AU3558102A

AU3558102A - Underwater antenna

Info

Publication number: AU3558102A
Application number: AU35581/02A
Authority: AU
Inventors: Rainer Busch; Christoph Hoffmann; Walter Sachs
Original assignee: STN Atlas Elektronik GmbH
Current assignee: Atlas Elektronik GmbH
Priority date: 2001-04-24
Filing date: 2002-04-22
Publication date: 2002-12-12
Anticipated expiration: 2022-04-22
Also published as: DE10119867B4; EP1253666A2; AU783946B2; ATE548780T1; EP1253666A3; EP1253666B1; DE10119867A1

Abstract

An underwater aerial comprising a housing (10) containing an integral transducer unit (13) made of numerous electro-acoustic transducers (131), and transducer operating components (17). The latter are fixed in place by holders (15), and are located in a receiving area (16) filled with a filler material whose acoustic impedance is close to that of water. The filler material is polyurethane.

Description

1

AUSTRALIA

Patents Act 1990 STN ATLAS ELEKTRONIK GMBH COMPLETE SPECIFICATION STANDARD PATENT Invention Title: Underwater antenna The following statement is a full description of this invention including the best method of performing it known to us:- The invention concerns an underwater antenna of the type defined in the generic part of claim 1.

Such underwater antennae are subjected to considerable shock loads by pressure waves produced by explosions in conjunction, for example, with mine search or mine protection sonar or a sediment sonar used for seismic tests on the seabed. In the antenna 'housings of such underwater antennae in addition to the electro-acoustic transducers to receive or transmit the sound further components and sub-assemblies are contained, e.g. electronic components, like re-amplifiers, transmission transformers, chokes etc. These components are accommodated in a mounting chamber formed in the housing and are fastened on a holder, that in turn is secured in the housing.

In the case of these shock loads considerable forces act on these components of the underwater antennae, so that the components must have a particularly shockproof design. But also the fastening of the components on the holder and of the holder in the housing have to be able to absorb extremely great forces and designed accordingly. Both these facts lead to a considerable increase of the manufacturing costs of such an underwater antenna.

The object of the invention is to reduce the forces acting on the components when the housing of an underwater antenna of the type described above is subjected to pressure waves triggered by explosions in the water.

According to the invention this objective is achieved by the features of claim 1.

The underwater antenna according to the invention has the advantage that by filling the accommodation chamber with a filling material that is adapted to suit the impedance of water the pressure wave impacting on the underwater antenna is not reflected on the boundary layer to the hollow accommodation chamber, but passes through the entire housing of the underwater antenna without any considerable reflection. Since no reflection wave will occur which would be superimposed on the incoming pressure wave, the components are accelerated to a considerably lesser extent by the pressure wave than would be the case in an accommodation chamber filled by air only, in fact approximately by half. In addition, the filler performs, on the one hand, a mechanical protective function for the components and on the other, by completely surrounding the components, it prevents their coming into resonance and the occurrence of a further increase of the oscillating force acting on the components, the so called resonance step-up, that in turn would result in the doubling of the acceleration value. Thus altogether smaller forces act on the components due to the filling material in the accommodation chamber, consequently placing lesser demands regarding the shock proofing of the components and lesser demands on the mounting forces necessary to fasten the components. Both measures result in the reduction of the manufacturing costs of the underwater antenna.

Appropriate embodiments of the underwater antenna according to the invention with advantageous developments of the invention become obvious from the further claims.

According to an advantageous execution of the invention the filling material is a liquid or a gel. A liquid filler facilitates the replacement or the repair of components. This is also valid for fillings with gel if the gel has the property that makes it liquid when heated.

The invention is described in the following in detail based on an embodiment illustrated in the drawing. It shows in: Fig.1 a longitudinal section of an underwater antenna, only schematically illustrated, Fig.2 a perspective view of a constructive execution of the underwater antenna with a partially sectioned housing, Figs.3 and 4 a diagram each showing, in the form of an example, the acceleration as a function of time, occurring in the gusset A of Fig.1 when the underwater antenna is subjected to a shock load in the case of non-filled (Fig.3) and filled (Fig.4) accommodation chamber.

The underwater antenna shown in longitudinal section in Fig.1 and only schematically as a constructive embodiment in Fig.2 is used preferably for mine detection and is an essential sensor of a mine evading device. The antenna has a rigid housing 10 enclosed by a lid 11, the housing being fastened on the free end of a support 12. The support 12 is held axially displaceably in the hull of a watercraft particularly of a submarine, so that the antenna can be extended or retracted through an opening in the hull. The carrier 12 may also be so constructed that it could rotate about its longitudinal axis.

As it is indicated in the sectioned schematic illustration of Fig.1, the underwater antenna has a transducer arrangement 13 forming a so called plane array from a plurality of individual transducers 131 which are horizontally and vertically distanced from one another and are embedded in a casting 14 made from synthetic material, e.g. polyurethane. The transducer arrangement 13 is accommodated in the front region of the housing 10 and fastened on a mounting plate 15 that extends transversely in the housing 10. On the rear side of the mounting plate 15, that is averted to the transducer arrangement 13, an accommodation chamber 16 is provided in the housing 10 for further components 17 of the antenna. These components 17 are, for example, preamplifiers, transmission transformers, chokes or other electronic components.

