JP2011196877A - Ultrasonic measuring method, and ultrasonic measuring instrument - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an echo signal having a high S/N ratio reduced in reverberation noise.SOLUTION: The ultrasonic measuring instrument is equipped with: a measuring signal acquiring portion 3 for transmitting ultrasonic waves with respect to a specimen from an ultrasonic probe 2 and acquiring the echo signal-containing measuring signal from the specimen by the ultrasonic probe 2; a noise signal acquiring portion 9a for acquiring the reference noise signal corresponding to the reverberation noise signal caused by the ultrasonic waves generated by the ultrasonic probe 2; a noise generating portion 4 for comparing a portion of the measuring signal with a part of the reference noise signal, determining the modulation parameter of the reference noise signal for forming the reverberation noise signal in the measuring signal in the receiving state of the measuring signal by the ultrasonic probe 2, and generating the adaptation reference noise signal corresponding to the reference noise signal in the measurement signal, by using the determined modulation parameter and a noise removing part 5 for removing the adaptation reference noise signal from the measurement signal.

Description

  The present invention relates to an ultrasonic measurement method and an ultrasonic measurement apparatus for measuring a defect or a structure of a subject using ultrasonic waves.

  Conventionally, there has been proposed an ultrasonic measurement method for nondestructively measuring a defect or a structure of an object using ultrasonic waves. In this ultrasonic measurement method, in general, an ultrasonic probe (ultrasonic probe) is in contact with an object such as a steel pipe or a steel plate, and ultrasonic waves are transmitted to the object, and an echo signal from the object is transmitted. Is received, a defect such as a scratch on the subject or a structure such as the thickness of the subject is measured. Since the echo signal from the subject includes noise, an echo signal having a high S / N ratio cannot be obtained, and ultrasonic measurement with high accuracy may not be performed in some cases.

  For this reason, in Patent Document 1, transmission / reception of ultrasonic waves under the same conditions is performed a plurality of times on the subject, and a process of adding a plurality of signals obtained from the subject in synchronization with the transmission timing is performed. ing. In this case, since the echo signal is always acquired at a timing delayed by a certain time with respect to the transmission timing, when the noise is temporally random, it has a high S / N ratio.

  In Patent Document 2, a predicted echo signal is prepared as a reference signal, and a correlation calculation between the reference signal and the measurement signal is performed. In this case, since an actual echo signal having a high correlation with the reference signal is emphasized and noise having a low correlation with the reference signal is reduced, an echo signal having a high S / N ratio can be obtained.

  Further, in Patent Document 3, the difference between the echo signal and the frequency distribution of noise is used to cut a frequency band that is included in a large amount of noise and not included in the echo signal. As a result, noise is effectively removed from the echo signal, and an echo signal having a high S / N ratio can be obtained.

Japanese Patent Laid-Open No. 7-294498 JP-A-2005-221321 JP 2004-333260 A

  By the way, what is described in Patent Document 1 is a method of reducing noise by synchronous addition, which is effective in reducing noise that appears randomly in time, such as electrical noise, but from an ultrasonic probe to a subject. The reverberation noise, which is the reverberation of the transmitted ultrasonic wave, is a noise that is synchronized with the echo signal from the subject. Therefore, it cannot be reduced even if the synchronous addition process is performed, and an echo signal having a high S / N ratio cannot be reduced. It is difficult to get.

  In addition, what is described in Patent Document 2 is a method of reducing noise using a matched filter, and predicts a signal waveform of an echo signal obtained from a subject that has transmitted ultrasonic waves, and is equivalent to this echo signal. This reference signal is required to be prepared in advance, and is difficult to apply to a subject for which it is difficult to predict an echo signal to be obtained, such as backscattered wave measurement. In addition, since reverberation noise has a large correlation with the reference signal, it is difficult to obtain an echo signal with reduced reverberation noise, as in Patent Document 1.

  Further, what is described in Patent Document 3 is a method of reducing noise using a frequency filter, and predicts a frequency band of an echo signal obtained from a subject that has transmitted ultrasonic waves, and performs filter characteristics of filtering processing. If it is difficult to predict this frequency band, it is difficult to apply to, for example, backscattered wave measurement as in Patent Document 2. Moreover, since the frequency band of the reverberation noise overlaps the frequency band of the echo signal, it is difficult to obtain an echo signal with reduced reverberation noise.

