JP5553463B1 - Pulse compression ultrasonic detector - Google Patents

Abstract

Side-lobe levels similar to those obtained when the frequency modulation sweep width of a transmission pulse is not enlarged by providing a frequency sweep width enlargement circuit of a received signal in the receiver of a pulse compression ultrasonic detector. Realize repression.
A sine wave signal that is an input signal is squared by a double multiplier 1 to obtain a double frequency sine wave signal including a DC component, and the DC component is removed by a DC component breaker 2. After that, the square root calculator 4 is passed through to return the amplitude characteristic to the square characteristic of the input amplitude to the linear characteristic, and unnecessary harmonic components generated as a result of processing the sine wave signal by the square root calculator 4 are converted into harmonics. Filter with wave breaking filter 5 and output. Since the frequency is doubled in this way, the frequency sweep width of f ₁ → f ₂ at the input becomes 2f ₁ → 2f ₂ = 2 (f ₁ → f ₂ ) at the output, which is twice as wide. When n stages of the present invention are stacked, the ^number becomes 2 ⁿ times.
[Selection] Figure 1

Description

  The present invention belongs to the field of technology for suppressing the level of a range side lobe that occurs due to pulse compression and adversely affects the received S / N and distance resolution in a pulse compression ultrasonic detector.

Conventional ultrasonic detection devices and radars that perform pulse compression processing generate window function coefficients and multiply the received signals in order to reduce range side lobes (Patent Documents 1 and 2). It is known that a signal subjected to pulse compression processing has a sharp main lobe when the frequency modulation sweep width of a transmission pulse is increased.
In order to reduce the range side lobe, a signal that has been subjected to pulse compression processing by multiplying the received signal by a window function will sharpen the main lobe and reduce the range side lobe level when the frequency modulation sweep width of the transmission pulse is increased. The inventors confirmed this through simulations and experiments (FIGS. 10 and 11) . Therefore, if the frequency modulation sweep width of the transmission pulse is widened, pulse compression with suppressed range side lobe becomes possible.

JP 2009-288038 A (paragraphs [0014] and [0026]) JP 2008-175552 A (paragraphs [0012] and [0026]) Japanese Patent Application No. 2013-155535 (paragraphs [0009], [0012], [0014])

However, increasing the frequency modulation sweep width of the transmission pulse has the following problems.
First, the piezoelectric ceramic elements used in transducers are not sufficiently widened. As a means of widening the band, the acoustic matching layer has been improved and multiple resonance points are provided, but the characteristics are stable. There is a problem that it does not become expensive and becomes expensive.
Secondly, when the frequency of transmission and reception is widened, there is a problem that the chance of receiving interference of ultrasonic waves generated by other underwater ultrasonic devices increases.
Thirdly, when the transmission / reception frequency is widened, the level of attenuation during underwater propagation varies depending on the frequency, so the level within one received pulse is not uniform, and the accuracy of the signal obtained by pulse compression of such a signal There is a problem with reliability.

The present invention provides a pulse compression ultrasound detection device, when expanding the frequency modulation sweep width of the transmitted pulse, considering that there are problems as described above, without expanding the frequency modulation sweep width of the transmitted pulse, received By devising the system, it is possible to obtain the same effect as expanding the frequency modulation sweep width of transmission and reception.

In the present invention, a transmission wave transmitted from a transducer to water is reflected from an underwater target and received by the transducer and transmitted to a reception device without increasing the frequency modulation sweep width of the transmission pulse of the transmission device. By multiplying the frequency of the input received wave, the transmission pulse whose frequency modulation sweep width has been expanded is transmitted and the reflected wave is received, so that the frequency modulation sweep of the transmission pulse is performed. It produces the same effect as the width is expanded, thereby trying to suppress the range side lobe.
That is, a frequency modulation sweep width expansion circuit by multiplying the frequency of the reception signal is provided in the reception device, and the reception signal is passed through this circuit.

  The generation of the pulse compression correlation coefficient is based on a leaked transmission pulse that leaks from the transmission end to the reception end of the transmission / reception switch and passes through the frequency modulation sweep width expanding circuit in the same manner as the received signal, and the sweep width is expanded. Therefore, there is no problem caused by providing a frequency modulation sweep width expanding circuit in the receiving unit.

  In this way, the frequency modulation sweep width is increased for both transmission and reception, and in combination with the window function applied to the pulse compression correlation coefficient, the level of the range side lobe after pulse compression is suppressed. There is an effect that can be.

