EP0506529B1 - Directional antenna for low frequency acoustic waves - Google Patents
Directional antenna for low frequency acoustic waves Download PDFInfo
- Publication number
- EP0506529B1 EP0506529B1 EP19920400754 EP92400754A EP0506529B1 EP 0506529 B1 EP0506529 B1 EP 0506529B1 EP 19920400754 EP19920400754 EP 19920400754 EP 92400754 A EP92400754 A EP 92400754A EP 0506529 B1 EP0506529 B1 EP 0506529B1
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- EP
- European Patent Office
- Prior art keywords
- antenna
- front face
- antenna according
- acoustic
- wavelength
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
- 239000000463 material Substances 0.000 claims description 2
- 238000010586 diagram Methods 0.000 description 5
- 230000005540 biological transmission Effects 0.000 description 2
- 230000005855 radiation Effects 0.000 description 2
- 241000251468 Actinopterygii Species 0.000 description 1
- 239000002131 composite material Substances 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 230000008878 coupling Effects 0.000 description 1
- 238000010168 coupling process Methods 0.000 description 1
- 238000005859 coupling reaction Methods 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 230000003071 parasitic effect Effects 0.000 description 1
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Classifications
-
- G—PHYSICS
- G10—MUSICAL INSTRUMENTS; ACOUSTICS
- G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
- G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
- G10K11/004—Mounting transducers, e.g. provided with mechanical moving or orienting device
- G10K11/006—Transducer mounting in underwater equipment, e.g. sonobuoys
Definitions
- the present invention relates to acoustic antennas which operate in the low frequency range, that is to say essentially below 5 kHz, and for which it is sought to improve the reception and / or emission diagram.
- the dimensions of the antenna are then small compared to the wavelength and typically they are of the same size as the latter.
- the acoustic radiation of such an antenna then essentially depends on the diffraction and becomes very sensitive to the arrangement of objects, in particular the support of the antenna, which are located near the latter, even when they are placed behind the emission face.
- the antenna is composed, in a known manner, of elementary sources of very small dimensions compared to the wavelength, for example 1/4 of this wavelength, which induces acoustic couplings between the acoustic projectors and strongly influences the total directivity pattern of the antenna.
- the directivity template of a sonar antenna must often be of complex shape. For example, we often need to emit a very open front lobe, for example 120 °, while obtaining a very weak rear parasitic lobe.
- the radiation pattern of a small acoustic base in front of the wavelength is in principle omnidirectional.
- this diagram depends essentially on the environment and the parts located near the base, which are likely to disturb the propagation of sound waves.
- Knowledge of the boundary conditions imposed by these parts, in particular by the load-bearing structures of acoustic projectors, is therefore very important for controlling the directivity in the far field.
- the invention proposes a low-frequency directive acoustic antenna comprising a set of acoustic transducers assembled along a front face to emit in a direction perpendicular to this front face, characterized in that the antenna further comprises two soft baffles located at the ends and behind the front face and substantially perpendicular thereto.
- the acoustic antenna which is shown in the appended figure comprises a front face 101 on which are grouped together a set of acoustic transducers (or projectors) 102, 6 in the example shown.
- These acoustic transducers are designed to emit low frequencies and their dimensions are calculated for a determined frequency, while being usable in a certain frequency band surrounding it. They are for example of the known type "Tonpilz".
- the diameter of these transducers is small compared to the wavelength used and a sufficient number is used to obtain the desired acoustic power.
- the width of the front face of the antenna is approximately of the order of 1 wavelength at the frequency used.
- the height is relatively arbitrary since the specifications of the directivity diagram to be obtained are essentially defined in the horizontal plane. By taking as in the figure a height appreciably smaller than the width, one obtains an omnidirectional diagram in the direction of the height.
- the structure of the antenna is arranged so that the ends of the front face fold back at an angle of 90 ° towards the rear to present two lateral faces 103 and 104.
