Underwater acoustic transceiver device.

Abstract

The invention relates to an underwater acoustic transceiver device, comprising: - a first annular FFR transducer (1) configured to operate in a first octave covering a first low-frequency range, and a second annular FFR transducer (2) configured to operate in a second octave covering a second high-frequency range, - the two FFR transducers (1, 2) are arranged coaxially, each transducer having a front face and a rear face, - the rear face of the second FFR transducer (2) is located in the plane of the front face of the first FFR transducer (1) or offset from said plane in the direction of emission. Figure 6

Description

Title of the invention: Underwater acoustic transmitter-receiver device. Technical field.

[0001] The present invention relates to an underwater acoustic transmitter-receiver device.

[0002] The invention relates to the technical field of acoustic transducers for acoustic data communication in underwater environments, and in particular to underwater acoustic transducers using piezoelectric materials. Prior art.

[0003] It is generally useful to have a transmitting / receiving device capable of operating at least two distinct frequency bands, for example, one octave each. A band covering low frequencies is useful for applications requiring long range but with reduced bandwidth, and a band covering high frequencies is useful for applications requiring shorter ranges but with wider bandwidth.

[0004] A broadband underwater acoustic transmission / reception device comprising a Tonpilz-type transducer configured to cover low frequencies and a Free Flooded Ring (FFR) transducer configured to cover high frequencies is known from patent document EP3359308. These two transducers are coaxial, with the Tonpilz transducer positioned rearward and the FFR transducer positioned forward, their respective front emission directions being oriented forward. The acoustic reflector, or "tape," of the FFR transducer also serves as a horn for the Tonpilz transducer.

[0005] By combining a Tonpilz transducer and an FFR transducer, this prior art device makes it possible to cover a frequency band of two octaves, with the Tonpilz transducer covering the low-frequency (LF) octave and the FFR transducer covering the high-frequency (HF) octave. Furthermore, thanks to the common tape, the Tonpilz transducer no longer has any parts masking its radiation.

[0006] The device described in EP3359308, however, has several drawbacks. Referring to the curve illustrated in [Fig. 2] of this document, it can be seen that the acoustic performance of the device is inefficient and unstable between the low-frequency (LF) and high-frequency (HF) octaves, with a variation of approximately 15 dB observed for a sensitivity that, in use, is less than 120 dB. This limited sensitivity impacts the performance of the device, which is particularly vulnerable to variations in sensitivity, potentially leading to signal loss and reduced communication. This device is effective, particularly in complex underwater environments where sound propagation is affected by numerous factors. This phenomenon limits communication capabilities, and in practice, it is difficult to simultaneously transmit multiple frequencies across the band covered by the two octaves. Therefore, the preferred method of using this device is to power only one of the two transducers, depending on whether low or high frequencies are desired.

[0007] Moreover, in use, it is observed that the device does not allow for a satisfactory hemispheric directivity, so that these acoustic performances are limited.

[0008] In addition, this device is heavy and bulky due to the very design of the Tonpilz transducer and the elements associated with it in order for it to be able to cover an octave.

[0009] The invention aims to overcome all or part of the aforementioned drawbacks. In particular, one objective of the invention is to provide an underwater acoustic transceiver device with improved communication capabilities and / or acoustic performance, especially over a two-octave frequency band. Another objective of the invention is to provide an underwater acoustic transceiver device that is compact, lightweight, and of simple design. Description of the invention.

[0010] The solution proposed by the invention is an underwater acoustic transmitter-receiver device, comprising: - a first annular FFR transducer configured to operate in a first octave covering a first low frequency range, and a second annular FFR transducer configured to operate in a second octave covering a second high frequency range, - The two FFR transducers are arranged coaxially, each transducer having a front and a rear face, - the rear face of the second FFR transducer is located in the plane of the front face of the first FFR transducer or away from said plane in the direction of emission.

[0011] The device of the invention now combines two FFR transducers, the first covering the low-frequency octave and the second covering the high-frequency octave. The device can thus cover two distinct octaves very simply, with increased sensitivity, without significant variation in performance between low and high frequencies, and with the ability to simultaneously transmit several frequencies over the operational band covered by the two octaves, so that communication capabilities are improved compared to the aforementioned prior art.

