JPH07167844A - Ultrasonic wave transmitting and receiving device - Google Patents

Abstract

PURPOSE:To obtain a high S/N ratio and a high resolution by a method wherein a wave parameter of a transmitting pulse signal to be applied to an ultrasonic contact probe can be designated from outside and a signal having a waveform corresponding to the designated parameter is used as a reference pulse signal for the pulse-compressing. CONSTITUTION:An operator inputs a waveform parameter of a transmission pulse signal corresponding to a material and a shape of an analyte 27 to a parameter memory 37 from an operation section 36a to store each element therein. An FM signal-forming section 21 a makes a waveform of the transmission pulse signal based on those parameters. A reference waveform-forming section 24a makes a reference waveform corresponding to each parameter and an echo signal. A reference waveform output section 24b receives a synchronizing signal and outputs the reference waveform to an FIR filter 35 in synchronism with a clock signal. The filter 35 executes the product and sum calculations of the reference waveform and the echo signal from an A/D convertor 34 to obtain a mutual relationship waveform between both of the waveforms and outputs it as an echo signal applied with the pulse compression.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention converts a transmission pulse signal (FM signal) whose frequency changes within a pulse width into an ultrasonic pulse by an ultrasonic probe, and makes the ultrasonic pulse incident on a subject. The ultrasonic pulse transmitted or reflected by the subject with the tentacle is received and converted into an echo signal, and the cross-correlation calculation between this echo signal waveform and the reference signal waveform is performed to compress the pulse and output it to the display. The present invention relates to an ultrasonic transmitting / receiving device.

[0002]

2. Description of the Related Art Generally, an ultrasonic flaw detector or thickness measuring apparatus is constructed as shown in FIG. The sync signal a from the sync generator 1 has a constant pulse period T _0.
Is transmitted to the transmission unit 2. The transmitter 2 transmits a transmission pulse signal b having a predetermined pulse width T _W to the next ultrasonic probe 3 in synchronization with a synchronization signal a having a pulse period T ₀ . The ultrasonic probe 3 makes an ultrasonic pulse c incident on the subject 4 in synchronization with the transmission pulse signal b. The ultrasonic probe 3 receives a reflected wave (echo) from the subject 4, converts the reflected wave into an echo signal d ₀ of an electric signal, and sends it to the receiving unit 5. The receiving unit 5 amplifies the received echo signal d ₀ and displays it on the display unit 6.

In the flaw detector or the thickness measuring device having such a structure, the waveform of the transmission pulse signal b output from the transmitting section 2 at the constant pulse period T ₀ is a fixed pulse waveform which is predetermined. In general, a pulse wave has a sharp waveform and a narrow pulse width T _W , and therefore has excellent time-axis resolution.

On the other hand, when the object 3 is made of a material having coarse particles, it is necessary to remove the noise called forest echo contained in the echo signal d ₀ in order to improve the flaw detection accuracy. As a method of reducing this forest-like echo, a method of selecting an optimum transmission frequency F for the material of the subject 3 has been put into practical use.

However, in the apparatus shown in FIG. 11, since the frequency characteristic of the ultrasonic pulse c depends on the oscillator characteristic of the ultrasonic probe 3, the frequency F of the ultrasonic pulse c is adjusted to the optimum value. Is difficult to do.

Further, when the subject 3 is made of a high attenuation material, the propagation characteristics for the ultrasonic pulse c are different for each material. Therefore, in the device shown in FIG.
Experienced technicians need to make measurements while adjusting the properties of the flaw detector with the material itself and the test piece. This adjustment work requires a lot of labor and time, and is practically impossible to carry out in practice.

As described above, the device shown in FIG. 11 has a problem that the method for easily reducing noise by controlling the frequency F in the transmission pulse signal cannot be applied. An ultrasonic flaw detector as shown in FIG. 12 has been proposed as a device for solving such inconvenience (Japanese Patent Publication No.
43586). In this ultrasonic flaw detector,
A wave number variable circuit 7 and a frequency variable circuit 8 are inserted between the synchronization generation unit 1 and the transmission unit 2 in the device of FIG. Then, the wave number changing circuit 7 sets the pulse number (wave number) included in one pulse period T ₀ of the synchronization signal a to the wave number setting unit 9
Set to the value indicated by. Further, the frequency variable circuit 8 sets the pulse period T ₀ of the synchronization signal a itself to a value instructed by the frequency setting unit 10.

