Patent Application
20190060954
The present invention relates to a broadband underwater acoustic transceiver device. This device finds applications in particular for positioning, detection, range finding or underwater acoustic communication.
The underwater acoustic transducers are known and used for long. There exist several types thereof, which may implement magnetostrictive, electrostrictive or piezoelectric materials. Among the knows types of transducers, the two following ones can be mentioned:
The performance increase of a great number of underwater acoustic devices requires the use of acoustic signals utilizing a broad frequency band.
The width of the frequency band utilizable by an underwater acoustic transducer is generally proportional to the central frequency of this band. The transducers of the prior art implemented for the aimed applications generally cover one octave, i.e. ⅔ of the central frequency.
As a function of the searched ranges, the frequency bands utilized are different. Indeed, for a same distance of propagation, the higher acoustic frequencies are more absorbed by the medium, herein the Ocean, than the lower frequencies.
Hence, as a function of the needs, it may be useful to have a transceiver device capable of utilizing at least two distinct bands, of one octave each for example. The band covering the low frequencies (of central frequency FLF) for the applications aiming at the long range, but of more reduced band widths (typically: ⅔ FLF), and the band covering the high frequencies (of central frequency FHF), aiming at shorter ranges but of wider band widths (⅔ FHF).
Finally, the acoustic transceiver devices consisted of electroactive elements generally require for their application an angular aperture that is at least hemispherical.
In order to increase the utilizable frequency band of the underwater acoustic transceiver devices, it has been proposed to modify the structure of the transducers or, for a better result, to associate together several transducers having different structures and/or dynamic characteristics, in particular different utilizable frequency bands.
For example, in the documents EP 0413633 A1 “Emetteur large-bande sous-marin” by Safare-Crouzet or U.S. Pat. No. 8,027,224 “Broadband Underwater Acoustic Transducer” by Brown et al., it is proposed to cover several sub-bands by implementing spheres and/or rings of the FFR (“Free Flooded Ring”) type, associated with each other. However, such a solution poses the difficulty of the radiation masking in the axis of alignment of the associated transducers.
Other modes of bandwidth broadening are also known from the documents U.S. Pat. No. 4,373,143 “Parametric Dual Mode Transducer”, U.S. Pat. No. 6,690,621 “Active Housing Broadband Tonpilz Transducer” and U.S. Pat. No. 5,579,287 “Process and transducer for emitting wide band and low frequency acoustic waves in unlimited immersion depths”.
Contrary to those solutions associating transducers, the present invention proposes a combination of transducers of different types, at least one element of the device being common to the operation of the combined transducers. Hence, the solution proposed by the present invention consists in freeing from the masking effects by using a functional part common to two transducers of different types and each transmitting in a desired band.
This approach is to be distinguished from that of the document U.S. Pat. No. 4,373,143, in which it is used a transducer of low-frequency Tonpilz type, whose horn serves as a countermass for a high-frequency Tonpilz antenna, hence with two transducers of the same type. Moreover, in this same document, the two transmitters are excited simultaneously to produce a non-linear transmission of the parametric type. It is also to be distinguished from the document U.S. Pat. No. 6,690,621, in which a Tonpilz transducer covering the low frequency is juxtaposed to an active annular ceramic covering the high frequency, the latter forming the annular casing of the system.
The invention considered herein consists in the functional combination of two transducers of different types: the Tonpilz and the FFR (“Free Flooded Ring”).
The present invention hence proposes to combine a Tonpilz transducer and an FFR transducer to cover a two-octave band, the Tonpilz covering the low-frequency octave (LF) and the FFR, the high-frequency octave (HF), the latter being placed forward in the direction of the transmissions. Moreover, one element of each transducer is made functionally common and it is the reflective “plug” of the FFR transducer, which is also the Tonpilz horn (and the reverse), in order to avoid in particular two problems resulting from a simple association of transducers. Namely, on the one hand, the transducer placed forward on the axis of transmission masks the transducer placed rearward and, on the other hand, the rearward transmission of the transducer placed forward reflects onto the transmitting surface of the transducer placed rearward (plug for the FFR, horn of the Tonpilz), this reflection being liable to interfere destructively with the direct/forward wave transmitted by the transducer placed forward.
Thanks to this implementation of a common element between the two transducers of different types, the Tonpilz no longer has a part masking its radiation along the axis and the wave transmitted rearward by the FFR is baffled by the Tonpilz stack and is unable to be reflected. Such a configuration has another advantage in the case where the two frequency sub-bands are adjacent to each other and where the Tonpilz covers the low band. Indeed, the cavity resonance of the FFR may be excited by the Tonpilz transmission and hence increase the sensitivity to the Tonpilz transmission in the upper part of the its band.
Moreover, if it is desired to further increase the utilizable frequency bands, additional means may be implemented. Indeed, an FFR naturally covers a one-octave band, by coupling between the cavity resonances and the radial mode of the ceramic. On the other hand, a Tonpilz naturally covers, in the best case, half an octave. It is hence useful to broaden the Tonpilz band by coupling the mass-spring mode of the Tonpilz with other modes. For the upper part of the band, the cavity mode of the FFR that is combined thereto may be used. In the lower part of the band, the proposed solution consists in integrating a cylindrical acoustic baffle about the Tonpilz transducer and in particular about its ring stack and/or about the element put in common, i.e. the horn serving as a “plug”, and hence generating a radial cavity mode in a similar way to what is obtained in a structure of the Janus-Helmholtz type (cf. U.S. Pat. No. 5,579,287) and whose frequency is adjusted to the lower part of the low-frequency band. It is hence possible to cover one octave with such a solution of the type: baffled Tonpilz combined with an FFR. It is to be finally noted that this baffle, which must be massive and be the less elastic possible, may fulfil other functions, as for example serving as a protection or a support for a protection cage for the complete transducer.