  The present invention has been made in view of the above, and an object of the present invention is to provide an ultrasonic measurement method and an ultrasonic measurement apparatus capable of obtaining an echo signal having a high S / N ratio with reduced reverberation noise. To do.

  In order to solve the above-described problems and achieve the object, an ultrasonic measurement method according to the present invention transmits ultrasonic waves from an ultrasonic probe to a subject, and the ultrasonic probe echoes from the subject. A measurement signal acquisition step for acquiring a measurement signal including a signal, a noise signal acquisition step for acquiring a reference noise signal corresponding to a reverberation noise signal caused by an ultrasonic wave generated by the ultrasonic probe, and a part of the measurement signal And a part of the reference noise signal to determine a modulation parameter of the reference noise signal for generating a reverberation noise signal in the measurement signal in a reception state of the measurement signal by the ultrasonic probe. A noise generating step for generating an adaptive reference noise signal corresponding to a reverberation noise signal in the measurement signal using the determined modulation parameter; and from the measurement signal A noise removal step of removing the serial adaptive reference noise signal, characterized in that it comprises a.

  In the ultrasonic measurement method according to the present invention as set forth in the invention described above, the noise generation step may be performed before the reflected ultrasonic wave and the scattered ultrasonic wave from the subject included in the measurement signal including the echo signal are received. The adaptive reference noise signal in comparison with the reference noise signal and a part or all of the time domain, or a part or all of the subsequent time domain, or a part or all of the previous and subsequent time domains. Is generated.

  In the ultrasonic measurement method according to the present invention as set forth in the invention described above, the noise signal acquisition step acquires the reference noise signal by transmitting and receiving ultrasonic waves from the ultrasonic probe.

  In the ultrasonic measurement method according to the present invention, in the above invention, in the noise signal acquisition step, the ultrasonic probe is arranged so that reflected ultrasonic waves and / or scattered ultrasonic waves from the subject are not observed. And obtaining the reference noise signal.

  Further, in the ultrasonic measurement method according to the present invention, in the above invention, the noise signal acquisition step includes arranging the ultrasonic probe so that the ultrasonic wave is transmitted to a subject having no defect inside the subject. The reference noise signal is acquired.

  Further, in the ultrasonic measurement method according to the present invention, in the above invention, the noise signal acquisition step performs measurement while moving the ultrasonic probe relative to the subject, and The reference noise signal is obtained by averaging the measurement results at the positions.

  In the ultrasonic measurement method according to the present invention as set forth in the invention described above, the echo signal from the subject is a backscattered wave that is a reflection from a defect inside the subject.

  In addition, the ultrasonic measurement apparatus according to the present invention transmits an ultrasonic wave from an ultrasonic probe to a subject, and acquires a measurement signal including an echo signal reflected from the subject by the ultrasonic probe. A noise signal acquisition unit that acquires a reference noise signal corresponding to a reverberation noise signal caused by an ultrasonic wave generated by the ultrasonic probe, and a part of the measurement signal and a part of the reference noise signal Then, a modulation parameter of the reference noise signal for generating a reverberation noise signal in the measurement signal in a reception state of the measurement signal by the ultrasonic probe is determined, and the measurement is performed using the determined modulation parameter. A noise generation unit that generates an adaptive reference noise signal corresponding to a reverberation noise signal in the signal, and a noise removal unit that removes the adaptive reference noise signal from the measurement signal. And said that there were pictures.

  In the ultrasonic measurement apparatus according to the present invention, in the above invention, the noise generation unit may receive a measurement signal including reflected ultrasonic waves and scattered ultrasonic waves from the subject included in the echo signal. The adaptive reference noise signal in comparison with the reference noise signal and a part or all of the time domain, or a part or all of the subsequent time domain, or a part or all of the previous and subsequent time domains. Is generated.

  According to the present invention, an ultrasonic wave is transmitted from an ultrasonic probe to a subject, the ultrasonic probe receives a measurement signal including an echo signal from the subject, and an ultrasonic wave generated by the ultrasonic probe is generated. A reference noise signal corresponding to a reverberation noise signal caused by a sound wave is obtained, a part of the measurement signal is compared with a part of the reference noise signal, and the measurement signal is received in the reception state of the measurement signal by the ultrasonic probe. A modulation parameter of the reference noise signal for generating a reverberation noise signal in the measurement signal is determined, and an adaptive reference noise signal corresponding to the reverberation noise signal in the measurement signal is generated using the determined modulation parameter. Since the adaptive reference noise signal is removed from the measurement signal, an echo signal having a high S / N ratio with reduced reverberation noise can be obtained. Thus, it is possible to measure a minute defect or a minute structure, which has conventionally been difficult to perform ultrasonic measurement.

