JPH11142378A - Method and apparatus for measuring electromagnetic ultrasonic wave - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and an apparatus whereby a high time-resolving power and a high S/N ratio are obtained in measuring electromagnetic ultrasonic waves. SOLUTION: There are provided an external magnetizer 3 applying a magnetic field to a body 1 to be measured and a transmitting-receiving sensor coil 2, an operating means 4 for operating a chirp signal changed in frequency and amplitude within a predetermined pulse width as numerical data, memory means 6, 5 for storing the chirp signal as a transmission signal, a reference signal respectively, a D/A converter 7 for converting an output of the memory means 6 to an analog signal, a power amplifier 8 for power amplifying an output of the D/A converter 7 and impressing to the sensor coil 2, a receiving amplifier 9 for amplifying a signal received by the sensor coil 2, an A/D converter 10 for converting an output of the amplifier 9 to a digital signal, and a correlating device 11 for operating a correlation of outputs of the A/D converter 10 and memory means 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to electromagnetically generating ultrasonic waves on a subject using Lorentz force or magnetostriction,
The present invention relates to an electromagnetic ultrasonic measurement method and apparatus for detecting an ultrasonic wave and measuring a subject.

[0002]

2. Description of the Related Art An electromagnetic ultrasonic method is known as one of methods for generating and detecting ultrasonic waves in a non-contact manner with a subject such as a metal plate or a tube. In this technology, a magnetic field is applied to a conductive object from the outside, and an electric current is caused to flow through a sensor coil close to the object to generate an eddy current in the object, which is generated by the eddy current and the magnetic field Ultrasonic waves are generated in the subject using the Lorentz force, and the same principle applies to detection.

When the subject is a ferromagnetic material, a bias magnetic field is applied with an external magnetic field, and the bias magnetic field is changed by a magnetic field generated from a sensor coil close to the subject, thereby changing the magnetostriction. There is also a principle of generating ultrasonic waves in a subject. Although such an electromagnetic ultrasonic method has a great advantage that it can generate and detect various modes of ultrasonic waves depending on the positional relationship between the external magnetic field and the sensor coil and is non-contact, it is currently generally used. As compared with the conventional ultrasonic generation detection method using a piezoelectric vibrator, there is a problem that the sensitivity and the SN ratio are poor because the electromechanical conversion efficiency is very low.

For this reason, various attempts have conventionally been made to improve the sensitivity of the electromagnetic ultrasonic method. For example, a protective plate made of a non-conductive magnetic material (JP-A-56-132558) or a sensor coil made of a magnetic material (JP-A-57-84350) is used to increase the magnetic flux density in the subject. To improve the sensitivity of the sensor itself by interposing a metal foil between the sensor coil and the subject (Japanese Patent Laid-Open No. 2-96607).
JP-A-5-288733) A method for reducing electric noise using two receiving sensor coils in a differential connection (JP-A-53-143388, JP-A-57-1987).
84352) a method of reducing noise.

In addition to these measures, a signal processing method has been proposed as a method of increasing the SN ratio. For example, as a method of increasing the voltage of a transmission signal, a method using a trigger type spark gap (Japanese Patent Application Laid-Open No. 53-89486) and a method using a two-way thyratron (Japanese Patent Application Laid-Open No.
No. 180947), a method using a voltage doubler pulsar (Non-destructive inspection magazine Vol. 34, No. 11, pp. 808-).
814), etc., there is a method of increasing the amplitude of the pulse-shaped transmission signal. However, the above-mentioned method of making the transmission signal a high voltage has the following problems. That is, if the peak value of the voltage is about 10 kV, a spark short-circuit occurs in the middle of the sensor coil or the connection line, or a noise source of another device. It is desirable that the sensor coil has a large number of turns in order to increase the sensitivity, but it is necessary to use a thick and covered wire in order to increase the withstand voltage, so that the number of turns cannot be increased much. Further, since a high voltage is generated, the pulse repetition frequency of the transmission signal can be increased only up to about several hundred Hz, and cannot be applied to a subject moving at high speed.

As a method of solving the above problem, electromagnetic ultrasonic resonance utilizing the resonance of ultrasonic waves in a subject (Non-destructive inspection magazine Vol. 43, No. 12, pp. 76).
4-770). However, in this method, a burst wave having a resonance frequency and a long pulse width is used as a transmission signal so that the multiple reflected waves of the ultrasonic wave perpendicularly incident on the subject resonate with the same phase (become coherent). However, the reflected echo cannot be separated individually and cannot be applied to an object having a plurality of reflection sources or an object having no parallel plane.