Configuration of the present invention, the following (a), is (b), (c), (d), (e), the pulse compression ultrasound detection device characterized by comprising the means of the (f) .
(A) An amplifier that amplifies a received signal, an A / D converter that converts the amplified signal into a digital signal, and a frequency sweep of the received signal, which are connected to the receiving end of the transmission / reception switcher described later (b) A frequency modulation sweep width expansion circuit of (a) or (b) below , which expands the width, and outputs the expanded output digital signal as a correlation coefficient RAM of a pulse compression correlation coefficient generation circuit (d) , Receiving unit to send to the pulse compressor described later (f)
(A) a double multiplier that squares and outputs an input frequency modulation pulse signal;
A direct current circuit breaker that receives an output of the double multiplier and blocks a direct current component included in the output;
A square root calculator for outputting a value obtained by multiplying the square root of the absolute value of the output of the DC circuit breaker by the sign of the output;
A frequency modulation sweep width expansion circuit for a frequency modulation pulse signal, comprising: a harmonic cutoff filter that removes and outputs a harmonic component other than the fundamental frequency in the output of the square root calculator
(B) a phase shifter that shifts and outputs an input sine wave signal by π / 2 radians;
A multiplier for receiving and multiplying an input signal to the (π / 2) phase shifter and an output signal of the phase shifter;
A square root calculator that outputs a value obtained by multiplying the square root of the output of the multiplier by the sign of the output;
A frequency modulation sweep of a frequency modulation pulse signal, which comprises an output signal of the square root calculator and a harmonic cutoff filter that removes and outputs harmonic components other than the fundamental frequency contained in the output signal Widening circuit (b) A transmission signal input to the transmission end is transmitted to the transmitter / receiver end, and a part of the transmission / reception switch (c) leaks to the reception end to which the receiver is connected. Transmitter connected to the transmission end of the transmission / reception switch and transmitting the frequency-modulated transmission pulse (d) The output of the reception portion of the transmission pulse leaked from the transmission end to the reception end in the transmission / reception switch during the output of the reception unit The signal is subdivided along the time axis and stored sequentially in the storage element array of the correlation coefficient RAM. After the transmission pulse, the signal read from the storage element array in the reverse order of the storage order is multiplied by the window function. The pulse compression correlation coefficient and Or the reception part leakage output signal of the transmission pulse part is subdivided by the time axis, and the result multiplied by the window function is sequentially stored in the storage element array of the correlation coefficient RAM, and the transmission pulse ends. A pulse compression correlation coefficient generation circuit (e) that outputs the data read in the reverse order as a pulse compression correlation coefficient (e) A transmitter / receiver (f) connected to the transmitter / receiver end of the transmission / reception switcher of (b) B) receiving the received digital signal from the receiving unit and the pulse compressed correlation coefficient signal from the pulse compression correlation coefficient generating circuit of (d) above, and performing pulse compression by convolution operation on the received digital signal with the correlation coefficient signal Perform pulse compressor

Those having a pulse frequency modulation sweep width expansion circuit of the compression the configuration to the receiver of the ultrasound detection device Waso of (i) (a) or (b) of the present invention, the frequency of the received wave with frequency-modulated pulses The sweep width is expanded and output.
In the configuration of (a) , as shown in FIG. 1, a double multiplier 1, a DC component breaker 2, a square root calculator 4, and a harmonic cut-off filter 5 are connected in cascade in this order.

Now, when a signal of Asinωt is input to the double multiplier 1, the output is A ² (1-cos2ωt) / 2. Here, it can be seen that the angular velocity of the input sine wave is ω, whereas the angular velocity of the output cosine wave is 2ω, which is twice, and the frequency is doubled. When this output is passed through the DC breaker 2 of the next stage and the DC component is removed, the output becomes (A ² cos2ωt) / 2, and this is calculated as the square root of the next stage in order to restore the linearity of the input / output amplitude characteristics. When input to the device 4, the output becomes A√cos 2ωt / √2. The output waveform of this equation is the square root of a sine waveform of cos 2ωt (see FIG. 3A), and its period is also 2ω, but the waveform is transformed from the sine waveform as shown in FIG. 3B. The harmonics are included. Therefore, when this signal is passed through the harmonic cut-off filter 5 and the harmonic component is removed, (A / √2) cos 2ωt, that is, a sine wave having a frequency twice is obtained.

