JPH0785076B2 - measuring device - Google Patents

Description

Description: [Industrial application] The present invention relates to a measuring apparatus that employs a pulse compression method using waves such as ultrasonic waves and electromagnetic waves.

[Prior Art] For a conventional measuring apparatus using this kind of ultrasonic wave, for example, see B. Bee. Lee and E. S. Ferguson "High Speed Digital Golay Code Flaw Detection System" Minutes of The Eye Triple E Ultrasonic Symposium 1981, pp. 888-
Page 891 (hereinafter referred to as Reference A) (BBLee and ES Furgason, “High-Speed Digital G
olay Code Flaw Detection System, "in Proceedings of
the IEEE Ultrasonics Symposium, 1981, pp.888-89
1), Bee. Bee. Lee and E. S. Ferguson "Evaluation of Ultrasonic N.D.E Correlation Detection System" Sonic and Ultrasonic Eye Triple E Bulletin vol.SU-29, no.6, November, 198
2 years, pp. 359-369 (hereinafter referred to as Reference B) (BBLee and ES Furgason, “An Evaluation of Ultr
asound NDE Correlation Flaw Detection Systems, "IEE
E Transactions on Sonics and Ultrasonics, vol.SU-2
9.no.6, November, 1982, pp.359-369) and B. Bee. Lee and E. S. Ferguson "High Speed Digital Golay Code Flaw Detection System" Ultrasound, July,
1983, pp. 153 to 161 (hereinafter referred to as Document C) (BBLee and ES Furgason, "High-Speed Digital G"
olay Code Flaw Detection System, "Ultrasonics, July,
1983, pp.153-161).

The configuration of the conventional example will be described with reference to FIG.

FIG. 19 is a block diagram showing a conventional measuring apparatus using ultrasonic waves shown in Document C, for example.

Referring to FIG. 19, the conventional measuring device includes a signal source (1),
Digital delay line (2) connected to this signal source (1)
A bipolar converter (3) connected to the signal source (1) and the digital delay line (2), a transmitter (4) connected to the bipolar converter (3), and also the signal source (1) and A bipolar transducer (5) connected to the digital delay line (2), an ultrasonic probe (6), an ultrasonic probe (6), a transmitter (4) and a bipolar converter (5). An analog correlator (7) connected,
It is composed of a display (8) connected to the analog correlator (7).

The ultrasonic probe (6) is installed in the water of the aquarium,
A brass target S is arranged at a position facing the ultrasonic probe (6). The analog correlator (7) is a multiplier (7a) connected to the ultrasonic probe (6) and the bipolar converter (5), and the multiplier (7a).
It consists of an integrator (7b) connected to a).
Furthermore, between the signal source (1) and the digital delay line (2),
A logic circuit such as an AND gate is inserted between the signal source (1) and the bipolar converters (3) and (5) and between the digital delay line (2) and the bipolar converters (3) and (5). Has been done. The system control (9) is connected to each device and circuit described above for controlling.

Next, the operation of the above-mentioned conventional example will be described with reference to FIGS. 20 and 21.

FIG. 20 is a waveform diagram showing a transmission signal of the conventional ultrasonic measuring device shown in Document B, and FIG. 21 is a compression of the conventional ultrasonic measuring device shown in Document B, for example. It is a wave form diagram which shows a pulse.

In FIG. 20, the horizontal axis is expressed in units of bits (BITS), but the unit of the horizontal axis can be read as time if the unit time is associated with the unit bit. Literature B
In, the unit time corresponding to the unit bit is represented by the symbol δ. Therefore, the pulse width of the transmission signal is 63 × δ.

This transmission signal is a signal whose frequency band is baseband and whose amplitude is encoded by a special sequence. The encoding of the amplitude will be described later, and the sequence used will be described first.

The sequence used is a finite length sequence having a length of 63 bits, and is formed by cutting off an m sequence (maximal length sequence), which is a periodic sequence having a period length of 63 bits, in one cycle.

The m-sequence is described in detail in "Code Theory" by Hiroshi Miyagawa, Yoshihiro Iwadari and Hideki Imai, June 29, 1979, published by Shokoido, pages 474-499 (hereinafter referred to as Document D). Stated.

The m-sequence is a periodic sequence having an infinite length and is a binary sequence in which the components forming the sequence are two elements. The two elements may be assigned a sign + and a sign −,
Numerical value +1 and numerical value -1, or numerical value 1 and numerical value 0 may be assigned. In the example of FIG. 20, a finite length sequence is created by extracting one period based on an m sequence having a period length of 63 bits and an infinite length.

Next, amplitude encoding using this finite length sequence will be described.

Amplitude +1 for element + and amplitude − for element − that form a finite length sequence
Corresponding to 1, the amplitude is modulated to ± 1 with a relative value for each unit time δ according to the order in which the elements ± of the series appear. Such a signal is called an amplitude-coded signal.

In FIG. 21, as in FIG. 20, the horizontal axis is displayed in bit units, but if the unit bit is associated with the unit time δ, the horizontal axis unit can be read as time. .

This compressed pulse is an example in the case of using a transmission signal amplitude-coded by a finite length sequence having a length of 64 bits. This sequence has a length of 63 that was used when generating the transmission signal in FIG.
It is created by adding 1 bit to a finite length sequence of bits. Therefore, the pulse width of this transmission signal is 64 × δ
Is. The pulse width of the echo is almost the same as this.

As shown in FIG. 21, most of the energy of the compressed pulse is concentrated within the central time width (several bits × δ) in the figure. This central high amplitude signal portion is called the main lobe of the compressed pulse. The pulse width of the main lobe is short. This means that the energy of the echo was compressed to almost one point on the time axis. The small amplitude signal portions on either side of the main lobe are called the range side lobes of the compressed pulse.

Now, the transmission signal as shown in FIG. 20 is generated from the signal source (1) and the digital delay line (2) via the bipolar converter (3) and the transmitter (4). The ultrasonic probe (6) is excited by this transmission signal.

The ultrasonic waves emitted into the water from the ultrasonic probe (6) are reflected by the target S and are received again by the ultrasonic probe (6). The echo received by the ultrasonic probe (6) is transmitted to the multiplier (7a) of the analog correlator (7).

The pulse width of the echo described above is as long as the transmitted signal.
That is, the energy of the echo is for a long time (approximately 63 × δ), which is approximately the pulse width of the transmitted signal,
It is distributed almost uniformly.

On the other hand, the same signal as the transmission signal is transmitted to the multiplier (7a) of the analog correlator (7) via the digital delay line (2) and the bipolar converter (5).

The analog correlator (7) performs a correlation operation between the echo and the transmitted signal. By this correlation calculation, the energy of the echo, which is distributed almost uniformly on the time axis over a long time period equivalent to that of the transmission signal, is compressed to almost one point on the time axis. The pulse obtained by being compressed is called a compressed pulse.

The compressed pulse obtained by the analog correlator (7) is transmitted to the display (8) and displayed as the final result.