[0007]

As described above, increasing the voltage of a transmission signal in the electromagnetic ultrasonic method has a problem of a withstand voltage of a sensor coil. On the other hand, there are a plurality of methods for resonating with a burst wave having a long pulse width. There is a problem that the method cannot be applied to a subject having a reflection source or a subject having no parallel surface. As a middle point between these two methods, it is conceivable to use a burst wave with a pulse width that is not too long or to use a sensor coil as a resonance circuit, but the time resolution of the received echo is significantly degraded compared to a pulsed transmission signal. Therefore, the application target is naturally limited. For this reason,
At present, there are only a few examples of the practical application of the electromagnetic ultrasonic method in industrial sites. The present invention has been made in view of such a situation, and an object of the present invention is to provide a measurement method and apparatus capable of obtaining a high time resolution and a high SN ratio in electromagnetic ultrasonic measurement.

[0008]

An electromagnetic ultrasonic measuring apparatus according to a first aspect of the present invention electromagnetically generates ultrasonic waves in a subject using Lorentz force or magnetostriction, and detects the ultrasonic waves. In an electromagnetic ultrasonic measurement method for measuring a subject, a chirp signal having a frequency and an amplitude changed within a predetermined pulse width is transmitted to the subject via a transmitting sensor coil, and the receiving sensor coil is transmitted from the subject. And a correlation operation between a reception signal obtained through the above-described method and a reference signal having the same or similar waveform as the transmission signal, and the measurement of the subject is performed using the reception signal after the correlation operation. It is.

An electromagnetic ultrasonic measuring apparatus according to a fifth aspect of the present invention electromagnetically generates ultrasonic waves in a subject using Lorentz force or magnetostriction, and measures the subject by detecting the ultrasonic waves. In the electromagnetic ultrasonic measurement device, an external magnetizer for applying a magnetic field to the subject, a sensor coil for transmission and a sensor coil for reception which is also used as or separate from the sensor coil for transmission, and changes frequency and amplitude within a predetermined pulse width A chirp signal calculating means for calculating the chirp signal as numerical data, a transmission signal storing means and a reference signal storing means for storing the chirp signal calculated by the chirp signal calculating means as a transmission signal and a reference signal, respectively, D / A conversion means for reading the transmission signal stored in the signal storage means and converting it into an analog signal;
Power amplifying means for power amplifying an analog signal output from the A converting means and applying the amplified signal to the transmitting sensor coil, receiving amplifying means for amplifying a received signal obtained by the receiving sensor coil, and amplification of the receiving amplifying means A / D conversion means for converting the received signal into numerical data, and correlation calculation means for performing a correlation operation between the numerical data output from the A / D conversion means and the reference signal read from the reference signal storage means. It is provided.

According to the method and apparatus for measuring electromagnetic ultrasonic waves according to the first and fifth aspects, it is possible to transmit high average power even at a relatively low transmission voltage, generate strong ultrasonic waves, and perform high-sensitivity measurement. . In addition, since the received signal performs a correlation operation with the reference signal, the compressed echo signal after the correlation operation can have a high time resolution and a high SN ratio. Furthermore, in addition to the above effects, it is possible to perform measurements that demonstrate the inherent broadband characteristics of electromagnetic ultrasonic waves that could not be used conventionally,
It can be applied to various measurement applications.

According to a second aspect of the present invention, there is provided the electromagnetic ultrasonic measurement method according to the first aspect, wherein the amplitude and phase of the chirp signal transmitted to the subject have a predetermined frequency characteristic. To change it. According to a third aspect of the present invention, there is provided the electromagnetic ultrasonic measurement method according to the first aspect, wherein a reference signal for performing a correlation operation with the received signal has a predetermined frequency characteristic so as to have a predetermined frequency characteristic. Is to change.

According to a sixth aspect of the present invention, there is provided the electromagnetic ultrasonic measuring apparatus according to the fifth aspect, wherein the chirp signal calculated by the chirp signal calculating means has a predetermined frequency characteristic. Modulation means for performing modulation for changing amplitude and phase and supplying a signal after the modulation processing to the transmission signal storage means is added. According to a seventh aspect of the present invention, in the electromagnetic ultrasonic measurement apparatus according to the fifth aspect, the chirp signal calculated by the chirp signal calculation means has an amplitude so as to have a predetermined frequency characteristic. And a modulation means for performing modulation for changing the phase and supplying the signal after the modulation processing to the reference signal storage means.

