here, the transmission part is composed of a material causing a piezoelectric effect and a fluid medium for bringing the material into contact with the inspection object, and in particular, a material having a frequency equal to the frequency of the input power is selected to cause a resonance phenomenon so that distortion does not occur. do.

은 전송부를 통과하여 기본 주파수와 동일한 단일 주파수를 갖는 음향 파워

로 전환된다.Input power

Passes through the transmitter and has a single frequency equal to the fundamental frequency

Is switched to.

로 정의할 수 있게 된다.
This acoustic power propagates inside the inspection target, which is a nonlinear medium, and causes harmonic distortion. Among them, the acoustic power including the fundamental harmonic components and the second harmonic components

It can be defined as.

The acoustic power including the fundamental harmonic component and the second harmonic component passes through the test object and passes through the test object, which, like the transmission part, consists of a material causing a piezoelectric effect and a fluid medium for contacting the material with the test object.

로 정의된다.
The output power converted to the piezoelectric effect while passing through the transfer section

.

Therefore, the transmission unit is selected to resonate with the fundamental frequency when the wave passes through the inspection object, and it is important to specify the transmission unit to specify the characteristics inside the inspection object.

2 is a schematic diagram illustrating a power transfer function in a transfer unit.

가 전달부를 통과하면서 압전 효과에 변환된 출력 전력

과의 전력 전달함수

를 정의할 수 있다.Sound power including fundamental and second harmonic components

Output power converted to piezoelectric effect while the transmitter passes through

Power transfer function

Can be defined.

If the power of Equation 2 is expressed differently, it may be written as the following equation.

는 절대 변위 진폭을 주파수 함수로서 나타낸 것이고,

는 검사 대상의 밀도(density)이며, v 는 검사 대상 내부에서의 종파 속도이고, a는 전달부의 면적을 의미하며,

는 측정된 출력 전류를 주파수 함수로서 나타낸 것이다.
From here,

Is the absolute displacement amplitude as a function of frequency,

Is the density of the test object, v is the longitudinal wave velocity inside the test object, a is the area of the transmission part,

Denotes the measured output current as a function of frequency.

Herein, in order to obtain the nonlinear parameter, it is important to determine the absolute displacement amplitude. Equation 3 can be converted as follows.

는 전달부 기준의 출력 임피던스를 의미한다.
From here,

Denotes the output impedance of the transmitter reference.

Equation 4 is expressed as follows, whereby the current-displacement transfer function H (w) for converting the amplitude of the output current into the absolute displacement amplitude of the harmonic frequency component can be defined as follows.

Also referring to Equations 4 and 5, the current-displacement transfer function may be expressed as follows.

Here, the case where the output impedance of the transmission unit reference is set to 50 kHz is added. Of course, different values may come depending on the design conditions.

를 특정하기 위해서는 절대 변위 진폭

가 필요하며, 이 절대 변위 진폭을 구하기 위해서는, 출력 전류

및 전류-변위 전달함수 H(w)가 구해져야만 된다는 것이다.Note that nonlinear parameters

To specify the absolute displacement amplitude

In order to find this absolute displacement amplitude, the output current

And the current-displacement transfer function H (w) must be obtained.

In addition, in order to obtain the current-displacement transfer function H (w), the power transfer function K _R (w) must be obtained.

를 측정함으로써 비선형 파라미터를 구할 수 있게 된다.
In summary, after calculating the power transfer function and the current-displacement transfer function through a calibration operation that specifies the characteristics of the transfer unit, the output current when performing the actual inspection

By measuring the nonlinear parameters can be obtained.

3 and 4 are diagrams schematically illustrating a principle of obtaining a transfer function using a calibration operation of the transfer unit.

First, it is assumed that the mutuality is established between the input and the output in the transfer unit, and it is revealed that the transfer unit is selected and configured.

Referring to FIGS. 3 and 4, it can be seen that the input power is reflected and output. Accordingly, the power transfer function can be expressed using Equation 2, but the acoustic power portion is removed.

