JPS6089781A - Receiver - Google Patents

Abstract

PURPOSE:To reduce the constitution of a delay part in size by selecting different-time values of plural singlas for synthesizing receive acoustic wave beams differing in the amount of delay, and selecting and outputting only the final sum value of them. CONSTITUTION:Identical parts la1, lb1, and lc1 of signals la, lb, and lc are se lected by multiplexers MXa, MXb, and MXc and applied to the same adder MA1. Simularly, la2, lb2, and lc2 are applied to MA2, and specific parts of the signals up to MA7 are applied to respective adders successively. Next la8, lb8, and lc8 are applied to the MA1 again, and this operation is repeated. Consequently, adders MA1-MA7 output V1-V7 and identical parts of the signals are separated and extracted. The outputs V1-V7 are integrated by integrators IT1- IT7 for a finite time tau8. The integrators output omega1-omega7, and the final value of integration is nearly equal to the amplitude obtained by making a time adjustment of la, lb, and lc and then summing them. This integral value is read out successively by an output multiplexer MPX right before resetting.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a device for observing the cross-sectional structure of an object using pulsed ultrasonic waves, and in particular a receiving sound wave beam of a falling ultrasonic tomography device for observing up to F motion of the object. Synthesis Method [Background of the Invention] The present invention can be considered as a receiving beam combination method in which a reflected sound wave signal and a reference sine wave signal are compared in phase, and this reference signal is delayed to perform sound wave scanning. Since this method focuses on the saturation line information of the received signal, the time accuracy of the delay signal is significantly reduced, and the device configuration can be made very simple.

The configuration of this system will be explained in detail below with reference to the drawings.

A transmitted sound wave a(t) shown in FIG. 1(1) is emitted to the target.

Here a (t, )=A(t) sin (7)
t −・−・(1). The above ω corresponds to the target object.
(=2πfc: fc is frequency), τ. is set. For example, in sonar, fc is about 100kHz and τ0 is about 100μs, and in medical applications, it is about 5MHz.
It is about 2 μs and varies variously. This transmitted sound wave is reflected by an object and is reflected by an array receiving element group d as shown in FIG. 1(iI). −d, 1. Therefore, as shown in Figure 1 (1), the time difference τ2 corresponding to the direction p in which the object exists
The element output a has a. -a, 1 is obtained. Here τ1
is the round trip sound wave propagation time to the object.

FIG. 1 (li+') shows the configuration of a receive beam combining system that is currently widely used. Here, DL is the received signal a
are analog delay circuits that delay D.
signal delay. Here, D=(n-p)·τ4, and by changing this basic delay time τ4, the reception beam direction is changed. Since the received signal % is p p a =a(t-rl-Pr2), the output b of this delay circuit DL is =a (t-T, -Pr2-D, )=a
(tr, -1-P(T4-r2)-n r4), and when the sound wave incidence direction and reception direction match (τ2=τ
4), as shown in Figure 1 (1v), = a(t
-r, -nr4), and all outputs have the same waveform. After such delay time matching, an adder S obtains a receiving signal path C in the direction of interest.

This target azimuth signal C becomes =na(t-τ1-nτ4) and is obtained as a large output. The above is about the signal arriving from the desired direction, but for the signal from the undesired direction (τ4-τ2=△), b , =a (tr
1+PΔ-nr4), the adder output C becomes an inflated output as each signal cancels each other out as shown in FIG. 1(V).

As can be understood from the above explanation of the basic operation, in the case of the conventional method, the delay time accuracy of the delay circuit DL is required to be as accurate as the carrier wave period (τ3), and if the accuracy is around τ3/2, the target azimuth signal will also decrease. As a result, delay time accuracy of about τ3/4 is usually required, making the configuration extremely difficult.

The configuration shown in Figure 2 is an improved version of this. Received signal a
Multipliers M, p, and MC each include a balanced modulator.

This is done by The internal configurations of the multipliers M, , Mcp are the same, and are given different symbols for convenience of explanation. This reference signal is a delayed sine wave, which changes in various ways due to convergence reception, which will be described later, but for the sake of simplicity, let the center frequency ω and the delay time of the reference signal be Pr4 with respect to a plane wave, e, p = 5in ( ω(t −Pr4)) −・−−
-(21ec, = cos (ω (t-Pr4))
. . . (3) are delayed signals whose phases are shifted by 90° from each other. FIG. 3 shows a configuration for creating such a waveform. A rectangular wave with a period τ3 is applied as data to the shift register SHR, and the contents of the SHR are moved by a clock with a period τ4. With this configuration, a waveform f delayed by Pr4 is obtained, and by delaying this f by a digital delay circuit DD using a monostable multivibrator having a delay time of τ3/4, as shown in FIG. A signal of g is obtained. By shaping with resonant p p filters F and F that have center frequencies in f and gt, ip c
p s e , e are obtained. Here ω=2π/τ3ap
It is cp.