FIG. 1 is a block diagram schematically showing the configuration of the ultrasonic measurement apparatus according to the first embodiment of the present invention. FIG. 2 is a flowchart showing an ultrasonic measurement processing procedure by the ultrasonic measurement apparatus. FIG. 3 is a waveform diagram showing an example of a measurement signal of a subject measured by transmission / reception of ultrasonic waves. FIG. 4 is a waveform diagram showing an example of an ultrasonic reference noise signal. FIG. 5 is a waveform diagram showing an example of the adaptive reference noise signal. FIG. 6 is a waveform diagram showing an echo signal obtained by removing the adaptive reference noise signal from the measurement signal. FIG. 7 is a schematic diagram illustrating a state in which a measurement signal of a subject is acquired by transmitting and receiving ultrasonic waves. FIG. 8 is a schematic diagram illustrating a state in which a reference noise signal is acquired without arranging a subject. FIG. 9 is a schematic diagram illustrating a state in which a reference noise signal is acquired using a reference object having no defect. FIG. 10 is a schematic diagram showing a state of ultrasonic measurement according to the second embodiment of the present invention. FIG. 11 is a waveform diagram illustrating an example of a measurement signal according to the embodiment. FIG. 12 is a waveform diagram illustrating an example of a reference noise signal according to the embodiment. FIG. 13 is a waveform diagram illustrating an example of an echo signal obtained by removing the adaptive reference noise signal from the measurement signal according to the embodiment.

  Embodiments of an ultrasonic measurement method and an ultrasonic measurement apparatus according to the present invention will be described below with reference to the drawings. Note that the present invention is not limited to the embodiments.

(Embodiment 1)
FIG. 1 is a block diagram schematically showing the configuration of the ultrasonic measurement apparatus according to the first embodiment of the present invention. As shown in FIG. 1, the ultrasonic measurement apparatus 10 transmits ultrasonic waves for nondestructive measurement of a defect or a structure of a subject, and transmits an ultrasonic signal (measurement signal) resulting from the transmitted ultrasonic waves. A measurement signal acquisition unit 1 to receive, a noise generation unit 4 that generates an adaptive reference noise signal that approximates reverberation noise included in the measurement signal, and a noise removal unit 5 that removes the adaptive reference noise signal from the measurement signal. . The ultrasonic measurement apparatus 10 includes an input unit 6 for inputting various information, a storage unit 7 for storing measurement data of the subject, a display unit 8 for displaying measurement results of the subject, and ultrasonic measurement. And a control unit 9 that controls each component of the device 10.

  The measurement signal acquisition unit 1 transmits the ultrasonic signal of the electric signal transmitted from the transmission / reception unit 3 to the outside from the ultrasonic probe 2 and converts the ultrasonic wave received by the ultrasonic probe 2 into the electric signal. It outputs to the transmission / reception part 3 as a measurement signal which is an ultrasonic signal. The ultrasonic probe 2 is realized by using a piezoelectric vibrator or the like, transmits an ultrasonic wave to the outside by applying a pulse signal from the transmission / reception unit 3, receives the ultrasonic wave from the outside, and converts it into an electric signal. The transmitter / receiver 3 outputs an ultrasonic wave from the ultrasonic probe 2 to the outside by applying a pulse signal having a resonance frequency of the ultrasonic probe 2 or a frequency in the vicinity thereof to the ultrasonic probe 2.

  The noise generation unit 4 generates an adaptive reference noise signal that approximates reverberation noise that is included in the received measurement signal and that is synchronized with the ultrasonic wave transmitted to the subject. This adaptive reference noise signal is a signal that approximates reverberation noise at least in the time domain in which an echo signal is received. The reference noise signal separately acquired by the noise signal acquisition unit 9a in the control unit 9 and the echo signal in the measurement signal It is calculated | required using the signal of the time domain which does not receive.