Therefore, in the ultrasonic flaw detector of FIG. 12, since the transmission frequency and the number of transmission waves can be varied, the frequency of the transmission wave can be controlled without replacing the ultrasonic probe 3. However, in the transmission wave generated by the ultrasonic flaw detector of FIG. 12, the pulse width T _W is longer than the pulse transmission interval, and there is a problem that the time axis resolution becomes poor when the obtained echo signal is analyzed.

Further, in order to solve such a problem, pulse compression technology (Radar handbook, Skolnik, et.al ,, McGraw-Hill Inc,
1970). As is well known, the pulse compression technique is a waveform obtained by encoding a phase or a waveform obtained by modulating a frequency (FM).
Signal) is used as the transmitted wave, and the cross-correlation calculation (pulse compression) between the received waveform and the transmitted waveform is performed to shorten the pulse time width of the received wave and at the same time eliminate the noise added during the propagation of the received signal. It is a technology to reduce.

The features of a general FM signal waveform will be described with reference to FIG. As for the transmission pulse signals b ₁ and b ₂ shown in FIG. 13B or _13D , the frequency F changes within the pulse width T _{W as} shown in FIG. 13A. The amplitude A of the transmission pulse signal b ₁ is constant within the pulse width T _W. Frequency change rate dF / dt with respect to time t of frequency F is constant (linear) and changes (non-linear)
In some cases Further, as shown in FIG. 13C, the FM signal changes in frequency F and has a pulse width T.
There are cases where the amplitude A also changes within _W and cases where the amplitude is constant. The frequency change rate dF shown in FIG.
An FM signal (transmission pulse signal b ₁ ) whose / dt is constant (linear) and whose amplitude A is constant is particularly called a chirp signal.

Here, the frequency change rate of the FM signal dF / d
As shown by the thin line characteristic of FIG. 13A, t is nonlinearly scanned within the pulse width T _W , and the amplitude A is changed within the pulse width T _W as shown by the thin line characteristic of FIG. 13C. By doing so, it is known that the side lobe generated in the autocorrelation function waveform of the FM signal can be reduced (Japanese Patent Laid-Open No. 5-273335).

Further, there has been proposed a pulse compression device to which a technique for performing pulse compression processing using the above-mentioned chirp signal as a transmission pulse signal is applied (Japanese Patent Laid-Open No. 63-233369).
Issue).

In this proposed pulse compression apparatus, as shown in FIG. 14, the transmission pulse signal b ₁ formed from the chirp signal having the waveform shown in FIG. The signal is transmitted from the signal transmitter 12 to the ultrasonic probe 13. The ultrasonic probe 13 transmits an ultrasonic pulse to a subject 14 such as a human body in response to the transmission pulse signal b ₁ and receives a reflected wave. The reflected wave received is converted into an echo signal and input to the quadrature detection unit 15. The echo signal is converted into a complex signal by the quadrature detection unit 15, low-frequency conversion is performed on the frequency band, and the result is input to the next correlation unit 16.

On the other hand, the reference wave setting unit 17 creates a reference wave signal using the transmission pulse signal b ₁ created by the chirp signal setting unit 11, and sends it to the correlation unit 16 via the reference wave transmitting unit 18. Send out. The correlator 16 pulse-compresses the echo signal by performing a correlation calculation between the echo signal and the reference wave signal. The pulse-compressed echo signal is converted into a time difference time signal by the quadrature modulator and displayed on the display unit 20.

[0015]

However, as shown in FIG.
In order to apply the pulse compression method shown in (1) to ordinary ultrasonic nondestructive inspection, there were still the following problems to be solved.
That is, the inspection target in the ultrasonic nondestructive inspection has various material characteristics. For example, even if the object to be inspected is a metal, the propagation characteristics of ultrasonic waves differ greatly depending on the material of the metal. Further, there are a coarse particle material in which the forest echo is likely to occur and a fine particle material in which the forest echo is unlikely to occur. Furthermore, the thickness d of the subject also changes variously.