[0012] In addition, the specific coaxial arrangement of the FFR transducers makes it possible to maintain hemispherical directivity over the entire frequency band of the two octaves, thus improving the acoustic performance of the device.

[0013] In addition, the use of FFR transducers to cover two distinct octaves helps to reduce the weight and compactness of the device.

[0014] Other advantageous features of the invention are listed below. Each of these features may be considered alone or in combination with the features defined above. Each of these features contributes, where appropriate, to the resolution of specific technical problems defined further in the description and in which the notable features defined above do not necessarily participate. Therefore, the following features may, where appropriate, be the subject of one or more divisional patent applications:

[0015] According to one embodiment, a first acoustic reflector is positioned at the rear face of the first FFR transducer.

[0016] According to one embodiment, the inner diameter of the first FFR transducer is greater than the outer diameter of the second transducer.

[0017] According to one embodiment, the first FFR transducer comprises a first stage and a second stage, which stages are separated from each other.

[0018] According to one embodiment in use, the first FFR transducer operates on the octave [fBF-2.fBF] and the second transducer operates on the octave [2.fBF - 4.fBF], fBF being the lower frequency of the effective frequency band of the first transducer FFR.

[0019] According to one embodiment, a sealed elastomer hood encloses the two FFR transducers so as to form an internal chamber filled with a fluid.

[0020] According to one embodiment, an internal space separates the hood from the FFR transducers, so that said hood is not in contact with said transducers.

[0021] According to one embodiment, the first acoustic reflector is moved away from the rear face of the first FFR transducer.

[0022] According to one embodiment, a second acoustic reflector is positioned at the rear face of the second FFR transducer.

[0023] According to one embodiment, the second acoustic reflector is moved away from the rear face of the second FFR transducer.

[0024] According to one embodiment, the first acoustic reflector is assembled to the first FFR transducer by means of an assembly comprising: - an elastomeric coating covering all or part of the annular internal wall of the first FFR transducer, which coating has one or more elastomeric tabs arranged in the annular internal space of said first transducer; - a fixing rod mounted in each tab, which rod is fixed to the first acoustic reflector.

[0025] According to one embodiment, a spacer is mounted on each fixing rod so as to move the first acoustic reflector away from the rear face of the first FFR transducer.

[0026] According to one embodiment, the second acoustic reflector is assembled to the second FFR transducer by means of an assembly comprising: - an elastomer coating covering all or part of the annular internal wall of the second FFR transducer, which coating has one or more elastomer tabs arranged in the annular internal space of said second transducer; - a fixing rod mounted in each tab, which rod is fixed to the second acoustic reflector.

[0027] According to one embodiment, a spacer is mounted on each fixing rod so as to move the second acoustic reflector away from the rear face of the second FFR transducer.

[0028] According to one embodiment, the two stages of the first FFR transducer are assembled by means of an assembly comprising: - an elastomer coating covering all or part of the annular inner wall of the first stage, which coating has one or more first elastomer tabs arranged in the annular inner space of said first stage; - an elastomer coating covering all or part of the annular inner wall of the second stage, which coating has one or more second elastomer tabs arranged in the annular inner space of said second stage, opposite the first tab(s); - a fixing rod mounted in each first tab and second tab.

[0029] According to one embodiment, a spacer is mounted on each fixing rod so as to separate the first floor from the second floor.

[0030] According to one embodiment, the fixing rods used to assemble the first acoustic reflector to the first FFR transducer are also fixed to the second acoustic reflector. Brief description of the figures.

[0031] Other advantages and features of the invention will become more apparent upon reading the description of a preferred embodiment which follows, with reference to the accompanying drawings, which are provided by way of illustrative and non-limiting examples and on which:

[0032] [Fig. 1] illustrates an FFR transducer.

[0033] [Fig.2] schematically represents a device that is the subject of the invention according to one embodiment.

[0034] [Fig.3] schematically represents a device that is the subject of the invention according to another mode of realization.

