Electroacoustic transmitter for underwater signalling and identification of ship

The subject of the invention is an electro-acoustic transmitter for underwater signaling and identification of a ship, intended to 'prevent, in the event of an armed conflict, inappropriate attack by a submarine on neutral, sanitary and rescue ships, and in general on ships protected by the Geneva Convention by transmitting (underwater acoustic signal.

'Sonars are used to detect and identify ships by submarines, which are directional listening systems that cover the horizon with sectors. They are composed essentially of hydrofoins, compensation circuits, amplifiers and various signal processing circuits. They are operated by trained operators who listen for the noises picked up and who are duplicated by automatic gauges. The amplification of sonar noise at a given bearing leads to the detection of a potential target. The isipektraine parameters of the signal, i.e. the acoustic signature, make it possible to identify the type of ship, such as cargo, submarine racing, warship, etc., which in practice is only realized for certain known ships.

There are various systems of underwater signaling and identification of a ship.

A torpedo detection and location system is known from the United States Patent No. 3,205,475¹which is a fixed system.

From the United States patent specification No. 388019 (0 (0-, an electroacoustic system for controlling the position of a towed underwater device is known. The position of the three dimensions (geographic location and depth) of equipment being towed underwater by a sailing vessel is continuously and accurately controlled by an acoustic system that includes a group of underwater acoustic impulse transmitters and a remote acoustic transducer, battery powered and associated with suspended equipment . Initially, an array of artificial satellites fixes the ship's position, and direct information from the Pulse transmitters is used by the ship's mathematical machine systems to determine three dimensions. Wówczais, when the ship moves above-. For a bundle of impulse relays with towed equipment, the impulse relays are periodically inspected from the ship. The information obtained about the acoustic path and the positions of the impulse transmitters enables the continuous calculation and prediction of the geographical position of the vessel. The resulting acoustic path times, positions, impulse transducers and predicted ship positions are used by mathematical machine systems to control the three dimensions of the position of the remote transducer and towed equipment.

From the United States Patent No. 3,830,110 (a suspended mine finder system capable of delivering from the air is known)

132 228 and including a lifter attached to the aircraft by the first unit (a finder and a submarine attached to the lifter by a second finder unit. The lifting unit and submarine are positioned to allow the submarine to be placed in the lift during ejection and retrieval of the system. . A source of hydraulic motive power is located in the hoisting unit and is attached to the submarine by a second finder unit so as to allow the submarine to have very small acoustic and magnetic markings. In addition, the hoisting unit includes load-bearing equipment and electro-acoustic transducers. :

U.S. Patent No. 3,9671233 discloses a do-it-sonar. classification of submerged objects which is applied near the bottom of the ocean. The transmitting and receiving transducers mounted on a common support unit containing a device for rotating the transducers in relation to the vertical axis were used. of the transducer. The sampling system for the successive sampling of the control paths supplies the signal to the screen monitor. and lens, memory. Possible applications include the detection and identification of proximity mines.

It is known from the United States Patent No. 4,009,463 a system for controlling acoustic emissions, which is used to identify ^:position of the source of acoustic waves generated in an acoustically conductive center divided into a number of quadrilateral control zones. A plurality of acoustic receivers are communicatively connected to the surface of the center at the corners of the zones. Each receiver is sensitive to acoustic waves to ensure an appropriate electrical output signal. The electric responses of the receivers are fed to the meters in a way (in a way that enables the meters to run¹traversing individual count states. The receiver outputs are controlled to identify the first zone having reception at all four corners. After identifying such a zone, all counters are stopped and^!blocked at last -Mom count. The location of the source of acoustic waves is determined. The electronic circuits of the device are made in a modular form with interlocks adapted to be connected to interlocks on similar modules in order to extend the system to support an infinite number of zones.

The transmitter according to the invention comprises an electroacoustic transducer mounted in the hull of the ship so that it is submerged and connected to an electric ¹the throne of a control circuit, preferably comprising in series connection a generator, an encoder, a shaper, an amplifier and relays connected to the electro-acoustic transducers, the connection cooperating with the automatic adjustment control unit 1 and the intermediate circuit. The transmitter 'is arranged to transmit at the acoustic frequency the ship identification signal in the form of a series of letters or * digits, coded, preferably in Morse code, with a frequency ranging from 4 to 6 kHz in the ship's own noise spectrum but above the frequency of the fringes. of this spectrum and different from the harmonics of the fringes and with a power such that> the level of acoustic intensity of the signaling signal is increased in relation to the noise level by the parameter

Bcs fs l A - 40 'a_s + 10¹ log - - 15 log -'— + 6

B_C.b fb

In a preferred embodiment, the transmitter comprises a plurality of electro-acoustic transducers, and the control circuitry is designed to power these transducers at least two in each, so that the horizon is covered by a plurality of sectors.