는 다음과 같이 정리된다.Here, if power is expressed as a current, the impedance is canceled, so the power transfer function

Is summarized as follows.

를 구할 수 있으며, 이를 수학식 6에 대입하면 전류-변위 전달함수 H(w)를 구할 수 있게 되므로, 교정 작업을 통해 전달부의 특징을 특정할 수 있게 된다.
Therefore, if the input current and output current are found through the calibration operation of the transfer unit, the power transfer function

By substituting this in Equation 6, the current-displacement transfer function H (w) can be obtained, so that the characteristics of the transfer unit can be specified through a calibration operation.

5 is a diagram schematically illustrating an example of measuring an input current in a calibration device for a calibration operation of a transfer unit.

First, it is noted that each component used in the calibration device may be selectively employed to suit the characteristics of the inspection object and the delivery unit, and is not limited to that shown in the drawings.

Preferably, the pulse generator employs a wideband pulse generator and is driven to generate a pulse after the damping is set to 50 Ohm.

Inductors are adopted to meet the specifications of the device to prevent sudden changes in current, and may not be included depending on design conditions.

The current probe senses the input current output from the pulse generator, and the oscilloscope (DC 50 Ohm setting) measures and records the input current.

Preferably, the current probe is designed to have an internal termination resistor of 50 Ohm (Ohm) to minimize reflected waves.

The other end of the current probe connects a 50 ohm terminator to eliminate echoes.

Here, the damping value of the pulse generator, the set value of the oscilloscope and the resistance value of the terminator are set to be the same, and configured to accurately measure the input current to be input to the inspection target in the pulse generator in the future.

Of course, depending on the design conditions, other resistance values may be employed.

를 구한다.
The measured input current signal in the time domain is converted into a signal in the frequency domain using a fast Fourier transform algorithm.

.

6 is a view schematically showing an example of measuring the output current in the calibration device for the calibration operation of the transfer unit.

The transmitter is formed on one side of the test object, and the pulse generated by the pulse generator is reflected from the opposite end of the test object by using a current probe and measured and recorded with an oscilloscope.

Preferably, when the delivery unit is formed by attaching using a contact medium, it is formed by holding at room temperature for a considerable time after removing the excess contact medium by pressing as much as possible.

The damper value of the pulse generator and the oscilloscope's set value remain the same as when the input current is measured.

를 구한다.
The measured output current signal in the time domain is a signal in the frequency domain using a fast Fourier transform algorithm.

.

및 출력 전류

를 구할 수 있으며, 이를 수학식 8에 대입함으로써 전력 전달함수

를 구할 수 있게 된다.Therefore, through the calibration operation described with reference to Figures 5 and 6, the input current

And output current

The power transfer function can be obtained by substituting this in Equation 8.

Will be available.

In addition, since the current-displacement transfer function H (w) can be obtained by substituting this in Equation 6, it is possible to specify the characteristics of the transfer unit through a calibration operation.

7 is a diagram schematically illustrating an example of measuring an output current in a nonlinear parameter measuring apparatus.

First, it is noted that each component used in the non-linear parameter measuring apparatus may be selectively employed to suit the characteristics of the inspection object, the transmitter, and the transmitter, and is not limited to the one shown in the drawings.

Preferably, the pulse generator is driven to generate a sine wave of frequency 5 MHz, 30 cycles.

In addition, the attenuator reduces the magnitude of the input wave by 1 dB, and the current probe is driven to detect a plurality of output currents, for example, 10 output currents output from the inspection object.

Preferably, the state of adhesion between the transfer portion used in the calibration operation and the inspection object is maintained as it is.

In addition, by selecting the transmission unit having the same frequency as the fundamental frequency generated in the pulse generator is formed so that resonance does not occur and distortion occurs.

Preferably, the oscilloscope setpoints, terminator resistance values, etc. set in the calibration operation are designed to remain the same.

8a, b and 9a, b are graphs recording the measured values after performing the actual inspection.