Therefore, as shown in FIG. 6, the frequency at the rising edge of the pulse is f ₁ and the frequency at the falling (end) time is f ₂ in the sine wave within a certain pulse width, and the frequency is f within the pulse width. _When a signal swept from ₁ to f ₂ (> f ₁ ) is input to the frequency modulation sweep width expanding circuit and passed therethrough, the frequency at the rising edge of the pulse becomes 2f ₁ , and the frequency at the end of the pulse It becomes a 2f _2.

Accordingly, it can be seen that the frequency sweep width is 2f ₂ −2f ₁ = 2 (f ₂ −f ₁ ), which is twice as large as the frequency sweep width f ₂ −f ₁ of the input signal. Expanded from the above, when the frequency modulation sweep width enlarging circuit is connected to the signal successively passes through the n-number cascaded frequency modulation sweep width of its output, to 2 ⁿ times the frequency modulation sweep width of the first input signal Will be.

  Therefore, if this frequency modulation sweep width expansion circuit is provided in the receiving part of the pulse compression ultrasonic detector, and the received signal and leaked transmission pulse are passed through it, their frequency modulation sweep width is expanded and the expansion is also increased. A transmission wave having a frequency-modulated sweep width is transmitted from the transmission unit, propagates in the water, is reflected by the reflector, is received by the transducer, and has the same effect as input to the reception unit. . As a result, it is possible to further suppress the range side lobe level in the pulse compression ultrasonic detector using the pulse compression correlation coefficient multiplied by the window function.

The configuration (b) (FIG. 2) is also a frequency modulation sweep width expansion circuit, and instead of the head double multiplier 1 in the configuration (a) , (π / 2) a phase shifter 7 and a multiplier 8 Is used.
When the input signal Asinωt is phase-shifted by π / 2 radians, Acosωt is obtained. When multiplied by the multiplier 8 to as input signal Asinomegati, amplitude sine wave frequency doubled 2ωt with ^{A 2/2 (A 2/} 2) sin2ωt is obtained.

Then, the amplitude √ square root calculator 4 so that changes input signal and a linear ^(A 2/2) and √sin2ωt = (A / √2) √sin2ωt , then included in the waveform of √Sin2omegati In order to remove the higher harmonics, the signal is passed through the harmonic cutoff filter 5 to output (A / √2) sin2ωt, and a sine wave signal having a frequency twice that of the input signal is output.

The configuration of the present invention has a frequency modulation sweep width expansion circuit of the configuration of (a) or (b) in the receiving section of (A) , and leaked from the transmission end of the transmission / reception switch to the reception end. Because the received pulse and the reflected received signal input from the transmitter / receiver end to the receiving end are received as input signals, and the frequency modulation sweep width of both the leaked transmitted pulse and reflected received signal is expanded. The suppression effect on the range side lobe in the pulse compression ultrasonic detector by the pulse compression correlation coefficient with the window function becomes large, and the frequency modulation sweep width of the transmission frequency, which has been considered conventionally, has been expanded to suppress the range side lobe. As a result, it is not necessary to expand the frequency band of ultrasonic vibrators, which are technically difficult, and therefore the ultrasonic vibrators are not expensive and have an economic effect. And the frequency band of the transmission and reception becomes wide, if the fact that although problems called interference with other underwater ultrasound equipment may not expand the frequency bandwidth of the transmission and reception, does not occur such a problem.

  In addition, when the transmission / reception bandwidth is widened, the level of attenuation during underwater propagation varies depending on the frequency, so the level within one received pulse is not uniform, and the accuracy and reliability of a signal obtained by pulse-compressing such a signal is reduced. However, if the transmission pulse and the reception bandwidth are not widened, such a problem does not occur.