The distance resolution of the above-described conventional measuring apparatus using ultrasonic waves is determined by the pulse width of the main lobe of the compressed pulse (abbreviated as the pulse width of the compressed pulse). Although the pulse width of the transmission signal is long, the pulse width of the compressed pulse is short as described above. Therefore, originally, a resolution equivalent to that of a measuring device using ultrasonic waves by the pulse echo method using a transmission signal having a short pulse width can be obtained.

On the other hand, the S / N ratio (signal to noise ratio) increases as the average transmission energy of the transmission signal increases. The average transmission energy increases as the pulse width of the transmission signal increases. Therefore, the conventional measuring apparatus can obtain a higher S / N ratio than the pulse echo method which originally uses a transmission signal having a short pulse width.

As described above, the conventional measuring apparatus using ultrasonic waves has excellent resolution and a high S / N ratio.

However, the conventional measuring device has a problem that if the level of the range sidelobe of the compressed pulse is high, it may be mistaken for a reflector (defect etc.) at the position in the test body corresponding to the time when it appears. is there.

To avoid this problem, it is necessary to lower the range sidelobe level of the compressed pulse. To achieve this, it is necessary to lower the range sidelobe level of the autocorrelation function of the sequence used to encode the transmission signal. In other words, it is necessary to use a sequence having a low range sidelobe level of the autocorrelation function as the sequence used for coding the transmission signal.

Hereinafter, the range side lobe of the compressed pulse and the range side lobe of the autocorrelation function of the series will be described with reference to FIG. Note that the definition of the autocorrelation function of the series is described in detail in Document D.

FIG. 22 is a waveform diagram showing an autocorrelation function of a finite length sequence used for coding the transmission signal of FIG.

The m-sequence itself is a sequence having a characteristic that the autocorrelation function has a sharp peak called a main lobe and the range sidelobe level is low, as described on pages 479 to 483 of Document D. However, as described on page 489 of Document D, when one period of a periodic sequence with a low range sidelobe level is extracted to create a finite length sequence, the range side of the autocorrelation function of the original periodic sequence is The low lobe level does not necessarily mean that the range sidelobe level of the autocorrelation function of the finite-length sequence created as described above is low, as shown in FIG.

The level of the range sidelobe of the autocorrelation function of the m-sequence itself is expressed as n, and when normalized so that the peak value of the main lobe becomes 1, the absolute value becomes 1 / n, See D, pages 479-480. Therefore, when the cycle length is 63 bits, 1/63 = 0.0159. However, looking at FIG. 22, in the finite-length sequence autocorrelation function used for coding the transmission signal in FIG. 20, the range sidelobe level is at least 0.1 or more, which is the range of the autocorrelation function of the m sequence itself. 1 more than sidelobe level
Digit larger.

That is, if a sequence formed by cutting off the m sequence with a finite length is used for encoding the transmission signal, there is a drawback that the range side lobe level of the compressed pulse is high. The compressed pulse shown in FIG. 21 is an example in which the range sidelobe level is high. Also, as described in Reference B,
It has also been tried using a sequence truncated at 63 bits. In this case, the range sidelobe shape (pattern)
Is different from that in FIG. 21, but the level of the range side lobe is not changed by more than 3 dB compared with the case in FIG. These examples are examples showing that the range sidelobe level of the compressed pulse cannot be lowered unless a sequence having a low range sidelobe level of its autocorrelation function is used as a sequence used for coding the transmission signal. .

From the above, it can be seen that it is the best if the sequence has no range sidelobes of the autocorrelation function. However, as described in Document D, there is no binary finite length sequence having no range sidelobe.

However, similarly, as described in Document D, if the autocorrelation functions of two binary finite length sequences having the same length are added, the range side lobe may be completely eliminated after the addition. Two sequences that form a pair and have such characteristics are called complementary sequences. For complementary sequences, see M. Jay. E. Golay "Complementary Sequence" Information Theory IR Bulletin vol.IT-7, pp. 82-87, April, 1961 (M.JB.E.Golay, "Complementary
Series, "IRE Transactions on Information Theory, vo
l.IT-7, pp.82-87, April, 1961). This complementary sequence is also called a Golay complementary sequence or, in short, a Golay code.

Here, the autocorrelation function of the complementary sequence will be described with reference to FIGS. 23 (a), (b) and FIG.

23 (a) and 23 (b) are waveform diagrams showing the autocorrelation function of the first and second sequences forming the complementary sequence shown in Document C, and FIG. 24 is the waveform diagram of the first and second sequences. It is a wave form diagram which shows the addition result of an autocorrelation function.

As can be seen from FIGS. 23 (a) and 23 (b), the level of the range side lobes of these two autocorrelation functions is high. As shown in FIG. 24, the autocorrelation function obtained by addition (hereinafter referred to as the composite autocorrelation function) has only a sharp peak corresponding to the main lobe in the center and has no range sidelobe at all.

Documents A and C also describe measuring devices with ultrasound using complementary sequences. Complementary series 2
The two series are used alternately and repeatedly. This will be described with reference to FIGS. 25 (a), (b) and FIG.

25 (a) and 25 (b), and FIG. 26 are waveform charts showing computer simulation results of the first and second compressed pulses and the synthetic compressed pulse shown in Document C.

The two sequences forming the complementary sequence will be referred to as the first and second sequences. Two transmission signals generated using the first and second sequences in the same manner as in the case of FIG. 20 will be referred to as first and second transmission signals, respectively. Further, the two echoes obtained when the ultrasonic probe (6) is excited by these first and second transmission signals will be referred to as first and second echoes, respectively.
Furthermore, these first and second echoes are respectively replaced by the first echo.
, And the two compressed pulses obtained by performing the correlation processing using the second transmission signal in the same manner as in FIG. 21 will be referred to as the first and second compressed pulses, respectively.

The first transmission signal and the second transmission signal are alternately repeated at a certain fixed cycle. A first echo is obtained in a cycle in which the ultrasonic probe (6) is excited by the first transmission signal, and the first echo is subjected to correlation processing in the same cycle using the first transmission signal. A first compressed pulse has been obtained. Similarly, a second echo is obtained in a cycle in which the ultrasonic probe (6) is excited by the second transmission signal, and the second echo is obtained within the same cycle by using the second transmission signal. And the second compressed pulse is obtained by the correlation processing. Further, by making the integration time of the analog correlator (7) longer than twice the transmission repetition period, an operation of adding the first compressed pulse and the second compressed pulse is performed.

The addition result of the first compressed pulse and the second compressed pulse is
It is called a synthetic compressed pulse. Synthetic compressed pulse
It is displayed on the display (8).

As shown in FIGS. 25 (a) and 25 (b), both the first and second compressed pulses have high range sidelobe levels. However, as shown in FIG. 26, the level of the range sidelobe of the composite compressed pulse shows only the main lobe in the center, and there is no range sidelobe at all.

As described above, the conventional measuring apparatus using the ultrasonic wave using the complementary sequence has an excellent advantage that there is no range side lobe.

