Differential property sensitive acoustic lens

Abstract

A differential property sensitive acoustic lens for non-destructive materials evaluation is described which in a preferred embodiment comprises first and second substantially semicylindrical shaped portions of fused silica disposed in closely spaced relationship along an axial plane, a substantially spherical depression defined in one end of each semicylindrical portion and a flat defined on each semicylindrical portion at the other end, a piezoelectric transducer attached to the flat of each semicylindrical portion, and a paraffin coated aluminum film of preselected thickness disposed between and in laminar contact with the semicylindrical portions for preventing acoustic and electrical cross talk between the transducers and between the semicylindrical portions.

We claim:  
     
       1. An acoustic lens for generating acoustic waves and transmitting the waves into a specimen of material and focusing the waves below the surface of the specimen in the nondestructive evaluation of the specimen, comprising: 
       (a) a substantially cylindrically shaped structure having first and second ends, said structure formed by the assembly of first and second substantially semicylindrical portions disposed in closely spaced relationship along an axial plane of said semicylindrical portions;  
       (b) a substantially spherical depression defined in each of said semicylindrical portions at said first end of said structure, each said spherical depression defining an acoustic lens of a preselected focal length, and a flat defined on each of said semicylindrical portions at said second end of said structure;  
       (c) first and second piezoelectric transducers attached to respective said first and second semicylindrical portions at said second end of said structure, said transducers configured for generating acoustic waves along said first and second semicylindrical portions and into a specimen of material, whereby the acoustic waves generated thereby are focused by said spherical depressions in said first and second semicylindrical portions at respective distinctly different and spatially separated focal points below the surface of the specimen; and  
       (d) a film of preselected thickness disposed between and in laminar contact with said first and second semicylindrical portions along said axial plane for preventing acoustic and electrical cross talk between said transducers and between said semicylindrical portions.  
     
     
       2. The lens of  claim 1  wherein said first and second semicylindrical portions comprise a material selected from the group consisting of fused silica, quartz, silicon, sapphire and aluminum. 
     
     
       3. The lens of  claim 1  wherein said film is paraffin wax coated aluminum, or copper coated rubber or a polymer coated metal. 
     
     
       4. The lens of  claim 1  wherein said semicylindrical portions have an overall diameter of about 0.5 to 2.5 inches and a length about 0.5 to 5 inches. 
     
     
       5. The lens of  claim 1  wherein a radius of curvature of each said spherical depression is in the range of about 0 to about 0.5 inch. 
     
     
       6. The lens of  claim 5  wherein said the radius of curvature of one said spherical depression is different from that of the other said spherical depression.