JPH0381684A - Wave receiver - Google Patents

Abstract

PURPOSE:To easily realize a delay distribution in optional pattern by time adjustment with a digital clock and to facilitate positioning reception from a short distance to a long distance with a delay distribution of curvature which varties with time by holding discrete values of received sighnals of plural channels and realizing delay. CONSTITUTION:When signals la, lb, and lc are obtained, they differ in time, but parts fa1, lb1, and lc1 of them are selected by multiplexers MXa, MXb, and MXc and applied to the same adder MA1. Similarly, la2, lb2, and lc2 are applied to MA2 and thus specific parts of the signals are applied to up to MA7 in order; and next la8, lb8, and lc8 are applied to the MA1 again and this operation is repeated. Consequently, the outputs of the adders MA1 - MA7 become V1 - V7 and the same parts of the signals are sampled, and separated and extracted respectively. Then the outputs V1 - V7 are integrated by integrators IT1 - IT7 for a time wherein the signals la, lb, and lc are obtained and the results are outputted from output MXa, MXb, and MXc.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a receiving sound wave beam synthesis method for a device for observing the cross-sectional structure of an object using pulsed ultrasonic waves, especially a high-speed ultrasonic tomographic imaging device for observing even the movement of an object. [Prior art] In order to obtain continuous ultrasound images at high speed, instead of mechanically scanning a fixed directional probe, a delay time according to a certain distribution is given to the signals of the arrayed ultrasound elements. , the directivity can be changed by changing element selection or delay time distribution.

An example thereof is described in Japanese Patent Application Laid-Open No. 49-43480.

The configuration for obtaining desired directivity using delay time distribution will be explained in detail below with reference to the drawings. Transmitted sound wave a shown in Figure 1(i)
(t) is emitted to the target.

Here a (t) = A (t) sinωt −
(1). Corresponding to the target object, the above ω(=2πfc
: fc is frequency), τ. is set. For example, in a sonar, fc4100kHz, t. It is about 4100 μS, and in medical applications, it is about 5 MHz and 2 μs, and varies variously. This transmitted sound wave is reflected by an object, and as shown in FIG.
It is incident on n-1. Therefore, as shown in FIG. 1(i), element outputs a0 to a11-0 having a time difference τ2 corresponding to the direction in which the object exists are obtained. Here, τ1 is the round-trip sound wave propagation time to the object.

FIG. 1 (■) shows the configuration of a receive beam combining system that is currently widely used. Here, D L p is an analog delay circuit that delays the received signal aF, and each delays the signal of Dp. Here, DP=(n-p)@τ, and by changing this basic delay time τ, the reception beam direction is changed. Since the received signal ap is ap:a (-τ, -Pr2), the output bP of this delay circuit DLp is bp=a (t-τ, Pτz-Dp-)=a (
t-τ1+P(τ, -τ2)-n, ) becomes 1. When the sound wave incidence direction and reception direction match (τ2=τ4), bp=a (−τ, −nτ4) as shown in FIG. 1(iv), and all outputs have the same waveform. After such delay time matching, an adder S obtains a received signal C in the direction of interest.

This target azimuth signal C becomes p=Q=na (-τ1-nτ,) 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 (τ, -τ, = Δ), bp=a (t-c1
+PΔ−nτ, ), the adder output C is as shown in Figure 1 (V
), the signals cancel each other out, resulting in a suppressed output.

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 equal to the accuracy of the carrier wave period (τ,). This also reduces the delay time accuracy, which normally requires a delay time accuracy of about 3/4, making the configuration extremely difficult.

The configuration shown in FIG. 2 is an improvement on this. Received signal aP
Multiplying by the reference signals e sr and e CF is performed by multipliers Msp and MCP constituted by balanced modulators. The internal configurations of the multipliers Msp and Mcp are the same and are given different symbols for convenience of explanation. This reference signal is a delayed sine wave with a center frequency ω, and the distribution of delay times between channels varies depending on what kind of directivity reception is performed, that is, convergence reception, which will be described later. To simplify the explanation, let us explain the case of obtaining directivity corresponding to a plane wave from an oblique direction as shown in Fig. 1. These reference signals are e.
sp==:sin (ω(t-P τ4) ) --
(2) ecp=cos ((1) (t-P τs)
) - (3) are delayed signals whose phases are shifted by 90' from each other. In other words, the basic delay time τ between adjacent element channels is
Each has a phase difference. A reference signal for each channel having such a delay distribution can be created without using an analog delay line. Its configuration is shown in FIG. 3(a). Figure 3(b)
A rectangular wave with a period τ and (τ3=2π/ω) shown in is applied as data to the shift register SHH, and the contents of SHH are changed to τ
, it moves according to a clock with a period of . With this configuration, the Pth bit of the shift register is delayed by Pτ, and a waveform fp with a period of Pτ is obtained. Also this f
By delaying p by a digital delay circuit D D p using a monostable multivibrator having a delay time of τ, /4, a signal g having a phase difference of 90' from fp as shown in FIG. 3 is obtained. By shaping this fpvg' with resonant filters F sp and F cp having a center frequency ω, esp+8cp is obtained.

