JPH0227630B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention comprises an array type converter and a mechanism that gives different delay times to the received signals from each element and adds them to each other (phasing and addition) for the purpose of forming a receiving beam. The present invention relates to an ultrasonic receiving device in which the element width is larger than the ultrasonic wavelength used.

In the directional characteristics of an element having the element width as described above, a zero point also exists in the front direction of the element. That is, when the element width is W and the ultrasonic wavelength is λ, the directivity characteristic A(θ) in a direction forming an angle θ with respect to the direction perpendicular to the element is expressed as follows.

A(θ)=sin ξ/ξ; ξ=(πW/λ) sin θ As an example, FIG. 1 shows A(θ) when W/λ=3. Not only do directivity zero points Z1, Z1', Z2, and Z2' appear in the front direction of the element EL, but also when the point at the center of the element is set as the phase origin, the directivity has a phase shift like A1 and A1'. A negative direction appears.
From the above equation, the orientation of the directivity zero points Z1 and Z1' is θ=±sin ^-1 (λ/W), and the direction of the next zero point Z
It can be seen that the orientation of 2, Z2' is θ=±2sin ^-1 (λ/W). FIG. 2 is a plot of the directivity of the elements with respect to one focal point F in the array direction for an array constructed of the elements shown in FIG. Regions such as G1 and G1' where the directivity of the elements is negative in terms of topology appear on the array.

As in the conventional method, for the purpose of forming a receiving beam, the delay time given to the received signal from each element is determined to compensate for the propagation time between the central point of each element and the focal point, and each received signal is encoded. When added together without consideration of G1 in Fig. 2,
When areas such as G1' and G1' are included in the aperture used,
When the focal point becomes closer or the aperture used is increased, a problem arises in that the imaging resolution and S/N ratio deteriorate.

In order to solve this problem, in the present invention, like the elements belonging to G1 and G1' in FIG. A received signal from an element whose phase is negative compared to element E ₀ is given a negative sign during phasing and addition, or is excluded from the addition.

An example of a phasing addition section in an embodiment of the present invention is shown in FIGS. 3 and 4. FIG. 3 shows an example of a configuration in which a received signal from a certain element is added with a plus or minus sign. The array type converter 10 is formed by arranging elements EL having a width W, for example. The signal lines of each element are connected to delay elements 1-1 and 1-, respectively.
2,..., 1-n. However, since it is sufficient to apply the same amount of delay to the received signals from the elements located at symmetrical positions with respect to the perpendicular line drawn from the focal point to the transducer, the signal lines from the elements at these symmetrical positions are connected in common. connected to each delay element. Each delay element consists of, for example, a delay line having a plurality of taps, and the amount of delay can be selected by selecting the taps. On the other hand, memory 11
has multiple (four types in this figure) focal lengths F ₁ ,
Corresponding to F ₂ , F ₃ , and F ₄ , the phase of data of the amount of delay given to the received signal of each channel to realize each focal position is stored. Actual data D ₁₁ , D ₁₂ ,…, D _1o , D ₂₁ , D ₂₂ ,…, D _2o ,
D ₃₁ , D ₃₂ , . . . , D _3o , D _{41 ,} D ₄₂ , . As time elapses from transmission, data corresponding to focal lengths F ₁ , F ₂ , F ₃ , and F ₄ are read out one after another from the memory 11, and the tap position of each delay element is sequentially changed according to the read data. be done. On the other hand, the received signals that have passed through the delay elements of each channel have their polarities inverted by inverters 2-1,..., 2-n, and one of the non-inverted delay element output and the inverted output is sent to the selector 3-
1,...3-n, respectively. memory 11
In addition to the delay amount data mentioned above, the directivity of each channel element corresponding to each focal position is stored as positive or negative phasewise with respect to the central element, for example, with a code of 0 or 1. This data is read out one after another at the same time as the delay amount data, thereby specifying the selection of each of the selectors 3-1, . . . , 3-n. The received signals of each channel selected by the selector are added by an adder. In this way, F ₁ ,
The focal length is changed to F ₂ , F ₃ , and F ₄ , which means dynamic focusing is achieved.
For each point, the received signals from the elements whose directivity is negative in terms of phase as described in FIG. 2 are added with their polarities reversed, so that the resolution of imaging is improved.

On the other hand, FIG. 4 shows an example in which received signals from elements whose directivity is negative in phase are excluded from signal addition. Each reference numeral indicates the same part as in FIG. However, the inputs of the selectors 3-1, ...3-n of each channel are the received signals from the delay elements 1-1, ...1-n and the ground potential, and the control flag read from the memory 11 is When it is "1", each selector selects the ground potential, and as the focal length is sequentially changed to F ₁ , F ₂ , F ₃ , and F ₄ , the directivity of each element at each focal point is correct. Only the received signals from the elements are added together by the adder 4 via the delay element.