The signaling and identification system uses a Mor.se code transmission of an identification code containing the ship's call sign.¹. Transmission is performed by zero-one modulation of the audio frequency signal. The frequency, power, duration and rhythm of the Morse code signals of the transmitted code are the characteristic parameters of the system. They were defined on the basis of two criteria. The first criterion is that the identification code absolutely must be recognized by the submarine when the latter detects underwater noise, its own vessel equipped with the system. The second criterion is that the power emitted should be as low as possible to limit the size and cost of the system and to allow it to be installed in small ships, but large enough to meet the first criterion. ^x [Determination of parameters is carried out by calculation, modeling and testing, taking into account certain factors such as ship's own underwater noise, ship identification, underwater and propagation, sound irregularities and masking of the identification code.

The subject of the invention is shown in an exemplary embodiment in the drawing, in. which fig.¹ 1 shows the general distribution of a typical underwater noise spectrum emitted by a surface ship at a distance of at least several tens of meters, Fig. 2 - a graphical representation of the basic code for signaling and identification⁵ a specific vessel, where _ this code is composed of letters transmitted in the Morse code, Fig. 3 - in vertical section an electro-acoustic transmitter, containing four 'transducers mounted in the double bottom of the rack, where »the transmitter emits signaling and identification signals through the hole for this purpose, we will make under the fuselage, fig. 4 - in the bottom view the transmitter shown in cross-section in fig. 3, showing four electro-electronic transmitting transducers, ₄ mounted on the base plate

192 228 forming part of the sealed connected housing, continues_#Fig. 5 is a functional diagram illustrating the method of selecting the horizon by transmitting a signaling and identification code in four successive sectors constituting the transmission sequence, and Fig. 6 is a block diagram of the control system of the transducers shown in ma. figures 3 and 4,

The spectrum of the ship's underwater own noise is shown in Fig. 1. A typical spectrum consists of a solid line 1, i.e. the stem track noise, the feed and pellet noise, and fringes 2, i.e. the noise of the engine and auxiliaries, corresponding to individual frequencies and decreasing with increasing frequency. The noise related to the ship's progress, indicated by the solid line 1, is composed of signals with frequencies up to 20 kHz. The fringes 2 representing the noise of the engine and auxiliaries inside the hull generally have frequencies the higher the faster or the lower the tonnage of the ship. Besides, the fringes 2 always have harmonics that should be taken into account. After much calculations and research, it has been established that the frequency band of the transmitted identification signals should be situated in the range between 4 kHz and 6 kHz. This 3 frequency band is shown in the ship's own noise diagram.

The acoustic signal of a ship essentially consists of fringes in the self-noise spectrum. For a ship to be identified, these fringes must be known. The broadcasting of the identification signal in the own noise spectrum of the ship is not-. unnecessary for determining the acoustic signal of this-ship, all the more that this signal may vary depending on external conditions, as explained below.

Normal propagation (sound is distorted by the reduction of sound intensity due to geometric divergence, according to the principle r^_1 or^-2where r is the distance from the source, and due to the attenuation by absorption, this attenuation increases exponentially with distance r and increases very quickly with the frequency of the sound.

Due to the conditions of sound propagation in the marine medium, such as reflections from the bottom and from the surface, constant mixing, bending of sound rays and batythermic phenomena, the acoustic signal received at a given point is subject to significant level changes, analogous to the fading of radioelectric waves in the atmosphere. In particular, a signal with a short transmission time, for example a dot or a dash in the Marse alphabet, can produce two signals in the background. In this way, a dot can be doubled by strong echoes and, when received, can be limited to two dots, a dash can be cut into two segments and interpreted as sounds like dots or lines dash or dot-dash, etc.

ff> la the code is received and identified by an operator or by an automatic analyzer in the ship's own noise or in the background noise oto-. in the background noise of the sea, this signal must be perceived in intensity depending on its frequency and on the spectrum of masking noise. Fig. 2 shows the identification code C which should meet the criteria and conditions mentioned above.