It is a block diagram of the frequency modulation sweep width expansion circuit of (a) in the receiving section (A) of the device of the present invention, and is an example in which a double multiplier is used at the input first stage. It is a block diagram of the frequency modulation sweep width expansion circuit of (b) in the receiving section (a) of the device of the present invention, and is an example using a π / 2 phase shifter and a multiplier at the first input stage. It is a figure which shows the waveform of a sine wave waveform, and the waveform of the square root value. It is a comparison figure of the frequency spectrum of the sine wave waveform of (a) of FIG. 3, and the frequency spectrum of the sine wave square root waveform of (b) of FIG. Digits set frequency modulation sweep width expansion circuit to the receiver, which is a block diagram of an ultrasonic detection device of the present invention. It is explanatory drawing of a frequency sweep modulation | alteration pulse. It is a block diagram which shows the structural example of a pulse compression correlation coefficient production | generation circuit, and is an example which multiplies the signal read from correlation coefficient RAM by the window function. It is a block diagram which shows the structural example of a pulse compression correlation coefficient production | generation circuit, and is an example which multiplies the window function to the leak transmission pulse digital signal in the receiver output memorize | stored in correlation coefficient RAM. It is a block diagram of FIR (Finite Impulse Respons) used as a pulse compressor in the Example of this invention. It is a simulation figure which compares the suppression degree of a range side lobe when the frequency sweep width in a reception pulse is expanded from 10 KHz to 20 KHz which is twice. It is a simulation figure which compares the suppression degree of a range side lobe when the frequency sweep width in a receiving pulse is expanded from 10 KHz to 40 times KHz.

As an embodiment of the present invention, the configurations (a) and (b) of the configuration (a) (receiving unit) of the problem solving means of the present invention include the frequency modulation of the frequency modulation pulse signal input to the receiving unit. Sweep width expansion circuit, which is composed of a plurality of functional units. However, these functions are combined to perform the function of expanding the frequency modulation sweep width, so that each functional unit is arranged in a single arrangement. (For example, a unit), and this may be incorporated in the receiving unit of an ultrasonic detector that performs pulse compression, but each component that constitutes the frequency modulation sweep width expansion circuit without being combined into a unit is super It is also possible to carry out in the form of distributed arrangement according to the relationship of signal transmission and reception in the acoustic wave detection device or the receiving unit and the situation of the mounting space.

In the frequency modulation sweep width expanding circuit of the present invention, the expansion width of one unit is doubled. Therefore, when 2 units are connected in cascade, the enlargement width is 2 × 2 and the enlargement width is 4 times. Similarly, when n units are connected in cascade, it is ²ⁿ times.
Therefore, if the unit enlargement circuit is unitized, a desired enlargement can be achieved by cascading a number of units corresponding to the desired enlargement width.

  Furthermore, by preparing a plurality of frequency modulation sweep width expanding units and allowing the number of cascaded units to be changed by switch switching, the frequency modulation sweep width within the receiving unit in one ultrasonic detector is obtained. Can be selected according to the situation.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram of an embodiment of a frequency modulation sweep width expanding circuit (a) .
The signal received by the transducer of the ultrasonic detector and input to the receiver is a sine wave of Asinωt. Here, A is the maximum amplitude value of the sine waveform and is a constant. ω is an angular velocity 2πf where f is a frequency, and t is time.

First, FIG. 1 will be described. When the input signal Asinωt is squared by the double multiplier 1, its output becomes A ² (1-cos2ωt) / 2. Here, cos2ωt whose frequency is twice appears. From this, when the DC component is interrupted by the DC component circuit breaker 2 at the next stage, the output becomes (A ² cos2ωt) / 2. As seen from this, the input amplitude is A, whereas the output amplitude is A ² , which is a square characteristic. Therefore, when this output is passed through the square root calculator 4 to return it to the proportional characteristic, A√cos 2ωt / √2. The period of the waveform of √cos 2ωt is 2ωt, which is twice the input signal. However, since it is the square root of a sine waveform, the waveform has a wide waveform at the peaks and valleys as shown in FIG. Such a waveform is due to the fact that some harmonics are included in addition to the sine wave having the fundamental frequency as shown in FIG.

  The frequency spectrum of the waveform in FIG. 3B is as shown by the thin line curve in FIG. On the other hand, the frequency spectrum of the waveform in FIG. 3A has a peak only at the fundamental frequency as shown by the thick curve in FIG. That is, the spectrum of the waveform of FIG. 3B has a plurality of peaks (harmonic components) in a higher frequency region in addition to a portion overlapping the spectrum of FIG. ) Therefore, if this peak component (harmonic component) is removed, a sine wave as shown in FIG.

The action of the harmonic cutoff filter 5 of FIG. 1 is a filter for blocking the passage of such harmonic components.
Thus, only a sine wave (Acos 2ωt) / √2 having a frequency twice the frequency of the input signal is output as the output.
Since the input signal is Asinωt, Acos2ωt is a sine wave having a double frequency. Here, the difference between sin and cos is not a problem. Further, since 1 / √2 is a simple fixed coefficient, there is no problem in leaving the level adjustment in the subsequent circuit.