Therefore, when the material and size of the subject are different as described above, the frequency F, the pulse width T _W , and the pulse period T ₀ , F of the ultrasonic pulse to be incident on the subject 14 are measured.
It is necessary to set the physical characteristics such as the frequency change rate dF / dt and the amplitude A of the M signal to the optimum values corresponding to the object to be measured.

However, the inspection measures in the pulse compression apparatus shown in FIG. 14 are limited to the human body (living body) and the like. Therefore, from the chirp signal transmission unit 12 to the ultrasonic probe 13
It is considered that the physical characteristics of the transmission pulse signal b ₁ sent to are fixed to one type. Therefore, this pulse compression device cannot be used in a general ultrasonic nondestructive inspection method having various materials and shapes.

Further, since the correlator 16 is composed of an analog circuit having a delay line incorporated therein, the reference wave signal which is the other input signal for performing the correlation calculation cannot be easily changed. Physical characteristics such as frequency characteristics of the signal b ₁ cannot be easily changed.

Further, in the pulse compression apparatus shown in FIG. 14, the waveform of the chirp signal applied to the ultrasonic probe 13 has the same amplitude A for the full pulse width T _W as shown in FIG. 13B. Since it is a rectangular wave, a large side lobe is generated in the pulse-compressed echo signal. That is, when an ultrasonic wave is incident on a subject with a large acoustic impedance, the dynamic range between the surface reflected wave and the reflected wave inside the subject is increased due to the acoustic impedance difference peculiar to ultrasonic nondestructive inspection. Side lobe is a problem.

Further, when the pulse compression apparatus shown in FIG. 14 is used for general nondestructive inspection, when the inspection target is a material having a poor S / N, a correlation device (quadrature detection) using a delay line and a multiplier is used. However, it is not applicable to tests that require selection of the optimum band in a wide frequency band such as material evaluation.

The present invention has been made in view of the above circumstances, and even if the material of the subject is variously changed, the excellent pulse compression function is maintained and the high SN ratio and high resolution are always maintained. It is an object of the present invention to provide an ultrasonic wave transmitting / receiving device that can obtain the above.

[0022]

In order to solve the above problems, the present invention applies a transmission pulse signal having a waveform whose frequency changes within a pulse width to an ultrasonic probe facing a subject, In an ultrasonic transmitter / receiver for pulse-compressing an echo signal output from this ultrasonic probe using a reference pulse signal and outputting it, a pulse width and a frequency change rate in a transmission pulse signal applied to the ultrasonic probe , Waveform parameters such as amplitude change rate can be specified externally,
The reference pulse signal for pulse compression is a reference pulse signal having a waveform corresponding to a designated waveform parameter.

Further, in the ultrasonic transmitting / receiving device according to the present invention, the parameter designating means for designating waveform parameters such as pulse width, frequency change rate, amplitude change rate of the pulse signal and the waveform designated by the parameter designating means. Transmission pulse signal waveform creating means for creating a transmission pulse signal waveform whose frequency changes within the pulse width based on parameters, signal waveform storage means for storing the created transmission pulse signal waveform, and storage in the signal waveform storage means The transmitted pulse signal waveforms are sequentially read out, D / A converted, and then applied as a transmitted pulse signal to the ultrasonic probe facing the subject. A reference pulse signal waveform generating means for generating a reference pulse signal waveform based on the Pulse compression of the echo signal by performing the sum-of-products operation of the echo signal receiving means for receiving the signal and A / D converting it, and the signal waveform of the A / D converted echo signal and the created reference pulse signal waveform. And a display means for displaying and outputting the echo signal after being pulse-compressed by the digital filter.

Further, in the invention of claim 3, an FIR (finite impulse response) filter is used as the digital filter. Further, in the invention of claim 4, the reference pulse signal is created from the transmission pulse signal waveform and the echo signal waveform.

[0025]

In the ultrasonic transmitter / receiver configured as described above, as the transmission pulse signal to be sent to the ultrasonic probe,
An FM signal whose frequency changes in the pulse width is used. Further, the waveform parameters such as the frequency change rate and the amplitude of the FM signal can be arbitrarily changed within the pulse width (within the FM signal). The reference pulse signal used for pulse compression can also be arbitrarily changed according to the change of the waveform parameter of the FM signal or the echo signal waveform. Therefore,
Good pulse compression is achieved.

