"UNDERWATER SOUND GENERATOR"

Technical field

[0001] The present invention relates to any process where the generation of high fidelity underwater acoustic signals is needed, such as but not restricted to the reproduction of acoustic fish signals.

Summary

[0002] The present invention provides a system for high fidelity underwater sound generation. The system includes an underwater sound actuator and the corresponding electronic driver. The sound is generated by a rigid plate whose vibration is both electromagnetically excited and attenuated, thus avoiding the use of any elastic membrane. It should also be noted that, since there is no compressible air inside the device, which is flooded by water, the operation of this device is independent from depth, broadening its applications to any water pressure.

[0003] The present invention provides a method and apparatus for high fidelity underwater sound generation, including an underwater sound actuator and an electronic driver. [0004] The invention includes a method for the generation of underwater sound, comprising the application of forces on a sound generation mean.

[0005] In the invention according to the previous paragraph said forces may be applied using permanent magnets fixed to an actuator body.

[0006] wherein said forces are applied using electric currents that run through a pair of coils fixed to said actuator body.

[0007] The invention also includes an apparatus for underwater sound generation, comprising:

[0008] a) an actuator whose vibrating part includes a rigid plate to generate the sound and contains a permanent magnet on its interior, so that the vibration of said vibrating part is caused by a force applied on said permanent magnet when a variable electric current is made to run through a pair of coils fixed in said actuator body;

[0009] b) a pair of permanent magnets fixed to said actuator body to maintain said vibrating part in an equilibrium position, avoiding the necessity to use any elastic membrane;

[0010] c) an electronic drive system that provides means to apply said variable electric current to said pair of coils in order to excite said vibrating part accordingly to the type of sound to be generated.

[001 1] The invention also includes an apparatus in accordance with the previous paragraphs that may further comprise: [0012] a) a second pair of coils fixed in the actuator body to maintain said vibrating part in an equilibrium position, by making a direct electric current to run through said pair of coils, avoiding the necessity to use any elastic membrane;

[0013] b) an electronic drive system that provides means to apply both said electric currents to both said pairs of coils in order to both support and excite said vibrating part.

[0014] The invention also includes an actuator that does not include any type of elastic membrane to support the vibrating part to said actuator body, this support being accomplished using the effect of electromagnetic forces on a permanent magnet embedded on said vibrating part.

Background Art

[0015] Commercial acoustic devices allowing low frequency sound playbacks in water are relatively scarce. Underwater loudspeakers developed for swimming pools, such as the UW30 from Lubell Labs or the Clark Synthesis AQ339 Aquasonic Underwater Speaker, although appropriate to playback music, do not represent well low frequency sounds with fast transients, such as the sounds of many fish species, and cannot be used in depths in excess of 3 m. Moreover, the power output of commercial loudspeakers is often affected by depth, a further complication for experiments requiring sound playback in places where the water level changes significantly, as is the case in sea shores and estuaries. [0016] Most devices for underwater sound playback use either 1 ) a piezoelectric effect, which is appropriate to produce medium to high frequency sounds above 1 kHz (e.g. patent US6098331 ), 2) a moving coil associated to a diaphragm, or 3) a system that incorporates both a diaphragm and an axial deformation mechanism (patent JP2001333487). Although these last devices can generate low frequency sounds, usually above a few tens of Hertz, the equilibrium position is dependent on elastic components, and so prone to resonation at certain frequencies.

[0017] In addition, some of those devices are sealed and incorporate air inside, creating a further constraint caused by increased pressures due to water depth. Thus, there was a need to develop a device that could overcome these limitations.

[0018] Several devices were created to produce underwater sounds, some of them described as appropriate to overcome some above mentioned problems. Moving coil (patents JP8256394, JP2005167565) or hydraulic (patent JP8009487) inventions use a piston and plate to drive oil that is circumscribed by an elastic membrane responsible for radiating the sound into water. Since those devices incorporate several elastic components they are more prone to resonances and as at least some air is kept inside, it is expected that they may be affected by water pressure, i.e. depth. [0019] The device described in the present invention does not keep any air inside, and thus its operation is water depth independent. Moreover, since both movement and damping of the rigid sound playback plate is magnetically actuated, the resonances are almost absent, allowing reproducing with very high accuracy low frequency sounds from about 15 Hz up to a few thousand Hertz even representing fast transients as is typical of many fish communication sounds.