It may finally be noted that the broadband underwater acoustic transceiver system of the invention has a hemispheric directivity.
Hence, the present invention relates to a broadband underwater acoustic transceiver device including at least one transducer of the Tonpilz type and a transducer of the FFR (“Free Flooded Ring”) type,
the Tonpilz-type transducer, cylindrical in shape, being symmetrical in revolution about an anteroposterior axis, said Tonpilz-type transducer including elements arranged from the rear to the front along its anteroposterior axis of revolution, said elements being at least: a rear countermass, electroactive elements and a front horn,
the FFR-type transducer being symmetrical in revolution about an anteroposterior axis, said FFR-type transducer including elements arranged from the rear to the front along its anteroposterior axis of revolution, said elements being at least: a “plug” and an electroactive ring.
According to the invention, the Tonpilz-type and FFR-type transducers are aligned with each other, their anteroposterior axes of revolution being superimposed, the Tonpilz-type transducer being placed rearward and the FFR-type transducer being placed forward and having their respective front transmission directions oriented forward, and the transducers are combined within the device by putting in common one of their elements, said common element, called the plug-horn element, being the “plug” of the FFR and the horn of the Tonpilz.
In various embodiments of the invention, the following means, which can be used alone or according to any technically possible combinations, are used:
The following description in relation with the appended drawings, given by way of non-limitative example, will allow a good understanding of what the invention consists in and of how it can be implemented.
In the appended drawings:
The sectional view of
The Tonpilz-type transducer includes, from the rear to the front of the device, a rear countermass 2, a stack of piezoelectric discs, and more particularly herein of piezoelectric rings 3, so that a pre-stressing rod 5 can pass in the centre of the stack, and a horn that is the common plug-horn element 4. The pre-stressing rod 5 is tensioned between the rear countermass 2 and the common plug-horn element 4 in order to apply a constraint to the stack of rings 3.
The FFR-type transducer includes, from the rear to the front of the device, the common plug-horn element 4 and a piezoelectric ring 6. The central part of the piezoelectric ring 6 is closed on the front by a front wall 8 and on the rear by the common plug-horn element 4 and forms a closed central cavity. A fluid 7, for example a liquid that is castor oil, is placed in this central part/cavity of the piezoelectric ring 6. The fluid hence come into contact with the common plug-horn element 4. In the embodiment shown in
This combination of two Tonpilz and FFR transducers has another advantage in the case where the two frequency sub-bands of each transducer are adjacent and where the Tonpilz covers the low band. Indeed, the cavity resonance of the FFR may be excited by the Tonpilz transmission and hence increase the sensitivity to the Tonpilz transmission in the upper part of the its band.
Generally, the Tonpilz-type transducer may be either resinated, or inserted into a casing filled with a fluid whose acoustic properties are adapted to the searched operation mode: for example, castor oil for the acoustic transparency or air for a baffling. It is to be noted that, in the case where air is used for the baffling, the baffle includes a rigid casing that encloses the air cavity and the transducer is then generally limited to less deep immersions.
In the device shown in
In an alternative embodiment, the fluid is air or a gas or a gaseous composition, in order to obtain a baffling effect. The pressure of the gaseous fluid will be adapted to the needs.
In order to further improve the width of the utilizable frequency band, a guard ring 10 has been placed at the periphery of the device, opposite the Tonpilz-type transducer. In this example, the guard ring 10 is distinct from the rear countermass 2 and is separated therefrom by a layer of material having elasticity properties, typically an elasticity module <100 MPa or, in a variant, by a fluid vent. Herein, this is the sealing membrane 11, which also covers the device, that forms the separation.
In
The action of the Tonpilz-type transducer is visible in the “LF Octave” part, with mainly the mass-spring mode MSM. It can be observed a rising of the curve towards the lowest frequencies thanks to the implementation of the baffling that creates a baffle cavity mode BCM.
The action of the FFR-type transducer is visible in the “HF Octave” part, with mainly a ring radial mode RRM, and, lower in frequency, a ring cavity mode RCM that allows broadening the low-frequency response.
In the preferred using mode of the device, as a function of the low or high frequencies that it is desired to produce, only one of the two transducers is supplied with an alternative current of frequency(ies) in relation with that(those) which it is desired to produce. If desired, the generated waves are generated discontinuously in order to allow a reception between the transmissions. The alternative current may have a wave shape other than sinusoidal and in particular any shape that is useful for generating pure waves and/or with harmonics and/or other linear or non-linear effects. It is however contemplated the case where the two transducers are supplied in the same time by alternative currents adapted to each one.
It is understood that the invention may be implemented in many other ways. For example, the guard ring 10 may be omitted or a single-piece element forming both the rear countermass 2 and the guard ring 10 may be implemented. Moreover, the discs or rings 3 of the Tonpilz-type transducer and/or the piezoelectric ring 6 may be made in various known manners, in particular as single-piece or composite transduction elements, in the latter case by assembly of elementary transducers forming a disc or a ring.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1559619 | Oct 2015 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/FR2016/052559 | 10/5/2016 | WO | 00 |