Therefore, now, in the frequency modulated ultrasonic pulse, the frequency at the rising edge of the pulse is f ₁ , the end of the pulse (at the falling edge) is f ₂ (> f ₁ ), that is, the intra-pulse frequency sweep width is f ₂ −f ₁ . In some cases, when one frequency modulation sweep width expanding circuit of the present invention is passed, the frequency sweep width becomes 2f ₂ −2f ₁ = 2 (f ₂ −f ₁ ), that is, doubles. If one more pass is passed, the sweep width is further doubled to 4 (f ₂ −f ₁ ). When n passes through the circuit of the present invention, the frequency sweep width is expanded to 2 ⁿ times. It will be. As described above, the increase in the sweep width contributes to the suppression of the range sidelobe level in the pulse compression ultrasonic detector using the window function.

FIG. 2 is a block diagram of an embodiment corresponding to the frequency modulation sweep width expanding circuit (b) .
In the embodiment of FIG. 1, the input signal is squared by the double multiplier 1, but in the embodiment of FIG. 2, the input signal is divided into two, one is directly input to the multiplier 8, and the other is (π / 2) The phase shifter 7 shifts the phase by π / 2 radians, inputs it to the multiplier 8, and multiplies it with the directly input signal.
Thus, multiplication of a sine wave having a phase difference of π / 2 radians is a product of a sin wave and a cos wave, and when the amplitude of both is A, the multiplication result (output of the multiplier 8) is
^(A 2/2) sin2ωt next, the angular velocity 2ω next frequency will be doubled with respect to the input signal omega.

Thereafter, in FIG. 2, the output of the multiplier 8 is set to (A / √2) √sin2ωt through the square root calculator 4, the input / output amplitude characteristics are set to linear characteristics, and finally the harmonics are filtered by the harmonic cutoff filter 5. Is cut off to obtain an output of (A / √2) sin2ωt. Further, 1 / √2 is the same as that described in FIG.

Figure 5 is a top distichum wavenumber modulation sweep width expansion circuit (Invention configuration in the (i) (a) or (b)), provided in the receiving unit (A), pulse compression ultrasound of the present invention It is a block diagram of the configuration of the detection device.
The ultrasonic pulse electric signal output from the transmitter 11 for performing pulse compression is subjected to frequency modulation. For example, as shown in FIG. 6 (a), the frequency is f ₁ at the rising edge of the pulse, and this frequency increases with time, and becomes f ₂ at the falling edge (end) of the frequency. Is receiving.

The sweep mode is such that the frequency increases linearly with the passage of time as shown in FIG. 5B, and the frequency increases with the passage of time as shown in FIG. those that continue to decline along with the frequency as (d) is high and will go now and what the rate of increase go I above together with the time, but if the other frequency is going to fall with the passage of time is considered, The present invention is not limited to these, and various modes can exist.

  In this way, the transmission pulse subjected to the frequency sweep modulation is sent to the transmitter / receiver 9 by the transmission / reception switch 10 in FIG. 5, and is radiated (transmitted) into the water as ultrasonic waves from the transmitter / receiver 9. Then, it propagates in the water, is reflected by the fish body, the bottom of the water and other reflectors, returns to the transducer 9 and is received, converted into an electrical signal, and input to the receiver 13. In addition, the transmission pulse output from the transmission unit 11 leaks to the receiver in the transmission / reception switch 10 to the receiving end to which the receiver 13 is connected, and the leaked transmission pulse is input to the receiver 13. ing. If this is seen in terms of time, the receiver 13 receives the leaked transmission pulse almost simultaneously with the transmission of the transmitter 11 and subsequently receives the reflected signal received by the transmitter / receiver 9.

The receiving unit 19 outputs a leaked transmission pulse and a received signal that are amplified as necessary and then expanded in frequency sweep width by the frequency modulation sweep width expanding circuit 15, and the leaked transmission pulse includes a pulse compression correlation coefficient. It is sent to the generation circuit 12 and becomes the original signal for generating the pulse compression correlation coefficient count with the window function, and the received signal is sent to the pulse compressor 16 where the correlation coefficient from the pulse compression correlation coefficient generation circuit 12 is sent. Although the signal is pulse-compressed, the frequency modulation sweep width is expanded, so that the range sidelobe level after pulse compression is lower than when the frequency modulation sweep width is not expanded. It is done.