  The noise removal unit 5 subtracts the adaptive reference noise signal generated by the noise generation unit 4 from the measurement signal acquired by the measurement signal acquisition unit 1 to remove almost all reverberation noise in the measurement signal, resulting in a high S / N. An echo signal having a ratio is output. In addition, it is preferable that the noise removal part 5 performs signal processing, such as a synchronous addition process, in order to remove noises other than the reverberation noise contained in a measurement signal, and performs noise removal.

  The input unit 6 is realized using an input device such as a power switch and an input key. The input unit 6 inputs various instruction information to the control unit 9 in response to an input operation by the operator. For example, the input unit 6 inputs instruction information such as measurement start or measurement end of the subject, instruction information for instructing display or storage of measurement data of the subject, and the like to the control unit 9.

  The storage unit 7 is realized using a storage medium such as a hard disk, and stores various types of information such as measurement data of the subject instructed by the control unit 9.

  The display unit 8 is realized by using a display device such as a liquid crystal display, and displays various information instructed to be displayed by the control unit 9. Specifically, the display unit 8 displays measurement data of the subject by ultrasonic measurement (for example, defect information such as minute flaws and structure information such as thickness). The display unit 8 may display waveform information of an echo signal obtained from the subject to be measured.

  The control unit 9 includes a noise signal acquisition unit 9a that acquires a reference noise signal, and controls each component of the ultrasonic measurement device 10 described above. Specifically, the control unit 9 is realized using a memory that stores a processing program and the like and a CPU that executes the processing program. Based on the instruction information input by the input unit 6, the control unit 9 determines the operation timings of the measurement signal acquisition unit 1, the noise generation unit 4, the noise removal unit 5, the storage unit 7, and the display unit 8 described above. Control.

  Here, an ultrasonic measurement processing procedure by the ultrasonic measurement apparatus 10 will be described with reference to the flowchart shown in FIG. In FIG. 2, first, the control unit 9 determines whether or not an ultrasonic measurement instruction is input to the subject (step S101).

  The control unit 9 starts ultrasonic measurement using the ultrasonic probe 2 only when an ultrasonic measurement instruction is input (step S101, Yes). That is, the control unit 9 controls the measurement signal acquisition unit 1 to irradiate the subject with ultrasonic waves, acquires a measurement signal including the ultrasonic signal from the subject, The noise signal acquisition unit 9a acquires a reference noise signal stored in advance in the storage unit 7 or measured immediately before (step S102).

  After that, the noise generation unit 4 generates at least the reverberation noise in the time domain including the echo signal based on the measurement signal that is the reverberation noise in the measurement signal in the time domain that does not include the echo signal and the reference noise signal. An adaptive reference noise signal that is a signal approximating the amplitude and phase is generated (step S103).

  Thereafter, the noise removing unit 5 subtracts the adaptive reference noise signal generated by the noise generating unit 4 from the measurement signal, and substantially removes reverberation noise in the measurement signal (step S104).

  Thereafter, measurement processing using the echo signal from which the reverberation noise is substantially removed is performed (step S105). For example, processing is performed to acquire defect information such as the shape and size of a defect present in the subject, and structural information such as thickness and internal shape. Thereafter, when there is no end instruction (No at Step S106), the process proceeds to Step S101 and the above-described process is repeated. When there is an end instruction (Step S106, Yes), this process ends.

Here, the reverberation noise removal processing described above will be described with reference to more specific signal waveforms. FIG. 3 shows the measurement signal y (t) acquired by the measurement signal acquisition unit 1. The measurement signal y (t) is a signal acquired during a period from an arbitrary time t ₁ to a time t ₄ , and a time region Δt _b between the time t ₂ and the time t ₃ of the measurement signal y (t). Includes an echo signal s (t) from the subject.

That is, the measurement signal y (t) is a signal obtained by superimposing the echo signal s (t) and the reverberation noise n (t), and is represented by the following equation (1). Note that the measurement signal y (t) includes a noise signal other than the reverberation noise n (t), but this noise signal is not included because it can be removed by signal processing such as synchronous addition processing.
y (t) = s (t) + n (t) (t ₁ ≦ t ≦ t ₄ ) (1)

Incidentally, since the echo signal s (t) is not included in the time region Δt _a from the time t ₁ to the time t ₂ and the time region Δt _c from the time t ₃ to the time t ₄ , the measurement signal y (T) is expressed by the following equation (2).
y (t) = s (t) + n (t) (t ₂ ≦ t ≦ t ₃ )
y (t) = n (t) (t ₁ ≦ t ≦ t ₂ , t ₃ ≦ t ≦ t ₄ )
... (2)

  Here, the reverberation noise n (t) is based on a phenomenon of ultrasonic reverberation, that is, acoustic reverberation inside and outside the ultrasonic probe 2, electrical reverberation due to impedance mismatch in the transmission / reception unit 3, and the like. On the other hand, the characteristics of the reverberation noise n (t) such as amplitude or phase change depending on the environment such as temperature. For this reason, the reverberation noise n (t) has reproducibility over time, but is not completely constant and becomes a similar signal over time.