Further, a transmission pulse signal waveform and a reference pulse signal waveform are digitally created using a computer,
In addition, since the pulse compression unit also employs a digital filter, it is possible to create a transmission pulse signal having a waveform that best matches physical characteristics such as the material and size of the subject and transmit it to the ultrasonic probe. Therefore, forest echo and side lobes can be effectively reduced.

Further, an FIR (finite impuls response) is used as a digital filter for performing a correlation calculation between an echo signal waveform corresponding to a received signal and an arbitrary reference signal waveform corresponding to a transmitted signal to compress the echo signal. By adopting this, the correlation calculation can be performed at high speed, and for example, this ultrasonic transmitter / receiver can be incorporated online in an actual product inspection line.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a schematic configuration of the ultrasonic transmitting / receiving apparatus of the embodiment. The FM signal generation unit 21 uses the waveform parameters set by the parameter setting unit 22 to perform FM
A signal is created and sent to the FM signal transmitter 23. The FM signal transmission unit 23 transmits the FM signal as a transmission pulse signal to the ultrasonic probe 26 in synchronization with the synchronization signal from the synchronization generation unit 25. The ultrasonic probe 26 has an ultrasonic transducer housed therein, and makes an ultrasonic pulse corresponding to the input FM signal incident on the subject 27. Further, the ultrasonic probe 26 receives the reflected wave of the incident ultrasonic pulse, converts it into an electric signal, and outputs it as an echo signal to the next pulse compression unit 28 and reference signal generation unit 24.

On the other hand, the reference signal creating section 24 creates an arbitrary reference signal corresponding to the waveform parameter of the FM signal or the echo signal from the ultrasonic probe 26 and sends it to the pulse compressing section 28. The pulse compression unit 28 performs a correlation process between the echo signal and the reference signal to pulse-compress the echo signal and send it to the display unit 29 configured by, for example, a CRT. The display unit 29 displays the pulse-compressed echo signal.

FIG. 2 is a specific circuit diagram of the ultrasonic wave transmitting / receiving apparatus shown in FIG. The FM signal generation unit 2 in FIG.
1, parameter setting unit 22, reference signal creation unit 24, FM
The signal transmission unit 23 is realized by a software method in the personal computer 30.

In FIG. 2, the personal computer 3
The digital transmission pulse signal b ₃ output from 0 is D /
After being converted into an analog transmission pulse signal b ₄ by the A converter 31 and amplified by the amplifier 32, it is sent to the ultrasonic probe 26. The echo signal d ₁ output from the ultrasonic probe 26 is amplified by the amplifier 33, then converted into a digital echo signal d ₂ by the A / D converter 34, and the FIR filter 35 as a pulse compression unit and a personal computer. Computer 30
It is input to the reference signal creating unit 24 in the inside.

The FIR filter 35 makes the digital values between the digital reference pulse signal waveform e output from the personal computer 30 and the digital echo signal d ₂ input from the A / D converter 34 different from each other. Is performed to calculate a cross-correlation waveform between the two waveforms, and the cross-correlation waveform is output as a pulse-compressed digital echo signal d ₃ . CRT display 29a displays the echo signal d ₃ which is the pulse compression.

FIG. 3 is a functional block diagram showing each function of the personal computer 30. In the personal computer 30, the operation unit 36a, the parameter memory 37, the FM waveform creation unit 21a, the reference signal creation unit 24.
a, FM waveform memory 38a, reference waveform memory 38b, F
The functions of the M signal transmission unit 23, the reference waveform output unit 24b, the synchronization generation unit 25, and the clock circuit 39 are stored.

From the operation section 36a corresponding to the parameter setting section 22 including, for example, a CRT display and a keyboard,
The operator inputs a plurality of waveform parameters that specify the waveform of the transmission pulse signal b ₃ shown in FIG. 5 according to the material and shape of the subject 27, and inputs them to the next parameter memory 37.