However, in the complementary sequence having the characteristic that there is no range side lobe of the combined autocorrelation function, the sequence length n does not exist for all natural numbers. Complementary sequences exist only for a limited length. For example, the length n is 50
In the following, as described in document D, n = 2,
It exists for 4, 8, 10, 16, 20, 26, 32, 40.
However, the existence in the case of n = 34, 36, 50 is unknown.

[Problems to be Solved by the Invention] In the conventional measuring apparatus as described above, when the range side lobe level is high and a complementary sequence capable of reducing the range side lobe level to zero is used, the sequence length n There was a problem that there were only a few.

The present invention has been made to solve the above-mentioned problems, and increases the degree of freedom in selecting the length n of a sequence while keeping the level of the range sidelobe of the composite autocorrelation function completely zero. The purpose is to obtain a measuring device capable of

[Means for Solving the Problems] The measuring apparatus according to the present invention includes the following means.

[1] Transmission signal generating means for generating a plurality of transmission signals based on a plurality of complementary sequences.

[2] A transmitting unit that is excited by the plurality of transmission signals and transmits a wave to an object.

[3] Receiving means for receiving a plurality of echoes respectively corresponding to the plurality of transmission signals.

[4] Correlation means for performing correlation processing on the plurality of echoes using a plurality of reference signals defined by the plurality of complementary sequences.

[5] An addition unit that adds the results of a plurality of correlation processes.

[Operation] In the present invention, the transmission signal generating means generates a plurality of transmission signals based on a plurality of complementary sequences.

Further, the wave is transmitted to the object by being excited by the plurality of transmission signals by the transmitting means.

Further, the receiving means receives a plurality of echoes respectively corresponding to the plurality of transmission signals.

Furthermore, the correlation means performs correlation processing on each of the plurality of echoes using the plurality of reference signals defined by the plurality of complementary sequences.

Then, the adding means adds the results of the plurality of correlation processes.

[Embodiment] Although the complementary sequence described above consists of two sequences having the same length, we have an even number of four or more sequences having the same length, and the autocorrelation of each sequence. We have found that there is a sequence with the characteristic that when the functions are added, the range sidelobes disappear. Up to now, there have been no reports of sequences having such characteristics. A sequence having such a characteristic eliminates a range side lobe by being complemented by a plurality of sequences, and is therefore referred to as a multiple complement sequence here for convenience.

The configuration of the first embodiment of the present invention will be described with reference to FIG.

FIG. 1 is a block diagram showing a first embodiment of the present invention, in which an ultrasonic probe (6) and an indicator (8) are exactly the same as those of the conventional device shown in FIG. .

In FIG. 1, the first embodiment of the present invention is exactly the same as that of the conventional apparatus described above, an amplitude-encoded transmission signal generator (1A), and this amplitude-encoded transmission signal generator (1A).
And a correlator (7A) connected to the ultrasonic probe (6),
An adder (10) including a memory whose input side is connected to this correlator (7A) and whose output side is connected to a display (8).

The ultrasonic probe (6) is also connected to the amplitude-coded transmission signal generator (1A) and is in contact with the test body S.

Next, the operation of the above-described first embodiment will be described with reference to FIGS. 2, 3, and 4.

2 (a), (b), (c) and (d) are waveform diagrams showing the transmission signal of the first embodiment of the present invention, and FIG. 3 is four transmission signals of the first embodiment of the present invention. FIG. 4 is a waveform diagram showing four echoes of the first embodiment of the present invention.

The transmission signals shown in FIGS. 2A to 2D are amplitude-encoded signals as in the conventional case. However, the sequence used for encoding is a multiple complementary sequence consisting of four sequences having a length of 5. Each of the four series has a first, second,
Calling the third and fourth sequences, the first sequence is (−, −, −, +, −), the second sequence is (−, −, −, +, +), the third sequence. The series is (-,-, +,-,-), and the fourth series is (-,-, +,-, +). In order to make the relationship between these sequences and the amplitude coding of the transmission signal easier to understand, the codes of the sequences described above are also entered in FIG.

Hereinafter, the transmission signals will also be referred to with serial numbers in correspondence with the serial numbers of the series, and the transmission signals shown in FIGS. 2A to 2D will be referred to as the first, second and third transmission signals, respectively. And the fourth
Will be referred to as a transmission signal.

The amplitude-encoded transmission signal generator (1A) sequentially generates the above-mentioned four transmission signals at a certain transmission repetition period Tr as shown in FIG. ).

The ultrasonic probe (6) is sequentially excited by four transmission signals and transmits ultrasonic waves into the test body S. Then, the echo reflected by the defect or the like in the test body S is received by the ultrasonic probe (6). The received echo is transmitted to the correlator (7A).

The echoes obtained when the ultrasonic probe (6) is excited by the first, second, third and fourth transmission signals are respectively represented by the first, second and third echoes as shown in FIG. Let us call them the 3rd and 4th echoes. Since a part of the transmission signal leaks into the receiving circuit side (correlator (7A) side), the state is also shown in FIG.

The correlator (7A) performs correlation processing on the i-th (i = 1,2,3,4) echo using the i-th transmission signal and compresses it. The compressed pulse obtained by compressing the i-th echo is
The second compressed pulse will be called. 1st, 2nd, 3rd
And the fourth compressed pulse are sequentially transmitted to the adder (10).

The adder (10) stores the first, second and third compressed pulses in the memory until the fourth compressed pulse is transmitted. When the fourth compressed pulse is transmitted, the first, second, third and fourth compressed pulses are added. Hereinafter, the addition result will be referred to as a synthetic compressed pulse. This composite compressed pulse is transmitted from the adder (10) to the display (8).

In this invention, since the relative level of the range side lobe of the synthetic compressed pulse is a problem, the adder (10) simply adds the four compressed pulses as described above, and the display (8). May be transmitted to the display unit (8), or four compressed pulses may be averaged and transmitted to the display unit (8).

On the display (8), the composite compressed pulse is displayed as in the conventional case.

Next, the effect of the first embodiment of the present invention will be described.
This will be described with reference to FIGS. 6, 6, 7, 8, 9, 10, 11 and 12.

5 (a), (b), (c) and (d) are waveform charts showing the calculation results of the autocorrelation functions of the first, second, third and fourth series, respectively, and FIG. It is a wave form diagram which shows the addition result of four autocorrelation functions of FIG.

The autocorrelation function is expressed by the equation (1
It was calculated from the following formula modified from 7.4).

ρ _aa (k) = Σa _{j + k} a _j (The sum is 0 to n−1 for j.) Here, ρ _aa is the autocorrelation function of the sequence a, and k is an integer. In addition, a _j is the j-th element (+1 or -1) of the sequence a, and n is the length of the sequence. For example, if the sequence a is the above-mentioned first sequence (−, −, −, +, −), then a ₀ = a ₁ = a ₂ = a ₄ = −1 and a ₃ = 1.