Base code C, which is an identification signal in the frequency band 4 to · 6 kHz, is composed of the incident start signal and the call signal of the transmitting vessel, possibly repeated a second time. The transmission start signal facilitates the recognition of sea signals, dots and dashes, the duration and mutual relations of which are different from those used in telegraphy, as they are determined depending on the sound propagation conditions in the water. For example, fig. 2 shows the code. of the Swiss vessel M / S (Regina, whose radio call sign is HBDR. The C code is_ transmitted in the Mbrse alphabet in the frequency range '4 to 6' kHz. Sea signals have a duration of 200 ms for a dot and 7010 ms for a dash. Intervals. between characters are 800 'ms, and between letters - 1000 ms. Depending on the specific conditions of sound propagation, the duration times can be programmed> and changed in 100 ms steps in the range from 100 to 80 °¹ bowls for dots and dashes and in increments of 200 'or 400 ms in the range 200' to 3200 ms * for intervals, '* Two different transmit frequencies and fg will be selected for each vessel in the range 4 to kHz, these frequencies being varied from several dozen to 200 Hz. Of course, they will be selected depending on the acoustic signal of the vessels equipped with them in such a way that they do not coincide with the bands of the natural spectrum or with their harmonics and taking into account the dimensions of the transmitter. For each code signal Cj, that is, for a dot or a dash, a series of sine waves (of proper duration alternating between one or the other of the two frequencies fj and ff) is transmitted. The series of odd characters are given with the frequency fj, and the series of even characters with the frequency f2. Between two characters, transmission is interrupted for the duration of either an inter-character space or an inter-letter space. .

In order to avoid the use of a high-power omnidirectional transmitter, the transmission is directional and has a step-changeable axis. The entire horizon is thus covered by sectors by sequentially switching the direction axes, the complete code being transmitted at each position;

i The send sequence S is made up of a number of codes. C separated by P pauses, that is, Periods of silence with programmable durations of '10, 20, 30, 40 or 80 seconds. For example, for selecting a horizon with four sectors, the transmit sequence consists of four C codes and three P pauses, i.e., C-iP-C-iP-C-PHC. The four sector horizon selection method will be explained below with reference to Fig. 5.

Transmission of the S sequence is fully automated. The time base allows you to set the number of sequences per hour to 1, 2, 3, 4 or

8. For a maximum range of 40 tom transmitting power P_and should be such that LI_sl LIb_ly? + + "Δ [idB], where LI_sl is the sound level 3, reduced to the unit distance. identification signal · with average frequency f_s [Hz], where this level is defined as the minimum value in the transmission directions corresponding to the intersections of the adjacent directionality lobes of the transmitter, in the case of selecting the horizon by sectors, while LI_bi is the sound pressure level, reduced to the unit distance, of the noise in the band around the frequency f_b [Hz], received at a great distance from the transmitting vessel, due to its underwater intrinsic noise in the surrounding background noise of the sea. LI_sl and LIbi are expressed in decibels with respect to intensity¹ reference Dr, equal in 'submarine acoustics 6.5 nw / m². War-²⁰the value of the parameter Δ is calculated from the general formula

B_C.s fs d = · r + iHO log -—: - - 1'5 'log --- +

Bcb. fb

I 25 + JM - »Δ, [dB], where dci [diBiltom]. is the difference of sound absorption coefficients in seawater for the frequency f_s and fb, r [tom] is the maximum detection range of a transmitting vessel using the frequency band around frequency f_{b 3}θ its own underwater noise in the surrounding background noise of the sea, B_cs and b_C.b [Hz] are the critical masking bands at frequencies f, respectively_s if_b, dM [dB] is the difference of the signal-to-noise detection coefficients in the output _3gpassive sonar for the frequency f_sand fb, while "dD [dB] is the passive sonar directivity difference for. frequency f_s if_b.

Considering the highest required range of 40 km and the most favorable detection situations _4Qof the ship and the most unfavorable for the reception of the identification signal, the simplification B is obtained_cfl practical formula d = 4O. «_S. + HO log- - ^Bcb "fs - 15 'log - + 6, where B_cs, B_cb, f_s and fb fb

And they are as above aa_s is the coefficient of sound absorption in the sea at the frequency f_s. 50

For example, for fb = 1 kHz and for frequencies f of 4, 5 and 6 kHz, respectively, the resulting d values ​​are 7.114 Ji 19 dB._with

The energy emitted - must be limited, however, to avoid cavitation in front of the converters. Particularly in the case of a shallow depth, the ship takes on the marching speed and the emitted energy is reduced.