In the parameter memory 37, an area 37a for storing the lower end frequency F ₁ and the upper end frequency F ₂ of the frequency range B _W in the transmission pulse signal b ₃ shown in FIG.
Area 37b for storing (maximum amplitude A ₂ when amplitude is converted), area 37c for storing transmission pulse period T ₀ , area 37d for storing transmission pulse width T _W , frequency change rate d
Area 37e for storing F / dt, amplitude change rate dA / dt
An area 37f for storing (when the amplitude is constant = 0) is formed.

The frequency change rate dF / dt and the amplitude change rate dA stored in the above-mentioned areas 37e and 37f.
/ Dt is a constant value (constant) as shown in FIGS. 5 (b) and 5 (c), and FIG. 13 (b) and (c) described above.
As shown in, the case where it changes with the passage of time is also included. That is, the frequency change rate dF / dt and the amplitude change rate dA / dt include a case where the function f (t) of the time t is shown.

The FM signal creating section 21a creates a transmission pulse signal waveform consisting of the digital FM signal waveform shown in FIG. 5 based on the waveform parameters stored in the areas 37a to 37f of the parameter memory 37. The created transmission pulse signal waveform (FM signal waveform) is temporarily stored in the FM waveform memory 38a.

The reference signal generator 24a generates an arbitrary reference waveform corresponding to each waveform parameter or echo signal d ₂ stored in each area 37a to 37f of the parameter memory 37. The created reference waveform is the reference waveform memory 3
It is temporarily stored in 8b.

Further, the synchronization generator 25 uses the clock signal ck of the clock circuit 39 based on the pulse period T ₀ of the area 37c of the parameter memory 37 to output the synchronization signal g of the pulse period T ₀ to the FM signal transmitter 23 and the FM signal transmitter 23. Reference waveform output unit 24
Send to a.

When the FM signal transmitter 23 receives the synchronization signal g, the FM signal transmitter 23 synchronizes with the clock signal ck of the clock circuit 39 and outputs the F signal.
The transmission pulse signal waveform (FM signal waveform) stored in the M waveform memory 38a is read out and the next D / A converter 32 is read.
Send to. The frequency of the clock signal ck input from the clock circuit 39 to the FM signal transmitting unit 23 is, for example, about _{1 to} 20 MHz of the transmission pulse signal b ₃ (F ₁ , F ₂ ).
It is a sufficiently high value compared to.

Further, when the reference waveform output section 24a receives the synchronization signal g, it reads the reference waveform stored in the reference waveform memory 38b in synchronization with the clock signal ck of the clock circuit 39, and outputs it as the reference waveform e. FIR filter 35
Send to.

The FIR filter 35 as a digital filter is, for example, as shown in FIG. 4, 128 multipliers 35a operating at the frequency (f _R ) of the clock signal ck.
, 128 adders 35b, and 128 delay devices 35
It is composed of c and.

The data values C _{1 to} C _{128 of the} reference waveform e output from the reference waveform output section 24a in synchronization with the clock signal ck are input to the multipliers 35a. On the other hand, each data value x of the digital echo signal d ₂ output from the A / D converter 34 in synchronization with the clock signal ck is input to the input terminal 35d.

Further, each delay device 35c has a clock signal c
A delay corresponding to the period T of k is performed. Therefore,
The FIR filter 35 carries out a product-sum operation represented by the following equation for each data x (kT ₁ ) of the echo signal d ₂ and each data C _i of the reference waveform e sequentially input to the input terminal 35d. , Output data y (kT ₁ ) is obtained.

[0045]

[Equation 1]

This product-sum operation is nothing but the execution of the cross-correlation operation between the variable C and the variable x. Further, since the waveform of the echo signal d ₂ and the reference waveform have FM signal waveforms, the output data y (kT
₁ ) becomes an echo signal d ₃ obtained by pulse-compressing the input echo signal d ₂ .

Therefore, the pulse-compressed echo signal d ₃ is displayed on the CRT display 29a. here,
An example of using a transmission pulse signal waveform and an echo signal waveform as reference waveforms used for pulse compression will be described.

When the Fourier transform of the transmission pulse signal h is H and the Fourier transform of the impulse response r in the transmission / reception system between the ultrasonic probe 26 and the subject 27 is R, the following equation is used as the reference wave.