[0020] According to the present invention, sound is generated by a rigid plate attached to a cylinder that contains a permanent magnet inside. The vibration of both the cylinder and the plate is accomplished by introducing a variable electrical current in a pair of coils surrounding the cylinder. A second pair of such coils is, for example, used for dampening the vibration of both the cylinder and the plate using another electric current.

[0021] This combination of both electromagnetic excitation and dampening makes it possible not to include any elastic membrane in the actuator, and thus avoids unwanted resonant modes. It should also be noted that, since there is no compressible air inside the device, which is flooded by water, the operation of this device is independent from depth, broadening its applications to any water pressure.

[0022] The present invention is applicable in any process where the generation of high fidelity underwater acoustic signals is needed, namely when low frequency sounds with short transients are to be reproduced, which is often the case in acoustic fish signals. From the exposed we believe the proposed device overcomes most of the limitations of available emitters of underwater sound, and since it is able to reproduce low frequency fast transient sound signals, such as fish sounds, independent of water depth and with negligible resonant effects, it may become an important tool for studies of fish behavior or other applications in deep water where low frequency signal playback may be requested.

Disclosure of the Invention

[0023] According to the present invention, sound is generated by a rigid plate attached to a cylinder that contains a permanent magnet inside. The vibration of both the cylinder and the plate is accomplished by introducing a variable electrical current in a pair of coils surrounding the cylinder. A second pair of such coils is used for dampening the vibration of both the cylinder and the plate using another electric current.

[0024] This combination of both electromagnetic excitation and dampening makes it possible not to include any elastic membrane in the actuator, and thus avoids unwanted resonant modes. It should also be noted that, since there is no compressible air inside the device, which is flooded by water, the operation of this device is independent from depth, broadening its applications to any water pressure.

[0025] The present invention is applicable in any process where the generation of high fidelity underwater acoustic signals is needed, namely when low frequency sounds with short transients are to be reproduced, which is often the case in acoustic fish signals.

Brief Description of Drawings

[0026] The following figures provide preferred embodiments for illustrating the description and should not be seen as limiting the scope of invention.

[0027] Figure 1 : Schematic representation of an 'exploded' cross-section of a preferred embodiment where:

(1 ) represents a plate for vibrating underwater,

(2) represents a cylindrical part,

(3) represents a screw,

(4) represents a permanent magnet,

(5) represents a second pair of coils for applying a force to the plate in the direction of its return to the equilibrium position,

(6) represents a first pair of coils for generating vibrations,

(7) represents a support,

(8) represents a spacing ring, (9) represents the actuator body, and

(10) represents a top lid.

[0028] Figure 2: Schematic representation of an assembled cross-section of a preferred embodiment.

Modes for Carrying Out the Invention

[0029] In the embodiment illustrated in Fig. 1 , a plate (1 ) is attached to a cylindrical part (2) using a screw (3). Said cylindrical part (2) contains in its interior a permanent magnet (4).

[0030] A pair of coils (5) is used to dampen said cylindrical part (2) and said plate (1 ) vibrations. For this purpose, the electronic driver unit applies an electric current to each of the coils that constitute said pair of coils (5), in such a way that said permanent magnet is forced to stay in equilibrium in a position between said coils (5).

[0031] Another pair of coils (6) is used to generate the wanted vibrations of said cylindrical part (2) and said plate (1). For this purpose, the electronic driver unit applies an electric current to each of the coils that constitute said pair of coils (6), in such a way that said permanent magnet is forced to move away from its equilibrium position between said coils (5) in a direction that depends on the sign of said current. [0032] Both said pairs of coils (5) and (6) are wounded on supports (7). The relative position of said supports (7) when the actuator is assembled is defined by a spacing ring (8). All these parts are assembled inside the actuator body (9), which is closed with a top lid (10). The preferred embodiment of the present invention as assembled is illustrated in Fig.2.

[0033] Having thus described a preferred embodiment of the present invention, it should be noted by those skilled in the art that the within disclosures are exemplary only and that various other alternatives, adaptations and modifications may be made within the scope of the present invention. Accordingly, the present invention is not limited to the specific embodiments as illustrated herein. The following claims set out particular embodiments of the invention.