Since the reverberation noise n (t) is caused by the ultrasonic wave transmitted from the ultrasonic probe 2, as shown in FIG. 4, the reverberation noise n (t) becomes a reference of the reverberation noise n (t) synchronized with the frequency of the ultrasonic wave. A reference noise signal n _ref (t) is acquired in advance. The reference noise signal n _ref (t) may be obtained in advance by measurement using the ultrasonic probe 2, a modeled waveform may be used, or may be obtained by simulation. Here, when the reference noise signal n _ref (t) is obtained by measurement, it is desirable to use the same ultrasonic probe as that used for actual measurement.

The noise generation unit 4 associates the time of the reference noise signal n _ref (t) with the measurement signal y (t), and measures the measurement signals (reverberation noise n) in the time regions Δt _a and Δt _c of the measurement signal y (t). and (t)), the time domain Delta] t _a, compared with the Delta] t _c of the reference noise signal n _ref (t), the time domain Delta] t _a, as measured signal y Δt _c (t) can be reproduced, the reference noise signal The modulation parameters (amplitude modulation amount A (t) and phase modulation amount d (t)) of n _ref (t) are obtained by the following equation (3).
y (t) = n (t) (t ₁ ≦ t ≦ t ₂ , t ₃ ≦ t ≦ t ₄ )
= A (t) × n _ref (t + d (t)) (t ₁ ≦ t ≦ t ₂ , t ₃ ≦ t ≦ t ₄ ) (3)

Then, the noise generation unit 4 uses the measurement signals y (t) of the time regions Δt _a and Δt _c obtained by the equation (3) to convert the time region Δt _b as shown in the following equation (4). Further, the adaptive reference noise signal n _ref (t) ′ interpolated is calculated (see FIG. 5).
n _ref (t) ′ = A (t) × n _ref (t + d (t)) (t ₁ ≦ t ≦ t ₄ ) (4)

Thereafter, the noise removing unit 5 subtracts the adaptive reference noise signal n _ref (t) ′ shown in the formula (4) from the measurement signal y (t) shown in the formula (1) (see the formula (5)). As shown in FIG. 6, the echo signal s (t) is output at a high S / N ratio. Note that, since the phase and amplitude of the reverberation noise n (t) and the adaptive reference noise signal n _ref (t) ′ are approximate, the reverberation noise n (t) is almost removed from the measurement signal y (t). Become.
s (t) = y (t) -n (t)
_{≒ y (t) -n ref (} t) '(t 1 ≦ t ≦ t 4) ... (5)

In the first embodiment described above, the time domain Delta] t _a measurement signal y (t), a signal of Delta] t _c (reverberation noise n (t)), the time domain Delta] t _a, Delta] t _c of the reference noise signal n _ref ( It had sought t) and by comparing the adaptive reference noise signal n _ref (t) ', not limited thereto, the time domain Delta] t _a, rather than all Delta] t _c, in the time domain Delta] t _a or time domain Delta] t _c compared to only one adaptive reference noise signal n _ref (t) 'it may also be determined, the adaptive reference compares only a portion of the time domain Delta] t _a or time domain Delta] t _c noise signal n _ref (t)' You may ask for.

(Reference noise signal acquisition example 1)
Here, a specific acquisition process of the reference noise signal n _ref (t) by measurement will be described. First, as shown in FIG. 7, the ultrasonic measurement by the ultrasonic measurement apparatus 10 is performed on a subject 15 such as a steel material by using a water immersion method. The ultrasonic measurement apparatus 10 acquires an ultrasonic reference noise signal n _ref (t) used for measurement and a measurement signal y (t) for the subject 15. The ultrasonic probe 2 is first brought into contact with an acoustic contact catalyst such as water between the subject 15 and thereafter ultrasonic measurement is performed in this state. Here, since the ultrasonic probe 2 transmits and receives ultrasonic waves to and from the outside other than the subject 15, as described above, the reverberation noise n (t) is included in the measurement signal y (t).