Hereinafter, the autocorrelation functions of the first, second, third, and fourth series are represented by ρ ₁₁ , ρ ₂₂ , ρ _33, and ρ ₄₄ , respectively. The formula is a formula in which the right side of formula (17.4) in document D is simply multiplied by n. Whether it is multiplied by n or not multiplied by n depends on whether the autocorrelation function is normalized so that the peak value of the main lobe is 1, or is normalized so that the peak value of the main lobe is n. Yes, when considering the relative level of the range side lobe, it does not change whichever one is considered.

The range sidelobe levels of the four autocorrelation functions ρ ₁₁ , ρ ₂₂ , ρ _33, and ρ ₄₄ shown in FIG. 5 are all high.
However, as shown in FIG. 6, ρ ₁₁ + ρ ₂₂ + ρ ₃₃
+ Ρ ₄₄ (hereinafter, referred to as a composite autocorrelation function) is
You can see that there is no range side lobe.

Note that there is no combination that becomes a complementary sequence even if any two sequences among the above-mentioned four sequences are extracted and combined. This is because even if any two autocorrelation functions among the four autocorrelation functions shown in FIGS. 5A to 5D are taken out and added, there is no combination in which the range side lobe disappears after the addition. I understand from that.

As shown in FIG. 6, the four autocorrelation functions ρ ₁₁ ,
When ρ ₂₂ , ρ _33, and ρ ₄₄ are added, the range sidelobe is completely eliminated, so that it can be expected that the range sidelobe is completely eliminated even in the synthetic compressed pulse.

Therefore, this was confirmed by computer simulation as follows.

The compressed pulse is given by the convolution integral of the autocorrelation function of the transmitted signal and the impulse response of the ultrasound probe (6), as described in document C. Here, the impulse response represents the impulse response of the ultrasonic probe (6) in the total transmission and reception when the transmission and reception of ultrasonic waves are comprehensively considered.

Here, FIG. 7 is a waveform diagram showing the impulse response of the ultrasonic probe (6), and FIGS. 8 (a), (b), (c) and (d) are the first, second and third waveforms. FIG. 9 is a waveform diagram showing the calculation result of the fourth compressed pulse, and FIG. 9 is a waveform diagram showing the composite compressed pulse.

The impulse response was calculated as a pulse with a vibration duration of 1.5 cycles shown in FIG. In the figure, f _c represents the center frequency of the ultrasonic probe (6).

As described above, the i-th compressed pulse corresponds to the auto-correlation function of the i-th transmission signal shown in FIGS. 2A to 2D and the ultrasonic probe (shown in FIG. 7). The impulse response of 6) was obtained by convolution integration. Note that the autocorrelation function of the i-th transmission signal is shown in FIGS. 5A to 5D if the unit time δ corresponds to the unit bits on the horizontal axis in FIGS. 5A to 5D. It is the same as the autocorrelation function of the i-th sequence shown in d). here,
It was calculated as δ = 1 / (2f _c ).

As shown in FIGS. 8A to 8D, the level of the range side lobe is high for all four compressed pulses. However, as shown in FIG. 9, the synthetic compressed pulse has no range sidelobes as expected. FIG. 8 (a)-
In (d) and FIG. 9, the unit time δ is 1 / (2
f _c ), but even if δ is changed from this value,
No range sidelobes occurred in the synthetic compressed pulse. In addition, the impulse response of the ultrasonic probe (6) is 1.
Calculated as a pulse of 5 cycles, but the number of cycles is 1.5
Similarly, changing from cycle did not produce range sidelobes in the synthetic compressed pulse.

As described above, the first embodiment of the present invention has a first advantage that a synthetic compressed pulse without range side lobes can be obtained by using a sequence having a length n of 5 in which there is no complementary sequence. I understood.

By the way, it is shown in Document B that the improvement amount of the S / N ratio in this type of measuring apparatus is given by SNRE = nNBδ. here,
The SNRE represents how much the S / N ratio after correlating the echo from the S / N ratio of the echo was improved.

In the equation, n is the length of the sequence, N is the correlation processing for each transmission repetition period to obtain compressed pulses, and the result obtained by adding these compressed pulses is displayed as the final result. The number of transmission repetitions, that is, N = 2 when the conventional complementary sequence is used, N = 4 when the plural complementary sequences of the first embodiment are used, B is the echo bandwidth, and δ Represents a unit time corresponding to a unit bit.

In the equation, the product of n and δ corresponds to the pulse width of the transmission signal. From the equation, it can be seen that the S / N ratio can be increased as the pulse width (nδ) of the transmission signal is increased. Therefore, considering only the improvement of the S / N ratio, it is necessary to lengthen the pulse width of the transmission signal.

However, if the pulse width of the transmission signal is lengthened, the following problems occur. While the signal is being transmitted, the transmitted signal leaks into the receiving circuit side as shown in FIG. 4, so that the echo cannot be accurately received. Therefore, the time (nδ) during which the transmission signal continues is a dead time that cannot be used for inspection. This is an area from the surface of the test body S corresponding to a time corresponding to half the pulse width of the transmission signal, that is, the test body S.
If the propagation velocity of the ultrasonic wave inside is represented by v, it means that the region of the depth from the surface of the test body S to (vnδ) / 2 becomes a dead zone and cannot be inspected. Here, the reason why the pulse width is halved is that the ultrasonic waves reciprocate in the test body S. To narrow this dead zone,
The pulse width of the transmission signal needs to be short.

That is, the demand for improving the S / N ratio and the demand for narrowing the dead zone are contradictory requirements. Therefore, it is necessary to determine the pulse width of the transmission signal so that the required S / N ratio can be obtained and the dead zone is within an allowable range in consideration of the type of the test object S and the purpose of inspection.

The pulse width (nδ) of the transmission signal can be set so as to have the required width determined as described above by changing n or δ.

However, in order to improve the energy utilization efficiency of the transmitted signal, δ is represented by f _{c as} the center frequency of the ultrasonic probe (6),
Normally, it is set near 1 / (2f _c ). About this, the first
This will be described with reference to FIG.

FIG. 10 shows the clock frequency and S /
It is a characteristic view which shows the relationship of N ratio.

FIG. 10 shows a relative change in S / N ratio caused by a change in energy utilization efficiency of a transmission signal when a clock frequency given by the reciprocal of δ is changed.

In Fig. 10, in order to increase the energy utilization efficiency of the transmitted signal and inspect with a good S / N ratio, the clock frequency is 2
It turns out that it is necessary to choose near f _c . That is, δ is 1 /
(2f _c ) Need to choose near.

Therefore, in order to set the pulse width (nδ) of the transmission signal to the required width, it is desirable to achieve it by changing the length n of the sequence.

However, when using a conventional complementary sequence, which has the advantage that range side lobes do not occur, the complementary sequence n does not exist for all natural numbers. Complementary sequences exist only for a limited length, and if the length n is 50 or less,
Only 2,4,8,10,16,20,26,32,40 exist. Therefore, for example, if n is set to 8, the pulse width of the transmission signal is long, so the S / N ratio can be obtained at a sufficient value, but the dead zone is not within the allowable range.
On the other hand, if n is set to 4, the pulse width of the transmission signal is short, so the dead zone falls within the permissible range.
A situation occurs in which the S / N ratio cannot be obtained. In such a case, if the multiple complementary sequence of n = 5 shown in the first embodiment of the present invention in which n is between 4 and 8 is used, the above-mentioned first advantage that no range side lobe occurs is generated. The required value of the S / N ratio can be obtained while maintaining the above value, the dead zone can be kept within the allowable range, and the second advantage that the inspection request can be achieved occurs.

