JPH0330087Y2 - - Google Patents

Description

[Detailed description of the invention] (Field of industrial application) The present invention is an ultrasonic probe that uses a coaxial cable as a transmission line for transmitting and receiving signals between a transmitting/receiving circuit and an ultrasonic transducer. Regarding.

(Prior art) Ultrasonic diagnostic equipment is a device that transmits ultrasound pulses into a subject and performs diagnosis by detecting the reflected waves of the transmitted ultrasound pulses that are reflected within the subject. . FIG. 4 is a circuit diagram showing an example of a wave transmitting/receiving circuit of a conventional ultrasonic diagnostic apparatus. In the figure, reference numeral 1 denotes a pulse generation circuit that generates pulses for transmitting ultrasonic pulses to the subject. This output pulse is amplified by the wave transmission driver 2, transmitted by the cable 3, and supplied to the ultrasonic transducer 4. This cable 3 is usually composed of a coaxial cable.
The ultrasonic transducer 4 is excited by the pulse, and transmits the generated ultrasonic pulse to a subject (not shown). This transmitted ultrasonic pulse is reflected at various parts within the subject. The reflected wave is detected by the ultrasonic transducer 4, converted into an electrical signal, and sent to the receiving circuit 5 via the cable 3 again.

Without considering the impedance of the ultrasonic transducer 4, for example, one 75Ω series (e.g. 1.5C-2V) or 50Ω series (e.g. 1.5D-2V) coaxial cable is connected to the ultrasonic transducer 4 in this cable 3. It was connected.

(Problem to be solved by the invention) When the area of the ultrasonic transducer 4 is large or the frequency is high, the impedance within the driving frequency band of the ultrasonic transducer 4 will be higher than that of the coaxial cable used. It is often much lower than the characteristic impedance. Therefore, the transmission signal that drives the ultrasonic transducer 4 suffers loss due to reflection at the connection with the coaxial cable, and the effective transmission waveform applied to both ends of the ultrasonic transducer 4 becomes small. or,
The mismatch between the coaxial cable 3 and the ultrasonic transducer 4 may distort the transmitted waveform. Therefore, the ultrasonic probe has a long pulse width and poor sensitivity.

The present invention was developed in view of the above-mentioned problems.The purpose of this invention is to solve the problem when the impedance of the connected ultrasonic transducer is low in a transmission line consisting of a coaxial cable that supplies a transmitted signal to an ultrasonic transducer. Another object of the present invention is to realize an ultrasonic probe whose characteristic impedance can always be approximately equal to the impedance of an ultrasonic transducer at a low cost and without impairing the flexibility of a transmission line.

(Means for solving the problem) The present invention to solve the above problem uses coaxial cables as each transmission line for transmitting and receiving wave signals between the wave transmitting/receiving circuit and each ultrasonic transducer. In the ultrasonic probe used, a plurality of coaxial cables are connected in parallel by connecting the center conductors and outer conductors of each end of the plurality of coaxial cables, and the plurality of coaxial cables are connected in parallel as each of the transmission lines, and The plurality of coaxial cables constituting each of the transmission lines are arranged such that the composite characteristic impedance of the plurality of coaxial cables constituting each of the transmission lines is approximately equal to the impedance of the ultrasonic transducer to which the plurality of coaxial cables are connected. The feature is that the number of pieces is selected.

(Function) Since multiple coaxial cables with high characteristic impedance are connected in parallel and matched with the impedance of the ultrasonic transducer, good signal transmission is achieved without loss or waveform distortion due to impedance mismatch.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of the present invention. In the figure, the same parts as in FIG. 4 are designated by the same reference numerals. In the figure, 4 is an ultrasonic transducer with an impedance of 10Ω near the center frequency, 10 is an ultrasonic transducer with five coaxial cables with a characteristic impedance of 50Ω, whose center conductors are connected to terminal R of ultrasonic transducer 4, and five external A group of coaxial cables whose conductors are connected to the ground terminal S of the ultrasonic transducer 4, and the coaxial connector 11 to which the opposite end is connected receives the transmitting signal from the transmitting driver 2, and also receives the transmitting signal from the receiving circuit. The received signal is supplied to 5.

