Communications – electrical: acoustic wave systems and devices – Distance or direction finding – By combining or comparing signals
Patent
1993-06-01
1994-06-07
Pihulic, Daniel T.
Communications, electrical: acoustic wave systems and devices
Distance or direction finding
By combining or comparing signals
367153, G01S 380, G10K 1100
Patent
active
053196120
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to unfolding, cylindrical sonars which can be used, for example, from a helicopter.
There is a method, known from the French patent No. 2 354 920, for making a sonobuoy comprising, on a body, a set of unfolding arms fitted with hydrophones When the buoy is released, the arms are folded against the body, thus facilitating its entry into the water and preventing these arms from being pulled off. When it is stabilized in water, at the desired depth, the arms get unfolded to give a cylindrical monitoring base with a diameter that is appreciably greater than the body of the buoy
A sonobuoy of the same type is also known from the patent GB-A-2 093 996, comprising, on each unfolding arm, five columns of hydrophones separated by a distance of .lambda./2 to increase sensitivity in reception. This spacing does not provide the characteristics of particular directivity. The electronic processing of the signals received by the hydrophones of each arm enable the localizing of the noise sources, for example, submarines. However, a cylindrical arrangement of this type, which is necessarily transparent owing to the structure of the device, is at the origin of a certain number of drawbacks, in particular ambiguities in detection and localization arising out of the minor lobes and the rear lobe of the different hydrophones.
To overcome these drawbacks, the invention proposes a sonar according to claim 1.
Other features and advantages of the invention will appear clearly from the following description, given by way of a non-restrictive example, with reference to the appended figures, which represent:
FIG. 1, a view in perspective of a sonar according to the invention;
FIG. 2, a diagram of the positioning of columns 4 and 7 of FIG. 1;
FIG. 3, an electronic circuit diagram of the signals coming from these columns.
In the embodiment represented in FIG. 1, the sonar comprises a body 1, kept in a vertical position at the end of a cable 8 which enables it, for example, to be let down from a helicopter to the water. Around this body, there is a set of folding arms 2, which get housed in folded-up position in a set of housings 9, located longitudinally along generatrices of the body 1. Each arm 2 comprises two rods 3 fixed at one end by two joints 5 to the body 1. A first vertical bar 4 is fixed to the other end of the rods 3 by joints 6 so as to form, with the rods 3, a deformable parallelogram located in the vertical plane passing through the axis of symmetry of the buoy, and such that it can get folded up against the body and can get unfolded up to a position where the rods 3 are horizontal and the bar 4 is vertical. One of the rods 3, at least, extends beyond the joint 6 to hold a second bar 7 similar to the bar 4. In order to keep this bar 7 parallel to the bar 4, a brace 10, for example, is used, hinged to these two bars, located towards that of their ends which is opposite the joint 6. The two signals, S.sub.c (t) and S.sub.i (t), are added up in first adder 30. They are phase shifted by .pi./2 in two phase shifters 40 and 50, and the signals thus phase shifted are subtracted in a second adder 60. The signal from the adder 60 is multiplied by a coefficient .beta. in a multiplier 70, then the signal obtained is added, in an adder 80, to the signal coming from the adder 30.
If A cos .omega.t is the signal received, the resultant signal x(t) delivered by the adder 80 is equal to: ##EQU1## with .lambda.=operating wavelength of the sonar, ##EQU2## for the external cardioid (200) and ##EQU3## for the internal diagram (300).
If d is smaller than .lambda., and at least smaller than .lambda./4, the formula comes down to:
It is noted, therefore, that the smaller d is, the closer we come to the shape of a cardioid. Nonetheless, we are limited by sensitivity to variations in the characteristics of the transducers, which increases with the value of the coefficient .beta..
There are a known way to form a channel pointed in a given direction by delaying (or phase-shifting) the signals of the sensors of an antenn
REFERENCES:
patent: 3665380 (1972-05-01), Stover
patent: 3886491 (1975-05-01), Jonkey et al.
patent: 3931607 (1976-01-01), Ingram
patent: 4661938 (1987-04-01), Jones et al.
patent: 5014953 (1991-05-01), Warnan et al.
Lemer Alain
Riccardi Guy
"Thomson-CSF"
Pihulic Daniel T.
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