JPS6348319B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a velocity measuring device that utilizes the Doppler effect, and particularly to a transducer that transmits and receives ultrasonic signals.

Conventionally known speed measurement devices for ships that utilize the Doppler effect, known as Doppler sonar or Doppler log, measure the ultrasonic frequency emitted from a ship and the surface of the water on the bottom or underwater surface. The ship's speed is measured by the occurrence of a Doppler deviation corresponding to the ship's speed between the frequency of the ultrasonic signal that is received again after being scattered and reflected by a minute object.

In such conventional devices, the emission angle of the ultrasonic signal changes as the ship oscillates, resulting in measurement errors.
In order to reduce this error, for example, when measuring the forward and backward speed of a ship, ultrasonic signals are emitted at equal depression angles in the forward and aft directions, and the difference in Doppler deviation of each received signal is determined. A method called the "JANUS method" is used to reduce measurement errors. However, in this method, the transducer device is large because the transducer is used separately for the forward direction and the backward direction, and it is difficult to accurately match the depression angle of the ultrasonic beam in each direction. Therefore, there was a drawback that the above-mentioned error reduction could not be sufficiently achieved.

The present invention aims to eliminate such drawbacks, and uses a single transducer to emit and receive ultrasonic signals in opposite directions, such as forward and backward directions, thereby making it possible to reduce the size of the device. The purpose of this is to ensure that the respective radiation directions are exactly the same.

An embodiment of the present invention shown in the drawings will be explained in detail below.

FIG. 1 is a diagram showing the principle of a phase array type transducer, where 2 ₁ . . . 2 _o are elements, and θ is the beam combining direction. As shown in Figure 1, in a phase array type transducer in which n elements are arranged on a straight line with an interval d, if the excitation amplitudes of the elements are equal and the excitation phase difference between the elements is δ, then this transducer The directional characteristic R(θ) is expressed by the following (1), which is widely known.

R(θ)=｜1/n・Sin(nφ/2)/Sin(φ/2
)｜……(1) However, φ=2π/λd・sinθ−δ λ: Wavelength d: Element spacing δ: Phase difference Equation (1) above is φ=2πm (however, m=0, ±1,...)
Therefore, in order for a unique main lobe to occur in the range |θ|<π/2, the following condition of equation (2) must be satisfied.

d≦λ(1−δ/2π) (2) If the element spacing d does not satisfy equation (2), two main lobes symmetrical with respect to the normal direction will be generated. On the other hand, when formula (2) is satisfied, only one main lobe is generated, and its direction changes symmetrically with respect to the normal direction depending on the direction of the equal sign of the phase difference δ between the elements. Based on this principle, the present invention is devised so that the condition of equation (2) is not equivalently satisfied when transmitting waves using a single transducer, and two main transducers symmetrical with respect to the normal direction are used. By creating a lobe and conversely satisfying the condition of equation (2) equivalently during reception, and by changing the equal sign of the phase difference δ between the elements, the signals from the front and rear directions can be It is configured so that it can be received separately.

According to an embodiment of the present invention shown in FIG. 2, 1 is a transducer, 2 ₁ ...2 _o is an element, 3 and 4 are phase inverters, 5 and 6 are transducers, and 7 is a transmitter. ,
8 is a phase advancer, 9 is a phase lag, and 10 and 11
is an adder.

The elements 2 ₁ to 2 _o of the transducer 1 are connected to each other every fourth as shown in FIG. 2, and are grouped into four types from 1 phase to 4 phases.

During wave transmission, a signal generated by the transmitter 7 passes through the transmitter/receiver switchers 5 and 6 and drives the transmitter/receiver 1. At this time, the phase inverters 3 and 4
The phases of the phase and four-phase signals are inverted compared to the one-phase and two-phase signals, respectively. Therefore, the drive phase of elements 2 ₁ to 2 _o becomes as shown in Fig. 3. If the inter-element spacing d is selected to be λ/2, the equivalent element spacing will be λ, and the phase difference δ
is π, so from equations (1) and (2) above, the direction of the main lobe is 30 degrees with respect to the normal line, and two main lobes are generated symmetrically.

Next, regarding the operation during wave reception, first the transducer 1
One phase of the signals from the two-phase signal and the two-phase signals passed through the phase inverter 3 are added to the upper transmission/reception switch 5. Similarly, the three-phase signal and the four-phase signal are introduced through the phase inverter 4 to the upper transmission/reception switch 6. One of the signals passing through the transmitter/receiver switch 6 is advanced in phase by π/2 by a phase advancer 8, and then added to the signal that has passed through the transmitter/receiver switch 5 by an adder 10, resulting in a forward reception signal E. You can get _F.

The other of the signals passing through the transmitter/receiver switch 6 is delayed in phase by π/2 in a phase delayer 9, and then added to the signal that has passed through the transmitter/receiver switch 5 by an adder 11 to produce a backward reception signal. _EA can be obtained. Therefore, the phase relationship between elements 2 ₁ to 2 _o is
As shown in FIG. 4 for E _F , and as shown in FIG. 5 for backward received signal E _A. Therefore, from equations (1) and (2), the directions of the main lobe are +30 degrees and -30 degrees with respect to the normal direction, making it possible to receive signals in the respective target directions.

In the above embodiment description, the inter-element spacing d was selected to be λ/2 and the phase difference δ was selected to be π/2.
They can be arbitrarily selected within a range that satisfies the above formulas (1) and (2). Furthermore, it is also possible to omit the phase inverters 3 and 4 by incorporating them into the transducer 1 or by modifying the polarization direction of the element 2.

Similarly, it is also possible to apply a shading technique that changes the excitation amplitude of the element 2 and suppresses the sidelobe level. In addition, although the above embodiment described speed measurement in which the emission direction was only in the front-rear direction, it is also possible to emit ultrasonic signals in the left-right direction as well, and simultaneously measure velocity components not only in the front-rear direction but also in the left-right direction. It is possible.

As mentioned above, with a single transducer,
When transmitting waves, two ultrasonic beams with approximately equal depression angles are combined in opposite directions, for example, in the front-back direction,
Ultrasonic signals are simultaneously emitted in the front and rear directions, while beams are combined separately in the front and rear directions when receiving waves, making it possible to downsize the transducer device in speed measurement devices that utilize the Doppler effect.
Furthermore, since the depression angles of the ultrasonic beams accurately match in the front-rear direction, the effect of reducing the above-mentioned oscillation error due to the JANUS method is significant in practical terms.

[Brief explanation of the drawing]

Fig. 1 is a diagram for explaining the operating principle of a phase array type transducer, Fig. 2 is a block circuit diagram showing a device according to an embodiment of the present invention, and Fig. 3 is a diagram showing beam combination during wave transmission in the embodiment. The explanatory diagrams, FIG. 4 and FIG. 5, are diagrams for explaining beam synthesis during forward reception and backward reception in this embodiment, respectively. Explanation of symbols 1... Transducer/receiver, 2 ₁ - 2 _o ... Element, 3, 4... Phase inverter, 5, 6... Transmitter/receiver switch, 7... Transmitter, 8... Phase advancer, 9... Phase delay device, 10, 11... Adder.

Claims (1)

[Claims] 1 By a single phase array type transducer,
a device that combines two ultrasonic beams having substantially equal depression angles in at least front and rear opposite directions when transmitting waves, and simultaneously emits the combined beams in the opposite directions; A wave transmitting/receiving device in a speed measuring device using the Doppler effect, comprising a device that performs beam synthesis in each direction and receives a signal in one of the desired directions among the opposing directions. Device.