F ⁻¹ (H ′ / R) where F ⁻¹ : inverse Fourier transform H ′: phase conjugation of Fourier transform H. Then, by using this equation as a reference waveform, pulse compression can be expressed by the following equation. it can.

H · R · F [F ⁻¹ (H ′ / R)] = H · R · (H ′ / R) = H · H ′ As described above, the probe and the object specific to ultrasonic measurement are used. It can be understood that only the autocorrelation waveform of the transmission pulse signal excluding the influence of the sample can be obtained.

In the ultrasonic transmitter / receiver configured as described above, the operator uses the operation unit 36a to determine the optimum waveform of the ultrasonic pulse to be applied to the subject 27 in accordance with the material and size of the subject 27. Frequency (F ₁ , F ₂ ) and amplitude A
₁ , the pulse period T ₀ , the transmission pulse width T _W , the frequency change rate dF / dt, the amplitude change rate dA / dt, and other waveform parameters can be specified.

Next, the features of the device of the present application will be described with reference to specific measurement results. FIGS. 6A and 6B show an ultrasonic probe (probe A) in which transducers each having a nominal vibration frequency F ₀ of 2 MHz are incorporated using the same subject 27 and a nominal probe. Each echo signal after pulse compression when an ultrasonic flaw detection test by a water immersion method is carried out using an ultrasonic probe (probe B) incorporating a transducer having a vibration frequency F ₀ of 5 MHz it is a signal waveform diagram of d _3. An FM signal waveform is used as the transmission pulse signal, and its center frequency F ₀ is set to 2 MHz and 5 MHz. In the figure, S is a surface echo, and F is a reflection echo at the defective portion.

The S / N of the echo signal d ₃ shown in FIG.
It can be seen that is higher than the S / N of the echo signal d ₃ shown in FIG. Therefore, it becomes possible to easily select the optimum transmission center frequency F ₀ according to the material of the subject 27.

In the conventional device shown in FIG. 14,
When changing the frequency F, it was necessary to replace the entire pulse compression device. Next, the effect obtained when the frequency band B _W , the transmission pulse width T _W, and the amplitude A are changed is shown in FIG.
A description will be given using (a) and (b).

Generally, in ultrasonic measurement, the ultrasonic probe 26 is used.
_Therefore, there is a problem that the frequency band B _W of the transmission pulse signal is limited. Therefore, the transmission pulse signal having a frequency component that does not match the frequency band of the ultrasonic probe 26 is band-limited in the ultrasonic probe 26. As a result, the transmission power is lost, the side lobe of the pulse compression waveform becomes large due to the collapse of the reception waveform, and the pulse width becomes long. Therefore, transmit pulse signal (FM signal)
It is necessary to match the frequency band B _W of the ultrasonic probe 26 with the frequency band of the ultrasonic probe 26.

FIGS. 7A and 7B are examples in which the frequency bands of FM signal waves for the above-mentioned two types of ultrasonic probes 26 are controlled. In the FM signal wave shown in FIG. 7A, it is the reception power under the condition that the frequency F is changed nonlinearly in the range of 2 to 8 MHz and the amplitude A is changed with the transmission pulse width T _W = 5 μs. b) the frequency F is 0 to
The transmission pulse width T is changed linearly in the range of 3.5 MHz.
The received power is shown under the condition that the amplitude A is changed at _W = 3 μs.

In FIGS. 7A and 7B, the solid line shows the ultrasonic probe 26, and the broken line shows the frequency spectrum of the transmission pulse signal (FM signal). As can be understood from FIG. 7, the frequency F of the transmission pulse signal (FM signal) is changed non-linearly, or the amplitude A is changed within the transmission pulse width T _W to match the frequency band of the ultrasonic probe 26. The transmission pulse signal (FM signal) can be transmitted, and the frequency component loss of the transmission pulse signal (FM signal) by the ultrasonic probe 26 can be suppressed to the minimum.