The reference noise signal n _ref (t) may be measured in the absence of an echo signal s (t) that is a surface echo or an echo (reflected ultrasonic wave and / or scattered ultrasonic wave) from the defect 15a. In the signal acquisition example 1, as shown in FIG. 8, the reference noise signal n _ref (t) is obtained by measuring without the subject 15 and without the echo signal s (t). .

  Of course, in this case, it is preferable that the frequency and time length transmitted and received by the ultrasonic probe 2 are the same as those in the ultrasonic measurement for acquiring the echo signal s (t). In particular, the temperature of water as an acoustic contact medium is preferably set to the same conditions as those during ultrasonic measurement.

The reference noise signal n _ref (t) obtained in this way may be obtained by a series of processing of ultrasonic measurement immediately before ultrasonic measurement, or when ultrasonic measurement under the same conditions is repeatedly performed, You may make it hold | maintain in the memory | storage part 7 previously.

(Reference noise signal acquisition example 2)
Next, Reference Noise Signal Acquisition Example 2 will be described. In this acquisition example 2, as shown in FIG. 9, by using a reference specimen 16 that is a normal specimen without a defect 15a as a dedicated test piece, and performing ultrasonic measurement on the reference specimen 16, A reference noise signal n _ref (t) is obtained.

In this case, the reference noise signal n _ref (t) includes a surface echo together with the reverberation noise n (t), and this surface echo is noise unnecessary for ultrasonic measurement. Therefore, by including the surface echo component as a component of the reference noise signal n _ref (t), a desired echo signal s (t) from the defect portion 15a can be obtained with a higher S / N ratio during ultrasonic measurement. it can.

  Further, in this acquisition example 2, as compared with the acquisition example 1, there is an advantage that it can be performed under conditions closer to actual measurement of the subject 15.

  In the first embodiment, an adaptive reference noise signal corresponding to reverberation noise included in a measurement signal from a subject is generated using a reference noise signal, and the adaptive reference noise signal is removed from the measurement signal. An echo signal having an S / N ratio can be obtained. As a result, the defect information and structure information of the subject can be nondestructively measured with higher accuracy.

(Embodiment 2)
In the second embodiment, the reference noise signal is not separately acquired, and the defect portion 15a is detected in the ultrasonic measurement including the acquisition of the reference noise signal.

First, in the second embodiment, as shown in FIG. 10, while the ultrasound probe 2 performs transmission and reception of ultrasound, the subject 15 is moved relative to the ultrasound probe 2, and the subject 15 is moved away from the subject 15. Measure a plurality of measurement signals y _i (t) (i = 1, 2, 3,..., N), and detect a defective portion of the subject 15 based on the obtained plurality of measurement signals y _i (t). An adaptive reference noise signal adapted to is acquired.

In FIG. 10, when the position P ₂ where the defective portion 15 a exists is the k-th position among the total N times of relative scanning (measurement) by the ultrasonic probe 2, the measurement signal y _i (t) is It represents with following Formula (5) and (6).
y _i (t) = s _{s, i} (t) + n _i (t) (i ≠ k) (6)
y _k (t) = s _{s, k} (t) + s _d (t) + n _k (t) (i = k) (7)

Note that s _{s, i} (t) is a surface echo signal at the i-th measurement, and n _i (t) is a reverberation noise signal at the i-th measurement. Further, s _d (t) is a defect echo signal measured only at the time of the k-th measurement.

Here, the reference noise signal n _ref (t) is obtained from the following equation ( _N ) based on the acquired measurement signals y ₁ (t),..., Y _i (t),. Based on 8), it is calculated approximately.

In the above equation (8), s _s (t) is an average surface echo signal obtained by averaging the surface echo signals for a total of N measurements, and n _s (t) is a total of N measurements. This is an average reverberation noise signal of minutes.

The noise generation unit 4 uses the reference noise signal n _ref (t) calculated based on the above equation (8), and the adaptive reference noise signal n ′ _{ref, i} adapted to the i-th measurement signal y _i (t). (T) is generated in the same manner as in the first embodiment. Thereafter, the noise removing unit 5 subtracts the adaptive reference noise signal n ′ _{ref, i} (t) from the measurement signal y _i (t) to obtain an echo signal s ′ _i (t) represented by the following equation (9).