These components 17 are fastened on the mounting plate 15 by means of suitable fastening pins 18. The constructive execution of the components 17, illustrated only schematically in Fig.1, can be seen in Fig.2. They have a double-layered printed circuit board 19, on which electronic components are fastened and joined electrically with one another. Each printed circuit board 19 is fastened on the mounting plate 15 by means of the above mentioned fastening pins 18. The plug-in connectors 20 fastened on the mounting plate establish the electrical connection between the electronic components and the transducers 131 of the transducer arrangement 13.

After securing in the components 17 the entire accommodation chamber 16 is filled with a filling material 21, the acoustic impedance of which approximates that of water. When a pressure wave, triggered, for example, by the explosion of a mine, hits the transducer arrangement 13 with a pressure amplitude of po, then, while passing through the casting 14 that has an acoustic impedance comparable to that of water, the pressure amplitude po remains approximately the same and impacts the boundary surface between the casting 14 and the filler material 21. This pressure wave generates on the mounting plate 15 an oscillation, whereby the mounting plate 15 is subjected to an acceleration of Po ao p where p is the mass density, c is the velocity of sound and E is the l/e width.

The l/e width is that time period in which the pressure amplitude p(t) of the pressure wave standardised to the pressure amplitude po fades out to the value l/e. In the case, for example, of a pressure wave of 200 bar, a l/e width of 9=1.10 3 sec and a sound velocity of c=1500 m/sec an average acceleration of ao=1.3o10 4 m/sec2 is obtained. If the components 17 have a mass of m, then the mounting forces with which the components 17 are held on the mounting plate 15 have to be greater than F=2mao. If there was no filling material 21 in the accommodation chamber 16, but it would be filled merely by air, then the pressure wave would be reflected on the boundary surface between the casting 14 and the accommodation chamber 16 and the reflection waves would superimpose the pressure wave. The pressure amplitude acting on the mounting plate 15 would be doubled, so that twice as large mounting forces would be required to prevent a detachment of the components 17 from the mounting plate The above described acceleration conditions are illustrated in Figs.3 and 4 in the case of an air-filled accommodation chamber 16 (Fig.3) and when the accommodation chamber 16 is filled with impedance-matched filling material 21. In this case the acceleration of the gusset A on the mounting plate 15 in Fig.1 is shown as a function of time, wherein at the time t=O the pressure wave impacts the transducer arrangement 13 with a pressure amplitude of approx.

190 bar. It can be clearly seen that the acceleration of the gusset A is considerably reduced by the filling material 21. Such a reduction will be even greater if one considers that in the case of an air-filled accommodation chamber 16 a resonance step-up may occur on the mounting plate 15 if 6 corresponds to the resonance frequency of the mounting of the components 17.

As filling material 21 preferably a fluid, e.g. oil or a gel that becomes fluid by heating, is used. In the case of such a filling material 21 the accommodation chamber 16 can be discharged for the purpose of repair or to replace components 17. However, as filling material 21 a liquid casting material, e.g.

polyurethane, that can be hardened, can also be used.

Claims

1. An underwater antenna with a housing, with a transducer arrangement of a plurality of electro-acoustic transducers integrated in the housing, with components to operate the transducer accommodated in an accommodation chamber formed in the housing and with a holder fastened in the housing on which holder the components are fastened, characterised in that the accommodation chamber is completely filled with a filling material the acoustic impedance of which approximates that of water.

2. An underwater antenna according to claim filling material is a gel.

3. An underwater antenna according to claim filling material is a fluid.

4. An underwater antenna according to claim fluid is oil.

5. An underwater antenna according to claim filling material is a hardenable casting material.

6. An underwater antenna according to claim casting material is polyurethane. 1, characterised in that the 1, characterised in that the 3, characterised in that the 1, characterised in that the 5, characterised in that the

7. An underwater antenna according to any one of claims 1 to 6, characterised in that the components are electronic components.

8. An underwater antenna according to claim 7, characterised in that the electronic components are arranged on printed circuit boards which are fastened on the holder.

9. An underwater antenna according to any one of claims 1 to 8, characterised in that the holder is a mounting plate.

An underwater antenna according to any one of claims 1 to 9, characterised in that the electro-acoustic transducer is embedded in a casting having an acoustic impedance that is matched to that of water and that the accommodation chamber is arranged on the rear side of the casting.

11. An underwater antenna according to claims 9 and 10, characterised in that the mounting plate abuts against the casting.

12. An underwater antenna according to any one of claims 1 to 11, characterised in that the housing is fastened on a support that can be pivoted about its longitudinal axis, said support being extendable from and retractable into the hull of a watercraft, in particular that of an underwater vehicle. DATED this twenty second day of April 2002 STN ATLAS ELEKTRONIK GMBH Patent Attorneys for the Applicant: F.B. RICE CO.