Furthermore, the use of multiple complementary sequences has the following advantages.

If you want to detect micro defects near the bottom of the test piece S,
The level of echo from microdefects is low. On the other hand, the level of echo from the bottom is large. When the pulse width of the transmission signal is long, these two echoes having a large level difference partially overlap each other on the time axis. A large dynamic range is required for a receiving circuit system such as a correlator (7A) in order to perform signal processing on two echoes having a large level difference and overlapping each other. However, if the pulse width of the transmitted signal is short and the above-mentioned two echoes can be separated on the time axis, a time gate is applied to the bottom echo, and this is deleted to amplify only the echo from the microdefects to obtain the signal. It can be processed. If such signal processing is possible, the dynamic range of the receiving circuit system does not need to be so large. The above signal processing using the time gate is
When the echo is A / D converted, captured as data in the computer, and the signal processing for the echo such as correlation processing and addition is performed using the computer, the bit number of the A / D converter can be small. Especially convenient.

When the dynamic range of the receiving circuit system is not sufficient and the above-mentioned signal processing using the time gate is desired to be performed, when the conventional complementary sequence is used, the pulse width is short when the length n is 4, so that the desired signal processing is not performed. Although possible, the S / N ratio is insufficient. On the other hand, when n is 8, the pulse width is long, so the S / N ratio is sufficient, but a situation may occur in which desired signal processing cannot be performed. At this time, by using a plurality of complementary sequences of n = 5 shown in the first embodiment of the present invention in which n is between 4 and 8, the S / N ratio is sufficient and desired signal processing can be performed. There is a third advantage that That is, in the first embodiment using a plurality of complementary sequences, considering the range of selection of usable sequence lengths, including complementary sequences, while maintaining the above-mentioned first advantage that there is no range sidelobe,
Since it is wider than before, the required dynamic range for the receiving circuit system can be small.

Furthermore, the use of multiple complement sequences has the following advantages.

If there is some habit in the noise that is superimposed on the echo and there is a correlation between this noise and the sequence used to encode the transmitted signal, the noise will also be compressed, so the compression caused by this noise There is a problem of erroneously recognizing the pulse as a compressed pulse generated by the defect of the test body S. Since only two series are used in the conventional complementary series, if there is a correlation between one of the series and noise, the first and second compressed pulses are arithmetically averaged and displayed as the final result, At the display stage, the level of the compressed pulse due to noise is only halved. On the other hand, since the first embodiment of the present invention uses four sequences, even if there is a correlation between any one sequence and noise, the first, second, third
When the averaging of the fourth compressed pulse and the fourth compressed pulse are performed and displayed as the final result, the level of the compressed pulse due to noise becomes 1/4 at the display stage, which is lower than that in the case of using the conventional complementary sequence. That is, the first embodiment of the present invention using a plurality of complementary sequences has a higher probability of erroneously recognizing a compressed pulse generated by noise as a compressed pulse generated by a defect, as compared with a conventional measuring apparatus using a complementary sequence. There is a fourth advantage of being small.

The use of multiple complement sequences has the following advantages.

In the nondestructive inspection using ultrasonic waves, for example, as shown in FIG. 3, the ultrasonic probe (6) is excited by repeating a transmission signal at a certain fixed cycle. At this time, the ultrasonic wave repeats multiple reflections in the test body S many times, and in the transmission repetition cycle after the transmission repetition cycle in which the transmission signal is generated,
May be received as an echo. Such an echo is called a reverberation echo.

FIG. 11 is a waveform diagram showing a reverberation echo in the first embodiment of the present invention.

FIG. 11 shows a case where the reverberation echo is received in the transmission repetition cycle next to the transmission repetition cycle in which the transmission signal is generated. In this case, the level of reverberation echo is the highest. This is because the reverberation echo received later from the time when the transmission signal is generated is received after passing through a longer propagation path, and thus the level becomes smaller. Hereinafter, the reverberation echo generated by the i-th transmitted signal will be
The second reverberation echo will be called. The reverberant echo is reflected once by the reflector in the test object S, and is indistinguishable from the echo received in the transmission repetition period that generated the transmission signal. Therefore, the reverberant echo interferes with the inspection.

The first embodiment of the present invention and a conventional measuring device using ultrasonic waves will be compared with each other with reference to FIG.

FIG. 12 is a waveform diagram showing reverberation echoes in a conventional measuring apparatus using ultrasonic waves.

As a conventional apparatus, consider the case of using a complementary sequence having a length of 4 shown below.

First sequence = (+, +, +, −) Second sequence = (+, +, −, +) Here, when the reverberation echo level is the highest and the most problematic, that is, the reverberation echo is Consider the case where a transmission signal is received in the next transmission repetition period of the transmission repetition period.

First, in the case of the conventional device, the reverberation echo appears as shown in FIG. That is, the first reverberant echo is received in the transmit repetition period that produces the second transmit signal,
The second reverberation echo is received in the transmission repetition period that produces the first transmission signal. Therefore, in the echo signal processing process, correlation calculation is performed on the first reverberation echo and the second transmission signal. Similarly, the second
The reverberation echo of is subjected to correlation calculation with the first transmission signal. Further, these two correlation calculation results are added and displayed as the final result.

The first and second reverberation echoes are echoes that are generated by the transmission signals amplitude-encoded by the first and second sequences, respectively. Therefore, if the cross-correlation function of the first series and the second series (hereinafter, referred to as the cross-correlation function ρ ₁₂ ) and the cross-correlation function of the second series and the first series (hereinafter, the cross-correlation function ρ) _{The value} of the addition result ρ ₁₂ + ρ ₂₁ (hereinafter, referred to as a composite cross-correlation function) is smaller than the peak value of the main lobe of the composite autocorrelation function ρ ₁₁ + ρ ₂₂ . It is considered that the reverberant echo has less effect on the examination.

Therefore, for the first series = (+, +, +,-) and the second series = (+, +,-, +), the above-described composite cross-correlation function is calculated, and then this is calculated as the composite autocorrelation. Calculation was performed by dividing by 8 which is the peak value of the main lobe of the function. The result is
(0, 1/8, 3/8, 3/8, 3/8, 1/8, 0). In this result, the peak value is 3/8 = 0.375.

The cross-correlation function was calculated from the following equation, which is a modification of the equation (17.8) shown on page 476 of Document D.

ρ _ab (k) = Σa _{j + k} b _j (where the sum is 0 to n−1 for j.) In the formula, ρ _ab is a cross-correlation function of the series a and the series b having the same length n. And the subscripts j and k are the same as in the formula. The formula is simply n times the right side of formula (17.8) in document D in order to be consistent with the formula used for calculating the autocorrelation function.