According to the method and apparatus for measuring electromagnetic ultrasonic waves according to the second, third, sixth, and seventh aspects, even when the frequency characteristics of the received signal are affected by the sensor coil or the connection cable, the frequency characteristics after the correlation processing are changed. Desired characteristics are obtained, and as a result, an echo signal with few side lobes and excellent in time resolution can be obtained.

According to a fourth aspect of the present invention, in the electromagnetic ultrasonic measuring method according to the first aspect, the amplitude and phase of the chirp signal transmitted to the subject are set so as to have a first predetermined frequency characteristic. And the amplitude and phase of the reference signal for performing the correlation operation with the received signal are changed so as to have the second predetermined frequency characteristic. An electromagnetic ultrasonic measuring apparatus according to an eighth aspect of the present invention is the apparatus according to the fifth aspect, wherein the chirp signal calculated by the chirp signal calculating means has a first predetermined frequency characteristic. A first modulation means for performing modulation for changing the amplitude and phase thereof and supplying a signal after the modulation processing to the transmission signal storage means, and a second predetermined frequency characteristic for the chirp signal. Modulation for changing the amplitude and phase is performed, and second modulation means for supplying the signal after the modulation processing to the reference signal storage means is added.

According to the method and the apparatus for measuring electromagnetic ultrasonic waves according to the fourth and eighth aspects, even if the subject changes or the frequency characteristic of the reception signal changes when the sensor coil or the connection cable is replaced, the transmission signal can be changed. Alternatively, by changing either one of the frequency characteristics of the reference signal, an echo signal having few side lobes and excellent in time resolution can be easily obtained.

[0016]

Embodiment 1 FIG. 1 is a configuration diagram of an electromagnetic ultrasonic measuring apparatus according to Embodiment 1 of the present invention. In FIG. 1, the sensor coil 2 is brought close to the subject 1, and a magnetic field is applied to the subject 1 from the external magnetizer 3 to generate and detect electromagnetic ultrasonic waves by Lorentz force. Here, the subject 1 was a ferromagnetic carbon steel, and the sensor coil 2 was used for both transmission and reception, and was wound in a circular shape, its major axis was 20 mm, and the number of turns was 20 turns. Further, two permanent magnets of 10 × 10 × 20 mm were used for the external magnetizer 3 and arranged as shown in FIG.

First, in the present invention, as a transmission pulse signal, a chirp signal that sweeps a frequency within a predetermined pulse width and changes its amplitude is used.
The chirp signal s (i) is generated by the chirp signal calculation means 4 of FIG. 1 based on the following equation (1). Here, f _C is the center frequency, B is the frequency sweep bandwidth, T is the pulse width, and f _S is the sampling frequency. In this example, a general-purpose computer was used as the chirp signal calculating means 4. Although the sensor coil 2 in FIG. 1 is used for both transmission and reception, it may be provided separately for the transmission sensor coil and the reception sensor coil.

[0018]

(Equation 1)

The chirp signal in this example has a center frequency of 5 MHz, a frequency sweep bandwidth of 10 MHz, a pulse width of 5.12 μs, and is discretized at a sampling frequency of 25 MHz, so that the number of data points is 128. The chirp signal generated by the chirp signal calculation means 4 is stored in the reference signal storage means 5 and the transmission signal storage means 6 each constituted by a RAM by serial transmission.

The chirp signal stored in the transmission signal storage means 6 is read out for 128 points in synchronization with the synchronizing signal generated by the synchronizing signal generating means 12, and D / A
The signal is converted into an analog signal at a predetermined sampling frequency by a converter 7 and amplified to a high voltage by a power amplifier 8. The output signal of the power amplifier 8 is applied to the sensor coil 2,
It is converted into an ultrasonic wave and transmitted into the subject 1. In this example, the synchronizing signal generated by the synchronizing signal generating means 12 has a cycle of 1 kHz, and the sampling frequency of the chirp signal by the D / A converter 7 is 25 MHz. The power amplifier 8 used had a bandwidth of 0.1 to 20 MHz and an output of a peak-to-peak voltage of 1000 Vpp under a load of 50Ω.