FIG. 5 shows the effect of the present invention,
When the focal length is f and the aperture used is D, W/λ
This is the beam pattern of the receiving beam when =3.2, f/λ=117, and D/λ=205. The solid line BO is
This is a conventional beam pattern in which received signals from each element are added without considering the sign. The broken line B1 is the beam pattern when the received signal from the element whose directivity is negative in terms of phase is excluded from the phasing and addition, and the dashed line B2 is the beam pattern when the received signal is phased and added with a negative sign. This is the beam pattern when added.

The present invention is particularly effective in lowering the grating level, and compared to BO, the grating level is lowered by 3 dB in the case of B1 and by 5 dB in the case of B2.

As a general means to improve the resolution and S/N ratio of imaging, the dynamic focus method, that is,
A method is known in which the focal length is successively changed from a near receiving focus to a far receiving focus in response to the arrival time of the reflected sound waves during the receiving period of reflected sound waves for one ultrasound transmission. . In this method, the focus is switched each time the wave is transmitted and received, and there is no increase in imaging synchronization as in the general variable focus method, in which only the depth zone near the focal point is imaged each time. Therefore, the focus can be switched in multiple stages as long as the performance of the switching control mechanism allows, so there is no need to increase the depth of focus of each reception focus.
Therefore, in devices using the conventional dynamic focus method, a large receiving aperture is used for a near focus as it is for a long distance focus, and the signals of all elements within that aperture have a propagation time. Compensation was added. However, considering the directivity caused by the width W of the elements described above, it is necessary to add a negative sign or to change the elements to be excluded in the phasing addition depending on the focal length. As an example,
FIG. 6 shows the situation under the same conditions as FIGS. 1 and 2. G0, G2, G
2' is a region of elements to be added with a positive sign and subjected to phasing and addition, and G1 and G1' are regions of elements to be given a negative sign or excluded.

In phased addition, as a special case of a method in which addition processing is performed only on signals from elements having directivity with the same sign in phase as the central element, a series of elements including E ₀ among those elements, that is, the second In Figure and Figure 6
There is a method of performing addition processing only for GO. By doing so, the control mechanism for determining whether or not to exclude from the phasing addition can be simplified. If this method and the dynamic focus method are used together, the number of elements used will change with the focal length. FIG. 7 shows this situation in the same way as FIG. 6. This means that the aperture is variable depending on the imaging depth. However, while the conventional variable aperture method aims to obtain a short-range depth of focus during non-dynamic focus, the variable aperture method of the present invention
It is completely different in that it focuses on the directivity of elements, and is rather a method that should be used during dynamic focus.

In the explanation of FIGS. 3 and 4, an example was given of a method using a delay element as a method of giving different delay times to the received signal from each element for the purpose of forming a receiving beam, but instead of using a sampling element. A combination of and memory elements can be used. In this case, instead of using an inverter as shown in FIG. 3, it is also possible to shift the sampling time by half a cycle with respect to the ultrasound signal.

Mechanically divided adjacent n (≧2)
In some cases, signal processing is performed by electrically coupling two elements without delay time. in this case,
The element width in this description means the electrical element width, which is n times the mechanical element width.

As explained above, according to the present invention, when using an element whose element width is larger than the wavelength and using a relatively large receiving aperture, it is possible to reduce unnecessary responses in the receiving beam by a simple mechanism. It is possible and the effect is great.

[Brief explanation of drawings]

Fig. 1 is a diagram of the directional characteristics of the elements, Fig. 2 is a plot of the directional characteristics of the elements on the array with respect to one focal point, and Fig. 3 is an example of adding positive and negative signs to the received signals. FIG. 4 is a diagram showing an example of switching between addition and non-addition of received signals. FIG. 5 is a diagram showing an improvement of the receiving beam pattern. FIG. FIG. 7 is a diagram illustrating the variable aperture in dynamic focus.

Claims (1)

[Claims] 1. An array type converter consisting of a large number of arranged elements, a focus beam forming means that adds a delay time element to the signals received by the element group of the array type converter and adds them together, and a focus beam forming means added to each element. An ultrasonic receiving device comprising a dynamic focus type variable focus forming means that changes the delay time element amount according to the movement of the focus,
The width W of each of the elements is larger than the wavelength λ of the ultrasonic wave used, and the directivity of the focal position corresponds to the directivity of each element determined by W and λ. An ultrasonic receiving apparatus characterized by having means for selecting an element to be used according to movement of a focal point so that a received signal is excluded from the addition.