Multiple field acoustic focusser

Abstract

The invention provides a highly focussed ultrasonic wave throughout a large depth of field without any mechanical motion. One embodiment of the invention providing two focussed fields includes a front to back arrangement of a converging lens, a transducer without any backing material to dissipate ultrasound, a converging lens, and a transducer. To focus in the far field, the front transducer transmits and receives via the front lens. To focus in the near field, the rear transducer transmits and receives via both lenses which collectively focus in the near field.

What is claimed is: 
     
       1. An ultrasonic apparatus for focussing ultrasonic waves comprising the following acoustical lenses and transducing elements located in order along an axis: a first acoustical lens,   a first transducing element,   a second acoustical lens, and   a second transducing element, and further comprising means for coupling the first lens to the first transducing element, the first transducing element to the second lens, and the second lens to the second transducing element so that ultrasonic waves can propagate from the first lens, to the first transducing element, to the second lens, and to the second transducing element.   
     
     
       2. The apparatus recited in claim 1 wherein the first transducing element is parallel to the second transducing element. 
     
     
       3. The apparatus recited in claim 1 wherein the first transducing element is coaxial with the second transducing element. 
     
     
       4. The apparatus recited in claim 1 further comprising electrodes attaching to the first and second transducing elements. 
     
     
       5. The apparatus recited in claim 1 wherein the coupling means comprise: matching means located between the first lens and the first transducing element, and matching the acoustical impedance of the first lens to the acoustical impedance of the first transducing element.   
     
     
       6. The apparatus recited in claim 1 wherein the coupling means comprise: matching means located between the first transducing element and the second lens, and matching the acoustical impedance of the first transducing element to the acoustical impedance of the second lens, and   matching means located between the second lens and the second transducing element, and matching the acoustical impedance of the second lens to the acoustical impedance of the second transducing element.   
     
     
       7. The apparatus recited in claim 1 wherein the second transducing element has a back located along said axis, facing away from the second lens, and said apparatus further comprises means for absorbing and dissipating ultrasonic waves, said absorbing and dissipating means located along said axis in back of the second transducing element.   
     
     
       8. The apparatus recited in claim 7 wherein the coupling means comprise: matching means located between the first lens and the first transducing element, and matching the acoustical impedance of the first lens to the acoustical impedance of the first transducing element,   matching means located between the first transducing element and the second lens, and matching the acoustical impedance of the first transducing element to the acoustical impedance of the second lens, and   matching means located between the second lens and the second transducing element and matching the acoustical impedance of second lens to the acoustical impedance of the second transducing element, and   said apparatus further comprises electrodes attaching to the first and second transducing elements.   
     
     
       9. An ultrasonic apparatus for focussing ultrasonic waves comprising the following lenses, transducing elements, and absorbing and dissipating means located in order along an axis: a first acoustical lens,   a first transducing element,   a second acoustical lens,   a second transducing element,   a third acoustical lens,   a third transducing element, and   means for absorbing and dissipating ultrasonic waves, and further comprising   electrodes attaching to the first, second, and third transducing elements, and   means for coupling the first acoustical lens to the first transducing element, the first transducing element to the second acoustical lens, the second acoustical lens to the second transducing element, the second transducing element to the third acoustical lens, and the third acoustical lens to the third transducing element so that ultrasonic waves can propagate from the first acoustical lens, to the first transducing element, to the second acoustical lens, to the second transducing element, to the third acoustical lens, and to the third transducing element. .Iadd.   
     
     
       10.  A unitary apparatus for focussing acoustic waves comprising: a first acoustic lens,   a first piezoelectric element,   a second acoustic lens, and   a second piezoelectric element, said acoustic lenses and said piezoelectric elements located in order and situated such that one line can intersect opposite faces of each acoustic lens and each piezoelectric element, said first acoustic lens focussing acoustic waves produced by said first piezoelectric element, and said first and second acoustic lenses collectively focussing acoustic waves produced by said second piezoelectric element..Iaddend. .Iadd.   
     
     
       11.  The apparatus of claim 10 wherein the first piezoelectric element is parallel to the second piezoelectric element..Iaddend. .Iadd.12. The apparatus of claim 10 further comprising electrodes attaching to said opposite faces of the first and second piezoelectric elements..Iaddend. .Iadd.13. The apparatus of claim 10 wherein said face of the second piezoelectric element located on said line, facing away from the second lens is the back, and said apparatus further comprises means for absorbing and dissipating acoustic waves, said absorbing and dissipating means located on said line in back of the second piezoelectric element..Iaddend. .Iadd.14. A unitary apparatus providing a large depth of field for acoustic waves comprising:   a first acoustic lens,   a first piezoelectric element,   a second acoustic lens, and   a second piezoelectric element, said piezoelectric elements being substantially coaxial, and said acoustic lenses and said piezoelectric elements being arranged in order and being coupled to one another such that acoustic waves can readily pass from the first acoustic lens, to the first piezoelectric element, to the second acoustic lens, and to the second piezoelectric element, said first and second acoustic lenses focussing acoustic waves proceeding toward said second piezoelectric   
     
     
        element..Iaddend. .Iadd.15.  The apparatus of claim 14 further comprising electrodes attaching to opposite faces of the first and second piezoelectric elements, said opposite faces being coaxial with the piezoelectric elements..Iaddend. .Iadd.16. The apparatus of claim 14 wherein said second piezoelectric element has a back located on said axis, facing away from said second lens, and said apparatus further comprises means for absorbing and dissipating acoustic waves, said absorbing and dissipating means located on said axis in back of said second piezoelectric element..Iaddend.