The reception signal detected by the sensor coil 2 is amplified by a reception amplifier 9 to a voltage required for A / D conversion.
2 is converted into a digital signal by a predetermined sampling frequency synchronized with the generated synchronization signal. The correlation of the received signal discretized into the digital signal with the reference signal stored in the reference signal storage means 5 is calculated by the correlator 11, and the result of the correlation calculation is output. In this example, the receiving amplifier 9 was set to have a bandwidth of 0.1 to 20 MHz and an amplification of 70 dB, and adjusted the echo used for measurement to an appropriate level by an amplification adjuster (not shown). The sampling frequency of the A / D converter 10 is 2
The sampling rate is set to 5 MHz, and sampling is started in synchronization with the synchronization signal from the synchronization signal generation means 12. The correlator 11 has an FIR (Finite Impulse Re).
A sponse (finite impulse response) filter was used.

FIG. 2 is a diagram showing the configuration of the FIR filter used in the correlator shown in FIG. 1. In FIG. 2, + indicates an adder, X indicates a multiplier, Z- ¹ indicates a delay unit, and each delay unit. Delays the input signal by a time corresponding to the repetition period of transmission and outputs the result. In the FIR filter of FIG. 2, a reference waveform for performing a correlation operation with a received waveform x (τ) discretized into a digital signal is sampled (discrete) at a certain fixed sampling frequency. The discretized data values are input as 128 C _{0 to} C _{127 to} one of the multipliers indicated by x. On the other hand, the discretized reception data x (τ) input from the input terminal for each transmission cycle is directly supplied to the other input of each multiplier, and the reference data C _{0 to} C
₁₂₇ and are respectively multiplied separately, each multiplication results except the multiplication result between C ₁₂₇ and each 127 delayer and the adder is supplied to one input of the series-connected corresponding adder alternately. Then, only the result of the multiplication with C ₁₂₇ is directly supplied to the first delay unit connected in series with the alternation, and the other input of the adder connected in series at the subsequent stage of this delay unit has C
_The result of multiplication with ₁₂₆ is supplied. Then, the output of the last adder in the serial combination becomes the correlation operation output.

The signal processing of the FIR filter of FIG. 2 is represented by a general formula. Let the input signal be x _j (i) and the coefficient (reference data)
Is c (k), the output signal is y _j (i), the number of taps is N _c , the repetition of the flaw detection signal is j, and the number of data points of the flaw detection signal in one cycle is n.
Then, the convolution operation of the following equation (2) is performed.

[0024]

(Equation 2)

When the reference signals in the above equation (2) are reversed, the following equation (3) is obtained.

[0026]

(Equation 3)

As a result, by writing the reference signal in the coefficient in the reverse order, the correlation operation can be performed using the FIR filter. This correlation operation is to calculate the cross-correlation while shifting the reference signal and the received signal by i.

FIG. 3 is a waveform chart for explaining the operation of the FIR filter of FIG. In FIG. 3, the point at time τ ₁ corresponds to the position of i = 0 in the equation. First, at the position of the tau _1, performs correlation calculation between the received signal and the reference signal by the data amount of 0 to N _c -1 points. Here, N _c is the tap length of the FIR filter, and is 128 here. The result of the correlation is output as the lowermost signal in the figure. Reference signal and the reception signal at the time of the tau ₁ because not similar, the output is almost zero. Next, i is increased one by one, and τ ₂ , τ ₃ ,.
The calculation is sequentially performed as shown in FIG. As a result, a correlation signal having a maximum peak is obtained at a point where the phase of the echo in the received signal matches the phase of the reference signal (substantially in the center of the time axis in the figure). As a result, the pulse width of the received echo is compressed, and the electrical noise signal uncorrelated with the reference signal is significantly reduced.

Next, an experimental example according to the first embodiment will be described. Although not shown in the figure to observe the received signal after the correlation processing from the configuration of FIG.
A converter was connected to convert the correlation calculation output into an analog signal, and the analog signal was observed with an oscilloscope. In the case of observation as a conventional technique, observation was performed using a signal immediately after the reception amplifier 9. 4A and 4B are diagrams showing transmission signals used in the experiment of the first embodiment. FIG. 4A shows a transmission signal by a chirp wave in the transmission signal storage means 6 of FIG. 1, and FIG. 6 shows a transmission signal by a burst wave having a wave number of 6 used for the above.

FIG. 5 is a diagram for explaining the correlation processing according to the first embodiment. FIG. 5A shows an actual transmission signal from the power amplifier 8, and its amplitude and phase are changed as compared with the chirp wave from the transmission signal storage means 6 shown in FIG. You can see that there is. FIG. 5B shows a reference signal for performing the correlation process, and the waveform is a signal having the same waveform as FIG. 4A. Here, considering the case where the sensor coil / cable or material has no frequency characteristics,
The compressed signal after the correlation processing is as shown in FIG. As can be seen from the figure, a large side lobe is generated around the compressed main lobe. This is because the transmission signal is caused by amplitude and phase changes as shown in FIG.