Therefore, when the total number of measurements N of the subject 15 is 3 or more (N ≧ 3), more generally, the measurement signal in which the defect echo is detected in the same phase is 1/3 or less of the whole. In some cases, the absolute value of the echo signal s ′ _i (t) is expressed by the following equation (10).
| S ′ _i (t) | <| s ′ _k (t) | (i ≠ k) (10)
For this reason, the ultrasonic measurement apparatus 10 can detect the presence or absence of a defect echo in the subject 15 based on the equation (10).

  In the second embodiment, it is not necessary to actually measure the reference noise signal separately from the measurement signal of the subject, thereby saving labor and time for actually measuring the ultrasonic reference noise signal. An echo signal having a high S / N ratio can be acquired in a short time and easily.

  In addition, since the measurement signal is acquired by scanning the vicinity of the position of the defective portion existing in the subject, it is possible to reduce the time-dependent change of the reference noise signal and the change according to the measurement position. A reference noise signal that follows the factors of the measurement environment such as the measurement position can be acquired.

(Example)
Next, an example corresponding to the first embodiment will be described. In the ultrasonic probe 2 in this embodiment, the nominal frequency is set to 75 MHz. The transducer diameter of the ultrasonic probe 2 is 3 mm, and the focal length of the ultrasonic probe 2 is 10 mm. Using the ultrasonic measurement apparatus 10 provided with such an ultrasonic probe 2, ultrasonic waves were obliquely incident on the subject 15 by a water immersion method, and ultrasonic measurement of the subject 15 was performed for 6.0 μsec.

  In the ultrasonic measurement method in this embodiment, a steel plate having a thickness of 2.6 mm is used as the subject 15. In addition, the steel plate that is the subject 15 is fully immersed or locally submerged in an acoustic contact catalyst such as water.

  With the ultrasonic measurement method according to this example, the ultrasonic measurement apparatus 10 acquired a measurement signal y (t) having a waveform as shown in FIG. Specifically, the ultrasonic measurement apparatus 10 measured the surface scattered wave of this steel sheet between the time t = 1.1 μsec and the time t = 2.0 μsec. Further, the ultrasonic measurement apparatus 10 measured the backscattered wave from the inside of the steel plate between the time t = 2.0 μsec and the time t = 3.2 μsec (see the inside of the rectangular frame shown in FIG. 11). ).

On the other hand, the reference noise signal n _ref (t), which is a standard signal of reverberation noise, was measured in advance by actually transmitting and receiving ultrasonic waves as described above. As a result, the ultrasonic measurement apparatus 10 acquired a reference noise signal n _ref (t) having a waveform as shown in FIG.

In the ultrasonic measurement method in this embodiment, the ultrasonic measurement apparatus 10 acquires the measurement signal y (t) and the reference noise signal n _ref (t) of the steel plate that is the subject 15, and then performs synchronous addition averaging processing. Then, non-reverberation noise components such as electrical noise were removed from the measurement signal y (t) and the reference noise signal n _ref (t).

Thereafter, the ultrasonic measurement apparatus 10 uses the reference noise signal n _ref (t) to _{generate a} time-domain waveform of the measurement signal y (t) of this steel plate that does not receive an echo signal, and the reference noise signal n _ref. Compared with (t), an adaptive reference noise signal n ′ _ref (t) is generated, and the adaptive reference noise signal n ′ _ref (t) is subtracted from the measurement signal y (t) and removed. As a result, a waveform as shown in FIG. 13 was obtained, and an echo signal s (t) having a high S / N ratio could be obtained.

  Here, when the waveform of the measurement signal y (t) of the steel plate (see FIG. 11) and the waveform of the echo signal s (t) (see FIG. 13) are compared, the surface scattered wave and the back scattered wave of the steel plate are measured. In the time domain (time domain within the rectangular frame in FIGS. 11 and 13), the waveform characteristics such as peak and amplitude are substantially maintained before and after the reverberation noise removal process. On the other hand, the amplitude is reduced outside this time region (the time region outside the rectangular frame in FIGS. 11 and 13). Therefore, it can be seen that the reverberation noise can be removed while maintaining the signal level of the echo signal s (t) from the steel plate during the measurement time of the steel plate that is the subject 15.