Next, an example in which the transmission pulse width T _W of the transmission pulse signal (FM signal) is selected as the optimum value according to the plate thickness d of the subject 27 will be described with reference to FIG. 8 (a) (b)
(C) is a waveform after the pulse compression processing of the echo signal of the steel plate as the subject 27 having different plate thicknesses d. The plate thickness d of the steel plate is 3 mm in FIG. 8 (a) and 6 m in (b).
m and (c) are 9 mm. The ultrasonic probe 26 used for the measurement has a nominal frequency F ₀ of 10 MHz. The frequency change range (F _{1 to} F ₂ ) of the transmission pulse signal (FM signal) is 2
.About.18 MHz, the frequency change rate dF / dt is constant, and the amplitude change rate dA / dt is changed. That is, the frequency is changed linearly. Pulse width T _W
Are different for (a) 0.5 μs and (b) 1.0
μs, (c) is 1.5 μs. FIG. 9 (a),
In (b) and (c), T is a transmission pulse, S is a surface reflection echo, and B1 is a bottom reflection echo. All amplifier gains are measured under the same conditions.

In the direct contact method, since the T pulse (transmitted pulse) and the S echo overlap, there is a problem that the T pulse portion having a larger signal strength than the S and B1 echoes becomes a dead zone. on the other hand,
The S / N of the echo signal waveform after pulse compression is proportional to the square root of the pulse width T _W of the transmission pulse signal (FM signal).

Therefore, when detecting flaws near the surface, the echo attenuation is small and the dead zone must be shortened, so the transmission pulse width T _W of the transmission pulse signal (FM signal) is shortened. On the other hand, when detecting a distance from the surface, the attenuation is large and the dead zone can be lengthened, so the pulse width T _W is lengthened.

8 (a), 8 (b), and 8 (c), the side lobes of the T pulse are large. This is because the saturated T pulse is pulse-compressed by the limiter. The dead zone is up to the side ropes of the pulse. The dead zone and the B1 echo do not overlap, and the SN ratio of the B1 echo does not change depending on the echo depth. As described above, when the flaw detection is performed by the direct contact method, the pulse width T _W of the transmission pulse signal (FM signal) can be set to an optimum length according to the flaw detection depth.

Next, each echo signal d after pulse compression according to the type of waveform of the transmission pulse signal (FM signal)
9 and 10 show the comparison results when the side lobe generated in ₃ is simulated.

The center frequency F ₀ = 5 MHz in each transmission pulse signal (FM signal) shown in FIGS. 9A to 9D,
Frequency range B _W = 6 MHz, transmission pulse width T _W = 2 μs
Is.

Further, the transmission pulse signals (FM signals) shown in FIGS. 9A to 9D have the following characteristics. (A) ... Frequency change rate dF / dt = constant, amplitude A = constant (chirp wave) (b) ... Waveform of (a) is transformed into rectangular wave (c) ... Frequency change rate dF / dt = constant, amplitude A = Change (d) ... Frequency change rate dF / dt = Change, Amplitude A = Change Then, each transmission pulse signal (F) in (a) to (d) of FIG.
When the autocorrelation waveform of the (M signal) is obtained by a simulation calculation, the respective pulse-compressed signal waveforms of (a) to (d) of FIG. 10 are obtained.

Here, the amplitude change dA in FIG.
The Hanning window function is used for / dt as an example. According to the calculation result, the autocorrelation waveform (a) of FIG.
In each of (b), (c), and (d), each S / N (amplitude ratio) between the main lobe (the portion where the amplitude of the waveform center is large) and the side lobe (the portion outside the main lobe) is 22. , 22, 37.6, 37.2 dB.

As described above, the frequency F and the amplitude A in the transmission pulse signal (FM signal) transmitted to the ultrasonic probe 26.
By appropriately adjusting and appropriately combining the respective change rates dF / dt, dA / dt, etc. of FIG. 13, comparison is made with the case of only the chirp signal waveform in which the frequency change rate dF / dt shown in FIG. 13B is constant. Thus, it is possible to compress the side lobes in the echo signal waveform after pulse compression.

[0067]

As described above, according to the ultrasonic transmission / reception apparatus of the present invention, the frequency change rate and the amplitude change rate for specifying the waveform of the transmission pulse signal to be transmitted to the ultrasonic probe facing the subject, The operator can arbitrarily change the waveform parameters such as the pulse width as required.