[0035] [Fig.4a] schematically shows a directivity diagram of a single-stage low-frequency FFR transducer, of the type illustrated in [Fig.1], and sized to operate over the octave [fBF-2fBF].

[0036] [Fig.4b] schematically shows a directivity diagram of a two-stage low-frequency FFR transducer, of the type illustrated in [Fig.5] and sized to operate over the octave [fBF-2fBF].

[0037] [Fig.4c] schematically shows a directivity diagram of a complete device according to the invention, using a two-stage low-frequency FFR transducer of the type illustrated in [Fig.5].

[0038] [Fig.5] illustrates a device according to the invention, using a two-stage low-frequency FFR transducer.

[0039] [Fig.6] is a cross-sectional view of a device according to the invention.

[0040] [Fig.7] is a cross-sectional view of the device of the [Fig.7], the hood waterproofing not being shown.

[0041] [Fig.8] shows a device according to the invention once assembled.

[0042] [Fig. 9] is a diagram illustrating the sound level in dB (or the performance) of the device of the invention over an operational frequency band. Description of embodiments.

[0043] As used here, and unless otherwise indicated, the use of the ordinal adjectives "first", "second", etc., to describe an object simply indicates that different occurrences of similar objects are being mentioned and does not imply that the objects thus described must be in any given sequence, whether in time, space, ranking, etc. Also, an expression of the type "X and / or Y" means: X alone or Y alone or X+Y.

[0044] The underwater acoustic transceiver device of the invention is used for precise and reliable data communications in an underwater environment. It can be integrated into various types of underwater vehicles, for example autonomous underwater vehicles (AUVs), underwater drones, buoys, fixed underwater stations, etc.Examples of data transmitted may include positioning data relative to the seabed; data on the detection of underwater objects or obstacles, including seabed mapping, wreck location, or recognition of underwater infrastructure such as pipelines or cables; telemetry data such as measurements of temperature, pressure, salinity, or other environmental parameters; multimedia data such as audio and / or video recordings; and command data, for example, transmitted or received for piloting AUVs or underwater drones.

[0045] According to the invention, the device of the invention comprises two annular FFR “Free Flooded Ring” transducers (which can be translated into French as “transducteur à bague mouillé libre”) each operating on a specific octave.

[0046] A first FFR transducer 1 (hereinafter referred to as "FFR-LF transducer") is configured to operate in a first octave covering a first low frequency range (hereinafter referred to as the "low frequency" range / band / octave) and a second FFR transducer 2 (hereinafter referred to as the "FFR-HF transducer") is configured to operate in a second octave covering a second high frequency range (hereinafter referred to as the "high frequency" range / band / octave).

[0047] Referring to [Fig. 1], the FFR-BF 1 and FFR-HF 2 transducers are each in the form of a radially or tangentially polarized piezoelectric ring (for example, in the form of a ring with a flange). When the FFR transducers are electrically excited, they contract or expand, causing vibrations transmitted to the fluid inside and outside the ring and then to the surrounding water, generating underwater acoustic waves. Conversely, when an underwater acoustic wave reaches an FFR transducer, mechanical pressure is applied to the ring, generating an electrical voltage. This property is exploited by the FFR transducers to convert electrical signals into acoustic waves (transmission) and vice versa (reception).

[0048] Each transducer involves two types of resonance modes whose frequencies depend on the dimensions of the piezoelectric ring: - Cavity resonance, which depends mainly on the volume of the cavity and therefore on the height h of the ring and the inner diameter Ci (the larger the volume, the lower the frequency). - Radial piezoelectric resonance, which depends on the inner diameter Ci and the outer diameter Oo (the larger the inner diameter (Ci), the lower the frequency).

[0049] The FFR-LF 1 and FFR-HF 2 transducers are each sized to operate within an effective frequency band (a low-frequency band for the FFR-LF transducer and a high-frequency band for the FFR-HF transducer). In practice, the frequency range in which each transducer operates optimally is proportional to the center frequency of its effective frequency band and generally covers one octave.

