JP2552475B2 - Phased Array Sonar - Google Patents

Description

TECHNICAL FIELD The present invention relates to a short-distance phased array sonar for medical use, industrial use, hydrosphere use, etc. An improved phased array sonar.

(Prior Art) A phased array sonar gives a delay distribution in the form of a linear function to each of a large number of transducer elements so that the ultrasonic wave to be transmitted has a uniform wavefront at a specific azimuth angle. To have directivity, and to perform electronic scanning by electrically or electronically oscillating the beam, and to improve azimuth resolution by an electronic focusing technique that narrows the beam by giving a quadratic function-like delay distribution. The ultrasonic beam is transmitted and received.

(Problems to be Solved by the Invention) Conventionally, in this type of sonar, the same transducer element is used for transmitting and receiving waves. Therefore, it was thought that the wave could not be received during transmission. As described above, since the same transducer element is commonly used for transmitting and receiving waves, it is unavoidable that the individual elements cannot receive waves when transmitting. Further, even if the transmission / reception changeover switch or the limiter of the input part of the reception amplifier operates to suppress the shunt of the transmission pulse to the reception beamformer, even if a very small amount of the transmission energy leaks to the reception amplifier side,
The energy is much stronger than the echo received at the time when the ultrasonic pulse is transmitted, that is, the echo from the farthest echo source by the transmission pulse immediately before this transmission pulse, The reality was that the echo was erased. Now, assuming that the repetition frequency of the ultrasonic pulse (hereinafter referred to as PRF) is f _R and the speed of sound is c, a dead sensitivity band occurs near the distance from the ultrasonic probe corresponding to d in the following equation.

d = c / (2f _R ) ... (1) On the contrary, there is a restriction on the PRF that can be applied to search for an echo from an echo source at a certain distance, and it cannot be freely selected. Inviting results. This is the most important reason for restricting the degree of freedom of PRF that can be taken, especially for the high repetition frequency method with a high PRF (hereinafter referred to as HPRF method).

The present invention has been made in view of the above points, and an object thereof is to realize a phased array sonar that can substantially receive a wave even during transmission.

(Means for Solving the Problems) The present invention which solves the above problems has a transducer array composed of a plurality of transducer elements, and electronically controls an ultrasonic beam to provide a medium. In a short-distance phased array sonar that irradiates and receives a reflected wave by the same transducer element, a transmission signal of a transmission circuit associated with each of the constituent transducer elements is processed to a reception circuit connected to the transmission circuit. It is characterized by comprising: a receiving circuit cutoff means for preventing a transmission signal from entering from the transmission circuit; and a means for introducing a part of the transmission signal into the reception circuit cutoff means.

(Function) A part of the transmission signal from the transmission circuit that accompanies each transducer element that constitutes the transducer array is introduced into the reception circuit, and the transmission signal responds at a high speed to input to the reception circuit. The circuit is grounded or disconnected to cut off the input signal to the receiving circuit only during a limited period of the transmitted signal.

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

FIG. 1 is a circuit diagram showing only one channel of a phased array sonar having a multi-channel transducer array according to an embodiment of the present invention. The other channels are exactly the same,
Only one channel will be described. In the figure, reference numeral 1 is a transmission beamformer that produces a time distribution by giving a predetermined delay amount to an input trigger signal in order to supply each constituent transducer element. Reference numeral 2 denotes a wave transmission pulse oscillator that generates a high frequency pulse signal or a high frequency burst signal in response to the output trigger signal of the wave transmission beamformer 1. The output signal is power-amplified by the wave transmission driver 3. Reference numeral ₄ is a switch circuit in which high-voltage operating diodes D ₁ and D ₂ connected in series in the same direction and high-voltage operating diodes D ₃ and D ₄ connected in series in the same direction are connected in antiparallel. Passes through the switch circuit 4, is input to the transducer element 6 via the cable 5, is converted into ultrasonic pulses, and is transmitted. The echo signal from the reflecting object is converted into an electric signal by the transducer element 6, and is input to the receiving amplifier 7 via the capacitor C ₁ and the coil L. The capacitor C ₁ , the coil L, and the capacitor C ₂ combine the distributed capacitance of the cable 5 and the electrostatic capacitance of the transducer element 6 to make π for impedance matching between the transducer element 6 and the receiving amplifier 7.
It forms an impedance match circuit. The circuit composed of the capacitor C ₁ , the coil L and the capacitor C ₂ serves to delay the input reception signal by about half a wavelength. A resistor R ₁ connected in parallel with the capacitor C ₂ is a resistor for lowering the Q of the impedance matching circuit to flatten the frequency characteristic of the circuit, and also serves as a direct current return circuit.

