Ships – Torpedoes – With homing means
Reexamination Certificate
2001-06-26
2003-09-23
Carone, Michael J. (Department: 3641)
Ships
Torpedoes
With homing means
C114S023000, C367S124000, C367S129000, C367S153000, C367S901000
Reexamination Certificate
active
06622647
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a sonar seeker head, and more particularly to a sonar seeker head employing active noise cancellation.
2. Description of the Background Art
Acoustic (i.e., sound) waves have long been used as a method of detecting objects undersea. Because acoustic waves are the type of waves that propagate best through water, they are the choice for applications such as undersea warfare (USW). Active sonar (i.e., Sound Navigation And Ranging), is an application of acoustic waves wherein direction and distance to a target may be obtained through the detection of reflected acoustic waves.
Sonar may be of two types, active or passive. Active sonar emits acoustic waves toward a target and picks up reflected waves to determine direction and distance. Passive sonar does not emit any acoustic waves, but only picks up acoustic waves emitted by the target. Passive sonar therefore has an advantage in that it is less likely to give away its own location. Passive sonar is often used when it is desired that the device not transmit any acoustic waves that might be used by the target to locate or track the emitting device, or even alert the target to the presence of the emitting device.
Sonar devices pick up undersea acoustic waves through the use of a transducer called a hydrophone. The hydrophone is capable of converting received acoustic waves into electrical signals that can be analyzed.
Sonar has practical application in the use of guidance of many types of marine vessels, including unmanned weapons such as torpedoes. A torpedo is essentially a warhead attached to a propulsion system and a guidance system. Without an effective guidance system, a torpedo is a blind missile. A sonar guidance system in the form of a seeker head is capable of detecting a target and guiding the torpedo to the target. The seeker head is capable of detecting target sound, whether it be reflected sound or sound emitted by the target (such as propulsion noise generated by the target).
FIG. 1
shows a first type of seeker head array that employs phase differences in received sound in order to determine the direction of origin of the sound source. The phased array seeker head is commonly located in a nose area of the torpedo
100
or other vessel, and is accompanied by amplifying and processing circuits. This torpedo seeker head configuration is generally constructed with a flat torpedo nose. Multiple hydrophone detection elements
103
, typically configured in an array, are used in these acoustic torpedo seeker heads to observe phase differences. This seeker head observes differences in phase of the incoming acoustic signal as detected by the detection elements to determine direction of the target. For example, if the phase angle of the signal produced by the hydrophone elements on the right-hand side of the array is ahead of the phase angle of those on the left-hand side, the seeker head calculates that the target lies to the right of the axis of the seeker head. Conversely, if the phase angle of the signal produced by the hydrophone elements of the left hand side, upper side, or lower side are ahead of the phase angle of the hydrophones on the opposite side of the array, the derived “look” angle (the discerned direction of the target relative to the axis of the torpedo) indicates that the target lies to the left, above, or below the seeker head, respectively. The greater the difference in phase angle, the greater the look angle between the direction to the acoustic source and the axis of the seeker head.
FIG. 2
shows a hydrophone cluster
200
of another torpedo seeker head configuration that is capable of direction detection independent of frequency. This torpedo seeker head configuration is disclosed in U.S. Pat. 6,108,270 to DePoy, and is incorporated herein by reference. This frequency-independent seeker head includes three orthogonal directional hydrophones
203
,
207
, and
215
, and one omni-directional hydrophone
212
. This enables the hydrophone cluster
200
to find a sonic direction in three dimensions. The hydrophone cluster
200
may be located in a forward portion of a torpedo weapon, a submarine, a surface ship, or other marine vessel. In an alternate embodiment, the hydrophone cluster
200
may contain only two directional hydrophones and an omni-directional hydrophone, enabling a sonic direction to be found in two dimensions, or in three dimensions, if a non-resolvable between directions on either side of the plane of the two directional hydrophones can be admitted.
In the figure, orthogonal directional hydrophone
203
has a response pattern aligned with its axis M—M, orthogonal directional hydrophone
207
has a response pattern aligned with its axis N—N (orthogonal to axis M—M), and orthogonal directional hydrophone
215
has a response pattern orthogonal to the response patterns of the other two directional hydrophones and aligned with an orthogonal vertical axis coming vertically out of the figure. Any suitable directional response pattern may be used for the orthogonal directional hydrophones
203
,
207
and
215
.
Hydrophone
212
is an omni-directional hydrophone, picking up acoustic signals in all directions. The omni-directional hydrophone
212
has a spherical response pattern with the omni-directional hydrophone
212
being located in the center of the sphere. An acoustic signal is received by the omni-directional hydrophone
212
at a constant phase and signal strength regardless of the directional position of the acoustic signal source in relation to the omni-directional hydrophone
212
.
In accordance with the present invention, a look angle ∝ in a plane defined by any two directional hydrophones may be found by combining the outputs from two of the three hydrophones and using a phase from the omni-directional hydrophone
212
. By using appropriate combinations of hydrophone pairs, look angles in all three dimensions may be found. The resulting look angles may be used to guide a torpedo or other such marine vessel.
A common problem for acoustic torpedo seeker heads or any type of sonar detector is “ownship” noise. Ownship noise has three principal components: screw noise, propulsion system machinery noise, and hydrodynamic noise.
Screw noise is the noise made by a turning propeller screw. At medium to high torpedo speeds, propeller noise occurs at medium to high acoustic frequencies, i.e., above the frequency passband of a seeker head operating at low frequency, hence screw noise need not be eliminated.
Torpedo machinery noise was extensively studied and measured during World War II. Machinery noise has been found to include mostly rather weak tonals occurring at low frequencies. Machinery noise is mostly independent of speed, and is chiefly structure borne. It occurs chiefly at low frequency, and is important at low speed, where other sources of low frequency noise are diminished. At higher speeds, such as at the speeds typically obtained by modern torpedoes, it is much weaker than hydrodynamic noise.
Hydrodynamic noise includes all noise resulting from the flow of water past the hydrophone, any hydrophone support structures, and the outer hull structure of the torpedo. It includes the turbulent pressures produced upon the hydrophone face in the turbulent boundary layer of the flow (flow noise), rattles and vibration induced in the hull plating, cavitation around appendages, and the noise radiated to a distance by distant vortices in the flow. Hydrodynamic noise increases strongly with speed, and because the origin of this noise lies close to the hydrophone, it is the principle source of noise at high speeds whenever the noise of propeller cavitation (itself a form of hydrodynamic noise) is insignificant.
A particular kind of hydrodynamic noise has been termed flow noise. Flow noise consists of the pressures impinging upon the hydrophone face created by turbulent flow. Although these turbulent pressures are not true sound, in that they are not propagated to a distance, they form what has b
Blackner H. A.
Carone Michael J.
Rothwell Figg Ernst & Manbeck
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