Acoustic reflectors

Abstract

An underwater location detection system comprising a number of acoustic reflectors at the location, wherein the acoustic reflectors emit acoustic signals in response to receiving an incoming acoustic signal. The frequency of the acoustic signal emitted by each of the acoustic reflectors is different from one another.

1 . An underwater location detection system comprising:
 a number of acoustic reflectors, wherein each of the acoustic reflector emits an acoustic signal in response to receiving an acoustic signal; and   wherein the frequency of the acoustic signal emitted by each acoustic reflector is different from that the other the acoustic reflectors comprising the number of acoustic reflectors.   
     
     
         2 . An underwater location detection system according to  claim 1  in which at least one of the number of acoustic reflectors is associated with an aircraft component. 
     
     
         3 . An underwater location detection system according to  claim 2  in which the aircraft component is an aircraft black box. 
     
     
         4 . An underwater location detection system according to  claim 1  in which one or more acoustic reflectors are tethered to objects of interest. 
     
     
         5 . An underwater location detection system according to  claim 4  in which the object of interest is an aircraft component. 
     
     
         6 . An underwater location detection system according to  claim 4  in which the object of interest is an aircraft black box. 
     
     
         7 . An underwater location detection system according to  claim 1  including a sonar system to emit acoustic signals and to detect signals reflected from one or more of the number of reflectors. 
     
     
         8 . An underwater location detection system according to  claim 1  in which an acoustic reflector in the number of acoustic reflectors is selected from the group comprising a spherical reflector, a cylindrical reflector, and a toroidal reflector. 
     
     
         9 . An underwater location detection system according to  claim 8  in which the acoustic reflector comprises a shell surrounding a core, said shell having one or a plurality of acoustic windows through which acoustic waves incident on the surface of the shell are transmitted into the core, and in which acoustic waves entering the core are reflected from the interior of the shell opposite the window(s) back towards and through the window(s) and in which the core is a join-free solid. 
     
     
         10 . An underwater location detection system according  claim 9  in which the ratio of the speed of acoustic wave transmission in the shell to the average speed of acoustic wave transmission in the core is in the range 2.5 to 3.4 or a multiple thereof. 
     
     
         11 . An underwater location detection system according to  claim 10  in which the ratio of the speed of acoustic wave transmission in the shell to the average speed of the wave transmission in the core is in the range of 2.74 to 2.86 inclusive or a multiple thereof. 
     
     
         12 . An underwater location detection system according to  claim 10  in which the core is a silicon or butyl elastomer cast as one moulding. 
     
     
         13 . An underwater location detection system according to  claim 12  in which the core contains up to 30% by volume calcium carbonate. 
     
     
         14 . An underwater location detection system according to  claim 10  in which the shell material is selected from the group comprising glass reinforced polyphthalamide, polypropylene, aluminium or an alloy thereof, a resin impregnated fibre, in which the fibre itself is selected from the group comprising carbon fibre, aramid fibre, poly(p-phenylene-2,6-benzobisoxazole) (PBO) fibre, nylon 6 and polythene fibre. 
     
     
         15 . An underwater location detection system according to  claim 10  in which the shell is spherical and comprises two halves having rims around their edges, the rim of each half having upstanding portions overlapping one another form a joint therebetween. 
     
     
         16 . An underwater location detection system according to  claim 15  in which the shell comprises two halves having rims round their edges, the rim of each half having one or more upstanding portions forming a tongue(s) and one or more groove(s) and in which the tongues of each half engage with the grooves of the other half. 
     
     
         17 . An underwater location detection system acoustic reflector according to  claim 16  in which the shell comprises two halves having a tongue and groove joint between the halves, and wherein the halves are identical, with each half having alternating grooves and tongues disposed in turn around the rim of the shell and each tongue is of equal length to a groove.