FIG. 6 is a diagram showing a received signal as an experimental result according to the first embodiment. In this experiment, the bottom echo from a carbon steel plate having a thickness of 8 mm was measured. As described above, a signal having the same waveform as that of FIG. 4A is used as a reference signal for performing the correlation process. FIG. 6A shows a received signal after the correlation processing using a chirp wave. The wave number of the echo is about 1.5 and a very high time resolution is obtained, and the SN ratio is good. On the other hand, FIG. 7B shows a received signal according to the conventional technique using a burst wave for comparison, which is an echo waveform having a large number of waves and a poor time resolution and a low SN ratio. However, in the case of the chirp wave according to the first embodiment, a high time resolution and a high SN ratio were obtained even when the peak-to-peak voltage of the transmission signal was a relatively low voltage of about 1000 Vpp.

According to the first embodiment as described above,
A chirp signal having a predetermined pulse width is used for the transmission signal, and since the pulse width is sufficiently long, a large average power can be transmitted without increasing the peak-to-peak voltage of the transmission signal too much. As a result, strong ultrasonic waves can be generated, and the measurement sensitivity can be improved. further,
Since the same chirp signal as the transmission signal is used as the reference signal, and the correlation operation between the reception signal and the reference signal is performed, the pulse width of the echo which was long in time is shortened by the pulse compression action of the reception chirp wave, and In addition, electrical noise uncorrelated with the transmission signal can be significantly reduced. Therefore, it is not necessary to take measures against electromagnetic ultrasonic resonance or deterioration of time resolution such as using a sensor coil as a resonance circuit, and a high time resolution and a high SN ratio can be obtained. Further, since not only the frequency but also the amplitude of the chirp signal is changed, a waveform having a high time resolution with few side lobes can be obtained as compared with a case where the amplitude is not changed.

Unlike conventional ultrasonic measurement methods using a piezoelectric probe, electromagnetic ultrasonic waves originally have broadband characteristics because there is no mechanical resonance of the probe. Due to the low frequency, the generation of a broadband pulse could not be realized, and this feature was not known. Embodiment 1
The present invention focuses on the inherent broadband property of electromagnetic ultrasonic waves, and combines it with signal processing of chirp wave pulse compression to not only increase measurement sensitivity but also to bring out the original wideband property of electromagnetic ultrasonic waves It is characterized by having

The compressed signal after the correlation processing of the received signal in the first embodiment is certainly a signal having a high resolution and a high SN ratio. However, as shown in FIG. Lobes are occurring considerably. If this side lobe can be reduced, more effective electromagnetic ultrasonic measurement can be performed. Therefore, in the following embodiments 2, 3, and 4, the respective side lobe reduction methods will be described.

It is generally known that in chirp wave pulse compression, side lobes are reduced when the frequency characteristic of the waveform after the correlation processing is made to have a cosine function.
Therefore, in the second and third embodiments, by considering the frequency characteristics of the power amplifier and the like used for the electromagnetic ultrasonic wave,
Modulation for changing the amplitude and phase of the chirp wave (see FIG. 4A) of the first embodiment is performed so that the frequency characteristic of the waveform after the correlation processing becomes a cosine function, and the signal after the modulation processing is performed. Is used as a transmission signal or as a reference signal. Embodiment 4
In the first embodiment, a signal obtained by performing the first modulation processing on the chirp wave according to the first embodiment is used as a transmission signal, and a signal obtained by performing the second modulation processing on the chirp wave is used as a reference signal. Hereinafter, each embodiment will be described.

Embodiment 2 FIG. 7 is a diagram showing the configuration of an electromagnetic ultrasonic measuring apparatus according to Embodiment 2 of the present invention. FIG. 7 shows a device having the configuration shown in FIG. It is a thing. FIG. 8 shows FIG.
FIG. 9 is a diagram showing a chirp signal modulated by the first modulation means 13 of FIG. 9, and FIG. 9 is a diagram for explaining a correlation process according to the second embodiment. In the modulation processing of the chirp signal by the first modulation means 13 of FIG. 7, the result of performing the modulation processing on the transmission signal of FIG. 5A is as shown in the transmission signal of FIG. The modulation is performed as follows. The result of performing such modulation on the chirp wave of FIG. 4 is the modulated chirp signal of FIG.