The outputs h and h of the multipliers M and M are ap cp
sp cp ith=a-e sp p 5p =A(r)sin(ωτ) −sin (ω(t-Pr
4))-cos (GJ (2t -r, -p(r2+
τ4)1) and h=a−e cp p p = A(rlsin (ωr) −cos (ω(t
-P r4)) Here, ψ, -ω (P (τ4 - τ2) - τ,) ψ,' = ω (P (τ4 + τ2) + τ11τ = 1 τ - P
τ2=τ(1). In these hc, , hSp, A(tl is the envelope component of the received waveform and 5in(2ωt), cog(
2ωt) has sufficiently lower frequency components. For this purpose, a low-pass filter L is used to reduce the 2ω frequency component.

With @p Lop, only the %+ frequency component can be separated and extracted. Such a filter output 1sp(t) + tap(
t) is only the first term on the right side of h and h, respectively, and sp
cp A(τ) I l1p(t) −e 08ψ, ・・・・・・(
6) A(τ).

ic, (t)=-s1nψ, (7). Such a waveform is converted into an analog delay circuit DSpDC,
Delayed by These DS, , and DC have the same configuration and variable delay time (n-p)τ.

is a delay line that gives Here, τ5 is a value related to the delay time setting value of the analog signal delay section DS, ,D(,), and the delay time setting value of each channel is a plane wave from infinity, which was used for simplicity in the example. , the delay time setting value for each element is the element number p
It is given as (n-p)τ5 corresponding to . Here, τ
5 is installation, and an error of Δp occurs in actual operation. Therefore, the output of DS, DC, j @ p *
jc.

Hato becomes. An adder S, , S which obtains the sum of each of n such signals j@pr J e p
Add by . The adder outputs 1c, , k, are respectively. If we consider the case where a sound wave is incident from the target direction, τ2 =: τ4 = τ5, so the signal becomes large and a large output is obtained. This signal is squared by T,, T
By squaring by c, adding by sB, and square rooting by square rooter R, an output signal C'H4'4 is obtained. With this configuration, the output C for the target direction signal is n A (tr t n r 4 )−□ .
...(14), which is unrelated to the distance to the target object (unrelated to τ1)
maximum output will be obtained. On the other hand, for sound waves from directions other than the target, τ4−τ2=Δτ5−τ2−Δ′
Then, when (n-1)ω△ becomes 2π or more, k.

kc becomes a small value and is suppressed. This will be explained with reference to 6 below. Note that the same applies to kc.

-cos (ω(p-Δ-71)), where (n-1)ωΔ〉2π, then 0 of p
Corresponding to the change from n-1 to
It changes up to π. For this reason, cog (ω(p・Δ−τ1
The value of )) changes by one period in response to the change in ωp·Δ, and the result of adding all of these changes is that the positive and negative values of are averaged and become a small value. Here, A(−τt+
pΔ/nτ5) usually does not change near the time τ1. The direction corresponding to (n-1)ωΔ=2π becomes the first zero point of the directional characteristic, and the same directional characteristic as in the conventional system is realized.

That is, as described above, with respect to changes in Δ and Δ', A(−τ, +pΔI nτ,) does not change near the center of the reflected wave. Therefore, if this value is B, then k, z E p'f,, B cos (ω(pΔ−
It will be November. Such a change in k with respect to Δ is zero at best. The direction corresponding to this Δ becomes the first zero point.

On the other hand, in the conventional method, if we use the formula b on page 4, line 4, we get (ω(−τ1+pΔ−nτ4)), and the change in Δ is the same as in the present invention.Therefore, the azimuth resolution is also exactly the same. becomes.

Next, we will discuss the influence of the delay time accuracy of the delay circuit.

The reference signal can be processed digitally, the required delay time can be easily obtained, and it is possible to set τ4 to τ2=0. On the other hand, the portions that delay the received signal components (DSp, DC, shown in FIG. 2) have amplitude information, making the configuration complicated and making it difficult to improve time accuracy.

So, this DS.

DC delay time error becomes a problem. If this delay time setting error is Δp, the DS for the set delay time pτ5 is
, DC actual delay time DE-ma, p p DFJ = (n-p) τ5-Δp. Therefore, the output js p + jcp from the delay means corresponding to Equation (8), (91) is as follows.Here, since we are considering the received signal strength with respect to the sound wave incident from the target direction, the set delay amount τ
5 has τ, -τ2(=Δ')=0. Therefore, τ,'=-τ1+Δp-nτ5, and the summation output obtained by adding these together is as follows: , kc is expressed by equation (10).