[0050] By combining the FFR-LF and FFR-HF transducers, the device is able to operate optimally on two distinct octaves, improving the quality and reliability of underwater communications. The device is thus capable of simultaneously transmitting a large amount of data on different frequency bands. The FFR-LF transducer, covering the low-frequency octave, maximizes the Communication range in water is limited, as low frequencies have superior propagation capabilities in the underwater environment. The FFR-HF transducer, by covering the high-frequency octave, allows for shorter-range communication but with better data resolution.

[0051] Referring to [Fig. 2], the two transducers 1, 2 are arranged coaxially. Their emission axes A (or radiation axes) are thus coincident, the emission direction being schematically represented by the arrow on axis A. The transducers 1, 2 are therefore positioned in series along axis A. Each transducer 1, 2 has a rear face and a front face, the emission being directed from the rear face to the front face and being the same for both transducers.

[0052] The FFR-HF 2 transducer is positioned beyond the front face of the FFR-BF 1 transducer. By "positioned beyond", for the purposes of the present invention it is understood that the rear face of the FFR-HF 2 transducer is located in the plane of the front face of the FFR-BF 1 transducer or that the rear face of the FFR-HF 2 transducer is moved away from the plane of the front face of the FFR-BF 1 transducer, in the direction of emission.

[0053] This specific coaxial arrangement of transducers 1 and 2 provides very good hemispheric directivity over both octaves. Furthermore, the applicant has observed that the wave emitted by the FFR-HF transducer 2 does not interfere with the wave emitted by the FFR-LF transducer 1.

[0054] The FFR-HF 2 transducer, which has the smallest dimensions, is thus positioned in front of the FFR-BF 1 transducer, so that the FFR-HF 2 transducer does not mask the radiation of the FFR-BF 1 transducer and the impact of the assembly of the two transducers on the hemispheric directivity is minimal.

[0055] To further reduce this masking phenomenon, the inner diameter Ci of the FFR-BF 1 transducer is advantageously greater than the outer diameter Oo of the FFR-HF 2 transducer. This masking is further reduced when the rear face of the FFR-HF 2 transducer is moved away from the plane of the front face of the FFR-BF 1 transducer.

[0056] According to one embodiment, an acoustic reflector 10 (or tape), for example in the form of a metallic disc, is positioned at the rear face of the FFR-BF transducer 1. The diameter of the tape 10 is advantageously greater than or equal to the outside diameter Oo of the FFR-BF transducer 1.

[0057] The coaxial arrangement of transducers 1 and 2, combined with the arrangement of tape 10, allows the device to maintain its very good hemispheric directivity over both octaves. Indeed, in this configuration, tape 10 not only provides excellent hemispheric directivity for the FFR-LF transducer 1, but also good hemispheric directivity for the FFR-HF transducer 2. Furthermore, the applicant has surprisingly observed that the forward reflection of the wave emitted to the rear of the FFR-HF transducer 2 does not destructively interfere with the direct wave emitted forwards by said FFR-HF transducer, nor with the wave emitted forwards by the FFR-BF 1 transducer.

[0058] Tape 10 may be located in the plane of the rear face of the FFR-BF 1 transducer or away from said plane of the rear face. The best results in terms of hemispherical directivity are obtained when tape 10 is away from the plane of the rear face of the FFR-BF 1 transducer, advantageously away by a distance of between 0.5 mm and 2 mm, preferably 1 mm.

[0059] In [Fig. 3], a second acoustic reflector 20 (or tape) is also positioned on the rear face of the FFR-HF transducer 2. The tape 20 is, for example, in the form of a metallic disc. Its diameter corresponds to the outer diameter Oo of the FFR-HF transducer 2. It can be located in the plane of the rear face of the FFR-HF transducer 2 or away from said plane, advantageously away by a distance of between 0.5 mm and 2 mm, preferably 1 mm to obtain good hemispherical directivity. The applicant has found that this second tape 20 does not increase the masking effect and improves the hemispheric directivity over both octaves.