Output fasLt of each bit of shift register SHH...
. . . Similarly, the digital delay circuit D
D. , DDo, ..., resonance filter Fs@,
Fs>...and F C11l FCl2...
. . . are provided, so that reference signals es, es, es, . . e east... is obtained.

Output h sc e of multiplier M s p * M c p
h cp is hip”: ay” esp = A(τ) sin(ωτ)◆5in(u(t-P τ4
)) A(τ) ” (cos(ω(P(τ, −τ, ) − 1)
= −cos(ω(2t−τ1−P(τ2+τ4))
] and hcp=apHep=A(t)sin(ωτ)・cos(ω(t−P τ4
)) φP = ω (P(τ, -τ2) - τ1) φP' = ω
(P(τ, +3) tenτ1)τ = oneτ1−Pτ2
= τ(1〉), in this h cp , h sp , A (t)
is the envelope component of the received waveform and is 5in(2ω1)+co
It has a sufficiently low frequency component compared to g(2ωt).

For this reason, a low-pass filter L s that reduces the 2ω frequency component
It is possible to separate and extract only the frequency components of p and L (A due to p). Such a filter output 11F(t)p
1 CP(t) is only the first term on the right side of hxp and hcp, respectively. These waveforms are connected to analog delay circuits DSp, D
Delayed by Cp. This D Sp.

D Cp has the same configuration and variable delay time (n-p
) τ, is the delay line. Here, τ5 is a value related to the delay time settings of the analog signal delay units DSP and DCP, and each channel delay time setting value is used in the example for simplicity when receiving a plane wave from an infinite distance. The delay time setting value for each element is given as (n-p) τ for element number p. Here, τ
6 is a set value, and an error of Δp occurs in actual operation. Therefore, the output of DSP and DCP j sp.

jcp becomes. These signals jliP+Jcp are added by adders Ss and Sc, each of which obtains the sum of n signals. The adder outputs ks and kc are each p=.

If we consider the case where a sound wave is incident from the target direction, τ2=τ and =τ5, so the signal becomes a large output. This signal is squared by squarers Ts and Tc, added by Sa, and square rooted by a squarer R to obtain an output signal C. With this configuration, the output C for the target direction signal is as follows, and the maximum output can be obtained regardless of the distance to the target object (irrespective of τ). On the other hand, for sound waves from directions other than the target, τ, - = Δτ5 - τ2 = Δ
' then n-1 ks"-ΣAct -c1+PΔ' nrs)IIc
os(ω(pΔ−τ,))2p=0.

(n-1) ks when ωΔ becomes 2π or more.

kc becomes a small value, resulting in a suppressed output. This will be explained regarding ks.

About KC The same is true.

Yes.

here (n-1) If ωΔ〉2π, then Corresponding to the change of p from 0 to n-1, ω p6 Δ changes from O to 2π.

Therefore, the value of COS (ω(p・Δ−τi)) changes by one cycle in response to the change in ωp・Δ, and the positive and negative values of ks, which is the result of adding all of these, are averaged. It will be a small value. Here, A(−τz+pΔ′pΔ′zpΔ×nΔ
z□=τ3(τ., and the reflected signal is obtained t=τ1
There is almost no change in the vicinity of the time when this(
n-1) The direction corresponding to 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 described above, with respect to changes in Δ and Δ', A (-τz+PΔl nτ5) does not change near the center of the reflected wave. Therefore, if this value is B, then the following equation is obtained.

Such a change in ks with respect to Δ is good. On the other hand, even in the conventional method, the bp in the 4th line of the 4th page
Using the equation (ω(−τ1+PΔ−nτ4)), the change with respect to Δ is the same as that in FIG.

Therefore, the azimuth resolution is also exactly the same.

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 τ, to τ2=O. On the other hand, the portions that delay the received signal components (D S p , D Cp shown in FIG. 2) have amplitude information, which makes the structure complicated, and it is difficult to improve the time accuracy. So, this DSP.

The delay time error of D Cp becomes a problem. If this delay time setting error is Δp, D for the set delay time pτ5 is
The actual delay time D E p of Sp and DCp is DEp=
(n p) τ, −Δp. For this reason, the formula (8
), the output from the delay means corresponding to (9) Jsp, j
cp becomes. Here, since the received signal strength with respect to the sound waves incident from the target direction is considered, the set delay amount τ5 is τ, -τ3 (=Δ')=O. Therefore, P'=-τ1+Δp−nτ.