Therefore, it is possible to perform pulse compression by a transmission pulse signal (FM signal) wave whose frequency is changed non-linearly and an FM signal wave whose amplitude is changed, so that pulse compression is applied to ultrasonic measurement in which side lobes are a problem. Can be applied, noise added during transmission can be reduced, and measurement accuracy using ultrasonic waves is improved.

Further, the optimum conditions of the transmission wave and the reference wave can be adjusted while observing the display according to the characteristics of the material to be examined and the ultrasonic probe, so that the operation is easy, and the waveform for each inspection object is stored in the parameter memory. If the parameters are stored in memory, the optimum test conditions can be automatically set easily by switching operation when changing the stage of measurement.

Therefore, it becomes easy to optimize the measurement such as the evaluation of the high damping material, which is difficult to adjust the device. Further, since an echo signal waveform having a high SN ratio and a high resolution can be obtained, it can be applied to ultrasonic measurement in which a SN ratio and resolution are problems, such as measurement in a high noise environment, detection of minute defects, and thickness measurement.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of an ultrasonic transceiver according to an embodiment of the present invention.

FIG. 2 is a hardware configuration diagram of the apparatus of the embodiment.

FIG. 3 is a functional block diagram of a computer in the apparatus of the embodiment.

FIG. 4 is a schematic configuration diagram of an FIR filter in the apparatus of the embodiment.

FIG. 5 is a diagram showing waveform parameters set by the apparatus of the embodiment.

FIG. 6 is a waveform diagram of each echo signal in the case of using ultrasonic probes having different nominal frequencies in the apparatus of the embodiment.

FIG. 7 is a frequency characteristic comparison diagram between an input signal and an echo signal for the ultrasonic probe in the apparatus of the embodiment.

FIG. 8 is an echo signal waveform diagram of subjects having different plate thicknesses in the apparatus of the embodiment.

FIG. 9 is a waveform diagram of a plurality of types of FM signals used in the apparatus of the embodiment.

10 is an autocorrelation waveform diagram of each FM signal waveform of FIG.

FIG. 11 is a block diagram showing a general ultrasonic flaw detector.

FIG. 12 is a block diagram showing a general ultrasonic flaw detector.

FIG. 13 is a diagram showing a general transmission pulse signal waveform.

FIG. 14 is a schematic configuration diagram of a conventional pulse compression device.

Claims (4)

[Claims] 1. A transmission pulse signal having a waveform whose frequency changes within a pulse width is applied to an ultrasonic probe facing a subject, and an echo signal output from this ultrasonic probe is used as a reference pulse signal. In an ultrasonic transmission / reception device for pulse-compressing and displaying output using, it is possible to externally specify waveform parameters such as pulse width, frequency change rate, and amplitude change rate in a transmission pulse signal applied to the ultrasonic probe, An ultrasonic transmitting / receiving apparatus, wherein the reference pulse signal for pulse compression is a reference pulse signal having a waveform corresponding to the designated waveform parameter. 2. A pulse width of a pulse signal, a frequency change rate,
Parameter designating means for designating a waveform parameter such as the rate of change in amplitude, and transmission pulse signal waveform creation for creating a transmission pulse signal waveform whose frequency changes within the pulse width based on the waveform parameter designated by this parameter designating means Means, a signal waveform storage means for storing the created transmission pulse signal waveform, and the transmission pulse signal waveforms stored in the signal waveform storage means are sequentially read and D / A converted, and then transmitted to the subject as a transmission pulse signal. Pulse signal transmitting means for applying to the opposing ultrasonic probe; reference pulse signal waveform creating means for creating a reference pulse signal waveform based on the waveform parameter specified by the parameter specifying means; and the ultrasonic probe Echo signal receiving means for receiving and echo-converting the echo signal output from the child; A digital filter for pulse-compressing the echo signal by performing a product-sum operation of the signal waveform of the co-signal and the created reference pulse signal waveform, and displaying and outputting the echo signal after being pulse-compressed by the digital filter An ultrasonic transmission / reception device comprising a display means. 3. The ultrasonic transmitting / receiving apparatus according to claim 2, wherein the digital filter is an FIR filter. 4. The ultrasonic transmitting / receiving apparatus according to claim 1, wherein the reference pulse signal uses a waveform created from a transmission pulse signal waveform and an echo signal waveform.