[0060] According to one embodiment, if fBF is the low frequency of the effective frequency band of the FFR-BF transducer, then the transducers are excited so that the FFR-BF transducer 1 operates in the octave [fBF - 2.fBF] and the FFR-HF transducer 2 operates in the octave [2.fBF - 4.fBF]. These two octaves are adjacent.

[0061] This octave segmentation optimizes the device's performance in terms of range, resolution, and reliability of underwater communications. The operational frequency band [fBF - 4fBF] is particularly wide, allowing for more comprehensive and / or complex communication compared to prior art devices. Furthermore, by clearly separating the octaves used for transmission, the probability of interference between signals from one transducer and those from another is reduced, and intermodulation phenomena are limited, as each transducer operates in a distinct octave with little or no overlap, resulting in more reliable communications.

[0062] The graph in [Fig. 9] illustrates the sound level (equivalent to the acoustic performance) produced by the device over the operating frequency band [fBF - 4fBF]. The solid line corresponds to the sound level along the emission axis A (emission angle = 0°) and the dashed line corresponds to the sound level in an emission direction normal to the emission axis A (emission angle = 90°). It can be seen first of all that the acoustic performance of the device is remarkable, its performance being greater than 125 dB regardless of the angle. transmission and can reach 140 dB along the A-axis. This capability not only enables extended effective communication range but also ensures reliable, robust, and stable data transmission across wide frequency bands in diverse underwater environments. Furthermore, the device's performance is particularly stable across the two octaves [fBF - 2fBF] and [2fBF - 4fBF], with the amplitude of variation decreasing with the transmission angle. In any case, the device's increased sensitivity makes its performance less vulnerable and / or more robust to these variations. As a result, the device has excellent communication capabilities across the entire operational frequency band.

[0063] By way of example, the FFR-LF transducer 1 operates in the low frequency octave between 16 kHz and 32 kHz, and the FFR-HF transducer 2 operates in the high frequency octave between 32 kHz and 64 kHz. Transducers 1 and 2 can, however, be sized to operate in other octaves; for example, the FFR-LF transducer can operate in the low frequency octave [8 kHz - 16 kHz], and the FFR-HF transducer can operate in the high frequency octave [16 kHz and 32 kHz].

[0064] By way of further example, for operation in the low-frequency octave [16 kHz - 32 kHz], the FFR-LF transducer 1 may have a height h between 14 mm and 18 mm, an inner diameter Ci between 18 mm and 20 mm, and an outer diameter Oo between 23 mm and 25 mm. And for operation in the high-frequency octave [32 kHz - 64 kHz], the FFR-HF transducer 2 may have a height h between 7 mm and 9 mm, an inner diameter Ci between 8 mm and 10 mm, and an outer diameter Oo between 11 mm and 13 mm.

[0065] The octaves can, however, be segmented according to another frequency, for example according to the fHF frequency corresponding to the low frequency of the band covering the high frequencies. In this case, the transducers can be sized so that the FFR-LF transducer 1 can operate in the octave [2.fHF] and the FFR-HF transducer 2 can operate in the octave [fHF - 2.fHF].

[0066] According to an embodiment that simplifies the design and operation of the device, the transducers 1 and 2 are excited simultaneously by the same signal. In other words, each transducer 1 and 2 is excited at the same frequency. For example, when the complete device operates in the high-frequency octave, for example at 4 fB, the two transducers FFR-BF 1 and FFR-HF 2 are excited at this same frequency 4 fB. Conversely, if the complete device operates in the low-frequency octave, for example at fB, the two transducers FFR-BF 1 and FFR-HF 2 are excited at this same frequency fB.

[0067] At high frequencies, the FFR-BF 1 transducer can generate parasitic modes that may limit the acoustic performance of the device. This phenomenon is illustrated by the directivity diagram in [Fig. 4a], for the FFR-LF transducer sized to operate in the octave [fBF - 2fBF]. The angle on the x-axis corresponds to the emission angle in degrees relative to the emission axis A. The density scale is chosen to show expected level sensitivities (density 1) and parasitic sensitivities (density 2). Parasitic modes are observed around 4fBF, generating directivity lobes that can impact the sensitivity in the octave where the FFR-HF transducer operates.