Fused silica (75 mm (3 inch) in length, 50 mm (2 inch) in diameter) was used as the test target, and the transfer part and the transfer part were LiNbO ₃ crystal (13 mm (0.5 inch) in diameter. diameter)).

FIG. 8A is a graph of time-domain output current measured by the oscilloscope of FIG. 7.

FIG. 8B is a graph showing the frequency spectrum of harmonics using the output current measured in FIG.

를 구한 후에, 교정 작업을 이용하여 미리 특정된 전달 함수 및 수학식 5를 이용하여 고조파 성분의 절대 변위 진폭

를 구하게 되며, 도 8b는 이를 도시한 그래프이다.
Using time-domain output current

After calculating, the absolute displacement amplitude of the harmonic components using the transfer function and equation (5)

8b is a graph illustrating this.

FIG. 9A is a graph illustrating a time domain displacement of a fundamental harmonic component in the frequency spectrum of FIG. 8B, and FIG. 9B is a graph illustrating a time domain displacement of a second harmonic component in the frequency spectrum of FIG. 8B.

A band-pass filter is used to find the components of the fundamental frequency of 5 MHz and the second harmonic frequency of 10 MHz, and then the inverse Fourier transform is applied to calculate the displacement in the time domain.

로 결정되었다.
Finally, the nonlinear parameter is obtained using Equation 1,

Was decided.

Meanwhile, the above descriptions using only FIGS. 1 to 9 describe only the main matters of the present invention, and as long as various designs are possible within the technical scope of the present invention, the present invention is applied to the configurations and functions of FIGS. 1 to 9. It is obvious that it is not limited.

Claims (8)

Input current input to the inspection target,
The input current is reflected inside the test object to measure the output current output through the transfer unit to obtain a power transfer function of the transfer unit, characterized in that using the following equation, the transfer unit for non-linear parameter measurement Calibration method.

Here, K _R (w) is the power transfer function of the transmitter, I _in (w) is the input current, I _out (w) is the output current. The method of claim 1,
Measuring the input current,
Maintaining impedance matching so that there is no reflected wave of the input current;
Measuring the input current generated in the pulse generator without connecting a pulse generator to the test target; transmitting unit calibration method for non-linear parameter measurement. The method according to claim 1 or 2,
And calculating the current-displacement transfer function of the transfer unit by using the following equation.

From here,

Is the current-displacement transfer function,

Is the power transfer function of the transmitter,

Is the density of the test object, v is the longitudinal velocity inside the test object, a is the area of the transmission,

Is the output impedance of the transmitter reference. Pulse generator; Including current meter;
A calibration device for nonlinear parameter measurement, characterized in that the delivery part is calibrated using the method of claim 1. Obtaining a power transfer function and a current-displacement transfer function of the transfer unit, using the method of claim 3;
Measuring an output current passing through the inspection object;
And calculating the absolute displacement amplitude (peak strain amplitude) of the harmonic component using the following equation.

Where A _inc (w) is the absolute displacement amplitude of the harmonic component,

Is the current-displacement transfer function of the transfer unit,

Is the output current passing through the inspection object. The method of claim 5, wherein
Measuring the output current passing through the inspection object,
Preventing frequency distortion from occurring when entering the inspection object;
Maintaining impedance matching so that there is no reflected wave of the output current passing through the inspection object;
Measuring the output current passing through the inspection object; characterized in that consisting of, non-linear parameter measuring method. The method of claim 5, wherein
After obtaining the absolute displacement amplitude of the harmonic component,
Obtaining the non-linear parameters using the following equation; further comprising, non-linear parameters measuring method.

From here,

Is the nonlinear parameter, A ₁ is the absolute displacement amplitude of the fundamental harmonic component, A ₂ is the absolute displacement amplitude of the second harmonic component, k is the wave number, x is the thickness of the test object, v is the velocity within the test object of the longitudinal wave ,

Is the fundamental frequency. Pulse generator; Including current meter;
A nonlinear parameter measuring device, characterized in that for measuring the nonlinear parameter using the method of claim 5.

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