In order to compare with the above-mentioned calculation result, the same calculation was performed in the case of the first embodiment of the present invention shown in FIG.

In FIG. 11, the first reverberation echo is received in the transmission repetition cycle for generating the second transmission signal, and the second reverberation echo is received in the transmission repetition cycle for generating the third transmission signal. The third reverberation echo is received in the transmission repetition period for generating the fourth transmission signal, and the fourth reverberation echo is received in the transmission repetition period for generating the first transmission signal. Therefore, in the echo signal processing process, the first reverberation echo is between the second transmission signal, the second reverberation echo is between the third transmission signal, and the third reverberation echo is between the fourth transmission signal and the fourth transmission signal. Correlation calculation is performed between the fourth reverberation echo and the transmission signal, and the fourth reverberation echo and the transmission signal. Then, these four correlation calculation results are added and displayed as the final result. Therefore, the first series = (−, −, −, +, −), the second series = (−, −, −, +, +), and the third series used in the first embodiment of the present invention. Sequence = (-,-, +,-,-), and fourth sequence = (-,-, +,-, +), the cross-correlation function of the first sequence and the second sequence (hereinafter, mutual Correlation function ρ ₁₂ ), cross-correlation function of the second series and the third series (hereinafter, cross-correlation function ρ ₂₃ ), cross-correlation function of the third series and fourth series (hereinafter , The cross-correlation function ρ ₃₄ ), the cross-correlation function of the fourth series and the first series (hereinafter referred to as the cross-correlation function ρ ₄₁ ) is calculated, and these four cross-correlation functions are added. Then, the composite phase correlation function ρ ₁₂ + ρ ₂₃ + ρ ₃₄ + ρ ₄₁ was obtained. Then, the above-mentioned composite cross-correlation function was divided by 20 which is the peak value of the composite autocorrelation function ρ ₁₁ + ρ ₂₂ + ρ ₃₃ + ρ ₄₄ .

The result is (0, 0, 0, 1/5, 1/5, 1/5, 0, 0,
It became 0). The peak value in this calculation result is 1/5
= 0.2, which is smaller than the peak value of 0.375 in the same calculation result of the conventional device. Therefore, the first embodiment of the present invention has the fifth advantage that it can be expected that the degree of interference with the reverberation echo inspection is small.

Although the first embodiment of the present invention has been described above, there are multiple complementary sequences other than those described above. Another example of the multiple complement sequence will be described with reference to FIGS. 13 (a) and 13 (b).

FIGS. 13 (a) and 13 (b) are explanatory views showing a multiple complement sequence consisting of four and six sequences.

FIG. 13 (a) is an example of a plurality of complementary sequences in which the range side lobe disappears when the autocorrelation functions of four sequences are added. The series is expressed numerically using the following correspondence.
That is, first, the code + is made to correspond to 1 and the code − is made to correspond to 0, and for example, the sequence (+, +, +, −) is [1110].
Express. Next, [1110] is regarded as a number in binary notation, and this number is converted into a number in decimal notation.
That is, [1110] is changed to [14]. Thereby, one series is associated with one numerical value.

As described on page 476 of Document D, a sequence in which the signs + and-are inverted and a sequence in which the order of the components is inverted with respect to a certain binary sequence have the same autocorrelation function. With. For example, for (+, +, +,-), (-,
-,-, +), (-, +, +, +) And (+,-,-,
-) Have the same autocorrelation function. These 4
If two series are numerically expressed using the above-mentioned correspondence,
[14], [1], [7], and [8]. In FIG. 13 (a), the minimum value [1] is used to represent the other three in such a case. .

FIG. 13 (b) is an example of a plurality of complementary sequences in which the range side lobe disappears when the autocorrelation functions of six sequences are added. How to read the numerical values is the same as in FIG. 13 (a). When using a plurality of complementary sequences shown in FIG. 13 (b), six transmission signals amplitude-coded by each sequence are sequentially and repeatedly generated, and six echoes respectively corresponding to these transmission signals are generated. Correlation processing is performed using corresponding transmission signals to obtain six compressed pulses. Then, by adding these to obtain a composite compressed pulse and displaying this, the same operation and effect as in the case of the first embodiment can be obtained.

FIGS. 13 (a) and 13 (b) are several examples of multiple complement sequences,
We have found a number of multiple complement sequences other than those shown in FIGS. 13 (a) and 13 (b). For example, as a multiple complementary sequence consisting of four sequences, there is one if the length n is 2, one if n is 3, 34 if n is 7, and n is 8. It is known that there are 56 combinations in the case of, and 477 combinations when n is 9. Here, the meaning of the word “combination” is the same as the meaning described in FIG. In addition, the number of combinations is, for a certain sequence, a sequence in which its sign is reversed, a sequence in which the order of components is reversed,
And the sequence obtained by continuously performing the above two operations is
They are counted as the same series. The same applies hereinafter.
There are 1 combination when n is 2 and 48 combinations when n is 6 as a multiple complementary sequence consisting of 6 series, and when n is 3, 5 and 7, 6 combinations are available. It is also known that there is no multi-complementary series consisting of one series.
In addition, n is 2 as a multiple complementary sequence consisting of 8 sequences.
If n is 3, there is 1 combination, if n is 4 there are 5 combinations, if n is 5 there are 35 combinations, and if n is 6 there are 517 combinations. I know things.

A plurality of complementary sequences consisting of four sequences of length n are represented by {a ₀ , a ₁ , ..., A _n-1 }, {b ₀ , b ₁ , ..., B _n-1 }, {c ₀ , c ₁ , ..., c _n-1 }, {d ₀ , d ₁ , ..., d _n-1 }, then {a ₀ , b ₀ , a ₁ , b ₁ , ..., a _n-1 , b _n-1 } {a ₀ , -b ₀ , a ₁ , -b ₁ , ..., a _n-1 , -b _n-1 } {c ₀ , d ₀ , c ₁ , d ₁ , ..., c _{n- 1} , d _n-1 } {c ₀ , -d ₀ , c ₁ ,, -d ₁ , ..., c _n-1 ,, -d _n-1 } is a multiple complementary sequence having a length of 2n. Similarly, a new multi-complementary sequence having a length of twice can be created from a multi-complementary sequence including six or more sequences.

Although the method of encoding the amplitude of the transmission signal by using a plurality of complementary sequences has been described above, the present invention is not limited to this and is also applicable to a method of encoding the phase of the transmission signal.

The configuration of the second embodiment of the present invention will be described with reference to FIG.

FIG. 14 is a block diagram showing a second embodiment of the present invention, which is exactly the same as that of the first embodiment except for the phase-coded transmission signal generator (1B).

In FIG. 14, the second embodiment of the present invention is the same as the first embodiment described above, and the phase-encoded transmission signal connected to the ultrasonic probe (6) and the correlator (7A). It is composed of a generator (1B).

Next, the operation of the above-described second embodiment will be described with reference to FIGS. 15 (a), (b), (c) and (d).