Hereinafter, the above-mentioned modulation processing will be described using mathematical expressions.
The following equations (4) and (5) were used for the transmission signal in (a) of FIG. However, here, the coefficient k was a value of 0.08 to 0.14.

[0038]

(Equation 4)

The first modulating means 13 performs a filtering operation represented by the following equation (6) on the signal s (i) generated from the chirp signal calculating means 4. Here, S (jω) is a signal s (i) from the chirp signal generating means.
Is a Fourier transform, and St (jω) is an output signal from the power amplifier 8 when no modulation corresponding to FIG. 5A is applied.

[0040]

(Equation 5)

As a result of such an arithmetic operation, the output signal from the chirp signal arithmetic means 4 is modulated, and a signal having a modulated waveform as shown in FIG. 8 is obtained. The transmission signal shown in FIG. 9A represented by 4) was obtained. As a result, the compressed signal as a result of the correlation processing between the transmission signal of FIG. 9A and the reference signal of FIG. 9B has a waveform as shown in FIG. 9C, the side lobe around the main lobe is reduced, A waveform with excellent time resolution was obtained.

Third Embodiment FIG. 10 is a block diagram of an electromagnetic ultrasonic measuring apparatus according to a third embodiment of the present invention. In FIG. 10, the second modulation means 14 is additionally provided to the apparatus having the configuration of FIG. It is a thing. 11 is a diagram showing characteristics of an ideal waveform, FIG. 12 is a diagram showing frequency characteristics of the second modulating means 14 in FIG. 10, and FIG.
FIG. 6 is a diagram for explaining a correlation process by using. In the third embodiment, the side lobe is reduced by modulating the amplitude and phase of the reference signal while the transmission signal remains as shown in FIG.

The characteristics of the second modulating means 14 of FIG. 10 were obtained as follows. First, a signal after correlation processing when no modulation is applied to the reference signal, for example, a signal shown in FIG. Here, this signal is sr (t). Next, this sr (t) is a preset ideal waveform, for example, FIG.
A filter H (jω) is designed so as to be an ideal compressed signal shown in FIG.

The filter H (jω) is obtained as follows.
As a result, the coefficients of the FIR filter used for the correlation are obtained as follows. (1) First, a reference signal is not subjected to modulation, and a signal sr (t) after correlation processing is obtained. (2) Desired compressed waveform after shaping (for example, (b) of FIG. 11)
In order to obtain the following ideal waveform, the following ideal waveform is set by the following equation (7). The ideal waveform is expressed in an ideal frequency characteristic (e.g., characteristic of FIG. 11 (a)), the center frequency of the frequency band of f _c is the ideal waveform in Equation (7), B is the bandwidth of the ideal waveform is there. Note that this bandwidth is set in the range of the zero point of the spectrum of the signal after the correlation processing.

[0045]

(Equation 6)

(3) The filter characteristic of the second modulating means is obtained by the following equation (8). Where Sr of the denominator of equation (8)
(jω) is the result of Fourier transform of the signal after correlation.

[0047]

(Equation 7)

FIG. 12 shows the frequency characteristics of the filter characteristics of the second modulating means thus obtained. (4) The coefficient c (t) of the FIR filter used for correlation is obtained by the following equation (9).

[0049]

(Equation 8)

Here, S (jω) is a signal obtained by Fourier-transforming the signal s (i) from the chirp signal generating means, and * indicates a complex conjugate. IFFT [] is an operator indicating an inverse Fourier transform.

The waveform of the reference signal obtained as a result of the above calculation is shown in FIG. 13A, which is the reference signal of FIG. 13B and the output from the power amplifier.
The result of correlation with the transmission signal is as shown in (c) of the same figure. Even when the method of the third embodiment is used, a waveform having small sidelobes and excellent time resolution can be obtained.

As described above, in the second or third embodiment, the amplitude and phase of the chirp signal are changed so that a transmission signal or a reference signal having a predetermined frequency characteristic is obtained, and this is changed to the transmission signal or the reference signal. It is characterized by being used as a signal. That is, in pulse compression using a chirp wave, the waveform and side lobe after pulse compression are determined by the frequency characteristics of the result of multiplying the frequency characteristics of the transmission signal and the frequency characteristics of the reference signal. Needs to be determined so as to have the following frequency characteristics. However, in the case of electromagnetic ultrasonic waves, it is desirable that the power amplifier for generating a transmission signal has a voltage as high as the withstand voltage of a sensor coil or the like permits, but the frequency band used is a few MHz and a high frequency band. It is difficult to make it constant. In addition, the frequency characteristics of the generated electromagnetic ultrasonic waves and the received signals slightly vary depending on the impedance of the sensor coil and the cable. Also,
Signal attenuation in materials also has frequency characteristics.