% expression %). Here, the phase difference is ψ−, ψ,=ω(p(τ4−τ2)−d,), and since it is an object in the target direction, similarly τ4−τ
2(-〇)-〇, and ψ ==-11t)Tl. From the above formula. The reception output C(t) for the target direction when such a delay time error Δp exists is as follows. Here, for A(t-τ, +Δp-nτ5), the reception start time is τ1-Δp-1-nτ5, which is the time length τ. This is a rectangular pulse. For this reason, since the error Δp changes depending on the receiving element p, the reception time changes, and the sum of these, C (t), becomes longer than τ0, as shown in FIG. 4. That is, as n increases and Δp is assumed to be uniformly distributed, it changes as shown in FIG. By configuring from this figure, it is possible to extract the target signal without reducing the maximum value.

On the other hand, in the conventional case, it is a direct delay addition of A(+1 sin(ωt), and the addition output is as follows due to the error of Δp. Therefore, in order to prevent the addition output from decreasing, ωΔp(π is required) Here, since this τ is usually much longer than the above-mentioned τ3, the delay time accuracy of DS and DC is much easier than that of the delay circuit DL in the conventional system.

In this way, it is possible to obtain a signal from a specific location, and by using this signal to modulate the brightness of the cathode ray tube, it is possible to learn the shape of an object, or to learn the nature of an object at a specific location by analyzing the reflected waveform. becomes.

The above is the operation when configuring the device faithfully, but various simplifications can be made by utilizing the feature of this method that focuses on envelope information.

Attention is paid to the output of the adder SS on one side in FIG. The received output from the target direction object is as shown in Equation 12, which is in the form of Equation 14 multiplied by COS (-ωτ1). This corresponds to the fact that the output amplitude changes (the sensitivity changes) as τ1 changes (the distance changes). This situation is shown in FIG. Like this ω
Fluctuations in sensitivity occur with a period corresponding to the sound wave propagation time τ6, which has a relationship of τ6=π. However, the distance interval Δr corresponding to this τ6 is given by the sound speed in the propagation medium as C8 and the sound wave wavelength as input, and when a 2MHz sound wave is used underwater, Δr
-o, 19 (mm) (C,: 1500 m/
) However, such minute sensitivity changes pose no problem at all for objects of finite size that are made up of a large number of reflection points.

In other words, if there is only one reflection point and the position is fixed at the zero point of lkl shown in Figure 5 (τ1 is fixed).
In this case, the reflected signal will be lost.

However, usually the object moves, such as a living body or the side of ice, or the observation point moves, and the relative position changes. Therefore, even if the dripping liquid propagation time τ□ changes and the reflected signal momentarily disappears, it immediately reappears. In particular, in the case of an object with a finite size, there are many reflection points, so even if the object is fixed, some reflection point will always be observed. There is no chance of losing sight of the reflector even if you only do so.

As a result of the above, as a modification of the method shown in Fig. 2, it is also possible to use a receive beam configuration method in which only one of e or e @p Op is used as a reference signal, and in this case, the configuration shown in Fig. 2 is reduced by approximately half. This greatly simplifies the device.

Furthermore, according to this method, the accuracy of the delay time of the DS is the accuracy of the length of the envelope, as shown in FIG.

Therefore, τ4 is τ. If it is small compared to , it is possible to group 1llp (or ic, ) into a plurality of groups and then delay them as shown in FIG. In this way, Sa
Signals added by adders 's and 'Sc! , ＋
IB + lc are as shown in FIG. 6, and no decrease in amplitude appears at all. This I! 8゜z, ,z
ci is 12τ2, by DSa, DS, , DSc, respectively.
By delaying 8τ2.4τ2, Figure 'zq, +
(1, I Ctc is obtained and these three signals are sent to the adder SS
By adding , it is possible to increase the target signal output U without reducing the maximum amplitude.

In order to simplify the explanation, the above explanation assumes that 4 signals (t, 6% t, 3, etc.) are all in one group (He, etc.), and the system is configured with 3 groups, but the system is not limited to this configuration. It is clear that any division is possible subject to the limit that the maximum amplitude is not degraded. With this configuration, as is clear from FIG. 6, the number of delay circuits is greatly reduced, and the device configuration becomes 1/4 of the complexity of the configuration shown in FIG.

In the received sound wave beam combining method described above, by delaying the receiving wave number component, the requirements regarding the accuracy of the delay circuit are relaxed. However, in the examples shown in Figures 2 and 6, analog delay lines are used as delay circuits, so the delay circuits needed to satisfy the required accuracy and obtain a large delay are large and expensive. You can't avoid becoming something.

Also, although omitted in the explanation of Figures 2 and 6, in reality, the delay amount of these delay circuits is not fixed, and it is necessary to switch the delay amount depending on the position of the reflected sound wave. It is necessary to use a delay line and to be accompanied by means for switching taps.