[0068] To avoid this phenomenon, the FFR-BF 1 transducer has been divided into two according to its height. In [Fig. 5], the FFR-BF 1 transducer thus comprises a first stage 1a and a second stage 1b, which are spaced apart from each other, for example by a distance of between 0.5 mm and 2 mm, preferably 1 mm, to obtain excellent hemispheric directivity D.

[0069] According to a preferred embodiment, the two levels aa, 1b are identical. Each level may, for example, have a height h between 7 mm and 9 mm, an inner diameter Ci between 18 mm and 20 mm and an outer diameter Oo between 23 mm and 25 mm.

[0070] Referring to the diagram in [Fig. 4b], this division of the FFR-BF transducer has the effect of preserving the cavity and radial resonances at the same frequencies, but of pushing the parasitic modes to a higher frequency, outside the band of interest, so that the high-frequency effect (4fBF) is largely attenuated compared to a solid ring ([Fig. 4a]). As illustrated in the diagram in [Fig. 4c], the result is that the complete device can exhibit very good hemispheric directivity over the entire frequency band from fBF to 4fBF.

[0071] According to another embodiment, the transducers 1 and 2 are excited simultaneously, but by separate signals. In other words, each transducer 1 and 2 is excited at the octave for which it was designed to operate. The FFR-LF transducer 1 is excited at the octave [fBF - 2fBF] by a first signal, and the FFR-HF transducer 2 is excited at the octave [2fBF - 4fBF] by a second signal. This operation avoids the aforementioned parasitic modes generated by the FFR-LF transducer 1 when it is directly electrically excited at high frequency. However, the FFR-BF 1 transducer can still be indirectly excited at high frequency, even without direct electrical excitation, due to the external environment (e.g. noise from ship engines or other underwater equipment) or other sources of vibration (e.g. acoustic waves or mechanical vibrations generated by the FFR-HF transducer).Therefore, even in this embodiment, the two-stage division of the FFR-BF transducer can be applied.

[0072] After numerous tests and trials, the applicant found that assembling the various parts of the device further reduced the masking effect and improved hemispheric directivity over both octaves, particularly at high frequencies. The best results are obtained when the assembly's footprint on the volume of the internal cavity of transducers 1, 2 is minimized. To achieve this, the attachment system illustrated in [Fig. 6] is preferably used.

[0073] On the FFR-HF transducer 2, the assembly between the piezoelectric ring 2 and the tape 20 is achieved by means of an elastomer coating 3 covering all or part of the annular inner wall of said transducer. This coating 3 prevents the piezoelectric ring from becoming rigid, thus minimizing the impact on the radial resonance frequency. The coating 3 has one or more elastomer tabs 30 inside the ring, i.e., in the internal annular space of the transducer 2. A fixing rod 31 is mounted in each tab 30, which rod is fixed to the tape 20. Each tab 30 is, for example, drilled to allow the rod 31 to pass through, which is screwed into the tape 20. A spacer 32 is advantageously mounted on each rod 31 so as to keep the tape 20 away from the rear face of the transducer 2, thus ensuring the positioning between said tape and the piezoelectric ring.The assembly can be held in position using a nut 33 or any other equivalent element. According to an embodiment illustrated in [Fig.7], this assembly is duplicated at three points inside the piezoelectric ring 2, spaced 120° apart, in order to guarantee robustness of the FFR-HF transducer.

[0074] For the FFR-BF transducer, this same assembly is advantageously duplicated to assemble the piezoelectric ring 1 and the tape 10.

[0075] When the FFR-BF transducer 1 has two stages 1a and 1b, this same assembly is also used. The coating 3 covering all or part of the annular inner wall of the first stage 1a has one or more first tabs 30a, and the coating 3 covering all or part of the annular inner wall of the second stage 1b has one or more second tabs 30b arranged opposite said first tabs. A retaining rod 31 is then mounted in each first tab 30a and second tab 30b. An additional spacer 34 mounted on each retaining rod 31 ensures the relative positioning of the two piezoelectric rings 1a and 1b.

