Communications – electrical: acoustic wave systems and devices – Signal transducers – Underwater type
Patent
1987-07-21
1989-04-11
Kyle, Deborah L.
Communications, electrical: acoustic wave systems and devices
Signal transducers
Underwater type
367165, 367167, 367172, 310337, H04B 1300
Patent
active
048212440
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to tubular acoustic projectors for use underwater.
A known tubular acoustic projector comprises a tubular ceramic piezo-electric transducer whose inner and outer cylindrical surfaces are electroded to convey a high differential drive voltage to the transducer. Electrical insulation is generally provided over the outer surface of the transducer to ensure that the two surfaces are isolated when submerged in water. The power handling capability of such transducers is limited by the ability of the ceramic material to withstand tensile stress, and by the ability of the projector to dissipate the heat generated by the transducer which is a large proportion of the input energy. Failure to dissipate heat causes high temperatures which result in changes in the electrical, and ultimately mechanical, properties of the transducer, and which can also cause cavitation of the surrounding water.
It is known to delay the onset of ceramic failure through tensile stress by applying a band or winding, e.g. of fibreglass, in tension around the circumference of the transducer. However, the presence of such a band or winding introduces thermal insulation and thus aggravates the problem of heat dissipation, which is already severe since the electrical insulation itself has a heat insulating effect.
According to the invention, there is provided a tubular acoustic projector for underwater use, comprising a tubular piezo-electric transducer having an outer cylindrical surface, and a housing including a side wall having a cylindrical inner surface which contacts said outer cylindrical surface of the transducer, said side wall compressing radially said transducer and, in operation, transmitting vibrations of the transducer to surrounding water, and the side wall being so thermally conductive as to dissipate to the surrounding water heat generated by the transducer.
The housing with the thermally conductive side wall thus removes heat from the transducer while radially compressing the transducer. This thus delays the onset of failure in a ceramic transducer without affecting adversely the electrical and mechanical properties of the transducer. This allows the transducer to be operated at higher powers than the transducers of known projectors.
The thickness of the housing provides an outer surface area for the projector which is greater than the outer surface area of the transducer, which has the beneficial effect of reducing the power output per unit area to the surrounding water, thus reducing the tendency to cause cavitation of the water.
Preferably said side wall of the housing is formed of a metal material. The side wall may have cylindrical inner and outer surfaces.
One terminal of said transducer is preferably provided on said outer surface of said transducer, the side wall of the housing being of a metal material and being in electrical contact with said terminal to provide an earth of the transducer.
The terminal may be provided by a metallic coating on said outer surface, said metal side wall being in direct contact with said coating.
The side wall is preferably of such an axial length as to extend beyond said transducer at both ends thereof.
The housing may be open ended, in which case the projector is provided with means for electrically isolating the inner surface of the transducer from its outer surface.
Alternatively, the side wall may terminate in open ends, with the housing including end closures which close said open ends to provide a sealed container for the transducer.
In this case, the interior of the housing is preferably filled with an electrically insulating liquid for insulating electrically the inner and outer surfaces of the transducer. One of said end closures may be provided with one or more closable apertures for the filling of the housing with said electrically insulating liquid.
The housing may contain a device for balancing the pressure in said electrically insulating liquid with the pressure in water around the projector. This device may include a balancing diaphragm.
Prefe
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Clarke Dennis P.
Eldred John W.
Ferranti International Signal plc
Kyle Deborah L.
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