JPS6051068B2 - receiving device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for observing the cross-sectional structure of an object using pulsed ultrasonic waves, and more particularly to a receiving sound wave beam synthesis method for a falling ultrasonic tomography apparatus for observing the motion of an object.

The present invention is a receiving beam combining method in which a reflected acoustic wave signal and a reference sine wave signal are phase-compared, and this reference signal is delayed to perform acoustic wave sweeping.

Since the present invention focuses on the envelope information of the received signal, the time accuracy of the analog delay section 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 transmission sound wave a shown in FIG. 1i is emitted to a target. J
Here, a(wo)=A(wo)sin6)(1)A(wo)=1(
0≦≦T0)0 (other).

The above ω (■2πf7c: fc is the frequency) and To are set corresponding to the target object. For example, in a sonar, fc: 100 kHz, To: about 100 μs, and in medical applications, each becomes about 5 MH 22 μs, which varies variously. This transmitted sound wave is reflected by an object and sent to an array receiving element group D as shown in FIG. -D. ．． -1. Therefore, as shown in FIG. 1, the element output having a time difference γ2 corresponding to the direction in which the object exists is also
n-1 is obtained. Here, τ1 is the round-trip sound wave propagation time to the object. FIG. 111 shows the configuration of a receive beam combining system that is currently widely used.

Here, DLp is an analog delay circuit that delays the received signal A9, and each delays the signal of Dp. Here, by changing this basic delay time γ4, the receiving beam direction is changed.

The output Bp of this delay circuit DLp is due to the received signal Ap, and when the sound wave incident direction and the receiving direction match (τ2
=τ4), all outputs have the same waveform as shown in FIG. 1v.

After such delay time matching, an adder S obtains a received signal in the direction of interest; a path C. This target direction signal C is obtained as a large output.

Is this the direction of the goal? Regarding the signal that arrived from
As for the signal from the undesired direction (.tau.4-.tau.2=.DELTA.), the adder output C becomes a suppressed output as the signals cancel each other out as shown in FIG. 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 of the system according to the present invention is shown in FIG.

The received signal A and the reference signal Esp-Ecp are multiplied by multipliers Msp and Mcp constituted by balanced modulators. The internal configurations of the multipliers Nlsp and Mcp are the same and are given different symbols for convenience of explanation. This reference signal is a delayed sine wave and changes variously due to convergence reception, which will be described later, but for the sake of simplicity, if we assume that the center frequency is ω and the delay time of the reference signal is pτ4 with respect to a plane wave, then the difference will be 90%.
This is a delayed signal with a 0 phase shift.

FIG. 3 shows a configuration for creating such a waveform. period τ
A rectangular wave of 3 is applied as data to the shift register SHR, and the contents of the SHR are moved by a clock with a period of τ4. With this configuration, the waveform F delayed by Pτ4
By delaying this Fp by a digital delay circuit DDp using a monostable multivibrator having a delay time of τ3/4, Gp is obtained as shown in FIG.
A signal will be obtained. Esp and eOp are obtained by shaping these Fp and gp using resonant filters Fsp and FOp having a center frequency ω. Here ω=2π/τ3
It is. The outputs Hsp and hOp of the multipliers Msp and Mcp are respectively and here.

In Hcp and hsp, A3γ is the envelope component of the received waveform and has a frequency component sufficiently lower than Sin(2ωt) and COs(2ωt). For this reason, A(γ,
Only the frequency components of 2ω can be separated and extracted by low-pass filters Lsp and LOp that reduce the 2ω frequency components. Such filter outputs Jsp(t) and 1cp(t) are only the first term on the right side of Hsp and hcp, respectively.

Such waveforms are delayed by analog delay circuits DSp and DCp. The DSp and DCp have the same configuration and are delay lines providing variable delay means (n-p) τ5. Here, τ5 is a value related to the delay time setting value of the analog signal delay unit DSp and In this case, the delay means setting value for each element is (n-p)τ corresponding to the element number p.
It is given as 5.

Here, τ5 is a set value, and in actual operation, Δ
An error p occurs. Therefore, the output J3 of DSp, ■ et al.
p, jcp become.