- These lateral faces can be constituted by the supporting structure of the acoustic projectors 102.
- these side faces are provided with baffles known as "soft baffles" in order to control the directivity of the antenna in the horizontal plane.
- These soft baffles cover the lateral faces over the entire height of the antenna and over a depth which is substantially equal to 1 / 5th of the wavelength.
- the baffles are slightly offset backwards with respect to the front face of the antenna, but this arrangement, used in the example shown for mechanical construction reasons, has no critical influence on the directivity of the 'antenna.
- two antennas are made to transmit on the right and on the left, so that the assembly is parallelepipedic and the addition of soft baffles therefore does not oblige to increase the size of the antenna.
- baffle Any type of known baffle can be used, for example those formed by panels of naturally compliant material as described in patent application FR-A-83 00753 of the applicant, or panels comprising an air gap in equipression such as described in patent application FR-A-89 17432 in the name of the applicant.
- a preferred solution consists in using compliant tubes of substantially flattened section, made of composite material and which resonate at frequencies of the order of the antenna transmission frequency. These tubes are fixed vertically to cover the side faces.
Landscapes
- Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Acoustics & Sound (AREA)
- Multimedia (AREA)
- Transducers For Ultrasonic Waves (AREA)
- Aerials With Secondary Devices (AREA)
- Measurement Of Velocity Or Position Using Acoustic Or Ultrasonic Waves (AREA)
Description
La présente invention se rapporte aux antennes acoustiques qui fonctionnent dans le domaine des basses fréquences, c'est-à-dire essentiellement en-dessous de 5 kHz, et dont on cherche à améliorer le diagramme de réception et/ou d'émission.The present invention relates to acoustic antennas which operate in the low frequency range, that is to say essentially below 5 kHz, and for which it is sought to improve the reception and / or emission diagram.
Dans le domaine de la détection sous-marine on cherche à détecter des objets qui sont situés de plus en plus loin et dont le coefficient de réflexion est de plus en plus faible. Ceci nécessite, pour des raisons bien connues, d'utiliser des fréquences de plus en plus basses et des puissances d'émission des sonars de plus en plus importantes.In the field of underwater detection, it is sought to detect objects which are located farther and farther away and whose reflection coefficient is lower and lower. This requires, for well known reasons, to use increasingly lower frequencies and more and more sonar transmission powers.
Lorsque l'on peut se permettre d'utiliser des antennes acoustiques dont les dimensions sont grandes devant la longueur d'onde, on sait résoudre sans trop de difficulté le problème de la directivité de ces antennes.When we can afford to use acoustic antennas whose dimensions are large compared to the wavelength, we know how to solve without too much difficulty the problem of the directivity of these antennas.
On ne peut pas toujours utiliser des antennes de ces dimensions, surtout pour des questions hydrodynamiques, par exemple lorsqu'elles sont placées dans des poissons dont les dimensions sont nécessairement restreintes. Les dimensions de l'antenne sont alors faibles devant la longueur d'onde et typiquement elles sont de même grandeur que celle-ci. Le rayonnement acoustique d'une telle antenne dépend alors essentlellement de la diffraction et devient très sensible à la disposition des objets, notamment le support de l'antenne, qui se trouvent à proximité de celle-ci, même lorsqu'ils sont placés derrière la face d'émission. En outre l'antenne est composée, de manière connue, de sources élémentaires de dimensions très faibles devant la longueur d'onde, par exemple 1/4 de cette longueur d'onde, ce qui indult des couplages acoustiques importants entre les projecteurs acoustiques et influence fortement le diagramme de directivité totale de l'antenne.Antennas of these dimensions cannot always be used, especially for hydrodynamic questions, for example when they are placed in fish whose dimensions are necessarily limited. The dimensions of the antenna are then small compared to the wavelength and typically they are of the same size as the latter. The acoustic radiation of such an antenna then essentially depends on the diffraction and becomes very sensitive to the arrangement of objects, in particular the support of the antenna, which are located near the latter, even when they are placed behind the emission face. In addition, the antenna is composed, in a known manner, of elementary sources of very small dimensions compared to the wavelength, for example 1/4 of this wavelength, which induces acoustic couplings between the acoustic projectors and strongly influences the total directivity pattern of the antenna.
