JPS6251434B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a parametric active sonar.

When sound waves of two frequencies are simultaneously transmitted to a sound field medium, the sound waves interact with each other due to the nonlinearity of the sound field medium, generating sum frequency and difference frequency components of the two frequencies. The difference frequency component at this time becomes a sound wave with extremely sharp directivity. A parametric active sonar is a sonar that actively utilizes this difference frequency component.

FIG. 1 is a block diagram of a conventional parametric active sonar. To explain this, in response to a synchronization trigger from a periodic circuit section 1, an oscillation/modulation circuit section 2 generates a signal having two frequency components. This signal is amplified by the transmitter 3 and radiated to the sound field medium via the transducer 4 as a sound wave. A sound wave having a difference frequency component generated due to the nonlinearity of the sound field medium is reflected by a foreign object 5 in the medium, and is received by a transducer 4. The signal that has been amplified, detected, or appropriately processed by the receiving section 6 is displayed on the recording display section 7 as the position of the foreign object 5, the strength of the echo, etc. An image can be displayed by moving the transducer 4.

In a conventional parametric active sonar, a transducer 4 having the same structure as used in a direct active sonar is used as the transducer 4. The direct active sonar referred to herein is a type of sonar that transmits a single frequency signal and receives an echo at that frequency.

Figures 2a and 2b show typical structural examples of the transducer 4 used in the conventional parametric active sonar described above. A cable 9 is connected to the electrodes, and the ceramic vibrator 8 is backed by a quilted rubber 10 and waterproofed by a molded rubber 11.

The resonant frequency of the transducer 4 having such a structure is determined by the thickness, and this resonant frequency is the same as the first one described above.
It is set near the transmission frequency of the sonar system shown in the figure. However, in the transducer 4 with the above structure,
Resonance due to the transverse effect of the plate-shaped ceramic vibrator 8 exists at a frequency lower than the transmission frequency. Therefore, the low frequency components of the electrical distortion of the transmitted signal in the sonar system shown in FIG.
The wave is transmitted at a strong level from the source, and the resulting echo is received by the transducer 4. This distortion component is not generated by the nonlinearity of the sound field medium, but is generated by the hardware of the oscillation/modulation circuit section 2, the transmitter section 3, and the transducer 4. It does not have a sharp directivity such as that caused by nonlinearity, that is, a parametric effect, but exhibits a wide directivity determined by the aperture area of the ceramic vibrator 8. However, in general, when trying to obtain information about the position or shape of an object, sharply directional sound waves are required. This is because information regarding the position and shape of objects smaller than the directivity, that is, the beam width, cannot be obtained. Therefore, with the conventional method, only images with extremely poor resolution, such as the one illustrated in the recording section 7 of FIG. 1, are displayed. Therefore, in conventional actep sonar, in which echoes due to electrical distortion components are received at the same time as difference frequency echoes due to parametric effects, in order to take advantage of the characteristics of a parametric active sonar, it is necessary to sufficiently suppress the electrically generated distortion. It is necessary to keep it.

The ratio of the sound pressure level generated by the parametric effect to the sound pressure level at the transmission frequency is called parametric gain, and its value is -80 dB.
It is as low as -40dB. On the other hand, the ratio of the transmitting sensitivity at the transmitting frequency of the transducer 4 with the structure shown in FIG.
When the frequency ratio is 10:1, it is approximately 40 dB or less. Therefore, when the parametric gain is -80 dB, the ratio between the low frequency sound pressure due to the parametric effect and the directly transmitted sound pressure of the intermodulation distortion component is 20 dB or less with an intermodulation distortion component of 0.1%. This is the factor that ultimately determines the signal-to-noise ratio of the received echo, and to improve the signal-to-noise ratio, it is necessary to further reduce the distortion rate. However, it is extremely difficult to reduce the distortion rate in the oscillation/modulation circuit section 2 and the transmitter section 3, which are electrical hardware, in a high-power system such as a parametric active sonar.