(Figures 3, 4 and 5 show an electroacoustic transmitter 5 and an electrical system consisting of ⁶⁰control system 6 of the transmitter 5. The electro-acoustic transmitter 5 is located in the double bottom of the ship and radiates energy directly to the sea through the opening 7, we will make it in the hull 8,

Control system. is located in the engine room -luib in adjacent rooms or in another room with the required conditions. It is connected on one side to the ship's electrical network and on the other side to the transmitter. electroacoustic 5 with appropriate power cables 30.

(The electro-acoustic transmitter 5 comprises four electro-acoustic transducers 10, 11, 12 and 13, positioned vertically facing the seabed, mounted at the vertices of the square and each separately powered by cables 30 routed from the control system 6. These electro-acoustic transducers 10, 11, 12) and 13 form a transmit matrix Configuration of this matrix_j that is, the distances between the axes and the phases of the supply voltages, are selected so as to obtain the various required orientations at the anticipated operating frequencies. The abruptly changed directions, covering the horizon with sectors, are realized by commutating the power supply of the transducers.

Figure 5 shows how the power supply of the four electroacoustic transducers 10, 11, 12 and 13 is commutated to transmit complete identification codes according to the configuration given in Figure 2, sequentially according to four different axes. According to the diagram of Figures 5, a, the two electroacoustic converters 10 are energized with the opposite phase, i.e. with a phase shift of 18O [deg.], Indicated by + and -. Thus, transmission in d * in opposite directions is achieved according to axis 14 in FIG. 5a. The entire code constituting the signal of Fig.

2, whereupon the control circuit of Fig. 6 changes the connection of the transducers to the connection according to the diagram of Fig. 5lb. After this connection changeover, code C is transmitted again in the directions along axis 15 in Fig. 5b. There is a pause between the two emissions as described above. It then proceeds to successive emissions with pauses in between in the directions shown in Figs. 5c and 5d. The four transmitted codes according to Figs. 5a to 5id constitute a sequence. In the second sequence, four codes are emitted according to Figures 5e, 5f, 5g and 5h, again according to the same four axes but from different transducers. In fact, according to Fig. 5e, it is emitted along an axis 16 parallel to the axis 14 in Fig.

5e, from the transducers 12 and 13 instead of the transducers 10 and 11. This commutation method makes it possible to equalize the usage times of all transducers and thus avoid faster wear of one transducer in relation to another. After two sequences of four codes each, the connection is returned to Figs. 5a and c and k and starts again. The described sequences make it possible, by means of four switched transducers of two, to select the horizon with four sectors according to the four axes shown in Fig. 5, while ensuring good signal spreading around the signal vessel. Of course, you can also select the horizon with more commutated transducers, two or three. They are possible

132 228 different combinations and the limitation is only due to the sizes and dimensions.

A transmitter with three transducers commutated by two or powered by a combination of one transducer, then two, and i and bd may also be preferable. One transducer can be used in the extreme case. In this case, the major component of the downward vertical emission will be lost. A single transducer must therefore have a much greater power, if a large part of the power transmitted from it is intended for losses when directed to the seabed.

'In case a single transducer is used, it is possible to locate it horizontally on a driven device, not shown, for full angle rotation about the vertical axis.

The combination of the four transducers described in the embodiment of FIGS. 3 to 45 gave very good results ^sThis is due to the fact that connecting the transducers in pairs at opposite phases introduces components of substantially horizontal radiation.

The electro-acoustic transmitter 5 is mounted in the circular opening of the hull in the double bottom of the ship, preferably in the ballast water tank. It is situated approximately one-third of the ship's guests from the rear and to the side of the keel at a sufficient distance to avoid damage by keel blocks when the ship is in dry dock or in a floating dock.