On sait par ailleurs que pour pouvoir détecter dans des conditions satisfaisantes les objets recherchés le gabarit de directivité d'une antenne sonar doit souvent être de forme complexe. Par exemple on a souvent besoin d'émettre un lobe avant très ouvert, par exemple 120°, tout en obtenant un lobe parasite arrière très faible.We also know that in order to be able to detect the desired objects under satisfactory conditions, the directivity template of a sonar antenna must often be of complex shape. For example, we often need to emit a very open front lobe, for example 120 °, while obtaining a very weak rear parasitic lobe.
Or le diagramme de rayonnement d'une base acoustique petite devant la longueur d'onde est en principe omnidirectionnel. En fait ce diagramme dépend essentiellement de l'environnement et des pièces situées à proximité de la base, qui sont susceptibles de perturber la propagation des ondes sonores. La connaissance des conditions aux limites imposées par ces pièces, notamment par les structures porteuses des projecteurs acoustiques, est donc très importante pour maîtriser la directivité en champ lointain.However, the radiation pattern of a small acoustic base in front of the wavelength is in principle omnidirectional. In fact this diagram depends essentially on the environment and the parts located near the base, which are likely to disturb the propagation of sound waves. Knowledge of the boundary conditions imposed by these parts, in particular by the load-bearing structures of acoustic projectors, is therefore very important for controlling the directivity in the far field.
L'approche théorique bien connue montre que pour obtenir un champ acoustique ayant la directivité décrite ci-dessus on devrait utiliser un baffle plan de dimensions infinies dans lequel sont implantés les projecteurs acoustiques. Comme cela n'est manifestement pas possible, on réduit les dimensions de ce baffle et on tente de manière empirique de placer divers écrans permettant d'obtenir le diagramme de directivité souhaité. Ceci nécessite donc des essais longs et coûteux et le résultat obtenu est médiocre et dépend fortement de la longueur d'onde utilisée.The well-known theoretical approach shows that to obtain an acoustic field having the directivity described above, a flat baffle of infinite dimensions should be used in which the acoustic projectors are installed. As this is clearly not possible, the dimensions of this cabinet are reduced and an empirical attempt is made to place various screens making it possible to obtain the desired directivity diagram. This therefore requires long and costly tests and the result obtained is poor and strongly depends on the wavelength used.
Pour pallier ces inconvénients et obtenir de manière systématique une antenne acoustique ayant la directivité souhaitée, l'invention propose une antenne acoustique basse fréquence directive comprenant un ensemble de transducteurs acoustiques assemblés selon une face avant pour émettre dans une direction perpendiculaire à cette face avant, caractérisée en ce que l'antenne comprend en outre deux baffles mous situés aux extrémités et en arrière de la face avant et sensiblement perpendiculairement à celle-ci.To overcome these drawbacks and systematically obtain an acoustic antenna having the desired directivity, the invention proposes a low-frequency directive acoustic antenna comprising a set of acoustic transducers assembled along a front face to emit in a direction perpendicular to this front face, characterized in that the antenna further comprises two soft baffles located at the ends and behind the front face and substantially perpendicular thereto.
D'autres particularités et avantages de l'invention apparaîtront clairement dans la description suivante faite à titre d'exemple non limitatif en regard de la figure annexée qui représente une vue schématique en perspective d'une antenne acoustique selon l'invention.Other features and advantages of the invention will appear clearly in the following description given by way of nonlimiting example with reference to the appended figure which represents a schematic perspective view of an acoustic antenna according to the invention.