[Purpose of the invention]

SUMMARY OF THE INVENTION Therefore, it is an object of the present invention to provide a method for combining received sound wave beams that can further reduce the size of the device configuration.

[Summary of the invention]

The present invention includes means for selecting values at different times of a plurality of signals for synthesizing received sound wave beams by delaying each signal by a different amount of delay, means for adding the selected values, and means for adding the selected values. The present invention is characterized by a wave receiving apparatus having means for selectively transmitting only the final value.

According to this configuration, the amount of delay can be controlled by controlling the time at which the signal value is selected, that is, by controlling the digital clock, and the device configuration becomes compact and inexpensive.

[Embodiment of the Invention] FIG. 9 shows the configuration of an embodiment of the invention. This example is the sixth
The analog delay numbers DS, , DSL shown in the figure.

Instead of the part consisting of DS and adder SS, adder S
8. S6. It is connected to the output of Sc. However, Sa ' Sb 'SC's output Z a * ' B
*Instead of aligning with respect to lo, 'l in Figure 2
A similar configuration can be used for alignment regarding lp''+1c.

FIG. 9 will be explained with reference to FIG.

As shown in FIG. 8, the signals l, *j? 6 + 1
Assume that c (a configuration in which alignment is performed for i, , ie, is also possible, but is omitted) is obtained.

1 to the same part of these signals (at different times)
．． l! , □1lc1ft multiplexer MX 1. b
, c and applied to the same adder MA.

Similarly, 21 ``b2 t'' C2 is applied to MA2, and in turn a particular portion of the signal is applied by each adder up to MA7. M again the next '181 'b8 ” c8
Apply voltage to A1 and repeat this operation. When such processing is performed, the outputs of adders MA□ to MA7 are respectively v1
~v7, and the same part of the signal is separated and extracted.

These adder outputs v1 to v7 are stored for a finite time τB (
'a * IB m lc ) is integrated by the integrators IT□~7. This integrator is I! . Each component can be reset immediately after being output to l.

The outputs of such integrators are ω1 to ω7, respectively, and the final values of the integrals are almost the same as the amplitudes added after adjusting the times of 'am' (, v l.).

When such integration results are sequentially read out by the output multiplexer MPX immediately before resetting, a waveform almost identical to that shown in FIG. 7U is obtained, as shown by X in FIG. has been realized. By configuring the system using multiplexer switches, adders, and integrators in this manner, time adjustment can be performed entirely using a digital clock, and the stability of the system is greatly improved. A control signal for controlling the signal selection and integral reset described here is created using the cxcy shown in FIG.

In the above explanation, the wave receiving device shown in FIG.
Although the present invention is applied to delay the low frequency component obtained by multiplying the received signal by a predetermined reference signal, the present invention is not limited to this. It can be widely applied as a practical realization.

The following explanation is based on the case where the target object is sufficiently far away and the reflected signal is incident as a plane wave as shown in Figure @1 (:1), but as in the present invention, the phase difference with the reference signal is Ili!
In the case of method 2, it becomes possible to receive spherical waves from distant objects with a simple additional circuit. As shown in Figure 10, by using a digital delay circuit DV that uses a monostable multipipe rake (l) to delay f by a delay time with a quadratic relationship and use it as a reference signal, the wavefront with curvature from a nearby object can also be phased. Furthermore, by changing the delay time of D'V so that it has a curvature that is inversely proportional to the time from the sound wave transmission time, it is possible to calculate the distance from the object at any distance. It is also possible to receive reflected signals with the same phase at all times. Such a configuration of V can be easily realized by using an ordinary monostable multivibrator whose output pulse width can be changed by voltage. Furthermore, the reference signal e
Considering that s, + e cp is a sine wave, it is obvious that the reference signal having such a quadratic curvature can be substituted by a simple phase shifter constructed only for a single frequency. Also, although the SHR configuration in Figure 3 is shown as shifting the contents only in one direction, this can also be simplified by using a shift register that shifts in both directions and further performing an envelope delay corresponding to the shift direction. It is also clear that reflected signals from both left and right directions are received.

Figure 2 Figure 74 Figure 3 887% Part 4 Door=H Ge Funi//~\-1-i Figure 7 1c Figure 7 No.! i′ diagram

Claims (1)

[Claims] 1. A first method for selecting different time values of a plurality of signals.
1. A wave receiving device comprising a combining means, a second means for adding selected values, and a third means for selectively transmitting a final value of the added values. 2. The wave receiving device according to claim 1, further comprising a control means for repeatedly operating the first, second, and third means a plurality of times. 3. The wave receiving device according to claim 1, characterized in that it has a plurality of sets of the first, second, and third means, and operates these at different times.