Figures 3 and 4 show a typical design of an electro-acoustic transmitter 5. In this example, the four electro-acoustic transducers 10, 11, 12 and 13 are commercially available TR-61A piezoelectric transducers from Massa, and any other transducers with similar characteristics may be used. or better. The pickups 10, 11, 12 and 13 are mounted vertically on the. base plate 21. In the view from below, from the sea, they are arranged at the vertices of a square, the lateral distance d between adjacent transducers is as small as possible, taking into account the design possibilities of the set.A circular opening 7 is cut in the hull of the ship, and its edge is reinforced with a reinforcing ring 22. The base plate 21 is attached to the reinforcement ring 22 of the screw 23. Two arrangements are possible. In the first, the sides of the square formed by the transducers are parallel and perpendicular to the longitudinal axis of the ship, and in the second, the diagonals of the square are respectively perpendicular. declining and parallel to this axis of the ship. A spacer ring 24 is disposed between the reinforcement ring 22 and the base plate 21, giving a distance e of 25 to 35 mm between the transducer faces and the outer edge of hull 8. The electro-acoustic transmitter 5 is surrounded by a slit by a housing 25_r A gasket 28 is placed between the housing 25 and the cover £ 7, welded to the gas ring 22 and closed with the cover 27. When the transmitter is not in use, a removable protective plate 29 is attached to the opening 7 of the fuselage 8. process 10 /

The conduits 10, 11, 12 and 13 pass through the sealed casing 25 through the glands 31 and are fed to an electrical control system, not shown, through the protective tube 32 and the ship's tubing tunnel. After insertion into cutout 34 'in plate 21, the transducers 10, 11, 12 and 13 are held on base plate 21 by screws 33. Said notches have a truncated cone profile carefully cut to fit the transducers to seal the transmitter. shown in Fig. 3 and the transducers 10, 11, 12 and 13 are still held in their upper part by a frame 35 connected rigidly to the plate 21 by screws 36, the distance between the plate 21 and the frame 35 being kept by. by means of spacer sleeves 37. The cables 30 are connected to each other inside the housing 25 by sealed connectors 9.

The dimensions and construction arrangement of the unit are determined individually, depending on the available space and the instructions of classification societies.

Fig. 6 shows a block diagram of the electric control system 6.

The power supply 41 is connected to the on-board network 40 via the manual and circuit breakers shown here and supplies the various voltages needed for the operation of the system. The control unit 42 allows the user to control the system and set transmission parameters. It is equipped with switches and buttons not shown, some of which are directly accessible on the faceplate and others are not. A control unit 42 is connected to the generator 43 and enables the duration of the marine signals to be selected, i. E. Dots and dashes, the duration of the code pauses, the time intervals between the sequences, etc.

The encoder 45 is connected on the one hand to the generator and on the other hand to the sequencer 44 and to the control unit 42 and produces strings of rectangular signals with a frequency alternating fj and f.₂, the duration and rhythm of these signals correspond to the transmitted signal code C. This code is contained in a permanent memory, programmed especially for each vessel, which cannot be changed afterwards.

The linkage 46 energizes the relays 50 on the basis of input signals from the sequence circuit 44 connected to the generator 43. The shaper 47 converts the strings of square-wave signals from the output of the encoder 45 into strings of continuous sine signals, the amplitudes of which are controlled by the connected automatic control circuit 49 to which the supplying amplifier 48 (needed. active energy to transmit, riika and compensate reactive energy with appropriate reiaictions.

The automatic regulation circuit 49 is also connected to the control unit 42 and allows the energy supplied to the transmitter to be regulated by influencing the gain of the shaper 47 connected to the amplifier 48 protected against overload, for example due to a short circuit.

Relays 50 connected to amplifier 48 and driven by an adapter 46 provide power commutation to the transmitter transducers for sequentially selecting horizon by sectors, as described with reference to FIG. 5.

The fans 51 attached to the power supply 41 ensure cooling of the amplifier 48.

Layout - It is made in the form of drawers placed in a metal wardrobe. This cabinet has ventilation openings equipped with dust filters. The control unit 42, the generator 43, the sequencer 44, the encoder 45 and the adapter 46 are digital, while the shaper 47 and the shaper¹ 49 automatic controls are made in analog technology. These circuits are made of analog and digital integrated circuits and discrete electronic and electrical components, assembled^ίβprinted on printed circuit boards.

The power supply 41, the amplifier 48 and the relays 50 are made using currently available electronic, electrical and electromechanical components.

As technology progresses, it will be possible to modify the design of the circuits, in particular by replacing the entire digital part with a microprocessor ^