  Since both the pulse compression correlation coefficient generation circuit (hereinafter simply referred to as a correlation coefficient generator) 12 and the pulse compressor 16 are generally composed of digital circuits, the receiver 19 sends the correlation coefficient generator 12 to the correlation coefficient generator 12. The leaky transmitted pulse portion and the received signal sent to the pulse compressor 16 are advantageously digital signals. For this reason, in the configuration block diagram of FIG. 5, after the analog processing such as amplification is performed by the receiver 13, the signal digitized by the A / D converter 14 is swept by the frequency modulation sweep width expanding circuit 15 having a digital configuration. The expanded digital signal is sent to the correlation coefficient generator 12 and the pulse compressor 16.

On the other hand, when the frequency modulation sweep width expanding circuit 15 has an analog configuration, it is provided on the upstream side of the A / D converter 14, and an analog signal with an expanded sweep width is provided to the A / D converter 14. Digitized and sent to the correlation coefficient generator 12 and the pulse compressor 16.
When the sweep width is further expanded, the sweep width is expanded ²ⁿ times by connecting a plurality (n) of sweep width expansion circuits in cascade on the downstream side or upstream side of the A / D converter. Will be.

The correlation coefficient of pulse compression is basically an amplitude signal obtained by reversing the time axis of one transmission pulse signal.
Therefore, the correlation coefficient can be generated by using the output of the transmission pulse portion leaked by the transmission / reception switch 10 and entered the receiver 13 among the outputs of the receiving unit 19 in FIG. Accordingly, the transmission pulse portion with an expanded frequency sweep width in the output of the receiving unit 19 is taken into the correlation coefficient generator 12.

First, a description will be given with reference to FIG.
The digital signal output from the receiving unit 19 in FIG. 5 is input to the correlation coefficient RAM 23. On the other hand, when a transmission pulse rising signal indicating that the transmission pulse rises is sent from the transmission information extractor 20 to the storage element addressing device 21 , the storage addressing device 21 sequentially writes the address to the correlation coefficient RAM 23. Send a signal. This is because the transmission pulse output input from the receiver 19 is sequentially stored in the time axis direction, for example, the amplitude information for each section divided into 1000 in each storage element 1 of the storage element array of the correlation coefficient RAM 23. This is for designating the address of the storage element to be followed.

When the transmission pulse end signal arrives at the storage element addressing device 21 from the transmission information extractor 20, the write addressing signal is sequentially stopped, and this time a reverse read addressing signal is output and stored at the end of the storage element array. Data is read from the correlation coefficient RAM 23 in the reverse order from the stored memory element. The signal read out in this way is a correlation coefficient signal.
This correlation coefficient signal is multiplied by the window function from the window function RAM 22 in the multiplier 24, and is output as a correlation coefficient signal with a window function, and is output to the pulse compressor 16 in FIG.

The correlation coefficient generator shown in FIG. 8 multiplies the receiver output digital signal with the window function signal from the window function RAM 22 by the multiplier 24 before storing it in the correlation coefficient RAM 23. Ru correlation coefficient signal read from is the same as in the configuration of FIG 7.
In the pulse compression, the phase relationship with the window function generated by the pulse compression correlation coefficient generation circuit 12 from the received signal whose frequency modulation sweep width is expanded by the receiving unit 19 and the leaked transmission pulse whose frequency modulation sweep width is expanded. This is done by sending a number signal to the pulse compressor 16.
As this pulse compressor, an FIR (Finite Impulse Response) is used, whereby a convolution operation between the received digital signal and the correlation coefficient is performed.

FIG. 9 is a diagram showing the configuration of the FIR.
Z- ¹ represents a shift register, a cross in the circle represents a multiplier, and a plus in the circle represents an adder. x (n) is an input digital signal, and a (0), a (1),..., a (N−1) are correlation coefficients read from the pulse compression correlation coefficient generation circuit 12. The FIR in FIG. 9 performs pulse compression on the received signal by performing a convolution operation.

FIGS. 10 and 11 are simulation diagrams for comparing the degree of suppression of the range sidelobe level when the frequency sweep width in the pulse is expanded, and a Hamming window is used as the window function. FIG. 10 shows a case where the intra-pulse frequency sweep width is expanded from 10 KHz to 20 KHz (2 times), and the range sidelobe level is suppressed by d1 (about 6 dB, about half the amplitude value). I understand. At the same time, the main lobe width of the pulse-compressed signal is about one-half as from t2 to t3.