[0076] In order to assemble the FFR-BF 1 and FFR-HF 2 transducers together very simply, the rods 31 installed in the FFR-BF 1 transducer are also fixed to the second tape 20. According to one embodiment, three tabs 200 are added to the outside of the second tape 20, for example spaced at 120° intervals ([Fig. 7]). These tabs 200 are, for example, drilled to allow the rods 31 of the FFR-BF 1 transducer. A spacer 35 ensures the relative positioning between the second tape 20 and the FFR-BF 1 transducer. The assembly can be held in position using a nut 33 or any other equivalent element. The rear face of the second tape 20 can be located in the plane of the front face of the FFR-BF 1 transducer or offset from this plane, for example by a distance of between 0.5 mm and 2 mm, preferably 1 mm.

[0077] With reference to [Fig.7], the tabs 200 make it possible to maintain an annular space E between the two transducers, so that the FFR-HF 2 transducer does not mask the radiation of the FFR-BF 1 transducer and that the assembly of the two transducers does not significantly impact the hemispheric directivity of the complete device.

[0078] To protect the transducers 1, 2 from seawater, a complete resin coating of said transducers can be considered, but this solution is likely to restrict the radial resonance modes and limit the acoustic performance of the device.

[0079] To overcome this problem, referring to Figures 6 and 8, a watertight hood 4, preferably made of elastomer, encloses the two transducers 1 and 2. This hood 4 forms an internal chamber filled with a fluid. This fluid is advantageously castor oil, whose acoustic behavior is similar to that of seawater. However, other acoustically conductive fluids can be used, such as mineral oils, silicone oils, or glycol-based fluids.

[0080] In order not to restrict the radial resonance modes, an internal space separates the hood 4 from the transducers 1, 2, so that it is not in contact with said transducers. The distance separating the inner wall of the hood 4 from the outer walls of the transducers 1, 2, is for example between 0.5 mm and 2 mm, preferably 1 mm.

[0081] The hood 4 can be positioned very simply by means of a circular lug 40 located inside the hood, at the base of the device, which fits into a groove formed on the circumference of the first band 10 of the FFR-BF transducer 1. At the top of the device, the hood 4 has lugs 41 into which the rods 31 of the FFR-HF transducer 2 are positioned, keeping the hood open. The seal of the internal chamber can be ensured by a fastening means that secures the hood 4 to the band 10. This fastening means can, for example, be in the form of one or more Serflex®-type hose clamps, installed at the base of the device, which press the hood 4 against the band 10.

[0082] The electrical signals used to excite transducers 1, 2 and / or generated by said transducers in response to the reception of an acoustic wave, The signals are communicated via electrical cables (not shown) connected to the transducers. In [Fig. 6], a hole 11, 21 is provided in each of the steps 10, 20 for the passage of these cables. In the step 10 in contact with the water, a resin coating is applied to ensure a watertight seal. Another hole 12 is made in the step 10 to allow the internal chamber to be filled with fluid. A plug 120 ensures the watertightness of this hole 12.

[0083] In the embodiment of [Fig. 6], the transducers 1 and 2 are assembled together by means of the rods 31 installed in the FFR-BF transducer. However, the transducers 1 and 2 can be separated. For example, the assembly formed by the FFR-HF transducer 2 and its tape 20 can be held in position by means of the cap 4, particularly at the points 41, without it being necessary to fix the rods 31 of the FFR-BF transducer in the second tape 20.

[0084] The arrangement of the various elements and / or means and / or steps of the invention, in the embodiments described above, should not be understood as requiring such an arrangement in all implementations. In any event, it will be understood that various modifications may be made to these elements and / or means and / or steps, without departing from the spirit and scope of the invention.

[0085] Furthermore, one or more features described only in one embodiment can be combined with one or more other features described only in another embodiment. Similarly, one or more features described only in one embodiment can be generalized to other embodiments, even if this or these features are described only in combination with other features.

