Broadband underwater acoustic transceiver device

Abstract

Disclosed is a broadband underwater acoustic transceiver device. The device can be used in particular for positioning, detection, range finding or underwater acoustic communication. The device coaxially combines, within a transceiver device, a Tonpilz transducer and a FFR transducer, the FFR being arranged in front of the transmission face/horn of the Tonpilz transducer. In such a configuration, the Tonpilz horn also acts as reflective tape for the FFR transducer, forming a common tape-horn element. Furthermore, an annular baffle surrounding the Tonpilz pillar creates a Helmholtz cavity for broadening the emission band towards the low frequencies.

Claims

1. A broadband underwater acoustic transceiver device comprising: at least one Tonpilz transducer and a Free Flooded Ring transducer, wherein the at least one Tonpilz transducer is cylindrical in shape, and is symmetrical in revolution about an anteroposterior axis of revolution extended between a front side and a rear side of the at least one Tonpilz transducer, said at least one Tonpilz transducer including elements arranged from the rear side to the front side along the anteroposterior axis of revolution, said elements being at least: a rear countermass, electroactive elements and a front horn, said at least one Tonpilz transducer having a front transmission direction, wherein the Free Flooded Ring transducer is symmetrical in revolution about an anteroposterior axis of revolution extended between a front side and a rear side of the Free Flooded Ring transducer, said Free Flooded Ring transducer including elements arranged from the rear side to the front side along the anteroposterior axis of revolution of the Free Flooded Ring transducer, said elements being at least: a plug and an electroactive ring, said Free Flooded Ring transducer having a front transmission direction, wherein the at least one Tonpilz transducer and the Free Flooded Ring transducer are aligned with each other, the respective anteroposterior axes of revolution being superimposed, with the at least one Tonpilz transducer being arranged rearward of the Free Flooded Ring transducer and the Free Flooded Ring transducer being arranged forward of the at least one Tonpilz transducer and having respective front transmission directions oriented forward, and wherein the at least one Tonpilz-type transducer and the Free Flooded Ring transducer are combined within the device by the front horn of the at least one Tonpilz transducer being the plug of the Free Flooded Ring transducer, the front horn of the at least one Tonpilz transducer and the plug of the Free Flooded Ring transducer being a common element of the Free Flooded Ring transducer and the at least one Tonpilz transducer.

2. The underwater acoustic transceiver device according to claim 1, wherein at least one pre-stressed rod is anteroposteriorly extended between the rear countermass and the plug-horn element.

3. The underwater acoustic transceiver device according to claim 1, wherein the plug-horn element serves as a support for the electroactive ring of the Free Flooded Ring transducer through elastomeric suspensions.

4. The underwater acoustic transceiver device according to claim 1, wherein an annular cavity containing a fluid is arranged against a lateral periphery of the at least one Tonpilz transducer, at least against the electroactive elements of the at least one Tonpilz transducer.

5. The underwater acoustic transceiver device according to claim 4, wherein the fluid of the annular cavity is chosen among: a gas, a gaseous composition, a liquid, and a gel.

6. The underwater acoustic transceiver device according to claim 1, wherein a guard ring comprising a rigid metallic mass is arranged at a lateral periphery of the device, at least opposite the at least one Tonpilz transducer.

7. The underwater acoustic transceiver device according to claim 6, wherein the guard ring and the rear countermass are distinct elements.

8. The underwater acoustic transceiver device according to claim 7, wherein the guard ring and the rear countermass are separated by a layer of acoustic damping material.

9. The underwater acoustic transceiver device according to claim 1, wherein the electroactive ring of the Free Flooded Ring transducer is coated at least in part with a protective material, the electroactive ring of the Free Flooded Ring transducer being applied against the plug-horn element through a layer of protective material and wherein the front side of the electroactive ring of the Free Flooded Ring transducer is closed and a fluid is placed inside said electroactive ring of the Free Flooded Ring transducer, said fluid coming into contact with the plug-horn element.

10. The underwater acoustic transceiver device according to claim 9, wherein the fluid placed inside the electroactive ring of the Free Flooded Ring transducer is chosen among: a gas, a gaseous composition, a liquid, and a gel.

11. The underwater acoustic transceiver device according to claim 1, wherein the electroactive elements of the at least one Tonpilz transducer and the electroactive ring of the Free Flooded Ring transducer are piezoelectric ceramics.

Description

DETAILED DESCRIPTION OF AN EXEMPLARY EMBODIMENT

(1) 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.

(2) In the appended drawings:

(3) FIG. 1 shows a sectional view of a device according to the invention, and

(4) FIG. 2 shows the transmission-response curve of said device.

(5) The sectional view of FIG. 1 passes through the revolution symmetry axis of the underwater acoustic transceiver device 1, axis that corresponds to the front axes of forward transmission of each of both Tonpilz and FFR transducers or, in other words, that carries these axes. The Tonpilz-type transducer 2, 3, 4, 5 is on the left in FIG. 1 and, also, on the rear of the device, considering the front transmission direction 13 of the device that is oriented toward the right in FIG. 1. The FFR-type transducer 4, 6 is on the right in FIG. 1 and, also, on the front of the device.

(6) 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.

(7) 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 FIG. 1, the piezoelectric ring 6 is not directly applied to the common plug-horn element 4 and a layer of material is interposed between both. In a particular embodiment, the plug-horn serves as a support for the electroactive ring of the FFR transducer through elastomeric suspensions. In FIG. 1, this is the sealing membrane 11 that also serves as a suspension between both 4, 6.

(8) 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.

(9) 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.

(10) In the device shown in FIG. 1, at the lateral periphery of the Tonpilz-type transducer, is arranged a lateral cavity 9 containing a fluid, for example a liquid that is castor oil. This lateral cavity 9 is annular due to the fact that the Tonpilz-type transducer is substantially cylindrical, just as the other transducer, the FFR one. The lateral cavity 9 extends opposite or against at least a part of the stack of rings 3. In the example shown in FIG. 1, this cavity goes up to a lateral part of the common plug-horn element 4 and does not come into contact with the rear countermass 2, a layer 12 of material being arranged between both 9, 2.

(11) 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.

(12) 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.

(13) In FIG. 2, the frequency-response curve, for the transmission, allows visualizing the effects of each type of transducer and the contribution of the common plug-horn element implementation. A baffle-based device has been analysed to produce this curve. The lowest frequencies are on the left along the frequency abscissa axis. The graduation pitch of the ordinates is 10 dB. The represented curve corresponds to the transmission ratio with respect to the voltage applied, in dB as an arbitrary unit.

(14) 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.

(15) 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.

(16) 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.

(17) 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.