L'antenne acoustique qui est représentée sur la figure annexée comprend une face avant 101 sur laquelle sont regroupés un ensemble de transducteurs ( ou projecteurs ) acoustiques 102, 6 dans l'exemple représenté. Ces transducteurs acoustiques sont prévus pour émettre des basses fréquences et leurs dimensions sont calculées pour une fréquence déterminée, tout en étant utilisables dans une certaine bande de fréquences entourant celle-ci. Ils sont par exemple du type connu "Tonpilz". Le diamètre de ces transducteurs est petit devant la longueur d'onde utilisée et on en utilise un nombre suffisant pour obtenir la puissance acoustique voulue.The acoustic antenna which is shown in the appended figure comprises a
La largeur de la face avant de l'antenne est sensiblement de l'ordre de 1 longueur d'onde à la fréquence utilisée. La hauteur est relativement quelconque puisque les spécifications du diagramme de directivité à obtenir sont essentlellement définies dans le plan horizontal. En prenant comme sur la figure une hauteur sensiblement plus petite que la largeur, on obtient un diagramme omnidirectionnel dans le sens de la hauteur.The width of the front face of the antenna is approximately of the order of 1 wavelength at the frequency used. The height is relatively arbitrary since the specifications of the directivity diagram to be obtained are essentially defined in the horizontal plane. By taking as in the figure a height appreciably smaller than the width, one obtains an omnidirectional diagram in the direction of the height.
Selon l'invention, la structure de l'antenne est aménagée de manière que les extrémités de la face avant se replient selon un angle à 90° vers l'arrière pour présenter deux faces latérales 103 et 104. Ces faces latérales peuvent être constituées par la structure porteuse des projecteurs acoustiques 102.According to the invention, the structure of the antenna is arranged so that the ends of the front face fold back at an angle of 90 ° towards the rear to present two
Selon l'invention, on munit ces faces latérales avec des baffles connus sous le nom de "baffles mous" afin de contrôler la directivité de l'antenne dans le plan horizontal. Ces baffles mous recouvrent les faces latérales sur toute la hauteur de l'antenne et sur une profondeur qui est sensiblement égale à 1/5ème de la longueur d'onde. Sur la figure, les baffles sont légèrement décalés en arrière par rapport à la face avant de l'antenne, mais cette disposition, utilisée dans l'exemple représenté pour des questions de construction mécanique, n'a aucune influence critique sur la directivité de l'antenne. Généralement, deux antennes sont réalisées pour émettre à droite et à gauche, de sorte que l'ensemble est parallélépipèdique et l'adjonction de baffles mous n'oblige donc pas à augmenter l'encombrement de l'antenne.According to the invention, these side faces are provided with baffles known as "soft baffles" in order to control the directivity of the antenna in the horizontal plane. These soft baffles cover the lateral faces over the entire height of the antenna and over a depth which is substantially equal to 1 / 5th of the wavelength. In the figure, the baffles are slightly offset backwards with respect to the front face of the antenna, but this arrangement, used in the example shown for mechanical construction reasons, has no critical influence on the directivity of the 'antenna. Generally, two antennas are made to transmit on the right and on the left, so that the assembly is parallelepipedic and the addition of soft baffles therefore does not oblige to increase the size of the antenna.
On peut utiliser tout type de baffle connu, par exemple ceux formés par des panneaux en matériau naturellement compliant tel que décrit dans la demande de brevet FR-A-83 00753 de la demanderesse, ou des panneaux comprenant une lame d'air en équipression tel que décrit dans la demande de brevet FR-A-89 17432 au nom de la demanderesse.Any type of known baffle can be used, for example those formed by panels of naturally compliant material as described in patent application FR-A-83 00753 of the applicant, or panels comprising an air gap in equipression such as described in patent application FR-A-89 17432 in the name of the applicant.
Une solution préférentielle consiste à utiliser des tubes compliants de section sensiblement aplatie, réalisés en matériau composite et qui résonnent à des fréquences de l'ordre de la fréquence d'émission de l'antenne. Ces tubes sont fixées verticalement pour recouvrir les faces latérales.A preferred solution consists in using compliant tubes of substantially flattened section, made of composite material and which resonate at frequencies of the order of the antenna transmission frequency. These tubes are fixed vertically to cover the side faces.