  In the above-described embodiment, non-reverberation noise components such as electrical noise in the measurement signal of the subject are removed by the synchronous addition averaging process. However, the present invention is not limited to this, for example, a method other than the synchronous addition averaging process, for example, The non-reverberation noise component may be removed by a method using a matched filter, or the non-reverberation noise component may be removed by a method using a frequency band filtering process.

  Furthermore, in the above-described embodiment, the reference noise signal of the waveform modeled based on the actual ultrasonic wave used for the measurement of the subject is prepared in advance. However, the present invention is not limited to this, and the waveform modeled by the numerical simulation is prepared. The reference noise signal may be used, or a reference noise signal derived based on an appropriate logical expression may be used.

DESCRIPTION OF SYMBOLS 1 Measurement signal acquisition part 2 Ultrasonic probe 3 Transmission / reception part 4 Noise generation part 5 Noise removal part 6 Input part 7 Memory | storage part 8 Display part 9 Control part 9a Noise signal acquisition part 10 Ultrasonic measurement apparatus 15 Subject 15a Defect part 16 Reference | standard Subject

Claims (9)

An ultrasonic signal is transmitted from an ultrasonic probe to a subject, and the ultrasonic probe acquires a measurement signal including an echo signal from the subject;
A noise signal acquisition step of acquiring a reference noise signal corresponding to a reverberation noise signal caused by an ultrasonic wave generated by the ultrasonic probe;
The reference noise signal for comparing a part of the measurement signal with a part of the reference noise signal and generating a reverberation noise signal in the measurement signal in a reception state of the measurement signal by the ultrasonic probe A noise generation step of generating an adaptive reference noise signal corresponding to a reverberation noise signal in the measurement signal using the determined modulation parameter;
A noise removal step of removing the adaptive reference noise signal from the measurement signal;
An ultrasonic measurement method comprising:   The noise generation step includes a part or all of a time region before receiving reflected ultrasonic waves and scattered ultrasonic waves from the subject included in a measurement signal including the echo signal, or a part of a subsequent time region. 2. The ultrasonic measurement according to claim 1, wherein the adaptive reference noise signal is generated by comparing the reference noise signal with a measurement signal of a part or all of a time domain before or after or all of the time domain. Method.   The ultrasonic measurement method according to claim 1, wherein the noise signal acquisition step acquires the reference noise signal by transmitting and receiving ultrasonic waves from the ultrasonic probe.   4. The noise signal acquisition step of acquiring the reference noise signal by arranging the ultrasonic probe so that reflected ultrasonic waves and / or scattered ultrasonic waves from the subject are not observed. The described ultrasonic measurement method.   The said noise signal acquisition step arrange | positions the said ultrasonic probe so that an ultrasonic wave may be transmitted to the test object without a defect inside a test object, The said reference noise signal is acquired. Ultrasonic measurement method.   The noise signal acquisition step performs measurement while moving the ultrasonic probe relative to the subject, and obtains the reference noise signal by averaging the measurement results at a plurality of positions of the subject. The ultrasonic measurement method according to claim 3, wherein:   The ultrasonic measurement method according to claim 1, wherein the echo signal from the subject is a backscattered wave that is a reflection from a defect inside the subject. A measurement signal acquisition unit that transmits ultrasonic waves from the ultrasonic probe to the subject, and acquires a measurement signal including an echo signal reflected from the subject by the ultrasonic probe;
A noise signal acquisition unit for acquiring a reference noise signal corresponding to a reverberation noise signal caused by an ultrasonic wave generated by the ultrasonic probe;
The reference noise signal for comparing a part of the measurement signal with a part of the reference noise signal and generating a reverberation noise signal in the measurement signal in a reception state of the measurement signal by the ultrasonic probe A noise generation unit that generates an adaptive reference noise signal corresponding to a reverberation noise signal in the measurement signal using the determined modulation parameter;
A noise removing unit for removing the adaptive reference noise signal from the measurement signal;
An ultrasonic measurement apparatus comprising:   The noise generation unit includes a part or all of a time region before receiving a measurement signal including reflected ultrasonic waves and scattered ultrasonic waves from the subject included in the echo signal, or a part of a subsequent time region. The ultrasonic measurement according to claim 8, wherein the adaptive reference noise signal is generated by comparing the reference noise signal with a measurement signal of a part or all of the time domain before or after or the entire time domain. apparatus.

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