Next, the operation of the circuit configured as described above will be explained. The transmission signal from the transmission/reception driver 2 is inputted to terminals R and S of the ultrasonic transducer 4 via a coaxial connector 11 and a coaxial cable group 10. The impedance of the ultrasonic transducer 4 is 10Ω, and the composite characteristic impedance Z ₀ of the coaxial cable group 10 is Z ₀ =Z _C /5=50/5=10Ω.

Here, Z _C is the characteristic impedance of each coaxial cable. Therefore, since the impedances of the coaxial cable group 10, which is a transmission body, and the ultrasonic transducer 4, which is a load, are matched, there is no loss due to reflection or waveform distortion. Transmission is performed from the coaxial cable group 10 to the ultrasonic transducer 4.

When N coaxial cables with characteristic impedance Z _C are connected in parallel, the composite characteristic impedance Z ₀ is
It will be explained that Z ₀ =Z _C /N. FIG. 2 is an explanatory diagram for determining the input impedance when N cables are connected in parallel and terminated at Z _C /N. In the figure, R and S are input side terminals, P and Q are output side terminals, and N coaxial cables are connected to the R terminal.
Connect the center conductors of W ₁ , W ₂ ...W _N , and connect the outer conductors of coaxial cables W ₁ , W ₂ ... W _N to the S terminal. Further, the inner conductor at the other end of the coaxial cable is connected to the P terminal, and the outer conductor to the Q terminal. P,Q
Assume that a load with an impedance of Z _C /N is connected to the terminal.

In this circuit, the input voltage is _VT , the input current is _iT , and the currents flowing into the cables _W1 , _W2 ... _WN are _i1 , _i2 ... _iN . Also, let the currents of each coaxial cable flowing into the load be I ₁ , I ₂ ... _IN , the total current I _L and the terminal current V _L. R of this circuit,
Find the impedance Z _N seen from the S terminal.

(1) First, find the impedance of a single cable. FIG. 3 is an explanatory diagram for determining the input impedance when a single cable is terminated with a characteristic impedance. In the figure, find the impedance Z _i seen from the input end when a load with characteristic impedance Z _C is connected. Let the input voltage and current be v and i, and the output voltage and current be _vL and _iL .
When the coaxial cable W is represented by an F matrix and the four-terminal constants are A, B, C, and D, the following equation holds for the transmission system shown in FIG.

v i=AB CD・v _L i _L ...(1) From equation (1), V/i=A・(v _L /i _L )+B/C・(v _L /i _L )+D...
...(2) Since the terminal impedance is equal to the characteristic impedance Z _c of the coaxial cable W ₁ , v _L /i _L = Z _C v/i = Z _C ... (3) Substitute equation (3) into equation (2) Then, Z _C =AZ _C +B/CZ _C +D...(4).

(2) Next, consider the transmission system shown in Figure 2.

W ₁ ; v _T i ₁ = AB CD・v _L I ₁ W ₂ ; v _T i ₂ = AB CD・v _L i ₂ W _N ; v _T i _N = AB CD・v _{L I} NAbove W ₁ , W ₂ ... Add the voltage formula of W _N to find V _T.

NV _T =N・A・V _L +B(I ₁ +I ₂ +……+I _N ) I ₁ +I ₂ +……+I _N =I _L , so NV _T =N・A・V _L +B・I _L ∴V _T = A・V _L・(1/N) B・I _L ...(5) Next, add the current formula to find i _T.

i ₁ +i ₂ +...+i _N =N・C・V _L +D(I ₁ +I ₂ +...+I _N ) i ₁ +i ₂ +...+i _N = i _T , so i _T =N・C・V _L +D・I _L ...(6) Find the input impedance Z _N from equations (5) and (6).