C ₃ and C ₄ are capacitors that divide a part of the input signal of the transmission signal from the switch circuit 4. 8 is a high-frequency transformer whose primary winding to the capacitor C ₄ is connected in parallel, 2 and winding of the midpoint is grounded, a diode D _5, D ₆ at both ends of the secondary winding A double wave rectification circuit 9 is connected. Further, the capacitor C ₅ and the resistor R ₂ connected in parallel are connected between the output end of the double wave rectification circuit 9 and the ground.

Q ₁ is an n-channel enhancement type MOS FET in which the output terminal of the double-wave rectification circuit 9 is connected to the gate, the input terminal of the receiving amplifier 7 is connected to the drain, and the source is grounded. C ₆ is a coupling capacitor for connecting the output signal of the receiving amplifier 7 to the next stage, which cuts the DC voltage and outputs only the high frequency signal. Q ₂ is normally a p-channel depletion type JFET in which the drain is connected to the capacitor C ₆ , the source is connected to the buffer amplifier 10 in the next stage, and the gate is connected to the full-wave rectification circuit 9 and is normally turned on. Reference numeral 11 is a receiving beamformer for phasing and adding signals from multi-channel transducer elements.

Next, the operation of the circuit configured as described above will be described. The transmission pulse oscillator 2 is excited by the trigger signal delayed by a predetermined delay in the transmission beamformer 1 to output a high frequency pulse signal. This output signal is power-amplified by the wave transmission driver 3 and passes through the switch circuit 4. Since the diodes D ₁ and D ₂ of the switch circuit 4 pass the signal on the positive side of the high frequency signal and the diodes D ₃ and D ₄ pass the signal on the negative side of the high frequency signal, the transmission signal can completely pass. However, the diodes D _{1 to} D ₄ do not operate with the received signal and do not input the received signal to the wave transmission driver 3. The high frequency pulse signal that has passed through the switch circuit 4 drives the transducer element 6 through the cable 5 to be converted into an ultrasonic signal and transmitted. The echo signal from the reflecting object is received by the transducer element 6 and converted into an electric signal,
The cable 5 travels in the opposite direction and is input to the receiving unit. The transducer element 6 and the transmission amplifier 7 are impedance-matched by the impedance matching circuit,
Further, since the impedance match circuit has the Q of the circuit dropped by the resistor R ₁ , the received signal is input to the receiving amplifier 7 in a state with little loss and little waveform distortion. This signal passes through JFET Q ₂ , is amplified by buffer amplifier 10, and is subjected to phasing addition with the signals of other channels by reception beamformer 11 and output.

On the other hand, when the transmission pulse signal is output from the switch circuit 4, a part of the output signal is divided by the voltage dividing circuit by the capacitors C ₃ and C ₄ , and the signal level becomes a fraction of the transmission pulse. Is input to the high frequency transformer 8 and the both-wave rectification circuit 9
It is rectified by and is charged in the capacitor C ₅ . This DC voltage is input to the gate of MOS FET Q ₁ , so
The drain and source of Q ₁ are electrically connected and the input side of the receiving amplifier 7 is grounded, and the input signal to the receiving amplifier 7 is set to zero.
The output voltage of the double-wave rectifier circuit 9 is input to the gate of the JFET Q ₂ , and the normally-on JFET Q ₂ is turned off to disconnect the input circuit to the buffer amplifier 10. in this case,
The transmission signal that proceeds to the receiving amplifier 7 via the capacitor C ₁ is delayed by about half a wavelength by the circuit composed of the capacitor C ₁ , the coil L, and the capacitor C ₂ , so that the MOS FET Q ₁ , J
Since the signal arrives after the operation of the FET Q ₂ , the transmission signal will not be input to the reception amplifier 7. The time constant due to the capacitor C ₅ and the resistor R ₂ is very small, which is 0 for normal equipment.
It is selected to be about 5 μS. Therefore, both MOS FET Q ₁ which is a shunt switch and JFET Q ₂ which is a series switch return from the operating state to the normal state within the time about the above time constant from the end of the transmission pulse, so very shortly after transmission. The reception signal can be received. Even if the received signal enters the double-wave rectification circuit 9, the signal is weak, so MOS FET Q ₁ and JFET
The switch circuit by Q ₂ does not work.

Since each channel is signal-processed in this way, when the azimuth angle of the ultrasonic beam is other than the front, the transmission signals from each transducer element are transmitted with different delay times, and the receiving circuit The dead time of each is also different, and because this dead time is extremely short, there are few receiving circuits that cannot receive even when the ultrasonic beam is transmitted. It is also possible to receive an echo signal that has arrived while some of the transducer elements of the antenna are transmitting. FIG. 2 is an explanatory diagram showing the state of transmission and reception of waves from the transducer array. In the figure, 14 is a transducer array composed of multi-channel transducer elements, which transmits a transmission beam 15. Reference numeral 16 is an echo signal generated by the previous transmission beam, which is traveling toward the transducer array 14. Figures (a) to (d) show the transmitted beam 15 and the echo signal 16 with the passage of time.
Shows the change in the relationship position. (B) In the figure, 17
Is a portion of the transducer element where the transmitted beam 15 and the echo signal 16 overlap at the end of the transducer array 14 and the echo signal in that portion cannot be received. Even at this time, the other portions do not overlap with each other on the transducer elements and can be received by the transducer array 14.

