Communications – electrical: acoustic wave systems and devices – Signal transducers – Underwater type
Reexamination Certificate
2001-05-25
2003-02-04
Pihulic, Daniel T. (Department: 3662)
Communications, electrical: acoustic wave systems and devices
Signal transducers
Underwater type
Reexamination Certificate
active
06515940
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to electrodynamic type transducers that enable the transmission, within the sea, of acoustic waves and more particularly sound waves. These transducers are particularly useful in sonar technology.
2. Description of the Prior Art
It is the practice in underwater acoustics to use towed fish comprising electronic instruments and various transducers that can work in transmission, reception and possibly in both transmission and reception.
It is known that, in order to be able to emit sufficient acoustic power at low frequencies, typically frequencies of 10 Hz to 1 kHz, it is necessary to move substantial masses of water. This requires a shift, itself substantial, of the active face of the transducer. This generally leads to the use, in this case, of an electrodynamic type transducer comprising a horn driven by a mobile coil located in a gap. Transducers of this type are thus quite similar to loudspeakers which are well known in musical acoustics.
To be able to obtain the acoustic power frequently needed in certain applications, given the sound level to be attained which can be as much as 150 dB at 10 Hz, it becomes necessary to use relatively large-sized transducers. This leads to constraints of both volume and weight, because the transducer has to be immersed in the sea while being placed in a fish that has to navigate at a predetermined depth of immersion.
In a French patent filed on May 27 1997 under No. 97 06457 published on Dec. 4, 1998 and under No. 2 764 160, delivered on Aug. 27, 1999, the present Applicant has described and claimed an electrodynamic transducer of this type that deliver high acoustic power. This transducer has a reasonable volume and mass while being especially designed to withstand underwater explosions that sometimes occur in the vicinity of these transducers.
This prior art transducer, shown in the appended
FIGS. 1 and 2
, comprises a body formed by a base
101
into which there is fixed a jacket
102
surmounted by a cup
103
. These different parts are fitted into one another so as to demarcate cylindrical cavities with a shape generated by revolution around the axis of the transducer. The other parts forming this transducer get inserted into these cylindrical cavities.
A first cylindrical cavity demarcated between the base and the jacket maintains a magnetic circuit formed by a first pole piece and a second pole piece,
104
and
105
, in the shape of crowns centered on the axis of the transducer. The first pole piece
104
is L-shaped with the inner arm of the L extending into the central chamber of the transducer. The second pole piece
105
has the shape of a flat washer or disc. Both are kept separate by a set of magnets
106
to which they are clamped by the adjustment of the jacket
102
in the base
101
. In this way, there is obtained a magnetic circuit that is stopped only by a thin gap
107
taking the shape of a cylinder centered on the axis of the transducer and coming to a position where it is flush with the internal lateral surface of the cup
103
.
The central space of the body of the transducer forms a second cylindrical cavity in which a mushroom-shaped core
108
gets embedded by its central stem in the central circular aperture of the pole piece
104
. The lower part of the head of the core, which has an appreciably hemispherical shape, rests on the upper part of this same pole piece
104
.
The mobile structure of the transducer is formed by a hollow part
109
having the shape of a dome capping a cylindrical part that gets engaged in the gap
107
. In order that this part may be very solid, very light and very rigid all at the same time, it is formed for example by a carbon fiber fabric embedded in a resin matrix. According to the invention, the upper surface of the dome
109
is covered with a part
110
whose upper surface is appreciably flat. This part
110
forms the radiating horn of the transducer. In order that it may be very light, it is made for example out of syntactic foam.
The horn
110
thus behaves like a piston whose lateral external surface is cylindrical. This piston slides in a cylinder formed by the lateral internal surface of the cup
103
, which is itself appreciably cylindrical. According to the invention, these two parts, and more particularly the horn
110
, are made so as to have an extremely tight-fifting clearance of about 0.2 mm for example. Thus a mechanical filter is formed. This mechanical filter slows down the propagation of the shock wave that could arise out of an external explosion if any by flattening, in this interstice, the fluid in which the horn bathes.
To protect the horn, the upper part of the central space of the body of the transducer is filled with a fluid, an oil for example, suited both to this protection and to the propagation of the acoustic waves. To prevent this oil from escaping, the space
113
is closed at its upper part by a membrane
112
fixed to the rim of the cup
103
.
To enable the play of the dome and the horn, the lower part of the central space, opposite the part in which this oil is located, is for its part filled with air. To then prevent the oil contained in the part
113
from re-entering the air-filled part
114
, another tight-sealing membrane
115
is used. This tight-sealing membrane is made of rubber for example. It is much more flexible than the membrane
112
and is fixed, on the one hand, to the external lateral wall of the horn
110
and, on the other hand, to the interior side wall of the cup
103
. This fixing is obtained by clamping between this cup
103
and the jacket
102
. To enable a free and appropriate play of this membrane between is the horn and the cup, the external side surface of the horn is machined on this level so as to be recessed with respect to the adjutage
111
which has the tight clearance described here above, and so as to form an unoccupied space for the membrane
115
.
Moreover, in order that the clearance of the adjutage
111
may be maintained despite the bending loads applied to the dome
109
and the horn
112
during the play undergone by these parts when the transducer works with high emission power, this assembly is stiffened by means of a set of radial ribs
116
that are distributed on the inner periphery of the dome
109
and meet in a star arrangement below the lower part of the stem of the mushroom forming the core
108
. These ribs slide in grooves
117
made in the core
116
and the first pole piece
104
. These grooves are relatively broad at the core and are narrower at the pole piece to minimize the loss of magnetic flux, which can be reduced to a very low value of a few percent.
An shaft
118
joins the center of the upper part of the dome
109
to the center of the star formed by the meeting of the ribs
116
, below the lower face of the core
108
. This shaft both stiffens the assembly and, at the same time, ensures its vertical centering in relation to the axis of the transducer. To fulfill this second function, the shaft is fixed by its lower part to the center of a leaf spring
119
that is itself fixed circumferentially in the lower part of the base
101
. This spring, of the type known as a “flector”, is formed by a flexible and elastic disc with circumferential apertures that let air pass freely into the lower part of the central space of the transducer, between the two parts demarcated by the plane of this spring. This spring not only ensures the centering but also prevents rotational movements in the mobile structure that make the ribs rub against the walls of the grooves in which they slide.
The driving action, which moves the dome-horn unit along the axis of the transducer to emit acoustic waves, is obtained by the interaction between the magnetic field that circulates between the pole pieces and the magnetic field delivered by a coil
120
wound on the lateral flanks of the lower cylindrical part of the dome
109
. This coil is thus plunged in the gap existing between the two pole pieces. This gives the standard a
Lattard Michel
Letiche Michel
Suppa Vito
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Pihulic Daniel T.
Thales
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