Z _N =V _T /i _T =A・V _L +1/N・B・I _L /N・CV _L +D
・I _L =A・V _L /I _L +1/N・B/N・C・V _L /I _L +
From D V _L /I _L =Z _C /N to Z _N =V _T /i _T =A・ZC/N+1/N・B/N・C・
Z _C /N+D = 1/N・AZ _C +B/CZ _C +D (4) From equation (7)... (7) Z _N = Z _C /N From the above, the input impedance including the load is equal to the load impedance. It was proved that the composite characteristic impedance Z ₀ of the cables W ₁ , W ₂ . . . W _N is Z ₀ =Z _C /N.

As explained above, when coaxial cables having the same characteristic impedance are connected in parallel, it can be seen that the composite characteristic impedance is the value obtained by dividing the characteristic impedance of each cable by the number of cables. Therefore,
As described above, when using a coaxial cable with a high characteristic impedance for a load with a low impedance, the coaxial cables may be connected in parallel until their impedances become approximately equal. It is convenient to handle these cables by putting them together in a sheath so that they appear to be one cable.

If you try to obtain a coaxial cable with an arbitrarily low characteristic impedance, it will be custom-made and will be expensive. Also, if you make a coaxial cable with a low characteristic impedance by increasing the withstand voltage of the coaxial cable to around 1000V, the internal conductor will be extremely thick, and the internal insulator must also be thick, resulting in a coaxial cable with poor flexibility. . However, according to the embodiment of the present invention, the characteristic impedance of each coaxial cable is easy to manufacture, so it is inexpensive, and the impedance of the coaxial cable used can be high, so the internal conductor can be made thinner. In the end, the amount of copper used is much smaller, so even if multiple cables are connected in parallel, there is play between the individual cables, and a flexible cable can be obtained. Also, this method is lighter and easier to handle.

In order to prevent differential mode from occurring between individual coaxial cables connected in parallel, common mode traps such as ferrite beads may be separately inserted as shown in FIG. In Figure 5, the first
The same parts as in the figure are given the same reference numerals. In the figure,
12 is a common mode trap made of ferrite beads. It is best to insert it at both ends of the cable like this. It is very effective to insert it at both ends as shown in the figure, but it is also effective if it is inserted only at one side.

(Effects of the invention) As explained in detail above, according to the invention, the characteristic impedance of the transmission line can be easily matched to the impedance of the ultrasonic transducer, enabling efficient power transfer and reception, and the waveform An ultrasonic probe that can eliminate distortion can be realized at low cost without impairing the flexibility of the transmission line.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of an embodiment of the present invention;
The figure is an explanatory diagram for calculating the impedance of multiple coaxial cables connected in parallel, Figure 3 is an explanatory diagram for calculating the impedance of a single coaxial cable, and Figure 4 is an explanation of transmission using conventional coaxial cables. Fig. 5 shows the case where a common mode trap is used. 1... Pulse generation circuit, 2... Wave transmission driver,
3... Cable, 4... Ultrasonic transducer, 5... Receiving circuit, 10... Coaxial cable group, 11... Coaxial connector, 12... Common mode trap.

Claims (1)

[Scope of utility model registration request] In an ultrasonic probe that uses coaxial cables as each transmission line for transmitting and receiving signals between the transmitting/receiving circuit and each ultrasonic transducer, the center conductors at each end of the plurality of coaxial cables and A plurality of coaxial cables connected in parallel by connecting external conductors to each other is used as each transmission line, and the composite characteristic impedance of the plurality of coaxial cables constituting each transmission line is the same as that of the plurality of coaxial cables. An ultrasonic probe characterized in that the number of the plurality of coaxial cables constituting each transmission line is selected so that the impedance of the ultrasonic transducer is substantially equal to the impedance of the ultrasonic transducer to which it is connected.