FIGS. 15 (a) to 15 (d) are waveform charts showing transmission signals generated by the phase-encoded transmission signal generator (1B) of the second embodiment of the present invention.

In FIGS. 15A to 15D, the transmission signal is a signal in which the phase is encoded using the same four sequences as in the case of the first embodiment described above. In order to make the relationship between the four sequences and the phase encoding of the transmission signal easier to understand, the symbols of the sequences are also shown in the figure.

The phase encoding method is described in detail in Japanese Patent Application No. 1-45316, which is related to the present invention.

In the second embodiment of the present invention, FIG. 2 (a) of the first embodiment is used.
15A to 15D, the transmission signals shown in FIGS.
The ultrasonic probe (6) is excited by replacing it with the transmission signal shown in (d). The echo signal processing is the same as in the first embodiment.

Next, the effect of the second embodiment described above will be described.

In the second embodiment of the present invention, the same operation and effect as in the case of the first embodiment are obtained, and as can be seen from Japanese Patent Application No. 1-45316 related to the present invention, the frequency characteristic of the transmission signal is The frequency response characteristics of the ultrasonic probe (6) can be approximated. Therefore, it can be expected that the utilization efficiency of transmission energy can be increased.

In the above first and second embodiments, the method of performing the correlation calculation between the echo and the transmission signal to obtain the compressed pulse has been described, but the present invention is not limited to this, and Japanese Patent Application No. As described in No. 1-45316, a filter having a frequency response characteristic that the ultrasonic probe (6) has in transmission and reception is prepared, and a reference signal is generated by passing the transmission signal through this filter. It may be applied to a method of obtaining a compressed pulse by performing a correlation calculation between a signal and an echo.

A third embodiment of the present invention to which this method is applied
It will be described with reference to FIG.

FIG. 16 is a block diagram showing a third embodiment of the present invention, which is exactly the same as that of the first embodiment except for the reference signal generator (11).

In FIG. 16, the third embodiment of the present invention is the same as that of the first embodiment described above, except that the input side is connected to the amplitude coded transmission signal generator (1A) and the output side is a correlator. It is composed of a reference signal generator (11) connected to (7A).

The reference signal generator (11) functions as a filter having a frequency response characteristic that the ultrasonic probe (6) has in transmission and reception,
Generate a reference signal used to correlate the echoes.

As can be seen from Japanese Patent Application No. 1-45316, it is expected that the third embodiment can further improve the S / N ratio as compared with the method of performing echo correlation processing using a transmission signal. Because the ultrasonic probe (6) has a finite bandwidth,
Since the filter action of the ultrasonic probe (6) acts on the signal at the time of transmitting and receiving the ultrasonic wave, the waveform of the transmitting signal,
It does not match the echo waveform. However, in the third embodiment, a waveform having the same waveform as the echo is generated as a reference signal by using the reference signal generator (11), and the echo is subjected to correlation processing using this reference signal. This is equivalent to performing signal processing of passing an echo through a matched filter, and the matched filter has an effect of receiving a signal buried in noise at the maximum S / N ratio.

The third embodiment of the present invention has the above-described actions and effects in the first embodiment.
It can be expected to synergize with the operation and effect of the embodiment.

When the ultrasonic wave propagates through the test body S, if the propagation characteristic has a frequency characteristic, the filtering action by this also acts on the signal at the same time. In such a case, the reference signal generator (11) has a filter having a frequency characteristic in which the frequency response characteristic of the ultrasonic probe (6) in total transmission and reception and the frequency characteristic of the test body S are combined. You can replace with.

A fourth embodiment of the present invention will be described with reference to FIG.

FIG. 17 is a block diagram showing a fourth embodiment of the present invention, which is exactly the same as that of the second embodiment except for the reference signal generator (11).

In FIG. 17, the fourth embodiment of the present invention is the same as that of the second embodiment described above, except that the input side is connected to the phase-coded transmission signal generator (1B) and the output side is the correlator. It is composed of a reference signal generator (11) connected to (7A).

The fourth embodiment has the same operation as the above-mentioned third embodiment,
It can be expected that, in addition to the effect, the effect of the second embodiment described above can be synergized.

A fifth embodiment of the present invention will be described with reference to FIG.

FIG. 18 is a block diagram showing a fifth embodiment of the present invention, which is the same as the above-mentioned fourth embodiment except for the ultrasonic probes (6A) and (6B).
It is exactly the same as that of the embodiment.

In FIG. 18, the fifth embodiment of the present invention is the same as that of the fourth embodiment described above, and ultrasonic waves for transmission whose input side is connected to the phase-encoded transmission signal generator (1B). It is composed of a probe (6A) and an ultrasonic probe for reception (6B) whose output side is connected to a correlator (7A).

In the fifth embodiment, as the frequency characteristics of the reference signal generator (11), the frequency response characteristics of the transmitting ultrasonic probe (6A) during transmission and the receiving ultrasonic probe (6B). The frequency characteristic obtained by combining with the frequency response characteristic at the time of reception is used.

The fifth embodiment has the same operation as the above-mentioned fourth embodiment,
Produce an effect.

Of course, the ultrasonic probe for transmission (6A) and the ultrasonic probe for reception (6B) may be applied to the first, second and third embodiments of the present invention.

Further, the present invention is not limited to the above-mentioned respective embodiments, and a plurality of complementary sequences of four or more sequences and a conventional complementary sequence may be used in combination for encoding the amplitude and phase of the transmission signal.

For example, when a complementary sequence of length 4 and a plurality of complementary sequences of length 5 consisting of 4 sequences used in the first embodiment of the present invention are combined, a total of 6 sequences are used to generate the first sequence of the present invention. Similarly to the second and sixth embodiments, six transmission signals whose amplitude and phase are encoded are repeatedly generated, and the echo is the same as in the first, second, third, fourth and fifth embodiments of the present invention. Processing may be performed. In this case, since N on the right side of the equation is 6, there is an advantage that the S / N ratio becomes larger. Further, the length of the complementary sequence and the length of the plurality of complementary sequences used for encoding the transmission signal may be the same or different as in the above case.

Also, a plurality of plural complementary sequences and a plurality of complementary sequences may be combined and used for encoding the transmission signal as described above. In this case, N on the right side of the equation becomes large, so S /
The cross-correlation function of the sequence used for coding the i-th transmission signal and the sequence used for coding the (i + 1) -th transmission signal has the advantage that the N ratio is larger and there are many types of sequences used. Gives you more freedom to choose small combinations. Therefore, there is an effect that the influence of the reverberation echo on the inspection can be further reduced.

By the way, in the above description, the case of using for the ultrasonic flaw detector is described, but it goes without saying that it can also be used for a device using other waves, for example, an electromagnetic wave.

In the above description, the case where the ultrasonic probe is in contact with the test body has been described, but the ultrasonic probe does not have to be in contact with the test body. In this case, transmission / reception of ultrasonic waves between the ultrasonic probe and the test body may be performed via a coupling medium such as water.