The summed outputs ks and kc obtained by adding these are expressed as follows.The phase difference φP is φde=ω(p(τ4−τ2)−τ1), and since it is an object in the target direction, similarly τ咄−τ2 (=0) =O, and φde=−ωτ.

From the above formula. When such a delay time error Δp exists, the reception output C(t) for the target direction is:
ts). Here, for A (-τ1+Δp-nτ5), the reception start time is τ1-Δp+nτ, which is the time length. This is a rectangular pulse. Therefore, the receiving element p
Since the error Δp changes correspondingly, the reception time changes, and the sum of these changes, C(t), is obtained. It becomes longer, as shown in Figure 4. In other words, if n is large and Δ
Assuming that P is uniformly distributed, it changes as shown in FIG. As can be understood from this figure, by configuring the delay circuit DCP so that Δll+a≦−, it is possible to extract the target signal without reducing the maximum value.

On the other hand, in the conventional case, A (1) sin ((,1
t), and the addition output is as follows due to the error of Δp.

For this reason, To prevent addition output from decreasing teeth.

ωΔp(π is required, which is π 1. Here, this τ is usually much longer than the above-mentioned τ, so the delay time accuracy of DSp and DCp is similar to that of the delay circuit D L p in the conventional system. It will be much easier in comparison.

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 object in the target direction is expressed by Equation 12, % Equation %, 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 Figure 5, as shown in ωτ
Sensitivity fluctuations occur with a period of 6 in the sound wave propagation time, which has a relationship of 6=π. However, the distance interval Δr corresponding to this τ6 is given by assuming that the speed of sound in the propagation medium is Cs and the wavelength of the sound wave is human.

When a 2MHz sound wave is used underwater, Δr”0.19 (mm) (Cs: 1500m/s), and in the case of an object with a finite thickness made up of many reflection points, such minute sensitivity is Change is not a problem at all.

That is, if there is only one reflection point and the position is fixed at the zero point of Iksl shown in FIG. 5 (τ1 is fixed), the reflected signal will be lost. However, usually the object moves, such as a living body or underwater side, or the observation point moves, and the relative position changes. Therefore, even if the sound wave 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, it has many reflection points, so even if the object is fixed, some reflection point will always be amped, and the output on one side will be 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 Figure 2, it is also possible to use a receiving beam configuration method that uses only either ESP or ECP as a reference signal, and in this case, the configuration shown in Figure 2 will be approximately halved and the The device becomes simple.

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

For this reason, τ. If it is small compared to , it is possible to group 1sp (or 1ce) into a plurality of groups and then delay them as shown in FIG. In this way, Sa, S
Signals Qa and Qb added by an adder bt sC
, Qc are as shown in FIG. 6, and no decrease in amplitude appears at all. This Qa, Qb.

The seventh
Figure q&*qb+ (Ic is obtained, and by adding these three signals using an adder SS, it becomes possible to obtain the target signal output U without reducing the maximum amplitude.

The above is 4 signals (ls6-1s3 etc.) for easy explanation.
Although the system was explained by configuring one unit (GA, etc.) and three groups, it is clear that the system is not limited to this configuration and that arbitrary division is possible as long as the maximum amplitude of U does not decrease. be. 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.

[Problem to be solved by the invention]

In the above-described received acoustic beam combining method, the requirement regarding the accuracy of the delay circuit is relaxed by delaying the low frequency component obtained by multiplying the received signal and the reference signal. 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.

Furthermore, although it was omitted in the explanation of Figures 2 and 6, as time elapses from the time of transmission, the reflected sound waves from the reflection point initially come from a short distance, and then gradually the reflected sound waves from a far distance. By gradually decreasing the curvature of the delay time distribution for phasing the received signal as the signal reaches the receiving element, reflected signals present at any distance are always received with the same phase. It is possible to do so. In order to use analog delay numbers as shown in Figure 1 or Figure 6 when adopting such a reception method, each delay line must have a large number of intermediate taps, and It becomes necessary to switch the taps at high speed during the reception period after one wave transmission.

SUMMARY OF THE INVENTION Therefore, it is an object of the present invention to provide a wave receiving apparatus that can accurately and easily sequentially switch the delay time distribution even when receiving waves whose phases are always matched after the time of wave transmission.

[Summary of the invention]

Rather than delaying the waveform of the received signal itself, the present invention discretely samples and holds the received signals of multiple channels, and adds the held received signals of the multiple channels to create a desired delay time distribution. The feature is that the configuration is controlled so that the curvature corresponding to the delay time becomes smaller as time elapses after the wave is transmitted.