The present invention is characterized by the use of a wave transmitter using a diced ceramic vibrator and a cylindrical wave receiver having a reflector. The purpose of this method is to suppress unnecessary signals such as distortion components by using filter functions in transmitting and receiving sensitivities, improve the signal-to-noise ratio, and obtain high-resolution image information.

An embodiment of the present invention will be described below with reference to the drawings.
FIG. 3 is a block diagram showing one embodiment of the present invention, in which a signal having two frequency components is generated from the oscillation/modulation circuit section 13 in response to a synchronization trigger from the synchronization circuit section 12. In FIG. This signal is sent to the transmitter 14
The signal is amplified by the wave transmitter 15 and radiated to the sound field medium as a sound wave. A sound wave having a difference frequency component generated due to the nonlinearity of the sound field medium is reflected by a foreign object 16 in the medium, and is received by a wave receiver 17 . The signal that has been amplified, detected or subjected to appropriate signal processing by the receiving section 18 is sent to the recording display section 1.
9, the position of the foreign object 16, the strength of the echo, etc. are displayed. Then, by moving the wave transmitter 15 and the wave receiver 17, an image can be displayed.

FIGS. 4a and 4b show the structure of the transmitter 15 used in the present embodiment described above. To explain this, a cable 21 is connected to electrodes provided on both sides of the diced ceramic vibrator 20. The diced ceramic vibrator 20 is made of Kirk rubber 22.
The molded rubber 23 is waterproofed by mold rubber 23.

Here, the diced ceramic vibrator 20 is a piezoelectric element plate that is polarized in the thickness direction and has electrodes on both sides, and a part of the other side is attached at an interval equal to or less than the thickness of the plate from one side. A mesh-like cut is made so that it remains intact. This diced ceramic resonator 20 has the characteristic of being able to suppress low frequency resonance modes due to transverse effects, and therefore the wave transmitter of this embodiment incorporating the diced ceramic resonator 20 The transmission sensitivity frequency characteristics of 15 are as follows:
This means that there is no peak due to low frequency resonance.

The transmission frequency in this embodiment as a parametric active sonar is set near the resonant frequency of the transmitter 15. The ratio between the transmitting sensitivity at the transmitting frequency and the transmitting sensitivity at direct transmitting corresponding to the difference frequency is approximately when the frequency ratio is 10:1.
It is 60dB or more. Therefore, when the parametric gain is -80 dB, 0.1% cross-modulation distortion causes oscillation.
Even if generated by the modulation circuit section 13 and the transmitter section 14, the ratio between the difference frequency sound pressure due to the parametric effect and the direct transmission sound pressure of the cross-modulation distortion component is
It will be more than 40dB. This is the final result of the received echo.
This is a factor that determines the SN ratio, and the SN ratio improvement is 20 dB.
becomes. In this way, in this embodiment, since the transmitter 15 using the diced ceramic vibrator 24 is used, the S/N ratio is improved compared to the conventional one, and the improved S/N ratio allows high-resolution image information to be transmitted. can be obtained, and the detection distance will also be extended.

Figures 5a and 5b show the structure of the transmitter 17 in this embodiment. To explain this, the cylindrical ceramic vibrator 24 has electrodes on its inner and outer surfaces. Cable 25 is connected. This cylindrical ceramic vibrator 24 is waterproofed by molded rubber 26, and has directivity by a tapered reflector 27 provided on the outer periphery. The receiver 17 having such a structure has a receiving sensitivity frequency characteristic that is flat from a certain frequency determined by the structure of the reflector 27 to the resonance frequency, and decreases by approximately 24 dB/octave at higher frequencies. At this time, the level of the echo received by the receiver 17 at the transmission frequency from the transmitter 15 is approximately 60 dB lower than when the conventional transmitter/receiver 4 is installed. Therefore, overloading of the receiving section 18 due to echoes at the transmission frequency from the transmitter 15 is prevented, and parametric echoes at short distances can be displayed.