Therefore, in the second and third embodiments, the amplitude and the phase of the transmission signal or the reference signal are changed by the modulation means for changing the amplitude and the phase of the chirp signal so as to eliminate the influence. As a result, after the correlation processing, it is possible to obtain a waveform having a small wave number and a small side lobe and excellent in time resolution.

Fourth Embodiment FIG. 14 is a configuration diagram of an electromagnetic ultrasonic measuring apparatus according to a fourth embodiment of the present invention. FIG. 14 shows a first modulation unit 13 and a second modulation unit in the device having the configuration of FIG. 14 is additionally provided. Theoretically, if ideal modulation is performed by either the first modulation means 13 or the second modulation means 14 in the second or third embodiment, a desired compressed signal can be obtained after the correlation processing. Will be done.

However, in actual online measurement, various subjects are measured, and if the subjects differ, the frequency characteristics of signal attenuation in the subject may change. Further, if the connection cable or the sensor coil from the power amplifier and the receiving amplifier to the sensor coil is replaced due to deterioration or damage during use, the frequency characteristics of the received signal may change. In such a case, initially, even if almost ideal modulation is performed by, for example, the first modulating means 13, the subject after the correlation processing is performed due to a change in the subject or replacement of the connection cable or the sensor coil. The compressed signal may deviate from the ideal waveform.

In order to correct the deviation from the initial ideal waveform as described above, while the modulation by the first modulation means 13 is performed as it is, a slight modulation is added by the second modulation means 14 and the ideal waveform is re-established. It is relatively easy to get In such a device having two modulation means, even if the connection cable and the sensor coil are exchanged, a rough modulation which can be applied in common is performed by one modulation means, and the subsequent fine modulation is performed by the other modulation means. , An ideal waveform can be obtained as a result of both modulations.

[0057]

As described above, according to the present invention, a chirp signal whose frequency and amplitude are changed within a predetermined pulse width is transmitted, so that a large average power is transmitted even at a relatively low transmission voltage and a strong super power is transmitted. Sound waves can be generated, and highly sensitive measurement can be performed. In addition, since the received signal performs a correlation operation with the reference signal, the compressed echo signal after the correlation operation can have a high time resolution and a high SN ratio. As a result, the problem of the withstand voltage of the sensor is eliminated, and a high pulse repetition frequency is obtained without being a noise source for other devices, and the present invention is applicable to an object having a plurality of reflection sources or an object having no parallel surface. The invention can be applied. In addition, the present electromagnetic ultrasonic measurement method can not only increase the sensitivity but also exhibit the wideband characteristic inherent to electromagnetic ultrasonic waves which has not been practically used in the past. As a result, the electromagnetic ultrasonic waves can be applied for various measurement purposes.

Further, according to the present invention, the amplitude and phase of the chirp signal are changed so as to obtain a transmission signal or a reference signal having a predetermined frequency characteristic, and this is used as the transmission signal or the reference signal. Even when the frequency characteristics of the received signal are affected by the sensor coil and the connection cable, the frequency characteristics after the correlation processing become the desired characteristics, and as a result, an echo signal with few sidelobes and excellent in time resolution can be obtained. .

According to the present invention, the amplitude and phase of the chirp signal are changed so as to obtain a transmission signal having a first predetermined frequency characteristic, and a reference signal having a second predetermined frequency characteristic is obtained. Since the amplitude and phase of the chirp signal are changed, even when the subject to be measured changes, or when the frequency characteristics of the reception signal change when the sensor coil or the connection cable is replaced, the transmission signal can be changed. Alternatively, by changing either one of the frequency characteristics of the reference signal, an echo signal having few side lobes and excellent in time resolution can be easily obtained.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an electromagnetic ultrasonic measurement device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of an FIR filter used in the correlator of FIG.

FIG. 3 is a waveform diagram illustrating an operation of the FIR filter of FIG. 2;

FIG. 4 is a diagram showing transmission signals used in the experiment of the first embodiment.

FIG. 5 is a diagram illustrating a correlation process according to the first embodiment.

FIG. 6 is a diagram showing a reception signal of an experimental result according to the first embodiment.

FIG. 7 is a configuration diagram of an electromagnetic ultrasonic measurement device according to a second embodiment of the present invention.