Les essais effectués avec une telle structure ont donné des résultats particulièrement intéressants quant à la directivité vers l'avant et à l'atténuation du lobe arrière.Tests carried out with such a structure have given particularly interesting results with regard to directivity towards the front and attenuation of the rear lobe.
Claims (7)
- Low frequency directional acoustic antenna comprising a set of acoustic transducers (102) assembled into a front face (101) in order to transmit in a direction perpendicular to this front face, characterized in that the antenna furthermore comprises two soft baffles (103) located at the ends and to the rear of the front face and substantially perpendicular to the latter.
- Antenna according to Claim 1, characterized in that the width of the front face is substantially equal to one wavelength at the transmitting frequency used.
- Antenna according to any one of Claims 1 and 2, characterized in that the width of the soft baffles (103) is substantially equal to 1/5 of the wavelength at the transmitting frequency used.
- Antenna according to any one of Claims 1 to 3, characterized in that the soft baffles (103) are formed from panels made of naturally compliant material.
- Antenna according to any one of Claims 1 to 3, characterized in that the soft baffles (103) are formed from a layer of air maintained at equi-pressure.
- Antenna according to any one of Claims 1 to 3, characterized in that the soft baffles (103) are formed from resonant structures substantially tuned to the transmitting frequency of the antenna.
- Antenna according to Claim 6, characterized in that the resonant structures are formed from compliant tubes.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FR9103853 | 1991-03-29 | ||
| FR9103853A FR2674717B1 (en) | 1991-03-29 | 1991-03-29 | DIRECTIONAL LOW FREQUENCY ACOUSTIC ANTENNA. |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| EP0506529A1 EP0506529A1 (en) | 1992-09-30 |
| EP0506529B1 true EP0506529B1 (en) | 1995-02-15 |
Family
ID=9411280
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| EP19920400754 Expired - Lifetime EP0506529B1 (en) | 1991-03-29 | 1992-03-20 | Directional antenna for low frequency acoustic waves |
Country Status (3)
| Country | Link |
|---|---|
| EP (1) | EP0506529B1 (en) |
| DE (1) | DE69201388T2 (en) |
| FR (1) | FR2674717B1 (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2725867A1 (en) | 1994-10-13 | 1996-04-19 | France Etat | AUTONOMOUS ACOUSTIC SOURCE FOR THE TOMOGRAPHY OF OCEANS |
| FR2731130B1 (en) * | 1995-02-23 | 1997-04-11 | France Etat | METHOD AND TRANSDUCERS FOR TRANSMITTING ACOUSTIC WAVES IN A LIQUID WITH LOW FREQUENCY DIRECTIVITY |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US1649113A (en) * | 1924-01-09 | 1927-11-15 | Harvey C Hayes | Submarine sound transmitter |
| US4140992A (en) * | 1977-08-17 | 1979-02-20 | The United States Of America As Represented By The Secretary Of The Navy | Baffled blanket acoustic array |
| FR2539541B1 (en) * | 1983-01-19 | 1986-09-19 | Thomson Csf | DEVICE WITH ACOUSTIC WAVE REFLECTIVE INTERFACE |
-
1991
- 1991-03-29 FR FR9103853A patent/FR2674717B1/en not_active Expired - Fee Related
-
1992
- 1992-03-20 DE DE1992601388 patent/DE69201388T2/en not_active Expired - Fee Related
- 1992-03-20 EP EP19920400754 patent/EP0506529B1/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| EP0506529A1 (en) | 1992-09-30 |
| DE69201388D1 (en) | 1995-03-23 |
| FR2674717B1 (en) | 1993-05-14 |
| FR2674717A1 (en) | 1992-10-02 |
| DE69201388T2 (en) | 1995-06-14 |
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