Claims

Demands

1. Underwater acoustic transceiver device, comprising: - a first annular "Free Flooded Ring" FFR transducer (1) configured to operate in a first octave covering a first low frequency (LF) range, and a second annular FFR transducer (2) configured to operate in a second octave covering a second high frequency (HF) range, - the two FFR transducers (1,2) are arranged coaxially, each transducer having a front face and a rear face, - the rear face of the second FFR transducer (2) is located in the plane of the front face of the first FFR transducer (1) or away from said plane in the direction of emission.

2. Device according to claim 1, wherein a first acoustic reflector (10) is positioned at a rear face of the first FFR transducer (1).

3. A device according to any one of the preceding claims, wherein the inner diameter ( <j>i) of the first FFR transducer (1) is greater than the outside diameter (Oo) of the second transducer (2).

4. Device according to any one of the preceding claims, wherein the first FFR transducer (1) comprises a first stage (1a) and a second stage (1b), which stages are separated from each other.

5. Device according to any one of the preceding claims, wherein, in use, the first FFR transducer (1) operates on the octave [fBF-2.fBF] and the second transducer (2) operates on the octave [2.fBF - 4.fBF], fBF being the lower frequency of the effective frequency band of the first FFR transducer (1).

6. Device according to any one of the preceding claims, wherein a sealed elastomer hood (4) encloses the two FFR transducers (1, 2) so as to form an internal chamber filled with a fluid.

7. Device according to claim 6, wherein an internal space separates the hood (4) from the FFR transducers (1,2), so that said hood is not in contact with said transducers.

8. Device according to any one of the preceding claims taken in combination with claim 2, wherein the first acoustic reflector (10) is moved away from the rear face of the first FFR transducer (1).

9. Device according to any one of the preceding claims taken in combination with claim 2, wherein a second acoustic reflector (20) is positioned at the rear face of the second FFR transducer (2).

10. Device according to claim 9, wherein the second acoustic reflector (20) is moved away from the rear face of the second FFR transducer (2).

11. Device according to any one of the preceding claims taken in combination with claim 2, wherein the first acoustic reflector (10) is assembled to the first FFR transducer (1) by means of an assembly comprising: - an elastomer coating (3) covering all or part of the annular inner wall of the first FFR transducer (1), which coating has one or more elastomer tabs (30) arranged in the annular inner space of said first transducer, - a fixing rod (31) mounted in each tab (30), which rod is fixed to the first acoustic reflector (10).

12. Device according to claim 11, wherein a spacer (32) is mounted on each fixing rod (31) so as to move the first acoustic reflector (10) away from the rear face of the first FFR transducer (1).

13. Device according to any one of the preceding claims taken in combination with claim 9, wherein the second acoustic reflector (20) is assembled to the second FFR transducer (2) by means of an assembly comprising: - an elastomer coating (3) covering all or part of the annular inner wall of the second FFR transducer (2), which coating has one or more elastomer tabs (30) arranged in the annular inner space of said second transducer, - a fixing rod (31) mounted in each tab (30), which rod is fixed to the second acoustic reflector (20).

14. Device according to claim 13, wherein a spacer (32) is mounted on each fixing rod (31) so as to move the second acoustic reflector (20) away from the rear face of the second FFR transducer (2).

15. Device according to any one of the preceding claims taken in combination with claim 4, wherein the two stages (the, lb) of the first FFR transducer (1) are assembled using an assembly comprising: - an elastomeric coating (3) covering all or part of the annular inner wall of the first stage (la), which coating has one or more first elastomeric tabs (30a) arranged in the annular inner space of said first stage, - an elastomeric coating (3) covering all or part of the annular inner wall of the second stage (lb), which coating has one or more second elastomeric tabs (30b) arranged in the annular inner space of said second stage, opposite the first tab(s) (30a), - a fixing rod (31) mounted in each first tongue (30a) and second tongue (30b).

16. Device according to claim 15, wherein a spacer (34) is mounted on each fixing rod (31) so as to separate the first stage (la) from the second stage (lb).

17. Device according to any one of the preceding claims taken in combination with claims 9 and 11, wherein the fixing rods (31) used to assemble the first acoustic reflector (10) to the first FFR transducer (1) are also fixed to the second acoustic reflector (20).< / j>

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