Abstract:
An underwater noise generator has a submerged housing containing a receiver section responsive to remotely originating acoustic signals or magneto-inductive signals in the ELF to VLF range. The submerged housing contains a composition that reacts with water to produce gas. The signals initiate an explosive squib that blows a lid off the housing and penetrates a wall that covers the composition. Water floods into the housing and onto the composition which produces gas that creates bubbles. The bubbles are buoyed from the noise generator to the surface and, in so doing, they produce noise. Underwater noise generators can be used singularly, in multiples, or in various patterns as needed to conceal activities or otherwise deceive remote listeners. Appropriately coded magneto-inductive control signals in the ELF to VLF range are transmitted from a variety of remote sources through the sea, air, vegetation, and sediment or any combination of these conditions to activate the underwater noise generators.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a continuation-in-part of U.S. patent applications entitled “Magneto-Inductively Controlled Limpet” by John Sojehei et al., U.S. Patent and Trademark Office Ser. No. 09/135,316 (NC 78,836), filed Aug. 10, 1998, now U.S. Pat. No. 6,112,668, “Magneto-Inductive Seismic Fence” by Robert Woodall et al., U.S. Patent and Trademark Office Ser. No. 09/030517 (NC 78,866), filed Feb. 23, 1998, now U.S. Pat. No. 5,696,608, “Magneto Inductive On-Command Fuze” by Felipe Garcia et al., U.S. Patent and Trademark Office Ser. No. 09/228074 (NC 78,802), filed Jan. 5, 1999, and “Magneto-Inductive Submarine Communications System and Buoy” by Robert Woodall et al., U.S. Patent and Trademark Office Serial No. 09/135316 (NC 78,948), filed Aug. 10, 1998, U.S. Pat. No. 6,058,071, and incorporates all references and information thereof by reference herein. 
    
    
     STATEMENT OF GOVERNMENT INTEREST 
     The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to noise generators. In particular, this invention relates to underwater noise generators actuated from a remote location by acoustic signals or magneto-inductive signals propagated at extremely low to very low frequencies to produce bubbles that create acoustic noise that may conceal movements or deceive listeners. 
     Currently, electromechanical pingers, sacrificial vehicles, and remotely controlled vehicles are used to create noise in a given area. Some systems use explosive charges to create underwater acoustic noise. These devices for producing noise, however, are difficult to inconspicuously emplace at one time and reliably actuate later by remote means when the tactical situation is more favorable. 
     Previously, acoustic command signals have been used to control a variety of instrumentation and ordnance packages. However, acoustic command signals have limited applications since sound cannot effectively be communicated through the air to receivers in the water. In addition, reliable communication with acoustic devices is affected by sediment, microorganisms, algae, changes in salinity, thermoclines, and multi paths in the water. Acoustic devices may also be unreliable at detecting acoustic command signals in the water in the presence of ambient noise that may come from ships, mammals, munitions, landing craft, sonar, and crashing surf. Acoustic devices are known to be incapable of reliable performance in the littoral regions associated with amphibious assault, particularly in the surf zone and noisy harbors. 
     A further limitation in the use of acoustic signals is that they are undesirable from a stealth perspective. If an acoustically responsive package is emplaced and an attempt is made to communicate with it using sonar from a friendly submarine, for example, the submarine&#39;s position may be given away and triangulated upon by others using passive acoustic detection in the area. 
     Thus, in accordance with this inventive concept, a need has been recognized in the state of the art for an underwater noise generator creating noise from bubbles in response to remotely originating acoustic or magneto-inductive signals. 
     SUMMARY OF THE INVENTION 
     The invention is directed to providing an underwater noise generator having a chamber containing a composition to react with water to produce gas. A lid closes the chamber, and a receiver section in the chamber is connected to an explosive squib. The receiver section is responsive to signals from a remote source to detonate the squib and blow the lid away. This allows water to flood the chamber and onto the composition to produce the gas and make bubbles that create noise. 
     An object of the invention is to provide an underwater sound generator using a composition to produce bubbles when it reacts with seawater to create noise. 
     Another object of the invention is to provide an underwater sound generator responsive to actuation by remotely originating command signals. 
     Another object of the invention is to provide a noise source pre-emplaced for later actuation by remote signals. 
     Another object of the invention is to provide underwater noise generators actuated singularly, in multiples, in various patterns, or all at once as tactics warrant. 
     Another object is to provide an underwater noise generator using inexpensive calcium carbonate instead of more complicated, less reliable electromechanical systems. 
     An object of the invention is to provide an underwater noise source reliably activated by magneto—inductive signals. 
     Another object of the invention is to provide a noise source actuated by acoustic signals or magneto-inductive signals in the ELF to VLF range from remote locations. 
     These and other objects of the invention will become more readily apparent from the ensuing specification when taken in conjunction with the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 isometrically depicts the invention flooded with seawater and producing noise generated by bubbles in response to command signals from a remote source. 