Further, the present invention may be applied to an ultrasonic wave transmission / reception circuit system of individual elements constituting an ultrasonic array probe.

Furthermore, in the present invention, a correlator (correlation means) may be provided independently for each of the N echoes.

In the above embodiment, the case where a transmission signal in which a rectangular wave or a sine wave is associated with a unit bit (positive sign or negative sign) of a plurality of complementary sequences is used has been described, but the present invention is not limited to this. A unit waveform is assigned to the positive sign, a waveform obtained by multiplying the amplitude of the unit waveform by -1 is assigned to the negative sign, and these two types of waveforms are arranged on the time axis in the order in which the positive and negative signs appear. A signal having the above waveform may be used as the transmission signal. The above unit waveform is
It may be a rectangle or a waveform similar to a rectangle. Further, the unit waveform may be a waveform including a smooth curved portion or a vibration waveform.

Further, in the above-mentioned embodiment, as the reference signal, the transmission signal itself, or the transmission signal, the signal passed through the filter having the frequency response characteristics that the ultrasonic probe has in the transmission and reception is used, but the following signals May be used as the reference signal.

1. When the ultrasonic probe (transmitting means) is excited by the corresponding transmission signal, the same or different ultrasonic probe (receiving means)
A signal having the same or similar waveform as the waveform of the echo from the object obtained by.

2. A signal having the same or similar waveform as the waveform of an echo from the surface or the bottom surface of the test body obtained by the same or another ultrasonic probe when the ultrasonic probe is excited by the corresponding transmission signal.

3. When the ultrasonic probe is excited by the corresponding transmission signal, it has the same or similar waveform as the waveform of the echo from the test object different from the object obtained by the same or different ultrasonic probe. signal.

4. When the ultrasonic probe is excited by the corresponding transmission signal, the ultrasonic probe as the transmission means, the object, and the output end of the amplitude or phase encoded transmission signal generator (transmission signal generation means), A signal having a waveform calculated on the basis of a frequency response characteristic of a signal propagation path reaching an input end of a correlator (correlation means) via an ultrasonic probe as a reception means and a waveform.

The frequency response characteristics include frequency characteristics related to the reflection of the reflector of the object.

[Effects of the Invention] As described above, according to the present invention, a transmission signal generating unit that generates a plurality of transmission signals based on a plurality of complementary sequences, and a wave that is excited by the plurality of transmission signals and transmits a wave to an object. And a receiving means for receiving a plurality of echoes respectively corresponding to the plurality of transmission signals, and a plurality of reference signals defined by the plurality of complementary sequences to correlate the plurality of echoes. Since the correlation means for processing and the addition means for adding the results of a plurality of correlation processings are provided, firstly, the range side lobe of the composite compressed pulse can be eliminated altogether, and secondly, the S / N ratio. The degree of freedom in selecting the dead zone can be expanded. Third, the dynamic range required value of the receiving circuit system can be reduced. Fourth, the influence of noise on inspection can be reduced. In an effect that it is possible to reverberation echo to reduce the effect on the test.

Further, when the phase of the transmission signal is encoded, there is an effect that the utilization efficiency of the transmission energy can be improved and the inspection can be performed with a larger S / N ratio.

Furthermore, when the transmission signal is passed through the reference signal generator having the frequency response characteristics of the ultrasonic probe and the test body, it is possible to inspect with a larger S / N ratio.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention, and FIGS. 2 (a), (b), (c) and (d) are waveform diagrams showing a transmission signal of the first embodiment of the present invention, FIG. 3 is a waveform diagram showing four transmission signals according to the first embodiment of the present invention, FIG. 4 is a waveform diagram showing four echoes according to the first embodiment of the present invention, and FIGS. ), (C) and (d) are waveform charts showing calculation results of the autocorrelation functions of the first, second, third and fourth series of the first embodiment of the present invention, and FIG. FIG. 7 is a waveform diagram showing the result of addition of the four autocorrelation functions of the first embodiment, FIG. 7 is a waveform diagram showing the impulse response of the ultrasonic probe of the first embodiment of the present invention, FIG. 8 (a), (B), (c) and (d) are waveform charts showing the calculation results of the first, second, third and fourth compressed pulses of the first embodiment of the present invention, and FIG. 9 is the waveform chart of the present invention. FIG. 10 is a waveform diagram showing the calculation result of the synthetic compressed pulse of the embodiment, FIG. 10 is a characteristic diagram showing the relationship between the clock frequency and the S / N ratio, and FIG. 11 is a waveform showing the reverberation echo of the first embodiment of the present invention. FIG. 12, FIG. 12 is a waveform diagram showing a reverberation echo of a conventional apparatus, FIGS. 13 (a) and 13 (b) are explanatory diagrams showing a plurality of complementary sequences consisting of four and six sequences, and FIG. 15 is a block diagram showing a second embodiment, FIGS. 15 (a), (b), (c) and (d) are waveform diagrams showing a transmission signal of the second embodiment of the invention, and FIG. 16 is a diagram showing the invention. FIG. 17 is a block diagram showing a third embodiment, FIG. 17 is a block diagram showing a fourth embodiment of the present invention, FIG. 18 is a block diagram showing a fifth embodiment of the present invention, and FIG. FIG. 20 is a block diagram showing a destructive inspection device, FIG. 20 is a waveform diagram showing a transmission signal of a conventional ultrasonic nondestructive inspection device, and FIG. 21 is a conventional ultrasonic nondestructive inspection device. A waveform diagram showing a compressed pulse of a destructive inspection device, Fig. 22 is a waveform diagram showing an autocorrelation function of a finite length sequence of a conventional ultrasonic non-destructive inspection device, and Figs. 23 (a) and (b) are conventional Waveform diagram showing the autocorrelation function of the complementary sequence of the ultrasonic non-destructive inspection device, FIG. 24 is a waveform diagram showing the addition result of the autocorrelation function of the complementary sequence of the conventional ultrasonic non-destructive inspection device, FIG. 25 (a) And (b) are waveform charts showing a compressed pulse of the conventional ultrasonic nondestructive inspection apparatus, and FIG. 26 is a waveform chart showing a synthetic compressed pulse of the conventional ultrasonic nondestructive inspection apparatus. In the figure, (1A) ... amplitude encoded transmission signal generator, (1B) ... phase encoded transmission signal generator, (6) ... ultrasonic probe, (6A) ... transmission ultrasonic waves. Probe, (6B) …… Reception ultrasonic probe, (7A) …… Correlator, (8) …… Display, (10) …… Adder, (11) …… Reference signal generation It is a vessel. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A transmission signal generation means for generating a plurality of transmission signals based on a plurality of complementary sequences, a transmission means for exciting a wave by the plurality of transmission signals to transmit a wave to an object, and the plurality of transmission signals. Receiving means for receiving a plurality of echoes respectively corresponding to, a correlating means for correlating the plurality of echoes with a plurality of reference signals defined by the plurality of complementary sequences, and a plurality of correlation processings. A measuring device comprising an adding means for adding the results.