Such signals Jsp and jcp are added by adders Ss and SO that obtain the sum of n signals, respectively. The addition outputs Ks and kO are each PV.

If we consider the case where a sound wave is incident from the target direction, τ2
= τ4 = τ5, so the signal becomes a large output.

This signal is squared by the squarer T5 and TO, added by SB, and square rooted by the squarer R, and the output signal C
get. With this configuration, the output C for the target direction signal
Therefore, the maximum output is obtained regardless of the distance to the target object (irrespective of τ1).

On the other hand, for sound waves from the direction beyond the target, τ4−τ2=Δ
If τ5−τ2=Δ″, then (n−1)ωΔ is 2
When the value exceeds π, Ks and kc become small values, resulting in a suppressed output.

This will be explained regarding Ks. Furthermore, K. The same applies to Here, if (n-1)ωΔ〉2π, then ω corresponds to the change from p(7)O to n-1.
p·Δ changes from O to 2π. For this reason, COs(ω
The value of (p・Δ−γ1)) changes by one period in response to this change in ωp・Δ, and when all these are added, the result, Ks, is a small value as the positive and negative values are averaged. . here,
Since A(t-τ1+PΔ″-nτ5) is normally Δ=Δ″, PA5 is pΔ<nΔz1, τ3, τo, and it hardly changes near the time t=τ1 when the reflected signal is obtained. The direction corresponding to (n-1)ωΔ=2π becomes the first zero point of the directional characteristic, and the same directional characteristic as the conventional system is realized. That is, as mentioned above, for changes in Δ, Δ″, A(t−τ1+P
Δ″−nτs) does not change near the center of the reflected wave.

Therefore, if this value is B, then it becomes.

The change of K9 with respect to Δ, such as β, is
127r well-known SirX/x
It becomes 0 at Δ-;. The direction corresponding to this Δ becomes the first zero point. On the other hand, in the conventional system as well, if the formula for Bp in the fourth line of page 4 is used, TωP FP−υ is obtained, and the change with respect to Δ is the same as in the present invention.

Therefore, the azimuth resolution is also exactly the same. Next, the influence of the accuracy of the delay means of the delay circuit will be described.

The reference signal can be processed digitally, the required delay time can be easily obtained, and γ4 to γ2 can be set to 0. On the other hand, since the portions that delay the received signal components (DSp, DCp shown in FIG. 2) require amplitude information, the configuration becomes complicated and it is difficult to improve the time accuracy. Therefore, the delay time error between DSp and DCp becomes a problem. If this delay time setting error is Δp, the setting delay time pγ
The actual delay time DEp of DSp and DCp for 5 is:
becomes. Therefore, the output Jsp9jcp from the delay means corresponding to equations (8) and (9) is as follows.

Here, since the received signal strength with respect to the sound wave incident from the target direction is considered, the set delay amount T5 is τ
5−τ2 (=Δ″)=0. Therefore, τ5
p=t−τ1+Δp−nτ5, and the addition output K3, kO obtained by adding these together is −I
) ″.

Here, the phase difference ψ9 is .Since the object is in the target direction, τ4-τ2 (=0)=0, which is 1.

From the above formula.

The received output C(t) for the target direction when such a delay time error Δp exists is:
n-1 C(t)2㇠■■=1ΣA(t-τ1+Δp-nτ5)
2p-0''.

Here, for A(t-τ1+Δp-nτ5), the reception start time is τ1-Δp+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 changes, C(t), becomes τ. It becomes longer, as shown in Figure 4. In other words, n is large and Δp is uniformly distributed.
Assuming n-1, X.

Is A(t-τ1+Δp-nτ5) the maximum of Δp? It changes as shown in FIG. 4 in response to ΔPm. As can be understood from this figure, by configuring the delay circuit DCp such that ΔPm≦K, it is possible to extract the target signal without decreasing the maximum value.
On the other hand, in the conventional case, it is a direct delay addition of A(t)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, it is necessary that .