     FIG. 2 is a cross-sectional view of the invention prior to initiation of its explosive squib by command signals. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1 of the drawings, underwater noise generator  10  is schematically depicted after it has been deployed to rest on bottom  12  of a body of water  11  that may be either fresh or saltwater. Remote source  13  transmits command signals  14  to activate it. Consequently, underwater noise generator  10  generates gas bubbles  15  that are released and rise as they are buoyed upward through water  11  to create noise  16  that radiates omnidirictionally away from generator  10 . 
     Noise generator  10  is actuated by remotely transmitted signals  14 , e. g., acoustic signals or magneto-inductive signals in the extremely low frequency (ELF) to very low frequency (VLF)range, (1-4000 Hertz). Acoustic signals may be suitable for some applications, but magneto-inductive signals are preferred for reliability in high noise backgrounds, such as those encountered during most combat or assault operations. Signals in ELF/VLF range also safely and reliably activate noise generator  10  through the sea, air, marine plant life, and sediment, or combinations of these conditions. 
     Magneto-inductive transmission with magneto-inductive signals relies on the use of the quasi-static AC magnetic field generated by a transmitting antenna operated with very low radiation impedance. The transmitting antenna at remote source  13  is either air-cored or may employ steel or ferrite for field enhancement. The receiver antenna at noise generator  10  may have a similar construction as the antenna at remote source  13 . 
     Referring also to FIG. 2, noise generator  10  has housing  20  fabricated from relatively heavy or non-buoyant materials that provide sufficiently rugged structures and assure that noise generator  10  sinks to bottom  12 . Housing  20  has chamber  21  having an open end that has rigid wall  22  that is fitted to extend across it. Wall is provided with a number of holes  22   a  and covers composition  23 . Composition  23  has foil seal  23   a  across its top to cover and seal moisture from it. Composition  23  is contained and pressed-in chamber  21  and has chemical properties to produce gas when it comes in contact with and reacts with water  11 . One such composition  23  is calcium carbonate. Other compositions or substances could be used to produce the same or other gasses when they react with water  11 . 
     Housing  20  is provided with annular recess  24  having O-ring  25  in annular groove  25   a . A non-metalic lid  26  snugly fits into recess  24 , and 0-ring  25  engages rim  27  of lid  26 . Rim  27  may or may not have an annular groove in it that corresponds with annular groove  25   a  to help retain O-ring  25 . In either case, this fitting, or engagement seals moisture out of chamber  21  and from composition  23  and secures lid  26  and housing  20  together to close an open end of chamber  21 . Lid  26  also may be used to support or mount receiver section  30  inside chamber  21  of housing  20 . 
     Receiver section  30  includes interconnected integrated battery  31 , receiver/logic board  32 , capacitor-discharge firing circuit  33 , and explosive squib  34 . Detonation of squib  34  is thereby assured when appropriate command signals  14  are sent from remote source  13 . 
     Receiver section  30  may be connected to hydrophone  36  mounted on the outside of lid  26  to receive the remotely originating acoustic command signals  14 . Optionally, when remote source  13  transmits magneto-inductive command signals  14  in the ELF to VLF range, antenna  37  may be mounted inside of lid  26  or wrapped around the inside of housing  20  to receive them. Either way, the received signals are fed to receiver section  30  inside housing  20 . 
     Squib  34  is mounted on squib holder plate  35  that is screwed into or otherwise secured to lid  26 . Plate  35  is interposed between squib  34  and wall  22  and is provided with a number of vent holes  35   a  between squib  34  and wall  22 . When squib  34  is detonated, it generates an explosive pressure wave that is forcefully directed between holder plate  35  and lid  26 . Lid  26  is blown off by this explosive pressure wave. The explosive pressure wave also ruptures holes  23   a ′ in foil seal  23   a . Holes  23   a ′ are aligned with holes  22   a  in plate  22  to expose calcium carbonate composition  23  to water  11  and cause a chemical reaction. Bubbles  15  produced by this reaction are freely vented back through holes  23   a ′ and aligned holes  22   a . The vented gas bubbles  15  rise from noise generator  10  to the surface of water  11 . During generation and buoying of bubbles  15 , noise  16  is created that lasts until composition  23  is depleted. 
     Remote source  13  usually is located a distance that may reach several kilometers away from noise generator  10 . Source  13  may be a land-based command station, surface craft, or submarine that transmits the appropriately coded or encrypted acoustic and/or magneto-inductive signals  14 . 
