Communications – electrical: acoustic wave systems and devices – Transmitter systems – Animal control
Patent
1993-01-29
1995-07-11
Lobo, Ian J.
Communications, electrical: acoustic wave systems and devices
Transmitter systems
Animal control
367147, G10K 1506, G01V 1157, C02F 136
Patent
active
054327563
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a method and apparatus for inhibiting or reducing the build up of incrustation of aquatic organisms in an underwater environment. In particular, the invention relates to a method and apparatus for inhibiting or reducing undesirable incrustations of zebra mussels over a defined area by means of acoustical pulses produced by a plasma sparking device sometimes also referred to as a "sparker", "plasma gun" or "plasma jet".
BACKGROUND ART
The propensity of certain marine organisms like mollusks to affix themselves to man-made underwater objects has long been a difficult and expensive problem for organizations engaged in marine operations. The most well-known aspect of the problem is the fouling of ships' hulls by marine organisms which can materially retard the progress of a vessel through water. Recently, a more celebrated aspect of the problem has occurred with the invasion of the Great Lakes by a non-indigenous mollusk known as the zebra mussel.
At maturity, the zebra mussel is only a few inches long but it proliferates at a tremendous rate, forming massive colonies on underwater objects. Of most immediate concern has been the way in which these colonies have collected around water intake pipes for hydro-electric projects and municipalities, retarding the flow of water and even threatening to block it.
So far the only proven method for controlling the growth of the mussels at water intakes has been the use of chemicals, particularly chlorination. This, however, has proved to be clumsy, expensive and of some potential hazard to the underwater environment.
Also, on the Great Lakes there has been growing concern, resulting in the introduction of controls, about the use of chemicals in anti-fouling paints for the hulls of vessels. It has been concluded that some of the most effective chemicals used in these paints may be having an adverse effect on the marine environment and water quality.
Much thought, therefore, has been given to the development of a practical means of generating acoustical pulses to kill or control unwanted aquatic animals like zebra mussels in specifiable or highly localized areas. It is well known that the acoustical shock wave of an underwater explosion can locally kill or stun aquatic animals. An acoustical pulse, generated by similar or other mechanical or electrical means, can have the same local effect.
Finding a practical and controllable method of generating acoustical energy that will adversely affect unwanted aquatic organisms has been difficult. The use of explosive or mechanical underwater acoustical generators has foundered due to the inability of researchers working with these devices to solve one or several problems involving repeatability, controllability, cost, complexity, bulkiness, efficiency and general effectiveness. For instance, the one-inch air gun which is used to generate acoustical pulses requires a floating platform equivalent to a tug. This makes it vulnerable to the hazards of weather and the sea while limiting how near it can be brought to the underwater target area. The pulses it produces are also spread over a broad band of frequencies thereby limiting the energy available to those frequencies that may be found to have the optimum deleterious effect on the target organisms.
Electrically operated underwater acoustical generators, however, have existed for many years. They were developed to provide variable sound sources for the seismic exploration of bodies of water and their underlying sediments. One category of these devices involves the creating of an electric arc between two electrodes which, in effect, closely resembles a tiny explosion of TNT which breaks down the gas or water at the electrodes (creating a "plasma") and generates an acoustical pulse. Known as sparkers or plasma guns, early versions of these devices have required high voltages when submerged to ionize the water and create the arc, or mechanical techniques to provide a conductive passage between the electrodes.
Recent improvements in plasma gun
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1008786 Ontario Limited
Lobo Ian J.
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