Here, usually this γ. is significantly longer than the aforementioned τ3, so the delay time accuracy of DSp, ■■ becomes much easier than that of the delay circuit D 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 Ks of the adder Ss on one side in FIG. The received output from the target direction object is 6 as shown in the first trial, and this is in the form of the first wipe 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. In this way, sensitivity fluctuations occur with the period of the sound wave propagation time γ6 having the relationship ωτ6=π. However, the distance interval Δτ corresponding to this τ6 is based on the assumption that the sound velocity in the propagation medium is the CSl sound wave wavelength, and when a 2MHz sound wave is used in water, an object with a finite size consisting of many reflection points In this case, such minute sensitivity changes pose no problem at all.

In other words, if there is only one reflection point and the position is fixed at the zero point of 1k51 shown in Fig. 5 (γ1 is fixed).
In this case, the reflected signal will be lost.

However, normally, as in biological or underwater measurements, the object moves or the observation point moves, and the relative position changes.
Therefore, even if the sound wave propagation time γ1 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. Even if you only do this, you will never lose sight of the reflector. Based on the above, Es or E is used as a reference signal as a modification of the method according to the present invention. A receiving beam configuration method using only one of p is also possible, and in this case, the configuration shown in FIG. 2 is approximately halved, which greatly simplifies the device. That is, the configuration of FIG. 2 includes the first system of multipliers MsO, M, , related to the adder S8.
l...MSn-1, low-pass filter L.

O, Lsl...Lsn-1, and delay lines DSO, DS
l...DSn-1, second system multiplier M(5:)9MC1 unit 0Mcr1-1) related to adder SO, low-pass filter LCO9LCI/OLcn-1, and delay lines DSO, D
Sl...DSn-1, but for example, ESO, eSl...E5. ．． If only −1 is used, the second system multiplier, low-pass filter, and delay line are not necessary, and the output of the adder Ss can be taken out as the received beam synthesis output. In this case, the adder SCl 2 multiplier T8 and the adder SB1 squarer R are of course unnecessary. Further, according to the present invention, the delay time precision of the DSP is the precision of the length of the envelope, as shown in FIG.

Therefore, τ4 is τ. For a small phase shift compared to , it is possible to group Isp (or Icp) into a plurality of groups and then delay them, as shown in FIG. In this way, Sa,S
Signals 1a, 1, , added by adders b, SO
10 as shown in FIG. 6, and no decrease in amplitude appears at all. These La, l, and 10 are respectively DSa and D
By delaying Sb and DSO by 12τ2, 8τ2, and 4τ2, Qa, qb, and qO in Fig. 7 are obtained, and by adding these three signals with an adder SS, the target signal output u can be obtained without reducing the maximum amplitude. It becomes possible. In order to simplify the explanation, 4 signals (IsO-1s3, etc.) are in one group (1a, etc.), and the system is configured with 3 groups. Although this configuration is not limited to this configuration, the U
It is clear that any division is possible subject to the limit that the maximum amplitude of is not degraded. With this configuration, as is clear from FIG. 6, the number of delay circuits is greatly reduced (114 in the configuration of FIG. 6), making the device configuration easier. In the above explanation, the delay circuit for the purpose of envelope alignment is
For the sake of simplicity, the explanation has been made assuming an ordinary analog delay line.

However, for the purpose of delaying the envelope signal as in this method, the following configuration is also possible. FIG. 9 shows its configuration. Signals 1a, 1b, 1 as shown in FIG. (I
It is assumed that a configuration in which alignment is performed with respect to sp and iOp is obtained (although it is also possible to consider a configuration in the same way, but this is omitted). The same parts 1a, 1b1, 101 of these signals are sent to multiplexer MX.
A, b, and c are selected and applied to the same adder MA. Similarly, 1a2, 1b2, and 1c2 are applied to MA2, and specific portions of the signals are sequentially applied to MA7 by respective adders.