FIG. 8 is a diagram showing a chirp signal modulated by the first modulation means of FIG. 7;

FIG. 9 is a diagram illustrating a correlation process according to the second embodiment.

FIG. 10 is a configuration diagram of an electromagnetic ultrasonic measurement apparatus according to Embodiment 3 of the present invention.

FIG. 11 is a diagram showing characteristics of an ideal waveform.

FIG. 12 is a diagram illustrating a frequency characteristic of the second modulation unit in FIG. 10;

FIG. 13 is a diagram illustrating a correlation process according to the third embodiment.

FIG. 14 is a configuration diagram of an electromagnetic ultrasonic measurement apparatus according to Embodiment 4 of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Subject 2 Sensor coil 3 External magnetizer 4 Chirp signal calculation means 5 Reference signal storage means 6 Transmission signal storage means 7 D / A converter 8 Power amplifier 9 Reception amplifier 10 A / D converter 11 Correlator 12 Synchronization signal Generation means 13 First modulation means 14 Second modulation means

Claims (8)

[Claims] 1. An electromagnetic ultrasonic measuring method for electromagnetically generating ultrasonic waves on a subject using Lorentz force or magnetostriction and detecting the ultrasonic waves to measure the subject. And a chirp signal of which amplitude has been changed is transmitted to the subject via a sensor coil for transmission, and a reception signal obtained from the subject via a sensor coil for reception and a waveform identical or similar to the transmission signal And a correlation calculation with the reference signal, and measuring the subject using the received signal after the correlation calculation. 2. The electromagnetic ultrasonic measurement method according to claim 1, wherein an amplitude and a phase of the chirp signal transmitted to the subject are changed so that the chirp signal has a predetermined frequency characteristic. 3. The electromagnetic ultrasonic measurement method according to claim 1, wherein the amplitude and the phase are changed so that the reference signal for performing the correlation operation with the received signal has a predetermined frequency characteristic. 4. A chirp signal to be transmitted to the subject, the amplitude and phase of which are changed so as to have a first predetermined frequency characteristic, and a reference signal for performing a correlation operation with the received signal is changed to a second predetermined frequency characteristic. 2. The method according to claim 1, wherein the amplitude and the phase are changed so as to have the following. 5. An electromagnetic ultrasonic measuring apparatus which electromagnetically generates ultrasonic waves on a subject using Lorentz force or magnetostriction and detects the ultrasonic waves to measure the subject, wherein a magnetic field is applied to the subject. An external magnetizer to be applied, a sensor coil for transmission, a sensor coil for reception which is also used as or separate from the sensor coil for transmission, and a chirp signal calculation for calculating a chirp signal having a frequency and an amplitude changed within a predetermined pulse width as numerical data. Means, a chirp signal calculated by the chirp signal calculating means,
Transmission signal storage means and reference signal storage means for respectively storing a transmission signal and a reference signal; D / A conversion means for reading out the transmission signal stored in the transmission signal storage means and converting it into an analog signal; A power amplifying means for amplifying an analog signal output from the means and applying the amplified signal to the transmitting sensor coil; a receiving amplifying means for amplifying a received signal obtained by the receiving sensor coil; and an amplified reception of the receiving amplifying means. A / D conversion means for converting a signal into numerical data, and correlation calculation means for performing a correlation calculation between the numerical data output from the A / D conversion means and the reference signal read from the reference signal storage means. An electromagnetic ultrasonic measurement device, characterized in that: 6. A chirp signal calculated by said chirp signal calculating means is subjected to modulation for changing its amplitude and phase so as to have predetermined frequency characteristics, and the modulated signal is stored in said transmission signal storing means. 6. An electromagnetic ultrasonic measuring apparatus according to claim 5, further comprising a modulating means for supplying a signal to said measuring device. 7. A modulation for changing the amplitude and phase of the chirp signal calculated by the chirp signal calculation means so as to have a predetermined frequency characteristic, and the modulated signal is stored in the reference signal storage means. 6. An electromagnetic ultrasonic measuring apparatus according to claim 5, further comprising a modulating means for supplying a signal to said measuring device. 8. A modulation for changing the amplitude and phase of the chirp signal calculated by the chirp signal calculation means so as to have a first predetermined frequency characteristic, and applying the modulation processing to the transmission signal. First to supply to storage means
And modulating the chirp signal to change its amplitude and phase so as to have a second predetermined frequency characteristic,
6. The electromagnetic ultrasonic measurement apparatus according to claim 5, further comprising a second modulation unit that supplies the signal after the modulation processing to the reference signal storage unit.