In order to prevent that the ultrasonic beam irradiation direction is in front of the ultrasonic probe and the transmission time of all transducer elements is almost the same and the channel for receiving waves cannot be taken, it is necessary to vibrate. A transducer array such as a curved surface array or a conformal array in which the child elements 6 are not aligned in a plane may be used. An example of this transducer array is shown in FIG. Figure (a) is an example of transducer elements arranged in a convex shape, and (b) is a single triangular roof shape.
(C) The figure shows an example of a double triangular roof. If the thickness of the transducer array is about twice or more the thickness of the transmitted pulse in water, the transmission time will not be aligned and the purpose will be achieved.

As described in detail above, according to the circuit of this embodiment,
From the viewpoint of the transducer array, it is always possible to receive even if there is a state that the transceiver circuit belonging to each transducer element cannot receive except when the azimuth angle of the ultrasonic beam is in front. You can now receive regardless of. Further, by properly selecting the arrangement of the transducer elements, it becomes possible to always receive the ultrasonic beam regardless of the azimuth angle of the ultrasonic beam.

In continuous wave Doppler in order to avoid the folding phenomenon of the high speed moving object caused by the pulse Doppler method in the ultrasonic Doppler device, it is difficult to transmit and receive at the same time. UHPRF method and quasi-continuous wave Doppler method (below)
QCW method) has come to be used. For example Q
Explaining the CW method, transmission is performed at the timing shown in FIG. In the figure, 20 is the time when the transducer array is transmitting ultrasonic waves, and 21 is the time when the echo signals are being received. In this method, since the transducer element is used for both transmission and reception, the transducer element cannot be transmitted in the receiving state, and a dead sensitivity band is generated. FIG. 5 is a diagram showing the rate at which echo signals are discarded and the dead zone in the QCW method. This figure shows the signal discard rate and the dead sensitivity band with respect to the distance from the transmission point when the duty ratio is 50% transmission and 50% reception. In the figure, 22 is a dead sensitivity zone, which is a point from which it is not possible to obtain an echo signal appearing at each distance shown by the equation (1) from the transmitting point. Also in this case, if the device of the present embodiment is used, since there is a transducer element that always receives the echo signal from the dead sensitivity band 22, there is no clear dead sensitivity band 22 as shown in FIG. Cease to exist.

The present invention is not limited to the above embodiment,
The series switch circuit by JFET Q ₂ is not always necessary and may be omitted. Further, other switching elements may be used without using the FET. Furthermore, it does not matter even if the switch circuit itself uses a different type.

(Effects of the Invention) As described in detail above, according to the present invention, by shutting off the input signal to the receiving circuit for each transducer element only during transmission and for an extremely short time thereafter, Along with the improvement of the arrangement method, it is possible to realize a phased array sonar that does not have a dead zone and can be always received as a transducer array, and the practical effect is great.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing only one channel according to an embodiment of the present invention, FIG. 2 is an explanatory diagram showing a state of transmission and reception of waves from a transducer array, and FIG. 3 is for eliminating an azimuth angle of death sensitivity. FIG. 4 is a diagram showing an arrangement example of transducer elements of FIG. 4, FIG. 4 is a diagram showing transmission / reception timing of the QCW method, and FIG. 5 is a diagram showing a discard rate and a dead sensitivity band of an echo signal in the QCW method. 1 ... Transmission beam former 2 ... Transmission pulse oscillator, 3 ... Transmission driver 4 ... Switch circuit, 5 ... Cable 6 ... Resonator element, 7 ... Reception amplifier 8 ... High frequency transformer, 9 …… Both-wave rectifier circuit 10 …… Buffer amplifier 11 …… Receiving beamformer Q ₁ …… n-channel enhancement type MOS FET Q ₂ …… p-channel depletion type JFET

Claims (2)

(57) [Claims] 1. A short distance having an oscillator array composed of a plurality of oscillator elements, electronically controlling an ultrasonic beam to irradiate a medium, and receiving a reflected wave by the same oscillator element. In a phased array sonar for a receiver, a receiver circuit is cut off to process a transmitter signal of a transmitter circuit associated with each constituent transducer element and prevent a transmitter signal from entering the receiver circuit connected to the transmitter circuit. Means and
A means for introducing a part of the transmitted signal into the receiving circuit cutoff means, the phased array sonar. 2. The phased array sonar according to claim 1, wherein the vibrator array is formed by arranging the vibrator elements in a curved shape.