The next 1a8, ]B8, IO8 is applied to MAl again and this operation is repeated. When such processing is performed, the adder MA
The outputs of I to MA7 are V1 to V7, respectively, and the same portions of the signals are separated and extracted. These adder outputs V1 to V7 are integrated by integrators 1T1 to 1T7 for a finite time T8 (time during which 1a, 1b, and 1 are obtained). This integrator can be reset immediately after the 1c component is output to 1. Each of these integrator outputs is ω1~
The value becomes ω7, and the final value of the integral is approximately the same as the amplitude added after adjusting the times of 1a, 1b, and 10, respectively. If such integration results are sequentially read out by the output multiplexer MPX immediately before reset, a waveform almost identical to that shown in Figure 7 u, as shown by X in Figure 8, will be obtained, equivalently realizing an envelope delay circuit. It means that it was done. By configuring the device using multiplexer switches, adders, and integrators in this way, time adjustment can be performed entirely using a digital clock, and the stability of the device is greatly improved. The control signals for controlling the signal selection and integral reset described here are shown in FIG.
Created by The above 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 Fig. With a simple additional circuit, it is possible to receive spherical waves from objects at close range.

As shown in Figure 10, by using a digital delay circuit DVp using a monostable multivibrator to delay Fp by a delay time in a quadratic relationship and use it as a reference signal, wavefronts with curvature from objects at close range are also added with the same phase. It becomes possible to do so. Furthermore, by changing the delay time of this DVp so that the curvature is inversely proportional to the time from the sound wave transmission time, it is possible to always receive reflected signals from objects at any distance with the same phase. It is possible. Such a configuration of Vp can be easily realized by using an ordinary monostable multi-pipulator whose output pulse width can be varied depending on the voltage. Furthermore, the reference signal E
Considering that sp and ecp are sinusoidal waves, it is clear that a reference signal having such a quadratic curvature can be replaced by a simple phase shifter configured for only a single frequency. Also, although the SHR configuration in Figure 3 is shown in such a way that the contents are shifted only in one direction, this can also be easily done 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 sound signals from both left and right directions are received.

[Brief explanation of the drawing]

1 and ii are explanatory diagrams showing the time relationship between the transmitted waveform and the receiver output, Ii, i and ■ are explanatory diagrams of the operation of the conventional method, FIG. 2 is a configuration diagram of the method of the present invention, and FIG. The figure shows an example of the configuration of the reference signal generating section of the present invention system, FIG. 4 shows the influence of error in the delay circuit section on the output waveform, and FIG. 5 shows the distance when configured with one type of reference signal. Figure 6 is a diagram showing sensitivity changes, Figure 6 is an explanatory diagram of a configuration that simplifies the delay circuit section, Figure 7 is a diagram showing the output from the configuration of Figure 6, and Figure 8 is a diagram showing the delay circuit section as a multiplexer and an integrator. FIG. 9 is a diagram showing an example of the configuration, and FIG. 10 is a diagram showing an additional circuit for maintaining focus at a short distance.

Claims (1)

[Scope of Claims] 1. A plurality of sound wave receivers, and a predetermined time relationship of which is controlled in accordance with the incident time of the wave front from the target object received at each position of the wave receiver. a reference signal generation means for generating a plurality of reference signals of different frequencies; a multiplication means for multiplying the received signal of the receiver by a corresponding one of the reference signals; 1. A receiving device comprising: a delay means for delaying in accordance with a difference in incident time, and obtaining a summed output of the outputs of the multiplication means each delayed by the output of the delay means. 2. In the receiving device according to claim 1, each of the plurality of reference signals is composed of two types of sine wave signals, first and second, having a phase difference of 90°, and the multiplication means and the delay means are Two systems, a first system and a second system, are provided corresponding to the first and second two types of sine wave signals, respectively, and furthermore, an additional output of the output of the delay means belonging to the first system and the second system are provided. 1. A receiving device comprising means for extracting envelope information of a received signal based on the summed output of the outputs of the associated delay means. 3. The receiving apparatus according to claim 1, further comprising an adding means for partially adding the multiplication results, and an output of the adding means is applied to the delay means. 4. The receiving device according to claim 1, further comprising means for giving the plurality of reference signals a second-order delay time difference corresponding to an incident time of a wavefront having a curvature from a nearby object. receiving device.