     Typically, remote source  13  could be a magneto-inductive signal transmitter that transmits command signals  14  in the ELF to VLF range to activate underwater noise generator  10 . Source  13  may include interface and control logic, power supply, power output stage, and magneto-inductive transmitter antenna. The firing command is sent to the interface and control logic unit. This unit may encode the command to a series of tones and may modulate these tones by using the audio frequency shift keying (AFSK) modulation technique at a carrier frequency between  1  and  4000  Hz. The AFSK technique allows generation of command signals  14  that may be encrypted and unique. The power supply drives power output stage consisting of power MOSFET drivers which drive the antenna to transmit command signals  14 . Because the frequencies of command signals  14  are in the ELF to VLF range, they propagate readily through water  11 , surrounding biota, sediments, and seabed to actuate underwater noise generator  10 . 
     Acoustic versions of remote source  13  and noise generator  10  operate at frequencies common to the sonar industry. When remote source  13  is a sonar transmitter, then effective propagation of sonar command signals  14  would be limited to noise generators  10  located in water  11 . This is because sonar command signals  14  are not likely to reach noise generators  10  buried in the ocean bottom or located where there is masking by large amounts of biota, sediment, or thermoclines that would distort the sonar signals. Consequently, sonar command signals  14  are less apt to be used to attempt to actuate these noise generators. 
     In operation, noise generator  10  is carried by swimmers or submersibles, dropped from aircraft or surface craft, or otherwise deployed in water  11 . After it comes to rest on bottom  12 , it could remain there for a considerable period of time that might be limited by the life of batteries  31 . 
     When the right tactical opportunity develops, signal  14  is generated at remote source  13  and transmitted. Signal  14  is received by either hydrophone  36  or ELF/VLF antenna  37  and is fed to receiver/logic board  32  of receiver section  30 . In receiver/logic board  32  received signal  14  is detected, amplified, compared to a stored signal, and evaluated by a logic circuit in logic board  32 . If the comparison and evaluation determine that the signal is valid, then the logic circuit initiates charging of a capacitor of capacitor-discharge firing circuit  33  via battery  31 . When a predetermined charge is accumulated, the current is dumped to interconnected explosive squib  34 . This detonates squib  34 , and a forceful pressure wave is produced inside of housing  20 . 
     The forceful pressure wave accomplishes two things:  1 .) it separates, or blows lid  26  from housing  20 , and  2 .) it ruptures, or blows holes  23   a ′ in foil seal  23   a . Holes  22   a  in wall  22  assure that only aligned holes  23   a ′ are made in foil seal  23   a , and calcium carbonate composition  23  is not exposed, or subjected-to the full impact of the explosive pressure wave from squib  34 . Otherwise, the unrestricted pressure wave might blow-apart or crater composition  23 , or otherwise impair its effectiveness to produce bubbles  15 . 
     Holes  23   a ′ in foil seal  23   a  allow water  11  to pour, or flood into chamber  21  and come in contact with composition  23  of calcium carbonate. The chemical reaction between calcium carbonate composition  23  and water  11  produces carbon dioxide gas which forms bubbles  15  in water  11 . As bubbles  15  travel to the surface, acoustic noise  16  is produced that continues for several minutes until all the calcium carbonate is consumed. 
     Underwater noise generator  10  may be used to create acoustic noise along a defended coastline to conceal the activities of friendly forces. Underwater noise generators  10  can be pre-emplaced in quantity or singularly, as tactics dictate, along a defended friendly or foreign shore. Later, noise generators  10  can be activated singularly, in multiples, or in various patterns as desired. This is because each noise generator  10  has receiver section  30  that actuates squib  34  upon receipt of remotely originating acoustic or magnetoinductive firing command signals  14 . Actuation of noise generators  10  reliably produces bubbles that create acoustic noise  15  in water  11  that is detected by foreign sensors. Inexpensive calcium carbonate may be used instead of more complicated, less reliable electromechanical systems or unstable chemicals, such as sodium, to produce bubble noise. The noise produced by one or more noise generators  10  in water  11  will mask the ability of foreign sensors to detect real activities and targets, and also may be used to deceive foreign listeners into believing that targets which are actual threats are in the area. 
     The invention herein has been described using an exemplary arrangement of components to remotely activate underwater noise generators  10 . Having this disclosure in mind, one skilled in the art to which this invention pertains will select and assemble suitable components from among a wide variety available in the art and appropriately interconnect them. This example, therefore, is not to be construed as limiting, but rather is intended to demonstrate this inventive concept. 
     The disclosed components as disclosed herein all contribute to the novel features of this invention. These novel features assure more reliable and effective use of underwater noise generators  10  to successfully perform a wide variety of tasks. The configuration and capabilities of underwater noise generator  10  could be modified to accommodate different requirements and still be within the scope of this inventive concept. For example, noise generator  10  could be adapted to release oxygen and used by the marine fisheries industry to introduce oxygen into an area having low oxygen levels to improve the survivability of fish. When the oxygen releasing chemicals of composition  23  are activated, life-saving oxygen is available for the fish, and a lower power squib  34  might be used to prevent concussions that might injure the fish. Such changes do not depart from the scope of this invention. 
     Many modifications and variations of the present invention are possible within the purview of the claimed invention. It is to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.