FIG. 11 shows the case where the intra-pulse frequency sweep width is expanded from 10 KHz to 40 KHz (4 times), and the range sidelobe level is suppressed by d2 (about 12 dB, about 1/4 of the amplitude value). I understand. At the same time, the main lobe width of the pulse-compressed signal is about 1/4 of the pulse width from t2 to t4.
Thus, it can be seen that when the frequency sweep width within the pulse width is increased, the range sidelobe level is suppressed and the pulse width is also compressed.

DESCRIPTION OF SYMBOLS 1 Double multiplier 2 DC component breaker 4 Square root calculator 5 Harmonic cutoff filter 7 (π / 2) Phase shifter 8 Multiplier 9 Transmitter / receiver 10 Transmission / reception switch 11 Transmitter 12 Pulse compression correlation coefficient generation Circuit (correlation coefficient generator)
DESCRIPTION OF SYMBOLS 13 Receiver 14 A / D converter 15 Frequency modulation sweep width expansion circuit 16 Pulse compressor 17 Rectifier 18 Display 19 Receiving part 20 Transmission information extractor 21 Memory element addressing device 22 Window function RAM
23 Correlation coefficient RAM
24 multiplier

Claims (1)

A pulse compression ultrasonic detection apparatus comprising the following means (a), (b), (c), (d), (e), and (f).
(A) An amplifier that amplifies a received signal, an A / D converter that converts the amplified signal into a digital signal, and a frequency sweep of the received signal, which are connected to the receiving end of the transmission / reception switcher described later (b) A frequency modulation sweep width expansion circuit described in (a) or (b) below , which expands the width, and outputs the expanded output digital signal as a correlation coefficient of a pulse compression correlation coefficient generation circuit described later in (d) RAM and receiver for sending to pulse compressor described later (f)
(A) a double multiplier that squares and outputs an input frequency modulation pulse signal;
A direct current circuit breaker that receives an output of the double multiplier and blocks a direct current component included in the output;
A square root calculator for outputting a value obtained by multiplying the square root of the absolute value of the output of the DC circuit breaker by the sign of the output;
A frequency modulation sweep width expansion circuit for a frequency modulation pulse signal, comprising: a harmonic cutoff filter that removes and outputs a harmonic component other than the fundamental frequency in the output of the square root calculator
(B) a phase shifter that shifts and outputs an input sine wave signal by π / 2 radians;
A multiplier for receiving and multiplying an input signal to the (π / 2) phase shifter and an output signal of the phase shifter;
A square root calculator that outputs a value obtained by multiplying the square root of the output of the multiplier by the sign of the output;
A frequency modulation sweep of a frequency modulation pulse signal, which comprises an output signal of the square root calculator and a harmonic cutoff filter that removes and outputs harmonic components other than the fundamental frequency contained in the output signal Widening circuit (b) A transmission signal input to the transmission end is transmitted to the transducer end, and a part of the transmission signal is leaked to the reception end to which the receiver is connected (c) The (b) Transmitter connected to the transmission end of the transmission / reception switch and transmitting the frequency-modulated transmission pulse (d) The output of the reception portion of the transmission pulse leaked from the transmission end to the reception end in the transmission / reception switch during the output of the reception unit The signal is subdivided along the time axis and stored sequentially in the storage element array of the correlation coefficient RAM. After the transmission pulse, the signal read from the storage element array in the reverse order of the storage order is multiplied by the window function. The pulse compression correlation coefficient and Or the reception part leakage output signal of the transmission pulse part is subdivided by the time axis, and the result multiplied by the window function is sequentially stored in the storage element array of the correlation coefficient RAM, and the transmission pulse ends. A pulse compression correlation coefficient generation circuit (e) that outputs the data read in the reverse order as a pulse compression correlation coefficient (e) A transmitter / receiver (f) connected to the transmitter / receiver end of the transmission / reception switcher of (b) B) receiving the received digital signal from the receiving unit and the pulse compressed correlation coefficient signal from the pulse compression correlation coefficient generating circuit of (d) above, and performing pulse compression by convolution operation on the received digital signal with the correlation coefficient signal Perform pulse compressor

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