FIG. 6 is a diagram comparing the transmitting sensitivity of the conventional example and an embodiment of the present invention described above, and FIG. 7 is a diagram comparing the receiving sensitivity. In both figures, the broken line indicates a conventional example, and the solid line indicates an embodiment of the present invention. In the figure, f0 is the resonant frequency of the transmitter,
Almost the same as the transmission frequency.

As explained above, in this example, a signal of two frequency components is applied to a wave transmitter using a diced ceramic vibrator, and the difference frequency sound wave generated by the parametric effect of the sound field medium is transmitted. the echo of
Since the configuration is such that waves are received by a cylindrical transducer with a reflector, unnecessary signal components can be suppressed by the filter function of the sensitivity of these transmitters and receivers, eliminating the need to determine performance limits. By suppressing signal components, high-resolution image information, which is a feature of parametric active sonar, can be obtained.

Furthermore, since the signal-to-noise ratio is improved, the detection distance limit is extended, and short-range parametric echoes can also be displayed.

FIG. 8 is an explanatory diagram showing another example of use of the present invention, and shows a case where mutual communication is performed between a submersible vessel 28 and an underwater base 29 underwater. The submersible 28 and the underwater base 29 are equipped with the parametric active sonar according to the present invention described above, and when communication information is transmitted from the submersible 28 to the underwater base 29 through the transmitter 15, A wave is received by the equipped wave receiver 17, and the received communication information is processed by a communication device within the underwater base 29. When communication information is transmitted from the underwater base 29 to the submersible vessel 28 through the transmitter 15, it is received by the receiver 17 equipped on the submersible vessel 28, and transmitted by the communication device inside the submersible vessel 28. It is processed.

In this way, the parametric sensor according to the present invention can be used not only to obtain echo information of objects in a sound field medium, but also to communicate between submersibles and underwater bases in the sea, etc., and has a low S/N ratio. It is possible to transmit waves with excellent directivity, so
It is possible to communicate with each other without leaking communication information to others.

As explained above, the present invention is a parametric active sonar configured using a transmitter using a diced ceramic vibrator and a cylindrical receiver having a reflector, so it has a good signal-to-noise ratio. It has high resolution, sharp directivity, and long detection and communication distances, so it can be used for precision sounding and secret communication.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing a conventional example.
Figures 2a and 2b are diagrams showing the structure of the transducer used in Figure 1, where a is a side sectional view, b is a partially cutaway front view, and Figure 3 is an embodiment of the present invention. Block diagram, Figures 4a and b are diagrams showing the structure of the transmitter used in Figure 3, where a is a side sectional view and b is a side sectional view.
5A and 5B are diagrams showing the structure of the receiver used in FIG. FIG. 7 is a diagram comparing the transmitting sensitivity with one embodiment of the invention, FIG. 7 is a diagram comparing the receiving sensitivity, and FIG. 8 is an explanatory diagram showing another usage example of the present invention. 12... Synchronous circuit section, 13... Oscillation/modulation circuit section,
14... Transmitter, 15... Transmitter, 16... Foreign object, 1
7... Receiver, 18... Receiving section, 19... Recording display section,
20...Dice ceramic vibrator, 21...Cable, 22...Kirk rubber, 23...Mold rubber, 2
4...Cylindrical ceramic vibrator, 25...Cable,
26...Mold rubber, 27...Reflector.

Claims (1)

[Claims] 1. A wave transmitter formed by applying backing and waterproofing to a diced ceramic vibrator, and a wave receiver formed by waterproofing a cylindrical ceramic vibrator and attaching a reflector to its outer periphery, A parametric active device characterized in that a signal having at least two types of frequency components is applied to a wave transmitter and transmitted, and a sound wave corresponding to a difference frequency between the frequency components is received by the wave receiver. Sona.