[Effect]

[Embodiment] FIG. 9 shows the configuration of an embodiment of the present invention. This example is the sixth
In place of the analog delay numbers DSa, DSb=DSc and the adder SS shown in the figure, the adders Sa, Sb
It is connected to the output of sC. However, Sa,
A similar configuration can be used when aligning 1sPyLsc in FIG. 2 instead of aligning outputs n&, Qb, and Qc of Sb and Sc.

FIG. 9 will be explained with reference to FIG.

As shown in FIG. 8, the signals Qa, Qb, Qc(i
It is assumed that a configuration in which alignment is performed for sp and icp is obtained (although it is also possible to consider a configuration in the same way, but this is omitted). The same part of these signals (different times) Q&0. flb
l+ QCz to multiplexer M X a, b
1c and applied to the same adder MA.

Similarly, MA the Q &2 * Q lsi y Q C2
, and sequentially apply a specific portion of the signal to MA by each adder. Next Q as t Q J?
MA again with Q C4.

and repeat this operation. When such processing is performed, the outputs of the adders MA, .about.MA become V1.about.V7, respectively, and the same portions of the signals are each sampled and extracted separately. Such an adder output v, “” v−
, is integrated by an integrator IT, ~7 for a finite time τs (time for obtaining Qa-Qb-Qc).

This integrator can be reset immediately after outputting to the Qc component Q.

The outputs of such integrators are ω, ˜ω, respectively, and the final values of the integrals are almost the same as the amplitudes added after time-aligning Qa, Qb, and Qc, respectively. In other words, 1211 which is sequentially sampled by multiplexers M X a , M X b , M X c and appears at the output of adder MA1
? Although the appearance times of the signals of each channel of Qb=Qc are different from each other, the values are sequentially held in the integrator and added together, so that a delay distribution is realized. Immediately before resetting such an integration result, output multiplexer M
When read out sequentially by PX, the seventh
A waveform almost the same as that in Figure U is obtained, meaning that an envelope delay circuit has been equivalently 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. The control signals for controlling the signal selection and integral reset described here are created by Cx and CY shown in FIG. Among these, if the control signal that controls the timing of sequential selection of multiplexers M If this curvature is further reduced over time, it becomes possible to receive reflected sound waves that are always in phase from objects close to objects and objects far away. on the other hand.

As in this embodiment, when performing phase processing on each received signal by multiplying it with a reference signal, it is necessary to give the above-mentioned curvature delay time that changes with time to this reference signal as well. . Therefore, instead of the circuit in Figure 3,
Use the circuit shown in the figure.

Delay circuits DV, DV2. ...DVp,
・・・・・・ is a delay circuit that can control the delay time, and the configuration of Vp like this can be easily realized by using a normal monostable multivibrator whose output pulse width can be changed depending on the voltage. be done. Furthermore, the reference signal e
Considering that sp, e cp are sinusoidal waves, it is clear that the reference signal having such a quadratic curvature can be replaced by a monocylindrical phase shifter configured for only a single frequency.

[Effects of the Invention] As described above, according to the present invention, delay is realized by holding discrete values of received signals of multiple channels, so any pattern of delay distribution can be easily realized by time alignment using a digital clock. It is possible to easily perform phase-aligned reception from short distances to long distances due to the delay distribution of curvature that changes over time.

[Brief explanation of drawings]

FIGS. 1(i) and (it) are explanatory diagrams showing the time relationship between the transmitted waveform and the receiver output, and (iii), (t
v). (V) is an explanatory diagram of the operation of the conventional method, FIG. 2 is a configuration diagram of the method that is the premise of the present invention, FIG. 3 is an example configuration diagram of the reference signal generation section used in the method of FIG. 2, and FIG. A diagram showing the influence of errors in the delay circuit section on the output waveform, FIG. 5 is a diagram showing sensitivity changes with respect to distance when configured with one type of reference signal, and FIG. 6 is a diagram showing a configuration that simplifies the delay circuit section. 7 is a diagram showing the output according to the configuration shown in FIG. 6, FIG. 8 is a diagram showing the time relationship when the delay circuit section is configured according to FIG. 9, and FIG. 9 is a diagram showing the output according to the embodiment of the present invention. The circuit diagram, FIG. 10, is a diagram showing an additional circuit for maintaining focus at close range. Day 2 Kuni 2nd ρ Day 1 → 1r-7th wheel 4th figure 27:-→ Ya”Otsu~/”\-1-τ J! . No. 1

Claims (1)

[Claims] 1. In a receiving device that delays and adds received signals of multiple channels obtained from a plurality of arrayed receiving elements, thereby synthesizing a received sound wave beam that matches the reflected waves from a predetermined direction or position. , a sampling phasing means for sequentially holding discrete values obtained by sampling each of the received signals of the plurality of channels to give a desired delay, and adding these values between the channels; A wave receiving device comprising means for sequentially changing the curvature of the delay realized by the phase means to a curvature that is inversely proportional to time.