(1) Field of the Invention
The field to which this invention relates is hull mounted acoustic sensor modules for towed array handling systems.
(2) Description of the Prior Art
During some submarine operations, a towed array for underwater acoustic reception extends by tow cable from the hull of the submarine. After use, the towed array is retrieved using an exterior retrieval system. Since the retrieval system is exterior to the submarine hull or otherwise separated from direct access by submarine personnel, acoustic sensors are used to detect retrieval of the towed array.
Typically, the acoustic sensors surround a passage tube in which the towed array is retrieved through a water-filled inner volume of the passage tube. The basic sensor design consists of an acoustic projector and a receiver. These two units are typically positioned on opposite sides of the passage tube. The projector transmits an acoustic beam which is detected by the receiver. The difference in signal level detected by the receiver when the towed array is/is not between the projector and receiver is used to determine when the array has been completely retrieved.
The acoustic sensors surrounding the passage tube are encased in a copper-nickel housing in order to position the sensors. The housing also provides a watertight enclosure that prevents exterior water from reaching the sensors and the interior components. Exterior water, typically in the form of seawater, can damage the sensors by corrosion or by the electrical conductivity associated with seawater. As such, the module must be water-resistant as possible and optimally watertight. For a metal module, a watertight condition requires multiple o-rings at the apertures and connection points of the module. However, the use of multiple o-rings increases the likelihood of problems associated with o-rings such as unpredictable failure and increasing replacement costs.
Also, because most sensors and their support components require periodic maintenance, the metal housing containing the sensors must be removed from the submarine and accessed. Since a metal module and interior housing is heavy and awkward for handling underwater, the module is often difficult for divers to remove and re-position during maintenance.
Accordingly, it is a general purpose and primary object of the present invention to provide a watertight acoustic sensor module for detecting when a towed array has been fully retrieved by its handling system in which the acoustic sensor module maintains it watertight integrity without the use of o-rings
It is a further object of the present invention to provide a light-weight watertight acoustic sensor module.
It is a still further object of the present invention to provide a watertight acoustic sensor module of easy fabrication and relatively low cost.
To attain the objects described there is provided a composite encapsulation method for an acoustic sensor module and a resultant lightweight watertight acoustic sensor module for towed array handling systems.
Prior to encapsulation, the component structure of the acoustic sensor module generally comprises two end plates removably connected by support posts to each other in which the end plates encompass a passage tube. Four transducers are attached to the passage tube at positions equidistant from each other on the circumference of the passage tube.
Each of the transducers is attached to the passage tube by a semi-rigid adhesive with an acoustic window that allows an acoustic beam to be transmitted from a piezoelectric ceramic element of two transducers onto the passage tube. A backing plate of the transducers further directs the acoustic beam to the passage tube. For the other two transducers, the acoustic window of the adhesive allows an acoustic beam to be received from the passage tube by the piezoelectric ceramic element of the transducers.
Telemetry lines from the transducers are conductive to an electrical conductor fitted in an aperture of one of the two end plates. The electrical conductor is attachable to an external signal generator that drives the two acoustic projectors and to a circuit that monitors the output levels of the acoustic recievers.
In the composite encapsulation method, an epoxy composite is injected into a cast. The epoxy composite is injected to encapsulate the support posts, the exterior of the passage tube, the transducers and the telemetry lines of the acoustic sensor module. A resin with micro-spheres is added to further lighten the weight of the acoustic sensor module. Once the epoxy composite with a micro-sphere resin is mixed, hollow glassine macro-spheres are added to the composite such that a composite with a syntactic construction results. The syntactic composite, in addition to being lighter than the epoxy composite, is also highly resistant to external pressure and impact forces.
The components, listed above, of the acoustic sensor module can be cast into a resultant light-weight block of the epoxy composite with or without micro-spheres and macro-spheres. The casting sets the arrangement of the components thereby minimizing vibration of the components.
The residual epoxy composite or syntactic composite emitting from the aperture of the end plate allows the electrical conductor to be potted directly into the composite thereby eliminating the need for sealing O-rings and reducing the chances of water penetration. Additionally, the need for tooling the acoustic sensor module to allow O-ring placement is eliminated, thereby greatly reducing the cost of fabrication.
The above and other features of the invention, including various and novel details of construction and combinations of parts will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular devices embodying the invention are shown by way of illustration only and not as the limitations of the invention. The principles and features of this invention may be employed in various and numerous embodiments without departing from the scope of the invention.